Chapter 18

Question 1

what is an operon?

Answer 1

an operon is the entire stretch of DNA that includes the promoter, the operator, and the genes that they control

Question 2

what can an operon be switched off by?

Answer 2

a protein repressor

Question 3

what is a corepressor?

Answer 3

a corepressor is a molecule that cooperates with a repressor protein to switch an operon off

Question 4

what is a trp operon?

Answer 4

by default a trp operon is on and the genes for tryptophan synthesis are transcribed, but it is repressible

Question 5

tryptophan and trp operon relationship

Answer 5

• when tryptophan is present, it binds to the trp repressor protein to turn it off
• the trp operon is repressed/turned off if tryptophan levels are too high (feedback inhibition)

Question 6

what does tryptophan act as?

Answer 6

tryptophan acts as the corepressor and can turn it off

Question 7

what is an inducible operon?

Answer 7

an inducible operon is one that is usually off but an inducer inactivates repressor to turn on transcription

Question 8

what is a repressible operon?

Answer 8

one that is usually on but binding of repressor shuts off the transcription

Question 9

what is a lac operon?

Answer 9

the lac operon is an inducible operon (usually off), an inducer is needed to inactivate repressor and turn it on

Question 10

what type of reaction are inducible enzymes?

Answer 10

inducible enzymes usually function in catabolic pathways (synthesis is induced by a chemical signal)

Question 11

what type of reaction are repressible enzymes?

Answer 11

repressible enzymes usually found in anabolic pathways (synthesis is repressed by high levels of end product)

Question 12

can you have positive control?

Answer 12

IT IS TRUE that you can have positive control through catabolite activator proteins (CAP)

Question 13

what can cause a lac operon to not turn on and why?

Answer 13

if there is high glucose compared to lactose because ECOLI prefers glucose

Question 14

what controls the lac operon?

Answer 14

the lac repressor and the CAP

Question 15

what are the best conditions for lac operon to turn on?

Answer 15

need lactose and low glucose

Question 16

is trp operon repressible or inducible?

Answer 16

trp operon is repressible; lac is inducible

Question 17

what is differential gene expression?

Answer 17

the reason there are differences between cell types, the expression of different genes by cells with the same genome

Question 18

define epigenetic inheritance?

Answer 18

the inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence

Question 19

what are examples of epigenetic inheritance?

Answer 19

genomic imprinting, X chromosome inactivation, histone tails modified and methylated

Question 20

define epigenetics

Answer 20

epigenetics is changing the base sequence and modifying histone tails because it affects how DNA acts together and how it is packed in the chromosome

Question 21

do chromatin modifications alter DNA?

Answer 21

no, but they can be passed to future generations of cells

Question 22

what is cell differentiation?

Answer 22

cell differentiation is the process by which cells become specialized in structure and function (ex: a stem cell becomes a liver cell)

Question 23

what is morphogenesis?

Answer 23

the physical processes that give an organism its shape constitute morphogenesis

Question 24

what are cytoplasmic determinants?

Answer 24

cytoplasmic determinants are maternal substances in the egg that influence early development
- as zygote divides by mitosis, cells contain cytoplasmic determinants

Question 25

what is cytoplasmic induction?

Answer 25

signal molecules from embryonic cells cause transcriptional changes in nearby target cells