Topic 6

Question 1

What are STR’s

Answer 1

Repeated sequence of DNA on introns

Question 2

What are introns

Answer 2

Non coding regions

Question 3

What are exons

Answer 3

Coding regions

Question 4

How do obtain a tissue sample

Answer 4

1)Broken down in buffer solution to disturbed membrane
2)Protease enzyme incubated and cold ethanol added to precipitate out DNA
3)Restriction enzyme used to cut DNA into fragments

Question 5

Describe PCR

Answer 5

1)Sample of tissue added to DNA polymerase, DNA primers and nucleotides
2)90 degrees DNA separated into 2 stands
3)55 degrees primers attached at start of STR sequence
4)70 degrees DNA polymerase attached and nucleotides added. The STR and DNA sequence are replicated to produce millions of STR fragments.

Question 6

Describe gel electrophoresis (separation of fragments according to size)

Answer 6

1)DNA placed on agar gel
2)Wells cut into gel at one end
3)Gel submerged in electrolyte solution so p.d can flow
4)DNA samples transferred into wells and fluorescent dye added
5)When p.d ran through electrolyte DNA fragments move toward anode and bands created
6)Probes added and UV light shone to compare bands. Similar banding shows close relating.

Question 7

What is a primer

Answer 7

Short pieces of DNA complementary to start of bases on the fragment you want

Question 8

What is DNA polymerase

Answer 8

Enzyme that creates new DNA strands

Question 9

Body temperature to determine time of death

Answer 9

After death body cools due to lack of heat producing reactions, only useful for first 24hrs.

Factors affecting:
Size,position,clothing,humidity and air movement.

Question 10

Rigor Mortis to determine time of death

Answer 10

Muscle cells have to respire anerobicaly so lactic acid is produced and then pH of cells fall inhibiting enzymes so anerobic respirations stops. So no ATP produced therefore muscles/joints become fixed.

Question 11

Decomposition to determine time of death

Answer 11

Autolysis happens when enzymes break down cells. Putrefaction is a green discolouration of lower abdomen due to formation of sulfhaemoglobin. Then turns red-green to purple-black. Gas or liquid blisters may appear and body bloats.

Question 12

Forensic entomology to determine time of death

Answer 12

Study of succession of insects on body after death

Question 13

Structure of virus and how it survives

Answer 13

Nucleic adid (DNA or RNA) surrounded by a protein coat. Single or double stranded.
Need host to survive, they use hosts protein synthesis machinery to produce new virus particles.

Question 14

How does a virus work

Answer 14

1)Virus attached to host cell
2)Inserts Nucleic acid which replicates
3)Viral protein coat synthesised
4)new virus formed and released due to lysis ( breaking of membrane )

Question 15

Differences between a virus and bacteria

Answer 15

-Virus require host cell to survive and bacteria don’t
-Bacteria are cells and virus are particles
-Bactria only have DNA but viruses can have both RNA and DNA
-Bactria have ribosomes but viruses do not
-Bacteria surrounded by cell wall and virus by protein coat

Question 16

How is TB spread and what bacteria causes it.

Answer 16

Caused by mycobacterium TB and is carried in droplets and can be caught when someone sneezes/coughs.

Question 17

Symptoms of TB

Answer 17

First infection may have no symptoms but tubercles form in the lungs due to inflammatory response. Some bacteria may survive in tubercles due to waxy coat and they can become active again. So lungs tissue can be destroyed causing breathing issues/coughs/fever/weight loss/immune system damage.

Question 18

What is HIV and how is it spread

Answer 18

Spread by unprotected sex or needle sharing
HIV is a virus that destroys T-helper cells in immune system leading to aids

Question 19

Symptoms of HIV

Answer 19

-First symptoms are fevers/headaches and tiredness
-After few weeks HIV antibodies appear in blood making person HIV positive
-After this symptoms disappear until immune system weakened again
-Leading to aids having symptoms of cancers/TB/maybe death.

