Download - Το Πειραμα του Griffith 1928
-
8/8/2019 Griffith 1928
1/93
-
8/8/2019 Griffith 1928
2/93
frederick griffithThe Pneumonia Guy
In 1928, a medical official at the Ministry ofHealth in London, England studied thepossibility of creating a vaccine against a typeof pneumonia called Streptococcus
pneumonia. His name was Frederick Griffith.The disease Frederick was working with was aserious cause of death in this period of time.
Griffiths experiments contained two strains
of a type of bacteria commonly calledpneumococci, which mainly caused his killerdisease. One of the two strains was deadly tohumans and the other was harmless.
-
8/8/2019 Griffith 1928
3/93
The only physical difference Griffith could find was that the deadly strain had asmooth-coated surface made of sugar surrounding it, and the harmless strain hada rough-coated surface with nothing protecting it. The reason the sugar-coatedstrain was so lethal was because the human white blood cells had trouble
penetrating the smooth, sugary coat.When testing his experiments, Griffith used lab mice to prove his theories. First,
Griffith injected the smooth-coated strain into the mice. As expected, they allcaught pneumonia and died. Then, Griffith tried to kill some of the deadly strainwith heat and injected it into the mice. Amazingly, the mice didnt getpneumonia. Next, he injected the rough-surfaced bacteria into the
mice.
-
8/8/2019 Griffith 1928
4/93
-
8/8/2019 Griffith 1928
5/93
-
8/8/2019 Griffith 1928
6/93
Griffith's experiment discovering a "transforming principle" in heat-killed virulent smoothpneumococcus that enables the transformation of rough non-virulent rough pneumococcus.
-
8/8/2019 Griffith 1928
7/93
Bacteria have no sexual reproduction in the
sense that eukaryotes do. The
haveno alternation of diploid and haploid
generations
no gametesno meiosis
But the essence of sex is genetic
recombination, and bacteria do have three
mechanisms to accomplish that:
transformation
conjugationtransduction
-
8/8/2019 Griffith 1928
8/93
Transformation
Many bacteria can acquire new genes by
taking up DNA molecules (e.g., a plasmid) fromtheir surroundings. The ability to deliberately
transform the bacterium E. coli has made
possible the cloning of many genes
including human genes and the
development of the biotechnology industry.
-
8/8/2019 Griffith 1928
9/93
-
8/8/2019 Griffith 1928
10/93
Streptococcus pneumoniae (pneumococci)
growing as colonies on the surface of a culture
medium. Left: The presence of a capsulearound the bacterial cells gives the colonies a
glistening, smooth (S) appearance. Right:
Pneumococci lacking capsules have produced
these rough (R) colonies. (Courtesy of Robert
Austrian,J. Exp. Med. 98:21, 1953.)
-
8/8/2019 Griffith 1928
11/93
The first demonstration of bacterial transformation was done with Streptococcus
pneumoniae and led to the discovery that DNA is the substance of the genes. The path
leading to this epoch-making discovery began in 1928 with the work of an English
bacteriologist, Fred Griffith.
The cells ofS. pneumoniae (also known as the pneumococcus) are usually surroundedby a gummy capsule made of a polysaccharide. When grown on the surface of a solid
culture medium, the capsule causes the colonies to have a glistening, smooth
appearance. These cells are called "S" cells. However, after prolonged cultivation on
artificial medium, some cells lose the ability to form the capsule, and the surface of
their colonies is wrinkled and rough ("R"). With the loss of their capsule, the bacteria
also lose their virulence. Injection of a single S pneumococcus into a mouse will kill themouse in 24 hours or so. But an injection of over 100 million (100 x 106) R cells is
entirely harmless.
The reason? The capsule prevents the pneumococci from being engulfed
(by phagocytosis) and destroyed by the scavenging cells
neutrophils and macrophages of the body. The R forms are completely at the mercy
of phagocytes.
-
8/8/2019 Griffith 1928
12/93
(S. pneumoniae apanhados emflagrante
delicto)
Streptococcus pneumoniae
-
8/8/2019 Griffith 1928
13/93
Streptococcus_pneumoniae.jpg
Scanning ElectronMicrograph of Streptococcus
pneumoniae. Pneumococcus, Streptococci
http://upload.wikimedia.org/wikipedia/comm
ons/2/20/Streptococcus_pneumoniae.jpg
-
8/8/2019 Griffith 1928
14/93
-
8/8/2019 Griffith 1928
15/93
Chlamydiae
Chlamydiae are also obligate intracellular parasites (they cannot
make their own ATP).Chlamydia trachomatisIts genome contains
1,042,519 bp of DNA encoding 938 genes.
