Notes : 6.5 + 6.6 TB and HIV

Question 1

What is a pathogen ?

Answer 1

Any organism which causes disease.

Question 2

What are viruses

Answer 2

Nucleic acids surrounded by protein coat (capsid). They are also non-living

Question 3

Blurt all the pathogenic microorganism you know

Answer 3

• Bacteria - Mycobacterium tuberculosis causes TB
• Virus - HIV causes AIDS, COVID-19 causes coronavirus, the influenza virus causes seasonal flu
• Protoctist - Plasmodium causes malaria
• Fungi - Trichophyton causes Athlete’s foot

Question 4

What is HIV

Answer 4

A virus that targets CD4+ cells ( A T helper cell)

Question 5

How does HIV spread ?

Answer 5

Through infected bodily fluids.

Question 6

HIV structure

Answer 6

• GP120 attachment proteins on the envelope (these attach to CD4+ cells on macrophages or T helper cell)
• 2 identical-single stranded RNA molecules
• Reverse transcriptase (An enzyme)
• a protein coat called a capsid
• Surrounding the capsid is an outer layer called the envelope

Question 7

How does HIV replicate ?

Answer 7

• The GP120 attachment proteins on the surface of HIV attach to the CD4 receptors on the surface of T helper cell.
• The HIV viral envelope then fuses with the cell membrane of the T helper cell.
• The viral RNA is then released into the cells cytoplasm where it releases its genetic material (RNA & enzymes)
• Inside the cell, the enzyme reverse transcriptase converts the viral RNA into double stranded DNA.
• The DNA is now inserted into the DNA of the T cell through the enzyme integrase
• The T cell now has the viral genetic material to produce viral proteins from the viral DNA.
• The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells.

Question 8

When do we diagnose a person with AIDS ?

Answer 8

• When their T helper cell count falls below a lower number than normal.

Question 9

What happens as AIDS progress ?

Answer 9

• The number of T helper cell decreases further and they become more susceptible to infections.
• Eventually their immune system will be so weak that they will die of an opportunistic infection because they do not have enough immune cells to defend themselves.

Question 10

The acute phase of HIV

Answer 10

• Rapid viral replication
• Rapid loss of T helper cells
• Symptoms: fever, headache, swollen lymph nodes - maybe none

Question 11

The chronic phase of HIV (Aka latent phase)

Answer 11

• Now prolonged due to antiretroviral drugs
• Virus is still replicating but but drops to a lower level.
• May be no symptoms - increasingly likely to suffer from colds or other minor infections. Take longer to heal from these.
• Dormant diseases e.g. TB and shingles reactivate

Question 12

The disease phase of HIV

Answer 12

• viral load increases
• T helper cell numbers decrease
• This indicates the onset of AIDS - the disease phase
• Initial symptoms of AIDs : recurring respiratory infections caused by a lower number of T helper cells
• Immune system is now vulnerable to other diseases - opportunistic infections

Question 13

Draw the structure of bacteria.

Answer 13

Question 14

Compare and contrast the structure of bacteria and viruses.

Answer 14

• Bacteria has Cell wall whereas virus has capsid
• Bacteria has ribosomes virus doesn’t
• Virus has attachment protein bacteria doesn’t

Question 15

How does TB spread

Answer 15

Droplet inhalation i.e. when an infected person sneezes or coughs

Question 16

What bacteria causes tuberculosis

Answer 16

Mycobacterium tuberculosis

Question 17

Why isn’t tuberculosis destroyed by a macrophage

Answer 17

• They have produce a protein that inhibits the binding of lysozyme to their cell wall so the bacteria isn’t broken down.

Question 18

What happens in latent TB

Answer 18

• The immune system seal off infected phagocytes inside tubercules so that it isn’t able to multiply.
• The bacteria lie dormant.
• They also have a thick waxy cell wall which is hard for the lysozyme to digest.
• The infected person shows no obvious symptoms

Question 19

Why does TB become reactivated ?

Answer 19

• As the person’s immune system is weak (e.g due to aids, malnutrition, age)

Question 20

How long can Mycobacterium tuberculosis remain dormant for and why ?

Answer 20

It varies for each individual so can be from week to a few years.

Question 21

What happens during active TB

Answer 21

• Bacteria multiply rapidly
• Which destroys the tissue within the lungs
• If left untreated it can cause respiratory failure, which can lead to death.
• B can also spread from the lungs to other parts of the body, e.g. the brain and kidneys. If it’s left untreated it can cause organ failure, which can lead to death.

Question 22

What are the initial symptoms of TB

Answer 22

• Severe coughing, fever and general weakness.