Exam #2 (7-9) Flashcards Preview

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Flashcards in Exam #2 (7-9) Deck (60):
1

Nucleic Acid Structure

Large molecules (DNA &RNA) composed of a chain of smaller nucleotides:
- one phosphate group (PO3)
- one 5-carbon ringed sugar
- one of five nitrogenous base molecules

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RNA

- Ribose sugar
- Adenine, Uracil, Cytosine, and Guanine base molecules
- 100-50000 nucleotides in a strand
- Single-stranded, linear
- Variety of functions related to protein synthesis

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DNA

- Deoxyribose sugar
- Adenine, Thymine, Cytosine, and Guanine base molecules
- Chromosomes have about 45 million nucleotides in a strand
- Double-stranded helix; bases bond by weak hydrogen bonds
- Stores genetic information (genes) that direct RNA to perform protein synthesis

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Complementary Base Pairs

Certain bases form weak hydrogen bonds between them (no exchange of electrons); allow the two long strands of DNA to stick together

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DNA Replication

A process that allow two identical copies of DNA for the bacterial chromosome; occurs prior to cell division:
- Helicase unwinds and unzips the double stranded helix at the origin of replication (both directions)
- DNA polymerase proofreads and joins new complementary base pairs together
- This proceeds until two identical strands are made (500-1000 base pairs in a second)
- Two identical strands will eventually separate

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Origin of Replication

Distinct region of a DNA molecule at which replication is initiated: one in bacteria, several thousand in eukaryotic cells

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Chromosome

Short, thick strand of DNA and protein; circular; divided into genes each of which is a sequence of DNA nucleotides; regulate cellular activity by controlling which genes are expressed to produce proteins

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Coding Region

Bacterial genes that code for the production of a single protein

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Regulatory Region

Bacterial genes that regulate the expression of genes

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Promotor

An area where RNA polymerase will bind (always unzipped)

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Operator

A gene can be turned off by placing a protein here

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Triplets

Division of genes composed of a sequence of three nucleotides found within the same gene; if the gene codes for a protein, then this will code for one specific amino acid found within the protein that will be produced; 64 possible combinations

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Stop Triplets

Found at the end of a coding region; stops the reading of a gene

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Stop Codon

Codon that does not code for an amino acid and is not recognized by tRNA; signals the end of the polypeptide chain; UAA, UAG, and UGA

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Start Condon

Codon at which translation is initiated; in prokaryotes, typically the first AUG after a ribosome binding site

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Lagging Strand

DNA replication occurs away from the replicating fork; nucleotides are added in segments in the 5' direction (Okazaki fragments)

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Lead Strand

DNA replication occurs towards the replication fork; nucleotides are added continuously in the 3' direction

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Transcription

The conversion of one gene found on DNA into mRNA:
- Initiation: The enzyme RNA polymerase attaches to the promotor region of a gene
- Elongation: The enzyme unzips the DNA molecule and moves along the template of DNA, synthesizing a single stranded mRNA strand one nucleotide at a time
- Termination: The enzyme encounters a stop signal and terminates the construction of mRNA

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Translation

The synthesis of an amino acid strand from codons found on mRNA:
- Initiation: mRNA binds to the 30S portion of the ribosome
- Elongation: Charged tRNA molecules bind to the 50S portion of the ribosome at two spots simultaneously (P and A sites); charged tRNA molecules release their amino acid which form peptide bonds between them, forming a short polypeptide; mRNA shifts over one codon and the process continues
- Termination: The ribosome reaches a stop codon which will terminate the production of the protein; the protein is released

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mRNA

A sequence of codons that is a complementary copy of a single gene; carries information from the DNA to the ribosome

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tRNA

Brings a specific amino acid to the mRNA and ribosome during translation:
- Sequence of three nucleotides (anti-codon) complementary to the codon foud of the mRNA
- Charged when specific amino acid is attached

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Erythromycin

An antibiotic that binds to the 50S ribosomal subunit, inhibiting protein synthesis

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Operon

Group of linked genes whose expression is controlled as a single unit

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End Product Represssion

The end product of a series of chemical reactions will inhibit the expression of a gene and prevent further synthesis of all those enzymes necessary to produce the end product (turns genes on and off)

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Feedback Inhibition

The end product will inhibit the function of one enzyme, of a series of enzymes, responsible for the synthesis of the end product; the product is never made as long as the end product of the series of reactions is in abundance

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Mutation

A change in the nucleotide sequence of DNA that results in a recognizable change in the organism; results in an altered mRNA sequence, which will possibly result in the formation of an incorrect protein synthesis

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Substitution

Type of mutation that occurs when one nucleotide is replaced with another of a different base

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Removal (Deletion)

Type of mutation that occurs when one nucleotide is removed randomly and not replaced with another nucleotide

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Addition (Insertion)

Type of mutation that occurs when a nucleotide is added randomly

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Thymine Dimer

Type of mutation that occurs when two adjacent thymine bases form a covalent bond between them and distort the double helix, damaging the DNA; caused by exposing DNA to UV or X-rays

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Cellular Effects of Mutations

- Death: most are detrimental
- Benefit: Some provide a benefit (increased antibiotic resistance)
- No change: some will not change the protein constructed or affect a portion of the chromosome that is not important

