Cell Recognition And Immune System

Question 1

What is immunity

Answer 1

Immunity - bodys ability to rapidly destroy before symptoms

Question 2

What is a lymphocytes

Answer 2

If a pathogen gets past the chemical and physical barriers (e.g. skin and stomach acid) and enters the blood then the white blood cells are the second line of defence.

Question 3

What is specific defense?

Answer 3

Specific —> can distinguish between different pathogens. Take slower to start but give longer lasting protection. Involves lymphocytes.

Question 4

What is a non specific defence

Answer 4

Non-specific —> do not recognise individual pathogens. Offer a quicker response in earlier stages of infection. Involves phagocytes and physical barriers.

Question 5

What is direct damage?

Answer 5

some pathogens attatch to your cells and tissues when they are released.

Question 6

What is indirect damage?

Answer 6

Indirect - waste products released from some pathogens are often toxic to the host and therefore cause disease

Question 7

How can our body identify self and nonself cells

Answer 7

• glycoproteins that act as a receptors on our cells plasma membranes signpost our cells as self.
• These receptors will be different to those of a nonself organism.
• The protein receptors on a pathogen are often referred to as antigens.

Question 8

What is a phagocyte and what is phagocytosis?

Answer 8

A phagocyte is a macrophage (type of white blood cell) that carries out phagocytosis.
They are found in the blood and in tissues.
Phagocytosis is a non-specific response. Any non-self cell (e.g. pathogen) that is detected will trigger the same response to destroy it.

Question 9

First four stages of phagocytosis

Answer 9

1. Phagocytes are in the blood and tissues and any chemicals or debris released by pathogens or abnormal cells attract the phagocytes and they will move towards these cells.
2. There are many receptor binding points on the surface of phagocytes. They will attach to chemicals or antigens on the pathogen via these receptors.
3. The phagocyte changes shape to move around and engulf the pathogen.
4. Once engulfed the pathogen is contained with a phagosome vesicle.

Question 10

Last four stages of phagocytosis

Answer 10

5. A lysosome within the phagocyte will fuse with the phagosome and release its contentz
6. The lysozyme enzyme is released into the phagosome. This is a lytic enzyme which hydrolyses the pathogen.
7. This destroys the pathogen.
8. The soluble products are absorbed and used by the phagocyte

Question 11

What is passive immunity

Answer 11

Antibodies are introduced into the body.

The pathogen doesn’t enter the body, so plasma cells and memory cells are not made.
No long-term immunity.
e.g. antibodies passed to a fetus through the placenta or through breast milk to a baby.

Question 12

What is active immunity

Answer 12

Immunity created by your own immune system following exposure to the pathogen or its antigen
Natural active immunity
Following infection and the creation of the bodies own antibodies and memory cells
Artificial active immunity
Following the introduction of a weakened version of the pathogen or antigens via a vaccine.

Question 13

lain why the number of HIV particles in the blood
(i) rises during the first few months after infection
Then
Remains low between 1 and 7 years after infection.

Answer 13

HIV is invading cells which make new viruses;
Cells release viruses into blood;

(ii) Virus remains dormant/exists as provirus/exists as DNA in host DNA;

Question 14

What is a vaccine

Answer 14

Small amounts of weakened or dead pathogen, or antigens are introduced in the mouth or by injection.

Question 15

What are B Cells role in vaccines

Answer 15

Exposure to the antigens activates the B cell to go through clonal expansion and differentiation (clonal selection)
B cells undergo mitosis to make large numbers of cells, these differentiate into plasma cells or memory B cells.
Plasma cells make antibodies
B memory cells can divide rapidly into plasma cells when re-infected with the same pathogen to make large numbers of antibodies rapidly.

Question 16

What are memory b cells

Answer 16

These can live for decades in your body, where as plasma cells are short lived.
Memory B cells do not make antibodies, rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered.
This results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms can occur.
This is active immunity

Question 17

What is herd immunity?

Answer 17

If enough of the population are vaccinated the pathogen cannot spread easily amongst the population.
This provides protection for those who are not vaccinated e.g those with already too ill to have a vaccine, or have lowered immunity unable, or those who are too young

Question 18

What is histamine

Answer 18

• Causes inflammation
• Causes capillary walls to become more permeable so that they lose more fluid to the surroundings.
• Speeds up the delivery of phagocytes to the site of infection.

Question 19

What are lympocytes and the two types?

