Chapter 7

transcript

PowerPoint Lecture prepared byJill Feinstein

Richland Community College

Fourth Edition

BIOLOGYScience for Life | with Physiology

Colleen Belk • Virginia Borden Maier

ChapterChapter 7 7

Genetically Modified OrganismsGene Expression, Mutation, and Cloning

1 Protein Synthesis and Gene Expression

In the early 1980s, genetic engineers began producing recombinant bovine growth hormone (rBGH)

Made by genetically engineered bacteria

The bacteria were given DNA that carries instructions for making BGH

In cows, growth hormones increase body size and milk production

1 Protein Synthesis and Gene Expression: From Gene to Protein

Protein synthesis – the process of using instructions carried on a gene to create proteins.

Several steps are involved and require both DNA and RNA.

Gene – a sequence of DNA that encodes a protein

Protein – a large molecule composed of amino acids

Double-stranded

Each nucleotide composed of deoxyribose, phosphate, and nitrogenous base

4 bases: adenine, thymine, guanine, cytosine

Single-stranded

Nucleotides comprised of ribose, phosphate, and nitrogenous base

4 bases: A, T, G, and Uracil

The flow of genetic information in a cell is DNA RNA protein and occurs in 2 steps:

Transcription (DNA RNA)

Translation (RNA Protein)

1 Protein Synthesis and Gene Expression: Transcription

Transcription occurs in the nucleus. RNA polymerase binds to the promoter region of

the gene. RNA polymerase zips down the length of gene,

matching RNA nucleotides with complementary DNA nucleotides

This forms messenger RNA (mRNA)

Animation: TranscriptionClick “Go to Animation” / Click “Play”

1 Protein Synthesis and Gene Expression: Translation

Translation occurs in the cytoplasm (outside the nucleus).

Translation requires: mRNA (made during transcription), amino acids, energy (ATP), and some helper molecules.

Ribosomes

Transfer RNA (tRNA)

Ribosomes

The ribosome is composed of ribosomal RNA (rRNA) and comprises a small and a large subunit.

Transfer RNA: tRNA carries amino acids and matches its anticodon with codons on mRNA

Codons are 3 nucleotides long

A protein is put together one amino acid at a time.

The ribosome attaches to the mRNA at the promoter region.

Ribosome facilitates the docking of tRNA anticodons to mRNA codons.

When two tRNAs are adjacent, a bond is formed between their amino acids.

Forms a peptide chain of amino acid

1 Protein Synthesis and Gene Expression: Genetic Code

The genetic code allows a specific codon to code for a specific amino acid.

A codon is comprised of three nucleotides = 64 possible combinations (43 combinations)

61 codons code for amino acids

3 others are stop codons, which end protein synthesis

Genetic code expresses redundancy

The genetic code is universal

1 Protein Synthesis and Gene Expression: Genetic Code

Animation: TranslationClick “Go to Animation” / Click “Play”BioFlix: Protein Synthesis

1 Protein Synthesis and Gene Expression: Mutations

Changes in genetic sequence = mutations

Changes in genetic sequence might affect the order of amino acids in a protein.

Protein function is dependent on the precise order of amino acids

Possible outcomes of mutation:

1 - no change in protein

2 - non-functional protein

3 - different protein

1 Protein Synthesis and Gene Expression: Mutation

Base-substitution mutation

Simple substitution of one base for another

Neutral mutation

Mutation does not change the function of the protein, it codes for the same amino acid

Frameshift mutation

Addition or deletion of a base, which changes the reading frame

1 Protein Synthesis and Gene Expression: An Overview of Gene Expression

Each cell in your body (except sperm and egg cells) has the same DNA.

But each cell only expresses a small percentage of genes.

Example: Nerve and muscle cells perform very different functions, thus they use different genes.

Turning a gene or a set of genes on or off = regulating gene expression

1 Protein Synthesis and Gene Expression: An Overview of Gene Expression

Nerves and cells have the same suite of genes, but they express different genes.

