I. DNA is the genetic material

A. Time Line1. 1866- Mendel's Paper2. 1875- Mitosis worked out3. 1890's- Meiosis worked out4. 1902- Sutton connect chromosomes to Meiosis (pg. 286)

a. Developed the “Chromosome Theory of Inheritance”. b. Mendelian factors or alleles are located on chromosomes. c. Chromosomes segregate and show independent assortment.5. 1911- Morgan (pg. 293)

a. discovered sex linked traits b. There are many genes, but only a few chromosomes. c. Therefore, each chromosome must carry a number of genes together as a “package”.6. 1928, 1944, 1950,1952 follow (see next slides)

B. Experiments show DNA is genetic material not protein 1. Frederick Griffith (1928 British) a. Studied two strains of Streptococcus

S strain has capsule and caused diseaseR strain does not have capsule and is harmless

b. saw process of transformation =

What substance was being transformed?

2. Avery, McCarty, Macleod

a. purified various chemicals from the heat-killed pathogenic bacteria (DNA, RNA, and protein).

b. tried to transform live nonpathogenic bacteria with each chemical. Only DNA worked.

a. 1944 announced that the transforming agent was DNA

b. received a lot of doubt

3. Alfred Hershey and Martha Chase (1952 American)

a. Studied bacteriophage T2 (virus that attacks bacteria)

b. Knew T2 was made of just DNA and protein

c. Knew T2 could make E. coli produce more T2

d. The experiment: next slide

Bacteria with Phages

Picture Proof

4. Erwin Chargaff 1950

a. knew components of DNA, not structure

b. analyzed base components of different organisms

c. amounts of bases vary, but are present in a characteristic ratio.

Adenines = Thymines and Guanines = Cytosines

in humans A = 30.9% G = 19.9% T = 29.4% C = 19.8%

C. Double Helix discovered by James Watson and Francis Crick 1953

1. Built models to conform to X-ray data

2. Knew arrangement of atoms, not 3D structure

3. Others working on this: Linus Pauling (California) Maurice Wilkins and Rosalind Franklin

(London)

4. Watson saw an X-ray photo of DNA produced by Rosalind while visiting Kings

a. crystallography was how photo was created

5. Published paper April 2, 1953

C. The structure

1. Monomer is a nucleotide

a. phosphate (source of the acid)

b. sugar (5 carbon)

c. nitrogen base (purine or pyrimidine)

II. DNA Replication

“ It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible coupling mechanism for the genetic material” –Watson and Crick

A. Meselson-Stahl experiment: 1950’s

1. Tested three hypotheses for DNA replication.

What data would look like with different densities.

RESULTS: semiconservative

B. Origins of Replication = 1. Bacteria 2. Eukaryotes 3. replication proceeds in both directions forming a bubble C. Replication Fork = D. Elongating a new DNA strand 1. Catalyzed by DNA polymerase 2. Nucleotides that serve as the substrate for DNA polymerase are actually nucleoside triphosphates.

a. as monomer joins, they lose 2 phosphates which provides energy for the reaction.

E. The two DNA strands are antiparallel =

1. DNA polymerase only adds nucleotides to free 3’ end of a growing DNA strand, never to a 5’ end.

2. Thus a new DNA strand can elongate only in the 5’---> 3’ direction.

3. Leading Strand

a. polymerase is located in replication fork and moves along template as fork opens.

4. Lagging Strand

a. polymerase works away from replication fork

b. Okazaki Fragments (100-200 bases long)

c. DNA ligase joins the fragments

F. Priming DNA synthesis

1. DNA polymerase can’t add nucleotides unless it is adding to an already existing chain.

a. Primase =

b. DNA polymerase III makes strand

c. DNA polymerase I later replaces the RNA nucleotides of primer with DNA

d. For lagging strand, each fragment must be primed, then primers are converted to DNA before ligase joins fragments.

G. Other proteins assisting replication1. Helicase =2. Single-strand binding protein =3. Topoisomerase =

H. Enzymes Proofread and repair mistakes 1. Mismatch Repair = a. A DNA polymerase does this as

soon as nucleotide is added b. other proteins do this as well

(they continually monitor) 2. Excision Repair = a. enzyme nuclease cuts segment

of strand containing damage b. resulting gap is filled (A DNA

polymerase and DNA ligase)

I. Replicating the ends of DNA strand

1. If ends are not replicated, DNA strand gets shorter and shorter

2. Prokaryotes = circular DNA, no problem

3. Eukaryotes = have telomeres at the ends of their DNAa. do not contain genesb. consist of multiple repetitions of one short nucleotide sequence

---> in humans, TTAGGGc. the # of repititions varies between 100 to 1000 or sod. protects the organism's genes from being eroded through successive rounds of DNA replication and protects DNA from unwinding and sticking together.e. Serve as a “clock” to count how many times DNA has replicated. Telomeres are involved with the aging process.f. When the telomeres are too short, the cell dies by apoptosis Limits how many times a cell line can divide.

4. Telomerase

a. Enzyme that uses RNA to rebuild telomeres b. Can make cells “immortal”. c. Found in cancer cells. d. Found in germ cells. e. Limited activity in active cells such as skin cells f. Control of Telomerase may stop cancer, or extend the life span.

Helicase unzips/unwinds DNA at origins of replication

Single strand binding proteins hold strands apart at replication forks

Primase constructs a primer

DNA polymerase III makes strand building in the 5’--3’ direction.

DNA polymerase I replaces the primer

For lagging strand, DNA ligase joins fragments

Telomeres are present at the end of the strand so DNA doesn’t shorten

DNA is proof read for mistakes

Enzyme Summary