NOTES: Italics indicates NOT from the mark scheme (often means no
mark schemes relating to the spec point). These are taken instead
from the CIE A Level textbook, which occasionally includes extra
detail to help my own understanding. All others are directly copied
from CIE 9700 mark schemes.
Mark scheme abbreviations: I = ignore, A = accept, R = reject. A
semi-colon “;” separates marking points, which are sometimes
numbered. “AVP” = any valid point. See the start of any mark
scheme for full abbreviations.
6. Nucleic acids and protein synthesis
Helpful tip: remember ‘y’ for pyrimidines. So cytosine, thymine are
pyrimidines. Remember thymine and uracil have very similar
structures (both pair with adenine). Uracil is also a pyrimidine. So
pyrimidines: C, T, U. (Purines: A, G)
Pyrimidines are single rings, purines are two/double ringed.
Nucleotide structure : nitrogenous base, pentose sugar
(deoxyribose or ribose), phosphate group
ATP structure: adenine, ribose (adenosine), three phosphates
mRNA structure: single polynucleotide strand. (i.e. many
nucleotides joined together in one strand)
structure of a DNA molecule as a double helix:
• the importance of complementary base pairing between the 5′ to 3′
strand and the 3′ to 5′ strand (antiparallel strands)
• differences in hydrogen bonding between C–G and A–T base pairs
C≡G (3), A=T (2)
• linking of nucleotides by phosphodiester bonds
Semi-conservative replication:
1 DNA (double helix / molecule) unwinds ; by DNA helicase
2 hydrogen bonds break between, base pairs / bases / strands ;
3 both strands used as templates ;
mark schemes relating to the spec point). These are taken instead
from the CIE A Level textbook, which occasionally includes extra
detail to help my own understanding. All others are directly copied
from CIE 9700 mark schemes.
Mark scheme abbreviations: I = ignore, A = accept, R = reject. A
semi-colon “;” separates marking points, which are sometimes
numbered. “AVP” = any valid point. See the start of any mark
scheme for full abbreviations.
6. Nucleic acids and protein synthesis
Helpful tip: remember ‘y’ for pyrimidines. So cytosine, thymine are
pyrimidines. Remember thymine and uracil have very similar
structures (both pair with adenine). Uracil is also a pyrimidine. So
pyrimidines: C, T, U. (Purines: A, G)
Pyrimidines are single rings, purines are two/double ringed.
Nucleotide structure : nitrogenous base, pentose sugar
(deoxyribose or ribose), phosphate group
ATP structure: adenine, ribose (adenosine), three phosphates
mRNA structure: single polynucleotide strand. (i.e. many
nucleotides joined together in one strand)
structure of a DNA molecule as a double helix:
• the importance of complementary base pairing between the 5′ to 3′
strand and the 3′ to 5′ strand (antiparallel strands)
• differences in hydrogen bonding between C–G and A–T base pairs
C≡G (3), A=T (2)
• linking of nucleotides by phosphodiester bonds
Semi-conservative replication:
1 DNA (double helix / molecule) unwinds ; by DNA helicase
2 hydrogen bonds break between, base pairs / bases / strands ;
3 both strands used as templates ;
