Download DNA (Deoxyribonucleic Acid)

Questions to ponder:
1. How are DNA, genes, and proteins related?
2. What determines the genetic code?
3. How does a cell “read” the instructions
found in the DNA?
What do we know about the
genetic material of cells…
• Classified as NUCLEIC ACIDS (DNA
and RNA)
• Chromosomes are long strands of DNA
• GENES – segments of DNA that CODE
FOR A SPECIFIC TRAIT (phenotype)
DNA is wrapped tightly around
histones and coiled tightly to form
chromosomes
Something new…..
DNA is made up of repeating molecules
called NUCLEOTIDES
What is a NUCLEOTIDE?
DNA
(Deoxyribonucleic Acid)
DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogenous base
(A, G, C, or T)
DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
A
T
C
G
“sides of ladder”
Phosphate
Sugar
A HISTORY OF DNA
Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor
in diseased bacteria can transform harmless
bacteria into deadly bacteria
(1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the
DNA molecule from Franklin’s X-ray.
(1953)
Watson & Crick proposed…
DNA is made of 2 long strands of
nucleotides arranged in a specific way
DNA has specific pairing between the
nitrogen bases:
“Complementary Rule”
ADENINE – THYMINE
CYTOSINE - GUANINE
DNA Double Helix
5
O
3
3
O
P
5
O
C
G
1
P
5
3
2
4
4
2
3
1
P
T
5
A
P
3
O
O
P
5
O
3
5
P
What do we know….
• DNA is copied (replicated) during
the_________
stage of the cell cycle.
S
nucleus of the cell.
• This occurs in the __________
• This process is called-
DNA Replication
DNA Replication
The DNA is copied to produce
2 IDENTICAL strands following.
Exact copies are produced
because of the base pairing
rules:
A always bonds with T
G always bonds with C
DNA Template
Parental DNA
New DNA
Each ½ strand
of the original
DNA serves as a
template.
DNA Replication
• Semiconservative Model:
Watson and Crick showed: the
two strands of the parental
molecule separate, and each
functions as a template for
synthesis of a new
complementary strand.
.
Replication Quiz
1. Why is replication necessary?
2. When and where does replication
occur?
3. Describe how replication works.
4. Use the complementary rule to
create the complementary strand:
A---?
G---?
C---?
T---?
A---?
G---?
A---?
G---?
C---?
A---?
G---?
T---?
Replication Quiz
1. Why is replication necessary?
So both daughter cells will have exact
copies of the chromosomes.
2. When and where does replication
occur?
Inside the nucleus, during S phase of the
cell cycle.
3. Describe how replication works.
Enzymes unzip DNA and complementary
nucleotides join each original ½ strand.
4. Use the complementary rule to
create the complementary strand:
A---T
G---C
C---G
T---A
A---T
G---C
A---T
G---C
C---G
A---T
G---C
T---A
We know….
• The nucleus is the control center of the
cell.
• Chromosomes are inside the nucleus.
• Chromosomes are long strands of DNA
So…….
How does DNA control the processes that
occur inside a cell and the phenotypes of
the organism?
(1961)
Watson & Crick proposed…
• …DNA controlled cell function by serving
as a template for PROTEIN structure.
• Remember: AMINO ACIDS are the
building blocks of proteins.
• What organelle makes proteins?
Ribosomes
• How does the DNA communicate with the
ribosomes?????
Genetic Diversity…
Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.
The Code of Life…
• The “genetic code” of the chromosome is
the SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…
AMAZING DNA FACTS…
• DNA from a single human
cell extends in a single
thread for almost 2 meters
long!!!
• It contains information
equal to some 600,000
printed pages of 500 words
each!!!
(a library of about 1,000 books)
LET’S REVIEW DNA…
1. Summarize the relationship between
genes & DNA.
2. Describe the overall structure of the
DNA molecule.
3. What are the 4 kinds of bases?
4. How is the “message” sent from the
DNA to the ribosomes?
5. How are proteins made correctly?