Exam 2 Study Guide

Question 1

Explain the rationale of fluorescence microscopy

Answer 1

Some molecules can absorb light at one wavelength and emit light at another wavelength. Fluorescence microscopy is used to see specific structures in a specimen.

Question 2

compare and contrast TEM and SEM

Answer 2

TEM: electrons pass through ultra thin sections of a specimen; internal structures can be seen
SEM: electrons SCAN the surface of an entire specimen; external structures and topography can be seen

Question 3

Explain the differences between eukaryotes and prokaryotes

Answer 3

Eukaryotes have a nucleus where all genetic information is stored meanwhile prokaryotes don’t. Eukaryotic cells are also larger, have multiple linear chromosomes, divide by mitosis, have organelles, etc. Prokaryotes divide by binary fission, have singular circle-shaped chromosomes, no organelles, etc.

Question 4

List common features that are found in all bacterial cells and those found in some
bacterial cells

Answer 4

ALL:
- cell wall (peptidoglycan)
- unicellular
-no membrane-bound organelles
-plasma membrane
SOME:
-capsule
- inclusions such as fimbriae, flagella or plasmids
-spore formation

Question 5

Describe the structure of the cytoplasmic membrane

Answer 5

Think of phospholipid bilayer

Question 6

Explain how molecules can move across the membrane, via active or passive mechanisms

Answer 6

Active transport: molecules move from LOW concentration to HIGH concentration; requires energy (ATP) and a transporter protein
Passive: molecules move from HIGH conc. to LOW conc.; does not require energy, 2 types (simple diffusion and facilitated diffusion; facilitated: ions and large molecules pass through a transporter protein)

Question 7

Describe the structure and function of ribosomes

Answer 7

Structure: made of protein and rRNA (50S + 30S= 70S); synthesizes proteins (translation)

Question 8

compare and contrast between chromosomes and plasmids

Answer 8

Both: contain genetic information
Plasmid: extra genetic material ( nonessential genes like antibiotic resistance)
Chromosome: makes up the entirety of DNA in eukaryotes

Question 9

Identify the components of peptidoglycan and describe its structure

Answer 9

chains of alternating sugar residues, NAG, and NAM
peptidoglycan is made up of chains of sugar residues linked together by polypeptide bridges

Question 10

describe the structure of the cell wall of a Gram pos. bacteria and a Gram neg. bacteria

Answer 10

Gram pos- thick cell wall
gram neg- thin cell wall

Question 11

identify differences in cell wall structure between GP bacteria and GN bacteria

Answer 11

GP bacteria have thicker cell walls so the initial dye can penetrate the wall and remain there after decolorization. GP bacteria cell walls are held together by teichoic acid and is anchored to the entire membrane by lipoteichoic acid facing the environment. Meanwhile, GN bacteria have thin cell walls that cannot retain the dye after it is decolorized. GN cells layers of peptidoglycan are contained w/in the periplasm (space between cell membrane and outer membrane). They also have porins that allow the entry/exit of molecules. Lastly, GN bacteria are composed of lipopolysaccharides found on the outer membranes leaflet.

Question 12

Provide a molecular explanation for why the Gram stain isn’t used to stain acid-fast bacteria such as Mycobacterium spp.

Answer 12

Because acid-fast bacterial species have a waxy outer layer, the stains used for a Gram stain will not hold.

Question 13

Explain HOW and WHY the bacterial cell wall is targeted by components of our immune system and antimicrobial drugs

Answer 13

Since the bacterial cell wall is integral for survival, it also makes it the Achilles heel of bacteria. Lysozymes and beta-lactam antibiotics found in the body attack bacteria in different ways.

Question 14

Describe the glycocalyx and give examples

Answer 14

The glycocalyx is a general term for the substance external to the cell wall. For example, the capsule of a virus or a slime layer.

Question 15

Describe the structure of the flagella and how it aids in bacterial motility

Answer 15

The flagella is composed of proteins and allows for motility via rotation and a molecular motor.

Question 16

Describe the role of fimbriae and pili

Answer 16

Fimbriae and pili are features mostly used for attachment. For fimbriae they are mainly used for biofilm formation and colonization w/in a host. Pili are mainly involved with motility but a conjugation pilus may be used to transfer DNA from one cell to another.

Question 17

Explain the purpose of endospores

Answer 17

Endospores are resting bacterial cells that are produced when nutrients are depleted. Because endospores are resistant to desiccation, heat, chemicals, and radiation, they make for the perfect shield to protect bacteria.

