Microbiology Exam 2

The component(s) of a virus that is/are extended from the envelope for attachment is/are the:

spikes

Which of the following does a virus lack? Select all that apply.

ribosomes and metabolic processes

What is another name for a nonenveloped virus?

naked virus

Which of the following leads to the destruction of the host cells?

lytic cycle

A virus obtains its envelope during which of the following phases?

release

Which of the following components is brought into a cell by HIV?

reverse transcriptase

A positive-strand RNA virus:

can be used directly to translate viral proteins

What is the name for the transfer of genetic information from one bacterium to another bacterium by a phage?

transduction

Which of the following tests can be used to detect the presence of a specific virus?

EIA, RT-PCR, and PCR

A virus that infects a bacterium is called a

bacteriophage

The _____ on the bacteriophage allow for binding to the bacterial cell.

tail fibers

An enzyme from HIV that can make a copy of DNA from RNA is called

reverse transcriptase

For lytic viruses, _____ is a phase during a viral growth curve when the virus is not detected

eclipse

Viruses can be diagnosed and observed using an ____ microscope

electron

Discuss the geometric differences among helical, polyhedral, and complex viruses.

• Helical: rod-shaped with a helical protein coat

• Polyhedral: roughly spherical with an icosahedral capsid

• Complex: mixed shapes with additional structures

Differentiate between lytic and lysogenic cycles.

• Lytic: rapidly replicates viruses within a host cell, leading to a cell lysis and release of new viruses

• Lysogenic: integrates viral DNA into the host’s genome, remaining dormant until triggered to enter the lytic cycle

Name each labeled part of the illustrated bacteriophage.

1. Capsid Head 

2. Nucleic Acid 

3. Sheath 

4. Tail Fiber

Label the five stages of a bacteriophage infection in the figure:

1. Attachment: The phage attaches to the surface of the host 

2. Penetration: The viral DNA enters the host cell  

3. Biosynthesis: Phage DNA replicates and phage proteins are made  

4. Maturation: New phage particles are assembled  

5. Lysis: The cell lyses, releasing the newly made phages

Which of the following is the name for molecules whose structures are nonsuperimposable mirror images?

enantiomers

By definition, carbohydrates contain which elements?

carbon, hydrogen, and oxygen

Monosaccharides may link together to form polysaccharides by forming which type of bond?

glycosidic

Which of the following describes lipids?

a source of nutrients for organisms, energy-storage molecules, molecules having structural role in membranes, and molecules that are part of hormones and pigments

Molecules bearing both polar and nonpolar groups are said to be which of the following?

amphipathic

Which of the following groups varies among different amino acids?

R group

The amino acids present in proteins differ in which of the following?

size, shape, and side groups

Which of the following bonds are not involved in tertiary structure?

peptide bonds

Aldehydes, amides, carboxylic acids, esters, and ketones all contain carbonyl groups.

True

Two molecules containing the same types and numbers of atoms but different bonding sequences are called enantiomers.

False

Lipids are a naturally occurring group of substances that are not soluble in water but are freely soluble in organic solvents.

True

 Fatty acids having no double bonds are called “unsaturated.”

False

A triglyceride is formed by joining three glycerol molecules to a fatty acid backbone in a dehydration reaction.

False

A change in one amino acid in a protein sequence always results in a loss of function.

False

Match each polysaccharide with its description.

1. energy storage polymer in plants

2. structural polymer found in plants

3. structural polymer found in cell walls of fungi and exoskeletons of some animals

4. energy storage polymer found in animal cells and bacteria

• chitin (C)

• glycogen (D)

• starch (A)

• cellulose (B)

Waxes contain esters formed from long-chain ____ and saturated___, and they may also contain substituted hydrocarbons

alcohols; fatty acids

Cholesterol is the most common member of the ___ group, found in animal tissues; it has a tetracyclic carbon ring system with a ____ bond in one of the rings and one free _____ group

steroid; double; hydroxyl

The sequence of amino acids in a protein is called its _____

primary structure

Identify the functional group in each of the depicted structural formulas

What are monosaccharides, disaccharides, and polysaccharides?

• Monosaccharides: simplest form of carbohydrates (composed of a single molecule or subunit)

• Disaccharides: composed of two monosaccharides linked together

• Polysaccharides: composed of three or more monosaccharides linked together

Describe the structure of a typical phospholipid. Are these molecules polar or nonpolar?

