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samfreak
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#1181
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#1181
Regarding gel electrophoresis, are dna probes used so that the separate strands can be seen?

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MLogan
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#1182
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#1182
(Original post by samfreak)
Regarding gel electrophoresis, are dna probes used so that the separate strands can be seen?

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I thought DNA probes are used to locate a particular gene on a DNA strand. So the DNA probe with be made of complementary bases to the desired gene on the DNA.
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Mocking_bird
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#1183
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#1183
(Original post by samfreak)
Regarding gel electrophoresis, are dna probes used so that the separate strands can be seen?


In gel electrophoresis we use a radioactively labelled DNA primer which allows the separate fragments to be seen under xray.
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samfreak
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#1184
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#1184
(Original post by Mocking_bird)
In gel electrophoresis we use a radioactively labelled DNA primer which allows the separate fragments to be seen under xray.
Why would primers be used if the DNA strands will be single stranded

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cheesypuff
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#1185
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#1185
(Original post by samfreak)
Why would primers be used if the DNA strands will be single stranded

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so the primers would have a complementary base sequence to the single stranded dna so the single stranded dna and complementary primer would form H2 bonds
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Mocking_bird
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#1186
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#1186
(Original post by samfreak)
Why would primers be used if the DNA strands will be single stranded

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It begins the sequencing.
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Starlight94
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#1187
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#1187
(Original post by rm.xo)
Im gonna say (using last years grade boundaries and that they do down every year unfortunatley )

Full ums: 47/48
A*: 45/46
A: 43/44
B: 41/42
C: 39/40
D: 37/38

But you never know, they could be pretty much the same as last year. I thought the ISA was quite hard this year!
I got 39 which I was really pleased with until I was told the boundaries, proper killed me when my teacher said this year it could potentially be a D I hate ISA's
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jess_m94
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#1188
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#1188
(Original post by samfreak)
Why would primers be used if the DNA strands will be single stranded

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The primer is needed to bind to the start of the DNA sequence and make the start of it double-stranded, because DNA polymerase can only work on a double strand
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erniiee
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#1189
(Original post by rm.xo)
Oh! i really hope so! that would be so so good!
:yep:

Which topic/chapter are you guys finding hardest?
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rm.xo
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#1190
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#1190
(Original post by erniiee)
:yep:

Which topic/chapter are you guys finding hardest?
Chapter 16 was wrote by satan
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MLogan
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#1191
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#1191
(Original post by rm.xo)
Chapter 16 was wrote by satan
Yeah i totally agree but tbh its actually ,in my opinion, not that bad when it comes to the papers! So don't worry
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JoshL123
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#1192
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#1192
Hey guys. Just going through some questions and wanted to clarify a few things. One question is on describing the function of anti-codon. The markscheme says:

Allows binding/ joining/ attaching to mRNA;
Codon/ complementary base sequence;

And I have put down, "It consists of a sequence of three organic bases that are complementary to the codon's sequence of three organic bases of the mRNA molecule, as to form hydrogen bonds. This occurs in the ribosome during the process of translation".

I know that I;ve got the second mark but how about the first one? I did mention hydrogen bonds, but without talking about the attachment. What I may be asking may seem a bit stupid but our teacher doesn't credit us the marks if we do not mention a given point specifically to the markscheme .

Also, there was a question as to why a fragment of DNA say had 330 bases whilst the mRna has say 300 bases. In my answer I tend to talk about pre-MRNA (formed from the DNA's gene consisting of introns, which are removed of in the process of splicing). The mark scheme always mentions about DNA rather than pre-mRNA. So, would I be wrong to mention pre-mRNA? Being a bit pedantic :L
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candyhearts
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#1193
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#1193
I'm a little confused about the resting potential, are there any Na+ channels open at this point and if so are they the voltage gated channels? Also what causes the more negative charge on the axon membrane relative to the tissue fluid outside?
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rm.xo
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#1194
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#1194
(Original post by MLogan)
Yeah i totally agree but tbh its actually ,in my opinion, not that bad when it comes to the papers! So don't worry
It isn't hard I don't think, it's just soooooo long
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Gnome :)
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#1195
(Original post by candyhearts)
I'm a little confused about the resting potential, are there any Na+ channels open at this point and if so are they the voltage gated channels? Also what causes the more negative charge on the axon membrane relative to the tissue fluid outside?
There are some Na+ channels open, but these are not the voltage-gated ones; these ones are just... there, letting the Na+ do it's thing

The negative charge inside the axon is a result of:
- The sodium-potassium pump actively transporting 2 K+ in for every 3 Na+ out (so there are more positive ions moving out of the axon)
- Negatively charged proteins in the axon
- There are more (NOT voltage-gated) channels for K+ than there are for Na+, so the axon membrane is more permeable to K+. This means that K+ diffuses along the concentration gradient (at a greater rate than Na+ diffuses in) , taking its positivity with it

Hope that makes sense!
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JoshL123
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#1196
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#1196
(Original post by candyhearts)
I'm a little confused about the resting potential, are there any Na+ channels open at this point and if so are they the voltage gated channels? Also what causes the more negative charge on the axon membrane relative to the tissue fluid outside?
Hey there Yes, there Na+ voltage gated ion channels that are open as are K+ voltage gated ion channels. However, there are many more K+ voltage gated ion channels open than Na+ voltage gated ion channels. I believe that at the given point in time, the plasma membrane is approximately 100 times more permeable to K+ ions than Na+ ions. These means that the majority of K+ ions diffuse down a concentration gradient from an area of high concentration (within the interior of the axon) to an area of low concentration (in the surrounding tissue fluid). It is important to note down that this doesn't occur at the point of resting potential (approximately -70mV) but rather when establishing it (i.e. following an action potential). The movement of ions occurs until the electrical and chemical gradient formed across the plasma membrane are balanced, as to ensure that there is no net movement of ions

Hope that helps!
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JoshL123
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#1197
(Original post by Gnome :))
There are some Na+ channels open, but these are not the voltage-gated ones; these ones are just... there, letting the Na+ do it's thing

The negative charge inside the axon is a result of:
- The sodium-potassium pump actively transporting 2 K+ in for every 3 Na+ out (so there are more positive ions moving out of the axon)
- Negatively charged proteins in the axon
- There are more (NOT voltage-gated) channels for K+ than there are for Na+, so the axon membrane is more permeable to K+. This means that K+ diffuses along the concentration gradient (at a greater rate than Na+ diffuses in) , taking its positivity with it

Hope that makes sense!
Hey there! Sorry, but I thought that it is the voltage gated ion channels that are open given that the active transport of Na+ and K+ ions trigger an alteration electrical potential difference.
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cheesypuff
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#1198
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#1198
so how does everyone feel at this stage about the exam?

what topics do you reckon will we tested?
:dontknow::yy:
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Gnome :)
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#1199
(Original post by JoshL123)
Hey there! Sorry, but I thought that it is the voltage gated ion channels that are open given that the active transport of Na+ and K+ ions trigger an alteration electrical potential difference.
Sorry, don't quite understand what you mean?:confused:

At 'rest', the voltage-gated channels are shut.
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MLogan
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#1200
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#1200
What is the purpose of Pacinian corpuscles occurring in joints,ligaments and tendons? Any help?
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