In 1998, this organism infected 604,420 people in the U. S. The
infection is usually spread by sexual intercourse making it the
most common sexually-transmitted disease (STD). It is easily cured
if diagnosed, but many infections remain untreated and, in
females, are a major cause ofpelvic inflammatory disease. This
causes scarring of the uterus and fallopian tubes and often results
in infertility.Mothers can pass the infection on to their newborn
babies causing serious eye disease and pneumonia. To avoid this,
pregnant women are usually tested for chlamydia and treated
with antibiotics if they are infected.
Several million people in the desert regions of Asia, Africa, and the
Near East have been blinded by trachoma. This eye infection is
caused by a strain of C. trachomatis (and is responsible for its
name).Chlamydia psittaci usually infects birds, but can infect their
human contacts causing psittacosis (a.k.a. ornithosis).
-
8/8/2019 Griffith 1928
16/93
(a) Scanning electron microscope (SEM) ofStaphylococci(b) Staphylococci haemolysis on
blood agar(BA) (c) Electron microscope picture
ofS. aureus
-
8/8/2019 Griffith 1928
17/93
(a) Mannitol salt agar (b) Nutrient agar (c) Blood agar
-
8/8/2019 Griffith 1928
18/93
(a) SEM ofStaphylococcus aureus (b) Electron
microscope (EM) ofVibrio cholera (c) EM of
Streptococcus pneumoniae (d) Ourgroup's
sample location (e) Group 12'ssample location(f) Group 20'ssample location
Staphylococcus aureusVibrio cholera Streptococcus pneumoniae
-
8/8/2019 Griffith 1928
19/93
transformation
-
8/8/2019 Griffith 1928
20/93
-
8/8/2019 Griffith 1928
21/93
-
8/8/2019 Griffith 1928
22/93
-
8/8/2019 Griffith 1928
23/93
-
8/8/2019 Griffith 1928
24/93
-
8/8/2019 Griffith 1928
25/93
Figure 362. Model for the structure of the
nucleosome,
in which DNA is wrapped around the surface ofa
flat protein cylinder consisting of two each of
histones
H2A, H2B, H3, and H4 that form the histone
octamer.
The 146 base pairs of DNA, consisting of 1.75superhelical
turns, are in contact with the histone octamer.
This
protects the DNA from digestion by a nuclease.
The position
of histone H1, when it is present, is indicatedby
the dashed outline at the bottom of the figure.
-
8/8/2019 Griffith 1928
26/93
Figure 363. Shown is the extent of DNA
packaging in metaphase chromosomes (top)
to noted duplex DNA (bottom).Chromosomal DNA is packaged and organized
at several levels as shown (see Table 362).
Each phase of condensation
or compaction and organization (bottomto
top) decreasesoverall DNA accessibilityto an
extentthatthe
DNA sequences in metaphase chromosomes
are almost totally transcriptionally inert. In
toto, these five levels of
DNA compaction result in nearly a 104-fold
linear decrease in end-to-end DNA length.
Complete condensation and
decondensation of the linear DNA in
chromosomes occur in the space of hours
during the normal replicative cell
cycle (see Figure 3620).
-
8/8/2019 Griffith 1928
27/93
Figure 365. The two sister chromatids of
human chromosome 12 (. 27,850). The
locationof the A+T-rich centromeric region connecting
sister chromatids is indicated, as are two of the
four telomeres residing at the very ends of the
chromatids that are attached one to the other
at
the centromere. (Modified and reproduced,with
permission, from DuPraw EJ: DNA and
Chromosomes.
Holt, Rinehart, and Winston, 1970.)
-
8/8/2019 Griffith 1928
28/93
Figure 366. A human karyotype (of a man
with a normal 46,XY constitution), in
which the metaphase chromosomes have been
stained by the Giemsa method and
aligned according to the Paris Convention.
(Courtesy of H Lawce and F Conte.)
-
8/8/2019 Griffith 1928
29/93
Figure 367. The relationship between
chromosomal DNA and mRNA. The human
haploid DNA complement of 3 . 109 base pairs
(bp) is distributed between 23 chromosomes.Genes are clustered on these chromosomes.
An average gene is 2 . 104 bp in
length, including the regulatory region
(hatched area), which is usually located at the
5
end of the gene. The regulatory region is
shown here as being adjacent to the
transcription
initiation site (arrow).Most eukaryotic genes
have alternating exons and introns. In
this example, there are nine exons (dark blue
areas) and eight introns (light blue areas).
