Describe the roles of coenzymes in the formation of ATP
Coenzymes, such as FAD and NAD, carry hydrogen ions and electrons to the electron transport chain in aerobic cellular respiration.
This enables ADP and Pi to join, forming ATP.
A higher concentration of oxygen is found in the stroma when a plant is photosynthesising comapred o when it is not photosynthesising. account for the differences in oxygen concentration found in this region. (2 marks)
- Water is split in the light-dependent reaction to produce oxygen gas.
- Oxygen produced diffuses into the stroma or When light is not available, oxygen is not produced.
Explain how scientists design sgRNA and outline the function of sgRNA in the editing of the gene. (3 marks)
- scientists identify a gene that acts as a template
- scientists design a complementary sgRNA that binds with cas9
- sgRNA guides cas9 to the required gene
how many times do you cut plasmid and gene of interest?
cut plasmid once and gene of interest twice with restriction enzymes
Outline the steps required for the human insulin gene to be clones and expressed in bacteria in 2020 (3 marks)
- insulin gene is isolated from humans or synthetically produced from known sequence
- insulin gene inserted into the plasmid using restriction enzymes to cut and ligase to join to form recombinant plasmid
- recombinant plasmids placed into bacteria which are grown in culture
How do the spacers incorporated into the bacterial genome assist with combatting future infections by the same virus? [3 marks]
- the CRISPR array is transcribed into crRNA which when combined with tracrRNA forms gRNA
- gRNA binds to Cas 9 enzyme
- if the same virus infects again, CRISPR-Cas 9 complex attempts to match gRNA to one of the viral strands
- if bases are complementary, the two active sites of cas 9 will cleave the phosphodiester bonds between nucleotides on both DNA strands of the viral DNA, disrupting its function
Outline how CRISPR-Cas9 may be used to insert new DNA into genome. (4 marks)
- sgRNA / crRNA is produced to be complementary to the target gene along with Cas 9
- sgRNA identifies the target gene and cas 9 cuts both DNA strands
- a new piece of DNA (donor DNA) is inserted at the cut site.
- the cell detects and repairs the DNA, integrating the new piece of DNA
Assume that infection has occurred in a plant.
b. Outline one way in which a plant responds to minimise damage to its tissues.
- growing ‘gall’ tissue around the area containing the infective agent to prevent spread to other areas
- producing chemicals such as tannins
- producing ‘gum’ to seal off the wounded area
- dropping the infected part (leaf) to inhibit spread to other parts.
explain how tears are used to defend against pathogens? 2 marks
- tears are a chemical barrier in the 1st line of defence
- tears help to flush or drain out pathogens
- they also contain enzymes like lysozymes that break down a component in bacterial cell walls to minimise or prevent colonisation by pathogens
Describe how the first line of defence protects Michelle from infection as the (salmonella infected) nuggets go from her hands to her mouth to her stomach. 3 marks
- intact skin on hands are physical barrier in 1st line of defence that prevents pathogens, (Salmonella bacteria), from entering into her body. [1]
- in mouth, salivary antimicrobial enzymes act as chemical barriers that prevent extensive microbial colonisation. [1]
- the acidic environment in stomach as a result of the gastric juices can also help to kill the ingested Salmonella bacteria as part of Michelle’s chemical innate immune barrier. [1]
Normally in mammals, if tissue from another individual enters the body, the foreign cells are recognised as ’non-self’ by the immune system. The tissue is then rejected unless special drugs are used.
a.
Question 1
i. Which cells of the immune system are initially responsible for recognising non-self cells introduced by an organ transplant?
ii. How do the cells you have named in part i. distinguish between self and non-self cells?
a. one of: phagocytes, antigen presenting cells, T helper cells
ii. have receptors that can detect self markers and non-self antigens
Plants and animals are both susceptible to infection.
Assume that infection has occurred in a human.
Outline two general features of inflammation that minimise the impact of the infection.
- presence of phagocytes
- increase in blood flow to area of infection
- chemicals released by damaged cells
- clot or scab forming at infected area
- increased permeability of capillaries, allowing free movement of white blood cells
Describe the process of tissue rejection after recognition of the non-self cells has occurred.
- effector T helper cells (specific to antigen on implanted tissue) secrete of interleukins and cytokines, signalling activates cytotoxic T cells (which also show specificity to antigen of foreign tissue)
- cytotoxic T cell target implanted tiissue thorugh secreting cytotoxic chemicals, leading to apoptosis of implanted cells
- macrophages come and engulf debris
Compare cytotoxic T cells and NK cells
TC
- adaptive immune response
- activated by a specific MHC-1 marker on target cell
- immunological memory formed
both:
- recognise virally infected cells
- release cytotoxic chemicals (perforin=cell lysis, granzymes=self destruction)
NK:
- innate immune response
- activated by a lack of or damaged MHC-I marker on target cell
- no immunological memory formed
when pathogenic bacteria become resistant to drugs, what are the ongoing challenges for treatment strategies as a result of this resistance?
- not enough money or development into new drugs or vaccines
- more time or money required to develop more drugs or vaccines
- doctors overprescribing new drugs
- patients not completing full course of treatment
- epidemics or pandemics more likely, making herd immunity difficult to achieve
