MCB 2610 Exam 1

what is a prokaryote

single-celled organism without a nucleus or membrane-bound organelles

what are examples of prokaryotes

archaea, bacteria, and cyanobacteria

what is a eukaryote

an organism whose cells have a nucleus and other membrane-bound organelles

what are examples of eukaryotes

algae, protozoa, fungi

what is the definition of life

an organismic state characterized by capacity for metabolism, growth, reproduction, genetic variation/evolution, response to the external environment, and homeostasis

what are the three domains of life

bacteria, archaea, eukarya

what are key features of bacteria

prokaryotic, no nuclei, single celled, have plasmids, peptidoglycan cell walls, no nuclear membrane, external structures

what are shapes of bacteria

bacillus-rod, coccus-circle, spirillum-spiral

do bacteria cause disease

some, but most are beneficial

what are key features of archaea

- prokaryotic

- lack peptidoglycan

- live in extreme environments

do archaea cause disease

not known to cause disease in humans

what are key features of eukaryotic cells

- contain a nucleus and organelles

- can be unicellular or multicellular

- includes plants, animals, fungi, protists

where do viruses fit into the 3 domains of life

viruses are not considered alive because they cannot reproduce or metabolize on their own; they require a host cell

what was the goal and outcome of Stanley Miller's experiment

- goal: to see if organic molecules could form under early Earth conditions

- outcome: he produced amino acids and other organic compounds, showing that life's building blocks could form naturally

what did Stanley Miller actually do in his experiment

worked with Harold Urey to simulate early Earth's atmosphere using a mixture of gases and added electric sparks to mimic lightning

what is the endosymbiotic theory

theory that eukaryotic organelles such as mitochondria and chloroplasts were once free-living prokaryotic cells that became engulfed by a larger cell and formed a symbiotic relationship

what is the endosymbiont hypothesis

a proposed explanation suggesting that organelles in eukaryotic cells originated from prokaryotes, which is tested and studied to support the theory

what are the 4 key pieces of evidence that supports the endosymbiotic theory

- double membranes

- ribosomes produce own proteins

- circular DNA

- grow independent within cell

how do you correctly name microorganisms

- use binomial nomenclature

- Genus (capitalized) + species (lowercase)

- italicize for typing, underline for handwritten

who was Robert Hooke and what was his contribution

- coined the term "cell" after observing cork under a microscope

- could only see large cells

- contributed to cell theory

who was antony van leeuwenhoek and what did he do

- "father of microbiology"

- improved the microscope and was the first to observe and describe microorganisms

what was the theory of spontaneous generation

the idea that living organisms could arise from non-living matter (vital force)

what was Francesco Redi's experiment

1. Placed rotting meat into 3 containers

2. Left one open (control), one covered with cloth, one sealed with lid

3. Observed flies appearing on meat in open container and on cloth, but NOT in sealed jar

what was the conclusion of Redi's experiment

showed that maggots on meat came from eggs, not spontaneous generation

who was John Needham and what did he do

- boiled broth in a flask, then sealed it

- microbes grew

- through spontaneous generation was possible

- famous for being wrong

what was the problem with Needham's experiment

- he didnt boil the broth long enough or seal it properly

who was Lazzaro Spallanzani and what did he do

- boiled broth longer and sealed flasks completely

- no microbial growth

- challenges spontaneous generation

who was Louis Pasteur and what did he do

- disproved spontaneous generation

- used swan-neck flasks containing boiled broth, allowing in air but trapped dust and microbes

- no microbial groth

who was John Tyndall

- showed that dust carries microorganisms, and if dust is removed, broths stay sterile even when exposed to air