The introns are removed from the primary
transcript by the processing reaction, and the
exons are ligated together in sequence to form
the mature mRNA. (nt, nucleotides.)
-
8/8/2019 Griffith 1928
30/93
-
8/8/2019 Griffith 1928
31/93
DNAREPLICATION begins at a defined origin, is bidirectional, and is semiconservative
(one new chain, one old chain in daughter DNA), and chain growth
occurs in the 5 to 3 direction.
-
8/8/2019 Griffith 1928
32/93
-
8/8/2019 Griffith 1928
33/93
Hierarchical Organization of a Multicel-
lular Organism: The Human Being
Multicellular organisms have several levelsof organization: Organ systems, organs, tis-
tissues, cells, organelles, molecules, and
atoms. The digestive system and one of its
component organs (the liver) are shown.
The liver is a multifunctional organ that has
several digestive functions. For example, itproduces bile, which facilitates fat diges-
digestion, and it processes and distributes the
food molecules absorbed in the small intes-
intestine to other parts of the body. DNA, one
molecule found in cells, contains the genetic
information that controls cell function.
-
8/8/2019 Griffith 1928
34/93
DNA
(a) A diagrammatic view of
DNA. The sugar-phosphate
backbones of the double helix
are represented by colored
ribbons. The bases attached
to the sugar deoxyribose are on
the inside of the helix, (b) An
enlarged view of two base
pairs. Note that the two DNA
strands run in opposite
directions defined by the 5' and
3' groups of deoxyribose. Thebases on opposite strands form
pairs because of hydrogen
bonds. Cytosine
always pairs with guanine;
thymine always pairs with
adenine.
-
8/8/2019 Griffith 1928
35/93
Membranes in Living Cells Membranes are an
essential feature of living cells. Most
biochemical
processes occur in or near these dynamic and
complex supramolecular structures.
Cells are the structural units of all living
organisms. One remarkable feature of cells is
their diversity. For example, the human body
contains about 200 types of cells. This
great variation reflects the variety of functions
that cells can perform. However, no
matter what their shape, size, or species, cells
are also amazingly similar. They are allsurrounded by a membrane that separates
them from their environment. They are all
composed of the same types of molecules.
-
8/8/2019 Griffith 1928
36/93
-
8/8/2019 Griffith 1928
37/93
-
8/8/2019 Griffith 1928
38/93
-
8/8/2019 Griffith 1928
39/93
Homologous sequences. Orthologs and
Paralogs are two types of homologous
sequences. Orthology describes genes in
different species that derive from a common
ancestor. Orthologous genes may or may not
have the same function. Paralogy describes
homologous genes within a single species that
diverged by gene duplication.
-
8/8/2019 Griffith 1928
40/93
Diverse living organisms share common
chemical features.
Birds, beasts, plants, and soil microorganismsshare with humans
the same basic structural units (cells) and the
same kinds of
macromolecules (DNA, RNA, proteins) made
up of the same kinds of
monomeric subunits (nucleotides, aminoacids). They utilize the same
pathways for synthesis of cellular components,
share the same genetic
code, and derive from the same evolutionary
ancestors. Shown here
is a detail from The Garden of Eden, by Janvan Kessel the Younger
(16261679).
or nucleoid (bacteria)
-
8/8/2019 Griffith 1928
41/93
or nucleoid (bacteria)
Contains genetic materialDNA and
associated proteins. Nucleus is
membrane-bounded.
Plasma membrane
Tough, flexible lipid bilayer.Selectively permeable to
polar substances. Includes
membrane proteins that
function in transport,
in signal reception,
and as enzymes.Cytoplasm
Aqueous cell contents and
suspended particles
and organelles.
Supernatant: cytosol
Concentrated solutionof enzymes, RNA,
monomeric subunits,
metabolites,
inorganic ions.
Pellet: particles and organelles
Ribosomes, storage granules,
mitochondria, chloroplasts, lysosomes,
-
8/8/2019 Griffith 1928
42/93
The universal features of living cells. All
cells have a
nucleus or nucleoid, a plasma
membrane, and cytoplasm. The cytosol
is defined as that portion of the
cytoplasm that remains in the
supernatant
after centrifugation of a cell extract at
150,000 gfor1 hour.
