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.

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 2,3,42. 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. structure1) double helix2) sides mad of alternating deoxyribose

sugar & phosphate3) 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 sugar3’ end – free hydroxyl group attached to the #3

C of the sugar6) 2 sides are up-side-down from each

other7) 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 togethera. 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’ end1. 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 opens1) short segments are called – Okazaki

fragments2) 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 forka. 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 System1. 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 100000000 base

pairs has an error!

b. error rate is reduced to 1/109 base pairs or…..

Question 9

What regulates DNA replication?

Central Dogma

DNA

hnRNA

mRNA

polypeptide