Bacterial Cell Structure and Function Quiz

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Questions and Answers

Which of the following is NOT a fundamental feature shared by most bacterial cells?

Linear chromosome (correct)

Complex cell envelope

Compact genome

Tightly coordinated cell functions

What technique is used to separate subcellular components based on size and density?

Cell fractionation (correct)

Genetic analysis

Spectroscopy

Microscopy

Which of the following is NOT a method used for breaking up cells in cell fractionation?

Fluorescence microscopy (correct)

Sonication

Enzymes

Mild detergents

What is the function of the flagellum in a bacterial cell?

Propelling the cell (D) Signup and view all the answers

Which of the following is a characteristic of the bacterial nucleoid?

Located within the cytoplasm (B) Signup and view all the answers

What is the primary function of the cell membrane in a bacterial cell?

Regulating the passage of molecules into and out of the cell (A) Signup and view all the answers

How is the outer layer of the bacterial cell called?

Cell wall (B) Signup and view all the answers

What is the significance of studying cells with different genotypes in genetic analysis?

Understanding the role of different cell components (D) Signup and view all the answers

What is the primary function of hopanoids in bacterial cell membranes?

To increase membrane rigidity and support cell shape (D) Signup and view all the answers

Which of the following is NOT a characteristic of phospholipids in bacterial cell membranes?

They are primarily composed of cholesterol instead of fatty acids (C) Signup and view all the answers

How do unsaturated fatty acids affect membrane fluidity?

They increase fluidity by introducing kinks into the fatty acid chains (C) Signup and view all the answers

What is cardiolipin, and what is its role in bacterial cells?

A double phospholipid that localizes to the cell poles and helps stabilize membrane curvature during starvation (C) Signup and view all the answers

What is the primary function of the cell membrane in bacteria?

To regulate the passage of molecules in and out of the cell (A) Signup and view all the answers

Compared to saturated fatty acids, how do unsaturated fatty acids affect membrane fluidity?

Unsaturated fatty acids increase fluidity by introducing kinks into the fatty acid chains. (A) Signup and view all the answers

What is the main difference between hopanoids and sterols?

Hopanoids are found in bacterial membranes while sterols are found in eukaryotic membranes. (C) Signup and view all the answers

What is a common characteristic of both phospholipids and hopanoids in bacterial cell membranes?

Both molecules are amphipathic, having both hydrophilic and hydrophobic regions. (D) Signup and view all the answers

Which of the following is NOT a characteristic of active transport?

Can occur through simple diffusion (B) Signup and view all the answers

What is the name of the largest family of active transport systems?

ATP-binding cassette (ABC) transporters (D) Signup and view all the answers

What is the primary function of the bacterial cell wall?

To confer shape and rigidity and withstand turgor pressure (D) Signup and view all the answers

The phosphotransferase system (PTS) is a type of ______ transport system?

Active (A) Signup and view all the answers

Which of the following is a characteristic of coupled transport?

It transports molecules against their concentration gradient using energy from a different molecule's concentration gradient (A) Signup and view all the answers

Which of the following is NOT directly involved in peptidoglycan synthesis?

Aquaporins (B) Signup and view all the answers

What is the primary function of transpeptidases in bacterial cell walls?

Cross-link wall peptides (A) Signup and view all the answers

Which of the following is a type of coupled transport system where both molecules move in the same direction across the membrane?

Symporters (C) Signup and view all the answers

How does the bacterial cell wall differ from the cell walls of eukaryotic cells?

Bacterial cell walls are made of peptidoglycan, while eukaryotic cell walls are made of cellulose or chitin (B) Signup and view all the answers

How does vancomycin inhibit bacterial cell wall synthesis?

It binds to the D-Ala-D-Ala dipeptide, preventing cross-bridge formation. (C) Signup and view all the answers

What is a characteristic feature of pseudomurein in archaea that distinguishes it from bacterial peptidoglycan?

It has a NAG-𝛽(1,3)-NAT linkage (C) Signup and view all the answers

What is the main structural difference between gram-positive and gram-negative bacteria?

Gram-positive bacteria have a thicker cell wall (C) Signup and view all the answers

What is the function of teichoic acids in gram-positive bacterial cell walls?

All of the above (D) Signup and view all the answers

Which of the following is a shared characteristic of gram-positive and gram-negative bacteria?

The presence of teichoic acids (B) Signup and view all the answers

What is the primary role of the S-layer in bacterial cell envelopes?

To protect the cell from osmotic stress (A) Signup and view all the answers

Which bacterial genus is known for having a unique cell envelope structure that includes a thick layer of mycolic acids?

Mycobacterium (B) Signup and view all the answers

What is the primary function of the contractile vacuole in paramecia?

To regulate osmotic pressure (D) Signup and view all the answers

Which of the following is NOT a characteristic of the Gram-negative cell envelope?

