molecular genetics - ms. kropac · 2019-10-28 · molecular genetics: the study of heredity...

Molecular GeneticsDNA Structure and Organization

Sunday, November 12, 17

Brainstrom: What do we know about genetics already?


Molecular Genetics: The study of heredity

Molecular Genetics


Review: DNADNA: Deoxyribonucleic Acid

OO=P-O O

Phosphate Group

CH2

O

C1C4

C3 C2

5

Sugar(deoxyribose)

NNitrogenous base (A, G, C, or T)


DNA: Double Helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

G CP

P

PO

O

O

1

2 3

4

5

5

3

5

3

T A


DNA structureHelicalDouble StrandedStrands run antiparallel

3’ to 5’ and 5’ to 3’Phosphate starts 5’ end and the hydroxyl starts the 3’ end


Base PairsPurines (2 rings)

1)Adenine2)Guanine

Pyrimidines (1 ring)1) Cytosine2) Thymine



1)Adenine2)Guanine


A or G



1)Adenine2)Guanine


A or G

T or C


Base Pairs

Purines and Pyrimidines are held together by hydrogen bonds

2 bonds between A and T3 bonds between C and G

P

P

P

O

O

O

1

23

4

5

5

3

3

5

G CP

P

PO

O

O

1

2 34

5

5

3

5

3

T A


Base Pairs

A always binds with TC always binds with GCalled complementary base pairing

P

P

P

O

O

O

1

23

4

5

5

3

3

5

G CP

P

PO

O

O

1

2 34

5

5

3

5

3

T A


History of DNA Structure


Fredrich Miescher (1869)

Investigated pus cells, and the non-protein compound found in the nucleus

Nuclein (later named DNA)


Frederick Griffith (1928)

Studied good(S) and bad(R) bacteria



Mice injected with heat killed S-strain mixed with living R strain somehow passed along its deadly properties



Idea of “transforming principal” (the passing on of information from one strain to another)


Alfred Hershey and Martha Chase (1952)

Worked with bacteriophage marked with S and P



First marked protein coat with S

Material NOT passed on



Then marked DNA with P

Material IS passed on



Results finally determined that DNA was the hereditary material.


Erwin ChargaffLooked at DNA differences between species

Discovered that nucleotides were present in characteristic proportions across species


Erwin Chargaff

Chargaff’s Rule: The percent composition is the same for adenine and thymine, and the percent composition is the same for guanine as cytosine


Rosalind FranklinUsed X-ray diffraction to capture DNA on film

Determined DNA had a helical structure

Determined nitrogenous bases in the centre, sugar phosphate backbone on the outside


James Watson and Francis Crick

Constructed a 3D model of DNA

Credited with discovering double helix structure

Awarded the Nobel Prize in 1962


molecular genetics - ms. kropac · 2019-10-28 · molecular genetics: the study of heredity...

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