Chapter 5: DNA, Gene Expression, and Biotechnology

Chapter 5: DNA, Gene Expression, and Biotechnology

What is the code and how is it harnessed?

Lectures by Mark Manteuffel, St. Louis Community College

Learning Objectives Describe what DNA is and what it does. Explain the process of gene expression and

the collaboration of nature and nurture. Explain the causes and effects of damage

to the genetic code. Describe biotechnology and its implications

for human health. Discuss biotechnology in agriculture. Discuss biotechnology today and tomorrow.

5.1 “The DNA 200”

Knowledge about DNA is increasing justice in the world.

What is the most common reason why DNA analyses overturn incorrect criminal convictions?

Selfish dictators may owe their behaviour partly to their genes, according to a study that claims to have found a genetic link to ruthlessness.

–Nature, April 2008

Whether a man has one type of gene versus another could help decide whether he’s good “husband material,” a new study suggests.

–Washington Post, September 2008

The “Age of the Gene”

Take-home message 5.1

DNA is a molecule that all living organisms carry in every cell in their body.


Unique in virtually every person, DNA can serve as an individual identifier, left behind us as we go about our lives.

This is a fact that is used increasingly to ensure greater justice in our society, such as through establishing the innocence of individuals wrongly convicted of crimes.

5.2 The DNA molecule contains instructions for the development and functioning of all living organisms.

Two Important Features of DNA

(1) DNA contains the instructions on how to create a body and control its growth and development.

(2) The instructions encoded in the DNA molecule are passed down from parent to offspring.

DNA “Double Helix”

Nucleic acids and nucleotides

Sugars, Phosphates, and Bases

A, T, C, and GBase pairs


DNA is a nucleic acid, a macromolecule that stores information.

It consists of individual units called nucleotides: a sugar, a phosphate group, and a nitrogen-containing base.


DNA’s structure resembles a twisted ladder, with the sugar and phosphate groups serving as the backbones of the molecule and base pairs serving as the rungs.

5.3 Genes are sections of DNA that contain instructions for making proteins.

Why is DNA considered the universal code for all

life on earth?

The number of chromosomes varies from species to species.

Corn has 10 unique chromosomes.

Fruit flies have only four.

Dogs and chickens have 39 different chromosomes.

Goldfish have 47 chromosomes.

Individuals in each of these species inherit one copy of each chromosome from each parent.

Genes

A sequence of bases in a DNA molecule that carries the information necessary for producing a functional product, usually a protein molecule or RNA


DNA is a universal language that provides the instructions for building all the structures of all living organisms.

The full set of DNA an organism carries is called its genome.


In prokaryotes, the DNA occurs in circular pieces.

In eukaryotes, the genome is divided among smaller, linear strands of DNA called chromosomes.


A gene is a sequence of bases in a DNA molecule that carries the information necessary for producing a functional product, usually a protein molecule or RNA.

5.4 Not all DNA contains instructions for making proteins.

An onion has five times as much DNA as a human.

Why doesn’t that make them more complex than

us?

The Proportion of the DNA

That Codes for Genes

Introns

Non-coding regions of DNA

May take the form of short (or long) sequences that are repeated thousands of times

May also consist of gene fragments, duplicate versions of genes, and pseudogenes


Only a small fraction of the DNA in eukaryotic species codes for genes.

The function of the rest is still a mystery.

5.5 How do genes work?

An overview

Genotype•all of the genes contained in an

organism

Phenotype•the physical manifestations of the

instructions


The genes in strands of DNA are a storehouse of information, an instruction book.


The process by which this information is used to build an organism occurs in two main steps:

transcription, in which a copy of the a gene’s base sequence is made, and

translation, in which that copy is used to direct the production of a protein.

5.6 Transcription: reading the information coded in DNA


Transcription is the first step in the two-step process by which DNA directs the synthesis of proteins.

In transcription, a single copy of one specific gene within the DNA is made, in the form of a molecule of mRNA, which moves where it can be translated into a protein.

5.7 Translation: using information from DNA to build usable molecules

Several ingredients must be present in the cytoplasm for

translation to occur.

Free amino acids

Ribosomal units

Transfer RNA


Translation is the second step in the two-step process by which DNA directs the synthesis of proteins.

In translation, the information from a gene that has been carried by the nucleotide sequence of an mRNA is read, and ingredients present in the cell’s cytoplasm are used to produce a protein.

5.8 Causes and effects of mutation

Alteration of the sequence of bases in DNA

• can lead to changes in the structure and function of the proteins produced

• can have a range of effects

Breast Cancer in Humans

Two human genes, called BRCA1 and BRCA2

More than 200 different changes in the DNA sequences of these genes have been detected,

each of which results in an increased risk of developing breast cancer.

Mutations

Bad reputation

Tend to be disruptive

Very, very rare

Why is it dangerous around the core of a nuclear power plant?

Chemical-induced mutations


Mutations are alterations in a single base or changes in large segments of DNA that include several genes.

They are rare and when they occur in a gene usually disrupt normal physiological functioning.

They play an important role in evolution.

5.9 Faulty genes, coding for faulty enzymes, can lead to sickness.

How can people respond so differently to alcohol?

A single difference in a single pair of bases in their DNA.

A “fast-flush”

response

Why do many Asians have unpleasant experiences associated with alcohol consumption?

From mutation to illness in just four steps:

(1) A mutated gene codes for a non-functioning protein, usually an enzyme.

