3.2.4 Cell Recognition and The Immune System Flashcards
How does the body identify ‘self cells’?
Each cell has specific molecules on the cell surface membrane to identify it
How does the body identify ‘non-self’ cells?
Non-self cells contain antigens
Where are antigens found from?
- Pathogens
- Transplanted cells
- Abnormal body cells e.g., cancer cells
- Toxins
Antigens
A foreign molecule, usually a protein that stimulates an immune response in the production of a specific antibody
If the body detects an antigen and recognises it as ‘non-self’, what will occur?
The body will initiate an immune response leading to destruction of cell/pathogen/protein
2 other names for phagocytes
- Neutrophil
- Macrophage
The objective of phagocytosis is to…
Destroy non-self pathogens
Which type of process is phagocytosis?
Non-specific process
Describe how phagocytosis occurs as an immune response within the body (6)
- Chemical products of pathogens/dead/damaged/abnormal cells act as attractants
- (Phagocytes) receptors (on the cell surface membrane) recognise and attach to chemicals on surface of pathogens
- Pathogens engulfed to form vesicle
Accept phagosome - Lysosome fuses with vesicle
- Lysosome/hydrolytic enzymes break vesicle down
- Debris/products/waste released out of the cell surface membrane
Allow exocytosis
State what is meant by antigen presentation (1)
After phagocytosis, phagocytes act as antigen presenting cells
What does antigen presentation allow?
Activation of other imminence cells e.g., lymphocytes which mount a specific immune response to help remove the pathogen more efficiently
How do lymphocytes bind to antigen being expressed in antigen presentation?
They have specific receptors complementary to the antigen being expressd
Describe what is meant by non-specific immune responses (1)
A response no matter the pathogen, requires phagocytes to undergo phagocytosis
Describe what is meant by specific immune responses (2)
- Reacts to specific antigen of pathogen
- Upon activation, many immune cells are produced providing a large and effective response
Explain how specific immune responses aid in providing immunity upon reinfection (2)
- This removes pathogen from body and creates immunity for the pathogen - memory cells are produced
- Upon re infection, these cells initiate a larger and faster response
Antigenic variability
When pathogens change antigen on surface during mutation (as they know they will die out)
Describe how phagocytosis of a virus leads to presentation of it’s antigens (3)
- Phagosome / vesicle fuses with lysosome;
Reject virus fuses with lysosome - (Virus) destroyed by lyzozomes / hydrolytic enzymes;
- Antigen (from virus) are displayed on the cell surface membrane;
Describe how presentation of a virus antigen leads to the secretion of of an antibody against a a virus antigen (3)
- Helper T cell / TH cell binds to the antigen (on the antigen-presenting cell / phagocyte);
- This helper T / TH cell stimulates a specific B cell;
- B cell clones OR B cell divides by mitosis ;
- (Forms) plasma cells that release antibodies;
What initiates the cellular response?
Antigen presentation
Which cells does the cellular response involve?
T helper cells/TH cells
Explain why T helper cells are able to bind to antigens (2)
- Receptors
- Complementary to the shape of the specific antigen
What occurs when T helper cells bind to an antigen?
They activate and divide by mitosis to create clones
Activated T helper cells release ____________ which are chemical messengers
Cytokines
List the 3 main effects cytokines have
- Stimulates B cells to divide by mitosis (humoral response)
- Stimulates phagocytes (allows more phagocytosis to occur)
- Stimulates cytotoxic cells
Cytotoxic cells contain _____________ which bind to ______________ on the surface of either _________-______________ or _____________ cells.
- Receptors
- Antigens
- Virally-infected
- Cancer
What occurs when cytotoxic cells bind to antigens?
- Release performing
- Makes holes in cell-surface membrane
- Leads to apoptosis
Suggest why T helper cells are most effective against viruses (1)
T cells kill multiplying cells
After activation, aside from stimulating the production of other cells, explain one other role of T helper cells (2)
- Become memory cells;
- Stay in blind for a faster immune response (upon reinfection)
The humoral response involves ________________
Antibodies
Explain a primary humoral response (3)
- B cells stimulated by antigen binding to receptors/antibodies on their surface or indirectly by release of cytokines from T helper cells
- Upon stimulation, these divide by mitosis to produce clones
- Some B cells differentiate into plasma cells producing large quantities of monoclonal antibodies secreted in the blood
Explain a secondary humoral response (2)
- Some B cells become memory cells;
- Exist in blood to allow faster immune response upon re-infection
How are B cells able to bind to antigens?
