Protein Synthesis 2.6-2.8 and 6.10

Question 1

What is a gene?

Answer 1

A sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain

Question 2

What are the three features of the genetic code + explain

Answer 2

1. Universal = same bases used for all organisms
2. Degenerate = several bases code for one amino acid as 20 amino acids but 64 possible triplets
3. Non-overlapping = each triplet is read in sequence, separate to its previous

Question 3

Why does DNA have to be copied into RNA for protein synthesis?

Answer 3

DNA molecules which are found in the nucleus are too large to leave so a section is copied into mRNA during transcription.

Question 4

Describe mRNA

Answer 4

• Made in nucleus during transcription
• Three bases = codon
• Carries genetic info from nucleus to ribosomes

Question 5

Describe tRNA

Answer 5

• Found in cytoplasm
• Amino acid binding site at one end and three bases at other (anticodon)
• Carries amino acids to ribosomes during translation

Question 6

Describe transcription

Answer 6

1) RNA polymerase attached to DNA at a start codon, breaking hydrogen bonds to separate the two strands. One strand is then used as the template to copy mRNA
2) RNA polymerase lines up free RNA bases which undergo complementary base pairing ( if DNA strand is ATC, RNA is UAG) and are joined by RNA polymerase forms an mRNA molecule
3) Moves along DNA and hydrogen bonds re-form between the two strands to form the double helix
4) RNA reaches a stop codon, detaching mRNA from DNA
5) mRNA moves out of nucleus via pores and attached to ribosomes

Question 7

Describe translation

Answer 7

1) mRNA attached to a rib dome and tRNA molecules carry amino acids to the ribosome
2) tRNA molecule with an anticodon complementary to the start codon on the mRNA attached by complementary base pairing
3) second tRNA molecule attaches in same way and the two amino acids are joined by a peptide bond
4) the first tRNA molecule move away and ribosome move along to the next codon
5) process continues until a stops codon is reached and polypeptide chain moves away from ribosome

Question 8

What is a section of DNA that doesn’t code for an amino acid called?

Answer 8

Intron

Question 9

What is a section of DNA that does code for an amino acid called?

Answer 9

Exon

Question 10

What name is given to a strand of mRNA that contains both introns and exons?

Answer 10

pre-mRNA

Question 11

By what process are introns removed?

Answer 11

Splicing

Question 12

Where and when does splicing take place?

Answer 12

In the nucleus after transcription

Question 13

What is alternative splicing?

Answer 13

When certain exons are removed, as well as the introns, to form different combinations of exons on the mRNA strand
Means that more than one protein can be produced from one gene