Download 4.2 Sources of DNA



Naturally occurs in cells
Scientists use cell cultures as a
source of DNA
Different types of cells are grown in
mediums
 Cell cultures are collected and lysed to
extract DNA





Do not contain a nucleus or any other membrane
bound organelles
DNA is usually found floating in cytoplasm
 attached at one spot to the cell membrane
One, long, circular chromosome
 supercoiled
 relatively small, several thousand genes
Very little spacer DNA
 Most DNA is necessary for survival
 Plasmids
 5 to 10 genes
 Code for proteins that offer some
additional characteristic that may be
needed only under extreme
conditions

R Plasmids
 contain antibiotic resistance genes
 allows bacteria to survive antibiotics
 transferrable
 allows bacteria to "evolve" into an antibiotic
resistant disease
 Scientists use this feature to transfer "genes
of interest" and transform bacteria genes

Different kinds of plasmids


Some bacteria have no plasmids
Some bacteria have more than one kind
 Often used as recombinant DNA vectors (rDNA) to
transform cells
 Cell will read DNA and synthesize proteins

Prokaryotic genes can be turned of during gene
expression using only a few controls

Makes the cells favorable for protein synthesis




R- Plasmids- a type of plasmid that contains a
gene for antibiotic resistance.
Transformed- refers to those cells that have
taken up foreign DNA and have started
expressing the genes on the newly acquired
DNA
Vector- a piece of DNA that carried one or
more games into a cell, usually circular as in
plasmid vectors
Operon- a section of prokaryotic DNA
consisting of one or more genes and their
controlling elements



RNA polymerase- an enzyme that catalyzes the
synthesis of complementary RNA strands from
a given DNA strand
Promoter- the region at the beginning of a gene
where RNA polymerase binds; the promoter
“promotes” the recruitment of RNA
polymerase and other factors required for
transcription.
Operator- a region on an operon that can either
turn on or off expression of a set of genes
depending on the binding of a regulatory
molecule.

Beta-galactosidae- an enzyme that catalyzes the
conversion of lactose into monosaccharides.
Figure 4.7 shows the prokaryotic cell of E.coli.
 Figure 4.8 shows the structure of a bacterium
showing the flagella, cytoplasm, cell wall,
chromosome and plasmid.
 Figure 4.9 shows beige and blue-black colonies of
bacteria transformed.
 Figure 4.10 shows an operon containing the
controlling elements that turn genetic expressions
On and Off.


Bacterial Cell Culture
Two types of mediums
 agar
 solid
 broth
 liquid
 reproduce quickly because cells have better access
to nutrients


Several chromosomes per cell




each chromosome is a single, linear, very long
molecule of DNA
may contain several million or more nucleotides
may contain several thousands of genes
Eukaryotic Genome is substantially larger than
that of prokaryotes


Bacterial cells have one chromosome
Humans have 46 chromosomes



The total amount of DNA per cell is not
directly related to an organism’s complexity.
Much of eukaryotic DNA is noncoding
meaning that is does not transribe into protein
Eukaryotes have a lack of operators in their
DNA, meaning that gene expression is
controlled differently


They are usually expressed at a very low level
Increases occur when enhancer molecules interact
with the RNA polymerase or with other enhancer
DNA regions where molecules attach to the DNA
and increase gene transcription



At the structural DNA, RNA polymerase
enzyme builds a complementary mRNA
transcript from one side of the DNA strand; the
enzyme transcribes the entire gene until it
reaches a terminal sequence
In eukaryotes, mRNA is often modified before
translation
Transcription factors turn genes “on”

These molecules either activate or repress gene
products, such as mRNA


Chromosomes in higher organisms are highly
coiled around structural proteins called
histones.
When genes are buried this way, RNA
polymerase cannot get them to transcribe them
into mRNA (so it has been essentially turned
“off”)



Enhancer- a section of DNA that increases the
expression of a gene
Intron- the region on a gene that is transcribed
into an mRNA molecule but not expressed in a
protein.
Exon- the region of a gene that directly codes
for a protein

It is the region of the gene that is expressed


Transcription factors- molecules that work to
either turn on or off the transcription
eukaryotic genes
Histones- nuclear proteins that bind to the
chromosomal DNA and condense it into highly
packed coils



Mammalian cells are more challenging to grow
because they normally grow within
multicellular organisms; they depend on other
cells for products and stimuli. So a
biotechnologist growing mammalian cells,
must provide it with a substitute but right
environment
Typically grown in broth cultures in fermenters
They have specific nutrients and special
indicators




Viruses infect organisms and are often the
target of biotechnology therapies
Used as vectors to carry DNA between cells
Do not have cellular structure; collections of
protein and nucleic acid molecules that become
active once they are within a cell. Are tiny
measure from 25 to 250nm
Viruses are either bacterial, plant or animal



Viruses are classified further based on the
specific type of cell infected an on other
characteristics, such as genetic material and
shape; they all have a thick protein coat
surrounding a nucleic acid core of wither DNA
or RNA
Lysogenic viruses incorporate their DNA in the
host chromosome while lytic viruses do not
Viral vaccine molecules recognize specific viral
surface proteins and target them for attack;
protease inhibitors destroy proteases made by
viruses in their attempts to take over host cells



Viral DNA or RNA molecules are short so easy
to manipulate, since they do not create as many
proteins as cells do. Viral DNA is sometimes
used as a vector because they can open to insert
genes of interest.
Some companies are exploring the use of gene
therapy to treat diabetes by replacing defective
insulin genes in the pancreas
Gene therapy is possible treatment for cystic
fibrosis and other genetic disorders