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

In this chapter

the process of gene expression.

the causes and effects of damage to the genetic code.

biotechnology and its implications for human health.

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?

DNA Characteristics

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

DNA Characteristics

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

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

Purines: Adenine, and Guanine - Two-ring

Pyrimidines: Thymine, and Cytosine - One-ring

Nucleic Acid

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.

Nucleic Acid DNA’s structure resembles a twisted

ladder,

sugar and phosphate groups serving as the backbone

base pairs serving as the rungs.

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

• Prokaryotes – information is contained within circular pieces of DNA

• Eukaryotes (including humans) – information is laid out in long linear strands of DNA

• 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!

FIGURE 5-6 The genome unpacked

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 Code

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

Genome - the full set of DNA an organism carries

Gene Characteristics

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

Introns

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

5.5 How do genes work?

An overview

Genotype•all of the genes contained in an

organism

Phenotype•the physical manifestations of the

instructions

Gene Expression

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

Gene Expression

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

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

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

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

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

Chromosomal Mutations

• Most crossing-over between chromosomes involves a change of genetic material

A B C D

p.125

Structural Changes


• Crossing over which goes wrong can have major effects on offspring

Structural Changes


• Crossing over which goes wrong can have major effects on offspring

• Four different crossing over changes are recognized

Duplication

• The one chromosome instead of trading a piece of DNA with its homologous partner, picks up a piece without losing one

normalchromosome

three repeats

one segmentrepeated

p.130

Duplication


• The result is that the new Chromosome has a repeat of the same information

Duplication



• Some Chromosomes have many hundreds of extra pieces

Duplication



• Some Chromosomes have many hundreds of extra pieces

• Mostly the resulting individual is unaffected

Deletion

• All of the DNA goes to one chromosome without an exchange

segment C deleted

p.130

Deletion


• Causes the first chromosome to lose several genes

Deletion


• Causes the first chromosome to lose several genes

• Usually results in death of the cell

Cri-du-Chat

• A genetic disease which results from a deletion on the #5 chromosome

Cri-du-Chat

• A genetic disease which results from a deletion on the #5 chromosome

• Severe mental retardation and misshapen larynx which gives the individual a weird cry as a baby

Inversion

• Part of the chromosome gets turned around in the cross-over

segmentsG, H, Ibecomeinverted

p.130

Inversion


• Since many chromosomes contain extra pieces, there may be no harm done

Inversion


• Since many chromosomes contain extra pieces, there may be no harm done

• In the next generation, the piece may get relocated and cause problems after meiosis

Translocation

• One piece of chromosome breaks off but does not get located on its sister chromatid.

chromosome

nonhomologouschromosome

reciprocal translocation

p.130

Translocation


• It gets located on another chromosome

Translocation


• It gets located on another chromosome• The individual receives all of the genes and

can be a normal person

Translocation

• The next generation will not receive the normal amount of genes and will have a disease

Translocation• The next generation will not receive the

normal amount of genes and will have a disease

• The translocation could only be to the opposite end of the chromosome which would make it still to be a chromosome with all of the normal genes

Translocation

• Some evidence of evolution has translocations

Translocation

• Some evidence of evolution has translocations• Humans have the same number of

chromosomes as chimpanzees and gorillas

Translocation


chromosomes as chimpanzees and gorillas• 18 of the chromosomes are identical

Translocation


chromosomes as chimpanzees and gorillas• 18 of the chromosomes are identical• The remaining 5 differ in translocations and

inversions

Point Mutations

• happens at a single base point to affect a single amino acid

Point Mutations


• Substitution – a single base gets changed in the DNA sequence

Point Mutations



• Insertion – a single base gets added at one point in the DNA sequence

Point Mutations



• Insertion – a single base gets added at one point in the DNA sequence

• Deletion – a single base gets deleted from the DNA sequence

Substitution

DNA TAC – GCA –TGG – AAT

Substitution

DNA TAC – GCA –TGG – AATRNA AUG – CGU – ACC – UUA

Substitution

DNA TAC – GCA –TGG – AATRNA AUG – CGU – ACC – UUAAmino Acids Met - Arg - Thr - Leu

Substitution


| Substitution|

DNA TAC – GTA – TGG – AAT

Substitution


| Substitution|

DNA TAC – GTA – TGG – AATRNA AUG – CAU – ACC – UUAAmino Acids Met - His - Thr - Leu

Frameshift Mutations

• Insertion –

• Deletion –



|



|| Insertion

DNA TAT – CGC – ATG – GAA –T



|| Insertion

DNA TAT – CGC – ATG – GAA –TRNA AUA – GCG – UAC – CUU –A



|| Insertion

DNA TAT – CGC – ATG – GAA –TRNA AUA – GCG – UAC – CUU –AAmino Acids lsoleu – Ala - Tyr - Leu


• The base sequence is completely changed creating a different protein or with the inability to produce the correct protein which would kill the organism.


• The base sequence is completely changed creating a different protein or with the inability to produce the correct protein which would kill the organism.

• A similar permanent change would occur with a deletion of a single nucleotide

Transposons

• Small pieces of DNA can move around the genome

Transposons


• One chromosome to another, a kind of regular translocation

Transposons



• About 40% of the human genome has ben transposed

Transposons



• About 40% of the human genome has been transposed

• Indian corn is different colors because of transposons moving color information around

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

Chemical-induced mutations

Mutations

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

Rare, usually disrupt normal physiological functioning.

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?

Missing Enzymes

• The inability to process alcohol “cheap drunk” is the lack of an enzyme aldehyde dehydrogenase which is very present in Asian people.

• Tay-Sachs disease is a similar lack of ability to deal with lipid breakdown

• Lactose intolerance is another

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.

Genetic Diseases

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

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

Biotechnology

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.

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

What is a DNA fingerprint?

DNA Fingerprinting

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

Chapter 5: DNA, Gene Expression, and Biotechnology

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