-
8/8/2019 Griffith 1928
43/93
-
8/8/2019 Griffith 1928
44/93
-
8/8/2019 Griffith 1928
45/93
-
8/8/2019 Griffith 1928
46/93
Bacterial PU1
In this electron micrograph, a sex pilus con-connects two conjugating E. coli cells. Note the
numerous smaller pili covering the surface
of one of the cells.
-
8/8/2019 Griffith 1928
47/93
-
8/8/2019 Griffith 1928
48/93
ExocytosisProteins produced in the ER and
processed by the Golgi apparatus are
packaged into vesi-
vesicles that migrate to the plasma
membrane and merge with it.
-
8/8/2019 Griffith 1928
49/93
Receptor-Mediated Endocytosis
(a) Extracellular substances may enter the cell during
endocytosis, a process in which receptor molecules in the
plasma membrane bind to the
specific molecules or molecular complexes called ligands.Specialized regions of plasma membrane called coated pits
progressively invaginate to
form closed vesicles. After the coat proteins are removed,
the vesicle fuses with an early endosome, the precursor of
lysosomes. The coat proteins
are then recycled to the plasma membrane. Duringendosomal maturation, the proton concentration rises and
the ligands are released from their
receptors which are subsequently also recycled back to the
plasma membrane. As endosomal maturation continues,
lysosomal hydrolases are
delivered from the Golgi apparatus. Lysosomal formation iscomplete when all the hydrolases have been transferred to
the late endosome and the
Golgi membrane has been recycled back to the Golgi
apparatus, (b) Electron micrographs illustrating the initial
events in endocytosis.
FIGURE Z Z4
-
8/8/2019 Griffith 1928
50/93
FIGURE Z.Z4
TheMitochondrion
(a)Membranes and crista. (b) Mitochondria
from adrenal cortex.
-
8/8/2019 Griffith 1928
51/93
-
8/8/2019 Griffith 1928
52/93
Replication of a Mitochondrion by Binary Fission
1.Mitochondria and chloroplasts are similar in size to many
modern prokaryotes.
2. These two organelles reproduce by binary fission, as do bac-
bacteria and the archaea (Figure 2A).
3. The genetic information (DNA) and the protein-synthesizing
capability of mitochondria and chloroplasts are similar to
those of prokaryotes. For example, both mitochondrial and
chloroplast DNA are circular and "naked" (i.e., not com-
plexed with histone proteins as nuclear DNA is). (There is
insufficient genetic information on these chromosomes to
account for all organelle components. However, the nuclear
genes that are responsible for synthesis of mitochondrial
components resemble prokaryotic genes.)
-
8/8/2019 Griffith 1928
53/93
-
8/8/2019 Griffith 1928
54/93
-
8/8/2019 Griffith 1928
55/93
-
8/8/2019 Griffith 1928
56/93
-
8/8/2019 Griffith 1928
57/93
-
8/8/2019 Griffith 1928
58/93
FIGURE 3.1 O
The Hydrophobic Effect.When nonpolar molecules and water are
mixed, a solvation sphere composed of many
lay-
layers of highly ordered hydrogen-bonded
water molecules forms around the
hydrophobic mol-molecules. Although nonpolar molecules,
when in close proximity, are attracted to each
other
by van der Waals forces, the driving force in
the formation of the solvation spheres is the
strong tendency of water molecules to form
hydrogen bonds among themselves. Nonpolar
molecules are excluded because they cannot
form hydrogen bonds.
-
8/8/2019 Griffith 1928
59/93
-
8/8/2019 Griffith 1928
60/93
-
8/8/2019 Griffith 1928
61/93
8. Stress response. The capacity of living
organisms to survive a variety of
abiotic stresses is mediated by certain
proteins. Examples include cytochrome
P450, a diverse group of enzymes found in
animals and plants that usually con-
convert a variety of toxic organic contaminants
into less toxic derivatives, and met-
allothionein, a cysteine-rich intracellular
protein found in virtually all mammalian
cells that binds to and sequesters toxic metalssuch as cadmium, mercury, and sil-
silver. Excessively high temperatures and other
stresses result in the synthesis of a
class of proteins called the heat shock proteins
(hsps) that promote the correct
refolding of damaged proteins. If such proteinsare severely damaged, hsps pro-
promote their degradation. (Certain hsps
function in the normal process of protein
folding.) Cells are protected from radiation by
DNA repair enzymes.
