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Transcript
DNA: The
Molecule of Life
Molecular Genetics

https://www.23andme.com/
DNA and RNA

Genes are segments of DNA on a
chromosome that code for specific traits
 DNA – nucleic acid called deoxyribonucleic
acid that contains the instructions necessary
for a cell to build proteins from amino acids.
 RNA – ribonucleic acid plays a role in gene
expression and protein synthesis
 http://www.youtube.com/watch?v=zwibgNGe
4aY What is DNA?
Isolating the Material of Heredity

1869 Friedrich Miescher isolated a weakly
acidic phosphorus-containing substance from
the nuclei of white blood cells
– Called it “nucleic acid”

Early 1900’s Pheobus Levene isolated two
types of nucleic acid
– Called them “ribose nucleic acid” (RNA) and
“deoxyribose nucleic acid” (DNA)

Soon after, Thomas Hunt Morgan provided
the first experimental evidence that genes
are located on chromosomes (fruit flies)
http://www.youtube.com/watch?v=5MQdXjRPHmQ
What is a gene?
Isolating the Material of Heredity

In 1928 Fredrick Griffith designed an
experiment to study the bacteria that were
responsible for a pneumonia epidemic in
London
– He discovered that the dead pathogenic bacteria
passed on their disease-causing properties to
live, non-pathogenic bacteria
– He called this the transforming principle

Griffith died during world war II but several
scientists built on his work
In notes
booklet
http://www.juliantrubin.com/bigten/dnaexperiments.html
Isolating the Material of Heredity

In 1944, Oswald Avery, Colin
MacLeod, and Maclyn McCarty
discovered:
– When they treated heat-killed pathogenic
bacteria with a protein-destroying enzyme,
transformation still occurred
– When they treated heat-killed pathogenic
bacteria with a DNA-destroying enzyme,
transformation did not occur

The results provided evidence that DNA
has a role in transformation
In notes booklet
http://courses.cm.utexas.edu/emarcotte/ch339k/fall2005/Lecture-Ch8-1.html
Isolating the Material of Heredity

In 1952, Alfred Hershey and Martha
Chase used radioactive labeling to
show that genes are made of DNA
– They used a virus that contains a protein
coat surrounding a length of DNA
– This virus attaches to a bacteria cell and
injects genetic information into the cell
– The infected cell produces new viruses
and bursts which releases the new viruses
to infect other cells
Isolating the Material of Heredity

Hershey and Chase created two
batches of the virus
– In one they labeled the protein coat with
radioactive sulfur
– In the other, they labeled the DNA with
radioactive phosphorus
– They found that the radioactive
phosphorus was found in the bacterial
cells
– They concluded that DNA must direct the
cell to produce new viruses
– animation
In notes booklet
http://www.accessexcellence.org/RC/VL/GG/hershey.html
Structure of DNA

After isolating DNA and RNA, Levene
determined that both molecules are made up
of nucleotides (in long chains)
 Nucleotide is composed of:
– 5-carbon sugar (deoxyribose in DNA, ribose in
RNA)
– Phosphate
– Nitrogen base (4 different types)

The 4 nitrogen bases belong to two chemical
groups called purines and pyrimidines
 Purines = Adenine (A) and Guanine (G)
 Pyrimidines = Thymine (T) and Cytosine (C)
Structure of DNA

In the late 1940’s Erwin Chargaff found that
nucleotides are not present in equal amounts
in DNA and RNA
– Nucleotides are present in varying proportions
– He found that the number of adenine in DNA is
equal to the number of thymine in a sample
– The amount of cytosine is approximately equal to
the amount of guanine

This constant relationship is called
Chargaff’s rule
 Video on Chargaff’s rule
Structure of DNA

In the early 1950’s, a British scientist
Rosalind Franklin used x-ray photography
to analyze the structure of DNA
– DNA has a helical structure with two regularly
repeating patterns
– Nitrogenous bases are located on the inside of the
structure, and the sugar-phosphate backbone is
located on the outside (near the watery nucleus)
– Many argue that Franklin should have shared in
the Nobel Prize for discovering the structure of
DNA, but she died before it was handed out
NOVA program on photo 51.
Structure of DNA

In 1953, James Watson and Francis Crick
were the first to produce a structural model
for DNA
 Watson and Crick’s model of DNA closely
resembles a twisted ladder
– Deoxyribose sugar and phosphate molecules
make up backbone (handrails of the ladder)
– Paired nitrogen bases held together by weak
hydrogen bonds make up the rungs (steps) of the
ladder
– The ladder twists to form a double helix

