RNA and protein synthesis

Question 1

Describe messenger RNA

Answer 1

Made during transcription
Carries the genetic code from DNA to ribosomes
Single stranded polynucleotide strand
Contains groups of 3 adjacent bases (codons/triplets)

Question 2

Describe transfer RNA

Answer 2

Involved in transcription
Carriers amino acids used to make proteins to ribosomes
Hydrogen bonds hold the molecule in place
Single polynucleotide strand folded into a clover strand
Contain an amino acid binding site
tRNA molecules have a specific sequence of 3 bases at one end (anticodon)

Question 3

What is transcription?

Answer 3

1st stage of protein synthesis where an mRNA copy of a gene is made from DNA

Question 4

Explain the process of transcription

Answer 4

1. RNA polymerase attaches to the DNA double helix at the beginning of a gene.
2. The hydrogen bonds between the 2 DNA strands in the gene are broken by DNA helicase attached to RNA polymerase. This separates the strands and the DNA molecule uncoils exposing bases.
3. On strand is used as a template to make a mRNA copy.
4. RNA polymerase links up free RNA nucleotides alongside exposed bases. Complementary base pairing occurs between the mRNA strands and the DNA template strand.
5. Once the RNA nucleotides are paired with the specific bases they are joined by RNA polymerase to form a mRNA molecules.
6. RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand
7. Hydrogen binds reform once the RNA polymerase has passed by and strands coil back into a double helix structure.
8. When RNA polymerase reaches a particular sequence of DNA (stop signal), it stops making mRNA and detaches from DNA.
9. mRNA moves out of nucleus and attaches to ribosome

Question 5

What does pre-mRNA contain?

Answer 5

Introns and exons

Question 6

What happens during splicing (eukaryotes)?

Answer 6

Introns are removed and exons join together to make mRNA. It occurs in the nucleus.

Question 7

What doesn’t splicing occur in prokaryotes?

Answer 7

mRNA is produced from DNA. No splicing needs to occur as there are no introns in prokaryotic DNA

Question 8

What is translation?

Answer 8

2nd stage of protein synthesis where amino acids join together to form a polypeptide chain

Question 9

Explain the process of translation

Answer 9

1. mRNA attaches to a ribosome. tRNA molecules carry amino acids to it. (ATP provides the energy for the bond between the amino acid and tRNA)
2. A tRNA molecules with an anticodon that is complementary to the 1st codon of the mRNA attaches itself
3. A 2nd tRNA molecules attaches itself to next codon on mRNA
4. 2 amino acids attached to tRNA are joined by a peptide bind. The 1st tRNA molecules moves away leaving it amino acid
5. The process continues to produce a polypeptide chain until there is a stop signal on mRNA
6. Polypeptide chain moves away from ribosomes