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A2 Biology OCR June 2015 Revision Thread

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Could someone kindly describe the stucture of the sliding filament model and explain how the sliding filament model works. The diagrams in the textbook look complicated.

1. Action potentials from motor neurones stimulate the muscle cell. This cause depolarisation of the sarcolemma
2.Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum.
3. This causes the sarcoplasmic reticulum to release Ca^2+ into the sarcoplasm
4. The Ca^2+ bind to troponin on the actin filaments causing the shape of troponin to change. This pulls the attached tropomyosin out of the actin myosin binding site.
5. This exposes the binding site allowing myosin to bind. This forms an actin myosin cross bridge.
6.Ca^2+ activates ATPase which breaks down ATP providing energy for muscle contraction which allows the myosin head to slide which pulls the actin filament along. This is called the power stroke.
7. ATP also breaks the cross bridge so the myosin head detaches from the actin filament and the myosin head reattaches to a different binding site further along the filament.
A sarcomere is a unit of a myofibril consists of:
An I band= this only has actin filaments
A M line= middle of myosin filament
A band= myosin and actin filaments
Z line= actin filaments are attached. One z line to another= sarcomere
H zone= myosin filaments only.

Hope this helps.

(edited 8 years ago)

Reply 981

ChoccyPhilly

Original post by kobobo

1. Action potentials from motor neurones stimulate the muscle cell. This cause depolarisation of the sarcolemma
2.Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum.
3. This causes the sarcoplasmic reticulum to release Ca^2+ into the sarcoplasm
4. The Ca^2+ bind to troponin on the actin filaments causing the shape of tropomyosin to change which causes it to move.
5. This exposes the binding site allowing myosin to bind. This forms an actin myosin cross bridge.
6.Ca^2+ activates ATPase which breaks down ATP providing energy for muscle contraction which allows the myosin head to slide which pulls the actin filament along. This is called the power stroke.
7. ATP also breaks the cross bridge so the myosin head detaches from the actin filament and the myosin head reattaches to a different binding site further along the filament.
A unit of myofibril consists of:
An I band= this only has actin filaments
A M line= middle of myosin filament
A band= myosin and actin filaments
Z line= actin filaments are attached. One z line to another= sarcomere
H zone= myosin filaments only.

Hope this helps.

Couple of tiny corrections:

CA ions bind to troponin, causing troponin to change shape and pull tropomyosin out of the actin-myosin binding site. Tropomyosin's shape does not change.

The unit isn't a myofibril, it's a sarcomere.

Reply 982

bakedbeans247

Original post by kobobo

1. Action potentials from motor neurones stimulate the muscle cell. This cause depolarisation of the sarcolemma
2.Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum.
3. This causes the sarcoplasmic reticulum to release Ca^2+ into the sarcoplasm
4. The Ca^2+ bind to troponin on the actin filaments causing the shape of tropomyosin to change which causes it to move.
5. This exposes the binding site allowing myosin to bind. This forms an actin myosin cross bridge.
6.Ca^2+ activates ATPase which breaks down ATP providing energy for muscle contraction which allows the myosin head to slide which pulls the actin filament along. This is called the power stroke.
7. ATP also breaks the cross bridge so the myosin head detaches from the actin filament and the myosin head reattaches to a different binding site further along the filament.
A unit of myofibril consists of:
An I band= this only has actin filaments
A M line= middle of myosin filament
A band= myosin and actin filaments
Z line= actin filaments are attached. One z line to another= sarcomere
H zone= myosin filaments only.

Hope this helps.

Should that be "causing the shape of troponin to change"? :smile:

Reply 983

bakedbeans247

I don't think there has been a single question about the process shedding leaves or how auxins cause the zones of elongation to elongate (the stuff about ATPase etc). Have they?

Reply 984

ChoccyPhilly

Original post by bakedbeans247

I don't think there has been a single question about the process shedding leaves or how auxins cause the zones of elongation to elongate (the stuff about ATPase etc). Have they?

I remember coming across a question asking about the differences and similarities between peat bog and a deciduous forest but that's it thus far but nothing on the latter.

