Chapter 18

Question 1

Prokaryotes and eukaryotes alter…

Answer 1

gene expression in response to their changing environment

Question 2

in multicellular eukaryotes, gene expression regulates …

Answer 2

development and is responsible for differences in cell types

i.e. neuron vs. fibroblast

Question 3

Gene regulation

Answer 3

a cell can regulate the production of enzymes by feedback inhibition

Question 4

Operon Model

Answer 4

control gene expression (in bacteria)

Question 5

E. coli, a type of bacteria that lives in human colon,

Answer 5

can tune its metabolism to the chaining environment and food sources at 2 levels:

1) adjusting the activity of metabolic enzymes already present
2) regulating the genes encoding the metabolic enzyme

i.e. enzymes that synthesize or metabolize tryptophan or lactose, respectively

Question 6

2 levels of metabolic control

Answer 6

1) adjusting the activity of metabolic enzymes already present
(regulation of enzyme activity in metabolic pathway by feedback inhibition)

2) regulating the genes encoding the metabolic enzyme
(regulation of enzyme production stops the metabolic pathway)

Question 7

in bacteria, genes are

Answer 7

often clustered into operons

composed of, an operator or “on-off” switch, a promoter, and genes for metabolic enzymes (lactose and tryptophan)

Question 8

Repressor

Answer 8

a protein that switches an operon off since its inital

Question 9

Corepressor

Answer 9

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

i.e. amino acid tryptophan

Question 10

trp operon

Answer 10

regulated synthesis of repressible enzymes: prevent RNA polymerase from working

the presence of the amino acid tryptophan binds to the repressor protein to stop tryptophan synthesis

when top levels are low, the repressor protein is not active and tryptophan is synthesized for energy

Question 11

in a repressible operon …

Answer 11

binding of a specific repressor protein to the operator shuts off transcription

i.e. trp operon

repressible operon on unless trp levels are high

Question 12

Lac operon

Answer 12

an inducible operon and contains genes that code for enzymes used in the hydrolysis and metabolism of lactose

Question 13

by default, the lac repressor is active and

Answer 13

switches the lac operon off

Question 14

when glucose is absent and lactose (allolactose) is present,

Answer 14

bacteria can utilize lactose for their energy

Question 15

inducer (allolactose)

Answer 15

inactivates the repressor to turn the lac operon on for metabolism of lactose

Question 16

in a repressive operon…

Answer 16

binding of a specific repressor protein to the operator shuts off transcription

usually anabolic

i.e. trp operon

Question 17

in an inducible operon…

Answer 17

binding of an inducer to an innately inactive the repressor and turns on transcription

i.e. lac operon

Question 18

regulation of both the trp and the lac operons involves the …

Answer 18

negative control of genes, because the operons are switched off by the active form of the repressor protein

Question 19

all organisms must regulate

Answer 19

which genes are expressed at any given time and in any given cell type

*all genes ARE NOT expressed at the same time

Question 20

almost all the cells in an organism are genetically identical however, differences between cell types result from …

Answer 20

differential gene expression, the expression of different genes by cells with the same genome

Question 21

errors in gene expression …

Answer 21

can lead to diseases, such as cancer

Question 22

how is gene expression controlled?

Answer 22

at the level of DNA, transcription (RNA synthesis) and translation

Question 23

All organisms must regulate which genes re expressed at any given time but the key step is…

Answer 23

transcription

Question 24

During development of a multicellular organism, its cells undergo a process of specialization in form and function called

Answer 24

cell differentiation

Question 25

each cell of a multicellular eukaryote expresses

Answer 25

only a fraction of its gene in each type of differentiated cell

Question 26

In eukaryotes, the DNA-protein complex is called

Answer 26

chromatin | and is ordered into higher structural levels than the DNA-protein complex in prokaryotes

Question 27

Eukaryotic DNA is precisely combined with a large amount of protein because

Answer 27

eukaryotic chromosomes contain an enormous amount of DNA relative to their condensed length

Question 28

Histones

Answer 28

proteins that associate with DNA and are responsible for the 1st level of DNA packing in chromatin and bind tightly to DNA throughout the cell cycle

Question 29

Unfolded chromatin

Answer 29

has the appearance of beads on a string and each "bead" is a nucleosome and the "string" in linker DNA

Question 30

Nucleosome

Answer 30

basic unit of DNA packing | consists of DNA wound around a protein core composed of 4 types of histone proteins

Question 31

1st level of DNA packing

Answer 31

nucleosome | histone and DNA

Question 32

2nd level of DNA packing

Answer 32

30nm chromatin fibers due to the interactions between histone tails of one nucleosome and the linker DNA (coiled nucleosome)

Question 33

3rd level of DNA packing

Answer 33

300nm chromatin fibers form looped domains attached to a scaffold of non-histone proteins

Question 34

mitotic chromosome

Answer 34

the looped domains themselves coil and fold forming the characteristic metaphase which is maximally compacted

Question 35

interphase cells

Answer 35

most chromatin is in the highly extended and uncompacted form called euchromatin but can also be found in the highly condensed areas called heterochromatin

Question 36

euchromatin

Answer 36

uncompacted form of chromatin

Question 37

heterochromatin

Answer 37

highly condensed areas of chromatin genes not expressed

Question 38

Chemical Modificaion

Answer 38

of histone tails affect chromatin structure and thus gene expression

Question 39

Histone Acetylation

Answer 39

the addition of an acetyl group (COCH3) loosens chromatin structure and enhances transcription relaxes the DNA, creating space

Question 40

Methylation of histones

Answer 40

condenses chromatin and reduces transcription the addition of phosphate groups (phosphorylation) next to a methylated amino acid can loosen chromatin to enhance transcription

Question 41

Histone code hypothesis

Answer 41

proposes that the combinations of modifications determine chromatin configuration and influence transcription

Question 42

Chromatin-modifying enzymes

Answer 42

provide initial control of gene expression by making a region of DNA either more or less able to bind the transcription machinery

Question 43

Associated with most eukaryotic genes are multiple Control Elements

Answer 43

that are segments of noncoding DNA that help regulate transcription by binding certain proteins

Question 44

to initiate transcription, eukaryotic RNA polymerase requires the assistance of proteins called

Answer 44

transcription factors that bind DNA near the promoter i.e. ELK-1 that can modify chromatin responds to ERK

Question 45

Proximal control elements

Answer 45

are located close to the promoter intrinsic means

Question 46

Distal Control Elements

Answer 46

called enhancers that may be far away from a gene or even in an intron intrinsic means

Question 47

Activator

Answer 47

a protein that binds to an enhancer and stimulates transcription of a gene CAAT region, an distal activator to increase gene expression