DNA and RNA Replication
Unit 6
Something to think about..
•When a species reproduces, there is geneticcontinuity maintained from one generation tothe next.
–WHAT is responsible for this continuity?
–HOW does this continuity happen?
What is DNA?
•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 whatcauses each individual’s DNA to be unique!
–Pictured below are small segments of DNA from three organisms, howdo they compare?
Plant Mammal Bacteria
DNA Code
•If we looked at the total DNA of each of thebelow organisms, which would have DNA withthe least amount of base pairs? Why?
Plant Mammal Bacteria
Structure of DNA
•Double Helix
Double Helix
•Which 2 scientists are credited with thediscovery 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 andsugars (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 tothe next generation and to preserve geneticcontinuity
•4 Steps
DNA Replication
1.“Unzip DNA twisted ladder” (HELICASE)
–Break H bonds between bases
DNA Replication
2.Match correct nucleotidesaccording to base pairrules (DNA POLYMERASE)
–There are free floatingnucleotides in nucleus
–Remember: A-T, G-C
DNA Replication
3.Bonding-hydrogen bonds form betweenbases; and phosphates bond to sugarmolecules to form the ‘backbone’ of DNA
4.Bonding continues until 2 new strands havecompletely formed
RESULT = 2 copies of the original DNA molecule
DNA Replication
Pink = parent strand
Blue = daughter strands
DNA Replication