DNA and RNA Replication
Unit 6
Something to think about..
• When a species reproduces, there is genetic
continuity maintained from one generation to
the next.
– WHAT is responsible for this continuity?
– HOW does this continuity happen?
What is DNA?
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DNA = DeoxyriboNucleic Acid
Genetic material present in ALL organisms
Different for each individual
Found in nucleus
Polymer- nucleic acids
– Monomer = nucleotides
• What three ‘parts’ are
nucleotides made of?
a. Phosphate group
b. Sugar
c. nitrogen base (A,T,C,G)
Nucleotides
• Monomer made of the following 3 parts:
– 1. a 5-Carbon sugar group (deoxyribose)
– 2. a phosphate group
– 3. a nitrogen base – 4 different possibilities!
(5 Carbon sugar)
4 Nitrogen Bases
Purines
Pyrimidines
Adenine, Guanine
Cytosine, Thymine
A, G
C, T
2 carbon rings
1 carbon ring
“Pure As Gold”
Nitrogen Base Pairing
• Adenine ALWAYS pairs with Thymine
– 2 hydrogen bonds
• Cytosine ALWAYS pairs with Guanine
– 3 hydrogen bonds
• “AT C-G”
DNA Code
• The order of the 4 nitrogen bases is what
causes each individual’s DNA to be unique!
– Pictured below are small segments of DNA from three organisms, how
do they compare?
Plant
Mammal
Bacteria
DNA Code
• If we looked at the total DNA of each of the
below organisms, which would have DNA with
the least amount of base pairs? Why?
Plant
Mammal
Bacteria
Structure of DNA
• Double Helix
Double Helix
• Which 2 scientists are credited with the
discovery of the structure of DNA?
– James Watson & Francis Crick (1953)
– Double Helix
– Nobel Prize for Medicine in 1962
Structure of DNA
1. Double Stranded
2. “Backbone” = alternating phosphates and
sugars (deoxyriboses)
3. Middle Portion = bases
– A-T (bonded by 2 H-bonds)
– C-G (bonded by 3 H-bonds)
4. In 3D: forms twisted ladder (spiral staircase)
Double Helix
On the diagram on the right, circle 1 nucleotide
DNA Replication
• DNA copying
• Why?
– in order for genetic material to be passed on to
the next generation and to preserve genetic
continuity
• 4 Steps
DNA Replication
1. “Unzip DNA twisted ladder” (HELICASE)
– Break H bonds between bases
DNA Replication
2. Match correct nucleotides
according to base pair
rules (DNA POLYMERASE)
– There are free floating
nucleotides in nucleus
– Remember: A-T, G-C
DNA Replication
3. Bonding-hydrogen bonds form between
bases; and phosphates bond to sugar
molecules to form the ‘backbone’ of DNA
4. Bonding continues until 2 new strands have
completely formed
RESULT = 2 copies of the original DNA molecule
DNA Replication
Pink = parent strand
Blue = daughter strands
DNA Replication
• DNA Replication Simulation