mb Flashcards
Explain the relationship between DNA content and the C-value.
*C value is the DNA content per haploid cell
*This correlation breaks down in several cases
of closely related organisms where the DNA
content per haploid cell (C value) varies widely
*The observation that more complex organisms
will not always need more genes than simple
organisms is called the C value paradox.
*C value paradox is probably explained by extra noncoding DNA in some organisms.
Write key issues during DNA replication.
*Unwinding of the helix
*Reducing increased coiling generated during unwinding
*Synthesis of a primer for initiation
*Discontinuous synthesis of the second strand
*Removal of the RNA primers
*Joining of the gap-filling DNA to the adjacent strand
*Proofreading
What does Trombone Model explain?
How DNA polymerases are kept attached to replication
fork during the synthesis of leading and lagging DNA
strands.
How Multiple Eukaryotic DNA Polymerases function during replication.
Pol a synthesis of RNA primers (Primase) during initiation on the Leading and Lagging Strands.
Pol δ synthesizes DNA on the leading strand
Pol ε synthesizes DNA on the lagging strand.
Describe the function and structural proporties of Telomerase enzyme.
Telomerase directs synthesis of the telomere repeat sequence to fill the gap.
This enzyme is a Ribonucleoprotein with an RNA molecule that serves as the template for the synthesis of its DNA complement.
TERC- It serves as a template.
TERT- Performs DNA synthesis.
What is sliding clamp?
It is the structure that allows DNA polymerase to hold onto DNA tightly. Increasing processivity. Beta subunit performs this task.
What is the mechanism that ensures that replication occurs only once.
ORC binds to DNA in the G1 phase. It is activated by kinases during the transition to the S phases. This complex dissipates when replication begins, so replication happens once.
What is homologous recombination?
It is exchange of genetic material between two homologous chromosomes that take place in similar DNA regions. It increases genetic diversity, repairs DNA damage.
Which proteins involved in homologous recombination?
RecA(in E.coli)
Rad51(in eukaryoticcells).
These proteins are loaded onto single stranded-DNA ends
What are the differences between viral/bacterial chromosome and eukaryotic chromosomes?
Viral and bacterial chromosomes are usually circular with little protein content and smaller. Eukaryotic chromosome are linear, packed with histones and larger.
What is supercoiling?
It is extra curling of the DNA to make it compact. Topoisomerases manage this process. DNA gyrase does negative supercoiling.
What are the types of repetative DNA?
Interspersed Repetitive Sequences
Minisatellites
Microsatellites
SINEs and LINEs retrotransposons
In what direction does DNA replication occurs?
Synthesis is always in the 5’ - 3’ direction.
What are the differences between Eukaryotes and Prokaryotes in DNA replication?
Prokaryotes
Occurs inside the cytoplasm.
Only have one origin of replication.
DNA gyrase is needed.
Only have replication fork is formed.
Eukaryotes
Occurs inside the nucleus.
The complex contains a large number of proteins and regularly elements.
DNA gyrase is not needed.
Have multiple origin of replication.
The genetic material must exhibit four characteristic
Replication
Storage of information
Expression of information
Variation by mutation
Three possible models of DNA replication.
Conservative
Semiconservative - Meselson-Stahl exp. - The Taylor-Woods Hughes experiment demonstrated that DNA replication is semiconservative in eukaryotes.
Dispersive
Core proteins at the replication fork
Topoisomerases : Prevents torsion by DNA breaks.
Helicases : seperates 2 strands.
Primase : RNA primer synthesis.
SSBP : prevent reannealling of single strands.
DNA polymerase: synthesis of new strand.
Tethering protein : stabilies polymerase.
DNA ligase : seals nick via phosphodiester linkage.
Topoisomerase I - E. coli serves to reduce the number of negative supercoils in a closed circular
Topoisomerase II - Introduces negative supercoils into DNA. (DNA Gyrase)
The mechanism of DNA replication.
Initiation - protein bind to DNA and open up double helix.
Elongation - proteins connect the correct sequences of nucleotids in to a continous new strand of DNA.
Termination - proteins release the replication complex.
How is DNA organized in eukaryotic cells?
Wrapped around histone proteins to form chromatin.
Nucleosome
DNA wrapped around group of 8 histone proteins. It helps organize and compact DNA.
Chromatin remodeling
Changing the structure of chromatin to make DNA easier to read by DNA binding proteins.
Euchromatin is uncoiled and active, whereas
Heterochromatin remains condensed and is in-active
Polytene chromosomes
Big chromosomes found in fruit flies.
Centromere
The center part of a chromosome. Helps during cell division, where spindle fibers attach.
Telomere
End part of a chromosome. It has repeating DNA that protects the chromosome from damage.
