OCR F215 Biology notes
Control, Genome and Environment
Cellular Control & Variation
Cellular Control
(a) state that genes code for polypeptides, including enzymes;
(b) explain the meaning of the term genetic code;
The sequence of the bases on a gene is a code with instructions for the construction of proteins. It has a number of characteristics:
It is a triplet code- three bases code of an amino acid
It is a degenerate code- All amino acids bar one have more than one code
Some codes don’t code for amino acids but are ‘stop’ codons- they indicate the end of the polypeptide chain
It is widespread but not universal- Codons generally always code for the same amino acid in every organism, but this is not always the case.
(c) describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid sequence in a polypeptide;
1. Free RNA nucleotides are activated, two extra phosphoryl groups are added to make ATP, GTP,
CTP and UTP.
2. The gene to be transcribed unwinds and unzips. To do this the length of DNA that makes up the gene dips into the nucleolus & the hydrogen bonds between the nucleotide bases break.
3. Activated RNA nucleotides binds, using Hydrogen Bonds, with their complementary exposed bases on the template strand. This is catalysed by RNA polymerase
4. The two extra phosphoryl are released, releasing energy for bonding two adjacent nucleotides
The mRNA produced is complementary to the nucleotide base sequence on the template strand of DNA and therefore is a copy of the base sequence on the coding strand of DNA
5. The mRNA is released from the DNA and passes out of the nucleus through a pore in the nuclear envelope to a ribosome
(d) describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes;
1. A molecule of mRNA binds to a ribosome. Two codons are attached to the small subunit of the ribosome and
Cellular Control & Variation
Cellular Control
(a) state that genes code for polypeptides, including enzymes;
(b) explain the meaning of the term genetic code;
The sequence of the bases on a gene is a code with instructions for the construction of proteins. It has a number of characteristics:
It is a triplet code- three bases code of an amino acid
It is a degenerate code- All amino acids bar one have more than one code
Some codes don’t code for amino acids but are ‘stop’ codons- they indicate the end of the polypeptide chain
It is widespread but not universal- Codons generally always code for the same amino acid in every organism, but this is not always the case.
(c) describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid sequence in a polypeptide;
1. Free RNA nucleotides are activated, two extra phosphoryl groups are added to make ATP, GTP,
CTP and UTP.
2. The gene to be transcribed unwinds and unzips. To do this the length of DNA that makes up the gene dips into the nucleolus & the hydrogen bonds between the nucleotide bases break.
3. Activated RNA nucleotides binds, using Hydrogen Bonds, with their complementary exposed bases on the template strand. This is catalysed by RNA polymerase
4. The two extra phosphoryl are released, releasing energy for bonding two adjacent nucleotides
The mRNA produced is complementary to the nucleotide base sequence on the template strand of DNA and therefore is a copy of the base sequence on the coding strand of DNA
5. The mRNA is released from the DNA and passes out of the nucleus through a pore in the nuclear envelope to a ribosome
(d) describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes;
1. A molecule of mRNA binds to a ribosome. Two codons are attached to the small subunit of the ribosome and