Transcript File

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 am I?
What type of macromolecule is DNA?
A.
B.
C.
D.
Carbohydrates
Lipids
Nucleic Acids
Proteins
DNA
• DNA is a type of nucleic acid
macromolecule.
• Deoxyribonucleic Acid
Which types of cells contain DNA?
A.
B.
C.
D.
Eukaryotic
ALL living things
Prokaryotic
(prokaryotes & eukaryotes)
contain DNA.
All of the above
None of the above
Where is DNA found in Eukaryotic cells?
A.
B.
C.
D.
Cytoplasm
Lysosomes
Nucleus
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.
B.
C.
D.
Monosaccharides
Fatty Acids
Amino Acids
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.
A
T
C
G
T
A
C
G
A
T
G
C
T
A
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.
B.
C.
D.
70%
35%
15%
Not enough info.
35%
If adenine (A) makes up 35% of a DNA molecule,
what percentage of the molecule is guanine (G)?
A.
B.
C.
D.
70%
35%
15%
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 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!
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 = Chromatin
Tightly Packed Chromatin = Chromosome