• Consists of a polar, hydrophilic head (phosphate group and an alcohol) and two nonpolar, hydrophic tails (fatty acids)

• Amphipathic means they are both polar and nonpolar the head is polar and the tail is nonpolar)

The structural formula shown corresponds to penicillin G, a narrow-spectrum antibiotic that is given intravenously or intramuscularly as a treatment for several bacterial diseases. The antibiotic is produced by fungi of the genus Penicillium. (a) Identify three major functional groups in this molecule that each comprise two simpler functional groups. (b) Name the two simpler functional groups composing each of the major functional groups identified in (a).

2. Amide groups are composed of carbonyl (C=O) and amine functional groups. Carboxylic groups are composed of carbonyl (C=O) and hydroxyl (OH) groups

The figure depicts the structural formulas of glucose, galactose, and fructose. (a) Circle the functional groups that classify the sugars either an aldose or a ketose, and identify each sugar as one or the other. (b) The chemical formula of these compounds is the same, although the structural formula is different. What are such compounds called?

Structural diagrams for the linear and cyclic forms of a monosaccharide are shown. (a) What is the molecular formula for this monosaccharide? (Count the C, H and O atoms in each to confirm that these two molecules have the same formula, and report this formula.) (b) Identify which hydroxyl group in the linear structure undergoes the ring-forming reaction with the carbonyl group.

Microorganisms can thrive under many different conditions, including high-temperature environments such as hot springs. To function properly, cell membranes have to be in a fluid state. How do you expect the fatty acid content (saturated versus unsaturated) of bacteria living in high-temperature environments might compare with that of bacteria living in more moderate temperatures?

Saturated fatty acids are solids at room temperature and become fluid when heated. At high temperatures, unsaturated fatty acids may be weakened to the point that the membrane dissociates.

Heating a protein sufficiently may cause it to denature. Considering the definition of denaturation, what does this statement say about the strengths of peptide bonds in comparison to hydrogen bonds?

Peptide bonds are stronger than hydrogen bonds as denaturation by heat disrupts hydrogen bonds without breaking peptide bonds

The image shown represents a tetrapeptide. (a) How many peptide bonds are in this molecule? (b) Identify the side groups of the four amino acids composing this peptide.

Which of the following is an organism that obtains its energy from the transfer of electrons originating from chemical compounds and its carbon from an inorganic source?

chemoautotroph

Which of the following molecules is reduced?

NADPH

Enzymes work by which of the following?

reducing the activation energy

To which of the following does a competitive inhibitor most structurally resemble?

the substrate

Which of the following are organic molecules that help enzymes work correctly?

coenzymes

Which of the following products is made during Embden-Meyerhof glycolysis?

pyruvate

During the catabolism of glucose, which of the following is produced only in the Krebs cycle?

FADH2

Which of the following is not a name for the cycle resulting in the conversion of a two-carbon acetyl to one ATP, two CO2, one FADH2, and three NADH molecules?

Calvin cycle

Which is the location of electron transports systems in prokaryotes?

the cytoplasmic membrane

Which is the source of the energy used to make ATP by oxidative phosphorylation?

the proton motive force

A cell might perform anaerobic respiration for which of the following reasons?

It lacks a cytochrome oxidase for passing electrons to oxygen.

Which of the following is the purpose of fermentation?

to make NAD+

Which molecule typically serves as the final electron acceptor during fermentation?

pyruvate

Which of the following molecules is not produced during the breakdown of phospholipids?

glucose

During the light-dependent reactions, which molecule loses an electron?

a reaction center pigment molecule

Which of the following are two products of the light-dependent reactions?

NADPH and ATP

Which of the following processes produces hydrogen sulfide?

anaerobic respiration

Competitive inhibitors bind to allosteric sites.

False

Glycolysis requires oxygen or another inorganic final electron acceptor to proceed.

False

All organisms that use aerobic cellular respiration have cytochrome oxidase.

True

Photosynthesis always results in the formation of oxygen.

False

Processes in which cellular energy is used to make complex molecules from simpler ones are described as _____.

anabolic

The loss of an electron from a molecule is called _______.

oxidation

The part of an enzyme to which a substrate binds is called the _____.

active site

Per turn of the Krebs cycle, one acetyl is oxidized, forming _ CO2, _ ATP, _ NADH, and _ FADH2 molecules.

