Protein Synthesis

Question 1

How is protein synthesis different in prokaryotes to eukaryotes?

Answer 1

• prokaryotes don’t have a nucleus, so transcription occurs in the cytoplasm.
• in prokaryotes, mRNA is produced directly from the DNA, without splicing taking place (there is no need for it as there are no introns in prokaryotic cells). However in eukaryotes, introns and exons are both copied to splicing takes place in the nucleus.

Question 2

What are the similarities between eukaryotes and prokaryotes in protein synthesis?

Answer 2

For both types of cells, it occurs at the ribosomes in the cytoplasm

Question 3

In prokaryotes, why does transcription occur in the cytoplasm?

Answer 3

Because they don’t have a nucleus.

Question 4

Which enzyme does transcription use?

Answer 4

RNA polymerase.

Question 5

Outline the process of transcription.

Answer 5

1. RNA polymerase attaches to the DNA double helix at the beginning of a gene.
2. The hydrogen bonds between the two DNA strands break, separating the strand, and causing the DNA molecule to unwind, and expose bases.
3. One strand is used as a template to make an mRNA template.
4. The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand, and complementary base pairing occurs.

Question 6

Outline transcription.

Answer 6

1. RNA polymerase attaches to DNA a double helix.
2. H bond between 2 DNA molecules in the gene break, separating the strands, and the DNA uncoils, exposing bases.
3. One is a template strand.
4. RNA polymerase line sun free nucleotides, specific complementary pairing occurs.
5. RNA polymerase joins specific bases, forming mRNA.
6. Continues assembling bases.
7. H bonds reform to coil back into double helix.
8. When RNA polymerase reaches stop signal, it stops making mRNA and detaches from the DNA.

Question 7

Outline translation.

Answer 7

1. The mRNA molecule attaches itself to a ribosome and tRNA molecules carry AAs to it.
2. A tRNA molecule (carrying AA) with an anticodon that’s complementary to the first codon on the mRNA, attaches to th mRNA by specific base pairing.
3. A 2nd tRNA molecule attaches itself to the next codon in the same way.
4. The two AAs are then joined by a peptide bond. The first tRNA molecule moves away, leaving its AA behind.
5. Same again with a third tRNA molecule.
6. This continues producing a polypeptide chain until there’s a stop signal in the mRNA molecule.
7. Polypeptide chain moves away.

Question 8

Describe structure of mRNA.

Answer 8

Single polynucleotide chain. Have codons.

Question 9

Structure of tRNA?

Answer 9

Single polynucleotide chain that’s folded into a clover shape. H bonds between specific base pairs hold the molecule in place.