Genetic Material

The genetic material of a cell or an organism refers to those materials found in the nucleus, mitochondria and cytoplasm, which play a fundamental role in determining the structure and nature of cell substances, and capable of self-propagating and variation.

1. Marwan Alhalabi
Professor of Reproductive Medicine and Infertility,
Damascus University
Head of Assisted Reproduction Unit, Orient Hospital
President of Middle East Fertility Society
President of Syrian Society of Obstetricians and
Gynecologists

2. •The progeny of organism develops characters similar to that
organism
•The resemblance of offspring to their parents depends on
the precise transmission of principle component from one
generation to the next
•That component is-
The Genetic Material

3. The genetic material of a
cell or an organism refers to
those materials found in
the nucleus, mitochondria
and cytoplasm, which play
a fundamental role in
determining the structure
and nature of cell
substances, and capable of
self-propagating and
variation.

4. DNA
Protein
RNA
Protein,RNAand
DNAwere thought
as genetic material.
But many
experiments
suggest DNA as
genetic material
rather than protein
and RNA

5. • Must carry information
–Cracking the genetic code
• Must self replicate
–DNA replication
• Must allow for
information to change
–Mutation
• Must govern the
expressionof the
phenotype
–Gene function

6. RNA
DNA
PROTEIN
DNA

7. •The process of identification of genetic material began in
1928 with experiments of Griffith and concluded in 1952
with the studies of Hershey and Chase.
•Between these two experiments other three scientists,
Avery, Macloedand McCarty were did an experiment to
identify the genetic material.

8. •1952 Alfred Hershey and
Martha Chase
•New York scientists
•Performed an experiment that
settled the controversy
•Proved that DNA carries the
genetic material

9. •Bacteriophage:avirusthat
infectsbacteria.
•WhenBacteriophagesinfect
bacterialcellstheyproduce
moreviruses.
•Thevirusesarereleased
whenthebacterialcells
rupture.

10. •How does the bacteriophage
reprogram the bacterial cell
to make more viruses?
•Does the bacteriophage
DNA, the protein, or both
give instructions to the
bacteria?

11. •Bacteriophage DNA was labeled with radioactive phosphorus
(
32
P)
•Bacteriophage protein was labeled with radioactive sulphur
(
35
S)
•only the bacteriophage DNA (as indicated by the
32
P) entered
the bacteria and was used to produce more bacteriophage
•Conclusion: DNA is the genetic material

12. •ThefinalevidencethatDNAtransmitsgeneticinformation
wasprovidedbyHersheyandChasein1952
•TheyexperimentedwithT2bacteriophages,virusesthat
attackbacteria.

16. •1928
•Fredrick Griffith
•Bacteriologist
•Trying to prepare a
vaccine against
pneumonia

26. Controls

27. •Twotypes,orstrains,ofS.pneumoniae
•Firststrainisenclosedinacapsulecomposedof
polysaccharides.
•Capsuleprotectsthebacteriumfromthebody’s
defensesystem.
•Formssmooth-edges(S)whengrowninapetridish
•Helpsmakethemicroorganismvirulent,orableto
causedisease.

28. •Second strain lacks the polysaccharide capsule
and does not cause disease.
•Forms rough-edges (R) when grown in a petri dish

29. •TheharmlessRbacteriahadchangedand
becamevirulentSbacteria.
•Transformationisachangeingenotype
causedwhencellstakeupforeignmaterial.

30. •Based on these observations he concluded that some of
the cells of type II R had changed into type III S due to
influence of dead type III S cells
•He called this phenomenon as transformation
•Principle Component of type III S cells which induced
the conversion of type II R cells into type III S was
named transforming principle.

31. The Structure of DNA

43. •Double Helix
•Nucleotide
•Deoxyribose
•Base-pairing Rules
•Complementary Base
Pair

44. •1953—James Watson and Francis Crick
determined the structure of the DNA
molecule to be a
double helix
•2 strands of nucleotides twisted around
each other

46. •TheyproposedthatDNA
asarighthandeddouble
helixwithtwopoly
nucleotidechainsare
coiledaboutoneanother
inaspiral.
(Watson and Crick,1953)

48. •Rosalind Franklin contributed
to this discovery by producing
an X-ray crystallographic
picture of DNA
•Determined helix was a uniform diameter and composed
of 2 strands of stacked nucleotides
DNA = tightly wound helix

50. •Nucleotides are the monomeric units that
make up DNA
Ø3 main parts:
Ø5 carbon sugar—deoxyribose
ØPhosphate group
ØNitrogenous base

51. Nitrogenous bases
Pyrimidines: single-ring structures
Thymine (T)
Cytosine (C)
Purines: larger, double-ring structures
Adenine (A)
Guanine (G)

54. •GenerateandstoreenergyinATPform
(eukaryotecells).
•HaveDNAandmtDNAisdouble
strandedcircularmolecule.
•CircularmtDNAhas37genes.1part(D-
loop)does’tcontaingenes.Why?
Becomesdisplacedduringreplication.

56. Notice:
DNA strands run in opposite directions =
ANTI-PARALLEL
P
S
S
S
P P
P
S
GC
AT

57. Chargaff’s base pairing rule:
Percent of adenine = percent of thymine (A=T)
Percent of cytosine = percent of guanine (C=G)
A+G = T+C (or purines = pyrimidines)
(Chargaff et al.,1950)

58. Erwin Chargaff showed the
amounts of the four bases on
DNA ( A,T,C,G)
In a body or somatic cell:
A = 30.3%
T = 30.3%
G = 19.5%
C = 19.9%
T A
G
C

59. ØThreemajorforms:
üB-DNA
üA-DNA
üZ-DNA
vB-DNA
isbiologicallyTHEMOSTCOMMON
üItisahelixmeaningthatithasaRighthanded,orclockwise,spiral.
üIdealB-DNAhas10basepairperturn
üSoeachbaseistwisted36
o
relativetoadjacentbases.
üBasepairare0.34nmapart.
üSocompleterotationofmoleculeis3.4nm.
üAxispassesthroughmiddleofeachbasepairs.

61. üMinor Groove is Narrow, Shallow.
üMajorGroove is Wide, Deep.
üThis structure exists whenplenty
of water surrounds molecule and
there is no unusual base sequence
in DNA-Condition that are likely to
be present in the cells.
üB-DNAstructure is most stable
configurationfor a random
sequence of nucleotides under
physiological condition.

62. A-DNA
üRight-handed helix
üWider and flatter than B-DNA
ü11 bp per turn
üIts bases are tilted away from
main axis of molecule
üNarrow Deepmajor Groove and
Broad, Shallow minor Groove.
üObserved whenless water is
present. i.e.Dehydrating condition.
üA-DNA has been observed in
two context:
•Active site of DNA polymerase
(~3bp)
•Gram (+) bacteria undergoing
sporulation

63. Z-DNA
•A left-handedhelix
•Seen in Condition of Highsalt concentration.
•In this form sugar-phosphate backbones zigzagback
•and forth, giving rise to the name Z-DNA (for zigzag).
•12base pairs per turn.
•Adeep Minor Groove.
•NoDiscernible Major Groove.
•Part of some active genes form
Z-DNA,suggesting that Z-DNA
may play a role in regulating
gene transcription.

64. Property B-DNA A-DNA Z-DNA
Strand Antiparallel AntiparallelAntiparallel
Type of Helix
Right-handed Right-handed Left-handed
Overall shape Long and
narrow
Short and wideElongated and
narrow
Base pair per turn 10 11 12
Distance between adjacent
bases
0.34 nm 0.23 nm 0.38 nm
Pitch/turn of helix 3.40 nm 2.82 nm 4.56 nm
Helical Diameter 2.0 nm 2.3 nm 1.8 nm
Tilt/inclinationof bp to axis 1
0
20
0
9
0

65. Property B-DNA A-DNA Z-DNA
Major Groove Wide &Deep Narrow & DeepNo discrenible
Minor Groove Narrow,shallowBroad,ShallowNarrow, Deep

68. •Twostrandswindabouteachother
inaright-handedmanner
•Diameter:~20Å
•Basesperturn:10(~34Å)
•Amajorandaminorgroove
20Å
Major
Minor

69. •One strand of DNA
goes from 5’ to 3’
(sugars)
•The other strand is
opposite in direction
going 3’ to 5’ (sugars)

70. •DNA is wrapped around
abundant nuclear
proteins called Histones
•This forms a complex
called a Nucleosome
•Histones are H1, H2A,
H2B, H3, H4