Cell Structure and Function Overview
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Questions and Answers

What effect do attractants have on the movement of bacteria during chemotaxis?

  • They cause the flagella to rotate counterclockwise, pushing the cell forward. (correct)
  • They cause the flagella to rotate clockwise, resulting in a tumble.
  • They prevent the cell from moving in any direction.
  • They cause the bacterium to stop moving completely.

How does a bacterium change direction when no attractants are present?

  • It stops moving altogether to reassess its environment.
  • It divides into two and explores different directions.
  • It rotates the flagella clockwise, causing a tumble. (correct)
  • It continues to run in the same direction until it encounters another attractant.

What is the role of chemoreceptors in chemotaxis?

  • They provide energy to the bacterium to facilitate movement.
  • They sense chemical gradients and help guide movement. (correct)
  • They assist in the replication of bacterial DNA.
  • They detect environmental light levels.

What structure in bacteria is primarily responsible for movement during chemotaxis?

<p>Flagella (B)</p> Signup and view all the answers

What happens to the behavior of a bacterium when the concentration of attractants increases?

<p>The runs last longer, leading to net movement toward the attractants. (A)</p> Signup and view all the answers

What is a key characteristic that differentiates bacteria from eukaryotic cells?

<p>Lack of a nucleus (D)</p> Signup and view all the answers

Which component comprises approximately 70% of the total weight of bacteria?

<p>Water (B)</p> Signup and view all the answers

Which type of bacteria is characterized by a thick cell wall outside the cell membrane?

<p>Gram-Positive Bacteria (C)</p> Signup and view all the answers

What role does the bacterial cell membrane primarily serve?

<p>Selectively permeable barrier (A)</p> Signup and view all the answers

Which of the following best describes the genetic material in bacterial cells?

<p>Compact and minimal noncoding DNA (C)</p> Signup and view all the answers

What distinguishes Gram-Negative bacteria from other types?

<p>Presence of an outer membrane with lipopolysaccharides (B)</p> Signup and view all the answers

Which specialized structure is involved in bacterial locomotion?

<p>Flagella (A)</p> Signup and view all the answers

What feature of Archaea allows them to survive in extreme environments?

<p>Unique membrane lipids (A)</p> Signup and view all the answers

What is the composition of peptidoglycan in bacterial cell walls?

<p>Polymers of disaccharides cross-linked with peptides. (C)</p> Signup and view all the answers

Which characteristic is specific to Gram-positive bacteria?

<p>Presence of teichoic acids in thick cell wall. (C)</p> Signup and view all the answers

What is the role of porins in Gram-negative bacteria?

<p>To allow nutrient passage through the outer membrane. (A)</p> Signup and view all the answers

Which protein is responsible for maintaining the diameter of bacterial cells?

<p>FtsZ (B)</p> Signup and view all the answers

What regulates the constriction of the septum during bacterial cell division?

<p>FtsN (B)</p> Signup and view all the answers

What structure helps protect bacteria against phagocytosis?

<p>Capsule (D)</p> Signup and view all the answers

Which feature distinguishes Gram-negative bacteria from Gram-positive bacteria?

<p>Thin peptidoglycan layer covered by an outer membrane. (A)</p> Signup and view all the answers

What is the main focus during the bacterial cell division process?

<p>Synchronous growth and formation of all cell parts. (A)</p> Signup and view all the answers

What is the main structural difference between ether links and ester links in membrane lipids?

<p>Ether links (C-O-C) are more stable than ester links, allowing growth at higher temperatures. (A)</p> Signup and view all the answers

Which fatty acid form is known for increasing membrane fluidity, particularly at low temperatures?

<p>Cis form of Oleic Acid (C)</p> Signup and view all the answers

What is the function of cardiolipin in bacterial membranes?

<p>Localizes to cell poles and increases under stress. (C)</p> Signup and view all the answers

What role do sterols, such as cholesterol, play in eukaryotic membranes?

<p>Adding flexibility and stability to the membrane. (A)</p> Signup and view all the answers

What type of transport moves molecules against their concentration gradient using energy?