Have antibodies on their surface complementary to the antigen
Definition of monoclonal antibodies
Have the same tertiary structure produced by identical or cloned plasma cells
Describe the structure of monoclonal antibodies (2)
- Monoclonal antibodies are quaternary proteins;
- Four polypeptide chains joined by disulphide bridges
If no other mark awarded, allow ‘Y shape’
What is the name of the complex formed when an antigen binds to the binding site of an antibody?
Antigen-antibody complex
Describe the role of antibodies in the stimulation of phagocytosis (2)
- 2 binding sites allow antibodies to bind to antigens and ‘clump’ them together (agglutination);
- This marks the antigens and helps attract phagocytes to site of infection (leading to destruction of antigens by phagocytosis)
Where are vaccines typically injected?
Intramuscularly
True or false: Vaccines contain live forms of pathogens
False
List what vaccines are mainly comprised of (2)
- Dead/weakened form of pathogen;
Allow attenuated - Specific antigen(s)
Another term for antigens ‘clumping together’
Agglutination
Which type of response are humoral and cellular responses?
Specific
What does both humoral and cellular responses require to stimulate them?
Antigen presenting cells
List the 4 main uses of monoclonal antibodies
- Used in the laboratory for medical diagnosis
- Pregnancy tests
- Treating disease
- ELISA test - adding dye/stain/fluorescent markers
Explain how monoclonal antibodies can be used in pregnancy tests (2)
- Attached to the pregnancy test;
- Upon ruination, HGC binds to antibodies causing a colour or pattern change
Explain how monoclonal antibodies can be used in cancer treatment (2)
- Carry anti-cancer drugs;
- Specific binding site allows them to target specific cancer cells
State the main concern ethically of using monoclonal antibodies
Mice - cancer induced upon them to produce cancer cells and genetically engineered to produce MA
How does the ELISA test use MA?
Uses MA to detect specific antigens in a sample
Explain how the ELISA test works
- MA fixed to the bottom of the test well, a sample (potentially containing the antigen) is added to the well and binds to the antigen-binding site on the antibody due to their complementary shape - well is washed to remove any unbound antigen
- A second MA is added which is attached to an enzyme and will bind to another part of the antigen if present - the well is washed again so any unbound antibodies with enzymes are washed away
- A substrate is added and the enzymes on the second MA will convert substrate to a different coloured product
Only of the enzyme is present will there be a positive result - represented by a colour change confirming antigen presence
Describe the role of antibodies in producing a positive result in an ELISA test (4)
- Antibody binds / attaches / complementary (in shape) to antigen;
- Antibody with enzymes is added;
- Antibody attaches to antigen;
- (Substrate/solution added) and colour changes;
Only award if enzyme is mentioned
Describe how an mRNA vaccine is made (6)
- Isolate virus and code for mRNA;
- mRNA inserted into the virus;
- Enters healthy cell, in the nucleus, it creates an mRNA sequence, the ribosomes synthesise the protein which in this case in an antigen;
- Antigen created and displayed on cell-surface membrane, forms antigen presenting cell;
- Stimulates humoral response;
- Plasma and memory cells formed;
Primary immune response
Stimulation of B cells leading to the differentiation into plasma cells and a small quantity of antibodies
Secondary immune response
Memory cells help produce a higher concentration of antibodies and faster
Explain herd immunity (2)
- The majority of population are vaccinated;
- People recover from pathogens quickly so less likely to spread to unvaccinated people;
Explain the ethics of vaccine research (4)
- Side effects;
- Tested on human cells and animal models, however, effects may be different on humans;
- Stops human suffering / develops useful medicine;
- If animal suffers, experiment is stopped and repeated at a low concentration to reduce side effects;
*Allow in any order*
What is antigen variability? (1)
Natural selection will select pathogens that can vary their antigens and evade detection by immune cells
What causes antigenic variability?
Random mutations
Why are T cell receptors unable to bind to antigens after antigen variability?
Binding sites no longer complementary to antigen
Which virus frequently undergoes random mutations?
