Micro Exam 3 - Anabolism: RNA

Describe RNA biosynthesis.

1 - nucleotide activation by phosphorylation (necessary for polymerization), 2 - polymerization in 5' to 3' direction (added to end of growing chain)

What is RNA polymerized by?

RNA polymerase (RNAP)

What is the transcriptional start?

promoter

What is the transcriptional stop?

rho-dependent/independent terminators

What is the "RNAP core" complex?

4 proteins: α, α', β, β'

What is the RNAP core responsible for?

catalyzing polymerization of RNA

What is the 5th subunit of the RNAP core and what does it do?

sigma - determines which promoters RNAP binds to and controls specificity

The core + sigma = ?

RNAP holoenzyme

Why can the core not function on its own?

because it cannot see/recognize the sequence where it should start transcription

What is sigma A?

housekeeping sigma

What does sigma A do?

direct transcription of genes that are essential or routine function

How do sigma factors work to begin transcribing?

pull strands apart to allow for reading of template

What are the binding sites for sigma A relative to the first base of the transcript (+1)?

-35 box and -10 box

What is a consensus sequence?

a short sequence of nucleotides which is found several times in the genome and is thought to play the same role in its different locations averaged out

The closer the site is to consensus...

the stronger the transcription initiation

What are the two transcriptional termination methods?

rho-dependent and rho-independent

Describe rho-independent termination.

terminated by a sequence in RNA itself - stable stem loop forms and is followed by polyU tract which knocks off RNAP from DNA template, halting transcription

Describe rho-dependent termination.

1. Rho binds to an exposed rut site on mRNA when a ribosome isn't blocking it.

2. Rho uses ATP to move along the mRNA toward RNA polymerase.

3. Rho catches RNA polymerase, causing transcription to stop and the mRNA to be released.

What is an operon?

a unit made up of linked genes that come from a single transcript and common promoter

In an operon, each gene has...

its own SD, start and stop codon

What cuts out rRNAs and tRNAs encoded in operons?

RNase III