What is Molecular Biology?

“Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology, particularly genetics and biochemistry.” Wikipedia

(from Weaver, “Mol. Biol.”)

Lecture 1 - DNA is the Genetic Material

The molecules of a cell...

“The Central Dogma”

DNA RNA PROTEIN

How do we know that DNA is the genetic material?

VS

MCB, 7th Ed, Figure 1.6

(from Weaver, “Mol. Biol.”)

The Hershey-Chase Experiments, 1952 Phage PROTEIN labeled

Phage

Bacterium

Phage DNA labeled

Bacterium

Phage

What molecule entered the bacterium to

code for more phage?

(from Weaver, “Mol. Biol.”)

DNA/ RNA - chains of nucleic acids Nucleotide: 1. 2. 3. (Note - “nucleoside” is just the pentose + base)

FIG 2-16

DNA/ RNA - chains of nucleic acids

FIG 2-16

RNA bases: A G C U

DNA bases: A G C T

The Bases

FIG 2-17

DNA - 5’ to 3’ directionality

FIG 4-2

The 3-D Structure of DNA

The 3-D Structure of DNA • Franklin’s X-ray diffraction data (1952): DNA is a helix, at least 2 strands

The 3-D Structure of DNA • Chargaff’s rules (1947): #Purines = #Pyrimidines (A = T, G = C BUT A + T = G + C in DNA)

The 3-D Structure of DNA

Nobel Prize for Medicine 1962 - Watson, Crick, Wilkins

• Watson and Crick (1953): model of double helix with purines base-pairing with pyrimidines

strands are antiparallel - opposite 5’ to 3’ directions

~ 10

.1bp

/ 1 tu

rn

FIG 4-3

O

O

H 3’

H 3’

The DNA Double Helix

CH3

Protein-DNA Interactions

•  helical DNA has major and minor grooves •  atoms at the edges of bases are accessible •  proteins can “read” the bases - sequence specific protein binding to DNA •  protein binding can bend DNA

-altered structure -regulation of gene expression

TBP binds specific DNA sequences, bends the DNA, enabling transcription

FIG 4-5

•  base pairs are complementary •  bonds connect the 2 DNA strands •  denaturation (melting) •  Tm

•  How can DNA be denatured?

O

O

H 3’

H 3’

Separation of DNA strands

Detection of DNA denaturation

FIG 4-7

What would happen to the absorption if you took the denatured dsDNA and slowly chilled it on ice?

If 2 samples of genomic DNA have different Tm’s, can they be from the same organism?

Higher GC content = Higher Tm

Why?