– DNA functions as the inherited directions for a cell or organism.

– How are these directions carried out?

Flow of Genetic Information

Gene

DNA

RNA

Protein

Amino acid

Nucleic acids

Gene

DNA

RNA

Protein

Amino acid

Nucleic acids

– An organism’s genotype is its genetic makeup, the sequence of nucleotide bases in DNA.

– The phenotype is the organism’s physical traits, which arise from the actions of a wide variety of proteins.

Flow of Genetic Information

Phosphategroup

Nitrogenous baseA, G, C, or U

Uracil U

Sugar ribose

Nitrogenous base(A,G,C, or T)

Phosphategroup

Thymine (T)

Sugar(deoxyribose)

Phosphate

Base

Sugar

●Nucleic acids are polymers of nucleotides

– DNA, deoxyribonucleic acid– RNA, ribonucleic acid

Nucleic Acids

Review nucleotide structure:

Nucleic Acids

Nucleic Acids●Each DNA nucleotide has one of the following bases:

Adenine (A)Guanine (G)Cytosine (C)Thymine (T)

Adenine A Guanine G

Thymine T Cytosine C

● Each RNA nucleotide has one of the following bases:

Adenine (A) Guanine (G) Cytosine (C) Uracil (U)

DNA Structure

*Early 1950’s Rosalind Franklin*1953 Watson and Crick

Sugar-phosphatebackbone

NucleotideBasepair

Hydrogenbond

Bases

a DNA strandpolynucleotide

b Double helixtwo polynucleotide strands

●Nucleic Acid Structure

DNA Structure

Sugar-phosphatebackbone

Phosphate group

Nitrogenous base

DNA nucleotide

Nucleotide Thymine (T)

Sugar

Polynucleotide

DNAdouble helix

Sugar(deoxyribose)

Phosphategroup

Nitrogenous base(can be A, G, C, or T)

DNA Structure

DNA Structure

•Complementarity

”It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism … “

•Mode of DNA ReplicationSemiconservative

DNA Replication

*Overview: DNA replication

*Complementarity determines which nucleotide will be added

*Chain elongation in a 5’-to-3’ direction

DNA Replication

Initiation

*Primase

*Strands must separate•Helicases•SSBPs•DNA gyrase

*Two are antiparallel•Continuous DNA synthesis = leading•Discontinuous DNA synthesis = lagging

DNA Replication

A large team of enzymes carry out DNA replication:

•Helicases

•SSBPs

•DNA gyrase

Elongation:

•Association of polymerase

•Sliding clamp

•Primase

•DNA synthesis (DNA pol)

•Primer removal and replacement (DNA pol)

•Ligase closes the gaps

DNA Replication