Chapter 17

Question 1

What is the main 3 differences between Eukaryotic and Prokaryotic transcription?

Answer 1

• Transcription occurs in the nucleus
• DNA is wrapped around nucleosomes
• more RNA processing & translation happens later

Question 2

Define chromatin

Answer 2

DNA and proteins combined.

Question 3

Define nucleosomes. How many bp per nucleosome?

Answer 3

Clusters of 8 histone proteins. There are ~150 base pairs wrapped per nucleosome.

Question 4

Define histone

Answer 4

Proteins that play a role in controlling transcription.

Question 5

How do nucleosomes control transcription?

Answer 5

By how tightly packed the histones in each nucleosome are to each other.

Question 6

What is chromatin compaction controlled by?

Answer 6

Histone modifications

Question 7

Define heterochromatin

Answer 7

Compact chromatin with low transcription

Question 8

Define euchromatin

Answer 8

Loose chromatin with high transcription

Question 9

Define intrinsically disordered tails

Answer 9

Long amino acid chains that extend out from the main histone protein.

Question 10

Define histone modifications

Answer 10

Enzymes binding to the intrinsically disordered tails and causing post-translational modifications - shifting chromatin between hetero- and eu-chromatin

Question 11

Define methylation

Answer 11

Addition of a methyl group. Reduces transcription.

Question 12

Define histone code

Answer 12

The sum of a histone’s modifications and it’s effects.

Question 13

What is an example of methylation? (2 of them)

Answer 13

Lysine can get anywhere beteen 1-3 methyls, causing different effects.
Cytosine bases can be methylated to cause less transcription (typically in promoters)

Lysine can also be acetylated*

Question 14

Define acetylation

Answer 14

Addition of an acetyl group (Me-C=O). Shifts chromatin towards euchromatin.

Question 15

Define acetyltransferases

Answer 15

Enzymes that add an acetyl (WRITERS)

Question 16

Define histone deacetylases (HDACs)

Answer 16

Enzymes that remove an acetyl (ERASERS)

Question 17

Define phosphorylation

Answer 17

Addition of a phosphorus group

Question 18

How many unique methylation combinations are there?

Answer 18

280 billion unique combinations JUST for histone 3

Question 19

Define writer enzymes

Answer 19

Enzymes that ADD histone modifications.
Different enzymes administer different mods

Question 20

Define eraser enzymes

Answer 20

Enzymes that REMOVE histone modification.

Question 21

Define reader enzymes

Answer 21

Proteins that interpret histone modifications.

Question 22

Define chromatin remodeling complexes

Answer 22

Subset of reader proteins that are recruited by histone modifications. They increase/decrease chromatin compaction.
Different complexes recognize different histone modifications.

Question 23

Define promoter

Answer 23

DNA sequence near the start of the gene. Different genes have different promoters with different promoter elements.

Question 24

Define promoter elements

Answer 24

Smaller sequences within the promoter that bind to specific transcription factors

Question 25

What is a promoter element example?

Answer 25

the metallothionein 2A (MT2A) gene. It is a stress and growth responsive protein that binds and protects against toxic heavy metals. Has a heavily regulated promoter, with it's transcription being induced by the relevant TFs ALL binding to the promoter Includes the need for the stress hormone (glucocorticoid), growth signal, and presence of metal.

Question 26

Define focused promoter

Answer 26

There is only ONE defined transcription start site for the gene

Question 27

Define dispersed promoter

Answer 27

Transcription can begin at different start sites. (Alternative transcription start sites!)

Question 28

Define alternative transcription start sites (TTS)

Answer 28

Transcription begins at different sites, producing distinct mRNA isoforms from the same gene.

Question 29

What can alternative TTS do? (2 things)

Answer 29

- alter the 5' UTR (altering translation) - add new 5' exons (alter protein) Different TTS are used in different conditions to produce mRNA suited to the environment.