1 Protein Synthesis and Gene Expression: Regulating Gene Expression

Regulation of transcription Prokaryotic cells use repressors to regulate gene

expression Repressors bind to the promoter and prevent the

RNA polymerase from binding

Regulation of transcription Eukaryotic cells use activators to regulate

gene expression Activators help the RNA polymerase bind to the

promoter

Regulation by chromosome condensation

Folding up of the chromosomes prevents transcription

Regulation by mRNA degradation

Nucleases cut mRNA

Regulation of Translation

Slowing of binding of the mRNA to the ribosome

Regulation of Protein Degradation

Proteases degrade proteins

2 Producing Recombinant Proteins: Cloning a Gene Using Bacteria

rBGH is a protein, and is coded by a specific gene.

Transfer of rBGH gene to bacteria allows for growth under ideal conditions.

Bacteria can serve as “factories” for production of rBGH.

Cloning of the gene is making many copies of that gene.

Restriction enzymes – Used by bacteria as a form of defense. Restriction enzymes cut DNA at specific sequences. They are important in biotechnology because they allow scientists to make precise cuts in DNA.

Plasmid – Small, circular piece of bacterial DNA that exists separate from the bacterial chromosome. Plasmids are important because they can act as a ferry to carry a gene into a cell.

Step 1. Remove the gene from the cow chromosome

Step 2. Insert the BGH gene into the bacterial plasmid

Recombinant – Indicates material that has been genetically engineered: a gene that has been removed from its original genome and combined with another.

After step 2, the GBH is now referred to as recombinant GBH or rGBH.

Step 3. Insert the recombinant plasmid into a bacterial cell

About 1/3 of cows in the US are injected with rBGH. rBGH increases milk volume from cows by about 20%.

The same principles apply to other proteins.

Clotting proteins for hemophiliacs are produced using similar methods.

Insulin for diabetics is also produced in this way.

FDA approval is needed for any new food that is not generally recognized as safe (GRAS).

Animation: Producing Bovine Growth HormoneClick “Go to Animation” / Click “Play”

3 Genetically Modified Foods

All agricultural products are the result of genetic modification through selective breeding. Artificial selection does not move genes from one organism to another, but does drastically change the characteristics of a population.

Genetically modifying foods

Increase shelf life, yield, or nutritional value

Golden rice has been genetically engineered to produce beta-carotene, which increases the rice’s nutritional yield.

3 Genetically Modified Foods: Modifying Plants with the Ti Plasmid and Gene Gun

Unlike rBGH, crop plants are directly modified. In order to do this, the target gene must be inserted into the plant cell. Two methods to do this:

Ti plasmid

Gene gun

3 Genetically Modified Foods: Modifying Plants with the Ti Plasmid

3 Genetically Modified Foods: Modifying Plants with the Gene Gun

3 Genetically Modified Foods: Modifying Plants with the Ti Plasmid and Gene Gun

Transgenic organism – the result of the incorporation of a gene from one organism to the genome of another. Also referred to as a genetically modified organism (GMO).

Benefits: Crops can be engineered for resistance to pests, thus farmers can spray fewer chemicals.

Concerns: Pests can become resistant to chemicals. GM crops may actually lead to increased use of pesticides and herbicides. GM crop plants may transfer genes to wild relatives.

4 Genetically Modified Humans: Stem Cells

Stem cells – undifferentiated cells, capable of growing in to many different kinds of cells and tissues

Stems cells might be used to treat degenerative diseases such as Alzheimer’s or Parkinson’s.

Using stem cells to produce healthy tissue is called therapeutic cloning. Stem cells could also be used to grow specific

tissues to treat burns, heart attack damage, or replacement cartilage in joints.

Stems cells are totipotent, meaning they can become any other cell in the body.

4 Genetically Modified Humans: Human Genome Project

Human Genome Project – international effort to map the sequence of the entire human genome (~20,000 – 25,000 genes). For comparative purposes, genomes of other model

organisms (E. coli, yeast, fruit flies, mice) were also mapped.

It was sequenced using the technique of chromosome walking.

4 Genetically Modified Humans: Gene Therapy

Gene therapy – replacement of defective genes with functional genes

Germ line gene therapy

Embryonic treatment

Embryo supplied with a functional version of the defective gene.

Embryo + cells produced by cell division have a functional version of gene.

