Unit 2: Metabolism and Survival Sub-Topic (2.7) Genetic Control of Metabolism (2… · 2017-08-03 · Higher Biology Pupil Course Notes Duncanrig Secondary JHM&MHC 2015 Page 1 of

Higher Biology Pupil Course Notes

Duncanrig Secondary JHM&MHC 2015 Page 1 of 18

Unit 2: Metabolism and Survival

Sub-Topic (2.7) Genetic Control of Metabolism

(2.8) Ethical considerations in the use of microorganisms



On completion of this topic I will be able to:

Explain that wild strains of microorganisms can be improved by alteration of

the genome (mutation). This could occur naturally, by selective breeding or

recombinant DNA technology (genetic engineering).

Explain that mutations can be induced by radiation or chemicals.

Describe how bacteria can transfer plasmids or pieces of DNA to each other or

from their environment.

Know that some fungi (eukaryotes) produce variation through sexual

reproduction.

Explain that plant and animal genes can be transferred to microbes causing

them to express the donor gene products (proteins).

Know that yields can be increased by gene manipulation.

Describe examples of genes which have been introduced to increase yield.

Know that safety mechanisms can also be introduced.

Describe examples of genes that can be introduced that prevent the survival

of microorganisms outside the laboratory setting.

Explain that extra chromosomal DNA can be transferred to microorganisms

which contain a variety of genes with specific functions.

Know that recombinant DNA technology involves the transfer of gene

sequences from plants or animals to microorganisms.

Describe and explain the structure of commercial plasmids with reference to

restriction sites, marker genes, origin of replication, selective markers and

regulatory sequences.

Describe the process of recombinant DNA technology including the terms

restriction endonuclease and ligase.

Know that some plant and animal proteins are best expressed in recombinant

yeast cells.

Describe the ethical issues and explain that biotechnological processes come

with some potential hazards and control risks which need to be assessed.



Prior Learning

Unit 1.1 Cell structure

Cells differ in structure as to whether they are animal, plant, fungi or bacterial

cells.

Nucleus contains genetic information and controls all cell activities.

Bacterium has a plasmids, and the chromosomal material is not in a nucleus.

Unit 1.2 Producing New Cells

Tissue culturing is a technique used to artificially produce new cells.

Variables such as oxygen concentration, pH and temperature must be

controlled when carrying out tissue culture techniques.

Tissue culture techniques must be carried out under sterile conditions by using

aseptic techniques.

Tissue culture techniques allow tissues to be mass produced.

Agar jelly and nutrient broth are both mediums that cells and

microorganisms can be grown on.

Unit 1.3 Genetic Engineering

Genetic information can be transferred from one cell to another naturally or by genetic by

genetic engineering.

Bacteria and viruses are used to transfer genetic material from one

organism to another.

Bacteria have one large chromosome in a ring and smaller rings called

plasmids.

Genetic engineering is the transfer of DNA from one type of organism to

another artificially.

The stages in genetic engineering.

Genetic engineering is used for the commercial production of medicines such as

insulin, human growth hormone and factor VIII.

Genetic engineering is used for the commercial production of crops with

disease resistance such as potatoes resistant to the Potato Blight virus or

tomatoes with a longer shelf life.



Genetic Control of Metabolism

Some bacteria can naturally transfer plasmids or chromosomal DNA to each other or

take up DNA from the environment to produce new strains.

Microorganisms are used by humans as they can be induced to make useful

products. Wild strains of microorganisms are often cultivated and modified to

improve them. They may need improvement because:

they lack genetic stability

they will not grow on low-cost nutrients

they do not produce vast enough quantities of the desired product

they are not easy to separate from the product.

Therefore strain improvement is carried out to alter the genetic make-up and include

addition genetic material to rectify these traits.

Techniques used to do this include:

mutations & mutagenesis

selective breeding and culture

recombinant DNA technology

1. Mutations & Mutagenesis

Mutations can arise naturally. When a change in the genotype produces a change

in the phenotype the organism affected is called a mutant.

Mutations are often harmful to an organism. Those which are beneficial are rare.

Mutagenesis is the creation of mutations. The frequency of mutations can be

increased by exposing the DNA to mutagenic agents. Examples of mutagenic

agents include:

__________________________________

__________________________________

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A wild strain (type) of microorganism is the naturally occurring strain found in

nature.

A wild strain that may be of use in industry is selected and cultured with optimum

growing conditions. Pure strains are then isolated and screened for desired traits.



Once the wild strain is isolated it may still be lacking important features.

The rate of mutagenesis can be increased by using mutagenic agents, which alter

the organisms DNA, resulting in a mutation. If a cell stops making a protein that

would have been coded for by a normal gene, it may block the metabolic pathway

and intermediate metabolites may build up. If they are desirable substances, then

these are harvested for use by humans.

Some mutations can be beneficial e.g. a strain that produces higher levels of a

desired product. However, mutant strains are often genetically unstable and revert

to the wild type in continuous culture. Therefore, it is very important that an

improved strain of a microorganism is carefully monitored to make sure that it is the

mutant that is selected for use.

2. Selective Breeding and Culture

Selective breeding is the process by which humans deliberately cross different strains

of organisms to produce new strains showing the desirable characteristics from each

parent.



Genetic Transfer

Scientists also attempt to produce new strains of useful bacteria by creating

conditions where transfer of genetic material may occur.

New strains of bacteria can occur by horizontal transfer of genetic material – this

occurs naturally when:

Bacteria transfer plasmids or pieces of chromosomal DNA from one strain to

another.

Bacteria take up and incorporate fragments of DNA from their environment.

This uptake, incorporation and expression of DNA from a bacterium's

surroundings is called transformation.

Horizontal Transfer – Use Torrance Fig 13.6 to label the following diagrams, and

beside them, write a description of the process.

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Transformation

In some species transformation occurs naturally when the cell takes up a piece of

foreign DNA from the remains of a cell that has been destroyed and has undergone

lysis.



3. Recombinant DNA technology

Scientists can use recombinant DNA technology to reprogramme microorganisms.

This means scientists can transfer plant or animal gene sequences to microorganisms

to make them produce plant or animal proteins.

Scientists can also use this technology to introduce a gene or genes to existing

microorganisms to:

Improve yield – by amplifying a specific metabolic step or

removing an inhibitory control that affects it

Improve extraction of product – by causing a cell to secrete the

product into surrounding environment

Add a safety mechanism - make the microorganism incapable of

surviving in another environment

A gene from one organism (e.g. a human or a plant) is transferred into a vector

(plasmid or artificial chromosome) of a microorganism so that the microbe

produces the protein that the gene codes for.



The previous diagram shows the introduction of a gene into a bacterium via a

plasmid.

The protein produced by the microorganism could be

Penicillin

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____________________

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Recombinant DNA Technology is a highly skilled process with many factors which

need to be taken into account and carefully controlled, including the following:

Enzymes

Two types of enzymes are required in recombinant DNA technology – one type to

cut open chromosomes and the other to seal pieces of DNA together.

1. Restriction endonucleases

These are enzymes which recognise specific short sequences of bases on DNA

(about 4–8 nucleotides in length), known as restriction sites. The sequence can be

found on both of the DNA strands and may be repeated at intervals along its length.

The restriction enzyme causes a cut to be made every time it meets this sequence.

The cut can either produce ‘blunt’ ends or ‘sticky’ ends.

If the cut goes straight through the DNA molecule, blunt ends will be produced as

the two strands of nucleotides will be cut at the same place.



If the nucleotides are cut at different points (several

nucleotides apart), each strand will be left with a short

single stranded sequence sticking out.

As restriction enzymes always cut at their own specifically

recognised sequences, the same enzyme must be used to

cut out the desired gene and o open the plasmid into

which it is to be inserted. This ensures complementary

sticky ends.

2. DNA ligase

DNA ligase is an enzyme which seals ends of DNA fragments together by making

bonds form between them. It is therefore applied to seal the introduced gene into

the plasmid before it is inserted back into a bacterium.

Ligase enzyme seals DNA at

these points



Vectors

A vector is something that can have DNA from another source inserted into it.

Recombinant (bacterial) plasmids

Artificial chromosomes are used as vectors to carry DNA from

one organism (e.g. human gene) into another (e.g. bacteria). This

brings about transformation in the bacterial cell.

1. Plasmids as vectors

To be effective as a vector, a plasmid must have the following features:

a. Restriction Site that is cut by the same restriction endonuclease that

cut the gene to be transferred in. This ensures the sticky ends are

complementary to the gene being inserted.



b. Marker Gene to allow the scientist to determine whether the host

cell has taken up the plasmid vector, e.g. if the plasmid takes up a gene

giving resistance to an antibiotic, the cells are then cultured in a medium

containing that antibiotic. Any cells that failed to take up the

recombinant plasmid will be killed by the antibiotic, leaving only the ones

with the modification. Fluorescent proteins can also be used as markers.

c. Origin of Replication these genes control self-replication and

regulatory sequences that allow control of existing genes and the

expression of the inserted gene.

This is essential if the transformed cell is to make more copies of the

plasmid and therefore make more of the desired product.

Use Torrance Fig 13.10 to label these three sites on the plasmid.

____

Bacteria with the gene inserted

do not turn blue



To be an effective vector the plasmid must have:

a. ___________________________

b. ___________________________

c. ___________________________

2. Artificial Chromosomes as Vectors

Artificial Chromosomes have been developed by Scientists to act as vectors.

They have all 3 features described for plasmids (restriction site, marker gene and

origin of replication). However, in addition to this they are also able to carry

much more foreign DNA than a plasmid.

Why might a DNA technologist choose to use an artificial chromosome as a vector

instead of a plasmid?

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Strain improvement

New genes introduced to a microorganism, such as a bacterium or a yeast cell can

confer an advantage on that organism by;

Improving the steps in a metabolic pathway or removing inhibitory parts of it

in order to improve the yield of production of a substance

Causing the cell to secrete the product allowing it to be harvested more easily

Acting a safety mechanism by ensuring that the altered microorganism cannot

survive in the wild, removing the possibility of it breeding with wild strains.

Limitations

The DNA of eukaryotes contains protein coding sections called ____________ as

well as non-coding DNA known as ____________.

The DNA of prokaryotes, such as bacteria, has exons but no introns.

When DNA is transcribed into mRNA in a eukaryote, the primary transcripts are

modified by splicing to remove introns (see previous notes on gene expression).

In addition to this, once the protein has been produced it is often modified further

(e.g. folded in a particular way or another substance added to it).

Neither of these processes occurs in prokaryotes.

As a result of these differences, problems can arise when a gene from a eukaryote is

expressed by a prokaryote. It may be that the protein produced does not function at

all as it is not folded properly or that it breaks down before it can be collected.

In order to overcome these difficulties, it is sometimes necessary to use genetically

modified eukaryotic cells, such as yeast, to avoid polypeptides being folded

incorrectly or lacking some other post translational modification.



Answer the ‘Testing Your Knowledge’ questions from Torrance Page 216.

Ethics

Describe the ethical considerations under both headings below:

Profit

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Patents

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Hazards and Risks

How long does it take to introduce a new microbiological product onto the consumer

market?

_______________________________________

Before the new product is granted a licence to manufacture and sell, what must they

ensure?

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Complete the risk assessment cycle below:

Research task:



Research the development of a microbiological product from discovery to market.

– Name the product and explain its use

– Describe each step of the process from development to market

– Summarise how long the process took, the problems encountered and

the benefits achieved from its availability

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Unit 2: Metabolism and Survival Sub-Topic (2.7) Genetic Control of Metabolism (2… · 2017-08-03 · Higher Biology Pupil Course Notes Duncanrig Secondary JHM&MHC 2015 Page 1 of

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