-
8/8/2019 Griffith 1928
62/93
-
8/8/2019 Griffith 1928
63/93
-
8/8/2019 Griffith 1928
64/93
-
8/8/2019 Griffith 1928
65/93
-
8/8/2019 Griffith 1928
66/93
-
8/8/2019 Griffith 1928
67/93
Phage T2 is a virus that infects the bacterium E.
coli. When phage particles are added to
bacteria, they adsorb to the outside surface,some material enters the bacterium, and then
~20 minutes later each bacterium bursts open
(lyses) to release a large number of progeny
phage
-
8/8/2019 Griffith 1928
68/93
-
8/8/2019 Griffith 1928
69/93
Lunar excursion module (LEM) ofApollo 16: courtesy NASA
-
8/8/2019 Griffith 1928
70/93
-
8/8/2019 Griffith 1928
71/93
-
8/8/2019 Griffith 1928
72/93
In a first experiment, they labelled the
-
8/8/2019 Griffith 1928
73/93
p , y
DNA of phages
withradioactive Phosphorus-32 (the
element Phosphorus is present in DNAbut not present in any of the 20 amino
acids from which proteins are made).
They allowed the phages to infect E.
Coli, then removed the protein shellsfrom the infected cells with a blender
and a centrifuge. They found that the
radioactive tracer was visible only in the
bacterial cells and not in the proteinshells.
-
8/8/2019 Griffith 1928
74/93
In a second experiment, they labelled the
phages with radioactive Sulfur-35 (Sulfur is
present in the amino
acids Cysteine andMethionine, but not in
DNA). After separation, the radioactive tracer
then was found in the protein shells, but not in
the infected bacteria, confirming that the
genetic material which infects the bacteria is
DNA.
Hershey shared the 1969 Nobel Prize in
Physiology orMedicine for his discoveries
concerning the genetic structure of viruses.
-
8/8/2019 Griffith 1928
75/93
The Hershey-Chase experiments were a series
ofexperiments conducted in1952 by AlfredHershey andMartha Chase, confirming
that DNA was thegenetic material, which had
first been demonstrated by Oswald
Avery in 1944.
-
8/8/2019 Griffith 1928
76/93
Alfred Hershey andMartha Chase
Alfred Hershey andMartha Chase
Independent Functions of Viral Protein
and Nucleic Acid in Growth ofBacteriophage. September 20, 1952.
-
8/8/2019 Griffith 1928
77/93
-
8/8/2019 Griffith 1928
78/93
-
8/8/2019 Griffith 1928
79/93
Life Cycle:
The virus attaches to the E coli cell (a) This requires a precise molecular interaction
-
8/8/2019 Griffith 1928
80/93
The virus attaches to the E. coli cell (a). This requires a precise molecular interaction
between the fibers and the cell wall of the host.
The DNA molecule is injected into the cell (b).
Within 1 minute, the viral DNA begins to be transcribed and translated into some of
the viral proteins, and synthesis of host proteins is stopped.At 5 minutes, viral enzymes needed for synthesis of new viral DNA molecules are
produced (c).
At 8 minutes, some 40 different structural proteins for the viral head and tail are
synthesized.
At 13 minutes, assembly of new viral particles begins (d).
At 25 minutes, the viral lysozyme destroys the bacterial cell wall and the viruses burstout ready to infect new hosts (e).
If the bacterial cells are growing in liquid culture, it turns clear.
If the bacterial cells are growing in a "lawn" on the surface of an agar plate, then
holes, called plaques, appear in the lawn
-
8/8/2019 Griffith 1928
81/93
Bacteriophage.jpg
The contractile tail sheath of phage T4
ofEscherichia coli, one of the best understood
phages. This computer-generated image is
based on the data of J. Lepault and K. Leonard
(46) and was generated by StevenMcQuinn.
-
8/8/2019 Griffith 1928
82/93
Bacteriophage phi 29 ...
-
8/8/2019 Griffith 1928
83/93
VIRIONS are virus particles: they are the INERT
CARRIERS of the genome, and
are ASSEMBLED inside cells, from virus-
specified components: they do not GROW,
and do not form by DIVISION
-
8/8/2019 Griffith 1928
84/93
-
8/8/2019 Griffith 1928
85/93
-
8/8/2019 Griffith 1928
86/93
-
8/8/2019 Griffith 1928
87/93
-
8/8/2019 Griffith 1928
88/93
-
8/8/2019 Griffith 1928
89/93
-
8/8/2019 Griffith 1928
90/93
-
8/8/2019 Griffith 1928
91/93
-
8/8/2019 Griffith 1928
92/93
-
8/8/2019 Griffith 1928
93/93