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 helixBlue 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/sourceshttp://www.brooklyn.cuny.edu/bc/ahp/LAD/C4/

C4_StagesReplication.html