• Defined: Molecule that stores genetic information

• Nucleotides: Three repeating units of nucleic acids–1) Sugar–2) Phosphate Group–3) Nitrogen Base

• Millions of nucleotides per strand of DNA

• Sugar (Deoxyribose) connects with the phosphate group

• 4 Different Bases:– Adenine (A)– Thymine (T)– Guanine (G)– Cytosine (C)

• Rule: A always joins with T• Rule: C always joins with G• Human DNA: ~3 billion pairs

• James Watson and Francis Crick identified DNA’s structure in 1953

• Double Helix: spiral shape of DNA• Nucleotide strands are connected by a hydrogen bond

• Defined: Process of copying DNA

– During interphase (S-stage)

• Step 1: DNA Helicase “unzips” the two DNA strands (breaks the H bonds)

• Step 2: Free floating nucleotides (A, T, C, G) match up

• Step 3: DNA Polymerase reconnects the two strands

Step 1:

DNA Helicase “unzips” the two DNA strands (breaks the H bonds)

Step 2:Free floating nucleotides (A, T, C, G) match up

Step 3:DNA Polymerase reconnects the two strands

Both strands are identical

Both strands are a mix of old and new nucleotides

Video Clip

• Mutation: change in DNA sequence

• Mutations can be corrected– Enzyme “proofreads” DNA

and check/correct errors• Pre-repair: 1 in 10,000

nucleotides has an error• Post-repair: 1 in 1 billion

nucleotides has an error

enzyme

Kobe Kuiz• Name the three parts of a DNA nucleotide.

• Name the four nitrogen bases and how they pair with others.

• Fill in the missing DNA nucleotides:

A C ? T ? ? ? G C T ? ? A ? C ? T T

? ? C ? T A T ? ? ? C A ? G ? G ? ?

• List what takes place during the three stages of DNA replication.

• Where is the DNA mutation?

T A G G C C T G T C G A A C A G T

A T C C G G A C A A C T T G T C A