From Franklin’s images, Watson and Crick
knew the distance between the sugarphosphate handrails remained constant
Structure of DNA

The two strands that make
up DNA are not identical,
they are complementary
to eachother
–

This is due to the
complementary base pairs of
A-T and C-G
The two strands are also
antiparallel
–
–
The phosphate bridges run in
opposite directions in the two
strands
Each end of a double
stranded DNA molecule
contains the 5’ end of one
strand and the 3’ end of the
complementary strand
http://www.synapses.co.uk/genetics/tsg19.html
http://www.youtube.com/watch?v=
p835L4HWH68&feature=youtu.be
5' and 3' ends of DNA.mov
In a segment of DNA, the number of
purines equals the number of
pyrimidines; this is because of the base
pairing rule
 RULE: nitrogen bases always pair in
complementary pairs

– Adenine = thymine
– Guanine = Cytosine
Ex) if 15% of the
bases were thymine,
what percentage
would be
a) adenine
b) guanine
c) cytosine
Example

Determine the complementary strand of
DNA:
A
I
T
I
G
I
C
I
A
I
G
I
C
I
Ribonucleic Acid (RNA)
compared to DNA
The sugar component of RNA is ribose
 RNA does not have the nucleotide
thymine (T), in its place is uracil (U)
 RNA remains single stranded
 There are several types of RNA

– mRNA, rRNA, tRNA
DNA, RNA animation
DNA Replication (Synthesis)
http://www.youtube.com/watch?v=8k
K2zwjRV0M Crash course
 Replication – DNA has the ability to
replicate (or duplicate) itself.
 This is why one cell is able to divide into
two cells and each cell has identical
genetic information
 Replication takes place during S phase
of interphase

DNA Replication (Synthesis)

Replication is semi-conservative
– Each new molecule of DNA contains one strand of
the original complementary DNA and one new
parent strand
– Each new strand conserves half of the original
molecule
– Meselson-Stahl Experiment

Replication takes place at several locations
along the DNA molecule simultaneously
– The steps are described in sequence to better
understand the concept
– BioFlix Replication
Replication starts at a specific nucleotide
sequence called the replication origin
2) During replication, weak hydrogen bonds
that hold complementary nitrogen bases
together are broken (This causes the two
edges to “unzip”) with a special group of
enzymes called helicases (gyrase breaks
the hydrogen bonds)
3) This creates two y-shaped areas
(replication forks) at the end of the
unwound area, the unwound area is called a
replication bubble
4) The parent (original) strands are conserved
while two new strands created from
nucleotides are formed with them (they act
as a template)
1)
5)
Free floating nucleotides (from diet) are
attached to the exposed nitrogen bases
according to the base pair rule with an
enzyme called DNA polymerase
– This process is called elongation
– DNA polymerase attaches new nucleotides to the
free 3’ end of a preexisting chain of nucleotides
– Elongation can only take place in a 5’ to 3’
direction
– This means that replication occurs in opposite
directions along each strand of the parent DNA
•
•
One strand is replicated continuously, it is called the
leading strand
The other strand is replicated in short segments, it is
called the lagging strand
– The short segments are called Okazaki fragments
– These fragments are spliced together by an enzyme
called DNA ligase
6)
Since DNA polymerase cannot synthesize
new fragments of DNA, and RNA primer
serves as a starting point for the elongation of
each new DNA strand


An enzyme called primase is required to
construct a primer
When finished the strand, DNA polymerase
removes the primer by eliminating the nucleotides
in a 5’ to 3’ direction
Hydrogen bonds form between the nitrogen
bases
8) Special proofreading enzymes (DNA
polymerase) check the new strand of DNA for
mistakes. Errors are removed by cutting the
mistake out and using an endonuclease and
replacing it with the correct nitrogen base
7)


As soon as the newly
formed strands are
complete, they rewind
automatically into the
helix structure
Replication continues
until the new strands are
complete and the two
DNA molecules separate
from eachother
– This is called
termination

