Trisha Dey

Protein synthesis is an elaborate process, starting from DNA being coded to mRNA which is converted to an amino acid chain.  These chains are joined to form polypeptide which is further aggregated to produce molecules.

Protein synthesized structures include traditional protein molecules that are components of muscles. But they also include other molecules like hormones and enzymes.

The main steps involved in protein synthesis structure include:

• Transcription
  1. Initiation
  2. Elongation and
  3. Termination
• Post-transcriptional processing
  1. Capping
  2. Splicing
  3. Tailing
• Translation
• Post-translational modifications

Protein Synthesis Structure:

Protein synthesis in prokaryotes consists of 3 steps- transcription, translation and post-translational processing. In eukaryotes, the subject is a bit more complex and consists of one extra step in between transcription and translation called post-transcriptional processing.

Here we will discuss the above-mentioned steps in detail:

Transcription:

Transcription is the process of producing mRNA or hnRNA (in the case of eukaryotes) by converting the template strand of DNA into its corresponding RNA molecule. This is done by complimenting the Nitrogen bases on the template DNA and adding the complementary ribosomal nucleotides side by side.

Initiation:

Refers to the beginning of the transcriptional process triggered by the arrival of the RNA polymerase enzyme and attaching itself to the promoter region of the DNA. This, in turn, sends a signal to the DNA double helix to unwind with the help of an enzyme called helicase. The RNA pol reads the Nitrogen bases and starts producing a complementary RNA nucleotide

Elongation:

After each complementary ribonucleotide is formed it attaches to the previous one by replacing a single oxygen atom from the phosphate moiety of the nucleotide

Termination:

Termination of the transcription occurs when RNA polymerase encounters something called a Stop Codon usually represented by one of the three of UAA, UAG or UGA. With this, the RNA polymerase and the mRNA or hnRNA in prokaryotes and eukaryotes detaches from the DNA strand and the DNA double strands wind up again in the original double-helix formation.

Post-transcriptional modification:

Eukaryotes have non-coding regions in their DNA which is also reflected in the RNA produced. So the hetero-nuclear RNA molecule undergoes some modification to produce functional mRNA. These modifications include- capping splicing and tailing of the hnRNA.

Capping:

Capping is simply the attachment of a molecule of 7-methylguanosine (m7G) to the 5′ end of the hnRNA molecule. The terminally positioned phosphate at the 5′ end must be eliminated during the capping process, which is accomplished by a phosphatase enzyme. Consequenctly the enzyme guanosyl transferase then catalyses the formation of the diphosphate 5′ end in plave of the cleaved phosphate group at the 5’ end.

Splicing:

Splicing is the process of removing introns (RNA segments that do not code for proteins) from pre-mRNA and linking the remaining exons to form a single, continuous molecule. Exons are mRNA sequences that are “translated” into proteins. Exons are the portions of the mRNA molecule that can actually code for specific amino acids. Although most RNA splicing happens after the pre-mRNA is fully generated and end-capped, transcripts with a significant number of exons can be spliced co-transcriptionally.

Polyadenylation or tailing:

The tailing of hnRNA reveals that roughly 250 adenine residues were added to the 3′ end of the hnRNA after it was cleaved. Scientists simply refer to this long chain of adenine residues as a poly(A) tail. Only when a specific signal sequence is identified on the 3′ end of the hnRNA does cleavage and adenylation (or the addition of additional adenine residues) occur. This is known as a polyadenylation signal sequence (5′-AAUAAA-3′) and must be followed by another sequence (5′-CA-3′) indicating the cleavage location.

Translation of mRNA:

The mRNA is turned, or “translated,” into a chain of amino acids by the genetic code found on the coding strand of the DNA. This is the relationship between the DNA sequence and the amino acid sequence in the polypeptide chain, which is the second primary stage in gene expression during translation. Each codon in mRNA is made up of three Nitrogenous bases, and each codon signifies or codes a specific amino acid, or some to start or stop the translation process. As a result, the mRNA sequence is used as a template to build the chain amino acid chain that produces a protein in the correct order.

Post-transcriptional modification of polypeptide chain:

The final phase of RNA protein synthesis refers to the modifications that the polypeptide chain goes through before it is assembled into protein macromolecules.

PTMs or Post Translational Modifications increase the functional diversity of the proteome by covalently attaching functional groups of proteins, proteolytically cleaving regulatory subunits, or deleting whole proteins. Phosphorylation, glycosylation, ubiquitination, nitrosylation, methylation, acetylation, lipidation, and proteolysis are all examples of protein modifications.

Cell protein synthesis process

In cells protein synthesis especially in eukaryotic cells starts from the nucleus and ends in the cytoplasm.

The process of transcription and post-transcriptional processing inside the nucleus as they involve the DNA and enzymes associated with DNA winding and unwinding that occur only inside the nucleus. For translation and PTM, the mRNA moves to the nucleus.

This is because translation required ribosomes that are found attached to the Golgi bodies. Whereas post-translational modification requires specific enzymes that are found or produced in the cytoplasm, so it occurs in the cytoplasm outside the nucleus.

However, in cells, DNA is present in another cell organelle- the mitochondria which can also participate in protein synthesis. There is a very important difference between nuclear and mitochondrial DNA. In the nucleus UAA, UAG or UGA all act as stop codons.

But in mitochondrial transcription, there is only one stop codon UAG. In the mitochondria UGA codes for tryptophan. Also in nuclear transcription UAU codes for Methionine while in the mitochondria it codes for Isoleucine.

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Protein synthesis is an elaborate process starting from the nucleus and ending in the cytoplasm.

Protein synthesis is referred to the process of producing new peptide molecules and then joining them together to produce proteins by coding genes into mRNA and then translating it.

In prokaryotes, the process involves fewer changes due to the simplicity of the DNA, but as it comes to eukaryotes the process becomes more complex.

Step by step relay of RNA protein synthesis Process and structure:

RNA  Protein synthesis process involves a total of 4 main steps:

• Transcription of genes
• Post-transcriptional processing
• Translation
• Post-translational processing

Transcription of genes to mRNA or hnRNA:

The initial stage in decoding a cell’s genetic information is transcription. RNA polymerases are the specific enzymes used to produce RNA molecules that are complementary to each nitrogen base present on the template strand of the DNA double helix during transcription.

DNA comprises two complementary polynucleotide strands that are kept together by hydrogen bonds between base pairs in an antiparallel double helix structure. The helicase enzyme then plays its role by breaking the hydrogen bonds causing a specific region of the DNA double helix to start unwinding. As this occurs the two strands are separated and the nitrogen bases are exposed to be transcribed as codons.

Even though a DNA molecule is two-stranded, only one of the strands serves as a template for hnRNA synthesis, which we simply refer to as the template strand. The coding strand is the second DNA strand complementary to the template strand as the transcripted hnRNA is identical to the coding strand, only replacing T with U.

Both DNA and RNA have an intrinsic directional sense which is biologically set in nature in how they wind or unwind, meaning there are two distinct ends of the molecule. Since all the nucleotide subunits are actually asymmetrical, due to the placement of a phosphate group on one side of the pentose sugar and the N-base on the other. This very arrangement gives rise to the directional property of the nucleic acid strands.

The numbering of the five carbons in the pentose sugar is from 1’to 5′. The two nucleotides on the complementary strand are joined together in a special chemical bond called phosphodiester bonds. The two strands in a DNA helix are antiparallel, i.e., one runs from 3′ TO 5′; while the other runs in the opposite direction from 5′ to 3′.

Post-transcriptional processing:

It is a set of biological modifications used to convert hnRNA to mRNA. It consists of a few steps including:

• Capping at the 5’ end:

 Capping is nothing but the attachment of a 7-methylguanosine (m7G) molecule to the 5′ end of the hnRNA molecule. In the process of capping the terminally located phosphate at the 5′ end has to be removed and a phosphatase enzyme does this. The process is then catalysed by the enzyme guanosyl transferase, which forms the diphosphate 5′ end.

This very 5′ end then reacts with a GTP molecule having three phosphate groups. It goes and attaches itself to the guanine reside by attacking and removing the alpha phosphorous atom of the GTP molecule.

The enzyme (guanine-N7-)-methyltransferase (“cap MTase”) adds a methyl group to the guanine ring from S-adenosyl methionine.

 A cap 0 structure is defined as a cap with only the (m7G) in place. The next nucleotide’s ribose can likewise be methylated to produce a cap 1. CaNucleotide methylation downstream of the RNA molecule results in cap 2, cap 3, and other structures. During this time the methyl groups go ahead and attach themselves to the 2’ oH groups of the ribose sugars. The cap protects the parent RNA transcript’s 5′ end from ribonucleases that are specialised for the 3’5′ phosphodiester linkages.

• Tailing at the 3’ end:

The tailing of hnRNA indicates the addition of nearly 250 adenine residues to the 3’ end of the hnRNA after cleaving it. This gives rise to something scientists refer to as a poly(A) tail. The cleavage and adenylation(or addition of multiple adenine residues) only occur when a specific signal sequence is found on the 3′ end of the hnRNA. This is called a polyadenylation signal sequence (5′-AAUAAA-3′) and needs to be followed by another sequence (5′-CA-3′), which indicated the cleavage site.

Only when this specific sequence is satisfied does the cleavage and adenylation begin. Using ATP as a precursor, Poly(A) polymerase adds around 200 adenine units to the new 3′ end of the RNA molecule. The poly(A) tail binds numerous copies of poly(A)-binding protein as generated. This is to protect the 3’end of the mRNA from being digestion by ribonuclease enzyme complexes such as the CCR4-Not complex.

• Splicing:

RNA splicing refers to the removal of introns (RNA sections that do not code for proteins) from pre-mRNA and connecting the remaining exons to form a single uninterrupted molecule. Exons are mRNA segments that are “translated” or converted into proteins. They are the mRNA molecule’s coding segments. Even though most RNA splicing occurs after the pre-mRNA has been fully produced and end-capped, transcripts with a large number of exons can be spliced co-transcriptionally.

 A huge protein complex termed the spliceosome catalyzes the splicing reaction, which is made up of proteins and tiny nuclear RNA molecules that recognize splice sites in the hnRNA sequence. Many hn-mRNAs, such as those coding antibodies, can all be spliced in a variety of ways to yield various mature mRNAs encoding different protein sequences. This is known called alternative splicing, and it allows for the creation of a wide range of proteins from a small amount of DNA.

Translation of mRNA to protein:

The mRNA is converted or in scientific jargon “translated”  to a chain of amino acids according to the genetic code present on the coding strand of the  DNA. This is how the DNA sequence relates to the amino acid sequence in the polypeptide chain which is the second primary step in gene expression during translation. Each codon in mRNA comprises three Nitrogenous bases, and each codon indicates or codes a particular amino acid, or some to start or stop the process of translation. The mRNA sequence is thus employed as a template to construct the chain amino acid chain that forms a protein in the correct order. mRNA translation occurs in a series of steps as mentioned below in detail:

• Initiation:

The ribosome comes and surrounds the mRNA of interest to be translated and then comes and attaches to the start codon.  The start codon does not code for any amino acid but rather only acts as the site of attachment of the ribosomes starting the process of translation.

• Elongation:

Elongation includes the final tRNA recognized by the smaller ribosomal subunit to carry the amino acid and transfer it to the larger ribosomal subunit. This larger subunit then attached this amino acid to the previously recognized and admitted tRNA molecule. These 2 simultaneous steps are called accommodation and transpeptidation. The ribosome then moves to the next codon and continues the process in the same way, called translocation. This continued moving of amino acids results in the formation of a large polypeptide chain, formed by amino acids joined by peptide links.

• Termination:

When the ribosome reaches a codon sequence like UAA, UAG or UGA referred to as stop codon, it detaches from the mRNA and the polypeptide it has translated. This marks the end of the process of translation causing termination.

Post-translational modifications of the polypeptide chain translated:

The last step of RNA protein synthesis refers to the changes that the polypeptide chain undergoes before being assembled into protein macromolecules.

Post-translational modifications (PTMs) promote the functional variety of the proteome by covalently attaching functional groups or proteins, proteolytically cleaving regulatory subunits, or destroying entire proteins. These alterations to the protein molecules include phosphorylation, glycosylation, ubiquitination, nitrosylation, methylation, acetylation, lipidation, and proteolysis.

These modifications are important and play a significant role not only in normal cell health and function but also in the treatment and prevention of diseases. Identifying and comprehending PTMs is therefore crucial in the study of cell biology as well as disease treatment and prevention. Here we will discuss some of them.

1. Phosphorylation:

Protein phosphorylation is one of the few biological reversible processes making it one of the best studies biological phenomena among scientists. It is mostly seen on amino acids like serine, threonine which have polar neutral side chains and tyrosine which has an aromatic side chain. Phosphorylation regulates several biological functions, including cell cycle, proliferation, death, and signal transduction pathways.

• Glycosylation:

Protein glycosylation is recognised as a fundamental post-translational modification that has a considerable impact on protein folding, shape, distribution, stability, and activity. Glycosylation refers to a wide spectrum of sugar-moiety additions to proteins, from simple monosaccharide changes in nucleus transcription factors to extremely complicated branched polysaccharide changes in cell surface receptors. Many cell surface and secreted proteins contain carbohydrates in the form of asparagine-linked (N-linked) or serine/threonine-linked (O-linked) oligosaccharides.

• S-nitrosylation

S-nitrosylation is a reversible process, and SNOs(S-nitrothiols) have a brief half-life in the cytoplasm due to a plethora of reducing enzymes that denitrosylate proteins, including glutathione (GSH) and thioredoxin. Due to their high reactivity, instead of free-floating in the cytoplasm, SNOs are retained in organelles like membranes, vesicles, interstitial spaces and even in lipophilic proteins so they are not simply denitrosylated.

 Caspases, which mediate apoptosis, for example, are stored as SNOs in the mitochondrial intermembrane gap.

Once extracellular or intracellular signals come through the Caspases are released into the cytoplasm. Since the cytoplasm is highly reducing in nature the proteins are rapidly denitrolysed. This denitrolysation activates the activation of the caspase and induces the process of apoptosis.

