lecture 24

Question 1

chromatin

Answer 1

state DNA is in during interphase
DNA + histones + non-histones proteins

Question 2

1ST Level of Chromosome Packing

Answer 2

Nucleosomes= DNA that is wrapped around a histone (beads on a string)
also know as the 11nm fiber

Question 3

Histones function

Answer 3

they wrap 146 base pairs around it leaving the 50bp to get eaten by nuclease

Question 4

What is histones made up by and why?

Answer 4

they are made up of 25% Lysine and Arginine to neutralize the highly negative DNA

Question 5

What are the 5 type of histones and what are their roles

Answer 5

• H1: clamps the DNA around the nucleosome and solenoids
• H2A, H2B, H3 & H4 : Core Histones 2 of each to build the octamer that DNA is being wrapped around

Question 6

How is the octamer is formed?

Answer 6

The H2 pairs would create called an handshake creating a dimer: 2 dimers from the 2 pairs
the H3 and H4 pairs would create a tetramer in a similar handshake way
2 dimers + tetramer = octamer

Question 7

What part of the histones stick out and why?

Answer 7

The N termini of each core sticks out to neutralize the negative phosphate backbone of DNA allowing packing into the 30 nm fiber

Question 8

2nd Level of Chromosome Organization

Answer 8

Called solenoids the stage were they are packed and now 30 mn fiber. This is the state they are in in interphase called uncondensed chromatin

Question 9

What can happen at the 30 nm fiber (solenoid) state

Answer 9

No gene expression (rna synthesis) because they are too tightly packed

Question 10

What can happen at the 11 nm fiber position (nucleosomes)

Answer 10

The histone are highly acetylated to thy have a lower affinity to DNA allowing for loose packing and DNA synthesis to occur

Question 11

Chromosomes

Answer 11

solenoids super coil around nuclear scaffolds

Question 12

Nuclear Scaffolds

Answer 12

they are protein with a H1 Hand topoisomerase 2 to encourage supercoiling

Question 13

What is chromosome remodelling?

Answer 13

when chromatin and enzymes are alter the chromatin to open it up for transcription
- histone modification: it alters the chemical structure so they don’t work properly
- ATP dependant chromatin remodelling complexes: they take out the H1 clips at certain parts of a solenoid so DNA synthesis can occur

Question 14

Chromosome transmission control what 3 DNA sequences

Answer 14

• replication origins
• centromere
• telomeres

Question 15

What is a replication origin?

Answer 15

the location, usually many, that replication occurs rapidly

Question 16

Centromere

Answer 16

where the kinetochore connect to pull site chromatids apart

Question 17

telomeres

Answer 17

ends of chromosomes that are repetitive sequences so the genetic part isn’t degraded

Question 18

how are telomeres formed?

Answer 18

they are made by telomerase which use the 3’ end as primer to elongate that strand and it folds up in a T loop to protect it from degradation