Biology Chapter on Cell Membranes

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Questions and Answers

Which of the following is NOT a function of the cell membrane?

Maintaining a mechanical barrier between the cell's interior and external environment

Providing a framework for the cell's shape and structure

Regulating the passage of water-soluble substances through the membrane

Synthesizing proteins and lipids for the cell's use (correct)

Which of the following statements about the fluid mosaic model of the cell membrane is TRUE?

It emphasizes that the membrane is a fluid structure with lipids and proteins constantly moving and interacting. (correct)

It describes a static, rigid structure with phospholipids forming a tightly packed, impermeable layer.

It suggests that the membrane is composed of a single layer of phospholipids with proteins attached to its outer surface.

It postulates that proteins are embedded in a rigid lipid matrix that restricts their movement.

Which type of cell junction is responsible for preventing the leakage of substances between cells?

Gap junctions

Tight junctions (correct)

Cell adhesion molecules

Desmosomes

Which of the following is NOT a function of the extracellular matrix (ECM)?

Directly participating in the synthesis of proteins and lipids Signup and view all the answers

Which component of the cell membrane plays a crucial role in maintaining the fluidity and stability of the membrane?

Cholesterol Signup and view all the answers

Which of the following is NOT a type of protein found in the cell membrane?

Microtubules Signup and view all the answers

What is the primary function of the glycocalyx on the cell surface?

Serving as cell-identity markers Signup and view all the answers

Which type of cell junction allows for direct communication and exchange of small molecules between adjacent cells?

Gap junctions Signup and view all the answers

What is the primary reason for the generation of resting membrane potential (RMP)?

Unequal distribution of Na+, K+, and anions across the membrane Signup and view all the answers

What does a negative membrane potential of −70mV indicate about the charges inside and outside the cell?

Inside the cell is more negative than the outside Signup and view all the answers

How does the Na-K-ATPase pump contribute to the maintenance of membrane potential?

It moves three Na+ ions out and two K+ ions in Signup and view all the answers

What is the equilibrium potential for K+ (EK+) calculated based on the provided concentration values?

-90mV Signup and view all the answers

Which ion's permeability has the highest relative value in the resting state according to the provided data?

K+ Signup and view all the answers

What does the Nernst equation express in the context of membrane potential?

The relationship between ion concentration and membrane charge Signup and view all the answers

Why is the equilibrium potential for Na+ (ENa+) lower than that for K+ (EK+)?

K+ is more permeable than Na+ at rest Signup and view all the answers

What is the significance of the leak channels for Na+ and K+ ions in the generation of RMP?

They allow passive diffusion of ions, maintaining charge separation Signup and view all the answers

What type of communication involves hormones secreted into the blood that act on distant target cells?

Endocrine communication Signup and view all the answers

Which type of ion channel opens in response to changes in the electrical status of the plasma membrane?

Voltage-gated channels Signup and view all the answers

What characterizes water-soluble chemical messengers during signal transduction?

They bind to receptors and transduce signals within the cell. Signup and view all the answers

Which of the following is an example of a second messenger in signal transduction pathways?

Cyclic AMP Signup and view all the answers

What process describes the way a chemical signal is converted or transduced inside a cell?

Signal transduction Signup and view all the answers

What is the primary function of receptor binding in the context of signal transduction?

To initiate intracellular events Signup and view all the answers

What distinguishes autocrine communication from paracrine communication?

Autocrine signals act on the same cells that secretes them; paracrine affects nearby cells. Signup and view all the answers

Which of the following best describes the role of transducers in signal transduction?

They convert signals from one form to another inside the cell. Signup and view all the answers

Which structure is responsible for the 'spot rivets' found in desmosomes?

Plaque Signup and view all the answers

In which junctions do cells adhere firmly and form seals at specific sites?

Tight junctions Signup and view all the answers

What is the main function of gap junctions?

Facilitates metabolic communication between cells Signup and view all the answers

What defines the movement of particles during passive transport?