Answer 19

Lymphocytes are white blood cells involved in the specific immune response.
All lymphocytes are made in the bone marrow, but T cells mature in the thymus.

• T Lymphocytes - cell mediated immunity (specific cells not antibodies)
• B Lymphocytes - humoral immunity (have antibodies in fluid in blood)

The cell mediated response is the response involving T-cells and body cells.

Question 20

What do T cells do

Answer 20

Stage of immunity is specific and occurs in response to non-specific methords
Self cells that carry the pathogen antigens are recognised by Tcells and dealt with accordingly

Question 21

What are antigen presenting cells.

Answer 21

Any cell that presents a non-self antigen on their surface:
• Infected body cells will present the viral antigens on their surface
• A macrophage which has engulfed and destroyed a pathogen will present the antigens on their surface
• Cells of a transplanted organ will have different shaped antigens on their surface compared to your self-cell antigens
• Cancer cells will have abnormal shaped self-cell antigens.

Question 22

Why are cell responses called cell mediated

Answer 22

Cell responses are described a ‘cell-mediated’ because T cells only respond to antigens which are presented on cells (APC), and not antigens detached from cells and within body fluids, such as the blood.

Question 23

First four stages of cell mediated response

Answer 23

1.One of the millions of specific T cells in the body will recognise and bind to the antigen being presented on the antigen-presenting cell membrane.

2. The T cell will begin to divide to make millions of clones
3. Some clones will stimulate phagocytes to phagocytose the pathogen
4. Others (killer tcells) will kill the antigen presenting cell in order to get the pathogen.

Question 24

Last four stages of cell mediated response

Answer 24

5. T cells do this by releasing a protein that punctures the antigen presenting cell membrane
6. Once punctured the membrane is no longer selectively permeable and will lose osmotic pressure. It will die along with the infecting pathogen/antigen
7. Other t cell clones will enter the blood stream and circulate around the body looking for other pathogens expressing the same antigens.
8. These memory cells will remain in the blood stream and are what allow our bodies to remember infection
9. This immunological memory means that repeat infections of the same pathogens are dealt with before an infection manages to take hold.

Question 25

Step one of miss estricj mediated response

Answer 25

. Once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface. This is now called an antigen presenting cell (APC)

Question 26

Step 2&3 of miss estricj mediated response

Answer 26

2. Helper T cells have receptors on their surface which can attach to the antigens on APC. 3. Once attached this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones

Question 27

Step four miss estrich cell mediated response

Answer 27

4. Cloned helper T cells differentiate into different cells • Some remain as helper T cells and activate B lymphocytes • Some stimulate macrophages to perform more phagocytosis • Some become memory cells for that shaped antigen • Some become cytotoxic T cells (killer T cells)

Question 28

What are cytotoxic tcells

Answer 28

Cytotoxicc T cells destroy abnormal or infected cells. They release a protein, perforin, which embeds in the cell surface membrane and makes a pore (a hole) so that any substances can enter or leave the cell. This causes the cell death. This is most common in viral infections because viruses infect body cells. Body cells are sacrificed to prevent viral molecule replication.

Question 29

What is the humoral response?

Answer 29

The humoral response is the response involving B cells and antibodies. Antibodies are soluble and transport in bodily fluids. 'humour' is an old term for body fluids, hence the name humoral response.

Question 30

What are B lymphocytes

Answer 30

Produce antibodies Millions of different types of B cells Each distinct B lymphocytes is specific to a certain antigen like T cells. Each specific B lymphocytes produces a specific antibody to a specific antigen.

Question 31

What are the two types of B Cells?

Answer 31

Plasma cells - secrete antibodies against the specific antigen that activated it. Memory Cells - circulate in the blood looking for a specific antigen. Once found they will turn into plasma cells which are a long lived response.

Question 32

What is immunilogical memory?

Answer 32

if memory cells specific to a certain pathogen are already present in large numbers, then the cloning of lots of new lymphocytes is not required should the pathogen be detected again. This means that the secondary response is much faster than the primary response so much so sometimes the individual doesnt suffer.

