BIOSCI 107: Cell Structure and Function - Gene Expression

Which enzyme initiates transcription?

RNA polymerase - starts at promoter, ends at terminator (= polyadenylation signal; AAUAAA)

Which DNA strand is 5' to 3'?

Nontemplate. Template is 3' to 5'.

TATA box is found in what region of the DNA?

Promoter region

RNA nucleotides are added to which end of the mRNA strand?

3'

Which bonds form between 3'OH and 5' phosphate of incoming nucleotide?

Phosphodiester bonds

Which bonds form between the template strand nucleotides and the incoming RNA nucleotides?

Hydrogen bonds

Introns vs exons?

Introns are removed via splicing so are not in the final mRNA, whereas exons (inc UTRs) remain and are expressed.

What is added onto mRNA during capping?

A modified guanine nucleotide - at the 5' end of the mRNA

What is added onto mRNA during tailing?

50-250 adenine nucleotides - added to 3' end

What is the purpose of capping and tailing?

Facilitate export, confer stability, facilitate ribsome binding once in cytoplasm

Where does splicing occur?

At the spliceosome within the nucleus

What bonds form between codons and anticodons during translation?

Hydrogen bonds

Which part of the ribosome holds the tRNA 'next in line'?

The A site

Which part of the ribosome does the polypeptide chain grow out of?

The P site

Which part of the ribosome will the tRNA exit?

The E site

The 3 steps of translation?

1. Initiation - already bound tRNA carrying Met binds mRNA. Complete when large subunit is bound. GTP needed.

2. Elongation - processing of all tRNAs

3. Termination - stop codon bound by release factor which promotes hydrolysis, releasing polypeptide

N terminus is what end of the RNA transcript?

5'. C terminus is 3' end.

How does a ribosome know if the protein needs to enter the ER or not (i.e. if it serves a cytosolic function or other function)

5' N terminus contains a SRP (signal recognition particle) which binds to a receptor on the ER.

What kind of modifications to proteins occur (either in the Golgi or the cytosol)?

- Addition of functional group so protein can interact with certain molecules

- Allow protein to carry out an activity e.g. by phosphorylation