Somatic cell gene therapy

Somatic cell gene therapy – fix or replace the defective protein only in specific cells

4 Genetically Modified Humans: Gene Therapy

Somatic cell therapy used as a treatment of SCID (severe combined immunodeficiency)

All somatic cells have limited lifetimes. Therapy is not permanent and requires several

treatments per year.

4 Genetically Modified Humans: Cloning Humans

Human cloning occurs naturally whenever identical twins are produced.

Cloning of offspring from adults has already been done with cattle, goats, mice, cats, pigs, and sheep.

Cloning is achieved through the process of nuclear transfer.

4 Genetically Modified Humans: Cloning Humans

Which of the following types of RNA carries amino acids to the growing polypeptide chain?

RNA does not carry amino acids

Which of the following types of RNA carries amino acids to the growing polypeptide chain?

RNA does not carry amino acids

A sequence of mRNA, called a codon, reads ACU. How will the set of nucleotides on the anticodon of the tRNA read?

Which of the following regulation techniques will result in increased gene expression?

condensing the chromosome

speeding up proteases

lengthening the adenosine nucleotide “tail”

slowing the movement of the mRNA through the ribosome

Which of the following regulation techniques will result in increased gene expression?

condensing the chromosome

speeding up proteases

lengthening the adenosine nucleotide “tail”

slowing the movement of the mRNA through the ribosome

Which of the following statements is accurate?

The plasmid is cut with the same restriction enzyme as the removed gene.

The plasmid is a circular piece of RNA.

The plasmid is part of the bacterial chromosome.

The plasmid replicates when the bacterial chromosome replicates.

Which of the following statements is accurate?

The plasmid is cut with the same restriction enzyme as the removed gene.

The plasmid is a circular piece of RNA.

The plasmid is part of the bacterial chromosome.

The plasmid replicates when the bacterial chromosome replicates.

Which of the following statements concerning rBGH-treated milk is correct?

The injected cows produce 20% more milk.

There is no evidence of the hormone being transferred to the milk.

Humans would be able to safely digest the hormone, just like any other protein in food.

All of the statements are correct.

Which of the following statements concerning rBGH-treated milk is correct?

The injected cows produce 20% more milk.

There is no evidence of the hormone being transferred to the milk.

Humans would be able to safely digest the hormone, just like any other protein in food.

All of the statements are correct.

Which of the following was used to treat SCID patients?

therapeutic cloning

nuclear transfer

somatic gene therapy

germ line gene therapy

Which of the following was used to treat SCID patients?

therapeutic cloning

nuclear transfer

somatic gene therapy

germ line gene therapy

Which of the following statements is incorrect?

Stem cells are undifferentiated.

Stem cells are totipotent.

Specialized stem cells divide to make undifferentiated stem cells.

Stem cells can be used for therapeutic cloning.

Which of the following statements is incorrect?

Stem cells are undifferentiated.

Stem cells are totipotent.

Specialized stem cells divide to make undifferentiated stem cells.

Stem cells can be used for therapeutic cloning.

When scientists try to replace defective human genes with functional genes they are performing ________.

gene therapy

in vitro fertilization

therapeutic cloning

nuclear transfer

When scientists try to replace defective human genes with functional genes they are performing ________.

gene therapy

in vitro fertilization

therapeutic cloning

nuclear transfer

What is happening in step 1 in this figure?

The embryo is being grown in culture.

The egg cell and mammary cell are fused together.

The nucleus is removed from the egg cell.

The embryo is being implanted into the uterus of a third sheep.

What is happening in step 1 in this figure?

The embryo is being grown in culture.

The egg cell and mammary cell are fused together.

The nucleus is removed from the egg cell.

The embryo is being implanted into the uterus of a third sheep.

When undergoing recombination, _______.

the plasmid and the cow gene are cut with different restriction enzymes

the recombinant plasmid is reinserted into the cow’s cell to increase milk production

the rBGH genes are injected into cows to increase their milk production

the recombinant plasmid is inserted in bacterium, making large quantities of rBGH proteins

When undergoing recombination, _______.

the plasmid and the cow gene are cut with different restriction enzymes

the recombinant plasmid is reinserted into the cow’s cell to increase milk production

the rBGH genes are injected into cows to increase their milk production

the recombinant plasmid is inserted in bacterium, making large quantities of rBGH proteins

Chapter 7

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