Download Biologists have learned to manipulate DNA

13.1 Biologists have learned to manipulate DNA
I. The beginnings of DNA technology
A. Biotechnology is the use of organisms to perform practical tasks for humans
1. Much of DNA technology has come from use of bacteria called Escherichia coli or E. coli
2. Three ways bacteria can include new DNA
a. 1940- Joshua Ledgerberg and Edward Tatum showed two bacteria can form a tunnellike connection
b. Viruses can take bacteria DNA from one to another bacteria
c. Can take up loose bacteria from surroundings
1) This occurred with Griffith’s mice experiment with harmless strain bacteria
B. Recombinant DNA technology combines genes from different sources – or species – into a
single DNA molecule
II. DNA technology and frontiers of research in biology
A. Human genome- map of all humans genes was completed by 2000
1. Other organisms sequenced: fruit fly, yeast, E. coli, or rice plant
B. Uses
1. Improve food nutrition
2. Help us understand how our genes work from others
13.2 Biologists can engineer bacteria to make useful products
I. Engineering bacteria: an introduction
A. Plasmids are small circle-shape DNA molecule separate from larger bacterial chromosomes
B. Plasmids can be shared between bacteria, for example to increase antibiotic resistance
C. Humans use plasmids to place DNA to make useful products from bacteria
1. Plasmid is removed and the desired gene is placed in the plasmid  recombinant DNA
2. Recombinant plasmid is placed back in bacteria to replicate over and over- gene cloning
II. Cutting and pasting DNA
A. Piece of DNA is cut from desired source by restriction enzymes
1. In nature used to defend bacteria from foreign invading DNA
2. Restriction enzymes recognize certain sequences to cut – eg. GATTC cuts after G
3. Usually make staggering cuts exposing a single strand known as the “sticky end”
B. DNA fragment from another source is added
C. The fragments stick together by base-pairing – a complementary strand
D. DNA ligase pastes the fragments together to form recombinant DNA molecule
III. Cloning Recombinant DNA
A. The Process of cloning recombinant DNA
1. Restriction enzymes cuts plasmid in one place, human DNA cut in many places with one
fragment code for protein-V
2. Sticky ends of human DNA and plasmid pair up by base pairing
3. DNA ligase joins plasmid and human DNA
4. Bacterial cell takes up recombinant plasmid
5. Many copies of recombinant bacteria are made; when human gene expressed protein V made
B. Libraries of cloned genes
1. Genomic library- the complete collection of DNA fragments from an organism
2. The total of all recombinant plasmids contain the entire genome of the organism – human
C. Identifying specific genes with probes
1. How do biologist locate a specific gene in the library?
2. Nucleic acid probe- a complementary radioactive nucleic acid strand used to find the desired
gene sequence
3. Heat or chemicals are used to break up DNA and probe tags the portion needed
13.3 Biologists can genetically engineer plants and animals
I. Producing Genetically Modified Plants
A. Genetically modified organism (GMO)- any organism that has gotten one or more genes by
artificial means
B. Transgenic- the source of new genetic material comes from a different species
C. Use in plants for delayed ripening, increased nutrition, prevent spoiling or resist diseases
D. Herbicide resistance so they survive when fields sprayed for weeds; fungi and pest resistance as
well
II. Producing Genetically Modified Animals
A. More difficult than in plants – egg and sperm are fertilized and desired trait added to embryo
B. Use to produce more wool on sheep, leaner meat, or mature fish in shorter time
C. Certain human proteins produced in animals milk for human use after purification
III. Animal Cloning
A. Plants have been cloned from a simple cutting of a plant
B. A empty egg and a complete nucleus from the organism are fused together exact copy of
original organism created
C. Mass production of animals with desired trait
IV. The GMO controversy
A. Possible that gene resistance passed onto other plants through pollen
1. Academy of Science feels that GMO are not a threat but needs to be regulated and researched
B. GM plants and animal products may be slightly differ than original – possible allergies or other
negative effects
13.4 DNA technologies have many applications
I. Mass-producing DNA
A. Polymerase chain reaction (PCR)- makes may copies of certain DNA segment without living
cells
B. Process
1. Targeted DNA, nucleotides, DNA polmerase and primers are added together
a. Primers- short strands of DNA that pair with known targeted DNA
2. Heat is added to separate or denature the DNA strand
3. Mixture cools and primers bind to strand