This replication produces
two strands of DNA from
one where each strand is
composed of “half-old
and half-new”
Replication Fork
http://www.bio.davidson.edu/Courses/Molbio/
Adding
Nucleotides
MolStudents/spring2005/Durnbaugh/yfp.html
Replication Animation
Replication Review
THINK WELL PART 1 AND 2
http://www.youtube.com/watch?v=aSI
LNKbhNLg&feature=related
http://www.youtube.com/watch?v=CR
http://www.biosci.ohio-state.edu/~mgonzalez/Micro521/04.html
http://distancelearning.ksi.edu/demo/bio378/lecture.htm
Genetic Engineering and
Recombinant DNA
Genetic Engineering – refers to the
alteration of an organism’s genome
(complete set of genes) by selectively
removing, adding, or modifying DNA
 Recombinant DNA – the process of
cutting out DNA from one genome and
placing the DNA into another genome
resulting in a transgenic organism


Examples of transgenic organisms:
– Genetically modified bacteria for use in
medicine and bioremediation
(environmental clean-up)
– Transgenic plants to improve crop yield
and resistance to environmental effects
– Cloned animals (livestock) and organs for
human use
Recombinant DNA –
How do they do it?

Use restriction enzymes
(endonucleases) to cut strands of DNA
within their interior (at specific
sequences)
– animation

Then ligase (enzyme that fuses
segments of DNA) is used as a
biological glue
Production of human insulin
Gene in the human genome that codes
for insulin is cut out using restriction
enzymes
 The plasmid of an E-coli bacteria is cut
using restriction enzymes so that the
gene for insulin can be inserted using a
ligase
 Bacteria can read the DNA and produce
insulin for us to later harvest and use


Another example is the insertion of the
gene that codes for growth hormone
into animals so that they grow faster
Note: Biotechnology refers to the use of
organisms or biological products for
commercial and/or industrial processes
- video

What are the Issues?
– Costs/where money is spent
– Motivation for the product
– Biological characteristics of the product
– Heath effects
– Environmental effects
– Freedom of Information/Privacy
– Who Owns the technology/patents
– Issues Animation
Gel Electrophoresis

1)
2)
Technique used to separate DNA fragments
by size for the purpose of identification in
paternal or criminal suits (animation)
Sample of DNA is cut using restriction
enzymes from hair, blood, skin, etc. This
produces a number of DNA segments of
different lengths.
The different pieces of DNA (referred to as
restriction-fragment-length-polymorphisms
or RFLP) are tagged with a radioactive
isotope
3) Using an agarose gel that contains
holes or wells along one side, the
samples of DNA are inserted into the
wells. A known sample is loaded with it
as a comparison
4) Electric current is run through the gel,
causing the movement of the negatively
charged DNA fragments. The shortest
strands move the farthest (lowest
weight) and the longer strands (heavier)
will not move as far.
5) This causes separation of the DNA into
bands. The gel is left to set
6) When combined with staining or X-ray
film, the patterns are used to determine
the presence or absence of particular
DNA or proteins
DNA Fingerprinting
Developed in 1985 – used to identify whether
or not a sample of DNA comes from a specific
person
 People have similar DNA, however every
human (with the exception of identical twins,
triplets, etc.) have some unique noncoding
segments of DNA called introns; exons are
segments of DNA that actually code for
proteins






Sample of DNA is placed through gel
electrophoresis as well as samples from
individuals who are suspected as “owners” of
the sample
Because of introns, each individual will have
a different number of sites where the
restriction enzyme will cut
This results in a unique number and length of
fragments which produces a unique banding
pattern (fingerprint) when x-rayed
Fingerprints are used to identify criminals,
paternity or kinship
Animation

Lane A: DNA from crime scene cut with Enzyme 1
 Lane B: DNA from crime scene cut with Enzyme 2
 Lane C: DNA from Suspect 1 cut with Enzyme 1
 Lane D: DNA from Suspect 1 cut with Enzyme 2
 Lane E: DNA from Suspect 2 cut with Enzyme 1
 Lane F: DNA from Suspect 2 cut with Enzyme 2
Protein Synthesis
http://www.youtube.com/watch?v=itsb2
SqR-R0 Crash course
 Genetic code is determined by the
arrangement of nitrogen bases within
the strands of DNA
 Each gene codes for the production of a
specific protein

transcription
– DNA
RNA
translation
protein
Proteins
Proteins are composed of 20 different
amino acids that are strung together in
endless combinations
 Compose cell membranes, cell
organelles, muscle filaments, hair, hair
color, enzymes (regulate speed of
chemical reactions in cells), antibodies
(disease-control agents), hormones

Genetic Code






It takes the code of 3 nucleotides (a codon)
to code for one amino acid
Humans can make 12 of the 20 amino acids,
we must consume the other 8 essential
amino acids
Simple protein = 8 amino acids
Complex protein = 50 000 amino acids
Sequencing amino acids is determined by
DNA
Replacement of a single amino acid can
change a protein
Genetic Code