Question 18

Explain the role of prokaryotes in the evolution of mitochondria and chloroplasts

Answer 18

Endosymbiotic theory: larger microbial cells engulfed smaller bacterial cells that formed into the first eukaryotes.
Ingested photosynthetic bacteria= chloroplasts
aerobic bacteria: mitochondria

Question 19

Define metabolism and distinguish between catabolism and anabolism

Answer 19

Metabolism: all chemical reactions w/in an organism
Catabolism: release energy (breaking down molecules)
Anabolism: require energy (building up of molecules)

Question 20

Describe the role of ATP and enzymes in metabolism

Answer 20

ATP provides energy for reactions that require it. Enzymes catalyze (speed up) reactions.

Question 21

explain how enzymes convert substrates into products

Answer 21

Enzymes have active sites that are developed during protein folding. The active sites are specific to a certain substrate. The substrate binds to the active site and becomes a product

Question 22

explain why enzymes exhibit specificity

Answer 22

Enzymes exhibit specificity because of their unique active sites that are formed during protein folding.

Question 23

Explain how temperature impacts microbial growth on the molecular and cellular level

Answer 23

Molecular: heat affects the rate of catalysis
Cellular: too much heat will denature proteins making them nonfunctional

Question 24

Describe how heat denatures enzymes using proper terminology

Answer 24

Enzymes can be denatured by heat because they are proteins. Since proteins are made up of specific sequences of amino acids held together by hydrogen bonds, the heat will break the weak H bonds and unfold the protein.

Question 25

explain how an inhibitor affects enzyme activity

Answer 25

If an inhibitor were to bind to an enzyme’s active site, the substrate would no longer be able to bind to the active site.

Question 26

Distinguish between a competitive inhibitor and an allosteric inhibitor

Answer 26

Competitive: inhibitor binds at the active site preventing the substrate from binding
Allosteric: inhibitor binds the enzymes at another location causing a conformational change and loss of the active site

Question 27

Explain how oxygen utilization distinguishes between cellular respiration and fermentation

Answer 27

respiration: requires oxygen as electron acceptor
fermentation: does not require oxygen as an electron acceptor

Question 28

Distinguish between cellular respiration and fermentation based on oxygen utilization

Answer 28

cellular respiration uses oxygen; fermentation does not

Question 29

Compare and contrast the processes of cellular respiration and fermentation
o Starts with glycolysis?
o Involves the Krebs cycle?
o Involves the electron transport chain?
o Uses an organic molecule as final electron acceptor?
o Energy yield/efficiency

Answer 29

Respiration: starts with glycolysis, then the Krebs cycle, then ETC; does not use an organic molecule; produces more energy per molecule of glucose but energy is produced slower
Fermentation: starts with glycolysis and does not use Krebs or ETC; has organic molecules synthesized w/in the cell as an electron acceptor; less energy per molecule of glucose BUT produces energy faster

Question 30

List the products commonly produced during fermentation

Answer 30

acid, alcohol, and/or gas

Question 31

Using the fermentation test as an example, explain how biochemical tests are used to
differentiate between bacteria

Answer 31

Because bacteria use different enzymes, we can differentiate between bacteria using biochemical tests.

Question 32

Classify bacteria based on their carbon and energy requirements

Answer 32

Chemoautotroph: CO2 as carbon source, chemicals as energy source
Chemoheterotroph: organic compounds for carbon source, chemicals for energy
Photoautotroph: CO2 as carbon source, light as energy
Photoheterotroph: organic compounds for carbon source, chemicals for energy

Question 33

Explain what is meant by ‘microbial growth’

Answer 33

Microbial growth describes the growth of a microbial population, not an individual.

Question 34

Classify bacteria based on their temperature requirements

Answer 34

Psychrophiles: cold temps
Mesophiles: moderate temps (such as room temp or body temp)
Thermophiles: hot temps

Question 35

Classify bacteria based on their pH requirements

Answer 35

Acidophiles: low pH
Neutrophiles: neutral pH
Alkaliphiles: high pH

Question 36

Explain how external solute concentration impacts the flow of water into/out of a cell

Answer 36

Osmotic pressure occurs when the concentration inside of the cell is different than outside of the cell. In a hypertonic environment, there is a high solute concentration OUTSIDE the cell. In a hypotonic environment, the solute concentration is higher INSIDE the cell.

