Download Genes get around

Genes get around
Old idea: species are “immutable”, that is,
unchanging
 Newer idea: species exhibit genetic
variability

 Genes
get combined in new ways within a
species
 Genes get passed around to other species
Vertical vs. Horizontal transmission

Vertical: passed from parent to offspring
 Crossing
over during meiosis, Mendel’s
independent assortment, sex
 Mutations: change in the DNA

All ensure that offspring have a variety of
combinations of genes

Horizontal: genes transferred from one
individual to another.
 Such
transfer can have a significant effect:
 Bacteria exchange genes, spread antibiotic
resistance
 2 Flu viruses infect the same cell, new viruses
get new combination of genes

Humans not resistant to new combination
 Genetically
modified plants spread pollen,
pass herbicide resistance to weds.
Genes can be spread by natural
and “unnatural” processes
Bacteria have several ways of acquiring
new genes
 Plants can spread pollen by wind

 Pollen

is male gametes
Mold spores can be spread by wind
 Germinate
in new area, fuse with different
individual by sexual reporduction.
Bacterial gene exchange-1

Transformation
 DNA dissolved
in liquid can be taken into
bacterial cell
 If bacterium is close relative, DNA can be
swapped for similar gene in chromosome.
Bacterial gene exchange -2
Transduction: bacterial DNA carried by a
virus.
 Virus life cycle

 A virus
that infects a bacterium:
bacteriophage (phage for short)
 Phage attaches, injects its DNA into cell
 Host cell DNA is chopped up, phage makes
copies of its own DNA and proteins
 New parts of virus assemble, cell lyses,
viruses escape to infect other cells.
Life cycle of bacteriophage, a
virus that infects bacteria
At this stage,
host DNA is cut
into pieces.
Virus packed
with bacterial
DNA finds its
way to
another cell.
Plasmids
Are small, circular pieces of DNA in
bacterial or yeast cells that contain 3 to
300 genes.
 Most plasmids exist separate from the
chromosome of the cell.
 Usually replicated when DNA is copied,
but some can reproduce at other times –
autonomous replication

A cell can have as many as 1,000 copies
of a plasmid and a cell may have more
than one plasmid.
 Plasmids can travel from one bacterial cell
to another when bacteria undergo a sexlike process called conjugation.
 Conjugation is 3rd process by which
bacteria can get new genes.

 Widespread
among bacteria (promiscuous),
does not require that they be related species.
Bacterial conjugation
– connected by a
pilus

Plasmids contain genes that benefit the host.
Antibiotic resistance
Resistance to heavy metal poisoning
Resistance to the toxins of other bacteria
Ability to infect
Unnatural ways to move DNA into
an organism

Electroporation
 Use
of DC current to destabilize membrane,
allow DNA to enter a cells.


Works on bacteria, animal cells, plant cells that
have had their cell walls removed.
Gene gun
 Small
shotgun that shoots tiny gold or
tungsten particles coated w/ DNA into cells
 Good for plant cells with cell walls.
I Put a flyer on your windshield; it doesn’t
mean you’re going to read it: How do
organisms use their new DNA?

DNA remains in cytoplasm
 Plasmids:
self replicate, can be transcribed,
direct synthesis of new proteins

Insertion of genes into chromosomes
 Plasmids
can sometimes “pop in”
 Viral DNA can insert

Bacteria can use viral DNA to cause disease
How do organisms uses their new DNA-2

Transposons
 Pieces

of DNA that can jump
Recombination
 If
new DNA is similar to old, pieces swap out,
new DNA is used, old DNA is tossed.
 Bacteria: this is how DNA from transformation
and transduction become permanent.
 Similar process to crossing over (except all
DNA kept, just pieces are swapped)
Transposons – “jumping genes” code for
the enzyme transposase.
A simple transposon codes for transposase
and nothing else
Can break DNA
Delete other genes
Disrupt another gene
A complex transposon

Two transposons, close together, may
carry another piece of DNA between them.
THEDOGHOWAREYOUSAWTHECAT
Can attach pieces of one chromosome
to another
Can duplicate sections of DNA
Overall effect is to increase genetic
variation
Biotechnology
The use of living organisms for practical
purposes.
 How long has biotechnology been around?
 Since man began planting crops, breeding
livestock and brewing beer – about 10,000
years! It is even mentioned in the Bible.
 A more restrictive definition: manipulating
DNA or using DNA as a tool.

