DNA Replication in Eukayrotes Flashcards
What are the Similarities between Prokaryotes ?
They are semi conservative meaning it starts with one DNA molecule , then produces two daughter molecules .
Read in 5-3 Synthesis .
What are the difference in Eukaryotes ?
Larger Genome : Much larger in Multi cellular animals/plants.
More variable relationship of gene number to physical genome size.
Unique size differences in DNA size linear end structure called Telomeres and distinctive .DNA Packing that involves histones
How does Eukaryotes initially start and the help of which enzyme ?
Initiation complex includes helicase activity ,unwinds the DNA double helix at origin site .
DNA polymerase a primarase complex synthesis the first primer .
It initiates DNA replication on the leading strand and okazaki fragments on lagging strand
In addition, to the polymerase a primarase two DNA polymerases &and e are required for DNA replication
What are Polymerase & and E ?
They are major polymerase in lagging strand synthesis .This is similar to the DNA polymerase 1 and 3 in lagging synthesis of prokaryotes .
When are okazaki fragments generated?
During lagging strand synthesis and are much shorter than E.coli/
How is DNA replication initiated formed ?
By forming many replication forks at multiple origins to compete DNA replication in the time available during the S phase of the cell cycle .
What are the two key structural features of Eukaryotic DNA which are different than prokaryotes ?
Presence of Histones complexes and telomere structures
What are Histones mainly responsible for ?
They are responsible for the structural organisations of DNA in eukaryotes .chromosomes
The positive charge of Histones are due to presence of various lysine and arginine residues and is a major feature of the molecules ,enabling them to bind the negatively charged phosphate backbone of DNA.
What are the different types of Histones ?
H2A H2B H3 AND H4 .They are combined to form eight proteins which DNA is wound .The bead like structure is called nucleosome .
What is a Nuclesome ?
a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones.
They have a diameter of 10nm and contains 200 base pairs .
Each nucleosome is linked to an adjacent one by short segment of DNA linker and another histone .
The DNA in a nucleosome is further condensed by the formation of thicker structure called chromatin fibres .
At higher level of organisations chromosomes are divided into regions called chromatin and herterhcorn
What are Telomerase main aim ?
Aids in their replication and prevent chromosomes degradation .
What are some facts /points on Nucleosomes ?
Nucleosome structure of 30nm fibres packing of nucleosomes .
Nucleosomes do not impede DNA binding of other proteins .
30 nm fibre forms loops with loose calling associated with high gene expression .
What are Eukaryotic DNA bound to ?
Bound to the proteins known as histones to form structures called nucleosome .
What seals the lagging strand left by the DNA polymerase ?
DNA ligase seals the lagging strand left by the DNA polymerase .
Dna replication uses the semi conservative method
What is the initial role for Telomerase ?
Binds to the 3 end of the leading strand .
Establishing a base pairing with short stretch of RNA sequence /telomerase carries/adds a 6 -nucleotide sequence (GGTTAG) to the 3 end by telomerase is completed.