<p>Active transport (D)</p> Signup and view all the answers

Which component primarily provides structural support to the cell envelope?

<p>Cell wall (A)</p> Signup and view all the answers

Which type of molecules can permeate cell membranes easily?

<p>Small uncharged molecules (B)</p> Signup and view all the answers

What unique feature do the membranes of Archaea possess compared to bacteria?

<p>They have ether links instead of ester links. (A)</p> Signup and view all the answers

What is the primary role of the replisome in DNA replication?

<p>Replicating DNA at each replication fork. (A)</p> Signup and view all the answers

How do prokaryotes achieve motility using their flagella?

<p>By rotating the flagella using a motor powered by the proton motive force. (B)</p> Signup and view all the answers

Which of the following correctly describes the nucleoid region in prokaryotic cells?

<p>DNA is coiled and bound to proteins, extending through the cytoplasm. (B)</p> Signup and view all the answers

What is the function of carboxysomes in prokaryotic cells?

<p>Carbon dioxide fixation using Rubisco. (C)</p> Signup and view all the answers

What structural feature is distinct to monotrichous cells?

<p>A single flagellum located at one end of the cell. (D)</p> Signup and view all the answers

Which of the following best describes thylakoids in photosynthetic bacteria?

<p>Folded membranes packed with chlorophylls and electron carriers. (B)</p> Signup and view all the answers

What is a key outcome of the spatial orientation of septation in bacteria?

<p>Determining the arrangement pattern of cocci. (B)</p> Signup and view all the answers

What are pili and fimbriae primarily used for in prokaryotic cells?

<p>Attachment to surfaces and genetic exchange. (C)</p> Signup and view all the answers

Flashcards

Membrane Lipids

The primary component of cell membranes, composed of glycerol linked to fatty acids and a phosphoryl head group.

Cardiolipin

A double phospholipid linked by a third glycerol molecule. It is concentrated at cell poles and increases under stress, like starvation.

Membrane Fluidity

The ability of a membrane to move and change shape. It is influenced by factors like temperature, the type of fatty acids present, and the presence of sterols.

Reinforcing Agents

Molecules that help strengthen and stabilize cell membranes. Examples include sterols in eukaryotes and hopanoids in bacteria.

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Archaea Membrane Lipids

Unique lipids found in archaea, characterized by ether links between glycerol and fatty acids, which are more stable than ester links.

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Membrane Proteins

Proteins embedded within cell membranes that carry out various functions, such as structural support, signal detection, secretion, and transport.

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Passive Transport

The movement of molecules across a membrane from a high concentration to a low concentration, without requiring energy.

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Active Transport

The movement of molecules across a membrane from a low concentration to a high concentration, requiring energy.

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What are the key traits of bacterial cells?

Bacterial cells are characterized by a thick, complex outer envelope, a compact genome, and tightly coordinated cell functions. This allows them to protect themselves from the environment, efficiently use resources, and reproduce quickly.

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What are the major components of a bacterial cell's chemical composition?

Bacterial cells are mainly composed of water, essential ions like potassium and magnesium, small organic molecules like lipids and sugars, and macromolecules such as nucleic acids and proteins.

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How are bacteria classified based on their cell wall?

Bacteria are classified based on their cell wall structure into Gram-positive, Gram-negative, and Mycobacteria. Gram-positive bacteria have a thick cell wall outside the cell membrane, Gram-negative bacteria have a thin cell wall within the periplasm surrounded by an outer membrane, and Mycobacteria have a complex, multilayered cell wall.

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What is the role of the cell membrane in bacterial cells?

The cell membrane acts as a selectively permeable barrier, controlling the movement of substances in and out of the cell. It is composed of a phospholipid bilayer with embedded proteins, providing fluidity and a constant thickness.

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What is the difference between bacterial and archaeal cells?

Both bacteria and archaea are prokaryotes, lacking a nucleus. However, archaea have a unique membrane lipid structure enabling them to survive in extreme environments, while bacteria have a typical phospholipid bilayer membrane. Both can be found in moderate environments.

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What are some examples of specialized structures in bacteria?

