Genetics: Lecture 2: DNA replication in both Prokaryotic & Eukaryotic

Prokaryotic (eukaryotic needs to constantly go back to make sure its accurate)

Where does DNA replication occur quicker?

Semiconservative

The original strand unwinds and is used as a template to generate the new strand

Conservative

When the original double strand serves as a template for a new molecule of DNA

Dispersive

When DNA would break up into multiple fragments and form together into new and old fragments within the new DNA molecule

Meselson and Stahl

Experiment that grew bacteria in heavy Nitrogen-15 for many generations, which made DNA heavy.
After that, the bacteria was switched to Nitrogen-14 to take additional samples over a few cell cycles.(new DNA contained Nitrogen-14). Ran on a density gradient to distinguish between heavy and light strands and concluded that there was half heavy and half light

Theta Replication

Takes place in circular DNA where the double strand begins to unwind and produce single strands that will function as a template for new strand (known as replication bubble) The unwinding continues as the bubble gets large and the replication fork is where unwinding occurs (bidirectional) and will have 2 strands and eventually split from one another

Rolling Circle Replication

A single strand break creating a 3’ OH and 5’ P group as new nucleotides are added on the 3 ‘OH break using the inner strand as a template and the original strand is rolled off to make way for the new strand (cycle is continuous)

Linear Chromosome Replication

These contain several origins in eukaryotes (bidirectional) and eventually meet up when the bubbles meet. Contains 4 stages: Intitation, Unwinding, Elongation and Termination

Intitation

When DNAa box binds to DNAa proteins to the origin of replication to cause a conformational change in the DNA to unwind so helicase can break hydrogen bonds and single strand binding proteins can prevent the strand from going back. Topimerase will then prevent supercoiling and torsional strain

DNAa proteins

Binds to protiens to unwind DNA and cause a conformational change

Topoisomerase I

Creates single stranded breaks in DNA →Take the 2 strands and clip one of them and twist it back on the other one so it can undo a single term to relax the DNA

Topoisomerase II

Creates double stranded breaks in DNA and breaks the double strand to pass through the double helix and resealing it again → Nick both strands and turn them around each other to undo a single term

DNA polymerase III

This type of DNA polymerase adds nucleotides after the primer and is able to travel back (3’ to 5’) to fix its mistakes in prokaryotes

DNA polymerase I

DNA polymerase that gets rid of the RNA primer in prokaryotes and replaces it with DNA. IT can move forward to replicate and track back to replace errors

Ligase

Stitches DNA phosphodister bonds together

Tus protein

This complex will block replication in prokaryotic termination

Okazaki Fragments

Fragments made in the lagging strand where it is read in the 3’ to 5’ direction but is synthesized from 5’ to 3’ direction

DNA replication (eukaryotic)

This type of replication is dependent on checking to make sure that there aren’t any errors with dna replication

Licensing factor

This is to ensure that replication forks initiate at the same time and doesn’t initiate more than once per cycle

Geminin

Binds to the licensing factor to remove it so replication isn’t initiated again

DNA polymerase alpha

Has primase activity in eukaryotes but generating a short primer

DNA polymerase delta

Polymerase is on the lagging strand after primer has been laid down in eukaryotes

DNA polymerase Epsilon

Functions like delta but on the leading strand

Trans Lesion Polymerase

A polymerase that will come in to add an incorrect base by binding to the site to bypass the error if delta and eplison cannot fix the error

Nucleosome

These contain 8 histone proteins with DNA wrapped around them and DNA typically unwraps so histones can be removed so DNA can be replicated. Old histones will find their way onto the new strand and attach to the new histones

Telomeres

Cannot be replicated and act as a buffer for the DNA that is removed (DNA is meant to get shorter) so critical genes are not impacted (some issues can lead to telomeres removing important DNA sequences)

Telomerase

This can prevent the telomere from shorterning, especially in sperm and egg cells so the child will not lose DNA

This can lead to diseases or sickness, especially cancer

When cells that have telomerase activity that is NOT necessary, what will happen in general?