watson and crick in 1800’s it was believed that protein carried genetic information. by late 1940s...
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Watson and Crick
• In 1800’s it was believed that protein carried genetic information.
• By late 1940s it was accepted that DNA was the genetic material.
• Discovered the structure for DNA in 1953– DNA made of nucleotides– Bases: A, T, C, and G– Used work of several other scientist to come up
with the structure of DNA
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Rosalind Franklin
• Used X-ray diffraction to study the structure of DNA– Technique uses x-rays of DNA. X-rays bounce off a
sample of material to determine characteristics of the sample such as physical structure and chemical composition.
– Watson and Crick attend her lecture in 1951 on the structure of DNA. They used her information that DNA is a twisted helix.
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Wilkins
• Maurice Wilkins was also studying DNA. He showed Franklin’s work to one of his peers- Watson
• 1952, Chargaff had found that DNA contained equal amount of A and T and equal amounts of G and C. – helped with base pairing.
• 1962, Watson, Crick, and Wilkins shared the Nobel Prize in physiology and medicine
• What happened to Franklin’s contribution to this project?
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Chargaff
• Studies the nitrogenous bases of DNA• He found that a cell always has an equal
amount of adenine and thymine• Also an equal amount of guanine and cytosine• Base pairing rules- A-T and C-G
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Chapter 8Medicine from Milk
Copyright © 2012 by W. H. Freeman and Company
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Medicine for Milk
• Art of “Pharming”• Using genetically engineered modified animals
to churn out therapeutic drugs• Transgenic animals• First drug produced by transgenic animals is
already available, human protein called antithrombin
• Extracted from transgenic goats’ milk
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Antithrombin Deficiency
• Antithrombin is most commonly used to treat patients who either inherit or acquire a deficiency of the antithrombin protein
• Patient develops dangerous blood clots• Antithrombin protein use to be isolated from
human blood – small amounts• Transgenic goat can produce large amounts of
antithrombin protein• Why is goat better than human?
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What is a protein?• A protein is a macromolecule made up of
repeating subunits known as amino acids.– Proteins have many functions: they
allow our muscles to contract, give our hair and skin its texture, and facilitate thousands of chemical reactions in our cells.
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Amino acids• Amino acids are the building blocks of proteins. • There are 20 different amino acids.– All amino acids have the same basic core structure, but
each also has a unique chemical side group.
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Sizes of proteins
• Human antithrombin is 432 amino acids– Many human proteins are in this size range
• Protein titin for muscle contraction is 34, 350 amino acids long- longest human protein
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Amino acids determine the shape and function of a protein
• Amino acids bond together to form linear chains. The sequence of amino acids in any given chain makes the chain unique.
• The chain folds into a 3-D protein based on the sequence of amino acids.
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Amino acids determine the shape and function of a protein
• Changing an amino acid in the sequence changes the 3-D shape of the protein.– The shape of
the protein determines its function.
– 801
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Where do protein’s come from?
• Cells make proteins using building blocks from our diet.
• The instructions to make the protein are encoded in our DNA – our genes.
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Chromosomes include gene sequences that code for proteins
• Chromosomes consist of many genes along their length.– A gene is a sequence of DNA that contains the instructions
to make at least one protein.
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Chromosomes include gene sequences that code for proteins
• Genes are expressed when the cell uses the DNA instructions to make proteins.
• Gene expression• 804
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Genotypes and phenotypes
• The genotype of an organism is the genetic make-up of that organism.– Genes provide our genotype, proteins specified by
these gene determine of physical traits.
• The phenotype is the physical attributes of the organism – Antithrombin gene is on chromosome 1 and holds
instructions to make 432amino acids of the protein.- Cells express the gene to make the protein
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Antithrombin prevents blood clots
• Antithrombin is a protein that helps prevent blood clots (thrombosis).– Rare condition (1 in 5000)
– The antithrombin gene is expressed by cells in the liver, which then release antithrombin protein into the bloodstream.
– Inactivates enzymes that promote blood clotting
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Antithrombin prevents blood clots
• When people inherit antithrombin deficiency, it means that both of their copies of the antithrombin gene are defective.– You inherit one copy of chromosome 1 from the
mother and one copy of chromosome 1 from your father.
– This can happen because there are alternate versions of genes.- differ slightly in the nucleotide sequence
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Different alleles influence phenotype
• Alleles are alternative versions of the same gene that have different nucleotide sequences.
• 807•
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Antithrombin Deficiency
• People with inherited antithrombin deficiency usually takes medication to thin their blood and prevent clots.
