Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Alex's Genetics > Lecture 17a > Flashcards

Lecture 17a Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

___ ___________ is a feature that is shared by all repressive chromatin in mammals.

A

DNA methylation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

T/F: DNA in euchromatin or yeast is methylated.

A

False! Only heterochromatin has DNA methylation. DNA is never methylated in euchromatin or yeast.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where does heterochromatin tend to form?

A

Over repetitive sequences.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does this symbol mean?

A

DNA methylation or methylated CpG

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does this symbol mean?

A

Unmethylated DNA or unmethylated CpG

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Where is DNA methylation in heterochromatin found on?

A

It is only found on cytosines that are followed by guanines residue.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

T/F: The DNA methylation that occurs in heterochromatin is asymmetric.

A

False! It is symmetric.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What two things are needed to add a methyl group to DNA?

A

DNA methyltransferase 1 adds the methyl group. Folate pathway indirectly provides the methyl.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

On what carbon is the methyl group added to the cytosine?

A

The 5th carbon gets the methyl group.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Generally, explain what happens with DNA methyltransferases during the replication of DNA thats in heterochromatin.

A

DNA methyltransferase 1 chases after the DNA polymerase and adds methyl groups where the newly synthesized strand does not have it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Define fully methylated.

A

Both strands are methylated.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Define hemi-methylated.

A

Only one strand is methylated and the newly synthesized strand is unmethylated.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Hemi-methylated ——> Fully methylated.

What performs this?

A

DNA methyltransferase 1 + folate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Relative to chemical modifications, what do histones have?

A

Histones also have chemical modifications that are specific to heterochromatin or euchromatin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where do histone modifications often take place? Where is this on the nucleosome?

A

Mostly on the N-terminal “tails” of all 4 histones (H2A, H2B, H3, H4). These tails are sticking out of the nucleosomes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the N-terminal end of the nucleosome?

A

This is the first part of each histone molecule where H2A, H2B, H3, and H4 are present.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Each _____ has, on average, ~__% of the amino acids of the histone.

A

tail, 25%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Generally, what effect do histone tail chemical modifications have?

A

They control chromatin structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does chromatin remodeling do?

A

It opens (loosens) or closes (tightens) chromatin structure, which regulates the ability of transcription factors to access genes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How are amino acids in each histone labeled?

A

Numbered starting at the tip of the N-terminal tail.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

T/F: In heterochromatin, all 4 histones have all of their Lysines acetylated in the N-terminal tails.

A

False! It is actually euchromatin that has all 4 of their histones with Lysines that are acetylated in the N-terminal tails.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

The __-terminal tails of the histones are modified by over __ different enzymes.

A

N, 50

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are 3 examples of covalent changes that can be made to modify N-terminal tails of histones?

A

Acetylation, methylation, phosphorylation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is acetylation ONLY added to? Is acetylation giving a positive or negative charge?

A

Lysines and Arginines. It provides a negative charge.

25
Q

What do the three alternate tri-methylation sites on the Histone H3 tail represent?

A

These are three alternative repressive chromatin (heterochromatin) structures, which are all mutually exclusive.

26
Q

If I wanted to convert euchromatin to heterochromatin, what needs to leave?

A

Acetyl groups

27
Q

Name the 3 types of repressive chromatin.

A

H3K9me3
H3K27me3
H3K36me3

28
Q

What does 3 methyl groups on Lysine 9 of H3 (H3K9me3) cause?

A

The nucleosome will be bound by a protein called Heterochromatin Protein 1 (HP1).

29
Q

What does 3 methyl groups on Lysine 27 of H3 (H3K27me3) cause?

A

The nucleosome will be bound by a complex of Polycomb (heterochromatin) proteins called PRC1.

30
Q

What does 3 methyl groups on Lysine 36 (H3K36me3) cause?

A

We actually do not know. We just know that there are proteins that bind nucleosomes with this histone modification, but we have not yet identified them.

31
Q

Is there potentially a 4th type of heterochromatin? Where may we find it?

A

Yes, likely in the regions where there are no genes but there are LINE elements.

32
Q

How many genes do standard histones have? Why?

A

Each have 10-17 genes. We need HELLA of these proteins.