• Ubiquitination:

Ubiquitination is the attachment of  Ubiquitin to protein, an 8-kDa polypeptide made up of 76 amino acids that attach to the Î-NH2 of lysine in protein targets via ubiquitin’s C-terminal glycine. After the first monoubiquitination event, a ubiquitin polymer may form, and polyubiquitinated proteins are subsequently identified by the 26S proteasome, which catalyses ubiquitin breakdown and ubiquitin recycling. The following experiment demonstrates a method for detecting ubiquitinated proteins.

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In simple terms, protein synthesis means to produce the production of protein molecules either from scratch or by breaking or converting other biomolecules.

Protein synthesis entails many smaller steps including- synthesis of amino acids, transcription of mRNA, translation of the mRNA to protein and post-transcriptional processing of that protein.  Proteins are nothing but long chains of amino acids joined together in an orderly fashion.

The process of making new proteins is known as protein synthesis. In biological systems, it occurs within the cell. Prokaryotes have it in their cytoplasm. It starts in the nucleus with the production of a transcript (mRNA) of the DNA’s coding sequence in eukaryotes. This mRNA transcript then leaves the cell nucleus. It makes its way to the ribosomes attached to the Golgi bodies in the cytoplasm, where it is translated into a protein molecule with a codon-specific amino acid sequence.

Steps of protein synthesis process:

There are 5 major steps of the protein synthesis process are:

1. Activation of amino acids
2. Transfer of amino acids to tRNA
3. Initiation of the polypeptide chain
4. Chain termination and
5. Translocation of the protein molecule

This is the basic thumb rule for prokaryotes, while eukaryotes have some extra steps due to their cell complexity. Hereafter we will discuss the above-mentioned steps in detail.

Activation of amino acids:

Thereaction is brought about when amino acids come to interact with ATP molecules catalyzed by aminoacyl RNA synthetase. The aminoacyl – AMP – enzyme complex is generated as a result of the reaction between amino acid (AA) and adenosine triphosphate (ATP), which is mediated by the aforementioned enzyme. The complex is as follows:

AA + ATP Enzyme -AA – AMP – enzyme complex + PP

 It’s worth noting that different amino acids require different aminoacyl RNA synthetases.

Transfer of the amino acid to tRNA:

The generated AA–AMP–enzyme complex responds with a particular tRNA. As a result, amino acids are transported to tRNA. As a result, the enzyme, as well as the AMP, are released.

So the complex becomes:

AA – AMP – enzyme Complex + tRNA- AA – tRNA + AMP enzyme

Initiation of a polypeptide chain:

The ribosome accepts charged tRNA. In all organisms, protein synthesis occurs in the ribosome that is normally attached to the Golgi bodies in the cytoplasm. The SOS subunit of the 70S type ribosome interacts with the mRNA. Ribosomes are small complex molecules, responsible for protein synthesis and made up of 2 components- rRNA (ribosomal RNA) and proteins. Ribosomes also catalyze the creation of peptide bonds (the enzyme—ribozyme—in bacteria). Ribosomes are classified into two types: large and tiny.

Scientists represent each amino acid by three nucleic acid sequences known as codons. Based on the arrangement of the nitrogenous bases, this information is present in the mRNA. The amino acid methionine is transcribed as an initiating codon by the codon AUG but rarely by GUG (for valine), which is always responsible for starting polypeptide chains in prokaryotes. In prokaryotes, the formation of the starting amino acid methionine is a must.

Ribosomes have two binding sites for amino-acyl-tRNA.

1. A site or amino-acyl (acceptor site).
2. The peptidyl site, often known as the “P” site, is a kind of peptide (donor site). Each site is made up of different parts of the SOS and 30S subunits. Only the P site may attach to the starting formyl methionine tRNA (AA, f Met tRNA).

In the first stage, the amino-acyl-tRNA complex is bound to an elongation factor called the “ Tu complex”. This complex contains a molecule of bound GTP. Thereafter the amino-acyl-tRNA-Tu-GTP complex is tied to the 70S initiation complex. The Tu-GDP complex is released from the 70S ribosome when the GTP molecule hydrolyzes. The new aminoacyl tRNA now comes and connects itself to the aminoacyl or A site of the ribosome.

The tRNAs on the A site and P sites of the ribosomes are connected using peptide bonds. We consider this as the initiation of the second step of elongation. In the next phase, the formyl methionine acyl group that was initially formed is transferred from the tRNA it was attached to to the amino group of the new amino acid that arrived at the A site. Peptide synthesis is catalysed by peptidyl transferase, a ribosomal enzyme found in the 50 S subunit. A dipeptidyl-tRNA molecule is generated at the A site, all the while with an empty tRNA remaining attached to the P site of the mRNA.  

