genetic biotechnology notes · bacteria genetics bacterial dna forms a circular, double stranded...
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Genetic Biotechnology Notes
YouTube Video on Gel Electrophoresis
Gel Electrophoresis
Gel Electrophoresis: A process and tool used to separate and sort the nitrogenous
bases within nucleotides, and determine a person’s genomic sequence (the sequence of
all of their nitrogenous bases).
How Does This Work?
o The DNA is cut into smaller pieces that can move more easily, by “Restriction
Enzymes”.
o The DNA is placed onto an agarose gel (like we used in our Surface Area vs
Volume lab!).
o The agarose gel is placed onto an electric field…. One end is the Cathode
(negatively charged) and the other end is the Anode (positively charged).
o Because the Phosphate group in each nucleotide is a Negatively Charged Ion, the
DNA naturally moves down the agarose gel from the Cathode to the Anode.
o Because each Nitrogenous Base (in each nucleotide of DNA) has a different
atomic composition, each has a different mass, and thus moves at a different
rate. (*Lighter bases move faster, heavier bases move more slowly.)
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(Read from the bottom, Anode End, to the top, Cathode End)
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Recombinant DNA & Cloning
YouTube Video on Recombinant DNA
Recombinant DNA = Taking multiple sources of DNA, and combining them into one
molecule.
Can happen naturally (like when viruses infect cells and acquire some of the host’s
DNA).
Scientists though use it to engineer genes.
These engineering genes can be implanted in bacterial cells that can then mass produce
useful proteins (like Human Insulin sold by Pharmaceutical Companies, or alter the
metabolism of bacteria to consume toxic waste in oceans)!
Vector Gene Therapy
Remember learning about DMD in Biology?
DMD is a muscle degeneration disorder, caused by a mutated gene that is inherited.
Kids born with this gene will eventually die from the disorder.
With genetic disorders like this, scientists can insert engineered DNA, from man-made
viruses, into the patient’s cells….
The engineered DNA has the correct version of the gene needed…
And this can help the patient’s cells make the proteins needed to be healthy!
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CRISPR
YouTube Video on CRISPR
CRISPR = Clustered Regularly Interspersed Short Palindromic Repeats (Freakin Scientists
haha)
Tool that can change an organism’s DNA.
Uses an enzyme called “Cas9”.
Scientists discovered CRISPR because bacteria contain enzymes and a process that naturally do
this (as a mechanism to destroy viruses that attempt to re-infect).
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Virus Genetics
Viruses are parasites that can only complete living functions when inside another living
cell. (For this reason, many scientists do not consider viruses to be living themselves.)
Virus Structure & Composition:
o Contains DNA or RNA which stores its genetic information.
o DNA/RNA is stored in a protein-based structure called a Capsid.
o Some viruses have an additional covering outside the Capsid, called the Envelope.
The Envelope is a portion of a host’s cell membrane (forming a vesicle around the
virus). This Envelope makes it easier for viruses to infect cells, because it contains
membrane receptors that already exist within that organism!
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Each virus can only infect specific cell types, based on the receptors they have, and the
receptors on the organism’s cells.
o Example Some viruses that cause the common cold in humans, can only bind
to the cell membranes of cells in respiratory tissue of humans.
o Example The HIV virus can only infect certain types of white blood cells within
humans.
o When viruses can infect different types of organisms (say humans and birds and
pigs, for example), this is because those organisms are all genetically related.
To be genetically related means that those animals all descended from the
same common ancestor.
As a result, they share certain genes/DNA, and have similar organ systems,
tissues, etc.
These similarities in DNA and organ tissues, also means that they have the
same types of receptors on their cells, allowing the virus to infect any
animals similar.
Sometimes, like in all of evolution, a virus can have a genetic mutation that
by just random luck and chance, allows it to infect a wider range of
organisms.
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Bacteriophage: A type of virus that only infects bacterial cells! ( A lot of kids recognize
these viruses from something on Jimmy Neutron hehe.)
o Lytic Cycle
Process in which the bacteriophage virus enters the host cell…
Takes control of cell machinery…
Replicates itself…
Causes the bacterial cell to explode because it is so full of newly made
viruses…
Newly made viruses are released to infect more cells.
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o Lysogenic Cycle
Process in which the virus is able to replicate, WITHOUT killing the host cell.
Virus DNA becomes embedded in host’s DNA…
As the host cell replicates and divides, the virus is also replicated…
The virus stays inside the cells, but because the cell replicates and divides
everything inside (including the viruses), it makes more and more infected
cells.
o Transduction: When bacteriophage viruses infect bacteria, some of the bacteria’s
DNA often becomes part of the viral DNA, leading to genetic recombination and
diversity in viruses.
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Retroviruses: Viruses that contain RNA, instead of DNA, and replicate in an unusual
way.
o Retrovirus Replication
Infect host cell…
Virus RNA is the template for complimentary DNA (cDNA) that is made…
(Yes that means the virus makes the cell do REVERSE transcription, RNA
DNA.)
The complimentary DNA becomes a permanent part of the host’s DNA.
This is why these types of viruses (like HIV) cannot EVER be “cured”.
Once the viral complimentary DNA is made, and is part of the person’s
DNA, there is no way to remove it, and no way to prevent cells from making
the viruses.
