Microbiology Chapter 6- The Genetics Of Microrganisms

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Chapter 6 - The Genetics of Microorganisms

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Angela Chan
TR 9:30

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(1928) He demonstrated the process of transformation by which monvirulent (not disease causing, harmless) bacteria were changed to virulent (disease causing) bacteria by mixing live nonvirulent bacteria with killed virulent bacteria.

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Griffith's experiment

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(1944) demonstrated that the transforming principle was DNA.

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Avery, MacLeod, & McCarty

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(1952) demonstrated that DNA is the genetic material.

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Hershey & Chase

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(1865) Austrian monk who discovered the principles of genetics. "Father of Genetics"

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Gregor Mendel

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(1953) used x-ray crystallography to see the structure of DNA.

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Rosalind Franklin

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(1953) They were awarded the Nobel prize for discovering the structure of DNA.

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James Dewey Watson, Francis Henry Campton Crick, and & Maurice Wilkins

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the science of heredity

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Genetics

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the genetic information in a cell

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Genome

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structures that contain DNA

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Chromosomes

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segments of DNA which code for particular traits

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Gene

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the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein

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Genetic code

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structure of DNA

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Right-handed double helix

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It looks like a ladder that is twisted to the right. It has alternating sugars (deoxyribose) and phosphates on the sides. The "rungs" of the ladder are made of nitrogenous bases.

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DNA

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4 Nitrogenous Bases for DNA and RNA

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A= Adenine
T= Thymine
C= Cytosine
G= Guanine

U= Uracil (instead of Thymine, used in RNA)

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How many hydrogen bonds are in A-T & C-G?

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A-T = 2 hydrogen bonds
C-G = 3 hydrogen bonds

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What are the sides of the DNA made of?

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Sugar & Phosphate

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Deoxyribonucleic Acid

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DNA

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Made of deoxyribose, phosphate, and a nucleoside (nitrogenous) base.

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Nucleotides

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2 types of nitrogenous bases

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Pyrimidines (small) are cytosine and thymine. Purines (big) are adenine and guanine.

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molecule made of repeating smaller units.

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Polymer

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(T or F) DNA is a polymer because it is made of repeating units of nucleotides. (A-T & C-G)

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True

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3 types of RNA

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1. Messenger (mRNA)- which copies the DNA.
2. Ribosomal (rRNA)- which provides the location for protein synthesis.
3. Transfer (tRNA)- which delivers the amino acids to the rRNA as they are coded by the mRNA.

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How many pairs of chromosomes in a DNA?

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23 pairs

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(T or F) DNA stays in the nucleus. mRNA takes the DNA and brings it into the cytoplasm.

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True

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have a circular chromosome made of a single circular molecule of DNA with associated proteins. It is usually attached to the plasma membrane.

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Bacteria

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The DNA of E. coli is made of about __ million base pairs and is about 1 mm long (1000x longer than the entire cell.)

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4.6

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DNA is __ ft. long.

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6

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is an enzyme which coils the DNA

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Topoisomerase II or DNA gyrase

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sequencing and molecular characterization of genomes.

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Genomics

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Human genomes ae made of __ billion base pairs.

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3

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Humans are 99% alike. Our __ __ makes us different. We are 50% genetically like a worm.

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base sequence

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process by which DNA is precisely duplicated to pass on to daughter cells. Make a copy because our cells constantly shed.

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Replication

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process by which DNA is read and the information gained is uesd to tell the cell what to do

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Gene expression

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process in which mRNA copies the DNA. All letters copy down. Occurs in the nucleus.

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Transcription

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process in which the tRNA aligns amino acids on the rRNA to make a protein. Occurs in ribosome.

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Translation

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"Central dogma of molecular biology"

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Transcription Translation
DNA --------------> RNA --------------> Protein
Nucleus Ribosome

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DNA must replicate for mitosis to occur.

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Replication of DNA

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Half of the old strand is saved to pair with the new DNA.

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Semiconservative replication

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bubble that initiates replication; where replication starts.

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Origin

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point at which DNA stops replicating; where replication stops.

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Terminus

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unwinds and separates the DNA before replication begins.

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DNA Helicase

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forms the new DNA strand in the only 5 to 3 directon.

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DNA polymerase III

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can be synthesized directly into the replication fork.

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Leading

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can only be synthesized a short amount at a time and then the pieces are tied together by DNA ligase.

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Lagging

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DNA is always __ which means that the two strands run in opposite directions.

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antiparallel

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RNA polymerase binds to DNA to make a complementary strand of mRNA.

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Transcription

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2 types of Transcription

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1. Promoter- site where RNA polymease binds to the DNA.
2. Terminator- site where RNA polymerase stops synthesis of RNA.

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3 differences in DNA and RNA

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1. DNA has deoxyribose and RNA has ribose as sugars.
2. DNA has thymine and RNA has uracil.
3. DNA is double stranded. RNA is single stranded.

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"Protein synthesis"- mRNA carries the information that determines the order of amino acids in the protein. tRNA translates information between RNA and protein. rRNA is the "workbench" where translation occurs.