33
Q

T/F: There is no such thing as non-standard proteins.

A

False! There are also non-standard proteins in addition to standard proteins (H2A, H2B, H3, and H4).

34
Q

What is the variant of H2A called? What does it do?

A

MacroH2A, which is a much larger histone than H2A.

This is present in a subset of heterochromatin nucleosomes and plays a role in chromatin compaction.

35
Q

What does the H2A.X variant do?

A

Accumulates at the site of damage on chromosomes (double-strand breaks) and recruits repair proteins.

36
Q

Where do we find the cenH3 variant?

A

This is in the nucleosomes of the kinetochores of centromeres.

37
Q

What do repetitive sequences promote?

A

The formation of heterochromatin.

38
Q

Where do constitutive heterochromatins?

A

Forms over repetitive sequences and can spread beyond the repetitive sequences.

39
Q

What are 3 examples of repetitive sequences?

A

LINE-1, ERV, and Alu elements.

40
Q

What do clusters of repetitive sequences form?

A

Heterochromatin domains, which can spread past repetitive sequences into adjacent euchromatin.

41
Q

Where are large and strong heterochromatin domains found?

A

Wherever there are lots of repetitive sequences, such as telomeres and centromeres.

42
Q

T/F: Many copies of a repetitive sequence go against each other in the formation of heterochromatin.

A

False! Many copies of a repetitive sequence reinforce each other in the formation of heterochromatin.

43
Q

T/F: Strong heterochromatin does not spread.

A

False! Strong heterochromatin spreads variable distances beyond the repeats. The boundary moves.

44
Q

What can happen to a gene near the heterochromatin-euchromatin boundary?

A

The gene will alternate between being silent and being expressed depending on the boundary.

45
Q

In the fruit fly, what does the expression of the gene produce? What does the silencing of the gene produce?

A

Expression is red eye color.

Silence is white eye color.

46
Q

T/F: The spread of heterochromatin is dependent in each cell of the Drosophila compound eye.

A

False! The spread of heterochromatin is independent of each cell. This means that we can have an eye that is both partially red and white.

47
Q

What did mutations in the heterochromatin genes of the Drosophila cause?

A

It weakened the heterochromatin causing it to be compressed and making more cells of the eye red.

48
Q

What did two of the mutations in the heterochromatin genes of the Drosophila turn out to be?

A

It turned out to be the enzyme that adds 3 methyl groups to H3K9 to obtain H3K9me3. The other was for HP1.

The heterochromatin produced by these repeats was therefore H3K9me3 and this was how it was discovered.

49
Q

T/F: Both the H3K9me3 and HP1 gene copies can be mutated.

A

False! Only one of the two copies of these genes can be mutated because they are essential.

50
Q

When one of the two copies of the H3K9me3 and HP1 gene copies were mutated, what happened to the heterochromatin?

A

It contracted rather than expanded, so more gene was expressed than silenced.

51
Q

What do mutations in euchromatin-promoting genes cause in the Drosophila?

A

Silencing of the gene causing the eye to be white. The euchromatin was weakened.

52
Q

How were most heterochromatin and euchromatin promoting genes originally discovered?

A

By using mutational screens to identify mutations that alter the heterochromatin-euchromatin balance.

53
Q

Heterochromatin and euchromatin can be said to “______________” for the genome.

A

compete.

Whichever is stronger will help to either express or silence the gene nearby.

54
Q

T/F: Some repetitive elements drift back and forth between heterochromatin and euchromatic states.

A

True!

55
Q

What is an example of repetitive elements drifting back and forth between heterochromatin and euchromatic states

A

Inbred mouse strain with an ERV element (repetitive) near Agouti gene.

56
Q

What did heterochromatin of the ERV element near the Agouti gene do?

A

Create brown fur which was normal

57
Q

What did euchromatin of the ERV element near the Agouti gene do?

A

Overexpressed creating yellow fur as well as more prone to obesity and unhealthy.

58
Q

What is pseudoagouti?

A

Coat looks agouti in mice but there are some yellow hairs in fur.

59
Q

What is epistasis?

A

When you have a mutation that causes 2 or more different phenotypes.

Alex's Genetics (38 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions