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Exam #1 Study Guide

by: Michelle Hatherley

Exam #1 Study Guide SCI 281

Michelle Hatherley
GPA 3.4

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Covers everything on the 1st exam! Chapters 2,3, 5-10
Medical Microbiology
Blake Whittaker
Study Guide
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This 9 page Study Guide was uploaded by Michelle Hatherley on Sunday October 2, 2016. The Study Guide belongs to SCI 281 at University of Southern Maine taught by Blake Whittaker in Fall 2016. Since its upload, it has received 5 views.


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Date Created: 10/02/16
Exam #1 Study Guide – What is the structure of the cell wall?  Composed of peptidoglycan (complex polysaccharide composed of NAG & NAM) What is the differences between Gram +/Gram-? Gram­positive: purple  Thick cell wall & minimal periplasm  Thick layer of peptidoglycan  Gram­negative: red  Extensive periplasm plus an outer membrane (asymmentrical bilayer  membrane) attached to peptidoglycan by lipoprotein o inner portion of membrane: integral proteins & phospholipid  bilayer o outer portion of membrane: Lipopolysaccharide (LPS), which is an endotoxin and released from dying bacteria o Thin layer of peptidoglycan o Outside membrane is called asymmetrical bilayer membrane  What two types of viruses are there? (Enveloped vs. Non-enveloped) Virus: minuscule, acellular, infectious agent having one or several pieces of nucleic acid  – either DNA or RNA. NO CYTOPLASMIC MEMBRANE. (not capable of  metabolic activity)  Virion: virus outside of a cell in the extracellular state   Consists of a protein coat (capsid or envelope)  Envelopes provide the virus with protection & recognition sites that bind to  complementary chemical of the surface   Capsid is removed when virus is inside the cell  Naked viruses: non­enveloped  Describe one complete line of a specific virus. Coronaviridae is an RNA virus that is single stranded + (+ meaning it is equivalent to mRNA) which is represented by the coronavirus, commonly known as the common cold and severe acute respiratory syndrome. Describe the process of viral multiplication Viruses are dependent on their host’s organelles and enzymes to produce new virions. Once a host cell is under the control of a viral genome, it’s forced to replicate viral genetic material and translate new proteins. Lytic replication: when cell undergoes lysis near the end of viral replication. 1. Attachment – virion attaches to host cell 2. Entry – virion or its genome enters the host cell 3. Synthesis – of new nucleic acids and viral proteins by the host cell’s enzymes and ribosomes 4. Assembly – of new virions with the host cell 5. Release – of the new virions from the host cell Know the differences between chemicals (Carbs, Proteins, Lipids, Nucleic Acids) Carbs  Organic molecules  Composed of atoms of carbon, hydrogen, and oxygen  Energy sources (long term energy source from large carbs and immediate/ready  energy from smaller carbs such as glucose)  Backbones of DNA and RNA   Some carbs are converted routinely into amino acids   Polymers of carbs form the cell wells of most fungi, plants, algae, and prokaryotes   Involved in intercellular interactions between animal cells  Proteins:  Most complex organic compound   Polymers composed of monomers called amino acids   Composed of mostly carbon, hydrogen, oxygen, nitrogen, and sulfur   Functions: Structure, enzymatic catalysis, regulation (hormones), transportation,  defense and offense   Structures: primary (sequence of amino acids in a polypeptide), tertiary (3D  shape defined by further hydrogen bonding as well as covalent bonding between  sulfur atoms of adjoining cysteine), quaternary (composed of more than one  polypeptide chain) Nucleic Acids:  Deoxyribonucleic acid (DNA) & Ribonucleic acid (RNA): vital genetic material  Cyclic nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T),  uracil (U) Glycine o Smallest amino acid   How does the growth of bacteria develop? Mostly done by binary fission: process in which a cell grows to twice its normal size and  divides in half to produce two daughter cells of equal size.  Growth Curve Lag phase ­   Little increase in reproduction  Actively synthesizing enzymes (metabolically active)  Can last for less than 1 hour or up to days Log Phase ­   Period of growth at a genetically & environmentally determined maximum growth  rate  Rapid chromosome replication, growth, reproduction (RRGR = Rude Roommates Go Running?)  DNA and protein syntheses are maximized  Population increases logarithmically (shortest generation time observed)  Limiting factor appears to be rate of ATP production Stationary phase ­   # of new bacteria = # of dying bacteria (no net increase in population of viable  cells ) o  New cells that produced at the same rate as old cells dying  Nutrient supplies limited  Toxic by­products (alcohols may be produced) o Metabolic rate of surviving cells decline Decline phase (aka “death phase”)  Population reaches a point @ which cells die faster than produced  Nutrient supply is exhausted  Cells assume unusual shapes due to involution  Attempt to maintain by self­digestion & cannibalism  DNA Replication Replication occurs using an existing strand of the DNA as a template to which is matched the  corresponding nucleotide base pair (semiconservative replication).  Leading strand: synthesized continuously as a single strand (5’ to 3’ direction, moving  towards the replication fork.   