CMB lecture 9

Question 1

Why do cells continually turn genes on and off?

Answer 1

In response to signals from their exgternal and internal environment.

Question 2

How do prokaryotes express different genes in response to changing environmental conditions?

Answer 2

By regulating transcription.

Question 3

Genes in tightly packed chromatin are usually __ _____.

Answer 3

not transcribed.

Question 4

Heterochromatin:

Answer 4

Highly condensed DNA

Question 5

Euchromatin:

Answer 5

less condensed DNA

Question 6

How can DNA be made accessible for transcription?

Answer 6

Acetylation of histone tails, loosens the chromatin structure,

Question 7

Methylation:

Answer 7

Leads to condensation of chromatin and reduced transciption

Question 8

Epigenetic inheritance:

Answer 8

Genetics transmitted by mechanisms not involving nucleotides.

Question 9

Transcription factors:

Answer 9

Proteins that can initiate and regulate transcription in eukaryotic cells.

Question 10

What is the most frequent way that gene expression is controlled in eukaryotes?

Answer 10

Regulating transcript.

Question 11

What is alternative RNA splicing?

Answer 11

Different mRNA molecules are prouced from the same pre-mRNA. Proteins of diff sizes and functions are produced from same pre-mRNA.

Question 12

How do noncoding RNAs control gene expression?

Answer 12

Chromatin packing, translation, mRNA degradation

Question 13

How do prokaryotes control gene expression?

Answer 13

By modifying their metabolism

Question 14

Metabolic control occurs at two levels:

Answer 14

Adjust catalytic activities of enzymes already made, or adjust the production of enzyme molecules, by regulating expression of the encoding enzymes.

Question 15

Abundance of tryptophan:

Answer 15

Inhibits the activity of the first enzyme in the pathway e.g. in feedback inhibition. This is a rapid response.

Question 16

E. coli can adapt to __ as a new food source by __ ___

Answer 16

lactose, by regulating transcription.

Question 17

Lactose is a:

Answer 17

Disaccharide

Question 18

When lactose is ___, only a few molecules of B-galactosidase are present

Answer 18

absent.

Question 19

What does b-galactosidase do?

Answer 19

Catalyses the hydrolysis of lactose into glucose and galactose

Question 20

When lactose is readily available, ____

Answer 20

the number of b-gal increasese a thousand fold.

Question 21

Lag phase:

Answer 21

Bacteria starts to transcribe b-gal mRNA which is translated into b-gal protein.

Question 22

What is the name of the gene which enables the cell to use lactose?

Answer 22

lac operon

Question 23

Name the 3 structural genes of lac operon

Answer 23

lacZ for b-gal, lacY for permease, lacA for transacetylase

Question 24

What is an operon?

Answer 24

A group of genes coding for proteins with related functions. Expression of these genes is under the control of a single promoter and operator.

Question 25

Negative regulation:

Answer 25

A repressor protein binds to the operator to prevent the gene being expressed.

Question 26

Positive regulation:

Answer 26

A transcription factor binds to promoter and enables RNA polymerase to initiate transcription.

Question 27

In negative regulation, the ___ codes for the ____ protein when lactose is absent.

Answer 27

Regulatory gene (lacI) codes for the lac repressor protein. Repressor binds to the operator and blocks the promoter. Transcription does not occur.

Question 28

When lactose is present in negative regulation:

Answer 28

It acts as an inducer, binds to repressor, changing its shape, so it can no longer bind to the operator. Transcription can occur.

Question 29

When glucose and lactose are both present, which one does E. coli prefer to use?

Answer 29

Glucose.

Question 30

When lactose is present and glucose is low:

Answer 30

E. coli will generate enzymes for lactose breakdown for energy.

Question 31

What molecule accumulates when glucose is low?

Answer 31

cyclic AMP, cAMP binds to and activates the cAMP receptor protein (CRP)

Question 32

What is the name of the cAMP receptor protein?

Answer 32

CRP, allosteric protein

Question 33

Positive control: What binds to the promoter to faciliate binding of RNA polymerase?

Answer 33

Active CRP, transcription of lac operon genes occurs.

Question 34

When lactose is present:

Answer 34

repressor is unable to bind to operon.

Question 35

If glucose is present, what happens to the level of cAMP?

Answer 35

Will fall, so cAMP can no longer activate CRP, which will detach from the lac operon. Transcription proceeds at low level.

Question 36

Mutations in the structural genes

Answer 36

May result in the production of a non functional protein.

Question 37

Mutations in the repressor gene or operator or promoter regions:

Answer 37

Abolish transcriptions, or permanently turn on transcription.