Membrane Structures Theories and Models
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Questions and Answers

Which scientist proposed the lipid bilayer model that includes proteins adhering to lipid-aqueous interfaces?

  • Gorter and Grendell
  • Danielli and Davson (correct)
  • Overton
  • Robertson

What is the main role of liposomes in biological studies?

  • To provide a source of energy
  • To act as carriers for molecules (correct)
  • To act purely as structural components
  • To enhance lipid solubility

In the unit membrane model proposed by Robertson, what comprises the central layer of plasma membranes?

  • Glycerophospholipids only
  • Proteins only
  • Hydrocarbon chains of lipids (correct)
  • Hydrocarbon chains of proteins

What does the fluid mosaic model recognize about the arrangement of lipids and proteins?

<p>They are in a mosaic arrangement with movement (D)</p> Signup and view all the answers

Which of the following is NOT a major function of lipids?

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

What type of molecules can form channels for ions in membranes?

<p>Certain proteins or polypeptides (D)</p> Signup and view all the answers

Which component is NOT part of glycerophospholipids?

<p>Three fatty acyl tails (D)</p> Signup and view all the answers

Which statement is true regarding the nonpolar/hydrophobic regions of integral proteins?

<p>They are embedded inside the lipid bilayer (D)</p> Signup and view all the answers

What is the primary function of the nucleolus?

<p>Assembly of ribosomal subunits (D)</p> Signup and view all the answers

Which structure surrounds the nucleolus and is formed of newly transcribed ribosomal RNA?

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

What significant change occurs in the Rdna intergenic region during the evolution from anamniotes to amniotes?

<p>It increases in size (A)</p> Signup and view all the answers

How can the Nucleolus Organizer Region (NOR) be identified in a cell?

<p>By karyotype analysis with silver nitrate staining (B)</p> Signup and view all the answers

Which of the following is NOT a function of the nucleolus?

<p>Transcription of DNA (D)</p> Signup and view all the answers

What property of membranes makes them highly selective barriers?

<p>Impermeability to ions and most polar molecules (B)</p> Signup and view all the answers

What is the role of liposomes in biological research?

<p>To act as vehicles for delivering chemicals to cells (A)</p> Signup and view all the answers

Which of the following accurately describes the function of channels and pumps in membranes?

<p>They act as selective transport systems. (D)</p> Signup and view all the answers

What effect do cis double bonds have on membrane fluidity?

<p>They disrupt ordered packing and increase fluidity. (A)</p> Signup and view all the answers

How does the length and saturation of hydrocarbon chains affect membrane fluidity?

<p>Longer and more saturated chains create a more ordered and rigid membrane. (D)</p> Signup and view all the answers

What is electrical polarization of a plasma membrane typically at rest?

<p>-60 millivolts (D)</p> Signup and view all the answers

What happens to the lipid bilayer above the transition temperature?

<p>It undergoes a phase change to a more fluid state. (D)</p> Signup and view all the answers

What is one of the key functions of membranes in terms of energy conversion?

<p>They organize reaction sequences and enzyme arrays. (A)</p> Signup and view all the answers

What is the primary mechanism for the bulk ingestion of solid materials by cells?

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

Which type of endocytosis is induced by proteins, amino acids, and certain ions?

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

What role does ATP play in the process of endocytosis?

<p>It increases the rate of endocytosis. (C)</p> Signup and view all the answers

Which cells primarily perform phagocytosis as a defense mechanism?

<p>Macrophages (C)</p> Signup and view all the answers

What is the structure that separates the two membranes of the nuclear envelope?

<p>Perinuclear space (C)</p> Signup and view all the answers

What is the diameter of the nuclear pore complex (NPC)?

<p>100 nm (A)</p> Signup and view all the answers

What is the function of the fibrous lamina associated with the inner membrane of the nuclear envelope?

<p>It maintains the shape of the nucleus. (D)</p> Signup and view all the answers

Which types of molecules can freely pass through the nuclear pore complex?

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

What is the approximate maximum mass of macromolecules that can passively diffuse across the nuclear pore complex (NPC)?

<p>60 kDa (B)</p> Signup and view all the answers

What are the nuclear localization sequences (NLSs) necessary for?

<p>Import of proteins into the nucleus (B)</p> Signup and view all the answers

Which of the following is considered a cargo for export from the nucleus?

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

What do the filaments of the nuclear basket help to extend into?

<p>Cytoplasm (C)</p> Signup and view all the answers

Which of the following describes the primary function of the nucleolus?

