Dna Replication in Eukaryotes 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 happens during DNA replication ?
The histone complexes of nucleosome are separated ; the leading strand retains old histone.
The lagging strand remains free of histone complexes while new histones are made and are assembled .
Since histones have greater affinity for double stranded DNA , newly synthesised histones, octamers are quickly added as the lagging strand is polymerised .
What problem is caused by eukaryotes being linear ?
They arise when replication comes to an end of the DNA.
The synthesis of the lagging strand at each end of the DNA requires a primer so that the replication can proceed in 5 -3 direction .
This becomes impossible at the end of the DNA and the portion of the RNA primer at the 5 end of both leading and lagging strand is lost at each time and chromosome is replicated.
What happens at each somatic cell of mitosis ?
The DNA in the chromosome becomes shorter and shorter to prevent the loss of genetic materials during replication the ends of the DNA in chromosomes contain special structures called telomeres .
What are Telomeres as well as Human telomeres ?
A telomere is a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighbouring chromosomes. … Over time, due to each cell division, the telomere ends become shorter.
Human telemores are repeated ends of the sequence TTAGGG.
Typical size of 15-20 kb at birth.
What are the main Points on Telomere ?
At each round of DNA replication , the telomere sequence of eukaryotic chromosomes are shortened .
The extension of telomere sequence by telomerase in the cells contribute to immortality .
The short stretch of RNA serves as a template for telomere extension and plays a major role in leading strand extension when DNA replication is completed.
