DNA Replication

By: Laura Keller

DNA

• The DNA double helix refers to the shape of the DNA molecule, or the twisted ladder. It has two intertwining strands made of sugar and phosphate with links across the middle. The rungs of the ladder are base pairs made of four different bases, represented by the letters A, T, G, and C.

The Enzyme DNA helicase “unzips” or unwinds the double stranded DNA at the origin of replication by breaking hydrogen bonds between complementary strands.

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Hydrogen Bond

3’

3’5’

5’

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

DN

A H

elic

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

DN

A P

oly

mera

se

III

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

DN

A P

oly

mera

se

III

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

DN

A P

oly

mera

se

III

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

DN

A P

oly

mera

se

III

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

DN

A P

oly

mera

se

III

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

DN

A P

oly

mera

se

III

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

DN

A P

oly

mera

se

III

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Then, on the leading strand, DNA Polymerase III adds the 5’ phosphate end of a free floating nucleotide to the exposed 3’ OH ends on the single stranded DNA in a continuous fashion. The leading strand elongates toward the replication fork.

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

`

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

5’ 3’

3’ 5’

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

5’

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.D

NA

Pri

mase

3’5’

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A

Pri

mase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DN

A P

rim

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

RNA Primer

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

RNA Primer

DN

A

Poly

mera

se I

I

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

RNA Primer

DN

A

Poly

mera

se I

I

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DNA

DN

A

Poly

mera

se I

I

When the DNA

Polymerase II reaches

the RNA primer, it turns into

DNA.

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DNA

DN

A

Poly

mera

se I

I When the DNA

Polymerase II reaches

the RNA primer, it turns into

DNA.

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DNA

DN

A

Poly

mera

se I

I

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DNA

DN

A

Poly

mera

se I

I

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DNA

DN

A

Poly

mera

se I

I

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Then, on the lagging strand, which has to be built discontinuously, a short RNA primer is synthesized from DNA primase. The primer is extended in a 5’ to 3’ direction, with short DNA segments called Okazaki fragments formed from DNA Polymerase II.

DNA

Okazaki fragments

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

5’

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

5’

DN

A

Lig

ase

Key

=

Phosphate

= Sugar

=

Adenine

=

Thymine

=

Guanine

=

Cytosine

Lead

ing

Str

an

d

Lag

gin

g S

tran

d

Lastly, DNA Ligase forms a phophodiester bond to finalize the connection of Okazaki fragments.

DNA

Okazaki fragments

5’ 3’

3’

3’

3’ 5’

5’

5’

Why Does DNA Need to Replicate?

• DNA needs to replicate because when a cell in your body divides, in order for your body to grow or repair itself it must also duplicate the cell's DNA. This is so the cell will then have it's own set of directions to know how to continue replicating.

In My Own Words...

• Telomeres- keep chromosomes from becoming attached to each other accidentally.

• Okazaki Fragment- a section of complimentary strands of DNA formed when the enzyme DNA Ligase is present.

• DNA Ligase- an enzyme that “stitches” a new complimentary strand of DNA called an okazaki fragment.

• Telomerase- an enzyme that helps a cell maintain the length of their telomeres.

In My Own Words… (Continued)

• Cancer- expresses the enzyme telomerase, which helps a tumor to grow.

• Transplanted Cells- cells that have been taken, added to, and then given back

• Cloning- taking a piece of something and making another copy

• Aging- the steady shrinking of cells in the body

Mutations (Mistakes)

• If there are any mistakes while replicating DNA, it will result in the mutation of a gene. An organism can only have up to 3 mutations, or it cannot live. Sometimes, mutations are minor, while other times, they can change one’s whole genetic makeup. For example, a mutation can result in the crossing over of a 21st chromosome, resulting in one having Down’s Syndrome.

Where in Mitosis Does DNA

Replication Happen?• DNA replication happens in S Phase and also in cytokinesis, or

the last phase of mitosis.

Where in the Cell?

•DNA replication happens in the nucleus of a cell.

Works Cited• http://wiki.answers.com/Q/What_happens_if

_there_is_a_error_in_DNA_replication?#slide=6

• http://www.nature.com/scitable/topicpage/dna-replication-and-causes-of-mutation-409

• http://www.chemguide.co.uk/organicprops/aminoacids/dna6.html

• http://www.biology.ewu.edu/aHerr/Genetics/Bio310/Pages/ch13pges/ch13note.html

• http://www.astrochem.org/sci/Nucleobases.php

The End