CS&B - Biochemistry - DNA Structure, Replication, Repair Flashcards
Euchromatin is known as ‘beads on a string’ due to its arrangement as nucleosomes connected by linker DNA. These fibers are commonly referred to by their width.
What width does euchromatin have?
11 nanometers
Approximately, how many basepairs (bps) are found twice-wound around the histone octamer?
And how many are found in the linker (spacer) DNA between nucleosomes?
146 bps;
90 bps
The weak forces connecting DNA to histones are primarily produced by electrical interactions between what structures?
DNA phosphate groups (-) and arginine and lysine side chains (+)
What are the proteins making up the histone octamer?
H2a (x2)
H2b (x2)
H3 (x2)
H4 (x2)
What histone protein is not part of the histone octamer?
H1
One fiber of euchromatin is ___ nm in width.
One fiber of heterochromatin is ___ nm in width.
11;
30
What portion of the nucleosome is the site of most modifications that allow for gene activation and silencing?
The histone tails
What major nucleosome modifier is responsible for decondensation (unwinding) of chromatin?
What effect will this have on the genes involved?
Acetylation;
increased gene expression
How does acetylation of the histone tails (specifically lysine residues) cause decondensation of the chromatin?
It neutralizes some histone positive charge
What enzyme is responsible for histone acetylation?
What enzyme is responsible for histone deacetylation?
Histone acetyltransferases (HATs);
histone deacetylases (HDACs)
Histone acetyltransferases (HATs) have what effect on chromatin?
Histone deacetylases (HDACs) have what effect on chromatin?
Decondensation (11 nm fibers);
condensation (30 nm fibers)
Histone acetyltransferases (HATs) have what effect on gene expression?
Histone deacetylases (HDACs) have what effect on gene expression?
Increased gene expression;
gene silencing
What effect does methylation typically have on chromatin?
Gene silencing
How does histone methylation cause gene silencing?
By preventing acetylation
What is the typical effect of histone phosphorylation?
To promote chromatin decondensation (unwinding)
Which histone modifications will typically result in chromatin decondensation (unwinding) and increased gene expression?
Acetylation (by HATs);
phosphorylation
Which histone modifications will typically result in chromatin condensation (coiling) and gene silencing?
Deactylation (by HDACs);
methylation
For what are SWI/SNF responsible in gene expression?
How?
Regulation of chromatin decondensation;
through HAT function
For what is H1 responsible in gene expression?
How?
Facilitating DNA condensation;
through HDACs
Which activators regulate HAT function and chromatin decondensation?
Which activators regulate HDAC function and chromatin condensation?
SWI/SNF;
H1
What is the function of the MECP2 protein?
To bind methylated DNA (not methylated histones)
and recruit HDACs
DNA methylation (as opposed to histone methylation) will result in activation of what protein and what effect?
The MECP2 protein;
HDAC recruitment;
chromatin condensation
What is the shortest phase of the cell cycle?
What phase is significantly shortened in rapidly dividing (e.g. tumor) cells?
M;
G1
How many chromosomal autosome pairs are there?
How many chromosomal sex pairs are there?
22;
1
What stain is often used in karyotyping so different chromosomes can be distinguished from one another?
What segments are marked using this staining process?
G-banding;
A-T rich sequences
What are some notable defects that can potentially be observed on karyotyping?
Chromosomal breaks, deletions, duplications, translocations, aneuploidy, and more
Define aneusomy.
What are the three types?
Aberrant number of chromosomes;
nullisomy, monosomy, trisomy
Define euploidy.
Correct number of chromosome pairs
What is the term if an embryo is missing both chromosomes of one chromosomal pair?
What is the term if an embryo is missing one chromosome of a chromosomal pair?
What is the term if an embryo has both chromosomes of one chromosomal pair?
What is the term if an embryo has an extra chromosome in addition to one chromosomal pair?
Nullisomy (-2);
monosomy (-1);
euploidy (0; just right);
trisomy (+1);
Describe chromosomal structure using the following terms:
chromatid
coil
11 nm fiber
loop
rosette
30 nm fiber
What enzyme cuts specific palindromic DNA sequences?