Influenza
Active immunity
Body produces antibodies and memory cells upon exposure to antigen
Passive immunity
Pre-made antibodies received from elsewhere, typically ‘antivenom’ and ‘antiserum’
Which type of immunity (active/passive) provides a faster response?
Passive
Explain the main issue with passive immunity (1)
Only provides short term protection because memory cells cannot be produced
Give an example of passive immunity
- Snake bites
- Antibodies received in breastfeeding
Which disease does HIV lead to?
AIDS
Which type of genome is HIV?
RNA genome
State the name and explain the function of the enzyme found in HIV (2)
- Reverse transcriptase (enzyme);
- Allows production of a copy of DNA from viral DNA;
Which protein coat does HIV contain?
Capsid
What is the HIV envelope formed from?
Phospholipids
What does the HIV envelope contain?
Attachment proteins
Which receptor is present on T cells?
CD4 receptor
HIV binds to the _____ receptor of T cells
CD4
What is the CD4 receptor on TH cells made from?
Glycoproteins
The CD4 receptor on TH cells is an ______________ _______
Outside link
Explain HIV replication in T helper cells (6)
- Attachment protein on HIV binds to specific receptors on TH cells;
AND - Viral RNA and reverse transcriptase (enzyme) enters cell;
- Reverse transcriptase converts viral RNA into DNA using host nucleotides (reverse transcription);
- Viral DNA moves into nucleus and is inserted into host cell’s genome (DNA);
Ignore person becomes infected - Transcription of HIV DNA into HIV mRNA producing HIV proteins;
- Infected TH cells assemble new virus particles;
Allow virions - Virus particles released rom TH cells leading to a reduction in the number of TH cells (eventually AIDS)
What does HIV reduce?
The ability of an individual to respond to pathogens as cell mediated and humoral immunity is compromised
HIV causes a reduction in….
T helper cells
List some secondary diseases/infections people with AIDS are prone to
- Lung/brain/eye/intestine infections
- Diarrhoea
- Weight loss
- Developing rare cancer
Why are we unable to detect AIDS using antigens/antibodies
It is not a pathogen
Explain two ways AIDS can be detected
- Checking number of TH cells in blood sample
- Using EISAs to measure concentration of HIV antibodies
How many TH cells does a healthy person have per mm3 of blood
800 - 1200
How many TH cells does a person infected with AIDS typically have in their blood?
Below 200
Explain how HIV affects the production of antibodies when AIDS develops in a person (3)
- Targets THC
- THC stimulates B cells to divide by mitosis
- Not enough B cells stimulated to produce antibodies
How do antibiotics destroy bacteria?
Prevents bacteria from synthesising murein cell walls or directly damaging murein cell walls - this leads to bacteria being destroyed by osmotic damage
Some antibiotics inhibit binary fission.
Explain how (2)
Prevents DNA replication and protein synthesis
Allow semi-conservative replication
Explain why antibiotics are ineffective against viruses
Viruses have capsids, not cell walls and they spend most of the time in their host cell away from antibiotics
The drug ADC treats breast cancer.
Scientists did a test on ADV by placing small pieces of breast cancer tissue under the skin of mice to see how effective the drug is against breast cancer.
Suggest and explain two further investigations that should be done before the ADC is tested on human breast cancer patients (2)
- Tested on other mammals to check for side effects;
Accept named animal, eg rat - Tested on (healthy) humans to check for safety/side effects;
Accept: Tested on (healthy) humans to check for safety/side effects - See if repeat doses stop the tumours regrowing;
- Investigate different concentrations of ADC to find suitable/safe dosage;
In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to Ranavirus group.
Previously, the viruses infected only one species of frog.
Suggest and explain how the viruses became able to infect other species of frog (2)
- Mutations in the viral DNA/RNA/genome/genetic material;
Accept named examples mutations - Altered (tertiary structure of the) viral attachment protein;
Accept ‘antigen’ for ‘attachment protein’ or antigenic variability - Allows it/attachment protein/virus to bind (to receptors of other species);
Accept descriptions of binding eg is complementary
Determining the genome of the viruses could allow scientists to develop a vaccine.
Explain how (2)
- (The scientist) could identify proteins (that derive from the genetic code);
OR
(The scientists) could identify the proteome;
- (They) could (then) identify potential antigens (to use in the vaccine);
Reject if answer suggests vaccine contains antibodies
When a person is bitten by a venomous snake, the snake injects a toxin not the person. Antivenom is injected as a treatment. Antivenom contains antibodies against the snake toxin. This treatment is an example of passive immunity.
