Communicable diseases - Animal and plant pathogens

Question 1

What causes communicable diseases?

Answer 1

Pathogens

Question 2

Sections of pathogens?

Answer 2

• Bacteria
• Viruses
• Fungi
• Protocista

Question 3

Vectors

Answer 3

Organisms that carry pathogens from one organism to another. Involved in the spread of a plant and animal diseases.

Question 4

Bacteria

Answer 4

• Prokaryotes
• Cell structure different from eukaryotic organisms they infect

Question 5

How can bacteria be classified?

Answer 5

Basic shapes:
- Rod shaped (bacilli) –> chain of bacilli (streptobacilli)
- Spherical (cocci) –> chain of cocci (streptococci) / cluster of cocci (staphylococci)
- Comma shaped (vibrios)
- Spiralled (spirilla)
- Corkscrew (spirochaetes)

By cell walls:
- Gram staining –> Gram positive bacteria and gram negative bacteria

Question 6

Gram positive bacteria:

Answer 6

• Blue purple under light microscope after Gram staining.
• Eg. methicillin-resistant

Question 7

Gram negative bacteria:

Answer 7

• Loose purple blue stain
• Eg. gut bacteria

Question 8

Viruses

Answer 8

• Non-living infectious agents
• All natural viruses are pathogens

Structure:
- RNA surrounded by protein

Question 9

How do viruses cause diseases?

Answer 9

• Invade living cells, where genetic material of the virus takes over the biochemistry of the host cell to make more viruses
• Viruses reproduce rapidly and evolve by developing adaptations to their host, very successful pathogens.

Question 10

Viruses that attack bacteria?

Answer 10

Bacteriophages

Question 11

How do scientists view viruses?

Answer 11

Ultimate parasites

Question 12

Why are all naturally occurring viruses pathogenic?

Answer 12

• They cause disease in every other type of organism.

Question 13

Protoctista:

Answer 13

• Wide variety of feeding mechanisms
• Single-celled organisms and cells grouped into colonies.

Question 14

Protoctista that act as pathogens?

Answer 14

• Parasitic
• Use people / animals as host organisms
• May need vector to transfer to their hosts
• Can enter body directly through water

Question 15

Are fungal diseases a problem?

Answer 15

• Problem for plants
• Not problem for animals

Question 16

Fungi:

Answer 16

• Multicellular
• Yeasts that cause human diseases (thrush) are unicellular

Question 17

Fungi feeding mechanism?

Answer 17

• Fungi cannot photosynthesise and they digest their food extracellularly before absorbing nutrients
• Saprophytes –> feed on dead and decaying matter.
• Some are parasitic and feed on living plants and animals.

Question 18

How do fungi infections kill plants?

Answer 18

• Leaves
• Stop them from photosynthesising

Question 19

Fungi reproduction:

Answer 19

• Produce millions of tiny spores that spread huge distances

Question 20

Modes of pathogen action:

Answer 20

• Damaging host tissues directly
• Producing toxins that damage hosts

Question 21

How do pathogens damage host tissues:

Answer 21

• Viruses take over the cell metabolism. The viral genetic material gets into host cell and is inserted into the host DNA. New viruses burst out of cell, destroying it and then spread to infect other cells
• Some Protoctista take over cells and break them open as the new generation emerge, but do not take over other genetic material of cell. Digest and use cell components as they reproduce.
• Fungi digest living cells and destroy them.

Question 22

How do pathogens produce toxins to damage host tissues?

Answer 22

• Most bacteria produce toxins that poison / damage host cells.
• Bacterial toxins break down cell membranes / damage and inactivate enzymes / interfere with host cells genetic material so they cannot divide.
• Toxins are a by-product of normal functioning of bacteria
• Some fungi produce toxins too.

Question 23

Viruses key point

Answer 23

Viruses invade cells before integrating their viral genome into the host cell’s genome. This causes the host cell to manufacture multiple copies of the virus which are released when the cell bursts.

Question 24

How do viruses enter the cell?

Answer 24

gp120 is an envelope glycoprotein that is exposed on the surface of the HIV lipid envelope and this structure is essential for the entry of the virus into a host cell

Question 25

What is the role of the T helper cell?

Answer 25

- Release chemicals that stimulate the T killer cells, the B plasma cells and phagocytes - CD4 receptor is a glycoprotein found on the surface of a T helper cell. Directly involved in infection of human cells by HIV

Question 26

HIV virus structure:

Answer 26

- gp120 glycoprotein - lipid membrane - capsid - viral strands of DNA - Enzymes

Question 27

3 enzymes found in HIV?

Answer 27

- Reverse transcriptase - Integrase - Protease

Question 28

Reverse transcriptase function -->

Answer 28

- Catalyses the use of viral RNA to form viral DNA, in a process called reverse transcription

Question 29

Integrase function

Answer 29

Catalyses the integration of the viral DNA into the genome of the host cell

Question 30

Protease

Answer 30

Catalyses the break up of large polyproteins into smaller pieces which is critical for the assembly of new viral particles called virons

Question 31

Process of infecting host cells by HIV:

Answer 31

- Using the exposed glycoprotein, gp120, HIV binds to the CD4 receptor on the T helper cells. A structural change in the gp41 envelope protein then enables the fusion of the viral and cellular membranes - The HIV virion is then able to penetrate the CD4 receptor membrane and enter the host cell. This allows the capsid to be injected directly into the cytoplasm of the T helper cell - The viral RNA, which was previously protected by the capsid, needs to be released to allow the virus to take over the host cell. Therefore, the capsid partially dissolves in a process called uncoating - Reverse transcriptase catalyses reverse transcription where the single-stranded viral RNA strands are used as a template by the DNA nucleotides to line up to form double-stranded DNA - The newly-synthesised viral DNA is transported across the nuclear membrane into the nucleus. Integrase then catalyses the integration of this viral DNA into the genome of the host cell. - The viral DNA is known as the provirus and will remain latent for a period of time whilst awaiting activation. Upon activation, the provirus instructs the cell machinery to form the components of HIV - The two strands of viral RNA are transported out of the nucleus. One strand moves through the ribosomes where it is translated into the subunits of HIV whilst the other strand becomes the genetic material for new viruses - The protease enzyme breaks up large polyproteins into smaller pieces to assemble the virions. During the final stage called budding, the newly formed virions are released out of the cell by exocytosis, and enter the circulation where they can attach to other T helper cells using gp120

Question 32

Why does HIV weaken the immune system?

Answer 32

- The number of T helper cells decreases - The number of virus particles in the blood increases

Question 33

Tobacco mosaic virus profile:

Answer 33

Infects: tobacco, tomato, pepper, cucumbers - First symptom is a light green colouration between the veins of young leaves - followed by a 'mosaic' or mottled pattern and dark green areas in the leaves Results: not death. Occurs early in season and plant growth is stunted

Question 34

Suggest two reasons why the staff responsible for the maintenance of the huge greenhouses at the Royal botanic gardens in Kew are always concerned by the spread of TMV

Answer 34

- High population density of possible hosts - Constant temperature throughout year (TMV is stable virus and can sustain form as long as temperature is below 40 degrees)

Question 35

Ring rot (bacteria)

Answer 35

- Potatoes - Tuberculosis

Question 36

Fungi that effects bananas?

Answer 36

Lack sigatoka

Question 37

How do protista damage cells?

Answer 37

they take over a cell, digest the insides and use this as a medium to reproduce, before bursting out.

Question 38

What causes malaria?

Answer 38

Protists