MCB Lecture 44 Introduction to Bacteria I

Question 0

What is the average size of a bacterium?

Answer 0

1-2 microns

Question 1

List the general features of bacteria

Answer 1

Size: 1-2 microns
No membrane bound organelles
Smaller ribosomes
Single, circular piece of DNA
Cell wall made of peptidoglycan

Question 2

Compare organelles in eukaryotic and prokaryotic cells

Answer 2

Prokaryotic cells have no membrane bound organelles

Question 3

Describe the genetic component of prokaryotic cells, including location and structure

Answer 3

Single, circular piece of dsDNA

Genetic material is located in the nucleoid, there are also RNA and protein

Plasmids can also be present in the cytosol

Question 4

What are plasmids?

Describe how they replicate, and their presence in a cell

Answer 4

These are small fragments of DNA present in a loop
They are not replicated at the same time as the chromosome
They use the bacteria’s machinery to replicate

They are variable in size and number

Question 5

Describe the features of a bacterial cell wall.

Answer 5

One or two plasma membranes

Layer of peptidoglycan

Question 6

Describe the process of the gram stain

Answer 6

1. Purple stain
2. Wash
3. Lipid solvent wash
4. Counter stain
5. Wash
6. Lipid solvent

Question 7

Why is the Gram stain useful?

Answer 7

It categorises a bacterium into either G+ or G-

We can tell much about a bacterium through this classification

Question 8

Describe the structure of a G+ bacterium cell wall

Answer 8

One plasma membrane surrounded by a thick layer of peptidoglycan

Much more simpler than G-
Less protective, has pores

Question 9

Describe the structure of a G- bacterium cell wall

Answer 9

Inner and outer membrane, sip which surround a thin layer of peptidoglycan

Much more complex than G+

The outer membrane forms a protective barrier, that only allows small molecules and glucose in
Antibiotics and bile salts are excluded
Complex secretory systems are required

LPS found on the outer membrane

Question 10

Describe the structure of Peptidoglycan

Answer 10

Alternating “bricks” of N-acetyl glucosamine and N-Acetyl muramic acid

Peptide chains: different amino acids
These connect the sugar to the pentapeptide bridges
Alternating D and L amino acids –> prevents flexibility
Rigid structure of peptidoglycan

Pentapeptide bridges: same amino acids
Connect to the peptide chains

Question 11

What is LPS?

Where is it found?

Answer 11

Lipopolysaccharide

It is a molecule that is always found on the outer membrane of gram negative bacteria

Question 12

What is the function of LPS?

Answer 12

1. Endotoxin: it is a major PAMP recognised by the innate immune system
2. It is vital for the integrity of bacterial cell walls

Question 13

Which type of bacteria (G- or G+) has a more protective barrier in its cell wall

Answer 13

G-

Question 14

What is an endotoxin?

Answer 14

It is a toxin produced by a bacterium that is not released into the environment, but instead localised in or on the bacterium

Question 15

Compare eukaryotic and prokaryotic ribosomes

Answer 15

Prokaryotic ribosomes are smaller: 50S + 30S = 70S

Question 16

What is important about the rRNA in the small ribosomal subunit?

Answer 16

It is highly conserved amongst all forms of life

Question 17

Describe the features of the prokaryotic cytoplasmic matrix

Answer 17

1. Hypertonic: potentially will take in water and swell. However, the cell wall prevents this
2. Many ribosomes present
3. Contains inclusion bodies: nutrition: storage of nutrients

Question 18

How do bacteria prevent lysis due to water entering the cell?

Answer 18

They have a rigid cell wall that prevents too much water entering

Question 19

What is the charge of bacterial cell walls?

Answer 19

Negative

Question 20

Which molecule is only found in Gram positive cell walls?

Answer 20

Teichoic acid

Question 21

The Gram negative cell wall acts as a protective barrier. Which things can it exclude?

Answer 21

Bile salts

Some antibiotics