DNA Replication ModelBy: Jessica Kerr

Pd. 1+2

4. Free nucleotides base pair to

original polynucleotide.

5. DNA polymerase

enzyme joins the

sugar phosphate

backbone.

6. An enzyme rewinds the

double helix

7. Two new

double helices

each containing

one of the original

polynucleotides

Key:

Red arrow: Original double helix

Blue arrow: Helicase

DNA’s main job

is to store

information, it is

a nucleic acid

made up of

nucleotides

joined into long

strands or

chains by

covalent bonds.

The nucleotides

that make up

DNA are

Adenine,

Thymine,

Cytosine, and

Guanine.

Unwinding-Replication

begins at a specific site in

the DNA called the origin

of replication. Unwinding

enzymes called DNA

helicases cause the two

parent DNA strands to

unwind and separate from

one another in both

directions at this site to

from two “Y”-shaped

replication forks. These

replication forks are the

actual site of DNA

copying.

Key:

-A polynucleotide chain can only elongate in one direction

-In the picture a new triphosphate is about to be added to

the growing chain.

Complementary pairing up of the nucleotide bases- Each separate DNA strand

now has its sequence of bases exposed and unpaired. Enzymes match up each one of

these exposed bases, in turn, with free nucleotide triphosphates; A with T, and G with

C. It is therefore the sequence of bases on an old original strand which dictates and

specifies the complementary order of bases on the newly created strand.

Key:

-one of the new

polynucleotide chains can

elongate continuously.

-the other growing chain

does so in short lengths

which must later be joined

together.

Continuous and Discontinuous- RNA are added to both strands of DNA in the 5’3’

direction. The replication fork opens unidirectional. The RNA primers are then extended in

the 5’ 3’ direction on both strands as DNA synthesis proceeds. On the leading strand,

synthesis is continuous because the primer is extended without interruption into the

replication fork as it continues to open to the right. On the lagging strand, synthesis is

discontinuous, since new RNA primers must be added as the opening of the replication

fork continues expose new template.

Key:

-One of the new

polynucleotide chains can

elongate continuously

-the other growing chain does

so in short lengths which

must later be joined together.

DNA- Deoxyribonucleic Acid

A-T

DNA builds up

nucleotides, Adenine

(A), Thymine (T),

Guanine (G), Cytosine

(C)

A-T

G-C Cytosine- it’s a

compound found in living

tissue as a constituent

base of nucleic acids. It

is paired with guanine in

double strands DNA.

A-T

G-C

C-G

Guanine-a compound

that occurs in guano and

fish scales, and is one of

the four constituent bases

of nucleic acids. A purine

derivative, it is paired with

cytosine in double

stranded DNA.

A-T

G-C

T-A

C-GThymine- a compound

that is one of the four

constituent bases of

nucleic acids. A

pyrimidine derivative, it

is paired with adenine

in double-stranded

DNA.

A-T

G-C

C-G

T-A

C-G

Adenine- a compound

that is one of the four

constituent bases of

nucleic acids a purine

derivative, it is paired

with thymine in double-

stranded DNA.

A-T

G-C

C-G

T-A

C-G

G-C

Thymine pairs up with

Adenine

A-T

G-C

C-G

T-A

T-A

C-G

G-C

Guanine pairs with

Cytosine

A-T

G-C

C-G

T-A

T-A

C-G

G-C

A-t

The two DNA

strands run in

different

directions and are

anti-parallel.

A-T

G-C

C-G

T-A

T-A

C-G

G-C

A-t

A-t

FINISHED DNA

A-T

C-G

G-C

T-A

A

T

G

C

Unzipped DNA

A-T

C-G

G-C

T-A

A

T

G

C

A-T

C-G

G-C

T-A

Helicase

splits the

DNA in the

middle like

a zipper.

A

T

G

C

A-T

C-G

G-C

T-A

A

T

G

C

A

T G

C

A-T

C-G

G-C

T-A

A

T

G

C

A

T G

C

Free Nucleotides

MutationsIn genetics, a mutation is a change of the nucleotide

sequence of the genome of an organism, virus, or extra

chromosomal genetic element.

Mutations result from unrepaired damage to DNA or to

RNA genomes (typically caused by radiation or chemical

mutagens)

Errors in the process of replication, or form the insertion

or deletion of segments of DNA by mobile genetic

elements.

Meiosis

Meiosis is a special type of cell division necessary for

sexual reproduction in eukaryotes, such as animals,

plants and fungi.

The number of sets of chromosomes in the cell

undergoing meiosis is reduced to half the original number.

Chromosomes are

combined in this

phase.

Mitosis Mitosis is the process, in the cell cycle, by which a cell

duplicates into two genetically alike daughter cells.

In mitosis, chromosomes in the cell nucleus are separated

into two identical sets of chromosomes, each in its own

nucleus.

It is a form of nuclear division.

Female

chromosome

Male chromosome

Male

Female

Male

Female

Citations/sources http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4/C4_Stag

esReplication.html