AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

hi, can anyone send me a document with details on the 25 mark essay?

Im doing an essay on "The causes of disease in humans" and for that can Lifestyle - food intake and exercise be a different point from deficiency diseases which is cause due to lack of specific nutrients in the diet?

Yeah, malnourished.

Dendrites don't join synapse with each other. (well, they can but we do not need to know this for our spec)
A dendrite synapses with a axon terminal.

Can someone please explain the roles of actin, myosin, calcium ions and ATP in myofibril contraction.


Thanks

Okay so..
Role of calcium starts with the "transmission across a neuromuscular junction":
- When the action potential is sent across the sarcolemma and into the muscle fibres
- This stimulates the release of calcium ions from the endoplasmic reticulum which initiates muscle contraction.

Role of actin/myosin/atp:
- Actin filaments have binding sites for myosin heads, in a relaxed muscle the binding site is covered by the protein tropomyosin.
- The calcium ions released from the endoplasmic reticulum bind to tropomyosin causing it to move and expose the binding site
- This enables actinomyosin crossbridges to be formed as myosin heads attach to actin binding sites.
- Calcium ions also stimulates the action of ATPase present in myosin heads.
- ATP binds to myosin head to break the cross bridge and ATPase quickly hydrolyses it into ADP + Phosphate to provide energy for the next formation.

Hope that helps, if something doesn't make sense let me know.

Most of this I understand, but for the last bit, isn't energy from ATP also used for the power-stroke (when myosin pulls actin over it) as well as the stuff you've mentioned (the detaching and going back to its original position)?

Rapid formation/detachment is what causes the actin to be pulled over the myson so... yeah? :P

Will it be considered irrelevant if i briefly mention genetic screening could be a method used to screen for the faulty gene under the essay title "causes of disease in humans"

Right, thanks. Also, is energy from ATP also used in the forming of cross bridges or not?

It would be irrelevant, but I doubt you would get marked down for it was very very briefly mentioned.

Oh okay! One more thing, is mutations a relevant point in this essay title? I split it into genetically inherited mutations such as CF and mutations caused by environmental influences - mutagenic agents?

Thank you

Quick question, to get the marks for the "off spec" stuff in the synoptic essay...
Can you get them for just adding little bits of off spec information into stuff thats already in the spec? (For example the names of the different types of bacteria in nitrogen cycle).

OR would it have to be a topic completely off the spec, such as something to do with the kidneys or the brain?