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Tikara
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#1901
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#1901
(Original post by master y)
loook pls
it's talking about inserting DNA into a gene so you know that it's cutting in some part of the child's DNA. if a proto-oncogene was cut into the proto-oncogene would stop working and therefore not stimulate cell division.

A proto-oncogene only leads to cancer if there is a mutation (leading to an oncogene).

it must be the tumour suppressor gene that the DNA is inserted in the middle of, inactivating it

hope that helped!
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homeworkwiz
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#1902
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#1902
Are stretch mediated sodium channels basically sodium ion channels whose permeability changes according to its shape which relies on pressure?

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neelam123h
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#1903
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#1903
Can someone please explain restriction mapping to me please.

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BetsieB
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#1904
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#1904
Could someone summerise in VIVO cloning please

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loveheartsandall
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#1905
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#1905
Hi all,

On page 241 of the AQA biology text books, it talks about how siRNA is derived from DOUBLE STRANDED RNA. My question is since when were RNA double stranded? I thought both mRNA and tRNA were single-stranded polynucleotide chains?
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iop horray
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#1906
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#1906
(Original post by homeworkwiz)
Are stretch mediated sodium channels basically sodium ion channels whose permeability changes according to its shape which relies on pressure?

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yes , as a stretch mediated sodium ion channel is one which is along the plasma membrane of the sensory neurone present within the centre of the pacinian corpuscle. When pressure is applied to the pacinain corpuscle , as it responds to mechanical stimuli, it would cause it to change shape and as an result cause the plasma membrane of the sensory neurone to stretch. This stretching of the plasma membrane would causes the sodium ion channels to widen and consequently increases the permeability of the sodium ions as before the sodium ion channels weren't wide enough to allow sodium ions to move across. This would allow an influx of positively charge sodium ions to diffuse in to the axon of the sensory neurone which creates an generator potential. If the generator potential exceeds an certain value it would result in an action potential being created. Hope this helps x
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anniedink
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#1907
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#1907
Do we need to know about REpolarisation? Because its not on the spec.

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Fergy94
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#1908
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#1908
(Original post by anniedink)
Do we need to know about REpolarisation? Because its not on the spec.

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yes we do
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DELETED ACCOUNT
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#1909
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(Original post by anniedink)
Do we need to know about REpolarisation? Because its not on the spec.

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Its pretty simple. The inside of a neurone returns to its negatively charged state by actively transporting NA+ ions out and K+ ions in, returning back to its resting potential.
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ahmmm
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#1910
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#1910
anyone got any model essays?
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SamEastie
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#1911
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#1911
(Original post by Tikara)
restriction mapping is cutting a large piece of DNA into smaller chunks using restriction endonucleases so that these chunks' DNA sequence can be determined by DNA sequencing.

this is because very large pieces of DNA are hard to work out the sequence of through DNA sequencing so they're cut into manageable chunks and pieced back together in the correct order to have the whole DNA base sequence.

(what my CGP book says :P)
okay thanks..
but i dont understand what the use of knowing how many bases are between each restriction site? is that just so, after they've been cut, they can be put back in the correct order?
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currydud
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#1912
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#1912
can someone explain 2c for me please?
the mark scheme says ATP causes cross bridges to form and is needed pull the actin. but in the book, it says ATP attaches to the myosin head after actin has been pulled and causes to detach cross bridges?!
http://filestore.aqa.org.uk/subjects...5-QP-JUN12.PDF
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JenLivYoung
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#1913
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#1913
This time next week it will all be over! Keep going guys, not long left *dances* *In a scared way*
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Spellstheend
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#1914
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#1914
The essays are never too specific are they?
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GemG
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#1915
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#1915
What are people doing in terms of questions in prep for the exam? I'm going to do the past papers obviously but as the exam is only sat in the summer there are only a few. Is the specimen paper really different to the actual ones? Are there any sites (a sister to A-Level Chemistry perhaps) that have past paper questions related directly to the syllabus?

Thanks
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charch95
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#1916
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#1916
(Original post by currydud)
can someone explain 2c for me please?
the mark scheme says ATP causes cross bridges to form and is needed pull the actin. but in the book, it says ATP attaches to the myosin head after actin has been pulled and causes to detach cross bridges?!
http://filestore.aqa.org.uk/subjects...5-QP-JUN12.PDF
The mark scheme says this:
(Idea ATP is needed for 1. Attachment/cross bridges between actin and myosin; 2. ‘Power stroke’ / movement of myosin heads / pulling of actin; 3. Detachment of myosin heads; 4. Myosin heads move back/to original position / ‘recovery stroke’;

p.191 of Nelson Thornes AQA text book says energy released from ATP is used for the movement of myosin heads.
Also if little ATP is produced in people with McArdle's disease, there will be less hydrolysis of ATP to ADP and Pi. The book says hyrdrolysis of ATP to ADP by ATPase provides the energy for the myosin head to resume its normal position. Then it says, Myosin head now attaches to the binding site on the actin filament (hence the cross bridge is formed between the actin and myosin filament). So maybe this questions doesn't specifically mean ATP (as in ATP molecule fixing to myosin head) but about ATP and the hydrolsis of it because if there is little ATP present then less energy will be provided for muscle contraction.

Sorry if that doesn't quite make sense, hard to describe my point, but hope that helps in some way
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currydud
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#1917
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#1917
(Original post by charch95)
Sorry if that doesn't quite make sense, hard to describe my point, but hope that helps in some way
thanks just a stupid question I guess haha
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Zazuwaved
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#1918
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#1918
Need a bit of clarification on two things if somebody wouldn't mind

Genetic fingerprinting, (using PCR) is this just to separate out the non-coding repeats from the whole sample of DNA, with primers being specific to the repeating sequences? Also is it the primers that have the fluorescent tag?

second,
During thermoregulation, are the thermoreceptors that detect change in blood temperature IN the hypothalamus or just on the walls of arteries (is this a similar mechanism to control of heart rate- where receptors send impulse to the hypothalamus, which then sends impulses to effectors)?


Thank you :
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samfreak
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#1919
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#1919
i got 84 in bio4, could i still be abl to fet an a star overall? do i hav to get atleast 90% in BOTH bio 4+5 for me to get an a star?

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Gulzar
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#1920
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#1920
(Original post by samfreak)
i got 84 in bio4, could i still be abl to fet an a star overall? do i hav to get atleast 90% in BOTH bio 4+5 for me to get an a star?

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Yes 90% across all a2 units including practicals. Plus you need at least A in AS alone.
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