The genetic code has three important
characteristics
1. The genetic code is redundant (more than one
codon can code for the same amino acid)
2. The genetic code is continuous (reads as a
series of three letter codons without spaces,
punctuation or overlap)
3. The genetic code is nearly universal (almost all
organisms use the same code – this is good for
genetic engineering and biotechnology)
Role of DNA in protein synthesis
DNA is in nucleus, but protein synthesis
occurs on the ribosomes in the
cytoplasm
 Carrier molecule (mRNA – messenger
RNA) is responsible for reading the
information from the DNA
(transcription) and carry it to the
ribosomal RNA (rRNA) in the cytoplasm
where it will be translated into an
amino acid sequence by transfer RNA
(tRNA)

RNA (Ribonucleic Acid)

1)
2)
3)
4)
5)
6)
Different from DNA in that:
It’s single stranded
It contains the sugar ribose
It is located throughout the cell (DNA is only
in the nucleus with some also in the
mitochondria)
It contains the base uracil (U) instead of
thymine (T)
There are three types: mRNA, rRNA, tRNA
It’s shorter (no introns)
Transcription


Protein synthesis begins with
transcription (RNA synthesis) of DNA
DNA never leaves the nucleus
(protected)
Steps of Transcription
1)
DNA molecule unzips (like in replication),
however, RNA nucleotides are now added to the
necessary areas (exons) by RNA Polymerases
 For each gene, only one strand of the DNA is
transcribed, this is called the sense strand. The other
is called the anti-sense strand.
2)
3)
4)
5)
6)
As double helix uncoils, nucleotides from the
mRNA find the appropriate pair by using single
DNA strand as a template (5’ to 3’ direction)
Uracil binds to exposed adenine bases and
cytosine binds to exposed guanine bases
mRNA joined and fused in a long chain
mRNA move away from DNA and the DNA
strands rejoin again
mRNA leave the nucleus in search of the
ribosomes
http://fig.cox.miami.edu/~cmallery/150/gene/mol_gen.htm
_____________________________DNA
I
I
I
I
I
I
I
I
A
G C
T
T
A
T
C
U
C
G A
A
U
A
G
I
I
I
I
I
I
I
I
_____________________________RNA






mRNA reads code from DNA
RNA codes for amino acids
Some codes in mRNA are not for amino acids
but are terminators and initiators
Terminators – end protein synthesis (stop
codon)
Initiators – turning protein synthesis on (start
codon). Also called promoter site, starts RNA
transcription
Transcription Animation
http://www.coolschool.ca/lor/BI12/unit6/U06L01.htm
Example

Original DNA sequence:
AAT GCC AGT GGT TCG CAC AAA
a)
Write the complementary DNA sequence
b)
Write the mRNA sequence
c)
How many amino acids are there?
d)
What is the amino acid sequence?
Do the same for the following DNA
sequence:
TAC CAC GTG GAC TGA GGA CTC
CTC ATC ATA

Translation



Translation is the next stage of protein synthesis
Involves translating codons found on the mRNA into
a chain of amino acids (to form a protein)
Transfer RNA, tRNA is made up of a single strand of
RNA that folds into a clover-leaf shape
– One lobe contains the anticodon, three nucleotides
that are complementary to the mRNA codon
– At the opposite end is a binding site for the amino acid
that corresponds to the codon

Ribosomal RNA, rRNA is a linear strand of RNA that
remains associated with the ribosomes
More on tRNA

The exposed bases are called the anticodon
 Each kind of tRNA molecule has a specific
anticodon
 Ex) Glutamate carried by a tRNA molecule
that carries either the CUU or the CUC
anticodon (opposite to mRNA codons)
 Ex) Valine carried by a tRNA molecule that
has the CAA anticodon
Steps of translation
1)
2)
3)
4)
5)
6)
Translation is activated when an mRNA molecule binds to
an active ribosome complex in such a way that two codons
are exposed
The first tRNA molecule carrying the amino acid
methionine, base pairs with the start codon on the mRNA,
(AUG)
Another tRNA molecule arrives at the codon next to the
first tRNA, and the first tRNA passes its amino acid on to
the second tRNA
Enzymes catalyze the formation of a peptide bond
between the two amino acids
The ribosome moves along the mRNA strand one codon at
a time
The first tRNA molecule detaches from the mRNA and
picks up another amino acid as another tRNA attaches to
the mRNA.





