MCB Lecture 44 Introduction to Bacteria I Flashcards

0
Q

What is the average size of a bacterium?

A

1-2 microns

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1
Q

List the general features of bacteria

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

Compare organelles in eukaryotic and prokaryotic cells

A

Prokaryotic cells have no membrane bound organelles

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3
Q

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

A

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

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4
Q

What are plasmids?

Describe how they replicate, and their presence in a cell

A

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

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5
Q

Describe the features of a bacterial cell wall.

A

One or two plasma membranes

Layer of peptidoglycan

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6
Q

Describe the process of the gram stain

A
  1. Purple stain
  2. Wash
  3. Lipid solvent wash
  4. Counter stain
  5. Wash
  6. Lipid solvent
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7
Q

Why is the Gram stain useful?

A

It categorises a bacterium into either G+ or G-

We can tell much about a bacterium through this classification

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8
Q

Describe the structure of a G+ bacterium cell wall

A

One plasma membrane surrounded by a thick layer of peptidoglycan

Much more simpler than G-
Less protective, has pores

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9
Q

Describe the structure of a G- bacterium cell wall

A

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

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10
Q

Describe the structure of Peptidoglycan

A

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

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11
Q

What is LPS?

Where is it found?

A

Lipopolysaccharide

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

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12
Q

What is the function of LPS?

A
  1. Endotoxin: it is a major PAMP recognised by the innate immune system
  2. It is vital for the integrity of bacterial cell walls
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13
Q

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

A

G-

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14
Q

What is an endotoxin?

A

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

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15
Q

Compare eukaryotic and prokaryotic ribosomes

A

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

16
Q

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

A

It is highly conserved amongst all forms of life

17
Q

Describe the features of the prokaryotic cytoplasmic matrix

A
  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
18
Q

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

A

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

19
Q

What is the charge of bacterial cell walls?

A

Negative

20
Q

Which molecule is only found in Gram positive cell walls?

A

Teichoic acid

21
Q

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

A

Bile salts

Some antibiotics