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General Biology I E4 > Chapter 18 > Flashcards

Chapter 18 Flashcards

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1
Q

Prokaryotes and eukaryotes alter…

A

gene expression in response to their changing environment

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2
Q

in multicellular eukaryotes, gene expression regulates …

A

development and is responsible for differences in cell types

i.e. neuron vs. fibroblast

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3
Q

Gene regulation

A

a cell can regulate the production of enzymes by feedback inhibition

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4
Q

Operon Model

A

control gene expression (in bacteria)

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5
Q

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

A

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

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6
Q

2 levels of metabolic control

A

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)

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7
Q

in bacteria, genes are

A

often clustered into operons

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

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8
Q

Repressor

A

a protein that switches an operon off since its inital

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9
Q

Corepressor

A

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

i.e. amino acid tryptophan

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10
Q

trp operon

A

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

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11
Q

in a repressible operon …

A

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

i.e. trp operon

repressible operon on unless trp levels are high

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12
Q

Lac operon

A

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

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13
Q

by default, the lac repressor is active and

A

switches the lac operon off

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14
Q

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

A

bacteria can utilize lactose for their energy

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15
Q

inducer (allolactose)

A

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

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16
Q

in a repressive operon…

A

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

usually anabolic

i.e. trp operon

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17
Q

in an inducible operon…

A

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

i.e. lac operon

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18
Q

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

A

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

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19
Q

all organisms must regulate

A

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

*all genes ARE NOT expressed at the same time

20
Q

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

A

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

21
Q

errors in gene expression …

A

can lead to diseases, such as cancer

22
Q

how is gene expression controlled?

A

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

23
Q

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

A

transcription

24
Q

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

A

cell differentiation

25
Q

each cell of a multicellular eukaryote expresses

A

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

26
Q

In eukaryotes, the DNA-protein complex is called

A

chromatin

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

27
Q

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

A

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

28
Q

Histones

A

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

29
Q

Unfolded chromatin

A

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

30
Q

Nucleosome

A

basic unit of DNA packing

consists of DNA wound around a protein core composed of 4 types of histone proteins

31
Q

1st level of DNA packing

A

nucleosome

histone and DNA

32
Q

2nd level of DNA packing

A

30nm chromatin fibers

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

33
Q

3rd level of DNA packing

A

300nm chromatin fibers
form looped domains

attached to a scaffold of non-histone proteins

34
Q

mitotic chromosome

A

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

35
Q

interphase cells

A

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

36
Q

euchromatin

A

uncompacted form of chromatin

37
Q

heterochromatin

A

highly condensed areas of chromatin

genes not expressed

38
Q

Chemical Modificaion

A

of histone tails affect chromatin structure and thus gene expression

39
Q

Histone Acetylation

A

the addition of an acetyl group (COCH3) loosens chromatin structure and enhances transcription

relaxes the DNA, creating space

40
Q

Methylation of histones

A

condenses chromatin and reduces transcription

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

41
Q

Histone code hypothesis

A

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

42
Q

Chromatin-modifying enzymes

A

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

43
Q

Associated with most eukaryotic genes are multiple Control Elements

A

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

44
Q

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

A

transcription factors that bind DNA near the promoter

i.e. ELK-1 that can modify chromatin
responds to ERK

45
Q

Proximal control elements

A

are located close to the promoter

intrinsic means

46
Q

Distal Control Elements

A

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

intrinsic means

47
Q

Activator

A

a protein that binds to an enhancer and stimulates transcription of a gene

CAAT region, an distal activator to increase gene expression

General Biology I E4 (6 decks)

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