(2) The non-functioning enzyme can’t catalyze the reaction as it normally would, bringing it to a halt.

From mutation to illness in just four steps:

(3) The molecule with which the enzyme would have reacted accumulates, like a blocked assembly line.

(4) The accumulating chemical causes sickness and/or death.


Most genetic diseases result from individual mutations that cause a gene to produce a non-functioning enzyme, which in turn blocks the functioning of a metabolic pathway.

Genetic Engineering

Adding, deleting, or transplanting genes from one organism to another, to alter the organisms in useful ways

5.10 What is biotechnology?

Biotech advances in human health fall into three categories:

(1) producing medicines to treat diseases

(2) curing diseases

(3) preventing diseases from occurring in the first place.


Biotechnology is the use of technology to modify organisms, cells, and their molecules to achieve practical benefits.


Modern molecular methods make it possible to cut and copy DNA from one organism and deliver it to another.

Biotechnology has achieved some important successes in medicine, agriculture, and forensics.

5.11 Treating diseases and producing medicines with biotechnology

cure diseases

treating diseases

• The treatment of diabetes

Why do some bacteria produce human insulin?

Recombinant DNA technology

Several important achievements followed the development of insulin-producing bacteria, including:

(1) Human growth hormone (HGH)

(2) Erythropoietin

What is “blood doping”?

How does it improve some athletes’ performance?


Biotechnology has led to some notable successes in treating diseases, usually by producing medicines more efficiently and more effectively than they can be produced with traditional methods.

5.12 Curing diseases with biotechnology

Gene therapy and the correction of

malfunctioning genes

Stem Cells

Cells that have the ability to develop into any type of cell in the body

Why has gene therapy had such a poor record of success in curing diseases?

Gene Therapy Difficulties

(1) Difficulty getting the working gene into the specific cells where it is needed.

Gene Therapy Difficulties

(2) Difficulty getting the working gene into enough cells and at the right rate to have a physiological effect.

(3) Problems with the transfer organism getting into unintended cells.


Gene therapy has had a poor record of success in curing human diseases.

This stems primarily from technical difficulties in transferring normal-functioning genes into the cells of a person with a genetic disease.

5.13 Preventing diseases with biotechnologyIntervening to prevent diseases using biotechnology focuses on answering questions at three different points in

time:

(1) Is a given set of parents likely to produce a baby with a genetic disease?

(2) Will a baby be born with a genetic disease?

cystic fibrosis

sickle-cell anemia

Down syndrome

others

(3) Is an individual likely to develop a genetic disease later in life?

breast cancer

prostate cancer

skin cancer

Ethical Dilemmas

Discrimination

Health insurance

How to proceed with the information?

Take-home message 5.13 Biotechnology allows us to identify:

• whether a given set of parents is likely to produce a baby with a genetic disease,

• whether a baby is likely to be born with a genetic disease,

• and whether an individual carriers certain disease-causing genes that may have their effect later in life.


These tools can help us to reduce suffering and the incidence of diseases, but they also come with significant potential costs, particularly the risk of discrimination.

5.14 Producing more nutritious and better food

with biotechnology

How might a genetically modified plant help 500 million malnourished people?

Nutrient-rich “golden rice”


Biotechnology has led to important improvements in agriculture by using transgenic plants and animals to produce more nutritious food.

5.15 More efficient and eco-friendly farming with biotechnology

And he gave it for his opinion, ‘that whoever could make two ears of corn, or two blades of grass, to grow upon a spot of ground where only one grew before, would deserve better of mankind, and do more essential service to his country, than the whole race of politicians put together.’

—Jonathan Swift, Gulliver’s Travels, 1726

Almost everyone in the U.S. consumes genetically modified foods regularly without knowing it.

What foods are responsible for this?

Insect Resistance

How can genetically modified plants lead to reduced pesticide use by farmers?

Herbicide Resistance

Faster Growth and Bigger Bodies


There has been a revolution through biotechnology.

Herbicide-resistant and insect-resistant crops help reduce the environmental and financial costs of producing food.

5.16 Fears and risks: the safety of genetically modified foods

Fear #1. Organisms that we want to kill may become invincible.

Fear #2. Organisms that we don’t want to kill may be killed inadvertently.

Fear #3. Genetically modified crops are not tested or regulated adequately.

Fear #4. Eating genetically modified foods is dangerous.

Fear #5. Loss of genetic diversity among crop plants is risky.

Fear #6. Hidden costs may reduce the financial advantages of genetically modified crops.


More and more genetically modified foods are being created using modern methods of recombinant DNA technology.

Some legitimate fears among the public remain, however, as to the safety of these foods given that their development relies on such new technology.

5.17 DNA as an individual identifier: the uses and abuses of DNA fingerprinting

What is a DNA fingerprint?


Comparisons of highly variable DNA regions have forensic value in identifying tissue specimens and determining the individual from whom they came.

5.18 DNA sequences reveal evolutionary relatedness

(1) Mapping Genetic Landscapes: The Human Genome Project

(2) Building Earth’s Family Tree

When we say humans and chimps are genetically 96% identical, what do we mean?


Comparisons of sequence similarities across species reveal the evolutionary relatedness and make it possible to construct detailed evolutionary trees.

5.19 The promise and perils of cloningFrom organs to individuals

Are there any medical justifications for cloning?

Is it possible to clone a dinosaur? How could it be done?


Cloning of individuals has potential benefits in agriculture and medicine, but ethical questions linger.

Chapter 5: DNA, Gene Expression, and Biotechnology

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