Bacteria

Question 1

Name 5 differences between prokaryotes and eukaryotes

Answer 1

1. Prokaryote cell walls contain peptidogylcan
2. Prokaryotes are not compartmentalised
3. Singular circular chromosome (nucleoid) with no membrane-bound nucleus
4. Mitochondria are 70s and not 80s
5. Bacterial cell membranes do not contain sterols

Question 2

In what ways can bacteria divide?

Answer 2

In chains - diplococci
Two planes - tetrad
Three planes - cluster

Question 3

What is the function of the bacterial cell wall?

Answer 3

To confer structure, rigidity, shape and protect from osmotic lysis

Question 4

What is the structure of peptidoglycan?

Answer 4

Overlapping lattice of 2 sugars linked by amino acid (tetrapeptide containing D and L amino acids) bridges
N-acetyl glucosamine (NAG)
N-acetyl muramic acid (NAM)

Question 5

What cell wall structure is targeted by penicillin?

Answer 5

Transpeptides

Question 6

What is the difference in structure between gram +ve and gram -ve bacteria?

Answer 6

Gram +ve - Peptidoglycan followed by plasma membrane

Gram -ve - Outer membrane followed by peptidoglycan, followed by a periplasmic space before the plasma membrane

Question 7

What are the 4 steps in gram staining? How do gram +ve and gram -ve cells differ?

Answer 7

1. Fixation of cells
2. Addition of crystal violet stain (stains indigo)
3. Treatment of iodine (cells now purple)
4. Decolorisation (Gram +ve remain purple, gram -ve now colourless)
5. Counterstained with safranin (gram +ve remain purple, gram -ve stained pink)

Question 8

How is DNA packed into bacterial cells?

Answer 8

Via supercoiling due to the action of DNA gyrase, removal of this is done by topoisimerase I

Question 9

How do bacteria replicate?

Answer 9

• Helicase unwinds at the origin to expose single-stranded DNA, synthesising DNA semi-conservatively with primase synthesis primers and DNA-dependant DNA polymerase
• Binary fission then occurs via the extension of the cell wall and the membrane, then septum formation
• Membrane attaches and pulls each daughter chromosome into a new cell

Question 10

What are spores?

Answer 10

Dormant survival structures that are resistant to high temperatures, disinfectants radiation and drying. Produced only by gram +ve and mainly by Bacillus and Clostridium

Question 11

What are capsules and their functions?

Answer 11

• Made from polysaccharide/polypeptide slime

- Protects bacterium from drying, phagocytic engulfment and flushing (adheres to surfaces)

Question 12

What are pilli?

Answer 12

• Protein tubes found mostly on gram -ve bacteria

- Have adhesive tip (lectin) and the end of a shaft that binds to specific sugars on glycoprotein/glycolipid receptors

Question 13

What are the 3 parts of flagella?

Answer 13

• outermost region composed of helical chains of flagellin with a hollow core
• hook
• basal body consisting of a rod and a series of rings anchoring the flagellum to the cell

Question 14

What 2 factors does virulence include?

Answer 14

1. Factors affecting colonisation

2. Factors affecting damage

Question 15

What factors affect the colonisation of the host cell?

Answer 15

Ability to adhere, invade, contact, resist phagocytosis, evade immune response and compete for nutrients

Question 16

What 3 methods can the body use to prevent adherance?

Answer 16

• shedding of skin
• coughing, sneezing, vomiting
• bodily fluids

Question 17

What 3 mechanisms can a bacteria have to aid in adhesion?

Answer 17

Pilli - Protenaceous tip can change to avoid the immune response
Adhesions - proteins on surface enabling them to bind to host cell surface
Capsules - avoid flushing response

Question 18

How do invasins work?

Answer 18

Allow pathogen to invade host cell by activating cytoskeleton machinery and allowing entry via phagocystosis. Once inside bacterium then has access to nutrients and is protected from body defenses

Question 19

How can bacteria increase the chance of contacting cells?

Answer 19

By being mobile e.g using flagella to move through mucous

Question 20

How can bacteria avoid the response of IgG antibodies?

Answer 20

• IgG contains fab portion which fits shape of the bacterial pathogen, protein C3b binds to bacterial surface proteins and phagocyte receptors (oponins)
• In some bacteria capsule cover oponin C3b so it cannot bind

Question 21

What 4 ways can a bacteria avoid phagocytic destruction?

Answer 21

1. Preventing acidification of the phagosome
2. Killing phagocytes with their own enzymes by producing leukocids which damage lysosomes
3. Resistance to toxic forms of oxygen and defensins
4. Blocking of vesicular transport machinery

Question 22

How can bacteria evade the immune response?

Answer 22

• Varying surface proteins so that antibodies no longer fit

e. g resembling carbohydrates found in the human body or coating itself in a protecting layer of antibodies

Question 23

How do bacteria compete for iron in the body?

Answer 23

Synthesize iron chelators called siderophores

Question 24

How do A-B toxins damage a host?

Answer 24

• Composed of active (A) and binding (B) component
• B component binds to cell and A component enters cell, passing through the membrane and causing damage via ADP-ribosylation of host cell protein
• Nicotinamide adenine dinucleotide (NAD) is cleaved into nicotinamide and adenine diphosphate ribose (ADPR) causes inactivation of covalently attached target protein

Question 25

How is LPS toxic?

Answer 25

• So immunogenic that it is toxic

- composed of O-antigen, core polysaccharide and lipide-A

Question 26

What occurs during septicaemia?

Answer 26

High levels of cell wall components (techoic acids composed of polymers of glycerol, phophates and sugar rubitol) result in damage to the body