- found evidence of heat-resistant bacteria

who was Ferdinand Cohn

discovered that heat-resistant bacteria can produce endospores, explaining why some bacteria survive boiling

what did Lister contribute to microbiology

introduced antiseptic techniques in surgery to reduce infections

what did Snow contribute to microbiology

traced a cholera outbreak to contaminated water, founded epidemiology

who was Robert Koch and what did he do

developed Koch's postulates, a set of criteria to prove a microorganism causes a specific disease

what are Koch's postulates

1. the microorganism must be found in all cases of the disease

2. it must be isolated from the host and grown in pure culture

3. the cultured microorganism must cause the disease when introduced into a healthy host

4. the same microorganism must be re-isolated from the newly infected host

what developments came from Koch's postulates

- Agar (Fanny Hess)

- Petri dish (Richard Petri)

- nutrient broth and nutrient agar

- methods for isolating microorganisms

- aseptic technique

who was Edward Jenner and what did he do

developed the first smallpox vaccine using cowpox to provide immunity

what was Edward Jenner's experiment

- He put pus taken from a milkmaid with cowpox into a cut made in the arm of a local boy. Then he exposed the boy to smallpox days later and he was immune.

- showed cowpox provided immunity

who was Alexander Fleming and what did he discover

discovered penicillin, the first widely used antibiotic

what is resolution

- the ability to distinguish between two points a specified distance apart

- the smaller the distance the better the resolution

why is resolution important

high resolution shows more detail

what factors influence resolution

- wavelength of light

- numerical aperture

- quality of lenses and optics

- refractive index

how do you determine total magnification of a microscope

total mag = ocular lense x objective lens

what is a bright-field microscope used for

- visualizes stained specimens (2D)

- produces a dark image on a bright background

what is the cone of light for a brightfield microscope

solid cone of light, light is absorbed

what is a dark-field microscope used for

- visualizes live, unstained specimens (2D)

- produces bright objects on a dark background

what is the cone of light for a dark-field microscope

- condenser lens focuses a hollow cone of light on the sample

- scatters light

what is a phase-contrast microscope used for

- allows viewing of internal structures in living, unstained microbes

- works because different cell parts bend light differently

- enhances contrast in transparent/living cells

what is the cone of light for a phase-contrast microscope

uses a special cone with a phase ring, bending light waves to highlight differences in density

what is DIC (differential interference contrast) microcopy used for

- produces 3D-like, colorful images of live specimens

- resolution is higher

- similar to phase-contrast

what is the cone of light for DIC microscopes

splits light into two cones that pass through the specimens at slightly different angles, then recombine for 3D contrast

what is fluorescent microscopy used for

- visualizes naturally fluorescent specimens or those stained with fluorescent dyes/antibodies

- allows to see specific structures

what is the cone of light for fluorescent microscopes

uses a cone of UV/blue light to excite fluorescent molecules, which emit light at a different wavelength causing them to glow against a dark background

what are the major differences between light and electron microscopes

- light: uses visible light, lower resolution (~200 nm), 2D or 3D depending on type

- electron: uses electrons, much higher resolution (~0.2 um), can see ultrastructure

what are the two types of electron microscopes

1. transmission electron microscope

2. scanning electron microscope

what is the Transmission Electron Microscope (TEM) used for

- electrons pass through thin specimen

- dense parts look darker (scatter electrons)

- must be cut thin and stained

- gives 2D images of inside structures

what is the Scanning Electron Microscope (SEM) used for

- electrons bounce off surface

- shows 3D image of outside

- good for surface details and microbes in natural places

what is a pure culture

population of cells arising from a single cell

what are aseptic culturing techniques

conditions maintained to limit contaminants, including sterile media and instruments.

what is streak plating

technique that helps to isolate colonies of a specific microbe for study

what is a colony

a grouping of cells that developed from a single parent cell

what is a CFU

Colony Forming Unit ; origin of the colony

why do we stain specimens

-increases visibility of specimen

-accentuates specific morphological features

-preserves specimens

what are dyes in microscopy

- chemicals that bind to cellular components to produce color

- can be basic (binds negative structures) or acidic (binds positive structure)

what is simple staining

- one dye used to stain all cells the same color

- used to see shape, size, and arrangement of cells

what is the Gram stain and what does it do

a differential stain that separates bacteria into Gram-positive (purple) and Gram-negative (pink/red) based on cell wall and structure

what are the steps of the Gram stain

1. crystal violet (primary stain)