NOTE: The process begins with the presence
of an initiator (start codon) AUG and ends
with the presence of a stop (terminator
codon) UAA, UGA, or UAG on the mRNA.
Remember that the sequence of amino acids
was originally derived from the message
carried by mRNA from the nucleus (DNA)
Translation animation 1
Translation animation 2 Translation 3
Protein Synthesis Process
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Translation.html
http://www.scq.ubc.ca/?p=263
Example
Write a tRNA and amino acid sequence
for the following DNA sequence:
TAC CAC TGA GGA CTC CTC CAT CAT

Protein synthesis animation
http://www.youtube.com/watch?v=983lhh20rGY
Analogy of protein synthesis and RNAi
http://www.pbs.org/wgbh/nova/body/rnai.html
DNA song http://www.youtube.com/watch?v=FUA6_Ucw3i4
Make a Recipe Card for Protein
Synthesis

Use your notes and the 4 by 6 index card I
gave to you to write your own “recipe card”.
Mutations
http://www.youtube.com/watch?v=ecZbhf96W9k
A mutation is a permanent change in
the DNA sequence caused by
mutagens (mutagenic agents)
 Mutations

– are inheritable
– Arise from mistakes in DNA replication
when one nitrogen base is substituted for
another
– Creates a new genetic code that gives
new instructions to make amino acids
(causes a different protein to be made)
Mutagenic agents







Physical:
– Pushing or tugging chromosomes
Chemical:
– Carcinogens, mustard gas, poor nutrition
Medications:
– Some antibiotics
Radiation:
– X-ray, ultraviolet radiation, cosmic rays
Replication mistakes:
– Natural mistakes occur during mitosis or meiosis
Nutritional:
– Lacking certain nucleotides in diet means you are unable to
provide the proper free nucleotide base and this causes a
mismatch
Biological:
– Most viruses use genetic material of chromosomes to
reproduce. They join existing DNA to cause permanent
damage
Mutation Animation
http://www.youtube.com/watch?v=efstlgoynlk&feature=fvw

If a mutation is present in the gametes, it will
be passed on to further generations. This is
why it is particularly dangerous for pregnant
women
 Mutations can be grouped under 2
categories:
1) Chromosomal mutations
2) Point mutations
Chromosomal mutations

Large mutations that visibly effect the
structure or number of chromosomes
– Ex) nondisjunction, fragile-X-syndrome
– http://www.youtube.com/watch?v=y1FOEteaM9Q&feature=related
Point Mutations
Alter a single gene. There are several
types:
1) Base substitution – a foreign base
replaces the normal base in each strand
of DNA. This could result in one amino
acid being different animation

– ACGCCA becomes CCGCCA
– Ex) Sickle cell anemia – substitution of one
nitrogen base causes an inability to carry
sufficient oxygen
2) Insertion: A base is added into the
normal DNA sequence
– ACGCCA becomes AACGCCA
3) Deletion: a base is removed from the
normal DNA sequence
– ACGCCA becomes CGCCA
– Ex) Cystic fibrosis – deletion of 7th, 8th, and
9th nitrogen bases causes an inability to
produce protein that regulates chloride
channels
– animation
NOTE: both insertion and deletion result
in a frame-shift mutation because every
amino acid after the point of mutation
may be affected
4) Translocation: a sequence of nitrogen
bases is removed from one area and
placed in another

– ABCDEFGHIJ becomes ABFGHIJCDE
5) Inversion: reversal of a sequence of nitrogen
bases
– ABCDEFGHIJ becomes ABEDCFGHIJ
6) Duplication: duplicating a set or sequence of
nitrogen bases twice in one location
– ABCDEFGHIJ becomes ABCABCDEFGHIJ
7) Silent mutations: no phenotypic effect
because certain amino acids have more than
one code
– GTA (CAU) and GTG (CAC) both code for
histidine
NOTE: The body can repair some mutations, but not
all
Human Genome Project
Human Genome Project –
 animation

Oncogenes and Cancer

In normal cells, protein synthesis is carried
out by structural genes only when required
 Because protein synthesis is not always
required, a regulator gene produces a
repressor protein which switches off protein
synthesis and reducing the rate of cell
division
 P53 animation
 http://www.youtube.com/watch?v=WZdErhuL
Ctc

