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AQA BIOL5 ~ 17th June 2013 ~ A2 Biology
Scroll to see replies
Original post by erniiee
Yea this is what my teacher said as well - you need to have breadth so cover all units, but go into fine detail with the A2 units rather than AS units, and link any details from A2 briefly to AS content you can remember.
Yep! How are you looking over the synoptic stuff? Although there are 3 marks for breadth, even if you say went into 2 topics in a lot of detail you are less likely to get the marks than compared to if you mentioned say 5 topics in less detail but showed a sufficient understanding
EDIT: Just wrote synaptic instead of synoptic :L
(edited 11 years ago)
Original post by JoshL123
Yep! How are you looking over the synoptic stuff? Although there are 3 marks for breadth, even if you say went into 2 topics in a lot of detail you are less likely to get the marks than compared to if you mentioned say 5 topics in less detail but showed a sufficient understanding
EDIT: Just wrote synaptic instead of synoptic :L
EDIT: Just wrote synaptic instead of synoptic :L
Haha can tell what you've been revising
Yea that's also what my teacher said, go for breadth rather than detail. So I'm going to come up with 5 main areas to focus on, but go into heavy detail on 2 (maybe also link to wider reading), and with the others keep it a little lighter, but still link to AS
I know I posted this a few time before, but i got no answer so i thought while we are talking about how the essay is marked, what marks would you give this essay?
The Importance of shapes fitting together in cells and organisms
There are many molecules within cells and organisms that must have complimentary shapes that fit together in order for them to carry out their function.
One type of molecule for which this is extremely important is enzymes. There are two models that demonstrate how this may work, the first of which is the lock and key model in which the substrate and enzyme binding site have complimentary shapes so that the substrate or subtrates fit perfectly into the enzyme, which joins or separates them. The second model, the induced fit model, is similar, however the enzyme moulds its shape to match the substrate.
There are many processes in which it is important that these shapes fit, for example DNA helicase, RNA polymerase and DNA polymerase must all have the correct shape in order for DNA strands to separate, mRNA to form and DNA to then rejoin during polypeptide synthesis. During polypeptide synthesis it is also important that Amino acyl RNA synthetase fits together with an amino acid and tRNA molecule in order to join them to form an amino acyl tRNA molecule, then for yet another enzyme to help form peptide bonds between amino acids.
Another enzyme for which it is very important to have the correct shape is caspase. Caspases are involved in cell apoptosis, in which a cell kills itself. This usually happens after a cell reaches its hayflick limit, the limit in number of times it can divide, and becomes senescent. However, if the P53 gene, a tumour suppressor gene, becomes mutated, these caspases may form with a different tertiary structure, meaning that the cell will not undergo apoptosis and will continue to divide uncontrollably, resulting in a tumour.
Yet another occasion in which enzymes and substrates must fit together is during digestion, in which maltase is required to break substances down into simple carbohydrates required in respiration. If lactase is an incorrect shape due to mutation, this can result in lactose intolerance, in which lactose cannot be digested.
Enzymes however are not the only molecules for which it is important for shapes to fit together, another being antigens and antibodies. When a bacteria enters the body it has antigens on its surface that are recognised by the white blood cells. B-Lymphocytes, with the help of T-Helper lymphocytes, produce antibodies with shapes complimentary that of the antigens, causing them to bind together. These antigens may then cause the antigens to join ready to be engulfed by a phagocyte, may cause lysis in which the cell membrane breaks, or may neutralise the toxins produced by the bacteria. The antibodies can however also attack some of the bodies own cells, known as an autoimmune disease, which can result in problems such as diabetes.
Another two molecules whose shapes must fit together are hormones and receptors, which join to form a hormone receptor complex, stimulating a chemical change within a cell, known as the second messenger model. If the receptor loses its receptiveness it can cause diseases such as type 2 diabetes where the insulin receptors and insulin can no longer form a complex.