The ribosome travels down the codons along the mRNA towards its 3′ terminal in the third phase of elongation (i.e., 1st to 2nd codon and then from 2nd to 3rd on the mRNA). Because the dipeptidyl tRNA is still connected to the second codon, ribosome movement causes the dipeptidyl tRNA to shift from the A site to the P-site. The empty tRNA is released as a result of this translocation.

The third mRNA codon is now on the A-site, while the second codon is on the P-site. The translocation step is the movement of ribosomes along mRNA. Elongation factor G is required for this step (also called translocase). In addition, another molecule of GTP is hydrolyzed at the same time. The translocation requires energy, which is provided by the hydrolysis of GTP.

The actions of three termination or releasing factors known as R1, R, and S are also required for termination. The translocation requires energy, which is provided by the hydrolysis of GTP. The polypeptide chain lengthens as a result of this recurrent process for chain elongation. As the ribosome moves down every codon towards the 3’ end of the mRNA, it is at this time that the polypeptide chain with the final amino acid comes to attach to it.

Chain termination:

One of the 3 terminal codons of mRNA marks the end of the polypeptide.  UAG (amber), UAA (ocher) and UGA (opal) are called stop codons. They can also be considered as stop signals.

The terminal codon follows immediately after the last and last amino acid codon. The polypeptide chain, tRNA, and mRNA are then released. Ribosome subunits become detached. The actions of three termination or releasing factors known as R1, R, and S are also required for termination.

Translocation of the protein molecule:

Two types of polyribosome shave been discovered that are involved in this process:

• Free polyribosomes
• Membrane-bound polyribosomes.

Upon termination of protein synthesis in the free ribosome, the prepared ribosome releases the protein into the cytoplasm. Special types of processes are used to transport some of these specialised proteins to the mitochondria and nucleus.

In membrane-bound polyribosomes, on the other hand, a polypeptide chain that develops on mRNA is introduced into the ER membrane’s lumen. Some of the proteins also compose parts of the membrane structure.

Even yet, only a few proteins are released into the lumen and integrated into Golgi body vesicles. They can also change the protein through glycosylation, which is the addition of sugar residues. As a result, the vesicles shape a bond with the plasma

membrane and the proteins are sooner or later released.

Protein synthesis process in prokaryotes:

Prokaryotes are simple creatures and have only these 5 steps involved in protein synthesis.

• Activation of amino acids
• Transfer of amino acid to tRNA
• Initiation of the polypeptide chain
• Chain Termination and
• Translocation of the protein molecule

Prokaryotes have a single DNA molecule that is used for protein synthesis by transcription and translation. The DNA molecule is so simple that it doesn’t even require post-transcriptional and post-translational modifications for its protein synthesis process.

Process of protein synthesis in eukaryotes:

Protein synthesis in eukaryotes is a bit more complicated due to the presence of introns in the RNA that is transcribed. Hence the introns must be removed by the transcriptional process of splicing to ligate only the exons and produce mRNA which can be translated into protein.

Post-transcriptional processing consists of a total of 4 steps in eukaryotic hnRNA:

1. Introns are removed from mRNA during splicing. Introns are areas of the genome that don’t code for a protein. The remaining portion of the mRNA is made up entirely of protein-coding parts called exons. In the diagram, ribonucleoproteins are tiny nucleoproteins that contain RNA and are required for the splicing process.
2. Some of the nucleotides in mRNA are changed during editing. Because of editing, a human protein called APOB, which aids in the transport of lipids in the blood, has two distinct versions. Because editing inserts an earlier stop signal in mRNA, one version is smaller than the other.
3. The “head” of the mRNA is given a methylation cap via 5’- capping. This cap helps the ribosomes identify where to bind to the mRNA and prevents it from breaking down.
4. Polyadenylation gives mRNA a “tail.” A series of As makes up the tail (adenine bases). It means that the mRNA has now exhausted its functional requirement and is no longer of any use and can be discarded. It also aids in the export of mRNA from the nucleus and shields mRNA from enzymes that could degrade it.

Protein synthesis example:

A type of protein synthesis that occurs in neurons is called de novo protein synthesis.

In neurons, “de novo protein synthesis” refers to protein synthesis that occurs outside of the soma or cell body’s limits. Both compartments of neurons i.e. dendritic compartment(the longer cavity) and the axonal compartment(the star or spider-shaped cavity) can produce such “extrasomal” proteins.

This means that the protein is synthesized without any prior knowledge of its codon composition, so the protein produced is also the origin and a puzzle for scientists as to regarding their function

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Chromosomes are lengthy DNA-carrying structures found in the center of the cell nucleus. DNA is a fundamental biomolecular component in most higher organisms as it is comprised of genes.

Basically, chromosomes refer to the wounded DNA treads to make them compact enough to fit inside the nucleus. And they serve several functions from carrying genetic information to protein synthesis.

Here we will discuss the chromosome function in plant cells. Plant chromosomes:

Even though both plant and animal cells are eukaryotic organisms they have different features. This means that they have different genetic requirements. Hence their chromosomal functions apart from the essentials also have some differences.

