RNA and Protein Synthesis

Question 1

What is mRNA?

Answer 1

Made during transcription. It carries the genetic code from DNA to ribosomes, where it’s used to make a protein during translation

Question 2

What is the structure of mRNA?

Answer 2

A single polynucleotide strand. Groups of three adjacent bases are called codons (or base triplets/triplets)

Question 3

What is tRNA?

Answer 3

Involved in translation. Carries the amino acids used to make proteins to the ribosomes

Question 4

What is the structure of tRNA?

Answer 4

A single polynucleotide strand folded into a clover shape. Hydrogen bonds between specific base pairs hold it in shape. It has a specific sequence of three bases at one end called an anticodon. They have an amino acid binding site at the other end

Question 5

Explain transcription

Answer 5

1. RNA polymerase attaches to DNA double helix at beginning of gene
2. H-bonds between two DNA strands are broken by DNA helicase attached to RNA polymerase. This separates the strands, DNA uncoils, exposing some bases
3. One strand is used as template to make mRNA copy
4. RNA polymerase lines up free RNA nucleotides alongside exposed bases on template strand. Complimentary base pairing means free bases are attracted to template strand and mRNA strand is complimentary copy of DNA template strand
5. RNA nucleotides are then joined together by RNA polymerase, forming an mRNA molecule
6. RNA polymerase moves along DNA, separating the strands and assembling the MRNA
7. H-bonds on DNA strand reform and the strands coil back into a double helix
8. When RNA polymerase reaches a stop signal it stops making mRNA and detaches from the DNA
9. mRNA moves out of nucleus through nuclear pore and attaches to ribosome in the cytoplasm

Question 6

What is splicing?

Answer 6

During transcription, introns are removed and exons are joined together, forming mRNA strands

Question 7

Where does splicing take place?

Answer 7

The nucleus

Question 8

Explain translation

Answer 8

1. mRNA attaches to ribosome and tRNA carry amino acids to it. ATP provides energy for this tRNA and amino acids to bond
2. A tRNA (carrying amino acid), with complimentary anticodon to first codon on mRNA, attaches to mRNA by specific base pairing
3. A second tRNA attaches itself to the next codon on mRNA in the same way
4. Two amino acids on tRNA join by peptide bond. First tRNA molecule moves away, leaving amino acid behind
5. Third tRNA molecule binds to next codon mRNA. It’s amino acid joins to the first two and second tRNA moves away
6. Process continues, producing chain of amino acids, until there’s a stop signal
7. Polypeptide chain moves away from ribosome and translation is complete