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Announcements. Exam 2 next week: 10/17, 18, and 20 . Same format as exam 1, a bit shorter. You will need a bluebook again. Answers from exam 1 will be removed from lab when exam 2 answers go up. Homework/ problem set 4 (15 pts) due next week in lab.

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slide1

Announcements

Exam 2 next week: 10/17, 18, and 20. Same format as exam 1, a bit shorter. You will need a bluebook again.

Answers from exam 1 will be removed from lab when exam 2 answers go up.

Homework/ problem set 4 (15 pts) due next week in lab.

Handout for transformation lab available Monday.

slide2

Homework (15 pts) - BIO 326 Genetics

  • Due 10/15,16 in lab
  • 1. Are sex chromosome aneuploids or autosomal aneuploids more common in humans? Give one reason to explain your answer.
  • 2. Red-green color blindness is an X-linked recessive disorder. A young man with a 47, XXY karyotype (Klinefelter syndrome) is color blind. His 46, XY brother is also color blind. Both parents have normal color vision. Where did the nondisjunction occur that gave rise to the young man with Klinefelter syndrome?
  • 3. Would a human with 2 X chromosomes and 2 Y chromosomes be male or female?
  • 4. Predict the sex of Drosophila with the following chromosome compositions (A = haploid set of autosomes):
  • a. 4X 4A
  • b. 3X 4A
  • c. 1X 2A
  • 5. Mark true or false for the following relations regarding the percentages of bases in a double-stranded DNA molecule:
  • a. A + T = G + C
  • b. A + G = T + C
  • c. A + C = G + T
  • d. A + T = 1.0
  • C + G
  • e. A = T
  • G C
slide3

Review of Last Lecture

Polyploidy

Variation in structure/arrangement of chromosomes

- deletion

- duplication

- inversion

-translocation

What are criteria for genetic material?

slide4

Outline of Lecture 19

I. Evidence that DNA is genetic material

II. DNA and RNA: Composition and Function

III. History of solving the structure of DNA

slide5

I. DNA Structure and analysis

What is the genetic material?

Chromosomes contain protein and DNA - which is it?

What must genetic material do?

1. Replication

2. Storage of information

3. Expression of information

4. Variation by mutation - evolution

slide7

Is the Genetic Material Protein or DNA?

  • Many favored proteins until the mid-1940’s.
  • DNA is simple chemically (4 nucleotides known); how could it then hold complex genetic information?
  • Proteins are much more complicated chemically (20 amino acids) and more abundant; perhaps they hold genetic information.
slide8

Evidence for DNA as Hereditary Molecule

  • Transformation studies
    • Griffith (1927)
    • Avery, MacLeod and McCarty (1944)
  • Hershey-Chase experiment (1952)
  • Chargaff’s Rules
  • Molecular Studies
slide9

Griffith’s Transformation Expt.

Bacteria Used

Living smooth

(virulent)

Living rough

(avirulent)

Killed smooth

Living rough +

killed smooth

Conclusion:

Killed smooth converted living rough to virulent cells

A Transforming Principle (some smooth component) is responsible.

Expected mouse to live

slide10

Avery, MacLeod, and McCarty Expt:DNA is the “Transforming Principle”

IIIS

IIIS filtrate

IIR + IIIS filtrate

Active factor

Is DNA!

slide11

Hershey-Chase Experiment

  • Study of infection of E. coli by T2 phage
  • Radioactively labeled DNA and protein:
    • 32P atom is in phosphate molecules in DNA and RNA, only at low levels in protein (phosphorylated proteins).
    • 35S atom is in sulfur-containing amino acids (cysteine and methionine); not in DNA or RNA.
slide12

Phage Made Radioactive

Non-radioactive medium

+ bacteria

slide13

Phage Infect Cells

32P Phage

35S Phage

Label

(protein)

is outside

Label

(DNA)

is inside

slide14

Is DNA the genetic material in eukaryotes?

Indirect evidence -DNA and RNA absorb UV Light

  • Action spectrum of UV-induced mutations in bacteria correlates with absorption spectrum of UV light for nucleic acids, not protein.
  • Can use to quantify amounts of nucleic acid and protein.

Direct evidence?

slide16

Reconstitution of Hybrid TMV (Fraenkel-Conrat & Singer)

Strain 1

Strain 2

Lesions corresponded

to RNA

slide17

II. Structure of DNA/RNABases and Sugars

pyrimidines

T

C

U

purines

G

A

Ribose

sugars

slide18

Bases and Sugars in DNA and RNA

  • In DNA: deoxyribose + A, T, G or C
    • dA deoxyadenosine
    • dT deoxythymidine
    • dG deoxyguanosine
    • dC deoxycytidine
  • In RNA: ribose + A, U, G, or C
    • A adenosine
    • U uridine
    • G guanosine
    • C cytidine
slide20

dNDP’s and dNTP’s:Note Errors in the Text

deoxy

deoxy

deoxy

deoxy

dNTP (dATP)

dNDP (dTDP)

slide21

3’ to 5’ Phosphodiester Bonds Make the Sugar-Phosphate Backbone

New monomers

add here

Strand has 5’-PO4

end and 3’-OH end

slide22

Chargaff’s Rules - also evidence for DNA as genetic material

  • 1949-1953, quantified amounts of each base in DNA from different species.
  • In every species, amount of A = amount of T, and amount of G = amount of C
  • If that’s true, then A + G = C + T
  • The % GC and % AT varied from species to species, but always adds up to 100%.
slide23

III. History of structure of DNA:Rosalind Franklin and Maurice Wilkins found X-ray Diffraction Evidence for DNA Double Helix

slide26

The DNA Double Helix

DNA structure

  • Double helical
    • major, minor grooves
    • right-handed
    • bases are 3.4 Å apart (10 Å = 1 nm)
    • 10 bases/turn
  • Complementary Base Pairing
    • through H bonds: A=T, GC
  • Antiparallel Strands
    • 5’ to 3’
    • 3’ to 5’
slide29

Reading DNA Strands

Single strand of DNA:

5’-AGCATTCG-3’

3’-TCGTAAGC-5’

Complementary strand of above, usually written 5’ to 3’:

5’-CGAATGCT-3’

Double-stranded fragment is written:

5’-AGCATTCG-3’

3’-TCGTAAGC-5’

slide30

Denaturation/Renaturation

Which DNA has higher GC content and why?

slide31

Nucleic Acid Hybridization

Molecular probes can “fish out”

a specific DNA from a mixture