Presence of mycolic acids (B) Signup and view all the answers

What is the role of the Braun lipoprotein in the Gram-negative cell envelope?

To anchor the outer membrane to the cell wall (A) Signup and view all the answers

Which of the following structures is involved in determining the shape of rod-shaped bacteria?

MreB (B) Signup and view all the answers

Which of the following is a key difference between prokaryotic and eukaryotic cell division?

Prokaryotes have a single origin of replication, while eukaryotes have multiple. (A) Signup and view all the answers

What is the primary function of the 'O-antigen' component of lipopolysaccharide (LPS)?

To evade host immune responses (B) Signup and view all the answers

What is the significance of the unusual sugars (arabinogalactans) found in the cell envelope of Mycobacterium leprae?

They contribute to the bacteria's resistance to antibiotics. (B) Signup and view all the answers

What is the primary function of the 'Z-ring' formed by FtsZ protein in bacterial cells?

To determine the plane of cell division (B) Signup and view all the answers

Which of the following statements accurately describes the rotation of bacterial flagella during chemotaxis?

Flagella rotate counterclockwise (CCW) in the presence of attractants, causing the bacterium to move in a straight line known as a "run". (B) Signup and view all the answers

How does the proton motive force contribute to bacterial flagellar movement?

The proton motive force directly powers the rotation of the flagellar motor. (C) Signup and view all the answers

Which of the following is NOT a characteristic of bacterial flagella?

They are typically attached to the cell wall and are not directly connected to the cell membrane. (B) Signup and view all the answers

What is the primary role of the "tumble" in bacterial chemotaxis?

To reorient the bacterium randomly, enabling it to explore new areas in search of attractants. (C) Signup and view all the answers

Bacterial flagella are described as "rotary" appendages. What does this mean?

Flagella can rotate in both directions, clockwise and counterclockwise. (A) Signup and view all the answers

Study Notes

Lecture 3: Cell Structure and Function

Bacterial cells have a complex cell envelope, a compact genome, and tightly coordinated functions.
Archaea, like bacteria, are prokaryotes but have unique membrane and envelope structures.
Eukaryotic cells have a nucleus and extensive membranous organelles.

Chapter Overview

3.1 The Bacterial Cell: An Overview: Provides general information about bacterial cells.
3.2 Membrane Molecules and Transport: Details how molecules move in and out of bacterial cells.
3.3 Cell Envelope: Describes the layers surrounding the bacterial cell.
3.4 Bacterial Cytoskeleton and Cell Division: Discusses the internal framework and how bacteria reproduce.
3.5 Cell Asymmetry: Explains the structural differences between various parts of a microbial cell.
3.6 Specialized Structures: Outlines specialized components like storage granules, magnetosomes, and pili.

The Bacterial Cell

Most bacterial cells share fundamental features, including a complex cell envelope, compact genome, and tightly coordinated functions.
Archaea are prokaryotes with unique membranes and envelopes.
Eukaryotic cells have a nucleus and extensive membranous organelles.
Early 20th-century models viewed the cell as a "soup" of ribosomes and enzymes. Modern research shows an ordered, yet flexible cell structure.

Model of a Bacterial Cell

Cytoplasm: Viscous, gel-like substance.
Cell Membrane: Encloses the cytoplasm.
Cell Wall: Covers the cell membrane.
Nucleoid: Non-membrane-bound area of the cytoplasm containing the chromosome.
Flagellum: External helical filament propelling the cell.

Studying Cell Components

Cell study requires isolating and analyzing cell parts.
Cell Fractionation: Cells are broken down allowing intracellular parts to remain intact. Methods include using mild detergents, enzymes, sonication, and mechanical disruption.
Subcellular components are separated using an ultracentrifuge.
Parts are then subjected to structural and biochemical analysis.

Studying Cell Parts

Employing genetic analysis (complementing cell fractionation).
Uses different genotypes (mutant strains selected for specific loss/alteration of gene function).
Uses Reporter genes to express protein function of interest (e.g., GFP).
The mutant cell phenotype reveals information about the function of the altered part.

Biochemical Composition of Bacteria

All cells contain common chemical components (water, essential ions, small organic molecules, and macromolecules).
Cell composition varies with species, growth phase, and environmental conditions.
A table provides the composition of Escherichia coli.

Cell Membrane

The cell membrane defines the cell's existence.
It's a two-dimensional fluid comprised of lipids and proteins.
Lipids are arranged in a bilayer.
It contains the cytoplasm, mediates transport, and carries proteins serving various physiological roles.

Membrane Lipids

Phospholipids consist of glycerol, fatty acids, and a phosphoryl head group.
Some phospholipids have side chains.
Phospholipids are amphipathic (polar/charged hydrophilic heads and hydrophobic fatty acid tails).
The two layers of phospholipids are called leaflets.

