A level Biology: Post your doubts here!

[KurayamiKimmi]

does anyone have a short summary of genetic control, because my book dosnt have that part and it requird in syllabus ??

DNA and RNA are polynucleotides ,made up of long chains of nucleotides.A nucleotide consists of a pentose sugar,a phosphate group and an nitrogen-containing base

.A DNA molecule consists of two polynucleotide chains ,linked by hydrogen bonds between the bases.Adenine always bonds with thymine and cytosine with guanine
.RNA which comes in several different forms , has only one polynucleotide chain ,although this may be twisted back onto itself like in tRNA .In RNA the base thymine is replaced by uracil.

DNA molecules replicate during interphase .The hydrogen bonds between the bases break ,allowing free nucleotides to fall into position beside their complementary bases on each strand of the original DNA molecule .Adjacent nucleotides are then linked ,through their phosphates and sugars ,to form new strands .Two complete new molecules are thus formed from one old one ,each new molecule containing one old strand and one new .

The sequence of bases on a DNA code for a amino acids in a protein (or polypeptide) .Each amino acid is coded for by three bases .A length of DNA coding for one complete protein or polypeptide is a gene.

During protein synthesis , a complementary copy of the base sequence on a gene is made by building a molecule of mRNA against one DNA strand .The mRNA then moves to a ribosome in the cytoplasm.
tRNA molecules with complementary triplets of bases temporarily pair up with the base triplets on the mRNA ,bringing appropriate amino acids .As two amino acids are held side by side ,a peptide bond is formed between them .The ribosome moves along the mRNA molecule , so that appropriate amino acids are linked together , following the sequence laid down by the base sequence on the mRNA

That should pretty much sum up the whole chapter .Hope this helps!

 

[raamish]

PLease explain what is the primary structure of protein is?

 

[KurayamiKimmi]

PLease explain what is the primary structure of protein is?

The primary sequence is the linear sequence of amino acids in that protein.It is specific for every protein

 

[Amaryllis]

Heyy man, first thing Viruses are are not living cells and they r just Proteins which require a hist in which they multiply so basically they do not have cell walls and antibiotics affect cell wall synthesis so they have no effect on viruses and as far as CO2 transport is concerned I advice you to go through Bohr's effect in addition to little bit Information of reactions of Co2 in redblood cells like formation of Carbonic acid and dissassociation of into HCO3-1 and H+ ions ....soo juss have an overall idea

hope this helped

thank u alot .....haha im not a man ^_^

 

[haroon740]

thank u alot .....haha im not a man ^_^

I'm sorry I was too busy answerin the question ...no offence

 

[raamish]

The primary sequence is the linear sequence of amino acids in that protein.It is specific for every protein

for example the making of polypeptides by DNA. where peptide bonds are built up that is a primary structure?

 

[TheMan123]

http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w10_qp_23.pdf
Can someone tell me why in Q1. fig1.1, the label B is a protein not a cholesterol?

 

[littlecloud11]

But in vaccination sometimes a live virus is used as well. And its apparently the most effective form of vaccination so why?

In case a live virus is used, it's attenuated, meaning it still has it's antigen but cannot cause the body harm. So, it is the most effective form of vaccination.

 

[littlecloud11]

for example the making of polypeptides by DNA. where peptide bonds are built up that is a primary structure?

Peptide bonds are always present between the amino acid, irrespective of the structural arrangement.

 

[raamish]

Peptide bonds are always present between the amino acid, irrespective of the structural arrangement.

ok. And why does increased blood pressure increase the risk of coronary heart disease?

 

[littlecloud11]

ok. And why does increased blood pressure increase the risk of coronary heart disease?

Persistent high blood pressure damages the lining of the arteries, in order to repair the damage cholesterol is deposited at the site of damage but this results in the build up of plaque over time. The plague hardens the arteries and also causes narrowing. This process leads to atherosclerosis which eventually leads to coronary heart disease.

 

[raamish]

Persistent high blood pressure damages the lining of the arteries, in order to repair the damage cholesterol is deposited at the site of damage but this results in the build up of plague over time. The plague hardens the arteries and also causes narrowing. This process leads to atherosclerosis which eventually leads to coronary heart disease.

What do the phosphate heads of the phospholips do.And why despite being polar they dont allow polar molecules to pass through them?

 

[raamish]

There was a qs in the pastpapers that how is DNA suited to do semi-conservation replication. Please answer and explain?

 

[geek101]

There was a qs in the pastpapers that how is DNA suited to do semi-conservation replication. Please answer and explain?

In semi conservative replication, the two strands of DNA unwind and each serves as a template for a new double helix to form. This produces two DNA molecules which are exact copies of each other, this helps maintain the genetic stability of the organism, and prevents any mutations from occurring. I hope this is what they are asking for...you can check the mark scheme though...

 

[haroon740]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w10_qp_23.pdf
Can someone tell me why in Q1. fig1.1, the label B is a protein not a cholesterol?

Remember that protein are big and scattered in the membrane and chloestrol are the ones with a phosphate head and and a wiggly tail in the phospholipid bi layer

 

[rogue94]

There was a qs in the pastpapers that how is DNA suited to do semi-conservation replication. Please answer and explain?

Answer:
There is complementary base pairing in a DNA molecule/double helix, so the double helix unwinds to give two complementary strands of DNA. Each strand acts as a template for the synthesis a complementary DNA strand, so two new DNA double helices are formed with each double helix having one original strand and one newly synthesized strand.

Basically, the property which allows semi-conservative replication is complementary base-pairing/strands, so you have to mention that, followed by the result of semi-conservative replication.

 

[raamish]

Answer:
There is complementary base pairing in a DNA molecule/double helix, so the double helix unwinds to give two complementary strands of DNA. Each strand acts as a template for the synthesis a complementary DNA strand, so two new DNA double helices are formed with each double helix having one original strand and one newly synthesized strand.

Basically, the property which allows semi-conservative replication is complementary base-pairing/strands, so you have to mention that, followed by the result of semi-conservative replication.

What do the phosphate heads of the phospholips do.And why despite being polar they dont allow polar molecules to pass through them?

 

[rogue94]

What do the phosphate heads of the phospholips do.And why despite being polar they dont allow polar molecules to pass through them?

Phosphate heads are responsible for the orientation of the phospholipid bilayer. In questions related to how the structure of a phospholipid allows it to form a bilayer, you have to mention that the phosphate heads are hydrophilic and therefore, water attracting so they face outwards towards the aqueous environment (cytoplasm, or fluid around the cell).

Phosphate heads are only a small part of the bilayer, the fatty acid/hydrocarbon, tails form the major part of the bilayer, which is the hydrophobic interior. This hydrophobic interior acts as a barrier to ions and polar molecules such as water. So basically, polar molecules can reach till the phosphate heads, but cannot pass through the hydrophobic interior of the bilayer!

 

[TheMan123]

Remember that protein are big and scattered in the membrane and chloestrol are the ones with a phosphate head and and a wiggly tail in the phospholipid bi layer

Thx, its just that certain diagrams draw cholesterol as a rectangular block, but I wasn't sure if CIE did that too. I guess you're right I've only seen CIE using the phosphate + tail diagram

 

[haroon740]

Thx, its just that certain diagrams draw cholesterol as a rectangular block, but I wasn't sure if CIE did that too. I guess you're right I've only seen CIE using the phosphate + tail diagram

Antyme mate