Bacterial Cell Wall | Gram positive & Gram negative bacteria cell wall| Structure|Salient features|

Summary

This video script explores the structural differences between Gram-positive and Gram-negative bacterial cell walls, highlighting key components such as peptidoglycan, teichoic acids, outer membranes, and surface proteins. It covers the roles of various molecules in bacterial interaction with their environment and pathogenicity. For Gram-positive bacteria, the thick peptidoglycan layer and teichoic acids are essential, while Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane with lipopolysaccharides (LPS) that enhance virulence. The script also discusses the function of periplasmic space and surface proteins in bacterial processes.

Takeaways

• 😀 Gram-positive bacterial cell walls contain a thick peptidoglycan layer that provides structural support and is key in bacterial protection.
• 😀 The peptidoglycan layer in gram-positive bacteria includes NAG and NAM sugars along with a tetrapeptide chain for cross-linking.
• 😀 Teichoic acid in gram-positive bacteria is covalently attached to both the peptidoglycan and plasma membrane, contributing to the cell's negative charge.
• 😀 The outer membrane of gram-negative bacteria is composed of lipopolysaccharides (LPS), which play a role in bacterial virulence and endotoxin production.
• 😀 LPS consists of three parts: lipid A (toxin), core polysaccharide (sugars), and the O-side chain, which can act as an antigen.
• 😀 Periplasmic space in both gram-positive and gram-negative bacteria acts as a region for proteins and enzymes that aid in nutrient acquisition.
• 😀 Gram-negative bacteria have an additional outer membrane that is crucial for pathogen defense and permeability regulation.
• 😀 Porin proteins in the outer membrane of gram-negative bacteria allow the passage of small molecules, such as glucose.
• 😀 Gram-positive bacteria often produce surface proteins that interact with the environment, such as host or soil, and contribute to bacterial pathogenicity.
• 😀 The periplasm of gram-negative bacteria contains hydrolytic enzymes and transport proteins that help acquire nutrients from the surrounding environment.
• 😀 M proteins in pathogenic Streptococci are surface proteins that contribute to the virulence of the bacteria, aiding in the pathogenesis of diseases.

Q & A

What is the primary structural component of the bacterial cell wall in gram-positive bacteria?

The primary structural component of the bacterial cell wall in gram-positive bacteria is peptidoglycan, which is composed of alternating sugar subunits (N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)) linked with peptide chains.

What is the difference in the thickness of the peptidoglycan layer between gram-positive and gram-negative bacteria?

In gram-positive bacteria, the peptidoglycan layer is thick (20-80 nm), while in gram-negative bacteria, the peptidoglycan layer is much thinner, usually between 2-7 nm.

What is the role of techoic acid in the cell wall of gram-positive bacteria?

Techoic acid is covalently bound to peptidoglycan and the plasma membrane in gram-positive bacteria. It helps to give the cell wall a negative charge, aids in structural integrity, and plays a role in the bacteria's interaction with its environment.

What is the function of periplasm in gram-negative bacteria?

The periplasm is the space between the outer membrane and the plasma membrane in gram-negative bacteria. It contains periplasmic proteins that are involved in nutrient acquisition, including hydrolytic enzymes and transport proteins.

What is the difference between the cell walls of gram-positive and gram-negative bacteria in terms of surface proteins?

Gram-positive bacteria have surface proteins bound to the peptidoglycan layer or techoic acids, which help the bacteria interact with its environment (such as host cells or soil). Gram-negative bacteria also have surface proteins, but these are often associated with the outer membrane.

How does the outer membrane contribute to the pathogenicity of gram-negative bacteria?

The outer membrane of gram-negative bacteria contains lipopolysaccharides (LPS), which contribute to the bacteria's virulence. LPS acts as an endotoxin, plays a role in bacterial adhesion, and acts as a permeability barrier.

What are lipopolysaccharides (LPS), and what are their components?

Lipopolysaccharides (LPS) are molecules found in the outer membrane of gram-negative bacteria. LPS consists of three components: lipid A (which is responsible for the endotoxin activity), core polysaccharide (which is made up of sugars), and the O side chain (which can act as an antigen).

What is the role of porin proteins in gram-negative bacteria?

Porin proteins are embedded in the outer membrane of gram-negative bacteria and facilitate the transport of small molecules such as glucose and other monosaccharides through the cell wall, which would otherwise not be able to pass through the plasma membrane.

What is the periplasmic space, and what does it contain in gram-negative bacteria?

The periplasmic space in gram-negative bacteria lies between the outer membrane and the plasma membrane. It contains periplasmic proteins that help in nutrient acquisition and include hydrolytic enzymes and transport proteins.

How does the presence of a peptide interbridge in gram-positive bacteria affect the peptidoglycan layer?

The peptide interbridge in gram-positive bacteria strengthens the peptidoglycan layer by linking individual peptidoglycan chains, adding structural rigidity. This interbridge is absent in gram-negative bacteria.