Question 37

Describe the optimal environmental condition for a halophile

Answer 37

A high salt environment

Question 38

Explain why some bacteria require oxygen (O2) while other bacteria cannot tolerate
oxygen

Answer 38

During respiration O2 is the final electron acceptor, however O2 is highly reactive and can damage bacteria

Question 39

Explain how aerobic bacteria handle reactive oxygen species (ROS)

Answer 39

They use a variety of enzymes to fight off ROS

Question 40

Classify bacteria based on their oxygen (O2) requirements

Answer 40

Obligate aerobes: require O2 and rely solely on respiration for energy
Facultative aerobes: can grow with or without O2, perform respiration when O2 is present and fermentation when O2 is absent
Anaerobes: unable to use oxygen and most are harmed by it; perform fermentation
Microaerophiles: require O2 concentration lower than air

Question 41

Define the following terms and use each appropriately
o Media
o Inoculate
o Incubate
o Culture

Answer 41

Media: collection of nutrients used to grow bacteria in lab
In lab today, we used solid media to grow bacteria
Inoculate: the process of transferring microbes onto media
To grow bacteria I needed to inoculate the media first
Incubate: placing inoculated media at an appropriate temp. for growth
After preparing a bacterial streak plate, I put it in an incubator to incubate and grow.
Culture: the practice of growing microbes in lab OR microbes grown in a lab
Today we are going to culture microbes in lab.
I examined a bacterial culture in lab

Question 42

Explain the purpose of solid media, liquid media

Answer 42

On solid media, you are able to view colonies easily and can be separated easily so that isolated colonies can form
In liquid media, when all cells are shaken in the broth they all experience the same environmental conditions

Question 43

Explain why agar is added to media

Answer 43

Agar is added to media to solidify it

Question 44

Distinguish between complex media and defined media

Answer 44

Complex media: used to grow many different kinds of bacteria; chemical composition is not defined
Defined media: used to grow specific bacteria; chemical comp. is defiined

Question 45

Explain the purpose of selective and differential media

Answer 45

Selective: designed to suppress the growth of certain bacteria while encouraging others
Differential: designed to distinguish bacteria based on observable characteristics when grown on media

Question 46

Explain the basis of MSA media as an example of selective and differential media

Answer 46

as a selective media: Contains a high conc. of NaCl which inhibits the growth of most bacteria
as differential media: contains mannitol that some Staphylococcus species ferment while others do not

Question 47

Describe how a streak plate is used to obtain a pure culture

Answer 47

A streak plate is used to obtain a pure culture because it allows for bacteria to be visible enough to isolate a colony aka pure culture

Question 48

Describe how bacteria reproduce

Answer 48

Bacteria reproduce via binary fission- cell gets bigger, the genome is replicated, and then it splits into two

Question 49

Describe how bacterial population size increase over time

Answer 49

bacterial populations double each time they reproduce; some bacteria can take less than 20 minutes to reproduce while some can take up to more than 24hrs

Question 50

bacterial growth curve: identify the 4 stages and explain what is occurring
during each stage

Answer 50

lag phase: bacteria are preparing for growth before reaching the maximum growth rate
log or exponential phase: unconstrained growth
stationary phase: plateau of growth; number of alive cells is the same as dead cells
death phase: cell death outweighs cell division

Question 51

Explain the concepts behind the following methods for quantifying bacterial numbers
o Direct microscopic count
o Most probable number
o Quantitative plate count
o Turbidity

Answer 51

Direct microscopic count: cells are counted within a specific parameter and then a calculation is done to determine cell count
MPN: used to estimate the amount of microbes in a sample; it is done using three tests to confirm the presence of coliforms and then to determine the MPN
QPC: involves diluting a sample and then placing the diluted sample on a plate and allowing it to grow, then you can count the colonies
Turbidity: quantifies the amount of light scattering due to a large amount of cells being present

Question 52

Define and distinguish between sterilization, disinfection, and antisepsis

Answer 52

Sterilization: removing/destroying ALL microbial life
Disinfection: destroying HARMFUL microorgs.; usually used on surfaces
Antisepsis: destroying harmful orgs. from living tissue; iodine, alcohol, hydrogen peroxide are antiseptics; safe for skin

Question 53

Explain the purpose of the following techniques and how each works:
o Autoclave
o Pasteurization
o Filtration
o Radiation

Answer 53

Autoclave: destroys bacteria at very high levels of heat/steam
Pasteurization: reduces # of microbes; put into high temps for a short time so thermoresistant bacteria survive
Filtration: the passage of a substance through a screen-like material; can remove bacteria up to less than 0.22 micrometers and specialized ones can remove microbes as little as 0.01 micrometers
Radiation: causes mutations–after too many some of them will end up lethal; ionizing: penetrates surfaces, high energy
nonionizing: does not penetrate surfaces

Question 54

Explain how low temperature impacts microbial growth

Answer 54

Low temps impact bacterial growth because for most species, the low temps will slow or even stop the growth of bacteria

Question 55

Describe how microbial populations decline

Answer 55

Microbial populations decline exponentially. Treatments can be more or less effective due to, # of microbes, environment, time of exposure, and microbial characteristics

Question 56

Explain how the disk diffusion method is used to determine the effectiveness of
chemical agents