Gram Negative And Gram Positive Cell Wall: 7 Important Facts


In this post, you will find the information about gram negative and gram positive cell wall, their differences, similarities and important facts.

Gram negative and gram positive cell wall are both made of peptidoglycan, which is a unique structure composed of modified sugar derivatives and short peptide chain.

What are the gram negative bacteria?

Gram negative bacteria are those having  cell wall of about 5-10nm thin and gives off pink colour after gram staining. Gram negative bacteria consists of cytoplasmic membrane, peptidoglycan and an extra outer membrane. This extra plasma membrane actually makes the complex structure of gram negative bacteria. The outer membrane is quite similar to the cytoplasmic membrane.

Peptidoglycan is sandwiched between cytoplasmic and outer membrane. Peptidoglycan is consists of two sugar derivatives and peptides. The two derivatives are NAG (N-acetyl glucosamine) and NAM (N-acetyl muramic acid). There is a gap between each membrane which is called periplasmic space. Apart from these structures, gram-negative bacteria has special structure present on the outer membrane called Lipopolysaccharide (LPS).

gram negative and gram positive cell wall
Gram-negative cell wall structure from Wikipedia

LPS is anchored into the outer membrane and projecting towards the environment. It is also called endotoxin. LPS is divided into three parts: Lipid A, core polysaccharide and O, polysaccharide or O antigen. Each part of LPS has its function, O-antigen triggers the immune response while Lipid A act as toxin developing the fever and illness symptoms in individual.

What are the gram positive bacteria?

Gram positive bacteria are those having their cell wall made of peptidoglycan. Peptidoglycan is thick in case of  of gram positive bacteria. The size of cell wall ranges from about 20-80nm. Peptidoglycan is consists of two sugar derivatives and peptides.

Gram positive bacteria contains cytoplasmic membrane, this structure is common in both gram-positive as well gram-negative bacteria. The second next structure present in gram-positive bacteria is peptidoglycan which is very thick and prominent in comparison to gram-negative bacteria. As stated earlier that peptidoglycan is made up of two sugar derivatives, NAG and NAM. They are also called glycans. Glycans are horizontally arranged or joined by β 1-4 glycosidic linkage.

Differences between the gram negative and gram positive cell wall.

Gram Positive BacteriaGram Negative Bacteria
They have peptidoglycan which is very thick in nature (20-80nm in size)They have peptidoglycan which is very thin in nature (5-10nm in size)
Gram positive bacteria retains crystal violet during gram staining and gives off purple colour to the bacteria.Gram negative bacteria loses crystal violet during gram staining and stains the bacteria in pink colour.
Gram positive bacteria have peptidoglycan and cytoplasmic membrane only.Gram negative bacteria have peptidoglycan, cytoplasmic membrane and extra outer membrane adhere outside the peptidoglycan.
They have special structures embedded in the peptidoglycan and cytoplasmic membrane called techoic and lipotechoic acid respectively.Gram-negative bacteria has special structure present on the outer membrane called Lipopolysaccharide (LPS).
They form multiple layers of peptidoglycan to make thick structured cell wall.Peptidoglycan is thin but outer membrane gives the bulk to the gram-negative bacteria
They are mostly  less pathogenic because they lacks lipopolysaccharides (LPS)They are mostly pathogenic in nature due to the presence of LPS.
Gram positive bacteria are likely  susceptible to antibiotics.Gram negative bacteria are more resistant to antibiotics because of gene modification.
Lipid content in gram positive bacteria is very lowLipid content in gram negative bacteria is about 20-30%
Their cell wall is made up of multilayer of peptidoglycanTheir cell wall is made up of may be single layer of peptidoglycan.
Examples are : Bacillus anthrax, Clostridium botulinum, Staphylococcus aureus etc.Examples are : Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, Hemophilus influenza etc.

Similarities between the gram negative and gram positive cell wall.

