2.1.1 How DNA codes for proteins

Question 1

What is a gene?

Answer 1

A gene is a length of DNA that codes for one or more polypeptides. Including enzymes.

Question 2

What is a polypeptide?

Answer 2

A polypeptide is a polymer consisting of a chain of monomers (amino acids), joined by peptide bonds.

Question 3

What is a genome?

Answer 3

A genome of an organism is the entire DNA sequence of that organism.

Question 4

What is a protein?

Answer 4

A protien is a large polypeptide, usually more than 100 amino acids. They can consist of one or more polypeptide chains.

Question 5

What is the genetic code?

Answer 5

The genetic code is the sequence of nucleotide bases on a gene, this provides instructions for the construction of a polypeptide or protein.

Question 6

What are the characteristics of the genetic code?

Answer 6

1. It is a triplet code, three nucleotide bases code for a specific amino acid.
2. It is a degenerate code. This means that all bar one amino acid have more than one code.
3. Some codes don’t correspond to an amino acid, however indicate “stop” - which is then the end of the polypeptide chain.
4. It is widespread but not universal. Therefore many organisms share the same triplet code for the same amino acid, this has proved useful in genetic engineering.

Question 7

What is transcription?

Answer 7

Transcription is the creation of a single-stranded mRNA copy of the DNA coding strand.

Question 8

Outline the events that take place during transcription?

Answer 8

1. The gene to br transcribed unwinds and unzips. To do this the length of the DNA that makes up the gene is dipped into the nucleolus. The hydrogen bonds between the base complementary bases break.
2. Activated RNA nucleotides (in the nuclelous), bind with their exposed complementary bases, via hydrogen bonds. T binds to A, A binds to U, G binds with C, C binds with G. This is catalysed by the enzyme RNA polymerase.
3. The two extra phosphoryll groups are released and this provides energy to bond adjacent nucleotides.
4. The mRNA produced is complementary to the nucleotide base sequence on the template strand of DNA and therefore is a copy.
5. The mRNA is released from the DNA and passes out of the nucleus, through a pore in the nuclear envelope, to a ribosome.