It is also important that the shapes of red blood cells and oxygen can fit together, so that oxygen can be carried to cells for respiration. This happens due to the biconcave structure of red blood cells which means it can associate with two molecules of oxygen.
Actin and Myosin must also fit together during the sliding filament mechanism of muscle contraction, in which the myosin head fits into the actin binding site and pulls it along, using ATPase to hydrolyse the ATP, providing energy.
If a gene is not expressed it is due to an inhibitor attached to the transcriptional fact, whose shape must fit perfectly. However, if there is an oestrogen receptor, that's shape will fit an oestrogen molecule, oestrogen can bind to it, changing the shape and releasing the inhibitor.
In conclusion, within cells and organisms the shapes of different substances have an extremely important link to their function, and even a slight change in shape can have a very significant effect on the cell, or organism as a whole.
The Importance of shapes fitting together in cells and organisms
There are many molecules within cells and organisms that must have complimentary shapes that fit together in order for them to carry out their function.
One type of molecule for which this is extremely important is enzymes. There are two models that demonstrate how this may work, the first of which is the lock and key model in which the substrate and enzyme binding site have complimentary shapes so that the substrate or subtrates fit perfectly into the enzyme, which joins or separates them. The second model, the induced fit model, is similar, however the enzyme moulds its shape to match the substrate.
There are many processes in which it is important that these shapes fit, for example DNA helicase, RNA polymerase and DNA polymerase must all have the correct shape in order for DNA strands to separate, mRNA to form and DNA to then rejoin during polypeptide synthesis. During polypeptide synthesis it is also important that Amino acyl RNA synthetase fits together with an amino acid and tRNA molecule in order to join them to form an amino acyl tRNA molecule, then for yet another enzyme to help form peptide bonds between amino acids.
Another enzyme for which it is very important to have the correct shape is caspase. Caspases are involved in cell apoptosis, in which a cell kills itself. This usually happens after a cell reaches its hayflick limit, the limit in number of times it can divide, and becomes senescent. However, if the P53 gene, a tumour suppressor gene, becomes mutated, these caspases may form with a different tertiary structure, meaning that the cell will not undergo apoptosis and will continue to divide uncontrollably, resulting in a tumour.
Yet another occasion in which enzymes and substrates must fit together is during digestion, in which maltase is required to break substances down into simple carbohydrates required in respiration. If lactase is an incorrect shape due to mutation, this can result in lactose intolerance, in which lactose cannot be digested.
Enzymes however are not the only molecules for which it is important for shapes to fit together, another being antigens and antibodies. When a bacteria enters the body it has antigens on its surface that are recognised by the white blood cells. B-Lymphocytes, with the help of T-Helper lymphocytes, produce antibodies with shapes complimentary that of the antigens, causing them to bind together. These antigens may then cause the antigens to join ready to be engulfed by a phagocyte, may cause lysis in which the cell membrane breaks, or may neutralise the toxins produced by the bacteria. The antibodies can however also attack some of the bodies own cells, known as an autoimmune disease, which can result in problems such as diabetes.
Another two molecules whose shapes must fit together are hormones and receptors, which join to form a hormone receptor complex, stimulating a chemical change within a cell, known as the second messenger model. If the receptor loses its receptiveness it can cause diseases such as type 2 diabetes where the insulin receptors and insulin can no longer form a complex.
It is also important that the shapes of red blood cells and oxygen can fit together, so that oxygen can be carried to cells for respiration. This happens due to the biconcave structure of red blood cells which means it can associate with two molecules of oxygen.
Actin and Myosin must also fit together during the sliding filament mechanism of muscle contraction, in which the myosin head fits into the actin binding site and pulls it along, using ATPase to hydrolyse the ATP, providing energy.
If a gene is not expressed it is due to an inhibitor attached to the transcriptional fact, whose shape must fit perfectly. However, if there is an oestrogen receptor, that's shape will fit an oestrogen molecule, oestrogen can bind to it, changing the shape and releasing the inhibitor.
