6A: Microbiology

Question 1

What are pathogens?

Answer 1

microorganisms that cause disease

Question 2

What main features do all bacteria (as typical prokaryotes) have?

Answer 2

• a bacterial cell wall containing peptidoglycan
• a cell surface membrane similar to those in eukaryotic cells
• a nucleoid (single, circular strand of DNA that is the genetic material of the bacterium)
• 70S ribosomes, site of protein synthesis

Question 3

What main features do only some bacteria have?

Answer 3

• pili: thread-like projections from the surface of the cell wall
• flagella: long rapidly rotating whip-like structures which can move bacteria about
• capsule / slime layer: thick slippery substance around outside of the cell wall
• mesosomes: internal extensions of membrane which fold into cytoplasm and may be site of cellular respiration
• plasmids: small circles of additional DNA that code for specific characteristics

Question 4

What can different bacteria act as?

Answer 4

• parasites
• mutualistic organisms
• saprophytes (organisms that feed on dead and decaying organic material)

Question 5

Description of what viruses are + what they do:

Answer 5

• smallest of microorganisms (0.02 - 0.3 micrometres)
• they are arrangements of genetic material and protein that invade living cells and take control of the cellular biochemistry to make more viruses

Question 6

Why are viruses classed as living organisms?

Answer 6

as they reproduce by invading living cells and taking control of their biochemistry and they change and evolve in an adaptive way

Question 7

What do scientists class viruses as and why?

Answer 7

• scientists class them as obligate intracellular parasites

- this means they only exist and reproduce as parasites in the cells of other living organisms

Question 8

What types of conditions can viruses resist and what ability do they maintain?

Answer 8

viruses can resist drying and long periods of storage and still maintain ability to infect cells

Question 9

What does a virus look like?

Answer 9

viruses are usually geometric shapes with similar basic structures but their genetic material and structure of protein coat vary

Question 10

All viruses have the following characteristics:

Answer 10

• protein coat or capsid
• nucleic acids acting as genetic material
• specific proteins (antigens) known as virus attachment particles (VAPs)

Question 11

Describe the virus characteristic of a protein coat/capsid

Answer 11

• consists of simple repeating protein units known as capsomeres arranged in different ways
• amount of genetic material needed to code for coat production is minimised by using repeated units
• units also making assembling protein coat in host cell as simple as possible

Question 12

Describe the virus characteristic of a nucleic acid acting as genetic material

Answer 12

• can be DNA/RNA and double/single stranded

- the viral genetic material is used differently in the host cell to make new viruses depending on which form it’s in

Question 13

Describe the virus characteristic of an antigen (VAP)

Answer 13

• they target proteins in host cell surface membrane

- that’s how viruses attach to cells they infect, VAPs respond to particular molecules on host cell surface

Question 14

Some viruses have the characteristic + explain:

Answer 14

• a lipid envelope:
  >produced from host cell membrane and covers genetic material and protein coat
  >presence of envelope makes it easier for viruses to pass from cell to cell but makes it vulnerable to substances like ether which dissolves the lipid membrane

Question 15

Describe DNA viruses that have DNA as their genetic material

Answer 15

• viral DNA acts directly as a template for both new viral DNA and for mRNAs needed to induce synthesis for viral proteins
  e. g. lambda phage, a type of bacteriophage

Question 16

Describe RNA viruses that have RNA as their genetic material

Answer 16

• these are much more likely to mutate than DNA viruses
• they don’t produce DNA
• majority contain a single strand of RNA
  e. g. tobacco mosaic viruses (TMV), Ebola fever

Question 17

Describe retroviruses (special type of RNA virus)

Answer 17

• have protein capsid and lipid envelope
• the single strand of viral RNA controls synthesis of enzyme reverse transcriptase which is responsible for making DNA molecules corresponding to viral genome
• DNA is then incorporates into host cell DNA and used as template for new viral proteins and new viral RNA genome
  e. g. HIV