2. iodine (mordant)

3. alcohol (decolorizer)

4. safranin (counterstain)

what are the key features of Gram-positive bacteria

- thick peptidoglycan layer

- no outer membrane

- stains purple with gram stain

what are the key features of a Gram-negative bacteria

- thin peptidoglycan layer

- has outer membrane with LPS (lipopolysaccharide)

- stains pink/red with Gram stain

why is the Gram stain medically important

- can provide information for treating bacterial infections

- guides antibiotic choice (many drugs work better on gram-positive vs gram-negative)

what is acid-fast staining used for

primarily to identify Mycobacterium tuberculosis (TB) in human sputum and mycobacterium leprae (leprosy)

what are the mechanisms of acid-fast staining

1. carbolfuschin (red dye) applied to slide

2. gentle heating -> helps dye enter waxy lipid walls

3. cooling & rinsing

4. treated with acid-alcohol (decolorizer) -> removes dye from non-acid fast bacteria

5. acid-fast bacteria keep the red dye

what are special stains

- used to color and isolate specific parts

- endospores, flagella, capsules

what is an endospore and why do bacteria produce it

- a protective structure formed inside a bacterial cell

- produced to survive harsh environments

- formed by a process called sporulation

how is an endospore stain performed

1. malachite green -> primary stain

2. wash the slide

3. safranin added -> counterstain for vegetative cells

(endospores appear green, vegetative cells red/pink)

which bacteria are important for endospore staining

bacillus and clostridium

what is a bacterial capsule and why is it important

- gel-like envelope around a bacterial cell

- made of polysaccharides

- helps bacteria resist host immune defenses

how is a capsule staining done

- use negative staining -> dyes the background, capsules remain clear

what is the purpose of bacterial flagella

used for locomotion

how is a flagella stain performed

- apply mordant (tannic acid) to coat flagella

- stain with basic fuchsin

- makes the thin flagella visible under the microscope

what are physical growth requirements

environmental conditions that affect microbial growth

what are the main physical growth requirements for microbes

temperature, pH, osmotic pressure, hydrostatic pressure

how does temperature affect microbial growth

every microorganism has an optimum, a minimum, and a maximum growth temperature

what are the 4 categories of temperature for microbes

psychrophiles, psychrotrophs, mesophiles, thermophiles

what are psychrophiles

- cold loving

- -20- 10°C

what are psychrotophs

- foodborne illness

- 0-30°C

what are mesophiles

- microbes that grow in moderate temperatures (human pathogens)

- 10-50°C

what are thermophiles

- heat-loving

- 40- 75°C

what temperature is optimal for extreme thermophiles

80°C and up

how does pH affect microbial growth

microbes grow best at a specific pH range

what are acidophiles

- bacteria that grow in acidic environments (1-5)

- ex: lactobacillus acidophilus

what are neutrophiles

- most bacteria prefer a neutral or slightly alkaline pH

- 7.0-7.4

what are alkaliphiles

- bacteria that grow in alkaline environments

- pH > 8.5

what is osmotic pressure

the effect of solute concentration on water availability

what are halophiles

- microbes that thrive in salty environments

- tolerate up to 35% salt

what are osmophiles

microbes that survive high sugar or solute concentrations

what is hydrostatic pressure

pressure from the surrounding water or medium

what are barophiles

organisms that live under such extreme pressure

what are chemical requirements for microbial growth

- elements and compounds microbes need to build cells and carry out metabolism

- also known as nutrients

what is carbon used for in microbes

- structural backbone of living matter

- needed for all organic compounds

why is oxygen a chemical requirement

some microbes need oxygen for metabolism, while others are harmed by it