Molecular Biology

Mader-Chapters 13

Genetic Material

From work on Drosophila, biologists knew that genes were on chromosomes and that genes controlled heredity… What they did not know

was the molecular composition of genes

Genetic material must:1.Store information2.Be replicable3.Undergo rare change

Griffith’s Transformation Experiment (1931)… What did it prove?

There must be a transforming substance that is able to alter the phenotype of an organism

This substance was later isolated by Avery, MacLeod, and McCarty in 1944. They exposed the transforming agent to DNAase and Protease to determine that the transforming agent is DNA and not Protein.

Hershey and Chase Transformation Experiment (1952)… What did it

prove?

DNA of the virus and not the protein of the virus enters the bacteria and conducts the transformation of the bacteria into a viral factory

This experiment is predicated on the idea that DNA contains P and not S… and Protein contains S and not P

Structure of DNA

Chargaff’s rules:1. The amount of A, T, G, and C in DNA varies from

species to species but is consistent amongst species2. In each species, the amount of A=T and G=C

Watson and Crick ModelI guess we should have called it the

Watson, Crick, and Franklin Model!

Structure of DNA

Released Practice Question

Segment 1: 5 - ′ ATATGAGTAGT - 3 Segment 2: 5 - ′ ′ GCGCAGACGAC - 3′ 3 - ′ TATACTCATCA - 5 3 - ′ ′ CGCGTCTGCTG - 5′13. The sequences for two short fragments of DNA are shown above. Which of the following is one way in which these two segments would differ?

(A) Segment 1 would not code for mRNA because both strands have T, a base not found in RNA.(B) Segment 1 would be more soluble in water than segment 2 because it has more phosphate groups.(C) Segment 1 would become denatured at a lower temperature than would segment 2 because A-T base pairshave two hydrogen bonds whereas G-C base pairs have three.(D) Segment 1 must be from a prokaryote because it has predominantly A-T base pairs.

Replication of DNAReplication is Semiconservative

1. Helicase unzips the DNA2. DNA polymerase positions complimentary base pairs3. DNA polymerase joins complimentary base pairs

Meselson and Stahl’s Experiment…How did it prove that DNA Replication is Semiconservative?

DNA Replication Movies

Wiley.com_DNA Replication

HHMI 3D DNA Rep. Animation

DNA Replication

Released Question

6. When DNA replicates, each strand of the original DNA molecule is used as a template for the synthesis of a second, complementary strand.Which of the following figures most accuratelyillustrates enzyme-mediated synthesis of newDNA at a replication fork?

Prokaryotic vs. Eukaryotic Replication

There are distinct differences between prokaryotic and eukaryotic DNA Replication

Prokaryotic DNA Replication•DNA is in a single circular loop•Replication begins in one location•May occur in one direction or in both directions•10 to the 6th base pairs are added per minute•Replication complete in 20 minutes

Eukaryotic DNA Replication•DNA is in chromosomes•Begins in numerous locations •Replication fork spreads bidirectional until forks meet•Slower than prokaryotes at 500 to 5000 base pairs per minute•Replication complete in several hours