Bacterial Classification and Characteristics Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of pili in bacteria?

Photosynthesis

Movement and plasmid transfer (correct)

Cell wall synthesis

Nutrient absorption

What is the size range of most bacteria?

0.2 to 5 μm (correct)

0.1 to 1 μm

5 to 10 μm

1 to 10 μm

Which term describes the naming of organisms in taxonomy?

Phylogeny

Identification

Classification

Nomenclature (correct)

What is the main purpose of bacterial classification?

To categorize organisms based on phylogeny and phenotype Signup and view all the answers

Which of the following is NOT a function of identification in microbiology?

Create new taxonomic categories Signup and view all the answers

Which type of bacteria is considered to be among the smallest and can exist outside a host?

Mycoplasma Signup and view all the answers

How are complex microbial floras generally distinguished?

Through a classification scheme for identification Signup and view all the answers

Which of these processes primarily relates to distinguishing organisms from each other?

Identification Signup and view all the answers

What characteristic is primarily determined by the bacterial cell wall?

Shape of the bacterium Signup and view all the answers

Which type of bacteria is described as having a spherical shape?

Coccus Signup and view all the answers

Which arrangement refers to bacteria that occur in pairs?

Diplococci Signup and view all the answers

What term describes bacteria that can exist in varied shapes?

Pleomorphic Signup and view all the answers

What process describes the way prokaryote cells increase in number?

Binary fission Signup and view all the answers

What property can be determined by using appropriate growth media regarding bacterial behavior?

Antibiotic resistance Signup and view all the answers

Which of the following is a characteristic of hemolytic bacteria?

Ability to lyse erythrocytes Signup and view all the answers

Which of the following describes a rod-shaped bacterium?

Bacillus Signup and view all the answers

What is the primary structural difference between prokaryotic and eukaryotic cells?

Prokaryotic cells are simpler in structure than eukaryotic cells. Signup and view all the answers

What do we call the area in a prokaryotic cell where DNA is located?

Nucleoid Signup and view all the answers

Which of the following statements about bacterial genomes is true?

Prokaryotes can have both circular and linear DNA. Signup and view all the answers

Which bacteria is known to have two circular chromosomes?

Vibrio cholerae Signup and view all the answers

Which organism represents one of the largest bacteria?

Bacillus anthracis Signup and view all the answers

What is a distinguishing feature of Gram negative bacteria?

They have a complex cell envelope structure. Signup and view all the answers

How many genes can the largest bacterial genome contain?

11,600 genes Signup and view all the answers

What is the primary reason peptidoglycan synthesis is targeted in antimicrobial chemotherapy?

It is essential for bacterial cell growth and division. Signup and view all the answers

Which characteristic is unique to Gram-positive bacteria?

Teichoic acids in the cell wall. Signup and view all the answers

What is the role of lipopolysaccharide (LPS) in Gram-negative bacteria?

It protects cells from certain antibiotics. Signup and view all the answers

Which statement correctly describes the structure of peptidoglycan?

It is made of alternating N-acetylglucosamine and N-acetylmuramic acid. Signup and view all the answers

Which of the following is NOT a feature of the Gram-negative cell wall?

Has teichoic acids. Signup and view all the answers

How does lipopolysaccharide (LPS) activate the immune response?

By binding to TLR-4 receptors on macrophages. Signup and view all the answers

Which of these statements about Gram-positive and Gram-negative bacteria is accurate?

Gram-negative bacteria have a thinner peptidoglycan layer but possess an outer membrane. Signup and view all the answers

Why is inhibiting peptidoglycan synthesis considered to have few side effects on human cells?

Human cells do not require peptidoglycan for growth. Signup and view all the answers

What is the primary function of actin homologs in bacteria?

Determining cell shape and protein localization Signup and view all the answers

Which statement correctly describes endospore formation?

It occurs when nutrients are depleted. Signup and view all the answers

What is the primary purpose of the thick coat around an endospore?

To protect against environmental stressors Signup and view all the answers

Which of the following statements about endospores is true?

They show no signs of life due to lack of water. Signup and view all the answers

Which of the following bacteria is known for its ability to form endospores?

Bacillus thuringiensis Signup and view all the answers

Why are endospores resistant to boiling?

They have a thick protective coat. Signup and view all the answers

What is the result of successful endospore formation in a Bacillus species?

