Download CB-Nucleic Acids

Searching for the “Secret of Life”
1.
What is the fundamental unit of all living
things?
The cell
2.
Which cellular structure controls the cell
and carries the hereditary information?
The nucleus
3.
What molecule in the nucleus carries the
code of life?
DNA
Nucleic Acids
I.
DNA
A.
Background Info
1. DNA is stored in the _______ of a cell
2. DNA is the basic substance of
heredity.
 Heredity is the passing of traits from
parent to offspring (baby).
 Traits are your physical characteristics
(eye, skin and hair color, height, etc)
3. DNA is a molecule that stores and
passes on genetic information (traits)
from one generation to the next
 It is why you look like your parents!
B.
Structure
1. DNA is made of repeating units called
nucleotides.
2. Nucleotides have 3 parts:
a. A nitrogen containing base
b. A 5-carbon sugar called
deoxyribose
c. A phosphate molecule
 What do you think DNA stands for?
DeoxyriboNucleic Acid
Nitrogen-containing
base
Phosphate group
Deoxyribose
NUCLEOTIDE (Draw Me!)
3. DNA has 4 different nucleotide bases.
a.
b.
c.
d.
Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
Adenine
Guanine
Phosphate
group
Cytosine
Thymine
Deoxyribose
C. DNA Discovery
1.
2.
3.
4.
Mid-1800s: scientists knew the nucleus
contained a nucleic acid molecule
By 1950, scientists knew what DNA was
made of, but didn’t know what it looked
like until…
1952, a woman named Rosalyn Franklin
took the first pictures of DNA using X-ray
diffraction
Using the work of Franklin, James
Watson and Francis Crick made a
model of DNA…
THE DOUBLE HELIX!
D. The Double Helix
1. The overall shape of DNA is described as
a double helix (a twisted ladder)
a. The “rails” of the ladder are made of
deoxyribose and phosphate molecules.
b. The “rungs” of the ladder are made of the
bases A, C, G, T.
2.
A simple model of DNA
 What holds the
bases together to
make the “rungs” of
the ladder?
 What holds the
deoxyribose and
phosphate
molecules together
to make the “rails”
of the ladder?
E.
Principles of Base Pairing (Chargaff’s Rule)
A. The opposing bases always pair the same:
 Adenine (A) pairs with Thymine (T)
 Guanine (G) pairs with Cytosine (C)
 What would be the complementary
base sequence for the strand of DNA
below?
A C G G T T A C A A T G A
T G C C AA T GT T A C T
II.
How does DNA control living organisms?
A. DNA contains the instructions to make
proteins.

What is so important about proteins?
1. Made of 20 different amino acids
2. Control many reactions in living organisms
3. Used for growth and repair of cells
4. Make hormones, enzymes and toxins
5. Make you, YOU!
B. A section of DNA that has the instructions
to make a specific protein is called a gene
III.
RNA: The Other Nucleic Acid
 What does RNA stand for?
Ribonucleic Acid
A. Differences between DNA and RNA
1. RNA contains the sugar ribose instead
of deoxyribose.
2. RNA is found in both the nucleus and
cytoplasm. DNA is only in the nucleus.
3. RNA contains uracil (U) instead of
thymine (T)
B. Three Kinds of RNA
1. Messenger RNA (mRNA)
a. Copies the DNA code in the nucleus and
carries the message to the ribosomes
2. Transfer RNA (tRNA)
a. It transfers amino acids to the ribosome and
places them in the correct position in the protein.
3. Ribosomal RNA (r-RNA)
a. Part of the ribosome that is involved in
making tRNA
IV. Protein Synthesis Summary
(Steps to make a protein)
1. Instructions to make proteins gets copied
from DNA to mRNA.
2. The mRNA molecule leaves the nucleus and
goes to a ribosome.
3. tRNA brings amino acids to the ribosome
where they are joined together to make a
protein using the instructions on the mRNA
molecule.
V. Mutations
1. Mutation is any change in the DNA
2. Mutations can happen when:
a. Chromosomes are copied
b. Nondisjunction (chromosomes go the wrong
way in meiosis)
c. Exposure to chemicals, X-rays, sunlight
3. Mutations can cause the wrong protein to
be made, which usually kills the organism
or…