Cell Recognition And Immune System 4

Question 1

Phagocytosis

Answer 1

• engulfing and destruction of microorganisms by phagocytic white blood cell
• phagocyte extends around pathogen and engulfs it forming a phagocytic vesicles
• lysosome containing lysozymes fuses with phagosome and enzymes hydrolyse pathogen
• phagocytes can also also act as ‘antigen presenting cells’

Question 2

Antibodies

Answer 2

Proteins produced by B lymphocytes
Plasma cells secrete specific antibody into blood plasma to destroy or neutralise the antigen and pathogen
Consists of 4 polypeptide chains - 2 heavy and 2 light joined by disulphide bonds
Constant region - sequence of amino acids is the same
Variable region - sequence of amino acids vary
Variable regions form 2 antigen binding sites - specific tertiary structure complementary to antigen

Question 3

Agglutination

Answer 3

Clumping together of cells possessing the antigen

The agglutinated mass that forms can be more easily destroyed

Question 4

Stimulation of phagocytosis

Answer 4

Antibody identifies pathogen to be destroyed by phagocytic white blood cells
Phagocytes have receptors in cell surface membrane which recognise the antibody and so destroy the pathogen

Question 5

Humoral response

Answer 5

If a specific antigen attached to antibody, the B cells are stimulated to divide by mitosis resulting in lots of plasma cells
Helper T cells stimulate B cells to form plasma cells and to secrete specific antibodies
Some B cells stimulated to become memory B cells
Antibody antigen complex stimulates the destruction of antigen
If same antigen is encountered the memory B cells divide and develop into plasma cells producing a quicker response

Question 6

Cellular response

Answer 6

Antigen presented to a T cell by an antigen presenting cell
T cells bind to antigen, stimulating T cells to divide by mitosis and to develop into 3 different types of T cell -
Cytotoxic T cell (attaches to antigen and secretes chemicals to destroy it)
Helper T cells (stimulate B cells to divide into plasma cells and secrete antibodies)
Memory T cells (remain in the bloody after infection and produce a quicker response if future infection occurs)

Question 7

HIV & AIDS

Answer 7

AIDS is caused by infection with HIV
HIV is a retrovirus containing RNA and reverse transcriptase
RNA and enzyme are surrounded by a capsid
Capsid is surrounded by lipid envelope containing glycoproteins

Question 8

Transmission of HIV

Answer 8

Sexual
Blood products
Needles
Mother to baby

Question 9

HIV replication

Answer 9

• virus attaches to helper T cells & lipid envelope fuses with cell surface membrane
• viral RNA and reverse transcriptase are released into helper T cell
• viral RNA converted into viral DNA using reverse transcriptase
• viral DNA enters nucleus, when T cell replicates so does viral DNA
• when activated viral DNA controls synthesis of viral proteins and viral RNA in cell
• t cell destroyed as viruses are released and numbers decrease
• immune system breaks down due to deceased numbers of helper T cells not stimulating antibody production by B cells

Question 10

Symptoms of HIV

Answer 10

1 short flu like illness
2 HIV positive phase - no real symptoms
3 AIDS related complex - Bactrial, viral and fungal infections - not life threatening
4 infection of body organs - eventually die from pneumonia as immune system cannot produce antibodies to combat infections

Question 11

Uses of Monoclonal antibodies

Answer 11

1 target medication to specific cell types

2 medical diagnosis - detect presence of antigens or antibodies

Question 12

ELISA Test

Answer 12

Method of measuring amount of antigen or amount of antibody in a sample
Involves monoclonal antibodies some with attached enzymes that catalyse easily detectable reactions
DIRECT - detects antigens
INDIRECT - detects antibodies