In conclusion, within cells and organisms the shapes of different substances have an extremely important link to their function, and even a slight change in shape can have a very significant effect on the cell, or organism as a whole.
Original post by helpme456
Is the post-synaptic membrane of a neuromuscular junction the same thing as a sarcolemma (cell membrane of muscle cell). I think it is, can anyone confirm
That would make sense in this case so I think yes
Posted from TSR Mobile
Original post by Gulzar
Has anyone started proper revision for this unit? If so how are you guys revising...just looking through notes or the book? Thanks 
I have written out everything in a massive mind map, now I'm linking things together
Wy exactly did this get a thumbs down?
(edited 11 years ago)
Original post by Gulzar
Has anyone started proper revision for this unit? If so how are you guys revising...just looking through notes or the book? Thanks
I still need to finish up my notes on DNA technology. Such a long chapter!
Original post by Beth_L_G
I have written out everything in a massive mind map, now I'm linking things together 
that pic is blurry cant see the writing. could you take a pic of it again ?
Original post by samfreak
that pic is blurry cant see the writing. could you take a pic of it again ?
Dont currently have a way of doing that. My mate stole my camera and my iPad camera is awful haha
It's all on the videos I put up though
Original post by DavidYorkshireFTW
By the way, if anyone else want it, just pm me with your email, and i'll send it, i would upload it, but it's too big :/
Hi, I'm about to send you my email address
Can anyone explain to me about muscle contraction and what you need to know please?
I'm really confused about the whole myosin 'cocked' business :/
I'm really confused about the whole myosin 'cocked' business :/
Original post by choco.chip
Can anyone explain to me about muscle contraction and what you need to know please?
I'm really confused about the whole myosin 'cocked' business :/
I'm really confused about the whole myosin 'cocked' business :/
what exactly about the myosin? is it when ca2+ ions bing with troponin pulling the tropomyosin away from the binding site so myosin can bind? or how myosin make up h zone, ect
Hope this helps:
SLIDING FILAMENT THEORY
Muscle contraction is caused by the contraction of the sarcomere.
- When a sarcomere is viewed under a microscope the I-bands shrink, pulling the z-lines closer to the A-band. The H-zone, a subsection of the A-band, also shrinks.
- During contraction the z-lines are pulled closer together by the movement of actin and myosin filaments. The filaments become more interlocked.
- The heads on the myosin filaments form cross-bridges with the surrounding actin filaments by attaching themselves to binding sites on the actin
- Upon binding to actin, the myosin heads change shape. They pull the actin filaments towards the centre of the sarcomere. This is called the power stroke.
- The myosin heads use the energy in ATP to detach from the actin and return to their original position. The entire process repeats, causing the entire sarcomere to contract fully.
- When the muscle relaxes, the myosin heads are prevented from binding to the actin. The actin and myosin can now be separated by the action of an antagonistic muscle.
- The entire cycle is repeated whenever a muscle contracts and relaxes.
CONTROL OF SLIDING FILAMENT
- In a relaxed muscle tropomyosin blocks the binding sites on the actin filament. This prevents the myosin heads binding to the actin, so contraction is impossible.
- Nerve impulses stimulate the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
- At high concentrations the calcium ions bind to troponin on the actin filament. This causes the tropomyosin to change shape, exposing the actin binding sites.
- The activated myosin heads can now bind to the actin filament. This produces tension in the muscle.
- Binding to the actin causes the myosin to change shape. This causes the entire myosin filament to be pulled along the actin. ADP and Pi are released from the myosin head.
- ATP can now bind to the myosin head. This is broken down to produce ADP, Pi and energy. The energy allows the myosin head to release the actin and return to its original state.
- The cycle can now repeat, dragging the myosin filament further along the actin. The sarcomere will continue to contract if there is a ready supply of ATP
- Calcium is actively removed from the sarcoplasm when the muscle is no longer stimulated by a nerve. This causes the tropomyosin to return to its original shape.
- Bridges between the actin and myosin can no longer form. With no force holding the fibres together the fibres can be pulled apart by antagonistic muscle action.
