AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

http://filestore.aqa.org.uk/subjects/AQA-BIOL5-W-QP-JUN11.PDF

Can anyone explain 5)c)ii

I just haven't got a clue what's going on.

I thought it wouldn't matter how many times your restriction enzyme cuts the DNA, surely when you add up the pieces again, you would get the same number

How did they calculate the answers for 2c pt. 2?

It only came up a couple of years ago, unlikely to again.

Can i ask what essays are you going to make plans for? really stressing to which essays to learn :/

it actually didnt why are you chatting **** ??

Only the target cells have the specific receptors

Have a similar affect to enzymes, Hormones have a complimentary shape to cell membranes' receptor complex making a hormone-receptor complex causing the cell to perform it's function, whatever it is.

EDIT:
Forgot to say bind. =l

Yep

Write an essay about the importance of ATP

ATP stands for Adenine triphosphate and is the most important energy source in living organisms. A cell can’t get it’s energy directly from glucose so during respiration, energy released from glucose is used to synthesise ATP. ATP is made from the nucleotide base adenine combined with a ribose sugar and three phosphate groups. ATP is synthesised from ADP (adenine diphosphate) and an inorganic phosphate using the energy released from glucose during respiration. The energy is stored in the phosphate bond. The enzyme ATP synthase synthesises the reaction.

ATP is extremely important in the cell as it stores and releases small, manageable amounts of energy so no energy is wasted. It is a small, soluble molecule so it can easily be transported around the cell and is easily broken down so energy can be released. Another useful property of ATP is that it can transfer energy to another molecule by transferring one of it’s phosphate bonds. ATP cannot pass out of the cell so the cell always has an immediate source of energy. It is these properties that makes ATP such an important energy source in the body.

The majority of ATP is made during aerobic respiration, although some is made during anaerobic respiration. During anaerobic respiration, glucose is converted to pyruvate which requires 2 ATP for phosphorylation, and is then oxidised by NAD during glycolysis. This needs 2 ATP but produces 4 ATP so there is a net gain of 2 ATP. The pyruvate is then converted to either lactate in animals or ethanol in plants to regenerate NAD so glycolysis can continue to generate small amounts of ATP. However, most ATP is made in aerobic respiration. During the Krebs cycle oxaloacetate combines with acetyl coenzyme A to produce a 6 carbon compound which then loses CO2 and is oxidised to produce ATP and regenerate oxaloacetate so the cycle can continue. The majority of ATP is produced during oxidative phosphorylation where energy carried by electrons from reduced coenzymes are used to make ATP from ADP and Pi by using energy provided by chemiosmosis as protons move down an electrochemical gradient.

ATP has a variety of uses within the body. Firstly ATP is used in active transport to transport substances against their concentration gradients. Plasma membranes contain many protein carriers which allow large or insoluble molecules to be actively transported across the membrane. As molecules attach to the carrier, ATP is hydrolysed to produce ADP and Pi which releases energy. This energy is used to help the carrier protein to change shape so that the substance can be released onto the other side of the membrane.

In plants, ATP plays an important role in photosynthesis. ATP is formed during the light dependent stage of photosynthesis during photophosphorylation and then travels to the stroma where it is needed in the light independent reactions. In these reactions, ribulose biphosphate combines with carbon to produce 2 glycerate 3 phosphate molecules. ATP is then required to convert this to triose phosphate. Triose phosphate can then be used to make many organic substances that the plant may need so ATP is very important here.

In animals, ATP is needed for muscle contraction. Calcium ions that are stored in the sarcoplasmic reticulum activate ATPase which hydrolyses ATP into ADP and Pi releasing energy which moves the myosin head to the side and pulls actin in a ‘rowing’ action which makes the sarcomere contract. ATP also provides energy to break the actin-myosin cross bridge so that the myosin head detaches from the actin binding site after it moves and so it is able to reattach further up the actin filament. ATP is important in allowing cross-bridges to form and break very quickly allowing the sarcomere to contract. Without the ATP muscles could not contract, or they may be unable to relax. WHen the muscle is no longer being stimulated, calcium ions leave their binding site on tropomyosin and are actively transported back to the sarcoplasmic reticulum which also requires ATP.

ATP is also vital for homeostasis and is used for many negative feedback mechanisms. For example, when blood glucose level falls below normal, glucagon and adrenaline are secreted and bind to specific receptors on the cell surface membrane of the liver. This causes adenylate cyclase to be activated inside the cell. This converts ATP into a chemical called cyclin AMP which is a second messenger. This activates a chain of reactions which breaks down glycogen into glucose (glycogenolysis). This is an example of how important ATP is as low glucose levels in blood can mean that there is not sufficient glucose for respiration to provide energy for all the metabolic reactions of the body. ATP is also needed in temperature control as mechanisms such as shivering require ATP for muscle contraction.

To conclude, ATP plays an important role in organisms as a major energy source providing energy for transport of substances, photosynthesis, muscle contraction and homeostatic mechanisms.

Have a similar affect to enzymes, Hormones have a complimentary shape to cell membranes' receptor complex making a hormone-receptor complex causing the cell to perform it's function, whatever it is.

EDIT:
Forgot to say bind. =l

Guys if you're stuck with out of syllabus stuff, try and draw in information from your other subjects. Ok i highly doubt my English lit will come in very useful - but physics (energy). Chemistry (biomolecules) geography (ecology) psychology could all inform your essays

Sorry, your right. I must have thought of us doing it in class for a set piece of work, my bad...

Haha yeah, I don't think the gothic elements of Macbeth is going to help me with gene mapping lol

It only came up a couple of years ago, unlikely to again.