4. DNA polymerase adds nucleotides to strands producing two DNA molecules
5. Procedure is repeated, 2 strands becomes 4 becomes 8 and so on
II. Comparing DNA
A. Gel electrophoresis- sorting molecules by or fragments by length
B. Process
1. DNA samples cut up using restriction enzymes
2. Few drops are placed in pocket called a well at the end of a thin gelatin-like material called gel
3. Other end is (+) charge, so the smaller pieces of DNA (-) charge move farther in the gel
4. Gel is stained to make DNA visible under UV light
5. Fragments show up as bands in the lanes
C. Genetic markers
1. Used to tell different in bands between samples
2. May use radioactive DNA labels to tag genetic markers
3. Genetic markers- specific portion of DNA varies from individual
a. May analyze to look at recessive disease as a carrier
D. DNA fingerprinting – unique banding pattern on gel, determined by restriction fragments of a
person’s DNA
1. Markers found in alleles for disease or in the introns (noncoding) regions
2. To use DNA he genetic markers that are not shared with others are used
3. DNA specimen from hair follicle or blood
4. 1 in 100,000 to 1 billion chance that two people have the same number of genetic markers
13.5 Control mechanisms switch genes on and off
I. Regulation of Genes in Prokaryotes
A. Bacteria do not have ability to turn genes on or off, but can change functions based on environment
1. E. Coli makes three enzymes in presence of milk, does not when milk not present
B. Genetics of breaking milk sugar / lactose into a usuable form (Fig. 13-18)
1. Operon- cluster of genes along with control sequence genes
a. lac operon includes two control genes and 3 genes for enzyme production are located
2. Promoter- first control sequence where RNA polymerase (makes mRNA) attaches itself to
DNA
3. Operator- second control gene, like a switch, that determines if RNA polymerase can attach
to the promoter
C. Activation or Repression of the lac operon (Fig. 13-19)
1. Repressor- a protein that binds to the operator and blocks the attachment of RNA polymerase
2. If lactose is absent then repressor is present and turns off the lac operon
3. If lactose is present then it binds to the repressor protein and changes the shape of the
repressor
a. When the repressor changes shape it no longer binds to the operator
b. The operator is open and RNA polymerase binds to the promoter
c. The lactose processing genes are turned on
d. When lactose is no longer present – the repressor can rebind to the operator
D. Prokaryotes waste little energy on unnecessary reactions due to many different operons
II Regulation of Genes in Eukaryotes
A. More elaborate and complicated than in prokaryotes
B. Eukaryotic DNA includes promoter sequences before the point that transcription takes place
C. Transcription factors- regulate transcription by binding to promoters or RNA polymerases
D. Transcription factors are activated and deactivated by certain chemical signals in the cell
1. Hormones may attach to transcription factors to signal gene expression- the transcription and
translation of genes into proteins
III. From Egg to Organism
A. Gene expression begins when an egg is fertilized and divides
1. The position of each new cell in the embryo promotes expression of particular groups of genes
2. Genes affecting the head are only expressed in the “pre-head region”
3. A cell’s position relative to its neighboring cells affects its gene expression
B. Cellular differentiation- cells become increasingly specialized in structure and function
1. Glycolysis gene expressed in all cell types, while insulin gene expressed pancreas cells
2. Hemoglobin gene would not be expressed in eye lens, nerve cell, or pancreas cell
C. DNA chip- help biologist track which genes are turned on in a given cell
IV. Stem Cells
A. Stem cells- cells that have the ability to differentiate into various types of cells
B. Blastocyst- embryo of about 100 cells, comprised mostly of stem cells
C. Most stem cells differentiate into different cell types, yet bone marrow has them in adulthood
1. Stem cells in bone marrow differentiate into different types of blood cells
2. Bone marrow transplants help people with leukemia
D. Stem cells either from embryonic or adult stem cells may help to fight other disease as well
1. Ethical debates surround the use of stem cells
V. Homeotic Genes
A. Homeotic genes- master control genes that direct development of body parts in specific locations
1. Homeobox- nucleotide sequence that codes for a protein that promotes the transcription of
genes involved in the development of specific body parts
2. A mutation in the Drosphila fruit fly homeobox can lead to eyes developing where legs or
wings or antenna should be.