Microbiology Flashcards
Difference between eukaryotic and prokaryotic transcription and translation
Eukaryotes
Transcription (nucleus) and translation (cytoplasm) occur separately
- Introns splicing post-transcription
Prokaryotes
Both processes take place in the cytoplasm stimultaneously
- Does not contain introns
Difference between eukaryotic and prokaryotic composition of ribosomes
Eukaryotes
- 40S and 60S subunits (larger) to yield 80S
Prokaryotes
- 30S and 50S subunits to yield 70S
The two prokaryotic domains
Archaea
Bacteria
Bacilli vs. cocci vs. spirilla
Bacilli
- Long and rod-shaped
- Strepts and staphyls
Cocci
- Spherical
- Flagellate rods (Salmonella typhi)
- Spore-former (Clastridium botulism)
Spirilla
- Helical/”spiral-shaped” (H. pylori)
- Vibrios (vibrio cholerae)
- Spirochaetes (Treponema pallidum)
Bacterial cell wall
CW is peptidoglycan
- Gram +: thick peptidoglycan (purple)
- Endospore: formed under harsh environment (mostly Gram +)
- Gram -: thin peptidoglycan with a outer membrane (pink); lipopolysaccharide
- The outer membrane may cause Gram - bacteria harder to treat with antibotics
(Fungal CW is chitin)
Flagellum
Facilitates bacterial motion
Most common form of bacterial reproduction
Binary fission
Bacterial gene transfer
Transformation
Acquiring DNA from environment (plasmid = small piece of circular DNA)
- Usually occur during crowding or starvation (aging colony); transformation can be triggered by starvation
Transduction
Being injected DNA by a bacteriophage
- May be detrimental to bacteria, but may be advantagous to the virus
Conjugation
Direct DNA transfer via contact bw bacterial cells with sex pilus
- An adaptive mechanism when resources are scarce
Transposon
A DNA sequence with the ability to excise itself from the genome and move to another location
- In both prokaryotes and eukaryotes, transposons are located in the chromosomes
Production of food of bacteria
Autotrophs
Can produce their own food
- Photoautotrophs & chemoautotrophs
Heterotrophs
Consume external organic compounds
- Photoheterotrophs & chemoheterotrophs
Bacterial ecology
Obligate anaerobes
Die in presence of oxygen
Facultative anaerobes
Can survive with or without oxygen
- E. coli
Thermophile
High temp
Mesophile
Medium temp
Psychrophile
Low temp
Symbiosis
Symbiosis: relationship between 2 species
- Mutualism
- Commensalism
- Parasitism
Characteristics of a virus
Virus can only replicate inside a host cell
(Virus are not living organisms)
Lytic cycle
- Viruses that replicate by the lytic cycle, killing their host cells, are called virulent
- If then virus does not lyse the cell, it becomes integrated into the bacterial genome in a less harmful form (provirus/prophage), lying dormant for one or more generations as a part of the lysogenic cycle (latent infection)
- Ex. HIV (also a retrovirus that infects helper T cells)
- Either spontaneously or environmental circumstances, the provirus cell enter a lytic cycle
- Superinfection: cells containing proviruses are normally resistant to further infection by similar phages
Atypical viruses
Prion
- Disease-causing protein
- Made up of only protein, no DNA
- Mad cow disease
Viroid
- Disease-causing molecule (mainly in plants)
- Made up of only a single-stranded RNA, no protein
Epidemiology of bacteria
Pathogen transmission from animals (zoonoses); from hosptial (nosocomial)
- Normal flora in large intestine help sythesize vitamin K and B groups
Pathogen mechanisms
- Bacteria cause diseases due to toxins
- Exotoxins: secreated by bacteria
- Endotoxins: part of CW of Gram - bacteria
- In small amounts –> inflammatory repsonse
- In large amounts –> DIC (clotting), sepsis, and fatal septic shock
Controlling infection
Physical method
- Heat
- Autoclaving achieves sterility
- Pasteurization reduces microbial number
- Radiation
Chemical method
- Mostly denatures proteins
- Antiseptic: on living tissues
- Disinfectants: on non-living
- Alcohol, I, Cl, H2O2, etc.
