Final Exam (Random Facts and Snippets that You should know)

Question 1

Why are there variation in genome sizes? What is the difference between us and bacteria?

Answer 1

We have ~1K more DNA than E.Coli but only 4-5 fold more genes. BC we have a shit ton of introns and other elements that are not coding

Question 2

How many meters of DNA in ONE human cell and how does it all fit?

Answer 2

2 meters of DNA per human cll (3.4 A per bp, ~ 6 Gbp in diploid genome)

Question 3

How is the nucleosome organized?

Answer 3

~200 bp of DNA with ~145 - 147 bp of DNA wrapped around the histone core. There are linker DNA between the nucleosomes and they are approximately 10 - 90 bp long.

Question 4

Why do histones have high content of basic amino acids? What does this tell you about the charge of histones? Why is this important in histones?

Answer 4

Histones are positively charged because DNA is negatively charged

Question 5

How is the DNA wrapped around the histone octamer?

Answer 5

1.65 turns of DNA are wrapped around the histone octamer in a left-handed fashion

Question 6

Why do histones contact DNA phosphodiester backbone and interact with the minor groove?

Answer 6

Other DNA binding proteins (such as TFs) to interact with major groove

Question 7

What are the nucleotide differences between the major and minor grooves?

Answer 7

AT bp are found more in the minor groove because they are more compressible as compared to GC (this is also known as the 10 bp periodicity in AT and GC bp)

Question 8

Does DNA wrapping introduce twists? And if so, how many?

Answer 8

DNA wrapping introduces ~ -1 suprhelical twist per nucleosome (with linking number of -1) in a nucleosomal fiber