Week 2 Lecture 2 Walling Off The Cytoplasm

Front 1

State what colour Gram-positive bacteria stain after the Gram stain procedure and briefly describe why.

Back 1

A Gram + bacteria are purple in colour because the bacteria retain the initial dye – crystal violet during the Gram stain procedure.

Front 2

Describe the composition of a Gram-positive cell wall indicating the possible or known functions of peptidoglycan, teichoic acids, and surface proteins.

Back 2

The Gram+ cell wall consists of numerous interconnecting layer of peptidoglycan. Interwoven in the cell wall are teichoic acids that extend through and beyond the rest of the cell wall and are composed of polymers of glycerol, phosphates and sugar alcohol (ribitol). The outer surface of the peptidoglycan is studded with proteins.
The peptidoglycan wall prevents osmotic lysis whereas the teichoic acids make the cell wall stronger. Both the peptidoglycan and teichoic acids function to stimulate the body’s defence systems:
- Trigger innate immune defences eg. Inflammation, fever, phagocytosis
- Activate alternative complement and lectin pathways
The surface proteins in the bacterial peptidoglycan carry out a variety of functions – functioning as enzymes etc.

Front 3

Describe what a peptidoglycan monomer consists of and state the function of peptidoglycan in bacteria.

Back 3

Peptidoglycan monomers (the NAG-NAM tetrapeptide building blocks of peptidoglycan) and teichoic acids from the Gram+ cell wall are recognised by defence cells of the body and initiate inflammation. They also bind to a receptor molecule (CD14) found on the surface of body defence cells.

Front 4

Briefly describe how bacteria synthesize peptidoglycan, indicating the roles of autolysins and transpeptidases.

Back 4

In order for bacteria to increase their size following binary fission, links in the peptidoglycan must be broken, new peptidoglycan monomers must be inserted and the peptide cross links must be resealed. Bacterial enzymes – autolysins break the peptide cross-links in the peptidoglycan while transpeptidase enzymes add the new peptidoglycan monomers and reseal the wall.

Front 5

State the structural component that makes peptidoglycan so strong.

Back 5

Peptidoglycan is a vast polymer consisting of interlocking chains of identical glycopeptide subunits or peptidoglycan monomers. A peptidoglycan monomer consists of 2 joined amino acids: NAG and NAM with a tetra-peptide coming off the NAM.

Front 6

State what colour Gram-positive bacteria stain after Gram staining and briefly describe why.

Back 6

Gram+ bacteria = purple because they retain the initial dye-crystal violet. E.g. Staph. Aureus.

Front 7

State what colour Gram-negative bacteria stain after Gram staining.

Back 7

Gram – bacteriea = pink because they decolorize during Gram staining and pick up the counter-stain – safranin. E.g. Salmonella species

Front 8

State what colour acid-fast bacteria stain after acid-fast staining.

Back 8

Acid fast bacteria resist decolorization with an acid-alcohol mixture during the acid-fast stain procedure and appear red when observed because they retain the initial dye carbolfushin.

Front 9

Describe the composition of a Gram-negative cell wall indicating the possible functions of peptidoglycan, lipopolysaccharide, porins, and surface proteins.

Back 9

In electron micrographs, the Gram- cell wall appears multilayered. It consists of an inner wall, an outer-membrane and a periplasm. The inner wall is composed of 2-3 layers of peptidoglycan and the outer membrane is composed of a lipid bilayer approx 7nm thick. (phospholipids, lipoproteins, LPS, proteins).
The peptidoglycan prevents osmotic lysis.
LPS provide strength to the outer membrane. It functions to stimulate the human body’s defence system. It also complements the host defence. The LPS portion of the outer membrane, when released, functions as a harmful endotoxin.
The surface proteins in the outer membrane function as: enzymes, adhesins, invasins and aid certain bacteria in resisting phagocytic destruction.

Front 10

Define periplasm.

Back 10

The periplasm is the gelatinous material between the outer membrane, the peptidoglycan and the cytoplasmic membrane. It contains enzymes for nutrient breakdown as well as binding proteins to facilitate the transfer of nutrients across the cytoplasmic membrane.

Front 11

Describe the composition of an acid-fast cell wall indicating the possible functions of peptidoglycan and the mycolic acid and other glycolipids.

Back 11

An acid-fast cell wall only contains small amounts of peptidoglycan. The acid-fast cell wall of Mycobacterium contains a large amount of glycolipids-mycolic acid for example.
Mycolic acid is a waxy lipid that makes up about 60% of the cell wall which makes it relatively impermeable.
Peptidoglycan prevents osmotic lysis.
The mycolic acid and other glycolipids also impede the entry of chemicals, therefore causing the organisms to grow more slowly and to become more resistant to chemical agents and lysosomal components of phagocytes.
NOTE: the mycolic acid molecules and muramyl dipeptides cause damage in the lungs during tuberculosis.

Front 12

Define the following: a. exoenzymes, b. endoenzymes. c. cytosol.

Back 12

Exoenzymes
Hydrolyse macromolecules into smaller molecules capable of being transported across the cytoplasmic membrane.
Endoenzymes
Control chemical reactions occurring within the bacterium
Cytosol
This liquid component of the cytoplasm

Front 13

State the primary function of the bacterial cytoplasm.

Back 13

The cytoplasm is the site of most bacterial metabolism. It includes catabolic reactions, and anabolic reactions.