• It takes 50,000 donors to produce 1kg of antithrombin.
• One trangenic goat can produce the same amount in 1 year.
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Genes have regulatory sequences and coding sequences
• Two parts of a gene:• Genes are organized into
two parts:– Regulatory sequences
determine when and how much protein a gene makes.
– Coding sequences determine the amino acid sequence of the encoded protein.
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MakingTransgenic Goats
• All mammals produce proteins and secrete them into their milk
• Isolate a human gene and transfer into DNA of a large mammal, like goat (goat embryo)
• Use regulatory sequence of goat and human protein.
• Gene is expressed in mammary gland.• Goat produces human proteins in milk• Collect protein in goat milk
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Making a transgenic goat• Transgenic organisms carry one or more genes from a
different species.– Transgenic organisms are also called genetically modified
organisms (GMOs) because they have been genetically altered by humans.
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Making a transgenic goat• Step 1: Create hybrid gene.– Goat regulatory sequence and human antithrombin coding
sequences are cut out of donor cell chromosomes and joined together using special enzymes.
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Making a transgenic goat
• Step 2: Microinjection and embryo transfer.
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Making a transgenic goat• Step 3: Purify antithrombin from transgenic milk.– Antithrombin protein is expressed in the milk of transgenic
females. This protein can be isolated from the milk and used to treat antithrombin deficient people.
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Gene therapy
• Gene therapy is a type of treatment that aims to cure disease by replacing defective genes with functional ones.
• Gene therapy is used to treat severe combined immunodeficiency syndrome (SCID)– Disorders in which babies are born with deficient
immune systems.
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Genetically modified organisms serve many purposes
• Crops can be modified to contain genes for natural pesticides, which reduces the amount of pesticide a farmer must use.
• Transgenic animals can be used to research a gene’s function or to produce marketable products like medicine and fibers.
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Gene expression: An overview
• Gene expression has two main steps: transcription and translation.
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Where does gene expression occur?• Transcription occurs in the nucleus of eukaryotic cells. • Transcription occurs in the cytoplasm of prokaryotic cells. Why?• Translation occurs on ribosomes. Ribosomes are the cellular
machinery used for protein synthesis.
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Gene expression: Transcription• Transcription copies the coding sequence of DNA into the
complementary messenger RNA (mRNA) sequence.
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Gene expression: Transcription
• RNA polymerase (function) binds to the regulatory sequence just ahead of the gene’s coding region. The DNA strands unwind, exposing the coding sequence of the gene.
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Gene expression: Transcription
• The RNA polymerase moves along the DNA strand, “reading” the DNA coding sequence and synthesizing a complementary mRNA strand.
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Gene expression: Transcription
• The complementary mRNA forms from a DNA template according to the rules of base pairing, except that in RNA, adenine (A) pairs with uracil (U).
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Gene expression: Transcription
• As the mRNA strand is formed, it detaches from the DNA sequence, and the DNA reforms its double-stranded helix.
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Gene expression: Transcription
• Once the mRNA molecule is complete, it leaves the nucleus. The gene remains part of the chromosome in the nucleus where it can be used again for transcription.
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Gene expression: Translation
• Translation uses the mRNA sequence to assemble the appropriate amino acid sequence of the protein.
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Gene expression: Translation• The transcribed mRNA associates with a ribosome.• What is the function of the ribosome?
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Gene expression: Translation
• The ribosome moves along the mRNA, “reading” it in groups of three nucleotides (codons).
• Each codon specifies a particular amino acid.
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Gene expression: Translation
• Transfer RNA (tRNA) carries an amino acid to the mRNA by using its anticodon to find a matching mRNA codon.
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Gene expression: Translation
• When the correct tRNA is in place, the specified amino acid is added to the growing chain, and the ribosome moves on to the next codon.
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Gene expression: Translation
• The finished amino acid chain detaches from the ribosome and folds into its 3-D shape.
• Animation 809
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The genetic code
• mRNA codons specify particular amino acids according to the universal genetic code.
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Transcription/Translation Exercise
DNA A G C G C G C T T A C G T A G T A G
mRNA U C G C G C GA A UG CA U C A U C
What is the role of tRNA?_correct AA________
Protein SER-ARG-GlU-Cys-ISO-ISO
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Predicting mRNA and amino acid sequences from DNA sequences
• It is possible to use the rules of base pairing and the genetic code to predict the amino acid sequence that will result from a particular DNA template sequence.