PlannersMONDAY: Study the “old dead

people” from this unit!

TUESDAY: QUIZ on DNA structure

WEDNESDAY:

THURSDAY:

FRIDAY: TEST—DNA

DNA Structure

What the heck is DNA made of?

Erwin ChargaffBiochemist

Discovered that the amount of A (Adenine) equaled the amount of T (thymine) in ANY DNA sample.

Erwin ChargaffAlso that the amount

of G (Guanine) equaled the amount of C (cytosine) in ANY DNA sample.

This idea is called “Chargaff’s Rule”

Rosalind FranklinFirst person to

“photograph” DNA.

Used an X-Ray machine to take the picture.

Her photograph revealed an “X” shaped pattern.

Rosalind FranklinThis is her famous

photograph.

The angle of the “X” shape

suggested that there were 2

strands, not 1!

Watson and CrickAt the same time

Franklin was taking pictures of DNA, Watson and Crick were trying

to make a 3D model of DNA.

Watson and CrickAs soon as Watson

saw Franklin’s photograph they

figured it out.

They discovered that DNA was

actually 2 strands twisted around

each other.

Double Helix A Double Helix looks like a twisted

ladder, or a spiral staircase.

The double helix model explains Chargaff’s rule of base pairing and how the two strands of DNA

are held together!

AntiparallelThe 2 strands of DNA run in

opposite directions.

The base pairs meet in the middle.

Start End

Stop End

Start End

Stop End

AdenineThymineGuanineCytosine

Antiparallel Lines

HydrogenThe two strands of DNA are held

together by hydrogen bonds!

The bonds form between certain base pairs.

Why would you want a WEAK bond to hold together something as

important as DNA?

Hydrogen Bonding is happening at the dotted

lines!

Watson and Crick showed that

hydrogen bonding only happens

between certain base pairs…Adenine and

ThymineGuanine and

CytosineThis perfectly fit between A-T and G-C nucleotides is called base

pairing!

Name one scientist who contributed to our understanding of the structure of

DNA.

Quiz1. What are the letters used to

represent the nitrogen bases?

2. Which base pairs up with (T)?

3. What kind of chemical bond holds nitrogen bases together?

4. What kind of sugar is in DNA?

PlannersMONDAY: Homework—DNA Base Pairing

and Structure Sheet

TUESDAY: Homework—DNA Replication Sheet

WEDNESDAY: Homework—What is a DNA mutation?

THURSDAY: Quiz

FRIDAY:

Parts of DNA

Phosphate Backbone

Deoxyribose (Sugar)

Nitrogen Base

AdenineThymineGuanineCytosine

These three molecules make up a

NUCLEOTIDE.

Many NUCLEOTIDES

make up a NUCLEIC ACID.

What are the chemical

components of DNA?

Phosphate Group, Deoxyribose, Nitrogen Base Pairs—Adenine, Guanine, Thymine, Cytosine

Why are hydrogen bonds essential to

the structure of DNA?

H-bonds hold the paired bases together. Because the bonds are weak

the two strands of DNA are easily separated.

Describe the discoveries that led to the modeling of

DNA.

Chargaff: (A) = (T) and (G) = (T)Franklin: 2 strands, maybe a spiral?

Watson and Crick: Double helix, base pairing

Why did scientists have to use tools

other than microscopes to

solve the structure of DNA?

DNA is too small to be examined with a light microscope—the only microscope available at the time.

Describe Watson and Crick’s Model

of the DNA molecule.

Two Antiparallel strands that are connected by hydrogen bonds between

nitrogenous bases…A = T and G = C

Did Watson and Crick’s model

account for the equal amounts of

(T) and (A) in DNA?Watson and Crick’s model showed a double helix with (T) and (A) paired

together…so, YES.

Sources http://www.apsnet.org/edcenter/K-12/TeachersGuide

/DNA_Easy/Pages/Background.aspx

http://www.nature.com/scitable/topicpage/discovery-of-dna-structure-and-function-watson-397

http://sites.google.com/site/aninditosen2004/home

What are the 3 parts of a

nucleotide?

Put your homework on your desk please!