Lecture 31

Question 1

Polycistronic

Answer 1

Bacterial mRNA

1 mRNA makes multiple proteins

Question 2

Beta-galactosidase

Answer 2

Encoded by Lac Z

Breaks 1-4 glycosidic link in the lactose disaccharide into galactose and glucose

Question 3

Permease

Answer 3

Encoded by Lac Y

Helps lactose move through the cell membrane

Question 4

Transacetylase

Answer 4

Encoded by Lac A
Unknown function
May help in detoxification of beta-galactosides

Question 5

Lac repressor

Answer 5

Encoded by Lac I
Binds to Lac O to inhibit mRNA transcription when glucose is present
constitutive, always aroung

Question 6

Why lac operon

Answer 6

Bac only produce the proteins they need

They live in competitive environment

Question 7

Negative regulation of Lac operon

Answer 7

Glucose is present and LacI makes the repressor which binds to LacO
Physically blocks RNA pol initiating tc
RNA pol cannot move along the DNA
Lac operon turned off

Question 8

Induction of the operon

Answer 8

When lactose is present:
Allolactose, isomer of lactose, bind to the repressor
Repressor undergoes a conformational change and dissociates from the operator
RNA pol is the free to initiate tc and makes polycistronic mRNA
Not sufficient for effective tc

Question 9

Positive regulation: activator

Answer 9

When glucose runs out cAMP is produced by adenylyl cyclase
Hunger signal: allows the expression of genes that break down other sugars including lactose
cAMP binds to and activates CAP = catabolite gene activator protein = CRP = cAMP regulatory protein
Active cAMP-CAP binds lacP to activate tc in the presence of lactose
Make more mRNA

Question 10

When both glucose and lactose present

Answer 10

No cAMP
Allolactose binds to repressor
Little mRNA
Little or no protein

Question 11

Mutations:
Lac Z-/Y-/A-
LacP-
LacIs

Answer 11

No functional protein
No functional promotor
Super-repressor, will not dissociate from operator

Cannot metabolize lactose

Question 12

Mutations:
LacI-
LacOc

Answer 12

No functional repressor
No functional operator

Constitutive expression of genes

Question 13

Gene regulation in Euk

Answer 13

DNA: transcriptional control
mRNA: mRNA processing, mRNA transport, mRNA stability
Protein: translation (cleavage, covalent modification)

Question 14

Control of gene transcription in Euk

Answer 14

Cis regulatory sequence: like enhancer sequence

Transcription factor complexes = trans acting factor: nuclear proteins bind to promoter or enhancer

Epigenetics: modify chromatin conformation: gene methylation, histone acetylation

Small nuclear RNAs: miRNA, siRNA: stay in nucleolus not translated
SiRNA is human made

Question 15

Cis regulatory elements 3

Answer 15

Basal promoter sequence: binds general tc factor associated with RNA pol

Proximal control regions: bind tc factor proteins, near promoter

Enhancer sequence: far away from promoter

Question 16

Cis factors in Euk promoters 3

Answer 16

TATA: 25bp upstream of start codon, also called hogness box
CAAT box: 80-80bp upstream
GC box: GGGCGG

Question 17

Enhancer binding proteins

Answer 17

Bind enhancer and bend DNA so that EBP can interact with the transcription factors and enhance tc by RNA pol II

High levels of tc = upregulation

Question 18

3 domains of trans elements = transcription factors

Answer 18

DNA binding domain
Dimerization domain
Activation/repression domain: binds to EBP

Question 19

Different genes can possess the same response element. Why?

Answer 19

Provides a mechanism to coordinate gene regulation
Allow multiple genes to be regulated together
Allow different genes to be turned on and off simultaneously
-stage specific expression
-tissue specific expression
-response to external stimuli: hypoxia, hormonal, stress and heat