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Translation

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each group of 3 nucleotides that codes for a particular amino acid.

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codon

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occurs when there is a mutation in the 3rd position of a codon and it still codes for the same amino acid. There are __ codons but only __ amino acids. (Leucine is coded for by 6 codons.)

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Degeneracy of the code ; 64; 20

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codons code for the same amino acids in all species.

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Univerality of the code

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code for amino acids

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sense codons

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are called stop codons and do not code for amino acids

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nonsense codons

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a sequence of 3 bases in tRNA that is complementary to a codon

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anti-codon

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regions of DNA that are expressed

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exon

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the noncoding region of DNA that is not expressed

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intron

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introns are called

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"Junk DNA"

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(T or F) Eukaryotes have intron. Prokaryotes are bacteria, no introns.

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True

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enzyme that removes the intron-derived RNA and splices together the exon-derived RNA to produce an mRNA

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spliceosome

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Regulation of gene expression

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1. Inducible enzymes- made only when their substrates are present.
2. Repressible enzymes- produced only when a signal molecule is scarce.
3. Constitutive enzymes- unregulated and always produced because it is always needed.

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set of genes that is regulated and transcribed together

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operon

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encodes the ability to use lactose (milk sugar) as a growth substrate. This is very important for bacteria. In the absence of lactose there is a Lac repressor which inhibits transcription of the Lac operon. In the presence of lactose the Lac operon is transcribed to make lactose.

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Lac operon

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sum total of DNA that a cell contains

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genome

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small circular strand of DNA in bacteria in addition to a chromosome

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plasmids

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some plasmids encode enzymes that make a bacterium resistant to antibiotics

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multiple drug resistance

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genetic make-up of an organism

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genotype

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physical appearance of an organism

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phenotype

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any chemical change in a cell's DNA

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mutations

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changes a single pair of bases to a different pair

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base substitution mutation

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occurs when a base substitution results in an amino acid substitution in the protein

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missense mutation

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occurs when a base substitution results in a stop codon. Stops production of protein.

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nonsense mutation

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removes a segment of DNA

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deletion

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occurs when bases are deleted or inserted and the entire reading frame is shifted

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frameshift mutation

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can't be exposed to sunlight. Cause lesions that leads to cancer.

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xeroderma pigmentosum

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reverses the order of a segment of DNA

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inversion mutation

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moves a segment of DNA to a different position on the genome

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transposition mutation

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add an identical new segment of DNA next to the original one

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duplication mutation

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every time the chromosome is replicated, mistakes can occur

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incidence of mutations

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number of mutations per cell per generation

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mutation rate

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mutations that occur in the natural course of microbial growth

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spontaneous mutations

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mutations caused by chemical, physical, and biological treatments

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induced mutations

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succeeding generations of daughter cells. (offspring)

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progeny

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an agent that induces mutations

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mutagen

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5-bromouracil, nitrosoguanidine, thalidomide (given for morning sickness)

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chemical mutagen

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given for morning sickness. (Angiogenesis- blood vessel protection.) Stopped blood vessel protection. Babies born with no arms or legs called Amelia. Meromelia or Phocomelia- flippers. Happened in Europe. Use to stop blood vessel protection for cancer.

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thalidomide

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U.V. light, x-rays, gamma radiation, decay of radioactive elements, heat

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physical mutagen

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transposing elements or "jumping genes" move around the genome and cause mutations

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biological mutagen

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two factors determine how serious a mutation will be for a cell:

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1. How much the mutation changes the gene product
2. How important the gene product is to the cell

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DNA leaves one cell and exists for a time in the extracellular environment and then it is taken into another cell where it may become incorporated into the genome to change it.

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Transformation

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plasmids are transferred from once cell to another by the pilus

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Conjugation

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transfer of chromosomal genes by phage (virus) particles containing bacterial DNA

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Transduction

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virus that can be carried passively within their host without harming it

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Temperate phage

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does not kill the cell but stays in the cell and may become incorporated in the host cell's chromosome

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Lysogenic cycle

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virus that infects bacteria by attaching themselves to the cell and injecting their DNA into the cell. It then directs the cell to make more of the virus.

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Virulent phage

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virulent phage life cycle

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Lytic cycle

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virus that infects bacteria

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Bacteriophage

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hospital-acquired infection- Many bacteria have antibiotic resistance because of mutations that occur in bacteria which are then passed on to other bacteria

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Nosocomial infection

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Example of temperate and lysogenic

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HPV (Human Papilloma virus)

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Example of virulent and lytic

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common cold

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2 million people get sick and 100 thousand die each year in the U.S. More than AIDS, breast cancer, and car accidents combined.

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nosocomial infection

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use of microorganisms, cells or cell components to make a product.

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biotechnology

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inserting a gene of interest into a cell to be used as a "factory" to produce a product.

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genetic engineering

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genes from one organism are inserted into another organism to make a commercially useful product.

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recombinant DNA technology