Microbiology Lecture Notes - Viruses and Enzymes

Microbiology for Nursing and Allied Health, BIO 185 Dr. Marjan Sharifi Lecture 4 Reference: Bauman, R.W. (2018). Microbiology with Diseases by Taxonomy (6th ed.). 1  Lytic and Lysogenic...

Microbiology for Nursing and Allied Health, BIO 185 Dr. Marjan Sharifi Lecture 4 Reference: Bauman, R.W. (2018). Microbiology with Diseases by Taxonomy (6th ed.). 1  Lytic and Lysogenic pathways Once inside the host cell, a viral genome can orchestrate one of two quite different events. In every infection, such viruses need to decide between the lytic and the lysogenic cycles, i.e., whether or to lysogenize and keep the host viable. Some viruses can reproduce using both the lytic and the lysogenic cycle. 2 Communication between viruses guides lysis-lysogeny decisions  1. Lytic pathway The virus may replicate and destroy the host in a virulent infection via a lytic pathway. They replicate inside the host and lyse their host. In a lytic infection, the virus redirects the host cell’s metabolism from growth to support virus multiplication and the assembly of new virions. New virions are released, and the process can repeat itself within new host cells. The Ebola virus undergoes a lytic cycle. 3 Communication between viruses guides lysis-lysogeny decisions  Lytic Replication of Bacteriophage Attachment Bacteriophage genome We learned tons Entry about animal virus Tail sheath replication by studying bacteriophage! Bacterial Cell lysis  new phage chromosome 2Entry released Attachment 1 Phage No envelope! DNA Bacterial 3 chromosome degraded 6Release New Synthesis 4 Phage Proteins & 5AssemblyGenomes  2. Lysogenic pathway Some viruses can cause a lysogenic infection. In this case, the host cell is not destroyed and the viral genome becomes part of the host genome. The herpes simplex virus, the human immunodeficiency virus (HIV) are examples for lysogenic pathway. 5 Communication between viruses guides lysis-lysogeny decisions  6 Viruses as Infectious Agents: Bacterial, Archaeal, Fungal, Algal, and Inverte  Lysogenic Replication of Bacteriophage 1Attachment Provirus 3 2 Entry in chromosome Lytic cycle Lysogenic Lysogeny cycle 6Synthesis 8Release 4 Replication of 7Assembly chromosome and virus; cell division 5Induction Further replications & cell divisions Some can do Triggered by good environment Genome integrates  provirus (like HIV!) Silent replication Bad environment (time to go!)  lytic cycle  millions!!  Viral Replication Lysogenic Cycle -bacteriophage Viral DNA does not assume control of cell Inserts DNA into Host’s DNA Integrate nucleic acid for generations Host cell acquires new genetic information Animal viruses versus bacterial viruses Basically the same as bacteriophage Latency similar to lysogeny  Mechanisms of Virus Entry Cytoplasmic membrane 1 Genome inside capsid 2 of host engulfs virus Capsid 3 (endocytosis) 1 2 3 4 Receptor Viral genome Viral Direct penetration (poliovirus)Viral 6 genome 5 glycoprotei 1 Viral ns glycoproteins 2 Envelope stay at 3 surface Endocytosis (non-enveloped adenovirus or 4 enveloped herpesvirus) Receptors Viral genome Membrane fusion (measles virus, HIV)  Synthesis of New Animal DNA Virus Genomes & Genome looks like oursProteins (DNA)  cell treats like self! Genome - Replicated by cell DNA polymerase (nucleus) Proteins - Host RNA polymersase transcribes DNA  RNA (nucleus) - Ribosomes translate RNA  proteins (cytoplasm) Release Attachment Assembly Entry New capsid proteins New genomes Synthesi s Viral genomes with cell DNA polymerase (nucleus)  Synthesis of New Animal RNA Virus Genomes & Proteins Genome does not look like ours!  