Phospholipid Diversity

Phospholipids vary, differing in phosphoryl head groups and fatty acid side chains.
Some examples include phosphatidyl-ethanolamine, phosphatidyl-serine, phosphatidyl-choline, sphingomyelin, and sphingosine.

Phospholipid Diversity (Cardiolipin/Glycerol)

Cardiolipin (diphosphatidylglycerol) is a double phospholipid.
It increases in bacteria grown to starvation, localizes to cell poles, and stabilizes membrane curves.

Phospholipid Diversity (Saturated/Unsaturated, Cyclization)

Unsaturated fatty acids increase membrane fluidity at low temperatures
Saturated fatty acids decrease fluidity at high temperatures.
Cyclization of fatty acids can decrease fluidity by forming rigid rings.

Hopanoids

Membranes include planar molecules that fill gaps between hydrocarbon chains.
Bacterial reinforcing agents are hopanoids/hopanes.
Hopanoids are pentacyclic lipids modifying membrane fluidity.
They comprise a small percentage of total lipids (not present in archaea).
Sterols (like cholesterol) are analogous components in eukaryotic membranes.

Membrane Lipids of Archaea

Archaea exhibit variations in phospholipid side-chain structures.
Some have ether linkages between glycerol and fatty acids.
Hydrocarbon chains may be branched terpenoids (containing isoprene rings).

Membrane Proteins

Membrane proteins perform various roles.
They provide structural support, detect environmental signals, secrete virulence factors, transport ions, and store energy.
Proteins possess hydrophilic and hydrophobic regions locking them into the membrane.

Transport Across the Cell Membrane

The cell membrane acts as a semi-permeable barrier.
Small uncharged molecules (O2 and CO2) diffuse across it.
Water diffuses across through a process called osmosis.
Solutes move along concentration gradients (high to low).

Transport Across the Cell Membrane (Weak Acids/Bases)

Weak acids/bases partially exist in uncharged forms in membranes.
Uncharged forms can move across the membrane and affect cell pH.

Transport Across the Cell Membrane (Passive/Active Transport)

Large polar molecules/charged molecules require protein transporters.
Passive transport: molecules move along concentration gradients (facilitated diffusion).
Active transport: molecules move against concentration gradients, requiring energy (ATP hydrolysis).
Coupled transport uses energy from one substance's gradient to transport another against its gradient (symporters, antiporters).

Passive Transport (Facilitated Diffusion)

Facilitated diffusion uses concentration gradients to transport molecules (high-to-low).
Moves large or too polar molecules for direct diffusion.
Example: aquaporins transport water and small polar molecules.

Active Transport: ATP Hydrolysis

ATP stored energy drives active transport.
ATP-binding cassette (ABC) transporters: the largest active transport family in prokaryotes.
These involve integral membrane permeases, ATP-binding/hydrolysis (ATPase), and substrate-binding subunits.

Active Transport: Coupled Transport

Coupled transport uses energy released from one substance travelling down its gradient to move a second substance against its gradient.
Symporters move two substances in the same direction.
Antiporters move two substances in opposite directions.

Active Transport: Group Translocation

Phosphoenolpyruvate (PEP) group translocation or Phosphate transfer energizes the import of substances like glucose into bacterial cells.

The Cell Wall

The cell wall provides shape, rigidity, and resistance to turgor pressure. It's a single molecule composed of peptidoglycan.
The peptidoglycan sacculus (cell wall) is a single, interlinked molecule. In Escherichia coli.

Peptidoglycan Structure

Bacterial cell walls are composed of peptidoglycan.
Peptidoglycan's two main components are N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
Peptides cross-link these sugars (peptidoglycan) and transpeptidases (PBPs) cross-link wall peptides.
Transglycosylases extend the polysaccharide chains of the peptidoglycan molecule.

Peptidoglycan Structure (Antibiotics)

Enzymes in peptidoglycan synthesis are excellent antibiotic targets.
Penicillin inhibits transpeptidases.
Vancomycin inhibits cross-bridge formation.

Peptidoglycan Structure (Bacteria Synthesis)

Cell walls are synthesized differently in various bacterial species.

Pseudomurein of Archaea

Pseudomurein is found in archaea and is structurally distinct from bacterial peptidoglycan.
It is insensitive to lysozyme due to NAT instead of NAM, and NAG-β(1,3)-NAT linkages.
It has unique side-chain peptide cross-links.

Gram-Positive and Gram-Negative Bacteria

Most bacteria have additional envelope layers providing structural support and protection.
Gram-positive bacteria have thick cell walls (e.g., Staphylococcus aureus).
Gram-negative bacteria have thin cell walls (e.g., Yersinia pestis).