No energy expenditure required Signup and view all the answers

What is the primary mechanism through which water moves across a semi-permeable membrane?

Osmosis Signup and view all the answers

Which of the following factors is NOT one that influences the rate of diffusion?

Osmotic pressure Signup and view all the answers

What type of transport applies when materials move through a cell membrane using energy?

Active transport Signup and view all the answers

What accurately describes the nature of tight junctions?

They form a selective barrier between compartments. Signup and view all the answers

How do cations move in response to an electrochemical gradient?

Towards the negatively charged area Signup and view all the answers

What happens when osmotic pressure is balanced by opposing hydrostatic pressure?

Osmosis ceases and a steady state exists. Signup and view all the answers

What is a key characteristic of facilitated diffusion?

It occurs through specific carrier proteins. Signup and view all the answers

Which transport mechanism involves movements using membrane vesicles?

Vesicular transport Signup and view all the answers

What is primarily moved during osmosis?

Water molecules Signup and view all the answers

Which of the following statements about carrier-mediated transport is NOT true?

Carriers are specific for the substance they transport, but they can transport multiple unrelated substances. Signup and view all the answers

Which of the following is a characteristic of facilitated diffusion?

It is limited by the number of carrier proteins available. Signup and view all the answers

The Na+/K+ ATPase pump is an example of which type of transport?

Primary active transport Signup and view all the answers

Which of the following statements about secondary active transport is TRUE?

It relies on the concentration gradient of another substance to move substances against their concentration gradient. Signup and view all the answers

Which type of endocytosis is responsible for the uptake of specific, large molecules?

Receptor-mediated endocytosis Signup and view all the answers

Which of the following is NOT a characteristic of exocytosis?

It transports substances from the extracellular fluid into the cell. Signup and view all the answers

Which of the following types of cell-cell communication is considered the most intimate and rapid?

Gap junctions Signup and view all the answers

Which of the following is NOT a characteristic of gap junctions?

They are found in all types of tissues. Signup and view all the answers

Which of the following statements about juxtacrine communication is TRUE?

It requires direct contact between cells. Signup and view all the answers

Which of the following correctly pairs a type of cell communication with its primary function?

Gap junctions - Rapid transmission of electrical signals Signup and view all the answers

Study Notes

Plasma Membrane: Structure and Function

Plasma membranes are crucial for homeostasis and cell survival, maintaining intracellular contents and coordination with other cells
Mechanical barrier- Prevents leakage, and keeps internal contents inside and external ones out
Adhesion- Holds cells together to form tissues
Exchange- Facilitates nutrients, wastes, and secretions
Response- Reacts to environmental changes and signals
Ionic gradient maintenance- Important for electrical activity

Components of Cell Membrane: Lipids

Lipids (phospholipids and cholesterol) form a barrier to water-soluble substances.
Provide fluidity and stability to the membrane.
Phospholipids- Have a hydrophilic head and hydrophobic tails.
Cholesterol- A steroid that stiffens the membrane.

Components of Cell Membrane: Proteins

Proteins are transmembrane or one surface-bound.
Integral (intrinsic) proteins- Embedded in the lipid bilayer.
Peripheral (extrinsic) proteins- Attached to the surface of the lipid bilayer.
Variety of roles in specific cell functions.
Includes aquaporins, ion channels, carrier molecules, membrane receptors, docking-marker acceptors, membrane-bound enzymes, and cell adhesion molecules (CAMs).

Components of Cell Membrane: Carbohydrates

Carbohydrates are present only on the outer surface.
Glycocalyx- The carbohydrate coat, involved in cell-cell recognition.
Glycolipids- Carbohydrates linked to lipids.
Glycoproteins- Carbohydrates linked to proteins.
Function as self-identity markers.

Structure of Cell Membrane: The Fluid Mosaic Model

The fluid mosaic model describes the trilaminar structure of the plasma membrane.
Composed of a lipid bilayer with proteins embedded and carbohydrates on the outer surface.

