Transcript 1 Protein Synthesis and Gene Expression

Chapter 7
Genetically Modified Organisms
Gene Expression, Mutation, and Cloning
Fourth Edition
BIOLOGY
Science for Life | with Physiology
Colleen Belk • Virginia Borden Maier
© 2013 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
PowerPoint Lecture prepared by
Jill Feinstein
Richland Community College
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
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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
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1 Protein Synthesis and Gene Expression:
From Gene to Protein
 DNA
 Double-stranded
 Each nucleotide
composed of
deoxyribose,
phosphate, and
nitrogenous base
 4 bases: adenine,
thymine, guanine,
cytosine
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1 Protein Synthesis and Gene Expression:
From Gene to Protein
 RNA
 Single-stranded
 Nucleotides
comprised of ribose,
phosphate, and
nitrogenous base
 4 bases: A, T, G,
and Uracil
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1 Protein Synthesis and Gene Expression:
From Gene to Protein
 The flow of genetic information in a cell is
DNA  RNA  protein and occurs in 2 steps:
 Transcription (DNA  RNA)
 Translation (RNA  Protein)
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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)
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Animation: Transcription
Click “Go to Animation” / Click “Play”
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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)
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1 Protein Synthesis and Gene Expression:
Translation
 Ribosomes
 The ribosome is
composed of ribosomal
RNA (rRNA) and
comprises a small and
a large subunit.
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1 Protein Synthesis and Gene Expression:
Translation
 Transfer RNA: tRNA
carries amino acids
and matches its
anticodon with
codons on mRNA
 Codons are 3
nucleotides long
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1 Protein Synthesis and Gene Expression:
Translation
 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
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1 Protein Synthesis and Gene Expression:
Translation
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1 Protein Synthesis and Gene Expression:
Translation
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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
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1 Protein Synthesis and Gene Expression:
Genetic Code
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BioFlix: Protein Synthesis
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Animation: Translation
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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
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1 Protein Synthesis and Gene Expression:
Mutation
 Base-substitution
mutation
 Simple substitution of
one base for another
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1 Protein Synthesis and Gene Expression:
Mutation
 Neutral mutation
 Mutation does not
change the function
of the protein, it
codes for the same
amino acid
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1 Protein Synthesis and Gene Expression:
Mutation
 Frameshift
mutation
 Addition or deletion
of a base, which
changes the
reading frame
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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
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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.
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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
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1 Protein Synthesis and Gene Expression:
Regulating Gene Expression
 Regulation of transcription
 Eukaryotic cells use activators to regulate
gene expression
 Activators help the RNA polymerase bind to the
promoter
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1 Protein Synthesis and Gene Expression:
Regulating Gene Expression
 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
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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.
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2 Producing Recombinant Proteins: Cloning a Gene
Using Bacteria
 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.
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2 Producing Recombinant Proteins: Cloning a
Gene Using Bacteria
 Step 1. Remove the gene from the cow
chromosome
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2 Producing Recombinant Proteins: Cloning a
Gene Using Bacteria
 Step 2. Insert the BGH gene into the bacterial
plasmid
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2 Producing Recombinant Proteins: Cloning a
Gene Using Bacteria
 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.
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2 Producing Recombinant Proteins: Cloning a Gene
Using Bacteria
 Step 3. Insert the recombinant plasmid into a
bacterial cell
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2 Producing Recombinant Proteins: Cloning a
Gene Using Bacteria
 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).
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Animation: Producing Bovine Growth Hormone
Click “Go to Animation” / Click “Play”
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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.
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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
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3 Genetically Modified Foods: Modifying Plants
with the Ti Plasmid
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3 Genetically Modified Foods: Modifying Plants
with the Gene Gun
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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.
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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.
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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.
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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
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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.
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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.
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4 Genetically Modified Humans: Cloning Humans
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Which of the following types of RNA carries amino
acids to the growing polypeptide chain?

mRNA

tRNA

rRNA

RNA does not carry amino acids
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Which of the following types of RNA carries amino
acids to the growing polypeptide chain?

mRNA

tRNA

rRNA

RNA does not carry amino acids
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A sequence of mRNA, called a codon, reads ACU.
How will the set of nucleotides on the anticodon of
the tRNA read?

ACU

UGA

TGA

AUG
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A sequence of mRNA, called a codon, reads ACU.
How will the set of nucleotides on the anticodon of
the tRNA read?

ACU

UGA

TGA

AUG
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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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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.
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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.
© 2013 Pearson Education, Inc.
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.
© 2013 Pearson Education, Inc.
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.
© 2013 Pearson Education, Inc.
Which of the following was used to treat SCID
patients?

therapeutic cloning

nuclear transfer

somatic gene therapy

germ line gene therapy
© 2013 Pearson Education, Inc.
Which of the following was used to treat SCID
patients?

therapeutic cloning

nuclear transfer

somatic gene therapy

germ line gene therapy
© 2013 Pearson Education, Inc.
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.
© 2013 Pearson Education, Inc.
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.
© 2013 Pearson Education, Inc.
When scientists try to replace defective human
genes with functional genes they are performing
________.

gene therapy

in vitro fertilization

therapeutic cloning

nuclear transfer
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When scientists try to replace defective human
genes with functional genes they are performing
________.

gene therapy

in vitro fertilization

therapeutic cloning

nuclear transfer
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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.
© 2013 Pearson Education, Inc.
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.
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.