8-DNA, Genes & Proteins Synthesis

Question 1

Gene

Answer 1

A base sequence of DNA that codes for amino acid sequence of a polypeptide or functional RNA (ribosomal RNA/tRNA).

Question 2

Degenerate Code

Answer 2

Most amino acids are coded for by more than one triplet.

Question 3

Non-Overlapping Code

Answer 3

Sequence is read on,y once so 123456 is read as 123 456. Not as 123 234 345 456.

Question 4

Universal Code

Answer 4

Each triplet codes for the same amino acid in all organisms.

Question 5

Chromosomes Structure

Answer 5

2 chromatids (threads) joined together at the centromere (a single point).
DNA is held in chromosomes by histones.
DNA is coiled and folded.

Question 6

Homologous Pairs of Chromosomes

Answer 6

2 chromosomes that carry the same genes but not necessarily the same alleles of genes.

Question 7

Allele

Answer 7

An alternative form of a gene (blue or green allele for the eye colour gene).

Question 8

Codon

Answer 8

Sequence of 3 bases on mRNA that codes for a single amino acid.

Question 9

Genome

Answer 9

Complete set of genes in a cell.

Question 10

Proteome

Answer 10

Full range of proteins produced by the genome.

Question 11

tRNA Structure

Answer 11

Roughly 80 nucleotides
Single-stranded chain folded into a clover-leaf shape
At far end of tRNA molecule is anticodon loop with an anticodon specific to one amino acid.

Question 12

Transcription

Answer 12

1) DNA helical acts on a certain area of DNA and separates strands.
2) Nucleotide bases on template strand pair with complementary nucleotides from pool present in nucleus and RNA polymerase moves along strand and binds them into a pre-mRNA strand.
3) As RNA polymerase makes pre-mRNA strand DNA strands rejoin.
4) When RNA polymerase reaches a ‘stop’ codon it detaches from molecule and pre-mRNA is formed.

Question 13

Splicing of pre-mRNA

Answer 13

Introns in strand are removed so functional Exxon’s join together to form mRNA strand.

Question 14

Intron

Answer 14

Part of a gene of DNA which doesn’t code for proteins.

Question 15

Exon

Answer 15

Part of a gene of DNA which codes for proteins.

Question 16

Translation (polypeptide synthesis)

Answer 16

1) Ribosome attaches to starting codon (AUG) at one end of mRNA molecule.
2) tRNA molecule with complementary anticodon (UAC) moves to ribosome and pairs up with codon on mRNA.
3) Ribosome moves along mRNA, bringing together 2 tRNA molecules at a time.
4) The 2 amino acids are joined by a peptide bond using an enzyme and ATP hydrolysed to provide energy.
5) Process continues until polypeptide chain is built up.
6) Polypeptide keeps synthesising until ribosome reaches a ‘stop’ codon where it, mRNA and last tRNA molecule all separate and the polypeptide chain is complete.