Bacterial cells can possess specialized structures such as vesicles, nanotubes, pili, stalks, and flagella which contribute to various functions like storage, communication, attachment, and movement.

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What is chemotaxis?

Chemotaxis is the movement of bacteria in response to chemical gradients. They move towards attractive chemicals and away from repellents.

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How do bacterial cells divide?

Bacterial cells divide through a process called binary fission, where a single cell splits into two identical daughter cells.

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Chemotaxis

The movement of bacteria in response to chemical signals.

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Attractants

Chemicals that cause bacteria to move towards them by promoting a 'run' behavior.

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Repellents

Chemicals that cause bacteria to move away from them by promoting a 'tumble' behavior.

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Run (in chemotaxis)

A period of directed movement in a straight line, caused by a bundled flagellum.

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Tumble (in chemotaxis)

A brief period of random reorientation, caused by a dispersed flagellum, allowing bacteria to change direction.

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Nucleoid

The region in prokaryotic cells where DNA is located. It's not enclosed by a membrane like a nucleus, but the DNA is supercoiled and bound to proteins.

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Replication Origin (ori)

The specific site on the DNA molecule where replication begins. It's a sequence recognized by proteins involved in starting DNA replication.

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Replisome

A complex of proteins, including DNA polymerase, that replicates DNA at each replication fork. It acts like a 'replication factory.'

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Thylakoids

Folded intracellular membranes found in photosynthetic bacteria that contain chlorophyll and other molecules involved in photosynthesis.

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Carboxysomes

Polyhedral protein bodies packed with Rubisco, an enzyme that helps convert carbon dioxide into organic compounds.

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Gas Vesicles

Hollow structures that help photosynthetic bacteria float in water by trapping gases like hydrogen and carbon dioxide.

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Peritrichous Flagella

Flagella that are randomly distributed around the cell and rotate together to propel the cell.

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Flagellar Motor

The structure in a flagellum that uses the proton motive force to rotate the flagellum. It's like a 'mini motor' that powers movement.

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Peptidoglycan

A complex polymer found in bacterial cell walls, composed of repeating disaccharides (N-acetylglucosamine and N-acetylmuramic acid) cross-linked by peptides.

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Gram-Positive Bacteria

Bacteria with a thick cell wall containing multiple layers of peptidoglycan, reinforced by teichoic acids. They also possess an S-layer and capsule.

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Gram-Negative Bacteria

Bacteria with a thin peptidoglycan layer covered by an outer membrane. The outer membrane has a unique composition, including lipopolysaccharide (LPS) and porins.

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Lipopolysaccharide (LPS)

A complex molecule found in the outer membrane of Gram-negative bacteria, composed of lipid A, core polysaccharide, and O antigen. It plays a role in immune responses and can be toxic.

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FtsZ

A protein that forms a ring-like structure called the Z-ring during bacterial cell division. The Z-ring helps to divide the cell by guiding peptidoglycan synthesis and constriction.

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Outer Membrane Proteins (Porins)

Proteins embedded in the outer membrane of Gram-negative bacteria that act as channels allowing small molecules to pass through.

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Periplasm

A space between the cell wall and the plasma membrane in Gram-negative bacteria, filled with enzymes and transport proteins.

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Septation

The process of forming a septum, a new cell wall that divides the bacterial cell into two daughter cells. This process is guided by the FtsZ protein and involves synthesis of new cell wall material.

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Study Notes

Cell Structure and Function Overview

  • Bacterial cells lack a nucleus.
  • Bacteria have a phospholipid bilayer membrane.
  • Archaea have unique membrane lipids supporting survival in extreme environments.
  • Eukaryotic cells possess a nucleus and extensive membranous organelles.

Bacterial Cell Overview

  • Thick, complex outer envelope protects from environmental stress, mediating exchange with the environment.
  • Compact genome maximizes cell production from limited resources.
  • Tightly coordinated functions enable high reproduction rates.

Biochemical Composition of Bacteria

  • Water (70% of total weight), essential ions, small organic molecules (lipids, sugars), and macromolecules (nucleic acids, proteins).
  • Variable composition depends on species, growth phase, and environmental conditions.

