CHAPTER 9 SECTIONS 2 & 3

Stores and passes on genetic information from one generation to another .

Sugar: deoxyribose

DNA Deoxyribonucleic acid

DNA STRUCTURE

Shaped like a spiral staircase, or twisted ladder.

Double Helix

DNA – Scientists who mapped its structure

Chargaff’s 1949 Observations:

The amount of adenine always equaled the amount of thymine (A = T)

The amount of cytosine always equaled the amount of guanine (C = G)

DNA – Scientists who mapped its structure

Wilkins & Franklin’s Photographs

Using x-ray diffraction, in 1952Developed high-quality photographs of strands of DNA

Suggested that DNA was a tightly coiled helix with 2 or 3 strands of nucleotides

DNA – Scientists who mapped its structure

Watson & Crick’s 3-D DNA model in 1953

“Watson & Crick, took a stick and built the DNA model.”

DNA STRUCTURE

The outer parts of the ladder are made of: a sugar (deoxyribose) +

a phosphate.

DNA STRUCTURE

The rungs (steps) of the ladder are pairs of nitrogen bases…

…held together with weak hydrogen bonds.

DNA STRUCTURE

1. ADENINE = A2. GUANINE = G3. CYTOSINE = C4. THYMINE = T

They are represented by their capital letter.

Base Pair Bonding Rules

ADENINE WITH THYMINE(“Stick” Family)

T & A

CYTOSINE WITH GUANINE(“Curve” Family)

C & G

DNA STRUCTUREQUESTION ?

CAN T JOIN WITH A

AND G JOIN WITH C

YES

NO

CORRECT

MOVE ON

SORRY REVIEW MORE

DNA STRUCTURE

ACTCATGGTCATG

TGAGTACCAGTAC

This is an example of a genetic code that may be found in your body.

DNA STRUCTURE

The combinations of the nitrogen bases is the code that produces the genes for a particular trait.

DNA STRUCTURE

Because there can be so many different combinations of the bases, the code can be limitless

DNA STRUCTURE

EXAMPLE:

ATCGTCAGG May be for hair color.

BUT

ATCGTCAGC May be for eye color

Stop

• Begin DNA Model

DNA Replication

• Replication: to make an identical copy of

Occurs during the “S” phase of the cell cycle.

(Just before mitosis)

DNA Replication

• Also known as:

Semi-Conservative Replication– semi: half–Conserve: to save or reuse–Replicate: to copy exactly

Semi-conservative Replication

• To reuse half of the original DNA strand to make an exact copy

DNA REPLICATION

1. DNA Ladder Splits (unzips)• enzyme DNA helicase

2. Free floating nitrogen bases begin to pair on each strand• Attached by the enzyme DNA

polymerase (the glue)

Semi-conservative Replication

Semi-conservative Replication (attaching bases)

3. Two new identical DNA chains are formed

Semi-conservative Replication

DNA REPLICATION

DNA REPLICATION

FYIEach human chromosome is replicated in about 100 sections that are 100,000 nucleotides long.

An entire human chromosome can be replicated in about 8 hours!

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#

DNA Animation

View “DNA Replication Fork”