YouTube Video on Viruses
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Bacteria Genetics
Bacterial DNA forms a circular, double stranded chromosome.
Some bacteria contain an extra circular pieces of DNA, called a Plasmid.
(Plasmids often contain genetic information to allow the cell to be antibiotic resistant.)
Binary Fission Asexual reproduction for bacterial cells.
o Bacterial cell makes a copy of itself (and all of its internal contents).
o Bacterial cell divides.
o *Very similar to Mitosis .
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Bacterial Conjugation Sharing of genetic information between bacterial cells.
o Bacterial cell copies their plasmid/s.
(Yes! Bacteria can have multiple plasmids… making them resistant to multiple
antibiotics!)
o Bacteria extend a tube-like, membrane projection, connecting to the other
bacterial cell, called a Pili.
o The plasmid copy passes through the Pili.
o Now the other bacterial cell has that plasmid!
(Good for bacteria, bad for humans.)
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The Operon
YouTube Video on Gene Regulation
Found only in bacteria.
Operon: A set of genes and the switches that control the expression of those genes.
2 Types of Operons:
o Repressible (Tryptophan)
o Inducible (lac)
The Repressible / Tryptophan Operon:
o Prevents RNA Polymerase from binding to DNA and transcribing a specific gene
(thus not producing a specific protein for that gene).
o “Turns a gene off”.
o Used when a cell has enough of a protein, and does not need to make any more.
o EXAMPLE:
When there is enough Tryptophan already made…
Tryptophan activates the “repressor”.
The activated repressor binds to the “operator”.
RNA Polymerase is prevented from binding to the promoter.
Transcription stops.
Tryptophan is not produced.
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When there is NOT enough Tryptophan made…
Nothing activates the “repressor”.
Nothing prevents RNA Polymerase from binding to the promoter on
DNA.
Transcription happens.
Tryptophan is produced.
The Inducible / lac Operon:
o Encourages / Allows RNA Polymerase to bind to DNA and transcribe a specific
gene (thus producing a specific protein for that gene).
o “Turns a gene on”.
o Used when the body needs to make more of a protein.
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The Human Genome
Human Genome = The entire sequencing of human genes within our DNA.
o Approximately 3 billion nitrogenous base pairs!
o Approximately 22,000 genes!
o Only about 1% of our DNA actually gets translated into proteins!!
o A good portion of our DNA is used to produce RNA, has regulatory sequences like
the operon in bacteria, and contains sequences that can alter gene expression.
Scientists discovered that the ends of DNA (Telomeres) are full of repeating genes. This
is so that if portions of the telomeres are lost during DNA Replication and/or aging, the
needed genes are protected.
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Short Tandem Repeats = Super short sequences of DNA (only 2-5 nucleotides) that do
not code for any protein.
o The amount of these in a person’s DNA, their location, etc. is UNIQUE TO EVERY
PERSON!
o Forensic Scientists can use the location/frequency of Short Tandem Repeats along
with gene variations to identify a person by their DNA!
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Regulating Gene Expression
Even though most cells contain a full copy of our DNA, each cell only expresses a small
percentage of our genes at one time.
o This allows all of our cells to be “differentiated” (have different structures and
functions)
o Similar, but much more complicated, to the Operon functioning in bacteria.
Way #1 to Regulate Genes Chromatin Formation
o Our DNA can be tightly wound up into Chromatin, and even more tightly wound
into Chromosomes.
o Proteins called Histones are used to coil and wind up DNA.
o “Turning Off a Gene”:
Changes to the structure of Histones can cause the Chromatin to coil tighter,
hiding the nitrogenous bases in the DNA in certain places, making it impossible for
the cell to transcribe those places/genes.
o “Turning a Gene Back On”:
An acetyl group gets added to histones, causing the DNA to loosen up so that the
nitrogenous bases can be exposed and transcribed.
Way #2 to Regulate Genes Methylation of DNA
o Methylation = Adding methyl groups to specific nitrogenous bases within DNA.
o Methylated Nitrogenous Bases cannot be transcribed, thus “Turning Off” the
gene/s.
o Removal of the methyl groups allows those regions/genes in DNA to be
transcribed, and “Turned On”.
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Way #3 to Regulate Genes Epigenetic Inheritance
o Epigenetic Inheritance = Changes to DNA, that are not permanent, and are the
result of environmental factors (diet, stress and stress hormones, nutrition,
drugs).
o Not well understood. Hypothesized that these factors, alter the ability of certain
genes to be transcribed, turning them “off”.
o It is then thought that once these factors change / improve, the genes can be
transcribed, turning them “on”.
Way #4 to Regulate Genes Transcription Factors
o The presence or absence of different enzymes during Transcription, allows genes
to be transcribed, and genes to be “Turned On” or “Off”.
Way #5 to Regulate Genes Introns & Exons
o Alternative RNA Splicing = When different mRNA molecules are made from the
same DNA template, but with different variations in which genes are Introns and
which are Exons.
o Intron = Nitrogenous Bases that are not expressed (or are not used to produce a
protein).
o Exon = Nitrogenous Bases that ARE expressed (or are used to produce a protein).
o The binding of different proteins to different genes determines if the gene will be
an Intron or an Exon.
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