Classification of Bacteria

  • Classified based on cell wall configuration:
    • Gram-positive bacteria have a thick cell wall outside the cell membrane.
    • Gram-negative bacteria have a thin cell wall with an outer membrane containing phospholipids and lipopolysaccharides.

The Cell Membrane

  • Selectively permeable barrier separating internal components from the external environment.
  • Phospholipid bilayer with lipid-soluble proteins, consistent thickness (~8 nm).
  • Membrane lipids (glycerol with ester links to fatty acids).
  • Diversity varies with environmental conditions and phosphoryl head groups, and fatty acid side chains.
  • Cardiolipin increases under stress (e.g., starvation).
  • Fatty acids can be saturated, unsaturated, or polyunsaturated.
  • Cis form of oleic acid increases membrane fluidity.
  • Cyclopropane fatty acids decrease membrane fluidity especially during stress.
  • Eukaryotes have sterols (e.g., cholesterol).
  • Bacteria have hopanoids for structural support.
  • Archaea have ether links (C-O-C) instead of ester links between glycerol and fatty acids.
  • Archaea forms a monolayer membrane by fusing tails.
  • Membrane proteins support structural support (anchoring cell envelope layers) and detect environmental signals (e.g., temperature).

Molecules Crossing the Cell Membrane

  • Mechanisms of molecule transport include semipermeable barriers, passive transport (high to low concentration using concentration gradient), and active transport (low to high concentration using energy).

The Envelope and Cytoskeleton

  • Cell envelope includes structural support (typically the cell wall).
  • Additional layers (outer membrane or S-layer) may be present in some bacteria.
  • Mycoplasmas lack an outer layer.

The Cell Wall

  • Confers shape and rigidity, withstanding turgor pressure.
  • Composed of peptidoglycan (murein) from repeating disaccharides (N-acetylglucosamine and N-acetylmuramic acid) cross-linked with peptides.
  • Peptidoglycan is a target for antibiotics like penicillin and vancomycin.
  • Gram-positive bacteria have a thick cell wall (3-20 layers) reinforced by teichoic acids; S-layer and Capsule layers are also present.
  • Gram-negative bacteria have a thin peptidoglycan layer (1-2 sheets), covered by an outer membrane.
  • Outer membrane components include lipopolysaccharide (LPS), lipid A, and O antigen.

Bacterial Cytoskeleton

  • Proteins (FtsZ, MreB, CreS) shape and maintain cell structure (diameter, rod shape, crescent shape).

Bacterial Cell Division

  • Highly coordinated growth, formation of cell parts, DNA replication, and cell wall expansion.
  • Septation forms the septum dividing the cell envelope.
  • FtsZ subunits assemble, treadmilling, and septal growth requires biosynthesis envelope components.
  • Divisome components include FtsZ for the Z-ring and FtsN regulating septum constriction.

DNA Organization and Replication

  • Prokaryotic cells contain a nucleoid region in their cytoplasm.
  • DNA is attached to the envelope at the origin of replication with supercoiled loops bound to proteins.
  • Ribosomes bind mRNA and start translating proteins before transcription is complete.

Specialized Structures

  • Thylakoids: Membrane-bound structures for photosynthetic reactions in bacteria.
  • Carboxysomes: Protein bodies for CO2 fixation.
  • Gas vesicles: Hollow structures for buoyancy.
  • Storage granules: glycogen, PHB, PHA and sulfur granules for energy storage.
  • Pili/Fimbriae: filaments for attachment, motility, and conjugation.
  • Stalks: Attachment organelles for holding fasts (enabling iron oxidation).
  • Rotary Flagella: Prokaryotic flagella for movement (peritrichous, lophotrichous, monotrichous).
  • Chemotaxis: Movement in response to chemical gradients (responding to attractants vs. repellents via CW vs CCW rotation).

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Explore the essential features of bacterial and eukaryotic cells in this quiz. Understand the differences in cell composition, classification, and the unique adaptations that enable bacteria to thrive in various environments. Test your knowledge on cell structure and functions.

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