Explain how the treatment with Antivenom works and why it is essential to passive immunity rather than active immunity (2)
- Antibodies bind to toxin and (causes) it’s destruction;
- Active immunity is too slow/slower;
Collagen is a protein produced by cells in joints, such as the knee.
Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease, a person’s immune system attacks their own cells. RA causes pain, stiffness and swelling in joints.
Scientists have found a virus that produces a protein very similar to human collagen.
Suggest how an immune response to this viral protein can result in the development of RA (2)
- The antibody against virus (antigen) will bind to collagen;
- Results in destruction of (human) cells/collagen;
Ignore attacks
A scientist hypothesised that memory B cells had formed in mice 180 days after having the third injection out of a series of injections in a vaccination programme.
Suggest and explain a practical method the scientists could use to test this hypothesis (2)
Mark in pairs 1 and 2, 3 and 4
- Injection vaccine again;
- (Memory cells present if) faster/more rapid production of antibodies;
- Add enzyme attached to an antibody against a memory cell;
- Colour change shows presence of memory cell;
HPV is transmitted through sexual contact.
More than 95% of cervical cancers (which only affects females) are due to HPV infection. HPV infection of other tissues increases the risk of cancer but this is rare compared with cervical infection.
A vaccine is available that is over 80% effective at preventing HPV infection, if given before the person has been exposed to HPV. There is evidence of herd immunity when more than 50% of the population have been vaccinated.
Evaluate whether 10- to 12-year old boys should be given the HPV vaccine (4)
For:
1. Needs to be given at early age before exposure to HPV;
2. Will reduce transmission to girls;
3. Boys can be infected with HPV;
OR
Vaccination prevents HPV;
- Need boys to ensure herd immunity
OR
Need boys to be over 50% vaccinated
Accepts ‘needs to be given before sexual transmission’ and ‘spread’ for ‘transmission’
Against:
6. Boys at less risk of cancer than females
OR
Cervical cancers only affects females
- May be side effects from vaccine
Give three structural features found in all virus particles and describe the function of one of these features (2)
- Genetic material, capsid and attachment protein;
- Genetic material codes for (viral) protein
OR
Capsid protects the genetic
material/RNA/DNA
OR
Attachment protein bind to receptors (on cell);
Explain why viruses are described as acellular and non-living (2)
- (Acellular) no cell(-surface) membrane
OR
Not made of cells; - (Non-living) have no metabolism/metabolic
reactions;
OR
Cannot (independently) move/respire/replicate/
excrete
OR
(Have) no nutrition;
Apart from age and general health, give two important factors when choosing patients for an investigation (1)
Accept any two for one mark
Severity of illness
Current medication
Weight and body mass
Ethnicity
An ELISA test identifies the presence of HIV antibodies in a persons plasma.
This test only detects the presence of HIV antibodies.
Give two reasons why it cannot be used to find out whether a person has AIDS (2)
- (Need to look for) AIDS related symptoms;
- Number of helper T cells;
An ELISA test identifies the presence of HIV antibodies in a persons plasma.
This test only detects the presence of HIV antibodies.
A positive result will process a colour change from yellow to blue.
The solution will remain yellow if a person is not infected with HIV. Explain why (2)
- HIV antibody not present;
- (So) second antibody / enzyme will not bind;
An ELISA test identifies the presence of HIV antibodies in a persons plasma.
This test only detects the presence of HIV antibodies.
A mother who was infected with HIV gave birth to a baby. The baby tested positive using this test. This does not prove he baby is infected with HIV.
Explain why (2)
- Children received HIV antibodies from mother / breast milk;
- Solution will always process a colour change
An ELISA test identifies the presence of HIV antibodies in a persons plasma.
This test only detects the presence of HIV antibodies.
A positive result will process a colour change from yellow to blue.
A control well was set up every time the test was used. This is treated the exact same way as the test wells, except, the blood plasma is replaced by salt solution.
Use the information above to suggest two purposes of the control well (2)
(Shows that)
1. Only the enzyme / nothing else is causing a colour change;
2. Washing is effective / all unbound antibody is washed away;