What am I?

I'm called by three lettersThough I have a long name.

I'm in all of you,But I'm never the same.

I'm all coiled upSo 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 meHe'll solve many mysteries.

What type of macromolecule is DNA?

A. CarbohydratesB. LipidsC. Nucleic AcidsD. Proteins

DNA

• DNA is a type of nucleic acid macromolecule.

• Deoxyribonucleic Acid

Which types of cells contain DNA?

A. EukaryoticB. ProkaryoticC. All of the aboveD. None of the above

ALL living things (prokaryotes & eukaryotes)

contain DNA.

Where is DNA found in Eukaryotic cells?

A. CytoplasmB. LysosomesC. NucleusD. Vacuole

Deoxyribonucleic Acid

What does DNA actually do?

• 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?

The Hershey-Chase Experiment

• 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. MonosaccharidesB. Fatty AcidsC. Amino AcidsD. 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.

Nucleotides

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

Purines vs. Pyrimidines

• Purines: 2 rings– Adenine (A)– Guanine (G)

• Pyrimidines: 1 ring– Cytosine (C)– Thymine (T)

Nucleotides

• 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.

G

G

A

T

T

A

A

C

T

G

C

A

T

C

What will the opposite strand look like?

5’-ATGGTTCCA-3’3’-TACCAAGGT-5’

Chargaff’s Rules

• 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%

X-Ray Evidence (1952)

• 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.

The Double Helix Model (1953)

• 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 3-dimensional 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!

DNA molecules are SUPER LOOOOOONG!

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

Chromosomes

How does DNA fit in the cell?

It’s supercoiled!

• The DNA & histone proteins are packed tightly together to make them fit.

DNA & Chromosomes

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

DNA + Protein = Chromatin

DNA + Proteins = ChromatinTightly Packed Chromatin = Chromosome