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DNA, Gene Expression, and BiotechnologyChapter 5

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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.

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Knowledge about DNA is increasing justice in the world

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What is the most common reason why DNA analyses overturn incorrect criminal convictions?• In more than three-quarters of the cases,

inaccurate eyewitness testimony played an important role in the guilty verdict.• Julius Ruffin• Ken Wyniemko

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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

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Take-home message 5.1 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.

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

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Two Important Features of DNA1. 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.

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DNA “Double Helix”

Nucleic acids and nucleotides

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Chargaff’s Rules

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Sugars, Phosphates, and Bases• Base pairs

• Adenine-thymine• Guanine-cytosine

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Which answer will base pair with the following sequence?

AGTTCTCATGT

1. AGTTCTCATGT2. ACATGAGAACT3. TCAAGAGTACA4. UCAAGAGUACA

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Take-home message 5.2• 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.

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Take-home message 5.2• 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.

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Genes are sections of DNA that contain instructions for making proteins.Why is DNA considered the universal code for all life on earth?

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DNA is the universal code for all life on earth• embodies the instructions for building the cells

and structures for virtually every single living organism on earth

• all living organisms use this same molecule to transmit this information to their offspring.

• DNA is like a universal language• “letters” are the bases A, T, C, and G• sugar-phosphate backbone serves to hold the

bases in sequence, like the binding of a book

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DNA is the universal code for all life on earth• Prokaryotes – information is contained within

circular pieces of DNA• Eukaryotes (including humans) – information is

laid out in long linear strands of DNA (numerous smaller, more manageable pieces, called chromosomes)

• Humans – 3,000,000,000 base pairs• 23 unique pieces of DNA • 2 copies of each piece

• 1from mom• 1from dad

• total of 46 chromosomes and 6,000,000,000 base pairs in every cell!

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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

• Chromosomes vary in length, too• Humans – longest chromosome has more than

200,000,000 base pairs; shortest has fewer than 50,000,000!

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Genes• Sequence of bases in a DNA molecule

• Carries information necessary for producing a functional product, usually a protein molecule or RNA

• Average gene is 3000 bases long

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Genes• Instruction set for producing one particular

molecule, usually a protein • Examples

• fibroin, the chief component of silk• triacylglyceride lipase (enzyme that breaks

down dietary fat)

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Genes• Within a species, individuals sometimes have

slightly different instruction sets for a given protein and these instructions can result in a different version of the same trait.

• These alternate versions of a gene that codes for the same character are called alleles.

• Any single feature of an organism is referred to as a trait.

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Different people can have free or attached earlobes. The DNA that encodes for making free or attached earlobes is called a(n) ________, and there are two different versions of it, called __________.1. allele; genes2. trait; alleles3. gene; trait4. gene; alleles

Take-home message 5.3• 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.

Not all DNA contains instructions for making proteins.

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Not all DNA contains instructions for making proteins.• Comparing the amount of DNA present in various

species reveals a paradox: • There does not appear to be any relationship

between the size of an organism’s genome and the organism’s complexity

• Complexity can be assessed in a variety of ways, such as by counting the number of different cell types in the organism

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

Take-home message 5.4• Only a small fraction of the DNA in eukaryotic

species codes for genes.

• The function of the rest is still a mystery.

How do genes work? • Every cell contains all of the information

needed to manufacture every protein in the body but having the instructions is not the same as having the products

Which molecule acts as a “middle man” between the nucleus, where transcription occurs, and the cytoplasm, where translation occurs?1. DNA2. mRNA3. Protein4. Choices 1 and 3 are

correct.

Take-home message 5.5• 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