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Spontaneous Mutation

Occurs randomly during DNA replication: 1 in 10000 to 1 in a million replications for every single gene

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Induced Mutation

DNA is exposed to mutagens; increases the risk by 10-1000X

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Mutagen

A physical or chemical agent that causes changes to genetic material

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Light Repair

Type of thymine dimer repair in which cells that posses the enzyme photolyase will repair these mutations when exposed to visible light; the enzyme breaks the covalent bond between thymines

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Dark Repair

Type of thymine dimer repair in which visible light is not necessary; one enzyme compares the complementary strand of DNA and finds and removes the mutation; DNA polymerase replaces the correct base back into the DNA sequence

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Proofreading by DNA Polymerase

The enzyme compares what base was incorporated to the template, if the bases are not complementary, then the correct base is incorporated into the new strand

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Mismatch Repair

Back-up system used to repair mutations in case DNA polymerase misses a wrong base - Ultraviolet Light Repair System

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Ultraviolet Light Repair System (Uvr)

- Two Uvr A proteins and one Uvr B (trimer) attach to the DNA molecule then move down the molecule scanning for damage
- Once damage is found, the trimer stops and the two Uvr A proteins are released; Uvr B remains
- Uvr C attaches to the Uvr B and cuts the DNA on both sides of the damaged DNA several nucleotides away
- Uvr D, a DNA helicase, releases the segment of DNA and Uvr B, C, and D are released
- The segment of DNA that needs to be replicated is filled in with complementary nucleotides using DNA polymerase and is sealed with DNA ligase

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Natural Selection

If a bacterial cell has some advantage over some other bacteria within a population, then it will survive longer and reproduce more often, becoming the most common type of bacteria within the population

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Transformation

Method of gene transfer by which bacterial cells take up naked DNA molecules; conducted by both gram+ and gram- organisms:
- If a bacterial cell wall is ruptured, then the chromosome will leak into the environment and break apart into smaller pieces (about 100), each containing about 20 genes
- The small sections of DNA are still very large, so another living cell must have large holes or pores in its cell membrane that will allow the DNA to enter the cell

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Competent Bacteria

Have large holes that allow sections of DNA to enter the cell:
- Natural: under certain environmental conditions or certain bacteria (soil microbes)
- Artificial: use of electrical current to create large holes

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Transduction

Method of gene transfer that occurs in every bacteria cell; most common type:
- A bacteriophage enters a bacteria cell and uses deoxyribonuclease to digest the chromosome into small pieces; the DNA or RNA of the virus is also replicated
- Some sections of the bacterial chromosome are integrated into the new viruses
- The viruses leave the infected bacterial cell and enter a new and uninfected bacterial cell, depositing the bacterial DNA section into the new cell

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Bacteriophage

A virus that infects and replicates within bacteria

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Conjugation

Method of gene transfer that requires physical contact between bacteria; uncommon, occurs mostly in gram- bacteria:
- Plasmids replicate and then are transferred from donor to recipient cells (only in one direction) using pili

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Plasmid

Small, circular DNA molecule that is physically separate from, and can replicate independently of, chromosomal DNA within a cell

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Donor (F+) Cell

Contains the genes on the plasmid that code for the pilus and the ability to be able to transfer DNA to other cells

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Recipient (F-) Cell

No plasmid that codes for the pilus; can only receive the plasmid

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R Factor Plasmid

Contains multiple genes that give plasmid holder resistance to a series of different kinds of antibiotics and even heavy metals; the most important plasmid to the medical profession

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Hfr (High Frequency Recombination)

Plasmids that my occasionally be incorporated into the bacterial chromosome; whole bacterial chromosomes can be transferred but it takes a very long time

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Features That the 3 Methods of Gene Transfer Have in Common

- Transfer only a few genes at once (portions of chromosomes or plasmids)
- Incorporation of gene only successful 1% of the time
- Once inside the cell, the new genes are incorporated into the bacterial chromosome by the same method: breakage-cleavage

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Breakage-Cleavage

- Corresponding homologous genes are paired together (side by side)
- An enzyme (deoxyribonuclease) will remove the "old" gene
- Another enzyme (DNA ligase) will join the "new" gene to the recipient's chromosome
- Recipient gene is destroyed by enzymes

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Biotechnology

The use of microbiological and biochemical techniques to produce medically and commercially valuable products

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Genetic Engineering (DNA cloning)

Occurs when genes are isolated from one organism and then transferred to another organism, giving the new organism new traits

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Restriction Enzymes

Used to cut DNA into fragments; allow scientists to remove genes from one organism and not the entire chromosome

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DNA Ligase

An enzyme that is used to join fragments of DNA into one unit; completes the transfer of DNA from one organism to another as it "glues" the DNA from the donor cell to the DNA of the recipient cell

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Gel Electrophoresis

Process used for separating DNA fragments by size

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Transgenic Organism

A plant or animal that has been genetically engineered

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DNA Probe

A single-stranded piece of DNA, complementary to the sequence of interest, that has been labeled with a detectable marker (radioactive isotope or fluorescent dye); used to locate specific nucleotide sequences in nucleic acid samples attached to a solid surface

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The Human Genome Project

The now-completed undertaking to sequence the human genome (complete set of genetic information in a cell); determine nucleotide sequences