<p>Synthesis of ribosomal RNAs (D)</p> Signup and view all the answers

What is a characteristic component of the nucleolus that stains lightly?

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

Which transport factor is also known as CRM1?

<p>XPO1 (B)</p> Signup and view all the answers

What role does turgor pressure play in plants?

<p>It provides mechanical support for non-woody tissues. (C)</p> Signup and view all the answers

Which component of the nucleolus is not primarily responsible for rRNA synthesis?

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

Which correctly describes water potential in plants?

<p>It is the tendency of water to move to more negative areas. (B), It is the sum of pressure potential and solute potential. (C)</p> Signup and view all the answers

How does active transport differ from passive transport?

<p>Active transport requires energy, while passive transport does not. (D)</p> Signup and view all the answers

What is the main source of energy for active transport in cells?

<p>ATP generated during respiration. (C)</p> Signup and view all the answers

Which example illustrates passive transport?

<p>Diffusion of oxygen across a lipid bilayer. (C)</p> Signup and view all the answers

Facilitated diffusion requires which of the following?

<p>Specific membrane proteins. (B)</p> Signup and view all the answers

What conditions apply to water movement based on water potential?

<p>Water moves to areas with higher solute concentration. (C), Water moves from regions of higher pressure to lower pressure. (D)</p> Signup and view all the answers

Which of the following correctly defines pressure potential?

<p>It represents the force exerted by the cell wall. (A)</p> Signup and view all the answers

Flashcards

Lipid Bilayer

A fundamental structure of cell membranes, composed of two layers of lipid molecules, with hydrophobic tails facing inward and hydrophilic heads outward.

Fluid Mosaic Model

The widely accepted model of cell membrane structure, describing the membrane as a fluid mixture of lipids and proteins (mosaic) with proteins embedded within or attached to the lipid bilayer that can move freely.

Integral proteins

Proteins embedded within the lipid bilayer of a cell membrane, with at least a portion of the protein extending into the hydrophobic interior.

Glycerophospholipids

A major class of membrane lipids with a glycerol backbone, two fatty acid tails, and a phosphate head group.

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Membrane Lipids

Lipids that form the fundamental structure of cell membranes, responsible for their spontaneous formation of bilayers.

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Amphipathic

Describing molecules with both hydrophilic and hydrophobic parts.

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Liposomes

Artificial lipid bilayer vesicles that act as models for cell membranes and drug delivery vehicles.

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Unit Membrane Model

An older model of cell membrane structure, suggesting that membranes have a consistent structure with proteins lining the interior of the membrane, visualized as a dense, uniform layer within electron microscopy images

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Turgor Pressure

The pressure exerted by water inside a plant cell against the cell wall, providing support to soft plant tissue.

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Water Potential

The tendency of water to move from one area to another; always negative, and water moves towards areas with lower water potential.

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Active Transport

The movement of molecules across a cell membrane against their concentration gradient, requiring energy (ATP).

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Passive Transport

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

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Simple Diffusion

The movement of molecules from high to low concentration across a cell membrane without help from proteins.

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Facilitated Diffusion

The movement of molecules across a membrane with the help of transport proteins, still from high to low concentration, without energy.

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Pressure Potential

The pressure exerted by the cell wall that influence water potential

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Solute Potential

Component of water potential that depends on the concentration of solutes.

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Membrane Permeability

Membranes control what enters and exits cells through selective filtering, favored permeability of nonpolar species over polar ones.

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Liposomes

Lipid vesicles with an aqueous interior used to deliver chemicals/drugs/DNA for studying membrane permeability and therapy.

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Membrane Functions

Membranes carry out diverse functions, acting as compartments, regulating environments, supporting transport systems and signaling, and converting energy.

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Membrane Permeability Barriers

Membranes have selective permeability; they maintain specific ion and molecule concentrations inside and outside the cell.

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Membrane Transport

Channels and pumps in the membrane regulate the passage of molecules and ions across the cell membrane.

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Membrane Fluidity

The ability of a cell membrane to change shape is influenced by the lipid composition and fatty acid chain length and saturation.

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Membrane Fluidity Regulation

Membrane fluidity depends on the length and saturation of hydrocarbon chains; longer and more saturated chains lead to less fluidity.

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Membrane Protein Roles

Membrane proteins like channels and pumps are involved in transport, signaling, and energy production; they maintain different protein ion concentrations on opposite sides of the membrane.

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Endocytosis

The process of cells taking up solid or liquid materials in bulk.

