DNA

REPLICATION and

MUTATIONS

DNA Replication

Replication – the process of copying a

DNA molecule.

So that genetic information can be passed on

from cell to cell.

DNA replicates before cells divide (S

phase)

DNA is made up of 2 strands of nucleotides.

The strands are held together by HYDROGEN BONDS between each of the bases.

The 2 strands are

COMPLEMENTARY

A pairs with T

C pairs with G

Quick Review…

How it Works

During replication EACH strand is used as

a pattern (template) to make 2 new DNA

molecules

This is called semi-conservative

replication

Original DNAOriginal LEFT with

new right strand

Original RIGHT with

new left strand

AND

How it Works

Steps in DNA Replication

1. Double helix unwinds.

2. DNA helicase (an ENZYME) ―unzips‖

the DNA molecule, breaking the

hydrogen bonds between the strands

DNA helicase

(enzyme)

Unpaired

bases

Steps in DNA Replication

3. DNA Polymerase (another ENZYME)

pairs up free nucleotides in the nucleus

with the nucleotides on the DNA strands

forming new hydrogen bonds.

Where do nucleotides come from? YOU ARE WHAT YOU EAT!

DNA

unzips

Original

DNAFree nucleotides

pair up with the

original LEFT

strand

Free nucleotides

pair up with the

original RIGHT

strand

Steps in DNA Replication

Steps in DNA Replication

4. The DNA winds back up into a double helix.

The final products of DNA replication are two molecules of DNA each having half new material and half old material… ―Semi-conservative‖

DNA Replication

Growth

Growth

Replication

fork

DNA

polymerase

Original

strand DNA polymerase

Nitrogenous

bases

Replication

fork

Original strandNew strand

New strand

Now all genetic information can be

passed onto new cells during cell

division.

DNA

copied

2 new identical cells

Why Replicate?

Polymerase Chain Reaction

(PCR)

Can be used to make millions of copies of

a DNA sequence from a very small sample

Forensics, paternity testing, etc.

PCR Video

Accuracy

Replication is also very accurate – only

ONE IN A BILLION base pairs are

incorrectly paired.

When mistakes are made, the DNA

molecule can correct itself so the genetic

code remains the same.

Sometimes they can’t… MUTATIONS

GENE MUTATIONS

(in DNA)

Point Mutations Happen At

Single Nucleotide Points in DNA

SubstitutionOne base changes to (―subs‖

for) another

Insertion Base added (inserted)

Deletion Base removed (deleted)

The Dog Ate The Fat Cat

Substitution

The Dog Ate The Fat Rat

Deletion

The Oga Tet Hef Atr At..

Insertion

The Dog Tat Eth Efa Tra t

What kind of point mutation?

What kinds of point mutation?

Insertions and Deletions Can Cause

FRAMESHIFTS in the code!

Uh Oh! One nucleotide affected every

codon down the line—a frameshift!

Now:

CHROMOSOMAL MUTATIONS

(affect whole chromosomes)

What Would You Call It?

Deletion

What Would You Call It?

normal chromosome

one segment repeated

three repeats

DuplicationOne or more segment is repeated

InversionA linear stretch of DNA is reversed within the

chromosome

What Would You Call It?

TranslocationEntire gene segments are exchanged between non-homologous

chromosomes!

chromosome

nonhomologou

s chromosome

reciprocal

translocation

Check Point

Mutations may be:

Silent or neutral (no effect)

Harmful or Fatal (bad effect)

Beneficial (good effect, low probability)