Reply 985

TheLegalDealer

Can someone explain to me how to produce Golden Rice + do we have to learn the exact rice species involved ?

Many thanks !

Reply 986

tomixox

anybody else avoiding F215 like the plague????

Reply 987

bakedbeans247

Original post by tomixox

anybody else avoiding F215 like the plague????

Haha, What grade do you need for bio?

Reply 988

maisie__x

Original post by tomixox

anybody else avoiding F215 like the plague????

I wish there was enough time to avoid it :')

Reply 989

tomixox

Original post by bakedbeans247

Haha, What grade do you need for bio?

An A, wbu?

Reply 990

evolve123

I didn't think we had to know about the tropomyosin part of the power stroke :frown:

Thank you though! :smile:

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(edited 8 years ago)

Reply 991

ChoccyPhilly

Original post by tomixox

anybody else avoiding F215 like the plague????

Redoing unit 2 makes unit 5 a joy as it's so much more interesting IMO.

Original post by TheLegalDealer

Can someone explain to me how to produce Golden Rice + do we have to learn the exact rice species involved ? 
 
Many thanks !

So we basically want rice to make beta carotene (vit a) which we extract from a soil bacteria and maize (someone please include species names). Isolate the allele that codes for it, insert it into a bacteria called Agrobacterium tumefaciens through standard procedures with BAC or bacteriophage vectors. A. tumefaciens is a bacteria that normally infects rice plants and will integrate its DNA with the rice plant.

I'm missing out a couple of details, so feel free to fill in the holes, people.

Original post by games211

How can you tell what vector to use ? I remember a question and the possible options were: liposomes. bacs, viruses etc etc ;/

For somatic therapy in humans, you'll always use a virus of some sorts and normally they'll allow just virus. Bacteria can use BAC or bacteriophage; the latter inserts its viral DNA into the bacteria

Reply 992

George444

Original post by TheLegalDealer

Can someone explain to me how to produce Golden Rice + do we have to learn the exact rice species involved ?

Many thanks !

Hey, the text book talks about inserting certain genes into a gene sequence that switches on genes which causes beta-carotene production. (The pre-cursor molecule that's converted into Vitamin A.) This was in one of the wishy-washy "How science works" part of the textbook and I don't recall any past paper questions on the production of Golden Rice so I wouldn't worry too much about it. Most questions I've seen on Golden Rice ask for the advantages and disadvantages. Hope I've helped :smile:

Reply 993

ChoccyPhilly

Original post by tomixox

anybody else avoiding F215 like the plague????

Redoing unit 2 makes unit 5 a joy as it's so much more interesting IMO.

Original post by TheLegalDealer

Can someone explain to me how to produce Golden Rice + do we have to learn the exact rice species involved ? 
 
Many thanks !

Original post by games211

How can you tell what vector to use ? I remember a question and the possible options were: liposomes. bacs, viruses etc etc ;/

For somatic therapy in humans, you'll always use a virus of some sorts and normally they'll allow just virus. It kind of makes sense as we learnt in unit 2 that viruses use reverse transcriptase to make their viral DNA in our cells and such. Bacteria can use BAC or bacteriophage; the latter inserts its viral DNA into the bacteria

Reply 994

TheLegalDealer

anyone have a model answer on how to sequence a genome ? :biggrin:

Thanks in advance !

Reply 995

student_05

anyone know where i can get the f214 & f215 past papers for 2014 please?

Reply 996

tomixox

Original post by student_05

anyone know where i can get the f214 & f215 past papers for 2014 please?

Thebiotutor.com

Reply 997

Shanahey

Hi,
Please could someone explain to me oxidative phosphorylation , chemiosmosis and electron transport chain? :s-smilie:

Thank you! :smile:

Reply 998

GXO

Hi, just a quick question about ultrafiltration- Is it the capillary pores that stop proteins and red blood cells being filtered out, or the basement membrane? From what I understand it seems to be both...

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Reply 999

TheLegalDealer

Original post by GXO

Only the basement membrane as it has a fine mesh of collagen fibres that don't allow large molecules e.g. proteins through . The fenestrations (holes) in the capillary wall allow all solutes to pass through except proteins