I'm called by three letters
Though I have a long name.
I'm in all of you,
But I'm never the same.
I'm all coiled up
So that I am quite small,
But if you stretch me out
I'll be really tall.
I could be the root
Of certain disease;
If man can unlock me
He'll solve many mysteries.

What type of macromolecule is DNA?
A. Carbohydrates
B. Lipids
C. Nucleic Acids
D. Proteins

DNA
• DNA is a type of nucleic acid macromolecule.
• Deoxyribonucleic Acid

Which types of cells contain DNA?
A. Eukaryotic
B. Prokaryotic
C. All of the above
D. None of the above
ALL living things
(prokaryotes & eukaryotes) contain DNA.

Where is DNA found in Eukaryotic cells?
A. Cytoplasm
B. Lysosomes
C. Nucleus
D. Vacuole

• Carries genetic information from one generation to the next
– Genes are made of DNA
• Be easily and accurately copied before cell division

DNA was identified as the material that carried our genes through a series of experiments.
• This was a breakthrough discovery that occurred less than 100 years ago!
• While DNA has been known to scientists since 1869, many scientists at that time assumed that genes were carried on proteins, not DNA.

Hershey & Chase confirm that DNA is the genetic material that carries genes, not protein.
• In 1944, Alfred Hershey & Martha Chase studied viruses that infect bacteria.
When viruses infect bacteria, they inject their genes into the bacteria.
Were the viruses injecting proteins into their hosts, or
DNA?

• They tagged viral DNA with radioactive phosphorous.
• They tagged viral proteins with radioactive sulfur.

Tagged DNA was found inside the bacteria, but proteins were not.

Remember that the 4 macromolecules are polymers, meaning they are made of monomers bonded together.
What is the monomer of DNA?
A. Monosaccharides
B. Fatty Acids
C. Amino Acids
D. Nucleotides

DNA is made of monomers called nucleotides.
• 3 parts of a nucleotide:
– a 5-carbon sugar called deoxyribose
– a phosphate group
– a nitrogenous base

When nucleotides bond together, they form DNA.

• 2 types of nitrogen bases found on nucleotides:
– Purines
– Pyrimidines

• Purines : 2 rings
– Adenine (A)
– Guanine (G)
• Pyrimidines : 1 ring
– Cytosine (C)
– Thymine (T)

• When nucleotides bind together, they form a chain, which is the polymer DNA.
– The sugar & phosphate groups form the backbone of the chain
(like the sides of a ladder).
– The nitrogenous bases stick out
from the chain (like the rungs of a ladder).

This is 1 strand of the DNA molecule.
What’s the difference between this side of the DNA molecule & this side of the DNA molecule?

Each strand of DNA has
directionality.
• One side ends in a phosphate, but the other ends in a sugar.
• Each molecule will have a phosphate, or a 5’ end (5 prime) and a sugar, or a 3’ end
(3 prime).

The 2 strands run in opposite directions, called antiparallel (like opposite flows of traffic).

One strand runs 5’ to 3’ while the other strand runs 3’ to 5’.
5’
3’
3’
5’

We now know that the backbone of a DNA molecule is made of the sugars & phosphates from the nucleotides.
The nitrogen bases from each strand meet in the middle to form the “rungs”.
Does it matter which 2 bases meet in the middle?

Base Pairing Rules
1. Each base pair is made of 1 purine & 1 pyrimidine.
2. Adenine from 1 strand & thymine from the other always pair together with 2 hydrogen bonds.
3. Guanine from 1 strand & cytosine from the other always bond together with 3 hydrogen bonds.

A
C
T
C
A
G
T
T
G
A
G
T
C
A

What will the opposite strand look like?
5’-ATGGTTCCA-3’
3’-TACCAAGGT-5’

• Erwin Chargaff (1905-2002) discovered that in any DNA sample, the amount of guanine is always equal to the amount of cytosine, & the amount of adenine was always equal to the amount of thymine.

If adenine (A) makes up 35% of a DNA molecule, what percentage of the molecule is thymine (T)?
A. 70%
B. 35%
C. 15%
D. Not enough info.
35%

If adenine (A) makes up 35% of a DNA molecule, what percentage of the molecule is guanine (G)?
A. 70%
B. 35%
C. 15%
D. Not enough info.
15%

• Rosalind Franklin studied the
DNA molecule using x-ray diffraction (bending of waves around an edge or barrier) to find the structure of DNA.
• From her work she was able to see that the DNA strands were twisted around each other forming a helix.

• Francis Crick & James Watson were trying to figure out the structure of DNA by building models with cardboard and wire.
• When they saw Franklin’s pictures, they soon were able piece all the information together to come up with the 3dimensional structure of DNA: a double helix with two strands winding around each other.

How does it fit inside our cells?
The DNA in just 1 of your cells is about 3 meters long.
The DNA in all of your cells combined is twice the diameter of our solar system & could go from Earth to the sun about
340 times!

In order to fit into our cells, they must fold up as much as possible.

It’s supercoiled!
• The DNA & histone proteins are packed tightly together to make them fit.

• In eukaryotic cells, the DNA is bound to histone proteins , forming chromatin in the nucleus.
DNA + Protein = Chromatin

DNA + Proteins = Chromatin
Tightly Packed Chromatin = Chromosome