9 Protein synthesis

Question 1

What is an allele?

Answer 1

A different form of a gene

Question 2

non coding dna

Answer 2

Eukaryotic DNA also contains non-coding sections called introns within genes

Question 3

Genome

Answer 3

The complete set of genes in a cell

Question 4

Proteome

Answer 4

The full range of proteins that a cell is able to produce.

Question 5

The proteome of a pancreas cell and liver cell would be different? Explain why

Answer 5

The genes to make some proteins may be switched off so the cell never produces that protein:

Question 6

Summary of Transcription

Answer 6

· The hydrogen bonds between DNA bases are broken (NOT hydrolysed) which separates the two strands of DNA

· One strand of the DNA acts as the template strand upon which pre-mRNA is built.

· Free RNA nucleotides are found in the nucleoplasm. They are attracted to the exposed DNA bases on the DNA template strand and align by complementary base pairing.

· E.g. Uracil with Adenine / Guanine with Cytosine

· RNA polymerase join RNA nucleotides together to make an RNA polynucleotide chain via phosphodiester bonds

· Introns are removed from the pre-mRNA and the exons spliced back together.

Question 7

Splicing of pre-mRNA (Eukaryotes only

Answer 7

· DNA is made up of sections called exons that code for the amino acid sequence of polypeptides

· Sections called introns do not code for amino acid sequences.

· Exons are sections of DNA that are expressed to produce proteins.

· In the pre-mRNA in eukaryotic cells the introns are removed by enzymes before the mRNA moves into the cytoplasm.

· The remaining exons are then joined together. This is known as splicing.

· Following splicing, mRNA molecules leave the nucleus through the nuclear pores.

Question 8

where does transcription occur

Answer 8

cytoplasm

Question 9

where does translocation occur

Answer 9

on ribosomes

Question 10

Summary of Translation

Answer 10

· mRNA attaches to ribosomes.

· tRNA anticodons bind to mRNA codons by complementary base pairing.

· Each tRNA brings a specific amino acid

· 2 tRNA molecules (with their amino acids) are held together at a ribosome at any one time.

· A peptide bond forms between adjacent amino acids. This requires the use of ATP.

· tRNA molecules are released after their amino acids have been joined to the growing polypeptide chain.

· The ribosome moves along the mRNA forming the polypeptide until a stop codon is reached, at which point the ribosome and mRNA dissociate.