AS LEVEL BIOLOGY... discuss here AS students only :)

[Moi]

can someone explain the role of tRNa in protein synthesis?

tRNA's are specific. the are clover shaped structure. at the buttom they have Anticodon ( 3 bases) . the anticodon is specific to a certain amino acid. that amino acid itself will get attached to the tRNA (on the top). you could have 3 or several base sequence in the anticodon that goes with the same type of amino acid. After amino acids get attached to tRNA in the ribosome, the tRNA-Amino Acid complex will attach its anticodon to complimentary codon (complimentary bases) on the mRNA that is in the subunit of ribosome. two tRNAs at a time. while the two of them are getting attached to mRNA codons, polypeptide chains form between the amino acids. once its done, tRBA get$ deattached from the mRNA and the amino acid (it goes back to the large unit in ribosone to get attached to another amino acid) meanwhile another tRNA-aminoacid complex comes bext to the mRNA, codon attach to anticodon, polypeptide chains form between a.a and the tRNA leaves and the cycle continues until the line of mRNA is over and and you have a polypeptide chain formed (which is the base of protien structure).........

understood or ?? Good luck

 

[daredevil]

There's one crucial mistake:
The bond between G and C is NOT a triple bond. It's three different HYDROGEN bonds. Same goes for the bonds between A and T/U.

ooh thanks for the correction

 

[daredevil]

Do we have to know the structure of deoxy ribose ,ribose ,and thebases?

yes to deoxyibose and ribose but the bases i don't think so. just know that A and G have a double ring structure with one double bond in each ring and the uracil, thyamine and cytosine have single rings with 2 double bonds each. and yes know that G and C hav triple bond whiile A and T or U have double bonds.

There's one crucial mistake:
The bond between G and C is NOT a triple bond. It's three different HYDROGEN bonds. Same goes for the bonds between A and T/U.

sorry for my mistake Ahmed

 

[daredevil]

Do we have to know causes of sickle cell anaemia??

(a) define the term disease (see page 37) and explain the difference between an infectious disease and non-infectious diseases (limited to sickle cell anaemia and lung cancer;

this is the part of syllabus dealing with sickle cell anaemia but in my notes the cause of sickle cell anaemia is explain under the base pair substitution heading so i'm not sure if it is included or not.... but i could give u the notes part if u want

 

[daredevil]

Do we have to know causes of sickle cell anaemia??

the question has come in some past papers so u might as well know the whole deal.
if u don't have it then tell me and i'll give u the notes or u can c in the bio book AS wali. =)

 

[daredevil]

can someone tell me the effect of wind velocity on the rate of tranpiration and its explanation... like i know that until a certain wind velocity the rate increases but after that increase in wind velocity results in a decrease in the rate of transpiration. but why?

 

[Moi]

can someone tell me the effect of wind velocity on the rate of tranpiration and its explanation... like i know that until a certain wind velocity the rate increases but after that increase in wind velocity results in a decrease in the rate of transpiration. but why?

i dont think u need to know, we've never been told such thing....all u need to know is, the presence of wind increases transpiration rate !

 

[daredevil]

i dont think u need to know, we've never been told such thing....all u need to know is, the presence of wind increases transpiration rate !

oh okay.... thanks

 

[lee mee..]

Can someone please explain me the ans for Q3b..
http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_s12_qp_21.pd
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_ms_21.pdf

 

[lee mee..]

explain the role of pre-capillary sphinchter muscles?? :/

Is this for AS ??

 

[Moi]

any one knows what is 'herd immunity' ? explination?

 

[lee mee..]

any one knows what is 'herd immunity' ? explination?

It means vaccinating large number of people at the same time .

 

[Moi]

It means vaccinating large number of people at the same time .

thx much

 

[lee mee..]

thx much

ur welcome

 

[airyhat]

What is the difference between macrophages and neutrophils

 

[Irfan1995]

Can someone please explain me the ans for Q3b..
http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_s12_qp_21.pd
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s12_ms_21.pdf

We know that people with SCA can't carry as much oxygen as they should.
But the curve tells us that at low partial pressures of oxygen (like in tissues), they can release the oxygen they have more easily than those with normal RBCs.
This is because the graph for SCA is "lower" than the normal graph.
So at the same partial pressure of oxygen, haemoglobin must be less saturated in those with SCA, so they're forced to release any oxygen they carry.
The easier release of oxygen compensates for the low total oxygen content carried. (i.e. they carry less oxygen, but they can give their oxygen easier to cells, which makes up for the low quantity of oxygen they carry)

 

[Irfan1995]

any one knows what is 'herd immunity' ? explination?

As everyone said, herd immunity is vaccinating a large proportion of the population (ideally, 95%)
When most people are vaccinated, the disease can only be transferred within the unvaccinated population (5%)
Since the number of unvaccinated people are very low, the disease will eventually die since it can't pass on from person to person easily.

 

[lee mee..]

We know that people with SCA can't carry as much oxygen as they should.
But the curve tells us that at low partial pressures of oxygen (like in tissues), they can release the oxygen they have more easily than those with normal RBCs.
This is because the graph for SCA is "lower" than the normal graph.
So at the same partial pressure of oxygen, haemoglobin must be less saturated in those with SCA, so they're forced to release any oxygen they carry.
The easier release of oxygen compensates for the low total oxygen content carried. (i.e. they carry less oxygen, but they can give their oxygen easier to cells, which makes up for the low quantity of oxygen they carry)

Thank you

 

[daredevil]

What is the difference between macrophages and neutrophils

Nutrophils are produced in the bone marrow and patrol the blood vessels. they can squeeze out of the blood vessels and access the infected region. they engulf the foreign particle by phagocytosis. they have a short life span and are non-specific.
Macrophages reside in organs like lover, kidneys, lungs etc. they have a longer life span and engulf the foreign partices by phagocytosis. they develop from monocytes that are pproduced in the bone marrowand circulate in the blood vessels and lymph.

 

[Bebeskii]

Does catalase have haem group? so confused