(All taken from here: http://www.boardworks.co.uk/a-level-biology_506/product-samples)
SLIDING FILAMENT THEORY
Muscle contraction is caused by the contraction of the sarcomere.
- When a sarcomere is viewed under a microscope the I-bands shrink, pulling the z-lines closer to the A-band. The H-zone, a subsection of the A-band, also shrinks.
- During contraction the z-lines are pulled closer together by the movement of actin and myosin filaments. The filaments become more interlocked.
- The heads on the myosin filaments form cross-bridges with the surrounding actin filaments by attaching themselves to binding sites on the actin
- Upon binding to actin, the myosin heads change shape. They pull the actin filaments towards the centre of the sarcomere. This is called the power stroke.
- The myosin heads use the energy in ATP to detach from the actin and return to their original position. The entire process repeats, causing the entire sarcomere to contract fully.
- When the muscle relaxes, the myosin heads are prevented from binding to the actin. The actin and myosin can now be separated by the action of an antagonistic muscle.
- The entire cycle is repeated whenever a muscle contracts and relaxes.
CONTROL OF SLIDING FILAMENT
- In a relaxed muscle tropomyosin blocks the binding sites on the actin filament. This prevents the myosin heads binding to the actin, so contraction is impossible.
- Nerve impulses stimulate the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
- At high concentrations the calcium ions bind to troponin on the actin filament. This causes the tropomyosin to change shape, exposing the actin binding sites.
- The activated myosin heads can now bind to the actin filament. This produces tension in the muscle.
- Binding to the actin causes the myosin to change shape. This causes the entire myosin filament to be pulled along the actin. ADP and Pi are released from the myosin head.
- ATP can now bind to the myosin head. This is broken down to produce ADP, Pi and energy. The energy allows the myosin head to release the actin and return to its original state.
- The cycle can now repeat, dragging the myosin filament further along the actin. The sarcomere will continue to contract if there is a ready supply of ATP
- Calcium is actively removed from the sarcoplasm when the muscle is no longer stimulated by a nerve. This causes the tropomyosin to return to its original shape.
- Bridges between the actin and myosin can no longer form. With no force holding the fibres together the fibres can be pulled apart by antagonistic muscle action.
(All taken from here: http://www.boardworks.co.uk/a-level-biology_506/product-samples)
(edited 11 years ago)
Original post by Anjna
what exactly about the myosin? is it when ca2+ ions bing with troponin pulling the tropomyosin away from the binding site so myosin can bind? or how myosin make up h zone, ect
I understand the structure of myosin but confused about how contraction works.
So far, I know ca2+ ions bind with troponin moving tropomyosin away from binding site.
I don't know what's happens next with ATP/ADP+p and how myosin head moves further along
Original post by HELPIMSTUCK
Hope this helps:
SLIDING FILAMENT THEORY
Muscle contraction is caused by the contraction of the sarcomere.
- When a sarcomere is viewed under a microscope the I-bands shrink, pulling the z-lines closer to the A-band. The H-zone, a subsection of the A-band, also shrinks.
- During contraction the z-lines are pulled closer together by the movement of actin and myosin filaments. The filaments become more interlocked.
- The heads on the myosin filaments form cross-bridges with the surrounding actin filaments by attaching themselves to binding sites on the actin
- Upon binding to actin, the myosin heads change shape. They pull the actin filaments towards the centre of the sarcomere. This is called the power stroke.
- The myosin heads use the energy in ATP to detach from the actin and return to their original position. The entire process repeats, causing the entire sarcomere to contract fully.
- When the muscle relaxes, the myosin heads are prevented from binding to the actin. The actin and myosin can now be separated by the action of an antagonistic muscle.
- The entire cycle is repeated whenever a muscle contracts and relaxes.
CONTROL OF SLIDING FILAMENT
- In a relaxed muscle tropomyosin blocks the binding sites on the actin filament. This prevents the myosin heads binding to the actin, so contraction is impossible.