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Phagocytosis

A type of endocytosis where cells engulf solid particles.

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Pinocytosis

A type of endocytosis where cells engulf fluids.

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Nuclear Envelope

Double membrane surrounding the cell nucleus, containing nuclear pores.

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Nuclear Pores

Openings in the nuclear envelope that allow the passage of substances.

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Perinuclear Space

The space between the two membranes of the nuclear envelope.

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Nuclear Lamina

Network of proteins on the inner nuclear membrane.

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Nucleoporins

Proteins forming the structure of nuclear pores.

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Nuclear Pore Complex (NPC)

A large protein complex in the nuclear envelope that regulates the passage of molecules between the nucleus and cytoplasm.

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Nuclear Localization Signal (NLS)

A short amino acid sequence within a protein that directs the protein to the nucleus.

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Nuclear Export Sequence (NES)

A short amino acid sequence within a protein that directs the protein out of the nucleus.

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Karyopherins

Transport factors that recognize and bind to NLSs and NESs to facilitate protein transport across the nuclear pore complex.

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Nucleolus

A sub-nuclear structure involved in ribosomal RNA (rRNA) synthesis and ribosome subunit assembly.

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Ribosomal subunits

Subunits produced in the nucleolus for protein synthesis (building proteins)

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Size limitation (NPC)

Molecules that are larger than approximately 60kDa must use active transport across the nuclear pore complex. Smaller molecules can pass passively

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Nucleolus Organizer Regions (NORs)

Regions of chromosomes that contain the genes for ribosomal RNA (rRNA) which are important for ribosome production.

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Nucleolus Structure Anamniotes vs. Amniotes

The nucleolus's structure differs between animals that don't have an amnion (anamniotes) and those that do (amniotes). A key difference is the increasing length of the DNA region between ribosomal RNA genes in amniotes.

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Nucleolus Organizer Region (NOR)

The specific region of DNA in a cell's nucleus where ribosomal RNA genes are clustered, which is used in nucleolus formation.

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Ribosomal RNA (rRNA) Production

Nucleoli are the main sites for producing rRNA, which combines with specific proteins to form ribosomes.

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Non-Ribosomal Nucleolus Functions

Nucleoli perform tasks beyond ribosome creation, including mRNA processing, protein sequestration, and cell cycle regulation.

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Karyotype analysis using silver nitrate

A method to detect the Nucleolus Organizer Regions (NORs) by staining chromosomes with silver nitrate.

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Study Notes

Theories on Membrane Structures

  • 1902, membranes were thought to consist only of lipids (Overton)
  • 1926, Gorter and Grendell proposed that lipids form a double layer
  • 1935, Danielli and Davson proposed a lipid bilayer model including proteins adhering to both lipid-aqueous interfaces
  • Artificial model systems (liposomes) supported the Danielli-Davson model
  • Droplets of lipid in organic solvent can be spread over a small hole to study biophysical properties of a bilayer (e.g. permeability and electrical resistance)
  • Channels for ions can be formed by adding proteins or polypeptides
  • Liposomes are effective carriers for molecules like chemotherapy drugs, insulin, and antibodies

Unit Membrane Model

  • Robertson (1959) proposed the unit membrane model
  • This model suggests the central layer of plasma membranes is made up of lipid hydrocarbon chains, with proteins forming dense surrounding layers
  • A simplified model, as it cannot account for the number of proteins across membranes

Fluid Mosaic Model

  • Singer and Nicolson (1972) proposed the fluid mosaic model
  • The model describes lipids and proteins in a mosaic arrangement
  • Lipids and proteins can move laterally within the lipid bilayer
  • Non-covalent interactions create a fluid-like state for membranes

Key Concepts

  • Major functions of lipids: energy storage, membrane components
  • Other functions of lipids: signals, electron carriers, emulsifying agents
  • Membrane lipids (amphipathic): responsible for the spontaneous formation of lipid bilayers
  • Glycerophospholipids: glycerol backbone + 2 fatty acyl tails + polar head group
  • Sphingolipids: sphingosine backbone + fatty acid chain + carbohydrate or phosphate ester
  • Cholesterol: affects membrane fluidity
  • Membrane fluidity depends on lipid composition (chain length, double bonds, cholesterol content)

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Description

Explore the evolution of theories regarding membrane structures from the early 1900s to modern models. This quiz covers significant contributions by scientists such as Overton, Gorter, Grendell, Danielli, Davson, and Robertson. Test your knowledge on lipid bilayers and their applications in biophysics and medicine.

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