DNA and RNA ReplicationUnit 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?

• 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 groupb. Sugarc. 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 BasesPurines 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 Stranded2. “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