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LIFE102, Week 13 Notes

by: Sydney Dingman

LIFE102, Week 13 Notes Life 102

Marketplace > Colorado State University > Biology > Life 102 > LIFE102 Week 13 Notes
Sydney Dingman
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These notes cover Monday and Wednesday (no class on Friday) of Week 13.
Attributes of Living Systems
Erik N Arthun
Class Notes
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This 6 page Class Notes was uploaded by Sydney Dingman on Monday April 18, 2016. The Class Notes belongs to Life 102 at Colorado State University taught by Erik N Arthun in Winter 2016. Since its upload, it has received 19 views. For similar materials see Attributes of Living Systems in Biology at Colorado State University.

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Date Created: 04/18/16
Week 13 LIFE 102 Notes 4/11/16, Chapter 17 No Chapter 18 Genetic code o Genetic code is redundant (more than one codon may specify a particular amino acid) o Codons must be read in the correct reading frame in order for the right polypeptide to be produced o AUG is at the start of every protein o UAA, UAG or UGA are at the end of every protein o TAC-ATA-AAA-ATTAUG-UAU-UUU-UAAStart(Met)-Tyr-Phe- Stop(Last period)  The Structure and Function of Transfer RNA o Molecules of tRNA are not identical  Each carries a specific amino acid on one end  Each has an anticodon on the other end  The anticodon base-pairs with a complementary codon on mRNA o A tRNA molecule consists of a single RNA strand that is only about 80 nucleotides long o Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a cloverleaf o Because of hydrogen bonds, tRNA twists and folds into a three- dimension molecule (roughly L-shaped)  Translation o mRNA- Protein o Codon- amino acid o Molecule that translates: Transfer RNA (tRNA) o Anticodon: tRNA triplet that binds to codon o mRNA binds to ribosome o tRNA bring amino acids to ribosome o Ribosomal enzymes connect amino acids into a polypeptide  Ribosomes o Facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis o 3 Binding sites for tRNA:  P site: holds tRNA that carries the growing polypeptide  A site: holds tRNA that carries the next amino acid to be added to the chain  E site: exit site where discharged tRNA leave the ribosome  Three Stages of Translation o The initiation stage of translation brings together mRNA, tRNA with the first amino acid, and the two ribosomal subunits o During the elongation stage, amino acids are added one by one to the proceeding amino acids o Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome  A site accepts a protein called a release factor  The reaction catalyzed by the release factor releases the polypeptide, and the translation assembly then comes apart  Polyribosome: A number of ribosomes can translate a single mRNA simultaneously forming a polyribosome o Polyribosomes enable a cell to make many copies of a polypeptide very quickly  Bacterial gene expression o Bacteria does not have a nucleus o Transcription and translation can occur at the same place, at the same time  Mutations: changes in DNA sequence o Point mutations: changes in just one base pair of a gene o A-T  G-C: Base pair substitution  o A-T  ---: base pair deletion o ---  G-C: base pair insertion o Possible consequences: 2  Less functional or non-functional protein  No protein  Sometimes they work better (Very rare)  Types of Small-Scale Mutations o Point mutations within a gene can be divided into two general categories:  Nucleotide-pair substitutions  One or more nucleotide-pair insertions or deletions o A nucleotide-pair substitution replaces one nucleotide and its partner with another pair of nucleotides o Insertions and deletions are additions or losses of nucleotide pairs in a gene  Substitutions o A nucleotide-pair substitution replaces one nucleotide and its partner with another pair of nucleotides o Silent mutations have no effect on the amino acid produced by a codon because of redundancy in the genetic code o Missense mutations still code for an amino acid, but not the correct amino acid o Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein  Insertions and Deletions o Insertions and deletions are additions or losses of nucleotide pairs in a gene o These mutations have a disastrous effect on the resulting protein more often than substitutions do o Insertion or deletion of nucleotides may alter the reading frame, producing a frame shift mutations  WATCH VIDEO ANIMATION ON CANVAS OF THE PROCESS 4/13/16, Chapter 19, Viruses  Structure of Viruses o Viruses are not cells 3 o Very small infectious particle consisting of nucleic acid enclosed in a protein coat, in some cases, a membranous envelope o Viruses are obligate intracellular parasites which means they can replicate only within a host cell  General Characteristics of Viruses o Cannot reproduce or multiply unless they invade a specific (specific cell/species) host cell and instruct its genetic and metabolic machinery to make and release new viruses o Can infect every type of cell (bacteria, fungi, algae, etc.) o Obligate intracellular parasites  Cannot exist independently from the host cell  Non-living infectious particles (acellular)  “Active or inactive” not “dead or alive” o contain only those parts needed to invade and control a host cell  Viral capsids o A capsid is the protein shell that encloses the viral genome composed of capsomeres o Capsids are built from individual protein subunits called capsomeres  Viral envelope o Some viruses have membranous envelopes (viral envelopes) that surround the capsid o Viral envelopes, which are derived from the host cell’s membrane, contain a combination of viral and host cell molecules  Viral Structures  Viruses that infect bacteria o Bacteriophages, also called phages, are viruses that infect bacteria o Phages have an elongated capsid head that encloses their DNA o A protein tail piece attaches the phage to host and injects the phage DNA inside  Viral Genome Types o Double- or single-stranded DNA or Double- or single- RNA 4 o Depending on its type of nucleic acid, a virus is called a DNA virus or an RNA virus o No virus will ever have both DNA or RNA  Host Range & Tissue Tropism o Viruses are obligate intracellular parasites, which means they can replicate only within a host cell o Each virus has a host range (a limited number of species that it can infect; type of species) and tissue tropism (tissue specificity within a host; type of cell)  General Features of Viral Replicative Cycles o Once a viral genome has entered a cell, the cell begins to manufacture viral proteins o The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP and other molecules o Viral nucleic acid molecules capsomeres spontaneously self- assemble into new viruses  Replicative Cycle of a DNA virus o Viral DNA enters cell  Replication, transcription, translation o Viral DNA and proteins made o Virus assembly, cell lysis  Replicative Cycle of Phages o Phages have two reproductive mechanisms  The Lytic cycle and Lysogenic cycle o Lytic Cycle  The lytic cycle is a phage replicative cycle that leads to the death of the host cell  The lytic cycle produces new phages and lyses (breaks open) the hosts cell wall, releasing the new virus o Lysogenic cycle  The lysogenic cycle replicates the phage genome without destroying the host  The viral DNA molecule is incorporated into the host cell’s chromosome 5  This integrated viral DNA is known as a prophage  Every time the host divides, it copes the phage DNA and passes the copies to daughter cells  An environmental signal can trigger the virus genome to exist the bacterial chromosome and switch to the lytic mode  6


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