Question 1 Are viruses alive?

Study of viral DNA helped unravel the key to the inheritable chemical. Protein – vs- nucleic acid Virus has both and not much else.

Griffith’s Work

Beadle & Tatum 1940’s Metabolic role of gene is to make enzymes 1 gene, 1 enzyme!

1944 Avery, MacLeod, McCarty Announced that the transforming agent in Griffith’s work was DNA. Worked with bacterial transformation techniques. The world was still skeptical.

1947 Chargaff DNA is species specific The ratio of Adenine equals that of Thymine, and Guanine equals that of Cytosine. (Chargaff’s rule)

1952 Hershey & Chase Radioactively label viral coats and then viral DNA to track where those isotopes end up in the host.

Questions 2,3,4 2. Who used bacterial transformation to show DNA is the genetic material? 3. Who showed viral DNA enters its host cell. 4. Who injected mice w/ rough and smooth streptococcus cells ?

Franklin & Wilkins 1952 used X-ray crystallography to take a “photo” of the DNA

H. Watson & Crick 1953!!! 1. used Franklin’s pics (& math) to derive structure of DNA

a. structure 1) double helix 2) sides mad of alternating deoxyribose sugar & phosphate 3) rungs made of nitrogenous bases Purines (A, G) & pyrimidines (C, T) 4) 2 sides of ladder are held together by hydrogen bonds between the bases!!

5) sides of ladder are directional – 5’ end – free phosphate attached to the #5 C of the sugar 3’ end – free hydroxyl group attached to the #3 C of the sugar 6) 2 sides are up-side-down from each other 7) 1 unit of DNA is called a nucleotide Sugar, phosphate & 1 base

DNA is made of nucleotides. Nucleotides are made of Sugar, phosphate and nitrogenous base. Bases are G, A, T, C Obj. 1

Double helical shape described by Watson and Crick.

A monomer of DNA = nucleotide

T

A

C

G

Question 5 What are the three parts of nucleotide?

II. DNA Replication 1 DNA strand has MULTIPLE SITES of replication at 1 time!

Question 7 What is semiconservative replication?

A. occurs during which phase of interphase? S phase (synthesis) B. Semiconservative process- parent strand splits in ½ & each ½ is used to build a new whole

1. determined by Meselson & Stahl 1950’s

C. Controlled & Driven by Enzymes 1. helicase- unwinds the DNA helix 2. DNA polymerase- lays down the bases (5’ 3’) a. it also – proofreads the strand as it goes 3. primase – brings the RNA primer into position (for the lagging strand) a. rna primer – starting point for lagging strand

4. DNA ligase – joins the Okazaki fragments together a. Okazaki fragments – lagging strand pieces 5. Gyrase – winds the DNA molecule up

D. Direction of replication is always from the 5’ end to the 3’ end 1. problem since 1 side is up-side-down from the other

a. leading strand – grows in a continuous stream 5’ to 3’ b. lagging strand – grows in short segments as the DNA opens 1) short segments are called – Okazaki fragments 2) needs an RNA primer to use as a template because it doesn’t have a free 3’ OH group to start on!

E. Process 1. helicase- unwinds DNA opening an area called a replication fork a. topoisomerase prevents twists & knots 2. primase – brings in the RNA primer to the correct bases for the lagging strand 3. DNA polymerase – attaches to RNA primer & begins elongation of lagging strand – it doesn’t need the intermediary on the leading strand

4. leading strand is assembled continuously 5. lagging strand is assembled in short Okazaki fragments 6. ligase joins the Okazaki fragments 7. RNA primers are replaced by nucleotides (on the lagging strand) p.298

III. Problems – Mutations must be dealt with A. mismatch repair – DNA polymerase checks everything as it makes it B. Excision Repair System 1. uses enzymes to scan the DNA, detect damage, cut it out, & replace cut out section a. more than 50+ enzymes to do this

only 1 in every base pairs has an error! b. error rate is reduced to 1/10 9 base pairs or…..

Question 9 What regulates DNA replication?

Central Dogma DNA hnRNA mRNA polypeptide