genome lecture 1

Question 1

how are chromatin packed?

Answer 1

• coiled and lopped in a complex yet orderly manner + both are associated with specific proteins
• euk is more complex

Question 2

STRUCTURE OF EUK GENOME

Answer 2

• chromatin are coiled and looped in a complex yet orderly manner

Question 3

PROTEINS INVOLVED

Answer 3

• histones and non-histone chromosomal proteins ie scaffold protein and DNA polymerase

Question 4

HISTONES

Answer 4

• basic proteins (+ve charged)
• exist as H1 H2A H2B H3 AND H4
• structural role in formation of chromatin

Question 5

NON HISTONE

Answer 5

• largely acidic (-ve charged)
• large number of heterogeneous proteins like they vary widely among diff cell types of the same organism
• likely to perform roles in the regulation of expression of specific genes or sets of genes

Question 6

INTERPHASE

Answer 6

• chromatin exist as diffused state
• euchromatin: actively transcribed regions where 30nm fibre has dissociated into the beads-on-a string structure
• heterochromatin: more highly condensed, less exposed, transcriptionally inactive

Question 7

METAPHASE CHROMOSOME

Answer 7

• further condensed and compacted tgt –> seen as sister chromatids

Question 8

BEADS ON A STRING (nucleosomes and linker DNA)

Answer 8

• histones are responsible for this because they have a high proportion of positively-charged amino acids (lysine and arginine) –> they bind tightly with the negatively charged DNA
• each bead and its adjacent DNA form a nucleosome
• the nucleosome consists of 146 DNA base pairs wound 1.65 times around a protein core (histone octamer) composed of 2 molecules each of four diff types of histones H2A H2B H3 AND H3

Question 9

30nm CHROMATIN FIBRE (MORE CONDENSED)

Answer 9

• undergoes higher-order packing with the aid of histone H1 it coils with 6-8 nucleosomes per turn forming a solenoid
• H1 is NOT part of the octamer, it is a linker protein that attaches to the DNA near the bead when the chromatin undergoes the next level of packing (helps to stabilize the 30nm fibre by neutralising the negative charge on DNA and by interacting with the histone octamer and non-histone protein)

Question 10

LOOPED DOMAINS

Answer 10

• this fibre then forms looped domains which are attached to a chromosome scaffold

Question 11

PROK GENOME

Answer 11

• large circular chromosome and smaller plasmids
• reproduce by binary fission

Question 12

BACTERIAL CHROMOSOME

Answer 12

double stranded circular DNA molecule
- associated w several type of DNA-binding proteins
- HU and H contain a high percentage of positively-charged amino acids –> can bind ionically to the negative charges of the phosphate in DNA (is like the histones in euk)
- HU PROTEINS are criticial to maintain the nucleoid structure !!!

Question 13

OK PLASMIDS

Answer 13

• small molecules of double stranded circular extra-chromosomal dna
• it is an autonomously replicating molecule means they have their own origin of replication (can replicate independently)
• they r non-essential ! (may contain supplemental information that might confer some advantageous characteristics)

Question 14

PACKING OF BACTERIAL CHROMOSOMES AND PLASMIDS: SUPERCOILING

Answer 14

• forms a very compact structure
• puts the DNA molecule in a torsion
• histone-like DNA binidng proteins (aka H AND HU) forms a protein core on which DNA anchors to, forming looped domains. –> individually supercoiled with the help of DNA gyrase
• can be unwounded by topoisomerase I (cause single or double strand breaks on the DNA, then they re-liagte the break)