Question 33

B cell activation pafrt 1

Answer 33

A B cell is triggered when it encounters its matching antigen. The B cell engulfs the antigen and digests it. Then it displays antigen fragments bound to its unique MHC molecules. This combination of antigen and MHC attracts the help opf a mature mathing TCell This

Question 34

Part two of B Cell antigen

Answer 34

Cytokines secreted by the TCell help the b cell to multiply and mature into antibody producing plasma cells. Released into the blood antibodies lock onto matching antigens. The antigenantibpdy compleced are then cleared by the comp;ement ascase or by thr liver and spleen

Question 35

How are b cells activated

Answer 35

Antigens in the blood collide with their complementary antibody on a B cell. The B cell takes in the antigen by endocytosis and then presents it on it's cell surface membrane. When this B cell collides with a helper T cell receptor, this activates the B cell to go through clonal expansion and differentiation (clonal selection) B cells undergo mitosis to make large numbers of cells, these differentiate into plasma cells or memory B cells. Plasma cells make antibodies B memory cells can divide rapidly into plasma cells when re-infected with the same pathogen to make large numbers of antibodies rapidly.

Question 36

What is agglutination

Answer 36

Antibodies can cause microbes to stick together. This makes it easier for phagocytes to engulf them Antibodies are flexible and can bind to multiple antigens to clump them together. This makes it easier for phagocytes to locate and destroy the pathogens.

Question 37

What is the opponisation/compliment cascade

Answer 37

The binding of an antibody to the surface of the pathogen can set of a chain reaction with blood proteins causes pathogens to swell up and burst because osmosis occurs. As proteins have opened letting water into the cell. Virus have proteins opn their surface which recognise and bind to receptors on surface of the host cell. This is how virus enter the host cell. Antibodies can bind to viruses and stop them attaching to their host cell.

Question 38

What is nuetralisation

Answer 38

• pathogens make us ill by producing toxins • Some antibodies work by nuetralising these toxins.

Question 39

How does your body identiy self and nonself cells

Answer 39

By cells and lymphocytes

Question 40

how can lymphocytes distinguish between pathogens and self-cells?

Answer 40

Each type of cell has specific molecules on its surface that identify it. These molecules are usually proteins, as their 3D tertiary structures enables lots of unique and identifiable shapes to be made.

Question 41

What can different surface molecules identify

Answer 41

1. Pathogens (e.g. bacteria, fungi or viruses such as HIV) 2. Cells from other organisms of the same species (harmful for those with organ transplants) 3. Abnormal body cells (e.g. cancer cells) 50 seconds 4. Toxins (some pathogens release toxins into the blood, such as cholera

Question 42

How can lymphocytes recognise cells

Answer 42

The lymphocytes complementary to the antigens on self-cells will die or production will be suppressed. This is to prevent your lymphocytes from attacking your own cells. This only remaining lymphocytes are complementary to pathogenic and non-self cells. The same process occurs after birth in the bone marrow. Any new lymphocytes made in the bone marrow which are complementary in shape to antigens on self-cells will be destroyed.

Question 43

What causes symptoms of auto immune diseases

Answer 43

lymphocytes will attack self-cells are produced, this is what causes the symptoms of autoimmune diseases.

Question 44

What is an antigen

Answer 44

Antigens are molecules that generate an immune response by lymphocyte cells when detected in the body. They are usually proteins and they are located on the surface of cells.

Question 45

What is antigen variability

Answer 45

Pathogens DNA can mutate frequently. If a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change. Any previous immunity to this pathogen (either naturally through prior infection or artificially through vaccination) is no longer effective, as all the memory cells in the blood will have a memory of the old antigen shape. This is known as antigen variability. The influenza virus mutates and changes its antigens very quickly and this is why a new flu vaccine has to be created each year.

Question 47

Give two ways pathogens can cause disease

Answer 47

(Releases) toxins; 2. Kills cells / tissues.

Question 48

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar. Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria.

Answer 48

Water potential in (bacterial) cells higher (than in honey) / water potential in honey lower (than in bacterial cells); Water leaves bacteria / cells by osmosis; (Loss of water) stops (metabolic) reactions.

Question 49

L enters the liver cells (lines 3−4). Using your knowledge of the structure of the cell-surface membrane, suggest how LDL enters the cell.

Answer 49

Lipid soluble / hydrophobic 2. Enters through (phospholipid) bilayer OR 3. 4. (Protein part of) LDL attaches to receptor Goes through carrier / channel protein.

Question 50

mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how.

Answer 50

umour suppressor) gene inactivated / not able to control / slow down cell division; 2. Ignore: references to growth Rate of cell division too fast / out of control

Question 52

Why does a person developed a large number of infections about 9 years after he first became infected with HIV.

