Year 12 biology

• How HIV is spread

  Infected bodily fluid comes into contact with:

  Mucosal surfaces

  Damaged tissue

  Injected into bloodstream

  Sexual intercourse
• How HIV replicates


  In T helper cell

  - HIVglycoproteinattaches to CD4 receptors on host T helper cell membrane

  -viral envelope: fuses with host cell's cell surface membrane + releases viral RNA into cytoplasm

  - reverse transcriptase make DNA complementary strand from viral RNA template

  —> double strand viral DNA & is inserted into human DNA using enzyme integrase

  - host cell enzymes: make viral proteins from viral DNA

  - viral proteins: assembled, bud from cell & infect others

  - host cell is killed
• What is the latency period

  - when HIV/TB replication decreases to a lower level after initial infection period: no symptoms will be displayed

  - bacteria/ virus becomes dormant
• What causes AIDS


  needs rephrasing- people with HIV have failing immune system / decrease in T Helper cells

  - opportunistic infection
• What causes TB?


  Mycobacterium tuberculosis

  - inhaled droplets of it into lungs
• How does TB replicate?

  - Mycobacterium tuberculosis is engulfed by macrophages

  - Inflammatory response causes more cells to arrive.

  - Dead bacteria and macrophages become encased in a tissue mass called a tubercle. These are often anaerobic.

  
  

  - bacteria produce substances that will prevent a lysosome from fusing with the phagocytic vacuole -survive + replicates in lungs

  - TB is not developed:

  • They are difficult to kill due to waxy cell wall layer

  Can remain dormant for many years (latent TB)

  
  

  - bacteria becomes dormant= latent TB= no symptoms are shown
• What are the symptoms of TB from initial to serious?

  - initials: fever, general weakness and severe coughing

  - respiratory failure

  -
• What causes active TB

  - Immune system cannot contain the first infection.

  - An old infection resurfaces due to a weakened immune system.

  - bacteria reproduce rapidly and rupture tubercle

  - bacteria damage lung tissue

  bacteria surpasses T cell activity + antibody production
• What happens during active TB?

  Bacteria reproduce rapidly and rupture the tubercle.

  Bacteria damage the lung tissue.

  Bacteria suppresses T helper cell activity and antibody production
• Explain how active TB leader to shortness of breath? (3 marks)

  - TB bacteria damage endothelial cells in alveoli

  - reducing SA: V

  - less O2 can diffuse into alveoli from oxygenated blood
• Suggest how active TB could lead to organ failure and death? (3 marks)

  - TB bacteria enters blood stream + be transported to different parts of the organ

  - causing further infection as it can replicate rapidly

  - damage to tissues in organ can cause organ failure

  
  

  - supression of T helper cell causes les cytokines to be produced

  - B cells are not stimulated to divide, less B effector cells

  - less plasma cells and antibody production

  - less T killer cell

  - immune system is weakened, put you at risk of opportunistic 2nd infection
• Explain how suppression of T-helper cells put TB patients at risk of opportunistic secondary infections (5marks)?

  - T helper cells can't produce cytokinins to synthesise the cell division of B cells + T killer cells

  - B cells can't be activated, less B effector cells. Less is differentiated into plasma cells to release antibodies

  - T killer cells can't be activated + release chemicals for lysis of infected cells.

  -weakenedimmune system puts patient at risk of opportunistic secondary infection
• What is pre-mRNA


  mRNA containing introns and exons (copied during transcription)
• What does post-transcriptional changes to mRNA do?

  = alternative splicing

  -one gene can give rise to more than one protein

  
  

  DNA--> pre mRNA (introns are removed, exon are spliced together )--> mRNA
• explain why modification of pre-mRNA enables one gene to give rise to more than one protein?

  - diff. sequence of amino acid is formed

  - exon can be spliced together in a diff. order
• how does the evasion mechanism of influenza/ other pathogens supports the evolutionary race between pathogens and host?

  influenza can cause new epidemic and some cases pandemics.


  - antigenic drifts: gradual, normally through mutation (unlikely to cause epidemic)

  
  

  - antigenic shifts:

  rapid, involves genetic reassortment (diff. strains recombine within an individual to make new subtype)
• Explain how a pathogen may be able to evade the host's defences and how the host would respond to this? (5M)

  - mutation occurs in pathogen's DNA

  - causing a change in antigen on pathogen surface= antigenic variation

  - memory cells can't recognise the mutated antigen

  - 2nd immune response is not stimulated

  - Phagocytes can't recognise + engulf pathogen, can't present antigen

  - triggering new 1st immune responses APC presents antigen on CD4 receptors to T helper cells
• bacteriostatic antibiotics VS bactericidal

  Bacteriostatic: slows growth/ reproduction of bacteria

  - host immune system can destroy pathogen

  
  

  Bactericidal: kill bacteria
• Virus structure


  (non living org)

  - Contains genetic material either DNA or RNA (single stranded, not wrapped around histones)

  - 20 sided protein capsid

  - reverse transcriptase and integrase enzymes

  - envelope obtain from host cell membrane

  - viral glycoprotein
• what is genetic reassortment?

  diff. strains recombine within an individual to make new subtype
• Which cell produces antibodies?

  plasma cells (B cells)
• What is an interferon

  a PROTEIN released by animal cells, usually in response to the entry of a virus

  - inhibiting virus replication.
• How does increasing the conc. of interferon have an effect on viruses?

  - Increases interferon concentration decreases the number of virus being produced

  - as it inhibits viral production
• What causes swelling at the site of inflammation?

  - CAPILLARIES becomes more permeable.

  - BLOOD PLASMA can diffuse to the infected area to cause swelling
• differences between virus and bacteria

  virus:

  - no cytoplasm, plasma membrane, ribosome

  - smaller
• How does bacteria in gut reduce multiplication of pathogens

  Bacteria in gut secretes lactic acid which destroys pathogens