Transcript Genetic Control of Metabolism

Higher Biology
Unit 2
2.7 Genetic Control of Metabolism
Wild Type Microbes
• Wild type is the typical form of a species
found in nature.
• A wild type microbe can be selected for
use in industry due to it exhibiting a
desirable genetic trait.
• Even with this desirable trait, it may lack
other important traits.
• Scientists try to improve the microbe to
include the genetic material for these
other traits.
Wild Type Microbes
Examples of traits hoped to be gained by
strain improvement include;
• the ability to grow on low cost growth
medium
• genetic stability
• production of large quantities of
secondary metabolites
Wild Type Microbes
Wild types of microbes are improved for
use in biotechnology by altering the
microbe’s genome.
This can be done in different ways;
• Mutagenesis
• Selective Breeding
• Recombinant DNA
Mutagenesis
Mutagenesis is the creation of mutations.
In nature, mutations;
• are rare
• occur spontaneously and at random
• are usually detrimental to the organism
Mutagenesis
The rate of mutation can be increased by
the use of mutagenic agents.
Examples include;
• radiation e.g. UV light and X rays
• chemicals such as mustard gas
Mutagenesis
• On very rare occasions, a mutant allele
can arise that confers an advantage to
the organism or endows it with a new
property that is useful to humans.
• Therefore, mutagenesis can be useful
during industrial processes as a microbe
may develop a new property that proves
useful to humans.
Mutagenesis
• Unfortunately, mutated strains of
microbes tend to be genetically unstable.
• This means they sometimes undergo a
reverse mutation, reverting to the original
(and less useful) wild type.
• This would be very costly in terms of time
and resources.
• In industry, an improved strain of microbe
must be monitored regularly to ensure that
it is still in its mutated form before it is
used.
Selective Breeding
Sexual Reproduction
Asexual Reproduction
• Two parents
• Fusion of male &
female gametes,
forming a zygote
• Offspring show
variation
• Some eukaryotic
cells e.g. yeasts
• One parent
• No gametes
involved
• Offspring are
clones
• Some eukaryotic
cells e.g. yeasts
• Bacteria
Selective Breeding
• By deliberately crossing different
strains during breeding programmes,
scientists are able to produce new
strains of microbes.
• On some occasions, a new strain
combines two desirable characteristics,
one from each parent.
Selective Breeding
Selective Breeding
Horizontal Transfer
Although bacteria don’t reproduce
sexually, new strains can arise as a result
of horizontal transfer of genetic material.
During this, plasmids or pieces of DNA can
be transferred from one strain to another
via a conjugation tube.
Selective Breeding
Horizontal Transfer
• New strains are also produced by
bacteria taking up DNA fragments
from their environment.
• Scientists try to produce new strains
of useful bacteria by culturing existing
strains together in conditions where
horizontal transfer of DNA is most
likely to occur.
Recombinant DNA
• This is the transfer of genes from one
organism to another (can be of
different species).
• Think: genetic engineering from
National 5.
• This allows bacteria to produce plant or
animal proteins e.g. human insulin.
• The bacterium is said to be artificially
transformed.
Enzymes
In recombinant DNA, two different
types of enzyme are used;
• restriction endonucleases
• ligase
Restriction Endonucleases
• These enzymes are taken from microbes
• They are used to cut DNA from both
the donor and the receiving plasmid
• They recognise specific sequences of
DNA bases called restriction sites
Restriction Endonucleases
• The same restriction endonuclease must
be used to cut both donor and plasmid
• This ensures the ends of both DNA
fragments have DNA bases that are
complementary to each other
• The ends of the cut DNA fragments are
described as “sticky”
Restriction Endonucleases
• The sticky ends of the required gene
and plasmid stick together because
their DNA bases are complimentary
Ligase
• These enzymes stick the DNA
fragments together.
• This seals the desired gene into the
plasmid
• Each end of the fragments must have
complementary bases
Vectors
• In recombinant DNA,
the gene is transferred
by a vector.
• The vector is usually a
plasmid or an artificial
chromosome.
• Artificial chromosomes
can transfer much
longer DNA sequences
Vectors
To be an effective
vector, a plasmid must
have three features;
• restriction site
• marker gene
• origin of replication
Restriction
site
Origin
of
replication
Marker
gene
Restriction site
• Must be able to be opened
with the same restriction
endonuclease used to cut
open the donor DNA
• This ensures that the
sticky ends of both donor
DNA and the plasmid DNA
are complementary
Marker gene
• This gene shows if the cell
has taken up the plasmid.
• It is usually a gene that
gives the bacterium
resistance to an antibiotic.
• Any cell that hasn’t taken
up the plasmid will die as it
has no resistance to the
antibiotic
Origin of replication
• This consists of genes
that control self
replication of the plasmid
• It is needed to make many
copies of the plasmid
(carrying the desired
gene) within the bacterial
cell.
Recombinant DNA
Improvements made to microbes include;
• Amplifying specific steps in a metabolic
pathway or removing inhibitors to
increase the yield of desired product.
• The ability to secrete product into the
surrounding medium. This allows it to
be collected easily, saving resources.
• Ensuring it can’t survive in the external
environment. This is a safety
precaution.
Recombinant Yeast Cells
Sometimes there are problems with
bacterial cells producing the desired
protein e.g.
• They don't secrete the protein into the
surrounding medium
• They degrade the protein before it can
be collected
Recombinant Yeast Cells
• In these cases, genetically transformed
eukaryotic cells e.g. yeast is a
preferable option.
• This is despite eukaryotic cells having
more demanding cultural conditions.