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Biology > B5 - Cell recognition and the immune system > Flashcards

B5 - Cell recognition and the immune system Flashcards

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1
Q

What defence mechanisms do we have?

A

Physical & chemical defences
Inflammation
Recognising ‘foreign’ cells & targeting any pathogenic cells

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2
Q

What do antigens do?

A

They allow the body to recognise its own cells (‘self antigens’) & foreign cells (‘non-self antigens’)

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3
Q

Do self antigens create a immune response?

A

No, only non-self antigens do (foreign cells)

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4
Q

What is antigen variability?

A

When antigens on their surface change frequently, due to mutations, meaning the specific immune response cannot occur, as antibodies from lymphocytes & memory cells no longer can bind to that antigen/pathogen

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5
Q

Where are phagocytes produced?

A

The bone marrow

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6
Q

What do phagocytes do?

A

Responsible for removing dead cells and invasive microorganisms
Carry out the non-specific immune response

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7
Q

What are the 2 types of phagocytes?

A

Neutrophils
Macrophages

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8
Q

What do neutrophils do?

A

Travel throughout the body and leave the blood via capillary walls to ‘patrol’ the body tissues
Short-lived cells

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9
Q

What is chemotaxis?

A

Chemical released by pathogens/infected body cells that can attract neutrophils to the site of infection

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10
Q

What is a lysosome?

A

It is a specialist form of vesicles which contains hydrolytic enzymes (enzymes that break biological molecules down)

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11
Q

How do neutrophils undergo phagocytosis?

A
  1. The phagocytes are attracted by chemotaxis
  2. Bacteria is attached to the cell surface membrane
  3. Bacteria is engulfed
  4. Bacteria is contained in a phagocytic vacuole
  5. The phagocytic vacuole fuses with a lysosome, forming a phagosome
  6. The enzymes from the lysosome digests the bacteria
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12
Q

What do macrophages do?

A

Larger than neutrophils, and are long-lived
Travel in the blood as monocytes → develop into macrophages and move into organs

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13
Q

What are macrophages mode of action?

A

They carry out phagocytosis, but do not destroy the pathogen completely
Instead they can display their antigens on their C.S.M - becoming an antigen-presenting cell (APC)
These displays can be recognised by lymphocytes → initiates the specific immune response

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14
Q

What are lymphocytes?

A

White blood cells that are smaller than phagocytes
Play a role in the specific immune response
Have a large nucleus
Produced in the bone marrow

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15
Q

What are the 2 types of lymphocytes?

A

T-lymphocytes (T cells)
B-lymphocytes (B cells)

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16
Q

What are the 2 stages of T cells?

A

Immature T cells
Mature T cells

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17
Q

What do immature T cells do?

A

Leave the bone marrow to mature in the thymus

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18
Q

What do mature T cells have?

A

They have specific cell surface receptors - T cell receptors
These receptors are similar in structure to antibodies, and are specific to one antigen

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19
Q

How do T cells activate?

A

T cells can encounter APCS (macrophages or infected body cells) → become activated → specific, activated T cells divide by mitosis → differentiate into two main types of T cell

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20
Q

What are the 2 main types of T cells?

A

Helper T cells
Cytotoxic (killer) T cells

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21
Q

Why are APCs important?

A

T cells will only bind to an antigen if it is presented by an APC
Without this cell-to-cell communication, mammalian immune systems would not be able to produce a specific immune response
They also recruit other immune cells to the site of infection

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22
Q

What is the role of T helper cells?

A

They release cytokines (hormone-like signal), which stimulates:
The maturation of B cells into antibody-secreting plasma cells
The production of memory B cells
The activation of cytotoxic T cells (which destroy virus infected cells and tumour cells)
An increased rate of phagocytosis

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23
Q

How do cytotoxic T cells work?

A

They punch a hole into the cell surface membrane, which secretes toxins into the cell membrane

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24
Q

Where do B-cells mature?

A

In the bone marrow

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25
Q

What happens during maturation of B-cells?

A

The genes that code for specific antibodies are changed to code for different antibodies
Each mature B cell can make one type of antibody molecule
Part of this molecule forms a glycoprotein receptor that can bind to its complementary antigen

26
Q

What is clonal selection?

A

Pathogen (antigen) enters the body → the B cell with the correct cell surface receptors recognise & bind to it

27
Q

What is clonal expansion?

A

The specific B cell divides repeatedly by mitosis and differentiate into:
Plasma cells
Memory cells

28
Q

What do plasma cells do?

A

Secrete millions of specific antibodies

29
Q

What do memory cells do?

A

Remember the specific antibody in the case of reinfection

30
Q

What are the 2 types of immune responses and what are they?

A

Primary: responding to a newly encountered pathogen
Secondary: responding to a previously encountered pathogen

31
Q

What are antibodies?

A

Globular glycoproteins called immunoglobulins

32
Q

What is the structure of antibodies?

A

Quaternary structure consisting of 4 polypeptide chains
2 heavy/long chains and 2 light/short chains bonded by disulphide bonds
Each chain has a constant region and a variable region
A variable region contains the antigen-binding site: where the antigen/toxin binds to the antibody; these sites vary and give antibodies their specificity
The ‘hinge region’ - where disulphide bonds join the heavy chains together

33
Q

What is an antibody + antigen?

A

antigen-antibody complex
Which forms at the antigen-binding site

34
Q

What is the benefit of multiple antigen-binding sites?

A

Allow antibodies to bind to more than one antigen/pathogen at a time, causes colonies of bacteria to group together - agglutination

35
Q

What happens when antibodies bind to pathogens?

A

Pathogen becomes neutralised
Acts as a marker to attract phagocytes
Agglutination allows phagocytes to engulf multiple pathogens at the same time

36
Q

What happens in the primary immune response?

A

Plasma cells are short-lived, but the antibodies they secrete remain in the blood for a long time
B cells that differentiate into memory cells can circulate the blood for a long time
The primary immune response is relatively slow

37
Q

What happens in the secondary immune response?

A

Memory cells can divide & differentiate into plasma cells (to secrete antibodies) and more memory cells
These antibodies are produced and secreted very quickly → infection is destroyed and removed before symptoms can occur

38
Q

What are vaccines?

A

A suspension of antigens (inactivated OR live attenuated) that are injected into the body to induce artificial active immunity
Creates a specific immune response where antibodies are created and released by plasma cells
Normally administered intravenously (vein), intramuscular (muscles) or orally (mouth)
Provide long-term immunity as they cause memory cells to be created

39
Q

What are the pros of vaccines?

A

Often gives an individual lifetime protection against certain diseases (some require booster injections)
Generally harmless - they cannot causes disease as the pathogen is quickly killed by the primary immune response

40
Q

What are the cons of vaccines?

A

People can have a poor response to vaccine
Antigenic variation - renders vaccines useless as the antibodies they would stimulate B cells to produce would no longer be specific to the antigen
Antigenic concealment - when a pathogen ‘hides’ from the immune system by living inside cells e.g., HIV

41
Q

What is live attenuated?

A

Contain whole pathogens that have been weakened → multiplies slowly → triggers a primary immune response → plasma & memory cells form
Tend to produce a stronger and longer-lasting response
May be unsuitable for immunocompromised individuals

42
Q

What is an inactivated vaccine?

A

Contain whole pathogens that have been killed or parts of them
Tend to produce a weaker and shorter-lasting response (+requiring booster doses)
Some people have allergic reactions to these vaccines

43
Q

What is herd immunity?

A

Herd immunity occurs when a large proportion of the population has been vaccinated (& immune) → pathogen has more difficulty spreading within that population

44
Q

What is active immunity?

A

This is acquired when an antigen enters the body → triggers the primary immune response (antibodies are produced)
Can be naturally acquired (through exposure to microbes) or artificially acquired (through vaccinations)
The body produces memory cells & plasma cells - gives a person long-term immunity

45
Q

What is passive immunity?