Virus needs special viral enzyme! Genome – Replicated by Viral RNA polymerase (cytoplasm) Proteins – Ribosomes translate RNA  proteins (cytoplasm) Release Attachment nucleus Assembly Entry capsid proteins Viral RNA Synthes is new new capsid viral proteins RNA Viral genomes with viral RNA polymerase (cytoplasm) Viral proteins with ribosomes (cytoplasm)  Assembly of New Viral Genomes and Proteins in Eukaryotes Assembly Think of where most of our DNA & RNA is found! – DNA viruses: nucleus – RNA viruses: cytoplasm  Release of Newly Assembled Viruses Non-enveloped viruses – Lysis – plasma membrane ruptures – Exocytosis – vesicle with virus inside fuses with plasma membrane Enveloped viruses – Budding – cell pushes through plasma membrane Non-enveloped Enveloped Viral Diseases Measles Mumps Chickenpox Shingles Influenza Common Cold  Viruses Role in Cancer 15% of human cancers are virus induced Burkitt’s lymphoma – Epstein-Barr Virus Hodgkin’s disease – Epstein-Barr Virus Kaposi’s sarcoma – Herpes 8 Virus Cervical cancer – Human Papilloma Virus  DNA Tumor Viruses Besides catalyzing lytic events or becoming integrated into a genome in a latent state, some DNA animal viruses can induce the formation of tumors. These include viruses of the polyomavirus family and some herpesviruses, both of which contain double-stranded DNA genomes. 16  Herpesviruses Herpesviruses are a large group of double-stranded DNA viruses that cause a variety of human diseases, including fever blisters (cold sores), chicken pox, shingles, and infectious mononucleosis. An important group of herpesviruses cause cancer. 17  Herpesviruses Herpesviruses can remain latent in the body for long periods of time and become active under conditions of stress or when the immune system is compromised. Herpesvirus virions are enveloped and can have many distinct structural layers over the icosahedral nucleocapsid. Following viral attachment, the host cytoplasmic membrane fuses with the virus envelope, and this releases the nucleocapsid into the cell. The nucleocapsid is transported to the nucleus, where the viral DNA is uncoated and mRNA are produced. 18 Viruses - cultivation Lawn of bacteria Live animals or plants Embryonated eggs Cell culture (tissues) HeLa - continuous  Subviral Agents A few noncellular microbes are even more streamlined than viruses; some contain RNA but lack protein while others contain protein but lack nucleic acids of any type. There are two subviral agents: the viroids and the prions. These are infectious agents that resemble viruses but lack either nucleic acid (prions) or protein (viroids) and are thus not viruses. 20  Viroids Viroids and plant diseases. Photograph of healthy tomato Viroids are infectious RNA molecules plant (left) and one infected with potato spindle tuber viroid that lack a protein component. (PSTV) (right). The host range of Viroids are small, circular, single- most viroids is quite restricted. However, PSTV infects tomatoes stranded RNA molecules that are the as well as potatoes, causing smallest known pathogens. growth stunting, a flat top, and premature plant death. Viroids cause a number of important plant diseases and can have a severe agricultural impact. No viroids are known that infect animals or microorganisms. 21  Prions Prions represent the opposite extreme from that of viroids. Prions are infectious agents whose extracellular form consists entirely of protein. A prion lacks both DNA and RNA. Prions cause several neurological diseases in animals. Besides the transmissible spongiform encephalopathies, amyloids are also associated with debilitating human diseases such as Alzheimer’s, Huntington’s, Parkinson’s, and type 2 diabetes. 22  Prion Misfolded normal cellular protein in brain cell Causes fatal spongiform encephalopathies Scrapie (sheep) Mad cow disease (cow) Kuru (New Guinea cannibals) Creutzfeldt-Jakob disease (spontaneous in humans) Spontaneous/transmitted Ingestion, transplantation, contact mucous membranes with infected nervous tissue Destroyed by Incineration/autoclaving in concentrated sodium hydroxide No cure Incubation: 5 – 40 years Illness: 12 – 14 months  Prion Disease How can a protein, that cannot replicate itself, be a transmissible pathogen & cause disease? Normal New prion protein Many prions Original prion prion protein If prion “infects” brain cell, it converts normal protein into misfolded form Prions build up  neuronal death Large vacuoles & plaques form  death of individual  The Role of ATP in Metabolism Metabolism – all chemical reactions in organism Catabolism – produces ATP Anabolism – uses ATP *ADP – adenosine diphosphate  Metabolism Metabolism = sum of all reactions Catabolism = energy releasing reactions EXERGONIC Complex organic compounds to simpler ones Degradative reactions Hydrolytic reactions – chemical bonds broken Anabolism = energy consuming reactions ENDERGONIC