Answer 52

HIV destroys T cells; More (free) viruses produced leads to fall in T-cells; (So fewer) T-cells activate B-cells/memory cells; Reduced/no antibody production; Immune system not working properly/inability to fight infection; Opportunistic infections;

Question 53

A test is carried out to see if a person is infected. Explain why antibodies used must be monoclonal antibodies And explain why that sepcific antigen binds to antibody

Answer 53

All have the same shape and only binds to the infection. This is because they have a complimentary shape due to specific tertiary structure

Question 54

Destruction of phagocytes causes the lungs to be more susceptiblke to infections explain why

Answer 54

Phagocytes engluf/ingest pathogens/microogranisms bacteria and viruses. They then destroy them And lung diseases are caused by thes epathogens

Question 55

Phagocytes and lysosomes are involved in destroying microorganisms describe how

Answer 55

Phagocytes engulf pathogens / microorganisms; Enclosed in a vacuole / vesicle / phagosome; Lysosomes have enzymes; That digest / hydrolyse molecules / proteins / lipids / microorganism;

Question 56

What is an antigen

Answer 56

Molecule / part of molecule / protein / glycoprotein / named molecule; that stimulates an immune response / eq

Question 57

Describe how B-lymphocytes respond when they are stimulated by antigens.

Answer 57

Divide by mitosis / form clones; produce plasma cells; (plasma cells) make antibodies; (plasma cells) produce memory cells;

Question 59

What is a vaccination eq

Answer 59

Injection of antigens / toxoids; (Antigen from) attenuated microorganism / non-virulent microorganisms / dead microorganisms / isolated from microorganism; Stimulates the formation of memory cells;

Question 60

Explain why there will be no colour change if mumps antibodies are not present in the blood.

Answer 60

No antibodies to bind (to antigen); Therefore 2 nd antibody (with the enzyme) won’t bind / no enzyme / enzyme-carrying antibody present (after washing in step 4);

Question 61

What is an antibody

Answer 61

Protein / immunoglobulin; specific to antigen; idea of ‘fit’ / complementary shape;

Question 62

Describe how antibodies are produced in the body following a viral infection

Answer 62

1. virus contains antigen; 2. virus engulfed by phagocyte / macrophage; 3. presents antigen to B-cell; 4. memory cells / B-cell becomes activated; 5. (divides to) form clones; 6. by mitosis; 7. plasma cells produce antibodies; 8. antibodies specific to antigen; 9. correct reference to T-cells / cytokine

Question 63

What is a monoclonal antibody

Answer 63

Reference to hybrid cell from tumour / cancer and B-lymphocyte / hybridoma; antibodies all the same / from one type of plasma cell; specific to / complementary to / fits only one antigen;

Question 64

Explain why a test detects prostate cancer, but not any other disease.

Answer 64

Antibodies specific / only binds to PSA; PSA only associated with prostate cancer / not with other diseases;a

Question 65

Giv e two factors, other than cost, that should be considered when selecting an antibiotic to treat a bacterial disease.

Answer 65

side effects / allergic reactions / low toxicity to cells; interaction with other drugs / effective in conditions of use / reasonably stable; should only act on the problem bacteria / narrow spectrum; how much resistance the bacteria have built uo

Question 66

An antigen in a vaccine leads to the production of antibodies. Describe the part played by B lymphocytes in this process.

Answer 66

Macrophages present antigens to B lymphocytes; 2 antigen binds to / is complementary to receptors on lymphocyte; 3 binds to a specific lymphocyte; 4 lymphocytes become competent / sensitised; 5 (B) lymphocytes reproduce by mitosis / (B) lymphocytes cloned; 6 plasma cells secrete antibodies;

Question 67

H epatitis B vaccine contains a viral antigen produced by genetically modified bacteria. Describe how the isolated gene that codes for a protein in the virus’s coat could be transferred to the bacterial cells.

Answer 67

Restriction enzyme / endonuclease; 2 to cut plasmid / to form sticky ends in plasmid; 3 (use) ligase(to join) gene to plasmid; 4 culture bacteria with (in medium containing) plasmids 5 to allow uptake of plasmids / transformation; 6 use of cold shock / chemical treatment (to enhance uptake) / heat shock;

Question 68

Describe how T lymphocytes recognise and respond to the influenza virus.

Answer 68

T ymphocyte receptors recognise shape of haemagglutinin / neuraminidase / viral antigen; clone (once only); destroy virus;

Question 69

D escribe how B lymphocytes respond to the influenza virus.

