Upload
vannga
View
214
Download
0
Embed Size (px)
Citation preview
Major Events in Genetics
A gene is a genetic sequence that codes for an RNA. In protein coding genes, the RNA codes for a protein.
A gene is a coding unit
DNA is the genetic material of bacteria, viruses and
animal cells
DNA, genetic material of bacteria
• The bacterium Pneumoccocus kills mice by causing pneumonia
• Pneumoccocus virulence is determined by its capsular polysacharide – component of cell surface allows the bacteria to escape
destruction by the host. • Several types of pneumoccocus have different types
of polysacharides. – Two groups S (smooth) and R (rough)
GRIFFITH
GRIFFITH
1928…
• Some properties from dead S-type bacteria can transform the live R-type bacteria and render it virulent (S-type)
Transforming Principle is DNA
Avery, MacLeod e McCarty
Bacteriophage
Bacteriophages attacking a bacteria
Il fago T2 e il suo ciclo vitale
Alfred Hershey and Martha Chase – Performed experiments showing that DNA is the genetic
material of a phage known as T2 – Used radioactive isotopes for labeling – Sulfur isotope, 39S, to label the protein – Phosphorous isotope, 32P, to label the DNA
HERSHEY e CHASE
Animal cells
• Cells that lack Thymidine kinase synthesize TK after transfection and survive in the absence of TK
• Not only DNA is the genetic material of the cells but DNA can be transferred among species and remain functional
Rosalind Franklin
La diffrazione ai raggi X permette di ricavare informazioni circa la struttura delle molecole.
Rosalind Franklin and Maurice Wilkins
• Were using a technique called X-ray crystallography to study molecular structure
• Rosalind Franklin – Produced a picture of the DNA molecule using this
technique – Already determined that the sugar-phosphate ladder was
on the outside of the molecule – Wilkins received Nobel Prize w/ W & C in 1962
James Watson and Frances Crick
• Watson and Crick published an article in the same Nature issue as Wilkins and Franklin in April 1953 that DNA was a double helix – Through observations of the X-ray
crystallographic images of DNA
Race to the structure
• Watson and Crick reasoned that there must be additional specificity of pairing
– Dictated by the structure of the bases • Each base pair forms a different
number of hydrogen bonds – Adenine and thymine form two bonds,
cytosine and guanine form three bonds
Race to the structure
A-DNA e B-DNA: Doppie eliche destrorse che portano rispettivamente 10,9 e 10 coppie di basi per giro completo dell’elica. Nella cellula il DNA si trova tipicamente come forma B, la forma A si riscontra solo in condizioni di umidità relativamente bassa.
Z-DNA: Elica sinistrorsa con 12 paia di basi per ogni giro completo dell’elica. Elica sottile ed allungata con solco minore profondo e solco maggiore poco evidente. Associato a particolari sequenze di basi, come basi puriniche che si alternano a basi pirimidiniche.
3 PROPRIETA’ DEL MATERIALE GENETICO: - Consente di contenere grandi quantità di informazioni - Consente una replicazione fedele con meccanismo di copiatura - Consente di tradurre le istruzioni in esso contenute in un fenotipo.
Strutture particolari dell’RNA e del DNA
Cromosomi dei procarioti -singolo cromosoma di DNA doppio filamento circolare -in alcuni casi un cromosoma principale ed uno o più cromosomi più piccoli (se non è indsipensabile=plasmide) Organizzato in NUCLEOIDE come DNA superavvolto
Cromosomi degli eucarioti -tipicamente numero diploide di cromosomi in tutte le cellule somatiche -cromosomi organizzato in cromatina con proteine istoniche e non-istoniche
- Domini di DNA ad ansa ancorati ad un’intelaiatura strutturale filamentosa all’interno della membrana nucleare = MATRICE NUCLEARE. - Sequenze di DNA associate a proteine della matrice nucleare = MAR (matrix attachment regions). -MAR generalmente fiancheggiano geni trascrizionalemnte attivi e regioni in attiva replicazione.
Cromatina: -eterocromatina facoltativa e costitutiva -eucromatina