One vegetative cell develops into one endospore. Signup and view all the answers

What common function do FtsZ and MreB serve in bacterial cells?

Determining cell shape and division Signup and view all the answers

What are the primary functions classified in bacterial metabolism?

Fueling, biosynthesis, polymerization, and assembly Signup and view all the answers

Which of the following pathways is NOT used by bacteria to break down glucose to pyruvic acid?

Krebs cycle Signup and view all the answers

What is a significant product of bacterial fermentation?

Organic acids and alcohols Signup and view all the answers

What role does pyruvic acid play in bacterial metabolism?

It serves as a precursor for various fermentation pathways. Signup and view all the answers

How do bacteria generate ATP during fermentation?

By direct transfer of electrons and protons via NAD+ Signup and view all the answers

Which pathway is primarily involved in the aerobic metabolism of glucose?

Embden-Meyerhof-Parnas (EMP) pathway Signup and view all the answers

What is the main reason that fermentation is considered inefficient for ATP generation?

It produces fewer ATP molecules per glucose molecule. Signup and view all the answers

What type of conditions allow for the processing of pyruvic acid in bacteria?

Both aerobic and anaerobic conditions Signup and view all the answers

Study Notes

Bacteria: Classification, Structure, Growth and Metabolism

Bacteria are classified, structured, grown, and metabolized.
Objectives include describing bacterial structures and functions, different classification schemes for grouping bacteria, types of bacteria, distinguishing characteristics of Gram-positive and Gram-negative bacteria, and growth, biochemical, and genetic characteristics used to differentiate bacteria.
Singular bacterium; common noun bacteria
Bacteria in size range from 0.2 to 5 μm.
Mycoplasma is the smallest, Bacillus anthracis is one of the largest.

Bacterial Structure

Prokaryotic cells are simpler than eukaryotic cells, except their cell envelopes.
Prokaryotic cells have a capsule, cell wall, plasma membrane, cytoplasm, ribosomes, plasmids, and pili.
Eukaryotic cells have a nucleus, nuclear pores, nuclear envelope, chromatin, nucleolus, ribosomes, plasma membrane, mitochondria, peroxisome, cytoskeleton, free ribosomes, Golgi vesicles, lysosome, smooth endoplasmic reticulum, rough endoplasmic reticulum, centrioles, Cytoplasm, and secretory vesicles.

The Bacterial Chromosome or "Nucleoid"

The nucleoid is the area of the cytoplasm where DNA is located most often as a single circular molecule, with exceptions such as Vibrio cholerae (two circular chromosomes), and Borrelia burgdorferi (linear chromosome with multiple circular and linear plasmids).
Bacterial genomes vary widely in size, the smallest containing over 130 genes, the largest approximately 11,600 genes.
Human DNA has approximately 25,000 genes.
Bacterial nucleoid contains no nuclear membrane, no nucleolus, no mitotic spindle, and no histones.
Haploid refers to a single set of chromosomes in an organism's cells.

Plasmids

Small extra pieces of genetic material (5–100 genes).
Not critical for everyday functions but can provide genetic information to promote antibiotic resistance, virulence factors, and some structures like pili.
Involved in the transfer of genetic material between bacteria through cell-to-cell contact.

Transposons

Pieces of DNA that move readily within or between the DNAs of bacteria, plasmids, and bacteriophages.
Nicknamed "jumping genes."
Can code for drug-resistant enzymes, toxins, or metabolic enzymes.
Can cause mutations or alter the expression of nearby genes.

Cytoplasm

Also known as protoplasm, gel-like substance in bacterial cells.
Contains the chromosome, ribosomes, macromolecules, and small molecules in water solution.
Location of growth, metabolism, and replication.
When viewed under electron microscope, two distinct areas: amorphous matrix (ribosomes, nutrients, granules, metabolites, and plasmids) and nucleoid region (DNA).