Primase synthesizes RNA molecule which then provides the 3’ hydroxyl group  required by DNA polymerase   Triphosphate deoxyribonucleotides form hydrogen bonds with their complements in the parental strand (Adenine binds to thymine & guanine binds to cytosine)  DNA polymerase III covalently binds them one by one by dehydration synthesis  to the leading strand.   Proofreading exonuclease: function that fixes mistakes in pairs   DNA polymerase I replaces the RNA primer with DNA  Lagging strand: synthesized in short segments that are later joined (synthesized away  from the replication fork)   Primase synthesis RNA primers   Nucleotides pair up with their complements in template  DNA polymerase III joins neighboring nucleotides & proofreads   Lagging strand is synthesized in discontinuous segments (okazaki fragments)  DNA polymerase I replaces the RNA primers of okazaki fragments with DNA and further proofreads the daughter strands.  DNA ligase seals the gaps between adjacent okazaki fragments to form a  continuous DNA strand  Transcription (Synthesize RNA) Transcription: process in which the genetic code from DNA is copied as RNA nucleotide sequence. Cells transcribe 4 main types of RNA from DNA, including: RNA primer: molecules for DNA polymerase to use during DNA replication Messenger RNA (mRNA): molecules that carry genetic info from chromosomes to ribosomes Ribosomal RNA (rRNA): molecules which combine with ribosomal polypeptides to form ribosomes – the organelles that synthesize polypeptides Transfer RNA (tRNA): molecules which deliver amino acids to ribosomes 1. Initiation a. RNA polymerase attaches nonspecifically to DNA and travels down its length until it  recognizes a promoter sequence. Sigma factor enhances promoter recognition in  bacteria.  b. Upon recognition of the promoter, RNA polymerase unzips the DNA molecule  beginning at the promoter.  2. Elongation  a. After triphosphate ribonucleotides align with their DNA complements, RNA  polymerase links them together, synthesizing RNA. b. The triphosphate ribonucleotides also provide the energy required for RNA synthesis c. No primer is needed 3. Termination a. In self­termination, the transcription of DNA terminator sequences cause the RNA to  fold, loosening the grip of RNA polymerase on the DNA. b. In enzyme­dependent termination, a termination enzyme pushes between RNA  polymerase and the DNA, releasing the polymerase.  Translation (Synthesize Polypeptides) Process in which the sequence of genetic information carried by mRNA is used by ribosome to construct polypeptides with specific amino acid sequences. 1. Initiation a. Smaller ribosomal subunit attaches to mRNA at a ribosome-binding site, with a start codon at its P site. b. tRNA attaches at the ribosome’s P site; GTP supplies the energy required for binding c. The larger ribosomal subunit attaches to form a complete initiation complex. 2. Elongation – sequential adding of amino acids to a polypeptide chain growing at the P site a. tRNAs sequentially deliver amino acids as directed by the codons of the mRNA. b. Ribosomal RNA in the large ribosomal subunit catalyzes a peptide bond between the amino acid at the A site and the growing polypeptide at the P site. 3. Termination a. Release factors halt elongation b. The polypeptides release are functional as proteins Operon Model Operon: consists of a promoter and a series of genes that code for enzymes and structures such as channel proteins. Inducible operons: not usually transcribed & must be activated by inducers Repressible operons: operate in reverse fashion Lac Operon  Inducible operon  When lactose is absent from the cell’s environment, the repressor binds to the operator, blocking the movement of RNA polymerase and halting transcription  When lactose is present in the cell’s environment, it acts as an inducer by inactivating the repressor so that it cannot bind to the operator, allowing transcription to happen.  Lactose bumps into repressor which then changes it shape  RNA polymerase drives down DNA which then makes proteins to break down lactose  No lactose present = OFF (RNA polymerase can’t move) Tryptophan Operons  Repressible operon  Promoter, operator, and 5 genes that code for the enzymes involved in the synthesis of tryptophan  When tryptophan is absent from the cell’s environment, the repressor is inactive, so the structural genes are transcribed and translated, and the 5 enzymes needed in the synthesis of tryptophan are produced.  When tryptophan is available it activates the repressor by binding to it.  The activated repressor then binds to the operator, halting the movement of RNA polymerase and halting transcription Fmet = first amino acid Transduction Involves the transfer of DNA from one cell to another via a replicating virus Bacterial Sex (Conjugation)  Can occur either between prokaryotic cells or between eukaryotic cells  Limited only the availability of a virus capable of infecting both donor & recipient cells   Bacteriophage (phage): virus that infects bacteria  1. Phage enzymes degrade the cell’s DNA  2. Phage genome now controls the cell’s functions & directs it to synthesize new phage DNA  and phage proteins.  3. Host cell lyses, releasing daughter and transducing phages. Transduction occurs when a  transducing phage injects donor DNA into a new host cell  4. Recipient host cell incorporates the donated DNA into its chromosome by recombination  Types of Cells  F + Cell  F ­ Cell  HFR Cell  Fprime cell Describe Plasmids Importance of generating ATP and what bacteria’s main goal is Know the function and process of glycolysis Electron Transport Chain Aerobic vs. Anaerobic activities o 19x more ATP aerobically vs. anaerobically to grow as fast as possible Control of microbial growth in environment or in human bodies


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