Notes:

DNA

I. What is DNA?• DNA (deoxyribonucleic acid) is a type of

molecule found in the nucleus of all cells

that contains instructions for the cell and

determines the traits of the organism.

• Important: All the somatic (body) cells in

an organism have the same exact DNA.

• Do you think every cell uses every gene?

_____No.

But, the code is identical in every

cell of your body because all of

these cells divided by mitosis from

the same cell (the first cell formed

by your mom’s sperm and your

dad’s egg).

II. How was DNA discovered?

• Rosalind Franklin

did experiments with

X-rays to determine

the structure of DNA.

• Watson and Crick

then completed the

model of the DNA

molecule.

II. How was DNA discovered?

• We now know that

DNA has a “double

helix” structure (like a

windy stair case).

II. How was DNA discovered?

Watson and

Crick:

III. What is the structure of DNA?

DNA is made of building

blocks called nucleotides.

Each nucleotide has 3 parts:

Phosphate group

Deoxyribose (sugar)

Nitrogenous base

Draw a nucleotide:

Deoxyribose

sugar

Which part of the nucleotide contains the genetic

instructions? The phosphate, the sugar, or the

nitrogenous base?

_______________________________The nitrogenous base (A, T, G, or C) –the order

of these determines the traits of the organism

Put these in order from smallest to largest:

Gene, nucleotide, chromosome

Nucleotide Gene Chromosome

Nucleotide: a small

piece of DNA

Gene: a small piece of

the chromosome

Chromosome:

an entire

strand of DNA

How do you know which bases

go with which?

• There are 4 base pairs in DNA

– Adenine

– Thymine

– Guanine

– Cytosine

Complimentary Bases

• Only certain bases can “pair up” along two

strands of DNA.

AT

GC“All Together, Go Cowboys”

• The two strands are called complimentary.

DNA Structure

• Each strand of DNA

has a 5’ end and a 3’

end. (This has to do

with the arrangement

of the molecules)

• The two strands are

called antiparallel

because the two

strands are facing

opposite directions.

Practice: Write the complimentary

strand:

5’ TTGCATTCA 3’

_________________3’ AACGTAAGT 5’

Question: If 20 % of a chromosome is made

up of guanine, what percent of the nitrogenous

bases are cytosine? ___________

Why? ___________________________

________________________________

20%

Because every C is paired with a

G. The same is true for A and T

How does DNA get replicated (copied)?

• Each time a cell divides by mitosis, the DNA in that cell must be replicated (copied).

• This insures that both daughter cells have a complete set of genetic material.

DNA

• Step 1: The DNA is unzipped at the base pairs by a protein called helicase.

• Step 2: Each nucleotide on the parent strands are paired with a new complimentary nucleotide. (A-T, G-C)

• Step 3: Nucleotides are bonded together by a protein called polymerase.

• Step 4: Two DNA molecules are formed - each with a parental strand and a new strand.

How does DNA get replicated (copied)?

• This process is

called

semiconservative

because the new

strand is ½ old

DNA and ½ new

DNA.

What does semiconservative mean?

Watch this animation of DNA Replication:

dna replication bozeman science - Bing video

Write this song down to help you remember the parts of

DNA: (to the tune of row row - row your boat)

We love DNA

Made of nucleotides

Sugar, phosphate, and a base

Going down the sides