Restriction endonucleases
DNA of interest can be recombined into a plasmid after cutting palindromic sequences on both using what type of enzyme?
What enzyme then seals their exposed palindromic sequences?
What then happens in the bacteria containing this recombined DNA?
An endonuclease;
DNA ligase;
replication (of the cell and DNA)
How can a radio-labeled probe be used to identify a single gene of interest in a genome?
Heat the cell (denaturing);
add a radio-labeled probe;
reduce the heat (the probe anneals to the gene of interest)
What in particular can in-situ hybridization be used to analyze?
Gene expression (through antibodies that show mRNA and/or protein expression)
What specialized base pairs are useful for Sanger DNA sequencing? What is important about the base pair insertions?
Dideoxynucleotides (ddATP, ddGTP, ddCTP, ddTTP);
one must attach after each base pair of the target sequence, creating sequences of all lengths from the full sequence to only one base pair
What is PCR good for?
Amplifying DNA sequences using a system of primers, heating, and Taq polymerases
How do we know that genetic polymorphisms are not simply new mutations?
They are present in ≥1% of the population
Per every 1 billion base pairs copied, how many mutations occur?
~1
What general term can be used to describe DNA replication in regards to the way older DNA strands are distributed amongst newer strands as replication occurs?
It is semi-conservative
True/False.
DNA is both antiparallel and complementary.
True.
What does it mean that DNA replication is semi-conservative?
Each new DNA duplex model is composed of one parent strand and one daughter strand
DNA origins of replication are characterized by a richness of what type of base pairing?
A-T pairings
Where on a replication bubble would the origin of replication be found?
Where would the replication forks be found?
In the middle of the bubble;
at the ends
All DNA replication occurs in what direction?
5’ to 3’
Which strand of DNA replication is the leading strand?
Which strand of DNA replication is the lagging strand?
The strand in which replication is continuous;
The strand in which replication is discontinous
What structure is used to provide a 3’-hydroxyl group so that DNA replication can initiate after the strands are denatured from one another?
An RNA primer
What enzyme ‘unwinds’ DNA helices from one another?
What enzyme releases the tension this creates by snipping and rejoining the strands?
What proteins prevent reannealing of the strands?
Helicase;
topoisomerase;
single-stranded binding proteins
In-vitro DNA replication mutations are 1 out of every 10,000 base pairs. In-vivo human replication mutations are 1 out of every 1,000,000,000 base pairs.
What explains this discrepancy?
Extensive DNA repair systems
What bacterial DNA polymerase is the main one synthesizing new strands?
DNA polymerase III (bacterial)
What bacterial DNA polymerase replaces RNA primers with DNA?
DNA polymerase I (bacterial)
What bacterial DNA polymerases are most involved in DNA repair?
DNA polymerase I and II (bacterial)
How does DNA polymerase I (bacterial) remove RNA primers to be replaced with DNA?
3’ to 5’ exonuclease activity
What enzyme connects Okazaki fragments?
DNA ligase
How many replication origin points do eukaryotes have in each contiguous piece of DNA?
(1 or many?)
Many
Where is the hydroxyl group that the triphosphate bond attacks in DNA polymerization?
(I.e. hydroxyl groups of what prime are attacked by phosphates of what prime?)
3’-hydroxyl
5’-phosphate
For what is eukaryotic DNA polymerase Alpha useful?
Synthesizing short stretches of DNA, works with RNA primase to make RNA primers
For what is eukaryotic DNA polymerase Delta useful?
Takes over after RNA primers; lagging strand synthesis (but also can be leading)
For what is eukaryotic DNA polymerase Epsilon useful?
Leading strand synthesis (but also can be lagging)
For what is eukaryotic DNA polymerase Beta useful?
DNA repair
For what is eukaryotic DNA polymerase Gamma useful?
Mitochondrial DNA replication
Which eukaryotic DNA polymerase is responsible for aiding in the synthesis of RNA primers and short stretches of DNA that follow?
DNA polymerase alpha
Which eukaryotic DNA polymerases are processive?
Delta, epsilon
Which eukaryotic DNA polymerases are involved in nuclear DNA replication?
Alpha, delta, epsilon