- Nerve impulses stimulate the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
- At high concentrations the calcium ions bind to troponin on the actin filament. This causes the tropomyosin to change shape, exposing the actin binding sites.
- The activated myosin heads can now bind to the actin filament. This produces tension in the muscle.
- Binding to the actin causes the myosin to change shape. This causes the entire myosin filament to be pulled along the actin. ADP and Pi are released from the myosin head.
- ATP can now bind to the myosin head. This is broken down to produce ADP, Pi and energy. The energy allows the myosin head to release the actin and return to its original state.
- The cycle can now repeat, dragging the myosin filament further along the actin. The sarcomere will continue to contract if there is a ready supply of ATP
- Calcium is actively removed from the sarcoplasm when the muscle is no longer stimulated by a nerve. This causes the tropomyosin to return to its original shape.
- Bridges between the actin and myosin can no longer form. With no force holding the fibres together the fibres can be pulled apart by antagonistic muscle action.
(All taken from here: http://www.boardworks.co.uk/a-level-biology_506/product-samples)
SLIDING FILAMENT THEORY
Muscle contraction is caused by the contraction of the sarcomere.
- When a sarcomere is viewed under a microscope the I-bands shrink, pulling the z-lines closer to the A-band. The H-zone, a subsection of the A-band, also shrinks.
- During contraction the z-lines are pulled closer together by the movement of actin and myosin filaments. The filaments become more interlocked.
- The heads on the myosin filaments form cross-bridges with the surrounding actin filaments by attaching themselves to binding sites on the actin
- Upon binding to actin, the myosin heads change shape. They pull the actin filaments towards the centre of the sarcomere. This is called the power stroke.
- The myosin heads use the energy in ATP to detach from the actin and return to their original position. The entire process repeats, causing the entire sarcomere to contract fully.
- When the muscle relaxes, the myosin heads are prevented from binding to the actin. The actin and myosin can now be separated by the action of an antagonistic muscle.
- The entire cycle is repeated whenever a muscle contracts and relaxes.
CONTROL OF SLIDING FILAMENT
- In a relaxed muscle tropomyosin blocks the binding sites on the actin filament. This prevents the myosin heads binding to the actin, so contraction is impossible.
- Nerve impulses stimulate the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
- At high concentrations the calcium ions bind to troponin on the actin filament. This causes the tropomyosin to change shape, exposing the actin binding sites.
- The activated myosin heads can now bind to the actin filament. This produces tension in the muscle.
- Binding to the actin causes the myosin to change shape. This causes the entire myosin filament to be pulled along the actin. ADP and Pi are released from the myosin head.
- ATP can now bind to the myosin head. This is broken down to produce ADP, Pi and energy. The energy allows the myosin head to release the actin and return to its original state.
- The cycle can now repeat, dragging the myosin filament further along the actin. The sarcomere will continue to contract if there is a ready supply of ATP
- Calcium is actively removed from the sarcoplasm when the muscle is no longer stimulated by a nerve. This causes the tropomyosin to return to its original shape.
- Bridges between the actin and myosin can no longer form. With no force holding the fibres together the fibres can be pulled apart by antagonistic muscle action.
(All taken from here: http://www.boardworks.co.uk/a-level-biology_506/product-samples)
Omg thank you so much!
Original post by choco.chip
Omg thank you so much!
The powerpoint in the link is really helpful (slide 11/12 are muscle contraction)
Original post by Beth_L_G
I have written out everything in a massive mind map, now I'm linking things together
Did you make the mind map from memory :O?
Original post by JoshL123
Did you make the mind map from memory :O?
Haha I wish
Naa I wrote out notes on the whole course, condensed them, then condensed them further onto this
Original post by Beth_L_G
Haha I wish
Naa I wrote out notes on the whole course, condensed them, then condensed them further onto this
Naa I wrote out notes on the whole course, condensed them, then condensed them further onto this
Oh wow, that is amazing!
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