DNA STRUCTURE
& FUNCTION
What are chromosomes
made of?
• One of the two Nucleic Acids
(DNA and RNA)
• DNA stands for
DeoxyRiboNucleic Acid
• DNA is a long chain of repeating
subunits called nucleotides
Nucleotide Components (parts)
• Each nucleotide
includes:
1. A deoxyribose sugar
2. A phosphate
3. One of 4 nitrogenous
bases:
•
•
•
•
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Draw and label this
picture
Who made DNA discoveries?
• Erwin Chargaff:
Draw me!
– Erwin Chargaff was a
biochemist who studied the
DNA of different organisms
– He found that for any DNA
sample:
• % adenine = % thymine
• % cytosine = % guanine
• This is known as Chargaff’s
Rule
– If there is 20% adenine what
percent of the DNA is
thymine, Guanine, and
Cytosine?
Rosalind Franklin (early 1950’s)
made X-ray photographs of DNA and figured out that
DNA was helical and had two strands
James Watson and Frances Crick (1953)
published a paper describing DNA as a double helix, or
a twisted ladder
What makes the DNA “ladder”?
alternating sugars and phosphates are the sides of the ladder
nitrogen base pairs are the rungs (steps) of the ladder
The strands of DNA run in opposite directions. This is called antiparallel. There is a 5’ and 3’ end to DNA
Base-Pairing in DNA
• Adenine (A) always
pairs with thymine (T)
– A to T (apple tree)
• Cytosine (C) always
pairs with guanine (G)
– C to G (chewing gum)
What holds together the two strands?
Hydrogen
bonding between
the base pairs
holds the two
strands of a DNA
molecule together
What are Functions of DNA?
• DNA is the genetic
information in every cell
• DNA holds the instructions
for making proteins
• The sequence of nitrogen
bases in DNA determines
the traits of an organism
• Every organism contains the
same genetic information
DNA Replication
What is DNA replication?
When DNA is
copied exactly,
making two
identical molecules
of DNA
When does DNA replication happen?
• DNA replication
takes place before
cell division
• During interphase
( as part of the s
phase)
Where does replication happen?
• DNA replication takes
place in the nucleus of
eukaryotic cells
• DNA replication takes
place in the cytoplasm
of prokaryotic cells
How does replication happen?
DNA Polymerase
• DNA polymerase
– “polymer” means “chain of”
– “-ase” means “enzyme”
• DNA polymerase is the
main enzyme (helper
protein) involved in DNA
replication
Functions of DNA Polymerase
• Adds nucleotides to the
new strands of DNA
according to base-pairing
rules and builds 5’ to 3’
• Proof reads the new strands
of DNA and corrects any
errors
The Results of DNA Replication
• DNA replication
produces two DNA
molecules that are
identical to the original
DNA molecule
• Each new DNA
molecule has one “old”
strand and one “new”
strand
Importance of DNA Replication
• Helps cells prepare for
cell division
• Ensures that every cell
in your body has a
complete, accurate
copy of your DNA
DNA and Replication POSTER
1. Draw and label the structure of DNA nucleotides (all 4)
1.
What type of sugar is in DNA….be specific
2. Identify nitrogen bases classified as purines and pyrimidines
3. Explain the contributions of the following scientists (summarize each):
1.
Rosalind Franklin, Griffith, Hersey and Chase, Chargaff, Watson and Crick
4. Draw and label the structure of DNA, drawing out the structure of
each nucleotide. Include hydrogen bases (correct number), show
5’ and 3’ ends of each strand.
1.
Use the following DNA sequence for one side: AT T C G A G G C
5. Summarize the role of the enzymes in DNA replication (3)
6. When during the cycle does Replication occur? Summarize the
steps of replication.
7. Explain how information for specifying certain traits is carried in
the DNA.