Chromosome function in plant cells:

Carrier of Mendelian factors:

The main chromosomal function is to carry information from one generation of the cell to the next in the form of genes. This included information about the features of the organism- length, height, colours they show or express etc. These features that are genetically passable from one generation to the next are called Mendelian factors.

Influencing DNA accessibility:

The accessibility of DNA is fine-tuned by chromatin structure, which affects gene expression and defines cell developmental and metabolic identity, as well as plant growth and development. The platform for recruiting protein complexes that act on chromatin is made up of nucleosomes, which have roughly 150 base pairs of DNA wrapped around each octamer of histones H2A, H2B, H3, and H4, as well as a linker histone H1. DNA can be methylated, and histones can be subjected to lysine or arginine methylation, lysine acetylation, lysine ubiquitination, or serine phosphorylation, among other post-translational changes.

Influence on gene expression:

The expression of metabolic genes is modulated by chromatin structure, which impacts metabolic states. Despite the importance of chromatin structure for transcription, evidence of chromatin modifiers directly controlling metabolic genes was just recently discovered. SDG8, the HKMT that catalyses gene-body H3K36me3, for example, directly targets genes involved in photosynthesis, nutrition and energy metabolism, as well as genes that respond to carbon or light therapy.

Gene control:

Though not a lot of research has been done on this topic, the function of chromosomes in gene control in plants cannot be denied as widely seen in animal and yeast cells. Chromatin modifying complexes such as – histone acetyltransferases, histone deacetylases and SWI/SNF complexes have significant roles in plant gene control.

Determining the sex of the plant:

Like all organisms, higher plants have male and female parts, especially in the floral parts that act as the reproductive parts. The sex chromosomes of most higher determine their gender. Plants, unlike most animals, can be either male or female, or even have both features at the same time.

However, a lot of plants to avoid being self-pollinated make sure that if the pollen is from a flower from the same plant become non-viable, or the male and female flowers mature at different times. Such features are determined by the adaptations of these plants that have been imprinted into their chromosomal information.

Carrying forward useful adaptations:

In the case of carnivorous plants that grow in soil that have very low nitrogen content, the plants have changed and modified their leaves to be able to photosynthesize and also catch live organisms to fulfil their nutrient content. Since they cannot absorb any such nutrients from their environment they have underdeveloped roots. This is a result of evolution over centuries that has been embedded into the chromosome with every single step. Since this is how they are genetically constituted they do not produce the required features to grow in a nutrient-rich media where they will probably end up dead.

Protein synthesis:

Chromosomes hold genes that express the proteins that are required by an organism to function properly including enzymes and hormones. Plants are not an exception in this are very dependent on the hormones produced in them to grow and function to their fullest.

Chromosome structure:

Every chromosome has something called a centromere also called the primary constriction- a small fixed part of the chromosome where the spindles attach to the chromosome during mitosis or meiosis. The centromere ensures that the sister cells have equal chromosomal distribution after division. They also have a telomere made up of tandem repetitions of short DNA fragments.

In mitotic metaphase, each chromosome has two symmetrical structures known as chromatids or sister chromatids. A single DNA molecule constitutes each chromatid. The centromere links sister chromatids together. The centromere is where spindle fibres connect during cell division. Varied chromosomes have different numbers and locations for the centromere.

Chromosomes also have secondary constrictions in addition to the centromere. Because there is only bending at the centromere during anaphase, secondary constrictions can be observed (primary constriction). The nucleolar organizer is a secondary constriction that contains genes that generate nucleoli.

The chromosome is divided into two sections by the centromere; usually where one arm is shorter than another. The shorter arm is called the ‘p’ arm, while the longer arm is called the ‘q’ arm. A disc-shaped kinetochore is found in the centromere and contains a unique DNA sequence as well as special proteins attached to it. The kinetochore is where tubulin proteins are polymerized and microtubules are assembled.

Chromatin is a component of the chromosome. DNA, RNA, and proteins make up chromatin. Chromosomes are evident in the nucleoplasm as thin chromatin threads during interphase. The chromatin fibres condense during cell division, revealing chromosomes with different characteristics. Heterochromatin is the darkly pigmented, compacted portion of chromatin. It comprises tightly packed and genetically inactive DNA. Euchromatin is the light-stained, dispersed portion of chromatin.

Chromatin contains genetically active and loosely packed DNA. During prophase, the chromosomal material appears as thin filaments called chromonemata. During interphase, chromomeres, which are bead-like structures made up of chromatin material, can be detected. Chromatin with chromomere resembles a beaded necklace.

The chromosome terminal is called the telomere. The telomere is polar by nature to avoid the ligation of the chromosomal segments.

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Chromosome structure refers to the way that the chromatin fibers are compacted in the cell.

