Dna Replication in Eukaryotes Flashcards

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1
Q

What are the Similarities between Prokaryotes ?

A

They are semi conservative meaning it starts with one DNA molecule , then produces two daughter molecules .

Read in 5-3 Synthesis .

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2
Q

What are the difference in Eukaryotes ?

A

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

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3
Q

How does Eukaryotes initially start and the help of which enzyme ?

A

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

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4
Q

What are Polymerase & and E ?

A

They are major polymerase in lagging strand synthesis .This is similar to the DNA polymerase 1 and 3 in lagging synthesis of prokaryotes .

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5
Q

When are okazaki fragments generated?

A

During lagging strand synthesis and are much shorter than E.coli/

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6
Q

How is DNA replication initiated formed ?

A

By forming many replication forks at multiple origins to compete DNA replication in the time available during the S phase of the cell cycle .

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7
Q

What are the two key structural features of Eukaryotic DNA which are different than prokaryotes ?

A

Presence of Histones complexes and telomere structures .

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8
Q

What are Histones mainly responsible for ?

A

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.

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9
Q

What are the different types of Histones ?

A

H2A H2B H3 AND H4 .They are combined to form eight proteins which DNA is wound .The bead like structure is called nucleosome .

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10
Q

What is a Nuclesome ?

A

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.

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11
Q

What happens during DNA replication ?

A

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 .

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12
Q

What problem is caused by eukaryotes being linear ?

A

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.

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13
Q

What happens at each somatic cell of mitosis ?

A

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 .

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14
Q

What are Telomeres as well as Human telomeres ?

A

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.

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15
Q

What are the main Points on Telomere ?

A

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.

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16
Q

What is the initial role for Telomerase ?

A

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.

17
Q

What seals the lagging strand left by the DNA polymerase ?

A

DNA ligase seals the lagging strand left by the DNA polymerase .

Dna replication uses the semi conservative method

18
Q

What are Eukaryotic DNA bound to ?

A

Bound to the proteins known as histones to form structures called nucleosome .

19
Q

What are some facts /points on Nucleosomes ?

A

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 .

20
Q

What are Telomerase main aim ?

A

Aids in their replication and prevent chromosomes degradation .