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AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

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I'm just wondering.... why don't fast twitch muscle fibres contain many mitochondria. I do know that they are adapted for anaerobic respiration, but surely having mitochondria around would help this type of muscle fibre if the supply of ATP gets really low. But then again, phosphocreatine is present which can regenerate ATP :tongue:

, kinda confused :s-smilie:

They probably do contain mitochondria, but not as many as slow twitch.

Reply 961

JenLivYoung

Original post by James A

, kinda confused :s-smilie:

They contain mitochondria, but not as many. This is because they're anaerobic fibres. As you mentioned, they use phosphocreatin to replenish ATP, however they also respire anaerobically. If you remember from Module 4, glycolysis takes places in the cytoplasm of cells not in the mitochondria, so that's where they get most of their ATP from.
As they're only used for sprinting and short bursts of activity they don't need to replenish large volumes of ATP like the slow twitch fibres so I don't think ATP would get that low.

Hope this made sense haha :tongue:

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Reply 962

F1's Finest

Original post by master y

They probably do contain mitochondria, but not as many as slow twitch.

Original post by JenLivYoung

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Made sense guys :yep:

I keep on forgetting that fast twitch fibres are only needed for short periods of time, which is why they don't need much ATP and hence can get away with anaerobic respiration, which produces little ATP :cute:

Reply 963

king101

Hello,

Guy's I have attached below an essay plan for the Causes of Disease in humans.

I hope you all will find it good :smile:

, But please do tell me what you think of it? Is it worth using that plan? Like what mark would you expect with a plan like that?

I also have a 'plea' to you guys. I really need some guidance on all this synoptic section of photosynthesis and respiration basically just the dead basics of of aerobic respiration and anaerobic respiration so I can understand that and incorporate that into my essays. If anyone could help/guide me would be great!

The causes of disease in humans.docx33.1KB

Reply 964

TauMuon

This exam will be the death of me!

It would be fine if not for this bloody synoptic essay; not only do I have to memorise the course content for Unit 5, but also dredge up all the information I've forgotten from the previous 3 Units. Grrrr.

Don't know about anyone else, but I'm planning to do as well on Qs 1-9 as possible to give as much leeway as possible for a crap essay at the end. :frown:

Reply 965

Mocking_bird

How are you all planning on doing the exam, order-wise?

I'm thinking read the synoptic questions first, but then go back to the start of the paper whilst jotting down ideas for the synoptic as they come to me.

Reply 966

785695

could someone summarise DNA fingerprinting for me please? i find the textbook so confusing :eek:

Reply 967

king101

Can anyone explain to me;
Insulin is a protein and can be made in vast quantities or the gene for insulin should I say via invivo cloning by bacterial cells. But my next question is, is the insulin gene extracted from these bacterial cells and placed into human bodies??? is this called gene therapy?

Reply 968

k1rby

Original post by king101

We insert the human insulin gene into the bacterial cells via plasmids so that the bacteria produce the insulin for us! We extract the insulin they produce and diabetics inject it into themselves :smile:

Reply 969

sechdent8

hey guys, does anyone have i really good way of remembering the sequence of events for getting a resting potential, generation of an action potential and passage across an unmyelinated neurone?
Thanks

Reply 970

erniiee

Original post by Mocking_bird

Aha I was just planning my exam strategy! Gonna try it out on the mock to see if it works. I didn't think about checking out the synoptic questions - that's a great idea. I think the idea of jotting down things for the essay is really good, I'll try and use the first 1-9 questions as a prompt (hopefully) and write down any buzzwords at the end of each question to help for the essay plan.

My plan is
-Spend around 90 mins on the first 9 questions
-15 mins max on question 9 seeing as its the repeat of horrendous old Q7 in BIOL4 (eurgh)
-max of 10 mins per question on 1-8. Hopefully this should give me 5 mins to check through the first 75 marks of the paper.

That should bring me to 95 mins, leaving 40 mins for the essay.

Then
-10 mins planning the essay in as much detail as possible with that time
-write for 25 mins
-remaining 5 mins I'd use to read through and add anything to the plan I don't think I'll have time to write into the essay (as that can apparently get you marks!)

