Lecture 4 Flashcards

1
Q

chromosome number and size

A

are species specific, but are not associated with the complexity of an organism

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2
Q

How many chromosomes do cats have?

A

38

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3
Q

How many chromosomes do carp have?

A

104

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4
Q

How many chromosomes do humans have?

A

46

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5
Q

What is a Karyotype?

A

An organized image of the chromosomes in a nucleus

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6
Q

What do chromosomes look like during interphase?

A

highly DEcondensed and difficult to visualize

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7
Q

In what phases can chromosomes be individually visualized and identified?

A

about mid-prophase to metaphase

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8
Q

Are centromeres always in the CENTER of a chromosome?

A

No, they are almost always of UNEQUAL lengths

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9
Q

What is a centromere?

A

What binds two chromatids together to form a chromosome. They determine chromosome shape.

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10
Q

What is chromatin?

A

nucleic acids (DNA) and proteins that make up chromosomes

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11
Q

What is euchromatin?

A

LOOSELY CONDENSED chromosome regions that are more ACTIVELY TRANSCRIBED

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12
Q

What is heterochromatin?

A

TIGHTLY CONDENSED chromosome regions with FEWER expressed genes

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13
Q

Why do euk. chrom. need to be compacted?

A

-essential for cell division
-regulating gene expression (position effect variegation- PEV, euch/hetero chromatin)
-saves space

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14
Q

In “beads on a string” what are the beads, and what is the string?

A

“beads”= nucleosome
“string”= linker DNA

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15
Q

What are the 5 components of a nucleosome core particle ?

A

1) 2 H2A
2) 2 H2B
3) 2 H3
4) 2 H4
5) 146s bps of “core” DNA
-(linker) DNA

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16
Q

What is PEV?

A

Position effect variegation: gene expression is controlled by the state of chromatin (euch/hetero) in which a gene is located, so if a gene is moved to a diff. region (euch/hetero) will change how it is expressed

17
Q

What is facultative heterochromatin?

A

Can switch between euch/hetero-chromatin to activate genes at certain times (eg. development) on in certain tissues

18
Q

What is constitutive heterochromatin?

A

Regions of the genome that are always heterochromatic and transcriptionally inert

19
Q

What kind of chromatin does a centromere lie in?

A

Heterochromatic chromatin/ heterochromatin

20
Q

At what point during the cell cycle are centromeres most important?

A

During metaphase, when the spindles attach to them

21
Q

Define open promoters.

A

initiate transcription of genes for constitutively active genes
eg. basic cellular functions

22
Q

Define closed/covered promoters.

A

-regulate transcription of genes by requiring chromatin remodeling (displacement or removal of nucleosomes) to enable RNA polymerase to bind
-generally contain TATA boxes
-competition of nucleosomes and transcript. factors for binding

23
Q

Define open chromatin.

A

-relaxed nucleosomes
-allows access by regulatory proteins
-DNase 1 sensitive–> transcribable

24
Q

Define closed chromatin.

A

-DNA covered by nucleosomes
-restrict access of regulatory to proteins–> transcriptionally silent

25
Where are DNase 1 hypersensitivity regions?
-at open regions
26
What does DNase 1 do?
-enzyme randomly cuts DNA in open regions -used to test if a region is open (hypersensitive) or closed
27
What are "writers?"
Enzymes that ADD chemical groups that modify histones
28
What are "erasers?"
Enzymes that REMOVE chemical groups to modify histones
29
What are "readers?"
Proteins that recognized modified histones; active or deactivate the site
30
What are HATs?
-histone acetyltransferases -writers -ADD acetyl groups --> euchromatin (increase transcription)
31
What are HDACs?
-histone deacetylases -erasers -REMOVE acetyl groups --> heterochromatin (decrease transcription)
32
What are the two primary mods added to histones?
1) addition or removal of acetyl groups 2) addition or removal of methyl groups
33
What are HMTs?
-histone methyltransferases -writers -ADD methyl groups
34
What are HDMTs?
-histone demethylases -erasers
35
Define epigenetic.
Heritable patterns or changes in gene expression that are not associated with any change in DNA sequence.
36
What is Nucleotide Methylation?
-epigenetic -adds methyl group to usually to cytosine (C) in DNA and usually turns expression off
37
What does Histone 1 (H1) do?
Stabilizes the nucleosome core particles
38
Rank the condensation of DNA.
naked DNA-->histones--> nucleosomes--> solenoid--> loop domains--> chromatid--> metaphase chromosomes