The Student Room Group

Biology pentose sugars

Hi please could i have help on this question? I know the answer is c or d because pyrimidines are single bases but i thought it would be C because the general formulas of ribose sugars is (CH20)n so there would be a 1:1 ratio between carbon and oxygen atoms?
Here is the question: https://app.gemoo.com/share/image-annotation/629165494436732928?codeId=v67OnOgoJbZgz&origin=imageurlgenerator

Thank you so much!
Original post by anonymous294
Hi please could i have help on this question? I know the answer is c or d because pyrimidines are single bases but i thought it would be C because the general formulas of ribose sugars is (CH20)n so there would be a 1:1 ratio between carbon and oxygen atoms?
Here is the question: https://app.gemoo.com/share/image-annotation/629165494436732928?codeId=v67OnOgoJbZgz&origin=imageurlgenerator
Thank you so much!

Adenine pairs with thymine, 1 ring.
It is a DNA base, so is deoxyribose, which has C:O of 5:4. It is D
C was for ribose, which is 1:1.
(edited 2 months ago)
Original post by anonymous294
Hi please could i have help on this question? I know the answer is c or d because pyrimidines are single bases but i thought it would be C because the general formulas of ribose sugars is (CH20)n so there would be a 1:1 ratio between carbon and oxygen atoms?
Here is the question: https://app.gemoo.com/share/image-annotation/629165494436732928?codeId=v67OnOgoJbZgz&origin=imageurlgenerator

Thank you so much!


An adenine base pairs with Thymine. Thymine has one ring structure and also 5 C-atoms and 4 H-atoms (if the H-atoms in the amino groups NH are ignored). Thus the ratio is 5:4. The only answer that matches with these properties is D.
(edited 2 months ago)
Reply 3
Original post by BankaiGintoki
Adenine pairs with thymine, 1 ring.
It is a DNA base, so is deoxyribose, which has C:O of 5:4. It is D
C was for ribose, which is 1:1.

Hi thank you so much for your reply! I was wondering whether we were supposed to know the structure of ribose and deoxyribose? Also what is the general formula (ch20)n for, why does it not apply here? Thanks!
Original post by anonymous294
Hi thank you so much for your reply! I was wondering whether we were supposed to know the structure of ribose and deoxyribose? Also what is the general formula (ch20)n for, why does it not apply here? Thanks!

The general formula applies for ribose.
But the question talks about the nucleotide pairing with adenine in DNA replication, so wanted deoxyribose.
Deoxyribose is ribose with 1 less O.
So instead of 5 carbon and 5 oxygen, giving ribose a ratio of 1: 1, deoxyribose is 5 carbon and 4 oxygen, having ratio 5:4.

You need the know the structures. Similar to how you need to know the structures of alpha and beta glucose.
But once you know ribose, deoxyribose is the exact same except instead of OH on 2’, there is just H.
(edited 2 months ago)
Reply 5
Original post by BankaiGintoki
The general formula applies for ribose.
But the question talks about the nucleotide pairing with adenine in DNA replication, so wanted deoxyribose.
Deoxyribose is ribose with 1 less O.
So instead of 5 carbon and 5 oxygen, giving ribose a ratio of 1: 1, deoxyribose is 5 carbon and 4 oxygen, having ratio 5:4.
You need the know the structures. Similar to how you need to know the structures of alpha and beta glucose.
But once you know ribose, deoxyribose is the exact same except instead of OH on 2’, there is just H.

Ohhhhh I can’t believe I didn’t get that, thank you this makes a lot more sense!

Quick Reply

Latest