Molecular Basis of Inheritance

Two strains of bacterium

were used in Griffith's experiment to demonstrate transformation, highlighting how genetic material can be transferred between organisms.

Pathogenic (strain S) and non-pathogenic(harmless) (strain R) strains were used, where heat-killed pathogenic bacteria transformed the non-pathogenic bacteria into pathogenic forms.

Transformation

Bacteria cable of transferring genetic material

now defined as a change in genotype and phenotypes due to the uptake and expression of foreign DNA.

evidence that DNA can transform bacteria

F, Griffith mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain, some living cells became pathogenic.

evidence that viral DNA can program cells

A. Hershey and M. Chase designed an experiment showing that only one od the components of T2 (DNA/ protein) enters E. coli cell during infection.

They concluded that the injected DNA of the phage provides the genetic information.

Chargaff rules (1950) - additional evidence that DNA is the genetic material

The base composition of DNA varies between species and the amount of adenine = thymine, while the amount of guanine = cytosine.

X-ray crystallography

Wilkins and Franklin used this technique to study molecular structure, helping to determine how DNA structure accounts for its role in heredity.

what did Franklin's x-ray crystallograph images of DNA show

DNA is a double helix

the helix is 2nm

.34nm of space between the nitrogen bases

One full turn every 10 bp = 3.4 nm

Linus Pauling

Father of structure and function

Determined that the essence of life is not from individual molecules but from the interactions between them

Studied how antibodies and enzymes work

Studied the molecular structure of sickle cell anemia

Discovered the Alpha Helix structure for proteins

base structure pairing (Watson and Crick)

Purine + Pyrimidine : A = T(U) , G = C

issue with pairing purine + purine and pyrimidine + pyrimkdine

Purine + Purine = too wide of a structure for the helix

Pyrimidine + Pyrimidine = too narrow for the helix

Watsons and cricks semiconservative model prediction

Predicts that when a double helix is replicated, each daughter molecule will have one old strand (conserved from the parent molecule) and one new strand

Conservative model of DNA replication

Original DNA is kept intact and creates a completely new copy

Dispersive model of DNA replication

During replication each strand is a mix of old and new strands

Origins of replication

the particular site where two DNA strands separate opening a replication “bubble”,

how eukaryotic replication different from bacteria replication

Many replication points, takes an hour to replicate entire genome

prokaryotic replication

1 point of origin

1-2 types of polymerases

No ends to synthesize

eukaryotic replication

C value paradox

Multiple points of origin

Telomere replication distinctive

4 types of polymerases

DNA Polymerase

enzyme used is replication,

catalyze the synthesis of new DNA at a replication fork

Most DNA polymerases require a primer & a DNA template strand

C value paradox

?

synthesizing new DNA strand

Primase can start an RNA chain from scratch & adds RNA nucleotides one at a time using the parental DNA as a template

3′ end serves as the starting point for the new DNA strand

(DNA polymerases require a primer to which they can add nucleotides, The initial nucleotide strand is a short RNA primer, This is synthesized by the enzyme primase)

Antiparallel Elongation

arrangement of two DNA stands in opposite directions, elongates only in the 5’ to 3’ direction

synthesis of lagging strand

synthesis leading strand

nucleotide excision repair of damaged DNA

evolutionary significance of altered DNA nucleotides

Helicases

enzymes that untwist the double helix at the replication forks

single - single binding proteins

binds to and stabilize single stranded DNA

Topoisomerase

relieves the strain of twisting of the double helix by breaking, swiveling, & rejoining DNA strands

Primase

Synthesize short RNA primer to it can be added to the DNAs original nucleotide

dehydration reaction

how monomers join the DNA strand, losing two phosphate groups as a molecule pyrophosphate

dATP

supplies adenine to DNA and differs from ATP as it has deoxyribose instead of ribose