2, 1, 3, 1

Most commonly, glycolysis occurs by the ______ pathway.

Embden-Meyerhof

The passage of hydrogen ions through ______ down their electrochemical gradient harnesses the energy needed for ATP synthesis by oxidative phosphorylation.

ATP synthase

Fermenting organisms make ATP through the process of ______.

glycolysis

The NADH and FADH2 produced during βoxidation are used to make ________

ATP by oxidative phosphorylation

In cells, can an oxidation reaction happen in the absence of a reduction reaction? Explain

No, both oxidation and reduction reactions always occur simultaneously in cells, which results in a redox reaction

What is the function of molecules like NAD+/NADH and FAD/FADH2 in cells?

They act as electron carriers, accepting and donating electrons during redox reactions, ultimately contributing to energy production through the electron transport chain

What is substrate-level phosphorylation? When does it occur during the breakdown of glucose to CO2?

• The direct transfer of a phosphate group from a substrate molecule to ADP, forming ATP

• Occurs during the breakdown of glucose to CO2 in both glycolysis and the Krebs cycle

Why is the Krebs cycle important in both catabolism and anabolism?

It serves as a central hub for metabolic pathways, generating energy-carrying molecules and providing precursors for building essential molecules

How does oxidative phosphorylation differ from substrate-level phosphorylation?

OP uses an electron transport chain and chemiosmosis to generate AT, while SLP directly transfers a phosphate group from a substrate to ADP, forming ATP

How can fermentation be used to differentiate various types of microbes?

Certain microbes can only ferment certain substrates

How are the products of lipid and protein degradation connected to glucose metabolism pathways?

• The degradation of lipids and proteins produces glycerol and amino acids that can connect to glucose metabolism pathways

• Glycerol can enter glycolysis, while fatty acids yield acetyl-CoA through beta-oxidation, which also enters the Krebs cycle

What is the function of photosynthetic pigments in the light-harvesting complex?

Absorbs light energy and then transfers it to the reaction center, where the energy is used to initiate photosynthesis

In which phase would you expect to observe the most endospores in a Bacillus cell culture?

death phase

During which phase would penicillin, an antibiotic that inhibits cell-wall synthesis, be most effective?

log phase

Which of the following is the best definition of generation time in a bacterium?

the length of time it takes for a population of cells to double

What is the function of the Z ring in binary fission?

It forms a contractile ring at the septum.

If a culture starts with 50 cells, how many cells will be present after five generations with no cell death?

1600

Filamentous cyanobacteria often divide by which of the following?

fragmentation

Which is a reason for antimicrobial resistance being higher in a biofilm than in free-floating bacterial cells?

Cells are metabolically inactive at the base of a biofilm.

Quorum sensing is used by bacterial cells to determine which of the following?

the density of the population

An inoculated thioglycolate medium culture tube shows dense growth at the surface and turbidity throughout the rest of the tube. What is your conclusion?

The organisms are facultative anaerobes.

An inoculated thioglycolate medium culture tube is clear throughout the tube except for dense growth at the bottom of the tube. What is your conclusion?

The organisms are obligate anaerobes.

Pseudomonas aeruginosa is a common pathogen that infects the airways of patients with cystic fibrosis. It does not grow in the absence of oxygen. The bacterium is probably which of the following?

an obligate aerobe

Streptococcus mutans is a major cause of cavities. It resides in the gum pockets, does not have catalase activity, and can be grown outside of an anaerobic chamber. The bacterium is probably which of the following?

an aerotolerant anaerobe

Why do the instructions for the growth of Neisseria gonorrhoeae recommend a CO2-enriched atmosphere?

It is a capnophile

Bacteria that grow in mine drainage at pH 1–2 are probably which of the following?

acidophiles

Bacteria isolated from Lake Natron, where the water pH is close to 10, are which of the following?

alkaliphiles

In which environment are you most likely to encounter an acidophile?

a hot vent at pH 1.5

A soup container was forgotten in the refrigerator and shows contamination. The contaminants are probably which of the following?

mesophiles

Bacteria isolated from a hot tub at 39 °C are probably which of the following?

mesophiles