Gram negative bacteria 

Gram negative bacteria consists of cytoplasmic membrane, peptidoglycan and an extra outer membrane. This extra plasma membrane actually makes the complex structure of gram negative bacteria. The outer membrane is quite similar to the cytoplasmic membrane. Peptidoglycan is sandwiched between cytoplasmic and outer membrane. Peptidoglycan is consists of two sugar derivatives and peptides. 

The two derivatives are NAG (N-acetyl glucosamine) and NAM (N-acetyl muramic acid). Peptides or small chain of amino acid(L-alanine, D-glutamine, L-lysine, and D-alanine) is vertically joined to the NAM molecule. Same the second glycan chain is arranged and joined by cross linking. The one peptide is cross linked with another peptide of glycan with the help of penta-glycine linkage horizontally.

Gram positive bacteria

Gram positive bacteria are those having their cell wall made of peptidoglycan. Gram positive bacteria contains cytoplasmic membrane, this structure is common in both gram-positive as well gram-negative bacteria. The second next structure present in gram-positive bacteria is peptidoglycan which is very thick and prominent in comparison to gram-negative bacteria.

As stated earlier that peptidoglycan is made up of two sugar derivatives, NAG and NAM. They are also called glycans. Glycans are horizontally arranged or joined by β 1-4 glycosidic linkage. Peptides or small chain of amino acid(L-alanine, D-glutamine, L-lysine, and D-alanine) is vertically joined to the NAM molecule. Same the second glycan chain is arranged and joined by cross linking. The one peptide is cross linked with another peptide of glycan with the help of penta-glycine linkage horizontally. Thus, it forms a huge cross linking network in gram positive bacteria.

Gram negative and gram positive cell wall structure

Gram positive and gram negative bacteria have same cell wall structure and composition, there is little difference of size and some additional structures that are present in both types. Gram positive bacteria have multi-layered peptidoglycan making it very thick structure, therefore it retains crystal violet and gives off purple colour when it is gram stained.

They also posses techoic and lipotechoic acid anchored in the peptidoglycan and cytoplasmic membrane. Peptidoglycan is formed from modified sugar derivatives , NAG and NAM, joined by β 1-4 glycosidic linkage. Gram negative bacteria are composed of single layer of peptidoglycan which make their cell wall very thin. Still the cell wall structure is quite complex as they posses extra outer membrane outside the peptidoglycan.

Gram Negative And Gram Positive Cell Wall structure from Wikipedia

The outer membrane is quite similar to the cytoplasmic membrane. They also posses porin channels which allows the passing of different molecules. The outer membrane is permeable in nature while cytoplasmic membrane is selectively permeable. Peptidoglycan is sandwiched between cytoplasmic and outer membrane. Peptidoglycan is consists of two sugar derivatives (NAG and NAM) and peptide chain. The composition of peptide chain may vary according to the bacterial species.

Which type of bacteria cell wall are thicker?

Gram positive bacteria have thicker cell wall than gram negative bacteria. The cell wall is thick because there is high cross linking between the peptide chain and glycans molecule. They are multilayered in structure. Due to the thickness of peptidoglycan, they retain and bind the crystal violet firmly and gives the purple colour when gram stained.

Conclusion

To wrap up this post, we conclude that gram positive  have thicker cell wall than gram negative bacteria. Cell wall composition is same  but they vary according to the shape, type and size of bacteria. The differentiation of bacteria can be done by using Gram staining technique.

Saif Ali

Hi, I am Saif Ali. I obtained my Master's degree in Microbiology and have one year of research experience in water microbiology from  National Institute of Hydrology, Roorkee. Antibiotic resistant microorganisms and soil bacteria, particularly PGPR, are my areas of interest and expertise. Currently, I'm focused on developing antibiotic alternatives. I'm always trying to discover new things from my surroundings.  My goal is to provide readers with easy-to-understand microbiology articles. If you have a bug, treat it with caution and avoid using antibiotics to combat SUPERBUGS. Let's connect via LinkedIn:http://linkedin.com/in/saif-ali-80b5098b

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