Gram-Positive Cell Envelope (Teichoic Acids/S-layer)

Gram-positive envelopes have multiple peptidoglycan layers, and teichoic acids (WTA/LTA) are present.
S-layer is an additional protective protein layer found in free-living bacteria, and archaea.

Mycobacterial Cell Envelope

Mycobacteria (like M. tuberculosis and M. leprae) have complex envelopes containing unique lipids (mycolic acids) and unusual sugar derivatives (arabinogalactans).

Gram-Negative Cell Envelope (LPS/Braun Lipoprotein)

The outer membrane of gram-negative bacteria is crucial for defense and toxin production.
Braun lipoprotein is covalently linked to peptidoglycan (PG).
Lipopolysaccharide (LPS) is a component of the outer membrane and can act as an endotoxin, causing septic shock.

Eukaryotic Microbes (Osmotic Shock)

Eukaryotic microbes have their own structures to prevent osmotic shock (water influx). Examples include algae (cellulose walls), fungi (chitin walls), diatoms (silica exoskeletons), and paramecia (contractile vacuoles).

Bacterial Cytoskeleton

Shape-determining proteins (like FtsZ, MreB, and CreS) in bacteria affect cell division and elongation.

Bacterial Cell Division (Binary Fission)

Prokaryotes divide by binary fission, where a single mother cell splits to form two daughter cells.
This process requires coordinated growth and expansion of all cell parts.

Bacterial Cell Division: Chromosome Replication

Replication of the circular chromosome precedes binary fission.
Replication starts at the ori site and proceeds outward in both directions (bidirectional).

Bacterial Cell Division: Divisome

FtsZ initiates divisome formation.
Divisomes' purpose is to coordinate peptidoglycan and lipid membrane synthesis, and coordinate chromosome segregation.

Bacterial Cell Division: Septation

The division septum is formed at the Z-ring, where the inward growth constricts and separates daughter cells to complete cell division.

Bacterial Cell Division: Septal Planes

The spatial orientation of septation influences coccus shape/arrangement (parallel planes, random planes, perpendicular planes).

Cell Asymmetry and Aging

Bacterial cells' poles differ in origin and age (polar aging).
Asymmetrical cell division (e.g., sporulation in Bacillus) creates differences in daughter cells.
Some bacteria only grow at a specific pole,
Differences in poles can affect susceptibility to antibiotics.

Cell Asymmetry (Daughter Cell Types)

Some bacteria generate two types of daughter cells (stationary or mobile).

Specialized Structures: Membrane Vesicles

Some microbes export cytoplasm via membrane vesicles.
These vesicles carry proteins, nucleic acids, toxins, and immunogenic molecules.

Specialized Structures: Thylakoids, Carboxysomes, Gas Vesicles

Thylakoids: extensively folded membranes for photon absorption and photosynthesis.
Carboxysomes: polyhedral bodies packed with Rubisco (CO2 fixation enzyme).
Gas vesicles: increase buoyancy.

Specialized Structures: Storage Granules and Magnetosomes

Storage granules: store things like glycogen (energy) and sulfur (oxidation).
Magnetosomes: membrane-embedded magnetite crystals that orient magnetotactic bacteria.

Specialized Structures: Pili and Stalks

Pili/fimbriae: straight filaments of protein for attachment, motility, or conjugation.
Sex pili: specialized pili for DNA transfer.
Stalks: membrane-embedded cytoplasmic extensions with adhesion factors (holdfasts).
Nanotubes: intercellular connections for material transfer.

Specialized Structures: Cryo-ET

Cryo-electron tomography (Cryo-ET) revealed novel structures.
Example features found include pearling tubes and nanopod extensions.

Specialized Structures: Rotary Flagella

Motile prokaryotes have flagella for movement.
Flagella types include peritrichous, lophotrichous, amphitrichous, and monotrichous, differing in arrangement and number.
Flagella rotate via a motor powered by the proton motive force, affecting movement and chemotaxis.

Chemotaxis

Chemotaxis is the bacterial movement in response to chemical gradients.
Attractants cause counterclockwise (CCW) rotation and flagella bundling ("run").
Repellents cause clockwise (CW) rotation and flagella unbundling ("tumble").

Chapter Summary

Prokaryotes share fundamental traits but are diverse.
Studying cells uses various methods including fractionation, structural, and genetic analysis.
Bacterial cell membranes have phospholipid bilayers and ether linkages while archaea have ether linkages.
Gram-negative cell envelopes are more complex than Gram-positive. Bacterial cell divisoin and septation are highly coordinated.
Prokaryotic cell division proceeds via binary fission involving the divisome complex. Different specialized structures aid in functions ranging from movement to nutrient acquisition and sensing external environments.

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Test your knowledge on bacterial cell features, including components, functions, and membrane characteristics. This quiz covers topics such as cell fractionation techniques and the role of unique cell membrane structures in bacteria. Perfect for biology students focusing on microbiology.