What will you learn?

DNA Replication

PLO It is expected that students

will…

B5 describe DNA replication

B6 describe recombinant DNA

DNA is composed of units called NUCLEOTIDES, which are composed of three

sub-molecules:

1. Pentose Sugar (deoxyribose)

2. Phosphate

3. Nitrogen Base (purine or pyrimidine)

DNA (Deoxyribonucleic Acid)

DNA Structure

p. 508

DNA

Functions:

• stores genetic information and copies itself (replication) to pass on the information

• contains genes (instructions to make proteins)

• DNA instructs cell’s activities

Complimentary Base Pairing

PU

RIN

ES

= A

& G

PY

RIM

IDIN

ES

= T

& C

Nucleotide Bases (Only copy chart, not structures)

PURINES PYRIMIDINES

Double N-ring Single N-ring

A & G C & T/U

# of purines always equals the number of pyrimidines

DNA is composed of two

complimentary strands of nucleotides

joined by hydrogen bonds:

Adenine with Thymine (A-T or T-A)

They join with 2 hydrogen bonds

Cytosine with Guanine (C-G or G-C)

They join with 3 hydrogen bonds

DNA twists into a double helix

http://www.biostudio.com/demo_freeman_dna_coiling.htm

DNA Structure

Chromatin = DNA

strand + proteins

wrapped abound the

DNA

Chromosome =

condensed

chromatin

Hierarchy of

DNA

Genome

full set of genetic information within a species

Chromosomes

condensed, coiled chromatin

Chromatin

DNA strand proteins (histones)

DNA

polymer of nucleotides

Nucleotide

sugar, phosphate, nitrogenous base

A gene is a section

of a chromosome

that codes for a

protein

Chromosomal

structure

Cell Cycle

DNA Replication

• Before cells divide, a

complete copy of their

DNA (DNA replication)

must be made

• Occurs in the nucleus

Steps of DNA Replication http://www.youtube.com/watch?v=zdDkiRw1PdU

Step 1: Unzipping

– DNA strand unwinds

– helicase (enzyme) breaks H-bonds

between N-bases →→ “unzipping”

Steps of DNA Replication

Step 2. Complementary base pairing

– DNA nucleotides move into position to

bond with their partners on the DNA

strands (“the templates” or “the parent

strands”)

Step 3: Joining of adjacent nucleotides

– 2 new sugar-phosphate backbone forms

when enzyme, DNA polymerase, forms

covalent bonds between new nucleotides.

End up with 2 identical DNA strands which

are semi-conservative (composed the

original “parent” and a new “daughter”

strand)

FYI: DNA replication occurs about 100 nucleotides per sec

Semi-conservative

Step 4: Proof reading

– DNA polymerase also checks for mistakes

(mutations)

Huh?

• Watch this....

http://highered.mcgraw-

hill.com/sites/dl/free/0072421975/196646/l

w09_dna_replication_final.html