Gram +, spherical
- Wide range of infections on skin
- Streptococci can cause pneumonia and strep throat
Gram -, coccobacilli
- Short rods that look like cocci
- Bordatella causes pertussis (whooping cough)
Gram +, rod-shaped
Clostridium (anaerobic) caused
- Tetanus (muscle spasms): from rusty nails
- Botulism (muscle weakness): from food poisoning
- Gas gangrene: gas produced in necrotic tissues due to poor blood supply
Mycobacterium caused
- Tuberculosis: lung infections
- Leprosy: skin lesion, loss of feeling in extremities
Bacillus caused
- Anthrax (skin lesion)
- Food poisoning
Gram -, rod-shaped
- Indicators of pollution bc they are found in the gut or feces
- Cause a variety of infections of the GI tract
- E.g. Salmonella, E. coli, Shigella
Gram -, spirals
Vibrios
- Vibrio cholerae causes cholera: vomitting, diarrhea due to contaminated food and water
Spirilla
- Helicobacter pylori causes gastric ulcersm chronic gastritis, linked to stomach cancer
Spirochaetes
Borrelia
- Causes Lyme disease (transmitted by ticks)
Treponema
- Causes syphilis, STD
Antibacterial drugs
- Selective toxicity
- Inhibit peptidoglycan synthesis and damage CW
- Effective against Gram + bacteria
- Developed my Alexander Fleming
- E.g. penicillin (reactive 4C ring irreversibly bind to bacteria)
- Interferes with protein synthesis
- E.g. erythromycin (broad spectrum)
- Blocks DNA, RNA synthesis by mimicking enzyme substrates
- E.g. sulfa drugs
Protozoans
- Usually found in water and moist area
- Single-cell eukaryotes that can move with flagella via amoeboid motion
- Traphozoite stage: protozans are absorbing nutrients from the host
- Cyst stage: tough survival stage that can be transmitted and cause diseases
- Photosynthetic: Euglena
- Predators: Paramecium, Ameoba
Protozan diseases
Malaria
- Caused by plasmodium falciparum
- Transmitted by mosquitos
- Sickle cell anemia patients are resistant to malaria
- Infects RBC of humans
- Yellow skin, fever, nausea, coma
Sleeping sickness
- Caused by trypanosoma gambiense (African trypanasomiasis)
- Cross blood-brain barrier
- Transmitted by Tse Tse fly
- Neurological disorder
Toxoplasma
- Usually no symptoms and untreated
- Fetus can be infected if patient is preganant
- Leading to abortion or neurological impairment in fetus
- Associated with cats
Protozan diseases of the intestine include amebiasis (caused by E. histolytica), giardiasis (caused by Giardia lamblia) and cryptosporidiosis (caused by Cryptosporidium)
Fungi
- Can be single (yeast) or multi-celled (mold)
- Anti-fungal drugs target plasma membrane of fungi
- Polyene or azoles
- CW contains chitin
Fungal diseases
- Most common on the skin
- Dermatophytes break down keratin in skin
- Ringworm occurs in various areas of the body
- Caused by Epidermophyton and Trichophyton
- Yeast Candida can infect mouth, intestine or vagina
- Esp. seen in immunosuppressed patients
Parasitic worms
- Helminths: via food or water
- Flatworms (flukes, tape worms) and roundworms (hookworm, pinworm)
- Trichinella aquired from undercooked pork and forms cyst in the muscle
- Schistosoma and hookworms enter body via skin
- Tapeworm from undercooked food
- Borrelia burgdorferi is a tick borne parasite and causes Lyme disease
Viral diseases
- Influenza virus
- Herpes, measles, rubella
- Varicella (chicken pox) can recur later as shingles
- HPV causes warts
- Hepatitis A, B, C
- Rabies, polio, yellow fever
- HIV (single-stranded RNA)
Antiviral drugs
- Acyclovir for herpes
- AZT reverse transcriptaase inhibitors for HIV
- Resembles nucleotides and blocks enzymes for DNA synthesis
The nitrogen cycle
- Bacteria fix free nitrogen gas into nitrates and nitrites that are useable by plants
- Plants produce ammonia and ammonium ions that are broken down by bacteria back into nitrite and nitrate
- Nitrogen fixation: atmospheric N (N2) –> ammonia (NH3)
- Nitrification: oxidation of ammonia or ammonium –> nitrile (ox) –> nitrate
- Ammonification: decomposition of organic nitrogen into ammonia
- Denitrification: nitrate reduced to produce N2
Growth phases of bacteria
- Stationary stage is characterized by both equal growth and death rates (0 growth)
- Lag phase occurs right after inoculation of bacteria and before growth begins
- Exponential phase is characterized by rapid doubling of bacteria population; growth rate is constant
- Death stage is opposite of exponential stage