Today we can alter an animal or plant one
gene at a time, more rapidly and precisely
producing altered organisms.
 Even the boundaries between species are
becoming blurred as we move genes from
bacteria into plants and animals.

 Cotton-polyester
blends grown in cotton plants
 Alter biochemical pathways to delay ripening
 Pharming: production of human proteins in
plants or livestock for medical purposes
Recombinant DNA
A DNA molecule consisting of two or more
DNA segments that are not found together
in nature.
 We can insert a gene into a plasmid, and
infect a cell with the plasmid.
 “designer genes” “genetic engineering”

Genetic Engineering: not just for
science anymore

The ability to move genes around from
one species to another has far ranging
effects:
 Economic
 Societal
 Religious
 political
Why do it?

In agriculture
 improve
yields
 make herbicide resistant plants
 increase nutritional content
 increase disease resistance

important in medicine
 produce
new medicines, especially proteins
 vaccines
 cure
genetic disease
Recombinant DNA can be inserted into the cells
of whole plants and animals – these animals
are called transgenic organisms.
 Transgenes
 Insulin in the milk of cows, polyester blends
from cotton plants.
 To produce an organism that has the transgene
in all the appropriate cells of the organism the
DNA must be added to:
The zygote – the original single celled
organism – this is called germ line gene
therapy

Tools of genetic engineering
Restriction enzymes
 Cloning vectors
 PCR

DNAase and RNAase cut up genetic
material at random.
Restriction enzymes cut only at certain
sequences of bases, called restriction sites.
Made by bacteria to fight off viral infection.
Restriction Enzymes
Bacteria produce many different restriction
enzymes that cut genetic material at different
sites.
Some make “blunt” ends: ATTC GGATC
TAAG CCTAG

Some make “sticky” ends: ATTCGG
ATC
TAA
GCCTAG
These pieces are restriction fragments.
For recombinant DNA to be useful, we
needed to be able to produce large
quantities of a gene.
One way is to use plasmids.
A plasmid can be cut down to an origin of
replication and one or more genes for
antibiotic resistance.
Now any other gene can be inserted into the
plasmid and the bacterium will copy it.
PCR – polymerase chain reaction

1.
2.
Now we can easily copy or amplify DNA
in the lab.
Produce two oligonucleotides that match
up with the DNA before and after the
DNA you want to copy.
Heat DNA to break the hydrogen bonds
and open the DNA.
3. Add oligonucleotides (primers)
4. Cool, allowing primers to bind to DNA
5. Add nucleotides and DNA polymerase.
6. Repeat
Can now do the whole thing at higher
temperatures using the more stable
enzymes from Thermos aquaticus

PCR can be applied to :
 Amplifying
DNA in a drop of blood
 Find DNA from the HIV virus
 Find early signs of cancer
 Find genetic defects in human embryos
 Examine the DNA of ancient organisms
If we want to put eukaryotic DNA into
prokaryotic DNA we have one more
problem:
Introns! Bacteria do not have a means for
dealing with introns, so we must give them
a copy of a gene without introns in it.
Start with mature mRNA.
Use reverse transcriptase to copy it into
DNA.
This DNA is called complimentary or cDNA.
Unfortunately, some proteins need to be
modified after they are translated, which
can only be done in eukaryotic cells.
To get our gene into another cell we need a
vector – a means to carry it there.
This vector can be a plasmid or virus or
another means of carrying the DNA into
cells.
Now we can have bacterial or eukaryotic
cells making useful proteins – purer
vaccines, enzymes, drugs and human
proteins.