Topic 13- Gene Expression

Question 1

Describe the Central Dogma of prokaryotes vs eukaryotes.

Answer 1

Prokaryotes- everything happens in the cytoplasm.
DNA gets transcribed into RNA which gets translated into Protein.

Eukaryotes- Transcription happens in the nucleus, then mRNA processing happens and translation happens in the cytoplasm.

Question 2

Describe the steps of Transcription.

Answer 2

1. Initiation- Puts everything in the right place. Transcription factor binds to the promoter which is a sequence of DNA that proteins can bind to. The RNA polymerase then binds and get pointed in the right direction to start making RNA.
2. Elongation- when the RNA polymerase makes the mRNA.
3. Termination- End

Question 3

Describe mRNA Processing

Answer 3

1. Caps mRNA
2. Tails mRNA
3. mRNA splicing by spliceosome- stitching the exons together and cutting out the introns

Question 4

What is mRNA and it’s structure.

Answer 4

Messenger RNA that gets translated by ribosomes.

Starts with cap and ends with a tail that identifies it as mRNA and prevents degradation.

Untranslated regions which won’t be coded.

Exons parts of transcript not in the final RNA sequence

Introns parts of transcript not in final sequence.

Question 5

What are the start Codons and end Codon

Answer 5

AUG- Start

UAG
UAA - End
UGA

Question 6

Describe the steps of Translation.

Answer 6

1. Initiation- Small subunit of ribosome attaches to mRNA at 5’ end and finds the start codon. The large subunit then slides on top of the small subunit with a tRNA in the P site.
2. Elongation- tRNA with matching anticodon binds to correspond mRNA in the A site of the tRNA. Spends GTP to break the bond in the polypeptide bond in the E site to put it on the new tRNA. Then it spends GTP to move each tRNA over one. The old one reaches the E site and gets ejected
3. Termination- When a stop codon reaches the A site a release factor binds with it in the A site causing the tRNA to be released and drop the polypeptide chain. More GTP is then used to break down the ribosomes.

Question 7

Describe the 2 categories of mutations and the types of mutations in each category.

Answer 7

Single nucleotide pair substitutions- when you switch one nucleotide for another
-Silent mutation- Switch occurs but the same amino acid is made
- Missing mutation- Changes one amino acid into another.
- Nonsense mutation- Turns amino acid codon into a stop codon.

Nucleotide pair insertion- adding or deleting a nucleotide
-Frameshift- Every codon after the added or deleted codon is incorrect.