L21 Flashcards
(17 cards)
What are the major landmarks on a chromosome (there are two) and what do they do?
Centromere - mitotic spindle attaches to it
Telomere - protect tips of chromosome to prevent it from getting too short
Most cells in your body are in ____phase
Interphase - consists of G1, S, G2
DNA has __ bp per full turn
10.5
Is DNA in the cell generally underwound or overwound? What does this mean?
Underwound/strained - can be twisted into larger coils, also making it easier for strands to separate for transcription
The more supercoils you have in DNA, the faster or slower it will travel?
Faster
What does a topoisomerase enzyme do to the structure (base pairs) of DNA? To the shape? To the size?
DNA is overwound after transcription and hence topoisomerase relieves the tension and returns it to the underwound state, does not affect base pairing.
What is the general mechanism (no detail required) by which Type II topoisomerase acts?
Cuts DNA to open middle section so another DNA strand can pass through the break, going from N to C gate, and relieve tension.
What is a nucleosome? What is chromatin?
Nucleosome - 8 histones molecules bound to DNA, basic unit of chromatin (7 fold compaction)
Chromatin - DNA and protein
What is a histone and what is in rich in?
Small basic proteins rich in basic AA Arg and Lys
Where are the 5 types of histones found in chromatin? What is important about the histone N‐terminal tails?
8 subunits (2 of each type -H2A, H2B, H3, H4)
- H2A, H2B
- H3, H4 are highly conserved across species
- H1 is found on the outside of nucleosome holding it stable
- Histone N-terminal tails are where histones can be modified
Name three types of histone modification that can be used to regulate chromatin packing.
Methylation of protein tails, acetylation of histone decondenses chromatin, phosphorylation
Histones are ______ modified
Covalently
What is meant by the ‘histone code’?
Modifications to histones to make a code recognised by proteins and marks the DNA for specific biological processes
What is a 30nm fiber?
Nucleosome wrapping plus one histone H1 between the nucleosome, 100 fold compaction
What DNA base is chemically modified in the regulation of gene expression? Is gene expression increased or decreased because of it?
Cytosine is methylated (no effect on base pairing), decreasing gene expression
What enzymes methylate CpG islands?
DNMT - de novo DNA methytransferases, directed to specific areas of the DNA by DNA specific binding proteins
What enzyme is used to acetylate chromatin?
Histone acetyl transferase