Inclusions in Bacterial Cells

Inclusion bodies store energy or structural building blocks.
Glycogen: polymer of glucose
Poly-betahydroxybutyric acid (PHB): lipid
Polyphosphates: polymers of PO₄
Sulfur globules: elemental S
Magnetosomes: magnetite (iron oxide)
Gas vesicles: protein shells inflated with gas
Parasporal crystals: protein

Ribosome Function

Ribosomes are the site of protein synthesis in all living organisms.
Prokaryotes have 70S ribosomes, while eukaryotes, larger 80S ribosomes in their cytoplasm.
70S ribosomes are made up of 50S and 30S subunits.
Ribosomes are found within the cytoplasm or attached to the plasma membrane.
Amino acids are assembled into proteins according to the genetic code on the surfaces of ribosomes during translation.

Cytoskeleton

Cellular "scaffolding" or "skeleton" within the cytoplasm.
Actin homologs (MreB and Mbl) help determine cell shape, segregate chromosomes and localize proteins.
Other nonactin homologs (e.g., FtsZ) and unique bacterial cytoskeletal proteins (e.g., SecY and MinD) are involved in shape determination and cell division and chromosome segregation.

Endospores

Intracellular structures within the cytoplasm of certain species (notably Bacillus and Clostridium).
Endospores provide resistance to dehydration, heat, and chemicals.
Are not a mechanism for reproduction, but for survival in harsh environments—sporulation occurs when nutrients (carbon or nitrogen); are depleted.
Spore formation takes about six hours.
Have a spore coat, cortex, and core wall.
Resting (dormant) cells show no signs of life due to lack of water in the spore, and are highly resistant to heat, acids, bases, dyes, irradiation, disinfectants, and antibiotics.
Spores contain bacterial DNA, a small amount of cytoplasm, membrane, peptidoglycan, and keratin-like coat—responsible for remarkable resistance.
The resistance of endospores may be related to dipicolinic acid, a calcium ion chelator found only in spores.

Medically-Important Endospore-Forming Bacteria

Bacillus anthracis, Bacillus cereus, Clostridium tetani, Clostridium botulinum, Clostridium perfringens, and Clostridium difficile.

The Plasma Membrane (cytoplasmic membrane)

Lies just inside the peptidoglycan layer.
Composed of a phospholipid bilayer.
Chemically similar to eukaryotic membranes, but prokaryotic ones don't contain sterols, except for the genus Mycoplasma.
Composed of 60% protein and 40% phospholipid.
Arranged as a bilayer formed by phospholipid molecules made up from glycerol and fatty acids.

Functions of the Cytoplasmic Membrane

Selective permeability and transport of molecules into the cells.
Electron transport and oxidative phosphorylation in aerobic species (energy generation).
Secretion of enzymes and toxins.
Contains enzymes and carrier molecules functioning in biosynthesis of DNA, cell wall polymers and membrane lipids (biosynthesis functions.)
Bears the receptors and other proteins of chemotactic and other sensory transduction systems.
Semi-permeable.
Impermeable to macromolecules.

Transport Systems in Bacteria

Iron (Fe) is an essential nutrient for the growth of almost all bacteria. Under anaerobic conditions, Fe is generally in the +2 oxidation state and soluble. Under aerobic conditions, iron is generally in the +3 oxidation state and insoluble.
Some bacteria secrete siderophores—compounds that chelate Fe and promote its transport as a soluble complex—to overcome this problem.

Excretion of Hydrolytic Exoenzymes and Pathogenicity Proteins

Organisms that obtain nutrients from macromolecules like proteins, polysaccharides, or lipids secrete hydrolytic enzymes.
In Gram-positive bacteria, proteins are secreted across the cytoplasmic membrane.
In Gram-negative bacteria, proteins must also traverse the outer membrane.
Type I, II, III, IV, and V secretion systems are found in Gram-negative bacteria.

Cell Walls

Cell wall is a structure that completely surrounds the cell protoplast.
The cell wall is the outermost component common to virtually all bacteria(except Mycoplasma.)
Peptidoglycan composed of murein, mucopeptide.
Important for osmotic protection and cell division and precursor to its own biosynthesis.
Peptidoglycan is the substance that gives cell wall strength.
Made up of 2 amino sugars and 4 amino acids (L-alanine, D-glutamic acid, DAP, D-alanine).

Characteristics of Gram-Positive Cell Walls

Contain teichoic acids, which may contribute to stabilization, adherence, and surface antigens.

Characteristics of Gram-Negative Cell Walls

Include an outer membrane.
Protect cells from permeability (penicillin and lysozyme).
Contain lipopolysaccharide (endotoxin), which is toxic to animals.

