#6: Controlling Gene Expression

Question 1

Controlling Gene Expression (Importance)

Answer 1

Organisms must be able to respond the their environment

If not regulated - waste of time, resources, and energy

Question 2

1. Transcriptional

Answer 2

regulates the transcription of a gene

Question 3

Examples of Transcriptional

Answer 3

• access of promoters provided by loosening of DNA molecule from histones
• activator and repressor protein binds to promoter and enhance/decrease rate of transcription
• methyl groups added to “C” bases, so RNA polymerase cannot bind and transcribe - silence genes

Question 4

2. Post-transcriptional

Answer 4

regulates the modification of mRNA strand

Question 5

Examples of Post-transcriptional

Answer 5

• alternative splicing occurs -different combos of interns removed and exons spliced together
• masking protein bind to mRNA and inhibit further processing
• rate of degradation of mRNA depends on cell need

Question 6

3. Translational

Answer 6

regulates the translation of mRNA

Question 7

Examples of Translational

Answer 7

• variation of lengths of poly-A tail related to rate of translation

Question 8

4. Post-translational

Answer 8

regulates the ability of a pr- to function

Question 9

Examples of Post-translational

Answer 9

• processing occurs -polypeptide chemical modification to render active protein
• present of hormones may lengthen/shorten length of time protein is functional
• Ubiquitin-tagged protein degraded

Question 10

Operons

Answer 10

used by prokaryotes to regulate gene expression at the transcriptional level

Question 11

Promoter (component of operon)

Answer 11

binding site for RNA polymerase

Question 12

Operator (component of operon)

Answer 12

will regulate whether or not RNA polymerase can pass through and transcribe the gene

Question 13

Gene(s) (component of operon)

Answer 13

sequence of DNA that is transcribed to produce specific pr-

Question 14

Inducible gene regulation

Answer 14

the genes are normally NOT expressed

the expression of the genes are INDUCED by the presence of another molecule

Question 15

Repressible gene regulation

Answer 15

the genes ARE usually expressed

the expression of the genes are REPRESSED by the presence of another molecule

Question 16

lac Operon

Answer 16

used by prokaryotes to control the production of b-galactosidase

Question 17

b-galactosidase

Answer 17

enzyme responsible for breaking down lactose

Question 18

Lactose

Answer 18

disaccharide consisting of glucose and galactose

found in milk products

the energy released from the breakdown of lactose can be used for growth in prokaryotes

Question 19

When lactose is absent…

Answer 19

lacI pr- binds to the operator and inhibits the transcription of the genes

Question 20

When lactose is present…

Answer 20

binds to the lacI pr- and changes its shape

after changing shape, the lacI pr- is no longer capable of binding to the operator and transcription occurs

Question 21

lac operon is an example of…

Answer 21

inducible gene expression

genes are normally not expressed and the presence of lactose induces their expression

Question 22

trp Operon

Answer 22

used by prokaryotes to control the production of tryptophan (an amino acid)

Question 23

tryptophan

Answer 23

prokaryotes contain enzymes that are used to produce tryptophan from precursor molecules

the trp operon controls the expression of these enzymes

Question 24

When tryptophan is absent…

Answer 24

trp repressor pr- (trpR) is unable to bind to the operator

as a result, the genes needed for the production of tryptophan are transcribed

Question 25

When tryptophan is present…

Answer 25

will bind to trpR

this changes the shape of trpR and trpR is now able to bind to the operator

as a result, the transcription of the genes necessary for tryptophan production are inhibited

Question 26

trp operon is an example of…

Answer 26

repressible gene expression

genes are normally expressed and the presence of tryptophan represses their expression