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Microbiology Ch.9
| Question | Answer |
|---|---|
| Viruses are self replicating nucleic acid molecules surrounded by a protein coat called a _________ | capsid |
| A signle virus particle is called a _______ | virion |
| Viruses are ________ outside the host cell | dormant |
| Baltimore classification classifies bacteria bases on? | genetic material |
| Describe the genomes of viruses | Can be ssDNA, ssRNA, dsDNA or dsRNA. The genome can be one molecule or several |
| Viral capsids are made of several molecular proteins called _________ | capsomeres |
| Because of their unique structure, the capsid proteins are able to _________ into a capsid | self-assemble |
| Some viruses have outer membranes composed of ___________ | lipid bilayers and glycoproteins |
| How do viruses acquire lipid bilayer? | When they pass through the membrane of their host |
| In the envelope, the lipid of the membrane comes from the host. But the _______ are encoded by the virus | proteins |
| What is a nucleocapsid? | Nucleic acid + capsid |
| Describe the capsid icosahedral symmetry | 20 sided, roughly spherical. This is a closed shell with the smallest number of capsomeres |
| To grow viruses, you must provide __________ | live and metabolically active host cells |
| Bacteriophage are viruses that infect bacteria. Therefore, bacteriophage require _______ to grow | live, growing bacteria |
| For animal viruses, you must provide _________ | living animal tissue cells |
| The RNA strand that is translated by the ribosomes (serves as the mRNA) is called the ________ | + strand |
| By convention, any strand of either DNA or RNA in the virus that has the same sequence as the mRNA is called the _________ | + strand |
| The complementary strand of the + strand is the ________ | - strand |
| Describe steps (in order) fir bacteriophage replication | adsorption (attachment of virion to host). Penetration (injection of virion into host). Synthesis of nucleic acid by virus. Assembly of capids and packaging of viral genomes. Lysis of mature virions from cell |
| Describe the two periods on a one-step growth curve for viruses | Latent period (eclipse) (virus genome separated from capsid and multiplication occurs) and maturation (assembly of virus particles) |
| Give a general description of the T4 bacteriophage regarding genome and symmetry | Icosahedral head with a collar, tail, endplate, and tail fibers. Genome consists of dsDNA |
| What are the two steps of bacteriophage penetration? | Attachment and penetration |
| Describe attachment of bacteriophage penetration | Tail fiber proteins on virus interact with specific receptor molecules on cell surface core polysaccharides. Tail fibers then retract and the tail pin proteins contact cell wall to form a small hole (similar to lysozyme activity) |
| Describe penetration of bacteriophage penetration | Tail sheath contracts and the genome is injected through cell envelope |
| After infection by dsDNA T even phages, what occurs? | Transcription begins and the early proteins are made. Early proteins are involved in replicating the virus genome and transcription of viral genes |
| What are the two early proteins? | Immediate early protein (first to be transcribed) and delayed early protein (1-2 minutes after infection) |
| As the genome is being replicated, the partially completed fragments recombine at homologous regions. This is called _____________ | homologous recombination |
| Homologous recombination forms _________ of viral genomic DNA in which several copies of the viral genome are connected in a single large DNA molecule | concatamers |
| When the concatamer grows, it is fed into the phage head. When the head is filled with DNA, an _________ cuts the DNA. This is called __________ | endonuclease; head-full packaging |
| What are late proteins? | Head, tail and lysis proteins. The head, tail and tail fibers are assembled separately and then when each is complete they are stuck together |
| What are virulent phages? | Viruses that always cause lysis |
| Resistance of the host to infection by the virus can involve ____________ that recognize and destroy foreigh ds viral DNA without destroying its own DNA | restriction-modification systems |
| __________ are enzymes that recognize and cut DNA on the inside | restriction endonucleases |
| For restriction and modification, Phage DNA is injected into a host where ____________ can digest it. Host DNA is protected because specific _________ of its own DNA prevent the restriction enzymes from cutting | restriction enzymes; Methylation |
| __________ are enzymes that degrade DNA from the ends | exonucleases |
| Bacteria protect their own DNA by ________ the base in one of the key nucleotides in the recognition sequence. This is called __________. | methylating; Modification |
| Methyl groups are _________ and bulky and function to ________ | hydrophobic; function to block the binding of the restriction enzyme |
| Instead of cytosine, the T-even phage have __________ and _______ is added to the hydroxyl of the hydroxylmethyl group | 5-hydroxylmethyl cytosine; glucose |
| Glucosylated DNA of T-even phage is resistant to virutally all ______________ | restriction endonucleases |
| Give a general description of bacteriophage lambda regarding genome and symmetry | Genome is dsDNA. Has icosahedral capsid head and helical tail |
