Molec Gene

Which of these is incorrect

• Chromatin is more compact in Eukaryotes

• Cotranscriptional Translation is possible in Eukayotes

• Pre-mRNA is modified only in Eukaryotes

• Gene regulation is simpler in Prokaryotes

Answer explanation

It is not possible, as transcription occurs in the nucleus and a Ribosome is required for Translation

What is the key function of the Prok RNA polymerase Sigma Factor

• Double checks the correct promotor has be identified

• Detects and binds Polymerase to a promotor

• Catalytic subunit for RNA nucleotides

• Structural subunit that forms a homodimer

Answer explanation

Structural = Alpha Subunit

Correct promotor ID = Omega subunit

Catalytic = Beta’ subunit

Sigma Factor 70 binds which type of Promotor

• -10 and -35 sites

• -12 and -24 sites

• Flagellate synthesis and Chemotaxis genes

• Starvation/stationary genes

Answer explanation

-12 and -24 sites are Sigma 54

Flagellar are Sigma 28

Starvation is Sigma 38

Which type of Euk RNA Polymerase transcribes mRNA genes

• Poly II

• Poly I

• Poly III

• Poly IV

Answer explanation

Poly I does rRNA

Poly III does tRNA

Prok Sigma Factor is Homologous to which Euk protein

• TFIIB

• TFIID

• TFIIK

• TATA binding Protein (TBP)

Answer explanation

Sigma factor function is matched by TBP, but it’s actually a homolog to TFIIB, which stabilises TBP to Promotor and recruits TFIIF.

TFIID includes subunits TBP and TAFs and coactivates transcription through TAF interactions.

TFIIK is a kinase attached to Helicase TFIIH, it phosses C-term doman of RNApoly to regulate it.

What is the definition of a Holoenzyme

• An enzyme that doesn’t complete all reactions due to allosteric

• An enzyme without all its cofactors/subunits

• An enzyme with all its cofactors/subunits

• An enzyme that is fully activated to complete all reactions due to allosteric

What is essential for RNA poly to work

• GTP

• Two Mg2+ ions

• One Mg2+ ion

• UTP

What is an important structure in RNA poly that splits DNA:mRNA complex

• Bridge Helix

• Rudder + Lip and Fork

• Trigger Loop

• RNAPoly Wall

Answer explanation

Bridge Helix unwinds DNA strand and allows RNA NTPs to enter

Trigger Loop provides a proton for catalytic reaction of adding dNTP to mRNA

RNApoly wall bends double helix to a right angle so it can be in correct strctural conformation for Transcription

With Euk transcription, which Transcription Factor binds Promotor BRE

• TFIID

• TFIIB

• TFIIF

• TBP

Answer explanation

BRE is the only Promotor that is recognised by TFIIB. Most others are by TATA-binding Protein TBP

With Prok RNA polymerase, which of the following helps orientate the RNAPoly

• Upstream elements of the gene bind the C-Terminal Domain

• Sigma Factor binds multiple consensus sequences at the same time.

• The Sigma Finger binds the protein complex

• TFIIK phosphorylates the C-terminal Domain when in correct orientation

Answer explanation

Sigma 70 region 4.2 binds -35 (TTGACA) whilst region 2.4 binds -10 (Pribnow [AT heavy]). This results in the sigma only orientated one way.