That would bring me to 135 mins - 2 loooong hours and 15 mins. This paper is gonna be beastly, lord help me

Reply 971

F1's Finest

Original post by erniiee

The worst thing is that this is a pm paper.

I was hoping this paper would be in the morning!

Reply 972

erniiee

Original post by James A

The worst thing is that this is a pm paper.

I was hoping this paper would be in the morning!

Aha why?! I think I prefer afternoon papers! Especially for sciences!

Reply 973

F1's Finest

Original post by erniiee

Aha why?! I think I prefer afternoon papers! Especially for sciences!

Afternoon I feel a little stressed/tired.

:emo:

Reply 974

erniiee

Original post by James A

Afternoon I feel a little stressed/tired.

:emo:

Aha fair enough, I feel like the morning ones are a little too early though. 11 would be perfect!

Reply 975

JAJC

Afternoon exams take their toll on me as well! I get so nervous i end up spending the majority of the day in the loo ;((

Reply 976

master y

Original post by erniiee

Aha fair enough, I feel like the morning ones are a little too early though. 11 would be perfect!

But if it was at 11, and a two hour exam, my stomach would be rumbling the whole way through because i want FOOD!

Reply 977

ahmmm

anybodys teachers given them some essay question predictions? :confused:

Reply 978

Anniestasia

Okay, the next thing confusing me with its lack of detailing is the sliding filament mechanism. I'm confused about the changing from ADP and ATP on myosin heads. So the first time at which ADP is mentioned is it being attached to myosin heads at the start of the cycle. This ADP allows the myosin to form cross bridges with the actin. The myosin heads then change angle and the ADP is released, so they now have no ADP attached to them. An ATP molecule then attaches to the myosin heads, causing it become detached from the actin, by breaking the cross bridge. So a molecule of ATP is still attached to the myosin heads at this point. This same ATP used to break the cross bridge is then hydrolysed by ATPase, and this energy is used to return the myosin to its original position. So now, as the ATP that was on the myosin head has been hydrolysed, it has turned into ADP and is still attached. The cycle can now begin again. Is this all correct? In particular, is it right that the ATP isn't hydrolysed to break the cross-bridge, and if so, how does it break the cross bridge? Have I also got it right about the when the ATP attached to the myosin head is hydrolysed, it stays attached but changes into ADP? Or does it detatch and another ADP from another source come along?

Reply 979

F1's Finest

Original post by Anniestasia

So the first time at which ADP is mentioned is it being attached to myosin heads at the start of the cycle.

Yes, it is attached when the cycle begins (ADP)

This ADP allows the myosin to form cross bridges with the actin.

The ADP isn't the cause of the formation of the actin-myosin bridges, it's rather the fact that Ca2+ ions are present which move the tropomyosin and then the myosin head binds to the exposed site on the actin filament.

The myosin heads then change angle and the ADP is released

so they now have no ADP attached to them.

an ATP molecule now comes along as you are sayi

An ATP molecule then attaches to the myosin heads, causing it become detached from the actin, by breaking the cross bridge. So a molecule of ATP is still attached to the myosin heads at this point.
This same ATP used to break the cross bridge is then hydrolysed by ATPase, and this energy is used to return the myosin to its original position.

Yes and yes to all.

So now, as the ATP that was on the myosin head has been hydrolysed, it has turned into ADP and is still attached.

The cycle can now begin again. Is this all correct?

yes.

In particular, is it right that the ATP isn't hydrolysed to break the cross-bridge

You said it yourself above, the ATP binds to the myosin head to break to actin-myosin bridge.

and if so, how does it break the cross bridge?

We aren't supposed to know why, but we are supposed to know that it does break the cross bridge. Heck, even wikipedia doesn't mention it.... I don't even know if it's even degree level knowledge, so you'll being going to extreme lengths to try and learn something you honestly don't need to know.

http://en.wikipedia.org/wiki/Muscle_contraction

look under part 10 of Skeletal Muscle Contraction

Have I also got it right about the when the ATP attached to the myosin head is hydrolysed, it stays attached but changes into ADP?