Unit 3 Biology: signatures of life
conceptual framework
Chemical nature
of the cell
The nature of
molecules
Interactions between
molecules determine
shape of
biomacromolecules
and produces
binding sites for:
•enzymes and
substrates
•Signals and
receptors
•Antibodies and
antigens
Explains how:
•various materials
enter and leave a
cell
•Cells receive and
respond to signals
•How the immune
system works
•How vaccines
work
•How we design
drugs
Molecular biology in medicine
EL: To explore the application of molecular
biology in medicine.
Molecular biology
Applications of molecular biology in medicine,
include:
Knowledge
the
◦
◦
the
and manipulation of genetic material
development of designer drugs to:
Prevent action of infective micro-organisms
Inhibit the action of specific chemicals in the body
production of hormones and plant vaccines
Inherited diseases

Also known as genetic disorders

Exist because of defect in kind or amount
of DNA in the affected organism

Many different types
◦ Eg a whole chromosome may be involved or
just a single gene (NB.We’ll only focus on single
gene defects)
Inherited diseases

Knowledge about the gene responsible
may allow:
◦ Testing for the presence of the defective gene
(eg breast cancer gene, phenylketonuria
(PKU)
◦ Special treatment to delay onset of the
disease
◦ Reducing severity of condition through
treatment (eg cystic fibrosis) or special diet
(eg galactosaemia, PKU)
Gene therapy

The insertion of a normal functional gene
into cells that contain a defect

Two types:
◦ in vivo: gene therapy given directly to patient
◦ ex vivo: gene therapy in which the patient’s cells
are manipulated outside the body and then
returned into the individual

The specially prepared functional piece of
DNA inserted into the cell is called a
cloned gene
Gene therapy
Viral Gene therapy
A vector is used to carry the gene into a cell

Most commonly used vectors are viruses
◦ Viruses with DNA replicate in the nucleus of the
cells they infect
◦ Viruses with RNA replicate in the cytoplasm of
the cells they infect
 Exception is RNA viruses called retroviruses – they also
replicate in the nucleus

Most commonly used vectors in gene therepy
are retroviruses and adenoviruses
Retroviruses

Only used in cells that are reproducing
when nuclear membrane breaks down
and chromosomes of infected cell
become accessible

Useful for cells that can be taken out an
cultured outside the body (eg blood,
bone marrow)
Adenoviruses

DNA viruses – enters nucleus but
remains separate from the host DNA

The cloned DNA is functional and
produces functional protein

May be short-lived as this small piece of
DNA doesn’t replicate when the host
cell does
Adenoviruses
Viral Gene therapy

Still experimental in humans and can
pose risks to patients safety, eg
◦ Temporary solution
◦ Insertion into wrong place on chromosome,
causing a different disease
◦ Immune response to virus
Non viral Gene therapy

As yet, not very successful

Methods include
◦ Transporting DNA into cells in lipid spheres
◦ Direct injection of DNA into cells
◦ Manufacture of artificial chromosomes
Medical diagnosis: Pre-Natal Testing

Used to determine if baby has a genetic
defect

Done via:
◦ Ultrasound: physical defects
◦ Biochemical test on embryonic cells or
amniotic fluid: metabolic defect
Medical diagnosis

Obtaining a sample of embryo cells can
be done through:
◦ Chorionic villus sampling:
 at 6-8 weeks
 Removal of a small piece of chorion tissue
◦ Amniocentesis
 At 16-18 weeks
 Collecting a sample of amniotic fluid surrounding
the fetus
Medical diagnosis
Medical diagnosis:
Presymptomatic testing

Breast cancer: women with BRCA1 or
BRCA2 gene have 80% risk of
developing breast cancer (compared
with 10% in rest of population)

Tests exist for the gene an women who
test positive may either:
◦ have their breasts removed before they
develop the disease, or
◦ get regular mamograms
Rational drug design

When a drug is designed to act against
an infective agent:
◦ The molecular structure of the active site of
the infective agent is established
◦ The drug is designed to have a
complementary structure
◦ The drug locks into the active site to
prevent development of the disease
Rational drug design

When a drug is designed to inhibit the
action of a chemical in the blood:
◦ The molecular structure of chemical is
established
◦ The drug is designed to have a structure
that locks into the active site of the
chemical
◦ The chemical is inactivated
Rational drug design

The delivery of vaccines in plant material as
food involves:
◦ Determining the molecular structure of the
proteins in the infective agent that cause the
immune response
◦ Introducing the DNA that codes for these
proteins into the plant genome
◦ Growing and harvesting the plants

eg measles vaccine in powdered lettuce,
cholera vaccine in rice
Manufacturing biological molecules
Genetically engineering proteins that are
deficient (eg insulin)
Nanoparticles

Nanoparticles are:
◦ Manufactured
◦ 1-100 nanometers (one billionth of a meter)
in diameter
◦ Made of a double layer of phospholipids to
mimic plasma membrane of the cell

Used to deliver toxic drugs directly to
target cells (eg tumour cells), reducing the
chance of affecting healthy cells
Activity/homework

Complete the Molecular Biology exam
questions

Chapter 4 Quick Check qu 1-16
Reflection

What did you learn about molecular
biology today?