Long strands of DNA holding genetic information make up chromosomes. Eukaryotic chromosomes are significantly bigger than prokaryotic chromosomes and are linear chromosomes.

The DNA condenses into chromosomes after replication. After replication, each chromosome is made up of a collection of a duplicate set of chromatids usually held together at the centre by a centromere. The centromere is where the kinetochore (a protein structure that connects the spindle fibres), attaches to the centromere, which pulls the sister chromatids to 2 opposites of the cell after chromatin division.

Below we will explain the chromosome structure in detail.

What are chromosomes?

A chromosome is referred to the compacted DNA molecule found in an organism carrying its genetic information.

Chromosomes are thread-like structures found in all organisms(prokaryotes, eukaryotes but not viruses) that carry and deliver genetic information. Each chromosome is made up of one molecule of protein and one molecule of deoxyribonucleic acid (DNA), but it can occasionally also be RNA.

 DNA is passed along from one generation to the next and carries the precise instructions and information that distinguish each living thing from the other. Viral chromosomes differ from those of prokaryotes and eukaryotes in both shape and position.

DNA (deoxyribonucleic acid) (chromosomes of nonliving viruses) and RNA (ribonucleic acid) (chromosomes of prokaryotic organisms like bacteria and blue-green algae) are the only varieties of chromosomes that are capable of replication. Since prokaryotes do not have a nucleus their chromosomal material is not surrounded by any sort of membranous structure.

Chromosomal Function:

• DNA structure is basically like long threads, hence for compactness and easy handling by the cell itself they are spooled around some circular proteins called histones.
• If DNA molecules were not packed in this fashion, it would be impossible for a cell to hold all its genetic material within itself.
• For example, if we laid out the entire human genome and unreeled it from the histone proteins, it would extend 6 feet when laid end-to-end.
• It’s critical for DNA to be intact and dispersed uniformly throughout cells during cell division.
• In the great majority of cell divisions, chromosomes play an important role in ensuring that DNA is appropriately copied and distributed.
• Each eukaryotic organism has a specific number of chromosomes, that determines its features, development and life.
•  During asexual reproduction, all of the organism’s cells, including its gametes, contain the same number of chromosomes.
• Somatic cells in the body are generally diploid (2n), i.e., they have a set or sets of paired chromosomes. On the other hand cells like gametes are what we call haploid (n), as they contain half of the chromosomal pairs. Gametes are normally produced by meiosis.
•  Meiosis produces haploid cells or gametes, containing one chromosome of a pair. When the two gametes join during fertilisation forming a zygote, the cell again becomes diploid having a pair of chromosomes.

Chromosome structure in bacterial cells:

Because of their tiny size, bacterial chromosomes were found considerably later than their eukaryotic counterparts. Furthermore, unlike eukaryotic chromosomes, bacterial chromosomes do not go through the dramatic metaphase condensation that makes eukaryotic chromosomes so visible.

Most bacterial chromosomes (also called genophores)can range from a mere 13,0000 base pairs to more than 14,000,000 base pairs depending on the size and complexity of the prokaryote. Nuclei are not seen in prokaryotes. Instead, their DNA is structured into a nucleoid-like structure. The nucleoid is a separate structure within the bacterial cell that occupies a specific area.

This structure, on the other hand, is dynamic and is maintained and reshaped by a group of histone-like proteins that connect with the bacterial chromosome. The DNA in archaea’s chromosomes is much better ordered, with DNA wrapped in structures akin to eukaryotic nucleosomes.

Chromosome structure in plant cells:

For plants in most angiosperm species, the chromosomal structure consists of a centromere (primary constriction) made up of condensed chromatin regions bordered by pericentromeric areas rich in heterochromatin and telomeres that mark the ends of chromosomes.

 The differential condensation pattern during the prometaphase/metaphase stage may often be used to identify individual chromosomes. Most higher organisms’ DNA is made up of repetitive DNA sequences. Various groups of repeated elements scatter throughout the genome in different ways; they might form distinct territories, such as NORs or centromeres, or they can be dispersed within a chromosome or across the genome.

Chromosome structure in animal cells:

Multiple big linear chromosomes are housed in the nucleus of eukaryotes. Each chromosome has one centromere and one or two arms that protrude from it, albeit these arms are rarely visible unless in the division phase. Eukaryotes can also have a mitochondrial genome, which can be linear or circular in nature, however, they do not participate in inheritance.

Among all eukaryotic chromosomes those in mammals, more specifically in humans is the most in number and also the most complex. Autosomes (body chromosomes) and allosomes (sex chromosomes) are the two kinds of chromosomes found in humans. Sex chromosomes pass on some genetic features that are connected to a person’s sex.

The autosomes hold the rest of the relevant and necessary genetic information. They all behave in the same way during cell division, because the autosomes are all clones of each other. Human cells have 46 chromosomes, including 22 pairs of autosomes and one pair of sex chromosomes or allosomes.