| Some viruses are virulent, causing _______ | lysis of the host cell |
| What are the two cycles that viruses can enter? | Lytic cycle (lysis the cells) and lysogenic cycle (integrates into the chromosome and becomes part of its host) |
| Viruses that enter the lysogenic virus (lysogeny) are called ___________ | temperate viruses |
| Bacteria that have a virus in their genome are called _______ and are said to be ________ | lysogens; lysogenic |
| When the virus is integrated into the genome of the host cell in the dormant state, the virus is said to be a ________ | prophage |
| When a bacterial cell is lysogenic for a particular bacteriophage, it is immune to infection by ____________ | bacteriophage of the same type |
| A culture of lysogenic bacteria can be treated with ___________ and this will cause the prophage to come out of the chromosome and enter the lytic cycle. This process is called ___________ | UV light or DNA damaging chemicals; Lysogenic induction |
| Lysogenic induction involves the _____ system | SOS |
| Bacteria cells have a system for repairing damaged DNA called the __________. One of the proteins in this system called __________ acts as a signal to the virus that the host chromosome is in danger host might be dying so the virus __________ | SOS system; RecA; leaves the host cell and enters the lytic cycle |
| When lambda DNA enters the host chromosome in the lysogenic cycle, what occurs? | upon penetration, the DNA ends base-pair (forming cos site) and the DNA ligates and forms ds circle. When lambda is lysogenic, its DNA integrates into E. coli chromosome at lambda attachment site (att-lambda) |
| What is lambda bacteriophage? | bacterial virus that infects E. coli |
| What is the cl protein? | AKA the lambda repressor, it represses lytic events (favors lysogenic cycle) |
| What is the Cro repressor? | Activator of lytic events (favors lytic cycle) |
| When lambda genome enters the lytic pathway, it synthesizes long, linear concatamers of DNA by ___________ | rolling circle replication |
| Classification of animal viruses is based upon? | type of nucleic acid, presence or absence of envelope and type of replication |
| Animal viruses replicate by __________ similar to bacteriophage but it generally takes much longer | one step growth curve |
| Describe the steps animal viruses take to enter cells | Enveloped virion is taken up by animal cell through endocytosis, which causes virion to lose envelope. Capsid of newly formed nucleocapsid is upcoated (removed). Virus nucleic acid multiplies |
| What are the four types of animal virus infections? | lytic, persistent, latent, transformation |
| What is persistant animal virus infection? | characteristic of enveloped viruses which when assembled can bud through the membrane without killing the cell. Therefore the host is always shedding the virus |
| What is latent animal virus infection? | After virus infects cells, it doesn't cause disease until later time (remains dormant) |
| What is transformation animal virus infection? | Conversion of normal cells into tumor cells |
| Cancer is caused by ___________ | cells that continue to divide without ever stopping |
| What are oncogenes? | Viruses that cause cancer by either affecting the cells gene regulation or by bringing a gene into the host while regulates the cell cycle |
| Certain viruses can transform cells (make them cancerous) and when they do the infected cells form ________ (densely packed areas of cultured cells in a tissue culture plate) | foci of infection (which form tumors in animals) |
| A _________ is a biological preparation that improves immunity to a particular disease | vaccine |
| How do vaccines work? | typically contain an agent that resembles a pathogen, and is often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins. This agent stimulates immune system to recognize agent as foreign, remember it and destroy it |
| Antibiotics don't work on viruses. To get rid of viruses, you either have to ________ or _________ | kill the cells that are infected or you must come up with a way to inhibit one of the viral-specific components or processes |
| What are viroids? | Small circular RNA molecules that are internally base paired (smallest known pathogens) |
| What are the smallest known pathogens? | Viroids |
| Do viroid genomes encode proteins? | No |
| What are viroids composed of? | Only naked RNA (no capsid) |
| Viroids infect __________ | plant cells and completely take over the cellular metabolic machinery for the production of more viroids |
| Viroids replicate _________ | in the chloroplasts or in the nucleus and move from cell to cell through the plasmodesmata that connect plant cells to each other |
| What are prions? | proteins that appear to be infectious and cause variety of diseases of nervous system |
| What is the host cell gene that encodes prpC? | PrnP |
| What is the pathogenic form of PrpC? | PrpSC |
| Naturally existing protein (prion) ________ is triggered for misfolding into ______ which aggregates and malfunctions, causing it to be pathogenic | PrpC; PrpSC |
| PrpC is mostly _________ while PrpSC is mostly _______ | alpha helices; beta sheets |
| A mutation in the prion protein PrP causes __________ | the protein to misfold, which causes other proteins to also misfold when they come in contact with it |
Created by:
JHaddad