Types Of RNA And Protein Synthesis

Question 1

Messenger RNA - mRNA?

Answer 1

• short, single-stranded molecules
• found in cytoplasm and nucleus
• made during transcription - copied from DNA and is therefore complementary to the DNA sequence

Question 2

Transfer RNA - tRNA?

Answer 2

• found in cytoplasm
• amino acids attach to molecules
• sequence of three bases called an anticodon. Complementary to codons on the mRNA molecule.

Question 3

Pre-mRNA?

Answer 3

• In eukaryotes, after transcription, pre-mRNA is made
• mRNA that still contains introns
• Introns spliced out - leaving only exons (coding regions)
• In prokaryotes, transcription directly creates mRNA - don’t contain introns in their DNA

Question 4

Transcription?

Answer 4

• Complementary mRNA or copy of one gene on the DNA is created in the nucleus.
• mRNA much shorter than DNA so is able to carry genetic code to ribosome in cytoplasm - enable protein making

Question 5

Steps of transcription?

Answer 5

1. DNA helix unwinds to expose the bases to act as a template
2. Only one chain of the DNA acts as a template
3. Unwinding and unzipping catalysed by DNA helicase
4. DNA helicase breaks hydrogen bonds between bases
5. Free mRNA molecules in nucleus align opposite exposed complementary DNA bases
6. RNA polymerase joins together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied.
   - Once copied, mRNA is modified and leaves the nucleus through the nuclear envelope pores.

Question 6

Translation?

Answer 6

• polypeptide chain is created using both the mRNA base sequence and the tRNA

Question 7

Steps of translation?

Answer 7

1. Once modified mRNA has left the nucleus it attaches to ribosome in the cytoplasm
2. Ribosome attaches to start codon
3. tRNA molecule with complementary anticodon to start codon aligns opposite the mRNA, held in place by ribosome
4. Ribosome moves along one codon on mRNA molecule to enable another complementary tRNA to attach to next codon on the mRNA
5. Two amino acids delivered by tRNA molecules are joined by peptide bond. Catalysed by an enzyme and requires ATP.
6. Continues until ribosome reaches stop codon at the end of mRNA molecule. Doesn’t code for amino acid so ribosome detaches and translation ends.
   - polypeptide chain now created and will enter the Golgi body for folding and modification

Question 8

Protein Synthesis?

Answer 8

• Proteins created on ribosomes
• Two main stages:
  1. Transcription - one gene on DNA is copied into mRNA
  2. Translation - mRNA joins with a ribosome and corresponding tRNA molecules brings specific amino acid that codon codes for.