Paper 2

Question 1

How does the lac person work when there is no lactose present?

Answer 1

The regulator gene is transcribed to produce the lac repressor protein
The repressor protein binds to the operator region which prevents the RNA polymerase from binding to the promoter region so there is no transcription of structural genes and no lactose enzyme is synthesised

Question 2

How does the lac operon work when lactose is present?

Answer 2

Lactose binds to the repressor protein and changes its shape so it can no longer bind to the operator region. This means that RNA polymerase can bind to the promoter region so that transcription can take place and lactase is produced.

Question 3

Outline the features of the 1st line of the non-specific immune response

Answer 3

-Skin - physical barrier made up a keratin(strong fibrous protein)
-Mucus membranes - found lining the gut, airways and reproductive system. Goblet cells secrete musus
-Expulsive reflexes - coughing and sneezing
-Lysosomes and hydrochloric acid

Question 4

Outline the features of the second line of the non specific immune response

Answer 4

-Blood clotting - when skin is damaged, platelets are activated which block the wound. They also release clotting factors including thromboplastin which converts prothrombin to thrombin. Thrombin then converts soluble fibrinogen to insoluble fibrin which forms the clot.
- Inflammation - mast cells realease histamines which cause vasodilation, leaky capillaries (causes swelling)

Question 5

What are the 4 types of T cells and what are their roles?

Answer 5

-T helper cells - release interleukins which activate B cells and increase phagocyte activity
-T Killer cells - attach to foreign antigens on infected body cells and insert porforins into the cells so that toxins can enter to kill cell
-T Regulatory cells - Dampen down the immune response when body is clear of the pathogen
-T Memory cells - remain in the blood so that clonal selection can happen faster

Question 6

What is the role of B cells in the specific immune response?

Answer 6

They are activated by interleukins and then undergo clonal section and clonal expansion.
Some B cells differentiate into plasma cells which secrete antibodies
Some become B memory cells

Question 7

What are the 3 types of antibodies and what are their roles?

Answer 7

-Agglutenins - clump together antibody antigen complexes so that they can be easily engulfed by pathogen
-Oppsonins - attach to pathogen so they can be identified by pathogen
-Antitoxins - bind to the toxin produced by pathogens to render them harmless

Question 8

What are the 2 methods of artificial cloning in animals?

Answer 8

1. Reproductive cloning- where nucleus is inserted into enucleated egg cell and allowed to divide
2. Embryo splitting - cells from a developing embryo are separated to produce 2 genetically identical organisms.