DNA Replication Cell Cycle- Interphase (S phase) - PowerPoint Presentation

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DNA Replication

Cell Cycle- Interphase (S phase)Honors BiologyMrs. Sims

Let’s Start with a Video

Please view the video before you start this presentation. DNA Replication Animation

**This animation is created by McGraw Hill, the publisher of your textbook.

Focus Questions

18) What does the ending –ase tell about a molecule?

19) In

which direction does DNA replicate?

20) Why

does one strand replicate faster and one slower?

Replication copies the genetic information.

A single strand of DNA serves as a template for a new strand.

The rules of base pairing

direct replication

.

DNA is replicated during

the S

(synthesis) stage of

the cell

cycle.

Each body cell gets a

complete set of

identical DNA.

Prokaryotes vs. Eukaryotes

Prokaryotes have ONE point of Origin on their circular chromosome Eukaryotes have MANY on their linear chromosomes!

Prokaryotes:

Eukaryotes:

Alternative Models of DNA Replication

Semiconservative

replication

Parental DNA

First generation

Second generation

Mutations

DNA Polymerase has an error rate of only 1 wrong nucleotide per 100,000!

Mutations

are any change in DNA sequence and can be caused by mutagen

A

mutagen

is any chemical or environmental condition that causes a mutation

Point Mutations

– mutations in a single nucleotide base

Substitution

– one nucleotide substituted for another

Insertion

– one nucleotide is inserted into the sequence

Deletion

– one nucleotide is deleted from the sequence

DNA Replication

1) DNA Helicase attaches to DNA and breaks the hydrogen bonds between bases to unwind it.

2)

Primase

puts down an RNA primer for DNA Polymerase to attach nucleotides to.

3)

DNA Polymerase III

adds nucleotides moving towards the 5’ end of the template strand building the new strand from the 5’ to 3’ direction.

Leading strand is continuous

Lagging Strand is slower, discontinuous and creates

Okazaki Fragments

4)

DNA Polymerase I

removes the RNA primers and replaces them with DNA nucleotides.5) Ligase

covalently bonds the replaced DNA nucleotides together.

DNA helix

RNA primer

DNA polymerase

Lagging strand (first

Okazaki fragment

)

Direction of replication

Replication

fork

(

Helicase

unwinding)

Leading strand

1

DNA

Helicase

attaches to DNA and breaks the hydrogen bonds between bases to unwind

it, creating a

Replication Fork

.

Primase

puts down an

RNA primer

for

DNA

Polymerase III

to attach nucleotides to

.

DNA Polymerase III

adds nucleotides moving towards the 5’ end of the strand it is

on, so it builds the new strand from the 5’ to 3’ direction.

Leading strand

Primase

:

makes RNA

primers

Two

Okazaki fragments

2

DNA Polymerase III

adds nucleotides to the Leading and Lagging strands as it moves towards the 5’ end of each strand it is using as a template. This creates

Okazaki Fragments

on the Lagging strand.

4) DNA

Polymerase I

removes the

RNA primers

and replaces them with DNA nucleotides.

5) DNA Ligase

covalently bonds the replaced DNA nucleotides together.

3

Leading strand

DNA ligase

Third

Okazaki fragment

Lagging strand

DNA Polymerase I

RNA

primer (

P

rimase

)

Helicase

DNA Polymerase III

Focus Questions

21) What are the three ways in which DNA was hypothesized to replicate

? Which is the actual method?

22) What

scientists performed an experiment to determine the way in which DNA replicates?

23) What

are the two different strands involved in DNA replication and which strand is replicated faster

?

24) Why is there a difference between the replication rate of each strand? (

Describe in terms of replication direction and

continuity.)

DNA Replication in Real Time

https://www.youtube.com/watch?v=yqESR7E4b_8