Unit 2: Gene Regulation

Question 1

gene regulation

Answer 1

• various ways in which cells control gene expression

Question 2

what are the characteristics of gene expression (3)

Answer 2

• where (in which cells) are genes turned on
• when (during development or in response to changes in the environment) are they turned on
• how much gene product is made

Question 3

positive regulation

Answer 3

• process where a regulatory molecule (usually a protein) must bind to the DNA at a site near the gene in order for transcription to take place

Question 4

negative regulation

Answer 4

• process where regulatory molecule (usually a protein) must bind to DNA site near the gene to prevent transcription

Question 5

What sequence do eukaryote promoters contain and where are they located? (2)

Answer 5

• 5’-TATAAA-3’

- about 25-35 base pairs upstream from the transcription start site

Question 6

Where are prokaryote promoters located and what are they called? (2)

Answer 6

• about 10 and 35 base pairs upstream of the transcription start site
• -10 and -35 sequence motifs

Question 7

transcriptional activator

Answer 7

• regulatory protein/compound that increases activity of an enzyme

Question 8

What are the 2 binding sites that DNA contains?

Answer 8

• an activator protein binding site and the RNA polymerase complex binding site

Question 9

In positive regulation, what occurs when the activator is successfully recruited to a site near the RNA polymerase promoter?

Answer 9

• RNA polymerase can bind to the promoter

Question 10

In positive regulation, what occurs when the activator is unsuccessfully recruited to a site near the RNA polymerase promoter?

Answer 10

• RNA polymerase cannot bind and transcription does not occur

Question 11

Where can the binding site for the activator be in positive regulation?

Answer 11

• upstream of the promoter, downstream of the promoter, or even overlap the promoter

Question 12

allosteric effect

Answer 12

• change in the activity or affinity of a protein as the result of binding of a molecule to a site other than the active site

Question 13

Why do activators change shape in different situations? (2)

Answer 13

• small molecules can bind to activators to change their shape so that they can bind to DNA
• small molecules can bind to activators to change their shape so they can no longer bind to DNA

Question 14

repressor

Answer 14

• a protein that, when bound with a sequence in DNA, can inhibit transcription

Question 15

In negative regulation, what occurs when there is no repressor bonded to the repressor bonding site?

Answer 15

• this allows RNA polymerase complex to be recruited and transcription takes place

Question 16

In negative regulation, what occurs when there is a repressor bonded to the repressor bonding site?

Answer 16

• the repressor inhibits the recruitment of RNA polymerase and transcription does not occur

Question 17

Where can the binding site for a repressor be located relative to a promoter?

Answer 17

• upstream, downstream, or overlapping with the promoter

Question 18

inducer

Answer 18

• small molecule that elicits gene expression by changing the shape of repressors so they cannot inhibit transcription

Question 19

what is the relationship between a strong promoter, a weak promoter, and a consensus sequence?

Answer 19

• strong promoters are closer to consensus while weak promoters are further from consensus

Question 20

What is transcriptional control?

Answer 20

• controlling the amount of transcription via promoter strength and regulatory proteins

Question 21

What is translational control?

Answer 21

• controlling the amount of translation by altering how fast a mRNA survives in the cell (for example by changing the length of the poly-A tail)

Question 22

What is post-translational control?

Answer 22

• modifying enzymes directly by changing their shape or blocking active sites

Question 23

constitutive gene expression

Answer 23

• when genes are expressed all the time (genes that code for RNA polymerases, ribosomes, tRNA, etc)
• this does not mean that there are high levels of expression

Question 24

Although two different genes are constitutively expressed, how can their level of transcription and translation differ?

Answer 24

• promoter strengths may be different resulting in different amounts expressed
• the RNA made may have different half lives which would results in different amounts of translation

Question 25

environmentally regulated gene expression

Answer 25

• expression of a gene is linked to a condition in the environment (either inside or outside of the cell)
• environmental conditions changes cause the expression of the gene to change as well

Question 26

operon (2)

Answer 26

• set of related coding sequences (that make related proteins) that all share the same promoter and terminator
• single mRNA is made from an operon, and from that single mRNA multiple different proteins are produced

Question 27

polycistronic mRNA

Answer 27

• mRNA molecule that contains more than one ORF and encodes for more than one protein
• typically products of operon transcription

Question 28

basal transcription

Answer 28

• minimal amount of (but not zero) transcription that occurs even when gene expression is turned off

Question 29

How can a cell achieve zero transcription?

Answer 29

• removing or destroying a promoter so that no RNA Polymerase (or more accurately, the transcription factors) can bind

Question 30

regulatory protein

Answer 30

• protein that regulates (controls) expression of a gene or operon in some fashion

Question 31

operator (2)

Answer 31

• DNA region where a regulatory protein binds

- sometimes the operator is the promoter itself but often they are different sequences or only have partial overlap

Question 32

Can genes that code for regulatory proteins be apart of the operons they control?

Answer 32

• no

Question 33

positive regulation (Jarod) (3)

Answer 33

• regulatory protein binds to a region near the promoter (the operator region) and INCREASES transcription
• regulatory protein is called an ACTIVATOR protein
• example is MalT

Question 34

negative regulation (3)

Answer 34

• regulatory protein binds to a region near the promoter (the operator region) and DECREASES transcription
• regulatory protein is called a REPRESSOR protein
• example is LacI