Uncontrolled cell division is cancer.
 Cancer is caused by a mutation due to an
environmental factor or carcinogen
 Mutation could be a base substitution that
prevents the production of the repressor
protein, or the movement of a gene from one
part of the chromosome to another
 If the structural gene is separated from its
regulator gene, it cannot be turned off (cancer
forms)
– These genes that cannot be turned off are called
oncogenes
Most common oncogene = ras
 Found in 50% of colon cancers and
30% of lung cancers
 Ras makes a protein that acts as an
“on” switch for cell division. Once a
sufficient number of cells are produced,
it should shut off
 Cancer-causing oncogene produces a
protein that blocks the “off” switch
(causes cell division to continue at an
accelerated rate)

Epigenetics

Epigenetics Explanation – Tale of Two
Mice
Diagnosing Genetic Disorders

Amniocentesis and Chorionic Villus
Sampling can take cell samples from a
developing fetus or embryo
– This sample can be screened for genetic
markers for certain disorders
• Uses a DNA probe which identifies problem
genes
Steps in Cloning a Gene

http://www.learnalberta.ca/content/seb3
0/html/interactiveLauncher.html?interact
ive=StepsInCloningAGene.swf
Gene Therapy


Targets genetic causes of diseases rather than their
symptoms
A DNA vector carries foreign DNA into target cells of
the patient
– The vector is usually a virus that has been genetically
altered to carry a desired gene
– The virus will eventually transfer the new gene into the cell’s
genome
– Sickle Cell Anemia -- Hope from Gene Therapy
– http://www.youtube.com/watch?v=ujf72mjy0Bg&feature=rela
ted
Gene Therapy

Somatic Gene Therapy – correcting genetic
disorders in somatic cells
– Mutations can still be passed on to offspring

Germ-line Therapy – correcting the genetic
information in sperm and egg
– Could have many negative effects on future
generations
– Currently banned in Canada
Ames Test
Technology to determine quickly,
cheaply, and accurately if a chemical is
mutagenic.
 Any chemical that is mutagenic has
potential to be carcinogenic
 We must test products for their cancercausing agents

http://diverge.hunter.cuny.edu/~weigang/Images/08-22_amestest_1.jpg
Performed on bacteria that have been
mutated so they cannot produce
histadine on their own (we must supply
them with it in order for them to survive)
 Plate this bacteria on a petri dish with
no histidine and the chemical being
tested (expect no growth)
 If bacteria are found, conclusion can be
made that microbe has been mutated
and is now producing its own histidine

» The more colonies that are found, the higher the
strength of mutagenic the chemical is which
indicates it is highly carcinogenic
Often chemical is added to liver
enzymes because chemicals are often
harmless to an individual until they are
broken down in the liver into toxic
metabolites
 NOTE: some chemicals can cause
cancer in some individuals and not in
others (because of different nitrogen
base sequences in each individual)

Biological Warfare
Most disease-causing agents can be
exploited for biological weaponry
 Microbe or toxin produced by microbe
may be harmful to livestock, grains,
bacteria in soil, or humans
 Fortunately, few organisms are suited
for mass destruction

Examples
AIDS – not transmitted by air
 Clostridium botulinum – deadly in water
(not air)…one kg of toxin in water
reservoir kills ~50 000 people (60% of
population dies in 24 hrs)

Research/Testing Stations
Britain = Porton Down
 USA = Camp Detrick in Maryland
 Canada = Suffield in Alberta


Preferred microbe was anthrax bacillus
(affects cattle and humans).
Anthrax

Deadly spores (rod-shaped bacterium) live
long periods of time, are highly contagious,
and resistant to many environmental factors

We currently have the ability to create the
“superbug” through merging genes for rapid
reproduction and environmental
resistance…what do you think would happen
then?
http://www.youtube.com/watch?v=CmtLYQKT21I&feature=related
Mitochondrial DNA
Mitochondria = responsible for cellular
respiration
 1960’s – discovered that mitochondria
contains its own DNA (mtDNA)
 They have an amount of control over
what they do (not completely controlled
by nuclear DNA)

Endosymbiotic Hypothesis
Mitochondria once were free living
bacteria that were engulfed by other
cells.
 The two cells developed mutualistic
relationship (mitochondria had
protection and food, engulfing cell had a
source of energy and oxygen)

Evidence to support theory
MtDNA resembles the loops of DNA found
in bacteria and viruses
2) The mtDNA is tiny compared to nuclear
DNA
3) Mitochondria divide and replicate
independently of the cell itself
* the same theory is used to explain how
photosynthetic cells gained chloroplasts
1)
NOTE: The mtDNA in our bodies is maternal
because sperm’s mitochodria are lost when
their tail falls off.