Unit 10 : DNA Structure & Replication

structure of a nucleotide

1. phosphate group

2. 5 C sugar (dna-deoxyribose, RNA-ribose)

3. nitrogenous base (dna: A,T,G,C rna: A,U,G,C)

differences between dna and rna

1. 5 C sugar: dna-deoxyribose; rna-ribose

2. DNA-double stranded; RNA-single stranded

3. DNA-thymine; RNA-uracil

4 dna bases and 4 rna bases

• DNA: adenine, thymine, cytosine, guanine

• RNA: adenine, uracil, cytosine, guanine

base pairing rules for DNA and RNA

• DNA: adenine bonds to thymine; cytosine bonds to guanine

• RNA: adenine bonds to uracil; cytosine bonds to guanine

chargaff’s rule

• in a given sample of DNA, the amount of A=T and C=G

purines vs. pyrimidines

• purines: double ring structure, adenine and guanine

• pyrimidines: single ring structure, cytosine and thymine (also uracil in rna)

  • purines always bond to pyrimidines

rosalind franklin

• used x-ray crystallography to determine the structure of dna

watson and crick

• credited with discovering the structure of dna

structure of dna

• sugar phosphate backbone; nitrogen bases form the “rungs”

• all the bonds are covalent EXCEPT the hydrogen bonds holding the nitrogen bases together in the center

where replication occurs

• the nucleus

template for replication

• dna (both strands)

enzyme required for replication

• dna polymerase (main enzyme; polymerizes dna nucleotides and proofreads)

• helicase (unwinds dna double helix), primase (makes an rna primer)

final product of replication

• exact copy of dna

error rate of replication

• 1 in 10,000,000,000 bases

definitions

• helix: spiral

• complementary base pairs: in dna, A bonds with T and C bonds with G

• replication: copying dna

• semi-conservative replication: at the end of replicatIon, each new DNA strand is made up of two strands; one is an old, template strand and one is a new strand

• mutagen: anything that causes a mutation (example: UV light, some chemicals, radiation)