Biology Unit 5 Revision Notes

Biology Unit 5 revision notes
The structure of mRNA differs from tRNA because it does not contain Hydrogen bonds/base pairs/contains codons/does not have an anticodon/it is straight/not folded/has no amino acid binding site and is longer.
Nervous stimulation produces a faster response for a shorter duration than hormonal stimulation.
Acetyl Choline contributes to a synapse being unidirectional as Acetylcholine is released from the presynaptic side and diffuses from a higher concentration to a lower concentration to receptors in the postsynaptic side where it binds.
Hormones are transported in the blood whereas local chemical mediators are spread directly by diffusion, hormones have a widespread effect, affect different organs and affect different parts of the body e.g. distant organs and only affect cells with the right receptor.
There is a thick cuticle on the upper surface of plant leaves so there is a shorter diffusion pathway on the lower surface.
Hydrolysis and condensation are important in the formation of new adult proteins as Hydrolysis breaks proteins/hydrolyses proteins and produces amino acids from proteins, protein synthesis from amino acids involves condensation and the hydrolysis of polysaccharides/lipids is the energy source for synthesising proteins.
Proteins can be broken down into amino acids and joined in different sequences.
Lysosomes are associated with tissue breakdown.
Transcriptional factors are important in the synthesis of particular proteins as they bind to DNA/gene at a specific region/base sequence/promoter sequence and stimulate transcription.
SiRNA means the target gene is no longer able to make a specific protein and mRNA cannot be translated because it has been cut into pieces.
Panting leads to heat being transferred from the blood.
Sexual reproduction leads to variation due to meiosis and independent assortment and crossing over of chromosomes leading to the fusion of genetically different gametes/random fertilisation.
When an action potential is trying to become established, channel proteins open and Sodium diffuses in, this changes to membrane potential making the inside of the axon less negative/more positive and causes depolarisation and the threshold potential to be reached, this causes more channels to open and positive feedback.
Repolarisation of the axon occurs when Potassium channels open, potassium diffuses out and Sodium channels close.
After exercise, some ATP is used to re-establish a resting potential in the axon as ATP is used by the Sodium-Potassium pump to actively transport Sodium ions out of the axon and Potassium ions are actively transported in.
LH and Progesterone have a negative feedback system in that as LH levels rise, there is an increase in progesterone, this progesterone then inhibits LH and so LH levels fall.
On a hormone graph, high levels of Progesterone indicate the egg has been released, ovulation has occurred and a corpus luteum has been produced.
On a hormone graph, a rise in oestrogen is associated with follicle growth/development and a surge in LH, a fall in Oestrogen is associated with the follicle breaking down and there is a surge in LH before ovulation, LH stimulates ovulation and the release of an egg, there is a fall in LH after ovulation as LH is inhibited by Progesterone.
A receptor/transcription factor binds to a promoter region, this stimulates RNA polymerase to transcribe a gene/increases

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