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MicroBio Exam 3
Terms in this set (38)
Describe the Fred Griffith experiment (mice with two strains of Streptococcus pneumoniae) that helped in the identification of DNA as genetic material.
Fred mixed heat-killed S with live R and injected the combination into mice: the mouse died.The dead mouse's tissues were found to contain live bacteria with smooth coats like S. These bacteria were subsequently able to kill other mice, and continued to do so after several generations in culture.
Describe the general features of DNA structure as discussed in class.
Double stranded helix where the strands are ruining antiparallel, complementary base pairs (A to T and G to C). Sugar phosphate backbone.
Describe (in general terms) the process of DNA replication in bacteria. Where does replication begin and end? Why does it end where it does?
-active replication at forks
-semi-conservative: one old strand, one new
Origin of replication is where replication starts
Ter(termination sequence) is where it ends
Tus Protein binds ter sequence and will not let forks pass.
How does the flow of genetic information occur in bacteria? In what way is this different than in Eukaryotic organisms (hint: order of when processes occur)?
Bacterial Flow: DNA (transcribed) to RNA, (translated) to protein
-Transcription and translation occur simultaneously because there is no nucleus
-mRNA have shine dalgarno sequence: helps ribosome find correct translation start site
Eukaryotic: DNA transcription to RNA, processing to translation
-Ribosome do not bind during translation because transcription occurs in the nucleus while translation occurs in the cytoplasm
What are three ways in which the expression of bacterial genes can be regulated?
The three ways bacterial genes can be regulated are through transcription, translation, and global regulation.
What consequences do repressor and activator proteins have on gene expression?
Repressor: If there is no lactose present the repressor will create a roadblock that prevents RNA polymerase from transcribing.
Activator: This is a DNA binding protein that increases transcription, if it is not present transcription will decrease
Describe the organization of the lac operon. How and why does transcription of the operon genes change in the presence/absence of lactose?
Lactose metabolism genes: Lac Z, Lac Y, and Lac A. Operator which binds the repressor, promoter which is the binding site for RNA polymerase, and the Lac I (repressor) make up the lac operon. If lactose is not present the repressor would be inactive, stopping transcription. If lactose is present the repressor will bind to lactose and the repressor will lose the operator sit and transcription will occur.
How does the sRNA transcribed from the micF gene regulate gene expression?
-expressed in low nutrient environment
-under high conditions, the bacterium makes mic F sRNA to "silence" expression of ompF proteins
-it binds to ompF which prevents the translation of ompF mRNA, closing odd the larger porins
What is quorum sensing? How does quorum sensing work? What are some of the results (in a large population of bacteria) of quorum sensing?
It is the exchange and detection of signaling molecules in the population of bacteria that coordinates gene expression. *It is essentially present in all bacteria.
The signaling molecule AI is continuously manufactured and secreted into the environment and detected by surrounding bacteria. If enough bacteria are around, the AI will reach high concentrations that stimulate the transcription of genes involved in biofilm formation.
What are some of the forms of mutations? What is the difference between a spontaneous and induced mutation?
Forms of mutations: Alterations in DNA sequence, spontaneous mutations, induced mutations.
Spontaneous: happens on its own, accident
Induced: External cause like: UV or X-ray radiation
Explain how populations of antibiotic resistant bacteria are generated. Name and describe three mechanisms of resistance.
Antibiotic sensitive bacteria are killed by antibiotic, leaving only antibiotic resistant bacteria to replicate and grow over time.
1. Target Antibiotic Changes
2. Antibiotic is pumped out of the cell before it can be accumulated
3. Antibiotic is enzymatically destroyed
What are three ways genetic material can be exchanged in bacteria?
-Transformation: naked DNA is taken up from the environment
-Conjugation: exchange of plasmid DNA
-Transduction: transfer or genes via viral infection
Describe the basic organization of naked and enveloped viruses. How are their structures different?
Naked: Spike Proteins + Capsid + Genome (nucleic acid)
Enveloped: Spike Proteins + Envelope + Capsid + Genome
The difference between the two is the envelope that is present in the enveloped cell and absent in the naked cell.
What are the three types of capsid organizations in viruses?
Complex- Example: bacteriophages (viruses that infect bacteria)
What are the five types of viral genomes?
DNA: dsDNA and ssDNA
RNA: dsRNA, +ssRNA, -ssRNA
Viruses usually have small genomes. What are some ways in which they can still form intact viral particles with such few genes?
Even though viruses have small genomes and fewer viral parts they use host enzymes and pathways and have very gene dense genomes leaving few to no gaps between the genes.
Attachment to viral receptor on host cell
Penetration of host cell plasma membrane
Uncoat the viral genome from capsid
Transcription of viral RNA
Translation of viral protein
Assembly of viral parts into intact viral particles
Release of virus to host cell
Describe the various mechanisms of viral entry (penetration) into cells.
Endocytosis: This is when the plasma folds around the virus, the endosome vesicle engulfs the virus, protons H+ are pumped and the capsid breaks down and the viral genome is uncoated.
Membrane Fusion: irreversible attachment, the viral envelope plasma membrane fuse, entry of the nucleocapsid happens and the nucleic acid is uncoated.
Describe the different ways in which viruses can shed their capsid coat after entry into cells.
-Capsid can fuse with plasma membrane
-Acidification breaks down capsid in the cell with H+ protons
How do positive (+) ssRNA viruses make protein and replicate their genome once they have invaded a cell?
Positive ssRNA uses translation to make viral proteins. RdRp makes a complementary negative ssRNA strand
What is the flow of genetic information in a retrovirus? What enzyme facilitates this?
-Uses viral machinery
-+RNA -> -DNA
-Makes ssDNA into dsDNA via reverse transcriptase
-dsDNA is made into +RNA
-used to make proteins or genes
Would genes for capsid formation be early or late genes? Why?
Late genes because it isn't needed until later in the process
What are two ways nucleic acid is packaged into capsids?
Concerted- genome associates with capsid during synthesis
Sequential- genome inserted into completed capsid
Describe how naked and enveloped viruses are released from the cell.
Naked: cell lysis- the breaking down of the membrane of a cell
Enveloped: membrane envelope is derived from host cell as virus leaves
What are cytopathic effects? What are some of the ways viruses cause cytopathic effects?
What does tropism mean with respect to viruses?
The specificity of a virus for a particular host tissue determined in part by the interaction of viral surface structures with receptors present on the surface of the host cell
What are three ways the cytokine interferon can induce an antiviral state in a cell?
What are persistent viral infections? How are they different than acute infections?
What are proto-oncogenes and tumor suppressors?
Proto-oncogenes - Control cell growth and division, need to be expressed at a certain time. Overexpresion/mutation can cause cancer.
Tumor surpressors - regulate cell cycle progresion, moniter DNA damage, can induce apoptosis if damage is detected
Know the different types of viruses we talked about and what types of cancer they can cause.
What are the mechanisms by which dsDNA viruses cause cancer? What about retroviruses?
Describe the different forms/levels of organization of fungi (yeast, hyphae, mycelium)
What are the ways fungi can reproduce?
asexually and sexually
How do fungi obtain energy from their environment?
Saprobes - live off dead/decaying matter, release enzymes digest external substrates
What are aflatoxin and ergotoxine? What are some of their effects?
What is the difference between protozoa and algae?
Protozoa - oxidize inorganic or organic compounds for energy.
Algae - photosynthetic protists.
What are the main functions of encystment?
o Survive harsh conditions
o Reproductive forms
o Serve as the mechanism of transfer between hosts in infectious species
What is the cause of malaria? What is the resting state of the causative microorganism called?
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