A

This is acquired without an immune response. Antibodies are not produced.
No memory cells & plasma cells - produced - long-term immunity NOT provided

46
Q

What is artificial passive immunity?

A

When someone is given an injection/transfusion of antibodies - e.g., antitoxins for tetanus

47
Q

What is natural passive immunity?

A

Antibodies can cross the placenta and enter a baby’s bloodstream and/or babies receives antibody through their mother’s breastmilk

48
Q

What is HIV?

A

Human immunodeficiency virus is a retrovirus
Transmitted by direct exchange of bodily fluids

49
Q

What does retrovirus mean?

A

RNA is the genetic material

50
Q

What is the structure of HIV?

A

Two RNA strands
Proteins: reverse transcriptase, attachment proteins
A protein coat (capsid)
Viral lipid envelope (lipid bilayer + glycoproteins)
This is derived from the membrane of the host helper T cell

51
Q

How does HIV replication occur?

A

HIV attaches to receptors on T helper cell
HIV injects its genetic material into the T helper cell, which becomes a host cell
HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat
The virus uses the cell machinery to multiply
Reverse transcriptase enzymes produce a inactive DNA copy of the viral RNA → inserted into the chromosomes of the cell
At this stage, the individual is HIV positive + will have antibodies against the virus
After a period of time (months - years)
Viral DNA within the host helper T cell becomes active → takes control of cell & makes more viral particles → T cell dies
Thousands of new HIV particles infect further helper T cells

52
Q

How does HIV lead to AIDS?

A

The virus gradually reduces the number of helper T cells in the body
B cells are no longer activated
Antibodies are not produced
This cycle of helper T cell death leads to acquired immune deficiency syndrome (AIDS)

53
Q

What are the symptoms of HIV and AIDS?

A

Initially - mild, flu-like symptoms → symptoms eventually pass & infected people may not know they are infected
Months/years pass and viral DNA becomes active → reduces helper T cell numbers
Eventually an individual can no longer produce antibodies → advanced AIDS
They are immunocompromised
AIDS patients start to suffer from opportunistic infections - diseases that would usually cause minor issues in healthy individuals e.g., Tuberculosis (TB), pneumonia → patients eventually die

54
Q

What is the treatment for HIV and AIDS?

A

There is currently no cure for AIDS

Antiretroviral drugs are effective in slowing the spread of the virus within the body. They are taken by HIV+ people, to keep their viral load low, to the point where they become undetectable & cannot transmit the virus
There are drugs to reduces the chance of being infected with HIV
Pre-exposure prophylaxis (PrEP) prevents viral replication

55
Q

What are antibiotics used for?

A

Antibiotics are used to kill bacteria or limit bacterial growth
Interfere with the metabolism of bacterial cells
Prevent protein synthesis

56
Q

Why are antibiotics ineffective against viruses?

A

they are non-living
They have no metabolism and/or cell structure to act on or disrupt

57
Q

What are monoclonal antibodies?

A

mAbs - antibodies which are produced by a single clone of a specific white blood cell.
They are specific to one binding site on one protein antigen, so they are able to target specific cells

58
Q

How does HIV testing work?

A

HIV antigen is attached to a test plate
Blood sample being tested is passed over the plate, if present, HIV antibodies will bind to the antigen
Plate is then washed to remove unbonded antibodies
A monoclonal antibody is then passed over the plate which will attach to the HIV antibody if present
A substrate is then added which reacts with the enzyme on the monoclonal antibody to create a colour change if HIV +

59
Q

What are monoclonal antibodies used for?

A

Targeting medication to specific cell types by attaching a therapeutic drug to an antibody
medical diagnosis

60
Q

What are ethical issues with vaccines and monoclonal antibodies?

A

Most ethical issues revolve around animal rights issues
New mAb therapies are tested on animals before they can move onto human trials
Even though animals are mostly used to produce cells for mAbs research, people believe this is unethical

Biology (17 decks)

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