Question 20

Lysozyme (Non specific response to infections)

Answer 20

Lysozyme is an enzyme founds in tears/sweat/nose, it destroys bacteria by breaking down cell wall (causing lysis)

Question 21

Inflammation (Non specific response to infection)

Answer 21

Inflammation- damaged white blood cells release histamine, this chemical causes arteries in affected aria to dilate increasing blood flow. Also histamine increases permeability of vessels so white blood cells/antibodies/plasma leak out causing oedema ( swelling caused by fluid build up) helping destroy bacteria

Question 22

Phagocytosis (Non specific response)

Answer 22

White blood cells engulf/digest/destroy bacteria and foreign material.Lysosome fuse with vacuole containing bacteria and enzymes released destroying bacteria .

Question 23

Types of white blood cells (4)

Answer 23

—> Neutrophils- Leave capillaries by squeezing between cells in capillaries wall, they ingest and destroy bacteria.
—>Lymphocytes- B/T cells involved in immune response (antibody production)
—>Monocytes- In blood then in tissue they become macrophages and engulf.
—>others- produces histamine

Question 24

Lymphatic system (Non specific response)

Answer 24

1)Tissue fluid drains into lymphatic vessels
2)Lymph (fluid) pass through lymph node then returns to blood via duct
3)pathogens present activate lymphocytes and macrophages to destroy microbes

Question 25

Interferon (non specific response)

Answer 25

Chemical released by infected cells inhibiting viral replication and protein synthesis. Also promotes inflammation.

Question 26

What are the two main types of lymphocyte (specific response)

Answer 26

-B cells (Bone marrow)
-T cells (Thymus gland)

Lymphocytes are white blood cells that defend against specific diseases. Reserve supplies are found in lymphoid tissue.

Question 27

B cells (specific response)

Answer 27

Produced and matured in bone marrow. Each B cell has a specific antigen receptor on surface. B cell activated when receptor binds to antigen with complementary shape. Once activated B cell secretes antibodies in response to antigen.

Question 28

Steps of antibodies attaching to antigens (after B cells are activated)

Answer 28

1)Antibodies from B cells bind to antigens and label them
2)Antibody binds to antibody receptor
3)Macrophage engulfs antibodies and bacterium
4)Lysosomes fuse with vacuole releasing digestive enzymes that destroy bacteria

Question 29

T cells (specific response)

Answer 29

Produces in bone marrow but mature in thymus gland
—>T helper cells- When activated they stimulate B cells to divide and become cells that can produce antibodies. They also enhance phagocytes.
—>T killer cells- destroy any cells with antigen on surface membrane as recognise as foreign. Disadvantage is that this can include transplanted tissue.

Question 30

Activation of T helper cells

Answer 30

1)Bacteria with antigen is engulfed by macrophage
2)Macrophage becomes an APC (antigen presenting cell)
3)APC binds to T helper cells with complementary CD4 receptors. T helper cell activated and divides
4) Each T helper cell divides to produce T memory and T helper cell clones

Question 31

Cell selection (B cell division)

Answer 31

1)antigens on bacteria bind to B cell with complementary receptor and B cell becomes APC
2)Activated T helper cell with complementary receptor binds to APC and produces cytokines that stimulate B cell
3)B cell divides to give B memory and B effector cells and B memory/effector cell clones are produced
4)B effector cell differentiate into plasma cells
5)Plasma cells secrete antibodies which bind to antigen, identifying them for easier destruction

Question 32

Role B effector and B helper cells

Answer 32

—>B effector cells- differentiate to produce plasma cells (short lived), these release antibodies into blood and lymph.
—>B helper cells- longer lived. They remain in body enabling individual to respond quickly to future antigens that they recognise.

Question 33

Role of T killer cells

Answer 33

1)Bacterium infects host cell and cell become APC
2)T killer cell with complementary receptor binds to APC
3)T killer cell divides to form two clones ( active and memory T killer cells). Cytokines from T helper stimulate differentiation
4)Active T killer binds to infected APC
5)T killer cell releases chemicals causing pores to form in infected cell causing lysis so infected cell dies.

Question 34

Secondary immune system

Answer 34

Much quicker and involves memory cells. B memory cells can differentiate into plasma cells and release antibodies. So quick no symptoms felt.