The main difference in the male and female chromosomal constitution is simply the difference in the final pair of chromosomes also called the allosomes. While females have the chromosomal structure of 44 autosomes+ XX allosomes, the male chromosomal composition is 44 autosomes+ XY allosomes.

As females have only one type of allosome, all eggs produce have the same X allosomes. The gender of the fetus is determined by the X or Y chromosome present in the sperm that fertilizes the egg. Sperm with a Y chromosome produces a boy (XY) while one with an X produces a girl (XX).

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There are three DNA splicing types are commonly seen in genetic and biotechnology labs. They are:

• Recombinant DNA
• Gene splicing and
• Microinjection.

Here we will discuss the above-mentioned DNA splicing types in detail.

RECOMBINANT DNA:

Recombinant DNA is the process of genetically modifying DNA molecules by cutting and pasting different fragments that produced desired features. 

rDNA or recombinant DNA is a process that uses enzymes to cut and paste DNA sequences of interest.

The recombined DNA sequences can then be placed into vectors that carry the DNA to a suitable host cell for replication or expression.

Splicing genes from one species and transferring them into the cells of a different creature or species such that the DNA gets duplicated and forms part of the organism’s genetic make-up. Restriction enzymes cleave them, and ligases connect them.

To create recombinant DNA, scientists must first isolate the DNA they intend to combine. DNA can be obtained from a variety of sources, including bacteria, plants, animals, algae, and fungus. Scientists use sophisticated laboratory procedures to cut the sections of DNA they desire and paste them together to create recombinant DNA or rDNA. They insert the new rDNA into a host cell, which will absorb and duplicate it, displaying the features for which it codes.

GENE SPLICING:

Genes are DNA segments that contain protein-coding instructions. Gene splicing is a type of genetic engineering that involves inserting certain genes or gene sequences into the genome of another creature. Splicing of genes is a process that takes place during the processing of deoxyribonucleic acid (DNA) to prepare it for translation into protein.

A single gene may code for numerous proteins thanks to gene splicing, a post-transcriptional alteration. In eukaryotes, gene splicing is accomplished by the differential inclusion or removal of pre-mRNA sequences before mRNA translation. Splicing of genes is a major source of protein variation. 

During a normal gene-splicing event, pre-mRNA from one gene might result in several mature mRNA

molecules, each of which can produce multiple functional proteins. As a result, gene splicing allows a single gene to enhance its coding capacity, permitting the production of physically and functionally different protein isoforms. Splicing of genes is seen in a large number of genes. Alternative splicing is known to occur in roughly 40-60% of genes in human cells.

MICROINJECTION:

Microinjection is a method of delivering genetic material into a nucleus that is very reliable and reproducible. The method of injecting genetic elements into a live cell using glass micropipettes or metal microinjection needles is known as microinjection. Glass micropipettes come in a variety of sizes, with tip diameters ranging from 0.1 to ten millimetres. DNA or RNA is directly injected into the nucleus of the cell. 

Large frog eggs, mammalian cells, mammalian embryos, plants, and tissues have all been successfully microinjected. Microinjection has traditionally been costly, time-consuming, and labour-intensive, but new technologies are making it more dependable, repeatable, and economical.

What is DNA splicing?

DNA splicing is the process by which the DNA sequence is altered by removing or adding part of its sequence.

Splicing is the process of removing unwanted parts and rejoining the necessary fragments to form a complete biomolecule chain. DNA splicing is when the DNA sequence and not the transcripted mRNA undergoes these changes.

DNA splicing is not something that occurs naturally. Rather it is a lab-produced endeavour to produce genetic modifications. Since the recombinant DNA revolution in the 1970s, splicing human DNA with non-human genetic material has been a common practice.

Human DNA has also been engineered in living animals, either for fundamental study or, more recently, to create enormous quantities of proteins for medical purposes.

There are 3 types of DNA splicing done in the laboratory. These include- Recombinant DNA, Gene splicing and microinjections.

DNA splicing in prokaryotes:

• The process of splicing does not occur naturally in prokaryotic cells as their RNA is devoid of introns. 
• So transcription in prokaryotes produces processed mRNA. A different type of splicing can be seen in the extrachromosomal or plasmid DNA of prokaryotes which is circular.
• The prokaryotic chromosome is made up of DNA and holds all of the information required for a bacterial cell to operate normally.
• In addition to the chromosome, bacteria can carry plasmids, which are tiny rings of DNA that contain genes.
• Plasmids can splice themselves to add antibiotic-resistant genes if the organism is in an environment induced with antibiotics.
• The gene is not present in the prokaryote naturally but is spliced into the plasmid DNA in times of requirement.
• Scientists have used this method to splice more than one single antibiotic-resistant gene into the same organism and then removed it from the organism to clone it.

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