4A - DNA, RNA and Protein Synthesis

Question 1

How do eukaryotic cells store DNA?

Answer 1

• DNA molecule is wound up so it fits inside nucleus
• DNA molecule is wound around histones (proteins)
• histone proteins help to support DNA
• DNA and protein is tightly coiled up to make chromosome compact

Question 2

What other organelles in eukaryotic cells have their own DNA?

Answer 2

• mitochondria

- chloroplasts

Question 3

What is the difference between the structure of DNA molecules in eukaryotes and prokaryotes?

Answer 3

• eukaryotes have linear molecules, longer

- prokaryotes have shorter and circular molecules

Question 4

How do prokaryotes cells store DNA?

Answer 4

• DNA isn’t wound around histones

- condenses to fit in the cell by supercoiling

Question 5

What is a cell’s genome and a cell’s proteome?

Answer 5

• genome is the complete set of genes in a cell

- proteome is the full range of proteins that the cell is able to produce

Question 6

What is Messenger RNA (mRNA) and how is it made?

Answer 6

• carries genetic code from DNA to ribosomes
• single polynucleotide strand
• made during transcription

Question 7

What is the first stage of transcription?

Answer 7

• RNA polymerase attaches to DNA double helix at beginning of gene
• H bonds break, strands separate and DNA uncoils
• one strand is used as a template to make mRNA copy

Question 8

What is the second stage of transcription?

Answer 8

• RNA polymerase lines up free nucleotides alongside exposed bases
• complementary bases pair up and are joined by RNA polymerase, forming mRNA molecule

Question 9

What happens in the third stage of transcription?

Answer 9

• RNA polymerase moves along DNA, separating strands and assembling mRNA strand
• H bonds between uncoiled strands of DNA re-form, strands coil back into double helix

Question 10

What happens in the fourth and final stage of transcription?

Answer 10

• when the enzyme reaches a stop signal, it stops making mRNA and detaches
• mRNA moves out of nucleus through a nuclear pore and attaches to a ribosome, where translation takes place

Question 11

What is Transfer RNA?

Answer 11

• carries amino acids used to make proteins to ribosomes

- involved in translation

Question 12

What happens during the first stage of translation?

Answer 12

• mRNA attaches itself to a ribosome and tRNA carries amino acids into it
• ATP is needed for the bond to form between amino acid and tRNA

Question 13

What happens during the second stage of translation?

Answer 13

• tRNA, with an anticodon, attaches itself to mRNA by specific base pairing

Question 14

What happens during the third stage of translation?

Answer 14

• a second tRNA molecule attaches itself to the next codon on the mRNA in the same way as the first

Question 15

What happens during the fourth stage of translation?

Answer 15

• two amino acids attached to tRNA are joined by peptide bond
• first molecule moves away, leaving amino acid behind

Question 16

What happens during the fifth stage of translation?

Answer 16

• third tRNA binds to next codon
• its amino acid binds to the first two and second tRNA moves away
• process continues until a stop signal is reached, creating a polypeptide chain

Question 17

The genetic code is ‘degenerate’. What is meant by ‘degenerate’?

Answer 17

• more possible combinations of triplets than there are amino acids
• some amino acids coded for by more than one base triplet.

Question 18

What is meant by ‘universal’?

Answer 18

• same specific base triplets code for the same amino acids in all living things.