Topic 4A: DNA, RNA and Protein Synthesis

Question 1

How is DNA stored in Eukaryotic cells?

Answer 1

DNA is wound around histones, which both coil up tightly to make a compact chromosome.

Question 2

How is DNA stored in prokaryotic cells?

Answer 2

DNA condensed until it is supercoiled and able to fit in the cell.

Question 3

What is a gene?

Answer 3

A short sequence of DNA bases which codes for a polypeptide of functional RNA.

Question 4

What is a triplet?

Answer 4

A sequence of 3 DNA bases that codes for a specific amino acid.

Question 5

What is functional RNA?

Answer 5

A molecule which performs a specific task during protein synthesis.

Question 6

What is a genome?

Answer 6

The complete set of genes in a cell

Question 7

What is a proteome?

Answer 7

The complete range of proteins which a cell is able to produce.

Question 8

What is an intron?

Answer 8

A section of DNA which doesn’t code for an amino acid.

Question 9

What is an exon?

Answer 9

The part of the gene which codes for amino acids.

Question 10

What is an allele?

Answer 10

A different form of the same gene.

Question 11

What is a homologous pair?

Answer 11

Pairs of matching chromosomes which contain the same genes.

Question 12

What is a locus?

Answer 12

A specific position on a chromosome where alleles of the same gene can be found.

Question 13

What is protein synthesis and what are the processes involved?

Answer 13

The production of proteins from a cell’s DNA.

1) Transcription - where DNA is copied into a mRNA molecule.
2) Translation - where mRNA joins with a ribosome to synthesis a protein.

Question 14

What is messenger RNA (mRNA)?

Answer 14

A molecule made during transcription which carries genetic code from the DNA to the ribosomes where it’s used to make a protein during translation.

Question 15

What is the structure of mRNA?

Answer 15

A single polynucleotide strand.

Question 16

What is a codon?

Answer 16

A group of 3 adjacent bases found in mRNA.

Question 17

What is transfer RNA (tRNA)?

Answer 17

A molecule which carries amino acids to the ribosomes where they are used to make proteins.

Question 18

What is the structure of tRNA?

Answer 18

A single polynucleotide strand which is folded into a clover shape by hydrogen bonds.

Question 19

What is an anticodon?

Answer 19

A sequence of 3 bases which is found on a tRNA molecule.

Question 20

What is the process of transcription?

Answer 20

1) DNA helicase breaks hydrogen bonds between two DNA strands, causing it to unravel.
2) RNA polymerase attaches to the start of the gene, and moves down the template strand joining RNA nucleotides together with complementary exposed bases.
3) Hydrogen bonds then re-form allowing the strands to cool back into a double helix.
4) When RNA polymerase reaches a stop triplet, it detaches leaving a fully formed complementary mRNA strand.

Question 21

How is mRNA edited?

Answer 21

Splicing occurs to remove introns, allowing exams to join together to form the correct mRNA strand.

Question 22

What is the process of translation?

Answer 22

1) mRNA attaches to a ribosome.
2) A tRNA molecule carrying an amino acid attaches to the mRNA molecule through complementary base pairing between the codon and anticodon.
3) A second tRNA molecule attaches to the next codon in the same way.
4) A peptide bond forms between the two amino acids, before the first tRNA molecule moves away.
5) This process repeats, until it reaches a stop signal, producing a chain of amino acids which then moves away from the ribosome.

Question 23

What is the genetic code?

Answer 23

The sequence of base triplets in mRNA which code for specific amino acids.

Question 24

What are the features of the genetic code?

Answer 24

Non - overlapping:
Base triplets do not share bases.

Degenerate:
Different base triplets can code for the same amino acid.

Universal:
A base triplet can only code for one amino acid.