Answer 69

Clone (once only); produce antibodies; effect of antibody e.g. stimulation of phagocytosis / precipitation of toxins;

Question 70

Describe the role of macrophages in stimulating B lymphocyte

Answer 70

Antigen in membrane presented to lymphocytes / produce cytokinins;

Question 71

What is an attenuated microorganism

Answer 71

Microorganism alive/active; But does not cause symptoms of disease/Avirulent;

Question 72

D escribe how HIV is replicated after it has entered a human cell.

Answer 72

Reverse transcriptase; Accept integrase/description of action of Enzyme uses (HIV) RNA to make DNA (copy); DNA joined to (host) cell’s DNA/chromosome; DNA used to make HIV RNA (copies); Accept (HIV) DNA replicated when (T) cell divides And HIV capsid proteins/enzymes; Made at (host) ribosomes; Assembly of new virus particles; Budding off from membrane (of host cell);

Question 73

The destruction of T-cells by HIV leads to the death of an infected person. Explain how.

Answer 73

Not enough/no T-cells to activate B-cells/lead to antibody production/ activate immune system; Accept death of T-cells weakens the immune system Person unable to fight /more prone to (opportunistic) infections/cancer; Accept diseases Example of infection/cancer;

Question 74

Describe how new viruses are produced after HIV has infected a T cel

Answer 74

DNA copy made (of viral RNA); Inserted into host DNA / chromosomes; (Uses viral DNA to) make viral proteins/particles; Makes viral RNA; (Host) cell makes new viruses; “Budding off” / wrapped in cell membrane;

Question 75

Describe how humans produce antibodies against a pathogen such as Salmonella.

Answer 75

S almonella pathogen has specific antigen on surface; Salmonella pathogen engulfed by macrophage; T-cells activate B-cells; B-cell with complementary/specific receptor antibody activated/ clonal selection; B-cells divide/form clone/clonal expansion; Plasma cells make antibodies; Specific to antigen/bind to salmonella bacterial antigen;

Question 76

Why dont antibiotics work for viral infection

Answer 76

tibiotics stop metabolism, viruses don’t have metabolism; Viruses hide in cells, antibiotics can’t reach; Two suitable cell components antibiotics work against that viruses don’t have;

Question 77

Give two ways in which pathogens can cause disease when they enter the body of their hos

Answer 77

Da mage / destruction of cells / tissues; Production of toxins;

Question 78

Replication of virus

Answer 78

Virus replicate inside of cells, making it difficult to destroy them without harming host cells. Viruses also have different mechanisms to replicate and no cell wall, like bacteria, and therefore cannot be destroyed by antibiotics.

Question 80

Hiv structure - core

Answer 80

Core = genetic material (RNA) and the enzyme regerse transcriptase, which are needed for viral replication.

Question 81

Hiv structure capsid

Answer 81

Capsid = = outer protein coat

Question 82

Hiv structure - envelope

Answer 82

Envelope = extra outer layer, made out of membrane taken from the host's cell membrane.

Question 83

Hiv structure - protein attatchments

Answer 83

Protein Attachments = On the exterior of the envelope to enable the virus to attach to the host's helperT cell.

Question 84

Replication of HIV in helper T cells part 1

Answer 84

HIV is transported around in the blood until it attaches to a CD4 protein on the helper T cells. The HIV protein capsule then fuses with the helper T cell membrane, enabling the RNA and enzymes from HIV to enter.

Question 85

Replication of hiv in t helper cells part 2

Answer 85

HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy and moves to the helper T cell nucleus, this is why it is called a retrovirus. Here mRNA is transcribed, and the helper T cell starts to create viral proteins to make new viral particles.re

Question 86

Main symptoms of aids

Answer 86

Central - encephalitis - meningitis Eyes Retinitis

Question 87

Main symptoms of aids lungs and skin and gastrointestinal

Answer 87

Lungs - Pneumocystis| pneumonia - Tuberculosis (multiple organs) - Tumors Skin - Tumors Gastrointestinal - Esophagitis - Chronic diarrhea - Tumors

Question 89

What is hiv and aids

Answer 89

HIV positive is when a person is infected with HIV. AIDS is when the replicating viruses in the helper T cells interfere with their normal functioning of the immune system

Question 90

What happens when someone has hiv

Answer 90

With the helper T cells being destroyed by the virus, the host is unable to produce an adequate immune response to other pathogens and is left vulnerable to infections and cancer. It is this destruction of the immune system that leads to death, rather than the HIV directly.