Integration of Metabolism Simpler organic compounds to more Reactions joined through intermediates complex Anabolic or biosynthetic reactions Dehydration synthesis reactions  How Do Chemical Reactions Occur? Atoms, ions, molecules continuously moving  collisions Energy in collisions can disrupt electrons  break & form bonds Activation energy – energy needed to disrupt electrons Reaction rate – how often collisions occur Increased by: ↑ Temperature/pressure Enzymes!! This Photo by Unknown Author is licensed under CC BY-SA-NC  Enzymes Chemical reactions Physiological temperatures and pressure too low for quick reactions to occur Enzymes lower activation energy Bring reactants closer together Orient reactants May put strain on reactant Enzyme—Substrate—ES—Enzyme--Product  Enzymes Chemical reactions Bonds either formed or broken Collision theory – activation energy Speed of particles Configuration of particles  Enzyme Structure Two types of enzymes: - Simple Enzyme: Protein only - Conjugated Enzymes (aka holoenzymes): Protein + non-protein molecules - Apoenzyme: Protein portion - Cofactor: Non-proteins (metallic cofactors, coenzymes) - Haloenzyme (active enzyme) = apoenzyme + cofactor (organi c) Cofactor – mineral ions Coenzyme – organic molecule derived from  Enzyme Structure Components 1. Apoenzyme = protein part 2. Cofactor = non-protein parts Inorganic – ions (Ca2+, Zn2+) Organic – coenzymes (NAD) Holoenzyme = fully functional unit Specific substrate binds active site Inorganic cofactor (ion) Active site Organic cofactor (coenzyme) Apoenzyme (protein) Holoenzyme Haloenzyme  How do enzymes work? Enzymes work by weakening bonds which in turn lower the activation energy. A+B Enzy me C Binding site Once bound, enzyme shape changes After product is released, slightly (induced fit) to form the enzyme is unaffected and can be enzyme-substrate complex. re-used. THE FINAL STRUCTURE OF AN ENZYME CAN INFLUENCE ITS FUNCTION. Product Substrate Proper Shape Enzyme Enzyme Substrate No product Improper Shape Enzyme  Enzymes and Chemical Reactions Catalyze (speed up) chemical reactions by lowering activation energy Each has specific substrate (reactant) Not altered during reaction A B A +B Substrate (reactant) Activation energy without enzyme A B Activation energy with enzyme This Photo by Unknown Author is licensed under CC BY-SA A +B Products  Mechanism of Enzyme Action Induced fit  substrate oriented in optimal position 2 Specific 1 substrate contacts enzyme active site 5 Enzyme unchanged; free to bind more substrate 3 Substrate transformed: 4 rearrangement Products of existing atoms/breakdown released: of substrate molecule no longer fit  Enzymes Enzymes specific – 1 enzyme = 1 reaction Enzymes – large globular proteins Lock and Key Model Factors that can Influence Enzyme Activity Substrate Concentration ↑ substrate will ↑ rate to a point! Maximum velocity (Vmax) Enzymes saturated (all active sites occupied) Will not ↑ unless add more enzyme  Factors that can Influence Enzyme Activity Temperature pH **Note: At LOW TEMPS, protein NOT DENATURED  FROZEN!  Regulation of Enzyme Function Environmental Conditions: Alter shape of the active site  Enzymes Enzyme inhibition Heat & acid denatures (non- functional) Chemical inhibition Competitive inhibition – compete with active site Non-competitive – allosteric site-change configuration  Factors that can Influence Enzyme Activity Competitive inhibitors Compete for active site i.e., sulfanilamide (sulfa drug) Inhibits PABA conversion to folic acid (bacteria need it to grow; we don’t use PABA) Substrate Competitive inhibitor Enzyme Para-aminobenzoic acid (PABA)  Factors that can Influence Enzyme Activity Noncompetitive inhibitors Binds allosteric site (not active site!) Changes active site shape → can’t act on substrate i.e., Feedback inhibition – occurs in metabolism Substrate Active site Enzyme Distorted active site Allosteric site Allosteric inhibitor Allosteric inhibition  Feedback Inhibition Substrate Pathway Pathway shuts down operates Enzyme 1 Bound end-product Allosteric  End-product of pathway (allosteric site inhibits enzyme at beginning inhibitor)  Don’t make more product Feedback inhibition Intermediate A than you need!! Enzyme 2 Intermediate B End-product Enzyme 3