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Alex's Genetics > Lecture 15a > Flashcards

Lecture 15a Flashcards

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1
Q

When is transcription above basal level?

A

When an enhancer is used.

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2
Q

When is transcription below basal level?

A

When a silencer is used.

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3
Q

T/F: When a silencer is used, RNA polymerase is not present.

A

False! RNA polymerase is present, however, initiation nor elongation cannot start.

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4
Q

What are 2 ways we can tell transcription is taking place in bacteria as opposed to in eukaryotes?

A

1) The mRNA is translated at the same time it is being transcribed.
2) The DNA that is being transcribed is stretched out and naked.

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5
Q

Where do transcription and translation occur in eukaryotes?

A

Transcription occurs in the nucleus.

Translation occurs in the cytoplasm.

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6
Q

What kind of proteins get transported into the nucleus?

A

Proteins with Nuclear Localization Sequences (NLSs) are transported into the nucleus.

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7
Q

What does importin do?

A

It is a protein that transports other proteins into the nuclear pores.

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8
Q

T/F: There is only one type of Nuclear Localization Sequence (NLSs).

A

False! There is a lot of diversity in NLSs.

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9
Q

What are steroid hormones?

A

They are produced by glands and secreted into the bloodstream, then taken up by cells.

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10
Q

What do steroid hormones bind?

A

Steroid receptors, which are transcription factors.

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11
Q

Generally speaking, what happens when a steroid receptor binds a steroid hormone?

A

This activates gene transcription/expression.

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12
Q

What type of hormone is glucocorticoid?

A

It is a steroid hormone.

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13
Q

What does glucocorticoid bind?

A

glucocorticoid binds a glucocortoid receptor.

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14
Q

When HSP90 is bound to the glucocorticoid receptor, is it active or inactive?

A

It is inactive.

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15
Q

When glucocorticoid binds the glucocorticoid receptor, what happens?

A

HSP90 is released.

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16
Q

When HSP90 is released, what is now exposed?

A

This exposes a nuclear localization sequence and a dimerization surface.

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17
Q

After the dimerization surface has been exposed on the glucocorticoid receptor, what occurs?

A

Two identical glucocorticoid receptors are able to dimerize to each other.

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18
Q

After the homodimer has formed, what occurs?

A

Importin will then bring it into the nucleus through the nuclear pores.

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19
Q

Generally speaking, what are Glucocorticoid Response Elements (GREs)?

A

They are enhancers.

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20
Q

Where are GREs located? What is the purpose of this location?

A

They are located near dozens of different genes.

The purpose of this is so that the hormone can activate many genes.

21
Q

When the glucocorticoid dimer binds to the GRE, what happens?

A

Transcription of the target gene is activated.

22
Q

T/F: Glucocorticoids are limited in what they do.

A

False! Glucocorticoids do a LOT of things depending on the cell type.

23
Q

What are examples of what glucocorticoids do?

A

Fat breakdown, stimulate glucose synthesis, anti-inflammatory response, etc.

24
Q

What is Chromatin?

A

This is the complex formed by the chromosomal DNA and the proteins that associate with the DNA across regions/domains of the chromosome.

25
Q

T/F: Chromatin is only in prokaryotes.

A

False! Chromatin is only in eukaryotes.

26
Q

T/F: Transcription factors are considered Chromatin.

A

False! While many transcription factors bind chromosomal DNA, they are not considered Chromatin, because they occupy sites rather than regions/domains.

27
Q

How did scientists discover nucleosomes?

A

Eukaryotic cells were broken open and things that looked like pearl necklaces spilled out. The round things were named ‘nucleosomes’ which translates to nuclear bodies.

28
Q

How many histone molecules make up a nucleosome?

A

8 histone molecules make up a nucleosome.

29
Q

What makes up a nucleosome?

A

Double-stranded DNA wrapped around the octamer of histone proteins.

30
Q

How many types of histones are there? How many of each type is present in a nucleosome?

A

There are 5 types of histones. However, H2A, H2B, H3, and H4 are the core histones. Two of each of these make up the octamer.

31
Q

Which histone is the linker histone? What does this mean?

A

H1 is the linker histone, meaning that it binds to linker DNA and also binds to nucleosomes.

32
Q

T/F: H1 binds to nucleosomes just as tightly as the core histones.

A

False! H1 binds to nucleosomes, but it does not do so as tightly as the core histones.

33
Q

What bp of DNA and what degree of turns makes up the octamer?

A

146 base-pairs of DNA make 1.65 negative superhelical turns around the octamer.

34
Q

Is the histone octamer positively or negatively charged? Why is this beneficial?

A

The histone octamer is postively charged, which is good, because the negatively charged DNA will be attracted to it.

35
Q

What is the benefit of the nucleosomes (beads on a strong)?

A

The structure of the nucleosomes shortens the DNA length about seven-fold.

36
Q

What is the size relation between DNA and histones?

A

In real life, the DNA is larger in relation to the histones.

37
Q

What causes the nucleosomes/beads on a string appearance?

A

Low salt concentration (0.001 - 0.05 M NaCl).

38
Q

When we are at a physiological salt concentration, what happens? What size are the fibers?

A

A 5th histone, called H1, becomes attached and causes the nucleosomes to be in 30-nm fibers.

39
Q

T/F: At low salt concentrations, H1 is present.

A

False! At low salt concentrations, H1 falls off and is not attached.

40
Q

What diameter is DNA normally at and what does it look like? What about at a low salt concentration?

A

DNA is naturally at 30 nm in a zig-zag configuration.

At low salt concentration, DNA is at 11 nm.

41
Q

How are the 30-nm fibers organized?

A

They are organized into loops.

42
Q

What two proteins are important in the formation of loops in 30-nm fibers?

A

CTCF proteins and SMC proteins.

43
Q

What does the SMC protein do in loop formation?

A

The loop will form in the chromatin and be passed through the SMC protein.

44
Q

When does the chromatin stop being pulled through the SMC protein?

A

Once the CTCFs on each side of the chromatin make contact with each other, stabilizing and forming the loop.

45
Q

T/F: In metaphase/mitosis, the chromosomal DNA is even more highly compacted.

A

True!

46
Q

What salt concentration are we at?

A

Low

47
Q

What salt concentration are we at?

A

Physiological level

48
Q

What salt concentration are we at?

A

Low

49
Q

What salt concentration are we at?

A

Physiological level

Alex's Genetics (38 decks)

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