• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

A level Biology: Post your doubts here!

qwertypoiu

qwertypoiu

Messages
924
Reaction score
1,096
Points
153
My Name said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_21.pdf
Question 2 d ii
Please and thank you!
Click to expand...
When CO2 dissolves and undergoes reaction with water to form H2CO3 (catalysed by carbonic anhydrase), H+ ions are formed as the acid dissociates. The H+ ions react with haemoglobin (Hb) to form haemoglobinic acid (HHb). This causes the shape of haemoglobin to change, thus reducing its affinity for oxygen. So haemoglobin loses oxygen at places with higher concentration of CO2 (bohr effect)
Hope that makes sense.
 
qwertypoiu

qwertypoiu

Messages
924
Reaction score
1,096
Points
153
My Name said:
http://studyguide.pk/Past Papers/CIE/International A And AS Level/9700 - Biology/9700_s10_qp_23.pdf
question 3 part a i
I know one answer is tertiary because of the disulphide bond.
But what about quarternary it is because it has more than one chain?
Click to expand...
I had a look at the diagram.

Primary structure: shows sequence of amino acids. This diagram does this. So the diagram DOES show primary structure.
Secondary structure: Alpha and beta coils being formed due to hydrogen bonds interacting every three amino acids or some fixed number.
Tertiary structure: shows the geometric shape of protein formed due to various bonds between R groups of amino acids. I think this is not shown here. You're right that there is one disulfide bond here between two amino acids within the right chain, but this doesn't indicate the SHAPE of the molecule.
Quaternary structure: shows the interaction between two or more polypeptide chains to form a protein molecule. The disulfide bonds between the two chains here indicate this. You might say this also doesn't show us the overall shape, but I think that may not be important for Quaternary structure, but rather the tertiary is involved with shapes.
 
qwertypoiu

qwertypoiu

Messages
924
Reaction score
1,096
Points
153
Oh and you had a post about glycosidic bonds in cellulose with beta glucose and blabla, I was gonna reply but it seems you took it off.
I think it would've gotten 4 marks ☺
 
M

My Name

Messages
4,988
Reaction score
23,955
Points
523
qwertypoiu said:
Oh and you had a post about glycosidic bonds in cellulose with beta glucose and blabla, I was gonna reply but it seems you took it off.
I think it would've gotten 4 marks ☺
Click to expand...
Yes I did.I guess it was fine.
qwertypoiu said:
I had a look at the diagram.

Primary structure: shows sequence of amino acids. This diagram does this. So the diagram DOES show primary structure.
Secondary structure: Alpha and beta coils being formed due to hydrogen bonds interacting every three amino acids or some fixed number.
Tertiary structure: shows the geometric shape of protein formed due to various bonds between R groups of amino acids. I think this is not shown here. You're right that there is one disulfide bond here between two amino acids within the right chain, but this doesn't indicate the SHAPE of the molecule.
Quaternary structure: shows the interaction between two or more polypeptide chains to form a protein molecule. The disulfide bonds between the two chains here indicate this. You might say this also doesn't show us the overall shape, but I think that may not be important for Quaternary structure, but rather the tertiary is involved with shapes.
Click to expand...
My answer was PRIMARY and TERTIARY.
qwertypoiu said:
When CO2 dissolves and undergoes reaction with water to form H2CO3 (catalysed by carbonic anhydrase), H+ ions are formed as the acid dissociates. The H+ ions react with haemoglobin (Hb) to form haemoglobinic acid (HHb). This causes the shape of haemoglobin to change, thus reducing its affinity for oxygen. So haemoglobin loses oxygen at places with higher concentration of CO2 (bohr effect)
Hope that makes sense.
Click to expand...
Oh sorry I knew this!
Sorry for wasting your time.


Thank you!
 
Last edited:
qwertypoiu

qwertypoiu

Messages
924
Reaction score
1,096
Points
153
My Name said:
Yes I did.I guess it was fine.

My answer was PRIMARY and TERTIARY.

Oh sorry I knew this!
Sorry for wasting your time.


Thank you!
Click to expand...
You're welcome.

Btw the answer is primary and Quaternary. Tertiary is incorrect.

Good luck for your exams :)
 
nehaoscar

nehaoscar

Messages
1,318
Reaction score
1,374
Points
173
View attachment 57272
Someone explain this please
the grade thresholds say that the maximum mark is 260 and 130
but then the components add up to 270 and 140 ...
Why do they say it as 260 and 130 then???
 
A41905

A41905

Messages
4
Reaction score
0
Points
11
9700/12/m/j/12

21. Which statements about tRNA structure are correct?

1. There is a binding site for the attachment of a specific amino acid, as well as a different binding site for the attachment to the ribosome, in order to allow translation to occur.
2. There is a ribose-phosphate backbone with strong covalent phosphodiester bonds and areas within the polynucleotide chain where base-pairing by hydrogen bonding occurs.
3. There is a section known as an anticodon that contains the same triplet of bases as the triplet of DNA bases that has been transcribed to produce the mRNA codon.

A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3

The answer given is B. Can anyone explain why the third statement is incorrect?
Thank you in advance :)
 
M

My Name

Messages
4,988
Reaction score
23,955
Points
523
A41905 said:
The
21. Which statements about tRNA structure are correct?

1. There is a binding site for the attachment of a specific amino acid, as well as a different binding site for the attachment to the ribosome, in order to allow translation to occur.
2. There is a ribose-phosphate backbone with strong covalent phosphodiester bonds and areas within the polynucleotide chain where base-pairing by hydrogen bonding occurs.
3. There is a section known as an anticodon that contains the same triplet of bases as the triplet of DNA bases that has been transcribed to produce the mRNA codon.

A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3

The answer given is B. Can anyone explain why the third statement is incorrect?
Thank you in advance :)
Click to expand...
Read it carefully.
There is a section known as an anticodon that contains the same triplet of bases as the triplet of DNA bases that has been transcribed to produce the mRNA codon.
Some anticodons on the tRNA would contain URACIL instead of of THYMINE.
 
_MoHD_E

_MoHD_E

Messages
49
Reaction score
41
Points
28
A41905 said:
9700/12/m/j/12

21. Which statements about tRNA structure are correct?

1. There is a binding site for the attachment of a specific amino acid, as well as a different binding site for the attachment to the ribosome, in order to allow translation to occur.
2. There is a ribose-phosphate backbone with strong covalent phosphodiester bonds and areas within the polynucleotide chain where base-pairing by hydrogen bonding occurs.
3. There is a section known as an anticodon that contains the same triplet of bases as the triplet of DNA bases that has been transcribed to produce the mRNA codon.

A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3

The answer given is B. Can anyone explain why the third statement is incorrect?
Thank you in advance :)
Click to expand...
Because it doesn't contain the same triplet as DNA well most of the times yes but sometimes no where there is thymine involved for example if the gene of the DNA coding for a specific polypeptide has the first triple as ATG then tRNA will be AUG as there is no thymine In tRNA
 
Last edited:
You must log in or register to reply here.
Top