2.2Prokaryotic Cells And Viruses

Question 1

How are viruses classified

Answer 1

According to structure and type of nuclei acid

Question 2

Name 3 types of virus and give examples

Answer 2

DNA virus eg lambda phage
RNA virus eg tobacco mosaic virus and Ebola
RNA retrovirus eg human
Immunodeficiency virus (HIV)

Question 3

Describe the structure of a DNA virus

Answer 3

Nucleic acid: DNA (which can act directly as a template for mRNA transcription/ DNa replication)

Geometrical shape

Protein coat (capsid)

Viruses can have membranes- the surfaces have attachment proteins (viral antigens)which allow the virus to attach to the host cells

Question 4

Compare and contrast the tobacco mosaic virus and Ebola

Answer 4

Both are RNA viruses

Tobacco mosaic virus contains ssRNA, which can be directly be translated into proteins by ribosomes

Ebola contains negative ssRNA, which needs to be transcribed to produce mRNA before translation

Question 5

Describe the features of an RNA retrovirus

Answer 5

Single strand of RNA

Reverse transcriptase enzyme produces cDNA from RNA template

Double-stranded viral DNA integrates into host cell’s genome

Question 6

Describe the lysogenic pathaway

Answer 6

1.Non-virulent viruses inject DNA into host cell DNA as provirus. Viral DNA replicates when host cell divides.
2. Virus produces repressor proteins to inhibit transcription.
3. Latent virus enters lytic pathway when host cell is damaged or immune system weakens.

Question 7

Describe lyctic cycle

Answer 7

1. Virulent viruses inject nucleic acid into host cell cytoplasm. Viral genetic information replicates immediately.
2. Many virions assemble, causing cell lysis to burst

Question 8

Why are viruses classsified as non-living

Answer 8

They are acellular: no cytoplasm, no metabolism and cannot self-replicate

Question 9

How do antivirals work?

Answer 9

Viruses have no metabolism = difficult to treat infection after initial contact. Antivirals inhibit viral replication by:

Targeting viral antigens to prevent entry into host

Targeting viral enzymes to prevent DNA replication and virion assembly

Question 10

What is the focus of disease control for viral infections?

Answer 10

Prevent spread (especially when there is no effective vaccine).

Question 11

Outline what happened during 2014 Ebola outbreak

Answer 11

Virus spread rapidly through areas of west Africa with poor hygiene. 4877 deaths. No effective vaccine, so disease control measures aimed to reduce spread

Question 12

Outline common methods of controlling viral outbreaks

Answer 12

• Rapid indentification and testing the individuals contacts for disease
• reduce peer to personal contact with virus:

B) Quarantine
Sterilisation of equipment
Protective clothing

Question 13

Suggest the ethical issue surrounding the use of untrialled drugs during epidemics

Answer 13

Severity of outbreak
How effective other avliable treatments are
Difficulty obtaining informed consent

Question 14

Suggest arguments against the use of untrained drugs during epidemics

Answer 14

Unanticipated severe side effects
Difficult to decide which individuals to treat first
Drug may be falsely attributed as the cause of death
Severely ill patients cannot give informed consent

Question 15

Structure and function of pili

Answer 15

Hair-like structures which attach to other bacterial cells and allow plasmids to move from cell to cell

Question 16

Structure and function of flagellum

Answer 16

Tail like structures which attach to other bacterial cells and allow plasmids to move from cell to cell

Question 17

What are 70s ribosomes composed of?

Answer 17

Composed of a large (50S) subunit and a small (30S) subunit. The site of protein synthesis

Question 18

Structure and function of cell wall (bacterial)

Answer 18

The cell’s rigid outer covering made of peptidoglycan. Provides the cell with strength and support.
Since the contents of bacterial cells are usually hypertonic to the medium around them, water tends to move into the cells by osmosis.

Th cell wall prevents the the cell from swelling and bursting.

Question 19

what is the nucleoid

Answer 19

irregularly-shaped region of cytoplasm where loop of bacterial DNA is located

Question 20

What is a plasmid

Answer 20

1 or more rings of DNA found in some bacterial cells contains non-essential genes(not needed for the survival of bacteria) can be exchanged between bacterial cells via conjugation

Question 21

describe the structure of a bacterial cell wall and slime capsule

Answer 21

peptidoglycan(murein) cell wall provides mechanical strength may be coated by slime layer to prevent desiccation(drying) ,adhere cells and provide nutrients

Question 22

outline process of gram staining

Answer 22

1. fixation-imobalises bacteria and makes it more permeable to dyes
2. crystal violet dye-absorbed by peptidoglycan
3. iodine solution forms crystals in violet dye
4. decorization- alcohol gram positive will be clear as dyes will be washed out. gram negative will stay purple as peptidoglycan has more layers
5. add red safranin to make negative appear red and examine under microscope

Question 23

describe gram positive cell walls

Answer 23

have thicker layer of pepidoglycan (insoluble in alcohol) purple under microscope when stained

Question 24

describe gram negative cell walls

Answer 24

thinner layer of petidoglycan with outer lipopolysaccharide membrane(surface membrane) (alcohol-soluble)
appear red under microscope when stained

Question 25

why do Gram positive and Gram negative bacteria respond differently to certain antibiotics

Answer 25

Gram negative bacteria have an outer membrane and a much thinner peptidoglycan layer, they are not affected.

Question 26

compare ribosomes in eukaryotic and prokaryotic cells

Answer 26

formed of protein and rRNA

made up of a large and a small subunit. During translation, the two subunits come together around a mRNA molecule, forming a complete ribosome.

Question 27

contrast ribosomes in eukaryotic and prokaryotic cells

Answer 27

larger subunit eukaryotic: 805 (bigger) smaller subunit prokaryotic 70S (smaller)

Question 28

What’s a capsid

Answer 28

Genetic material is contained inside a protein structure called a capsid

Question 29

Why can you not use antibiotics to treat viruses

Answer 29

Viruses are not living cells

They do not have a cell wall4