Acid-Fast Bacteria

Mycobacteria, such as Mycobacterium tuberculosis, have an unusual cell wall. This results in an inability to be stained using the Gram stain technique.
Resist decolorization with acid-alcohol after being stained with carbolfuchsin.
A high concentration of lipids (mycolic acids) in their cell wall is the factor that results in acid-fastness.
Nocardia asteroides is a weakly acid-fast bacterium.

Glycocalyx

Additional layer outside the cell wall; a polysaccharide coating secreted by many bacteria.
Slime layer: glycoproteins loosely associated with the cell wall; helps adhere to solid surfaces to form biofilm or buildup of plaque.
Capsule: polysaccharides firmly attached to the cell wall; helps with adherence to surfaces and protection against phagocytosis.

Surface Appendages

Some bacteria have distinct appendages (flagella, axial filaments, fimbriae, and pili) for motility or adherence to surfaces.
Flagella: long, thin extensions for motility in aqueous environments.
Axial filaments (endoflagella): wind around bacteria, causing movement in waves.
Fimbriae: short, fine appendages for adherence to solid surfaces, crucial for virulence.
Pili: longer appendages, used for motility (grappling hooks) and conjugation pili (DNA transfer between cells).

Bacterial Morphology

Size, shape, and configuration of the organisms (cocci, rods, curved, or spiral) are important for classification.
Cocci: spherical bacteria; arranged in pairs (diplococci), chains (streptococci), clusters (staphylococci), tetrads, and cubes(Sarcina.)
Rods can be straight (E. coli), club-shaped (Corynebacterium), branching (Actinomyces), comma-shaped (Vibrio), or spore-forming (Bacillus and Clostridium).
Spiral: Treponema.
Pleomorphic: variable in shape.

Binary Fission

Bacteria divide by binary fission, which is an asexual reproduction method.
The replication of the bacterial chromosome triggers the process.
Metabolism produces cell materials from nutrients in the environment, essential for the progress of hundreds of independent biochemical processes (regulated).
This leads to cell division that creates two independent living units from one.

Generation Time

The time taken for a bacterial population to double in number (replication time.)
Depends on the species, medium, and temperature.
Bacteria have a relatively fast generation rate, compared to other living things.
Typical range is 30–60 minutes (optimal conditions); examples include Escherichia coli (20 minutes), Mycobacterium tuberculosis (12–24 hours), and Mycobacterium leprae (10-30 days.)

Culture Systems and Growth Curve

Lag phase: bacteria are readapting to a new medium and increasing their metabolic activity.
Exponential/log phase: exponential increase in the number of bacteria.
Stationary phase: growth rate slows as the nutrients are consumed and waste products accumulate.
Death phase: bacterial death rate exceeds the growth rate and population size decreases.

Obligate Intracellular Growth

Some bacteria need to grow inside living cells (host cells).
Bacteria lack the ability to produce enough adenosine triphosphate (ATP) to support their metabolism independently and must use ATP from host cells.
These bacteria are referred to as obligate intracellular bacteria.
Examples: Chlamydia, Rickettsia, Ehrlichia, and Anaplasma.

Environmental Conditions

Factors that affect bacterial growth include:
- Acidity (pH values)
- Water activity
- Temperature
- Oxygen
- Toxins
- Antimicrobial substances

Biochemical Reactions

Identification and classification of bacteria involve observing traits and characteristics (phenotype).
Biochemical tests identify and classify bacteria that involve the observation of phenotypic characteristics, such as growth on media (selective/nonselective/ differential media), characteristic colony appearance under a microscope, the Gram stain technique, biochemical tests (e.g., fermenting specific sugars or producing certain enzymes), and immunologic tests (antigenicity) and genotypic characteristics.

Criteria for Identification and Classification of Bacteria

Phenotypic criteria are used to identify and classify bacteria, including growth on media, colony appearance, bacterial microscopy appearance, Gram stain technique, biochemical properties, and immunologic tests (antigenicity)
Genotypic criteria include sequencing of rRNA (ribosomal RNA).

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the fundamental aspects of bacteria, including their classification, characteristics, and functions. This quiz covers topics such as taxonomy, morphology, and bacterial growth processes. Perfect for students studying microbiology or anyone interested in the fascinating world of bacteria.