Cell-Cell Adhesions

Extracellular matrix: A biological glue secreted by cells that holds cells together.
Specialized cell junctions:
- Desmosomes - "Spot rivets" for strong cell adhesion.
- Tight junctions - Tightly seals cells together.
- Gap junctions - Channels between cells, allow passage of small substances.
Cell adhesion molecules (CAMs) - The "velcro" proteins.

Extracellular Matrix

AKA interstitial fluid, present in the space between cells.
A gel-like meshwork of fibrous proteins.
Collagen- A fibrous protein providing structural strength.
Elastin- A fibrous protein providing elasticity.
Fibronectin- A glycoprotein that acts as an important signaling factor.
Important for cell function and signaling pathways.

Desmosomes/Adhering Junctions

Desmosomes are strong cell junctions, also called "spot rivets".
Plaque forms a thickening of the cytoplasm.
Glycoprotein and keratin filaments connect cells.
Found in tissues subjected to stress (e.g., skin, heart, uterus).

Tight/Impermeable Junctions

Tightly seals adjacent cells together.
Prevents leakage between cells.
Found in epithelial tissues (e.g., intestines, kidneys).
Materials pass through the cells, not between them (as in channels or carriers)

Gap/Communicating Junctions

Channels between cells, allowing for ion movement.
Connexons are the protein subunits that make up the channel.
Involved in electrical signaling between cardiac and smooth muscle cells.
Enables synchronized action and metabolic/communication links.

Membrane Transport

Crucial for homeostasis.
Selectively permeable- Allows some substances to pass through, but not others.
Factors affecting permeability:
- Lipid solubility
- Particle size
Forces required for transport:
- Passive transport (no energy required) - Includes diffusion & osmosis
- Active transport (energy required)
Types of transport:
- Unassisted (diffusion, osmosis): Substances move down their concentration gradient.
- Assisted (Carrier-mediated, Vesicular): Substances require carriers or vesicles.
- Carrier-mediated transport- Proteins that carry substances across the membrane.
  - Uniport- One substance moved across
  - Symport- Two substances moved in the same direction`
  - Antiport- Two substances moved in opposite directions.
- Vesicular transport- Materials are enclosed in a vesicle for transport.
  - Endocytosis- Into the cell
  - Exocytosis- Out of the cell
Specific examples: Glucose transport (facilitated diffusion), Na+-K+ pump (primary active transport), and SGLT (secondary active transport).

Diffusion

Movement of substances from high to low concentration.
Passive process- No energy required.
Factors influencing the rate of diffusion (Fick's Law):
- Concentration gradient
- Surface area
- Lipid solubility
- Molecular weight
- Distance

Osmosis

Net diffusion of water across a semipermeable membrane.
From high to low water concentration.
Affects cell volume.
Tonicity - The ability of a solution to cause a cell to gain or lose water.
Isotonic- Concentration of solutes inside and outside the cell are equal
Hypotonic- Concentration of solutes outside the cell is less than inside
Hypertonic- Concentration of solutes outside the cell is more than inside

Electrical Gradient

Charge difference between adjacent areas.
Promotes movement towards the opposite charge, influenced by concentration gradient. Electrochemical gradient - electrical and concentration gradient together.

Carrier-mediated Transport

Proteins (carriers) facilitating the movement of water-soluble substances across the membrane.
Specific for a particular substance.
Important for transport of many nutrients.
Types of carrier-mediated transport:
- Uniport
- Symport
- Antiport
Characteristics: Specificity, Saturation, Competition, Tm- Transport maximum (rate-limiting factor)
Facilitated diffusion- Passive transport that uses carriers
Active transport - Requires energy (ATP) for movement of substances against their gradient

Facilitated Diffusion

Passive transport using carrier proteins.
Movement of substance from high to low concentration.

Active Transport

Movement of substances against their concentration gradient.
Requires energy (ATP).
Primary active transport-ATP directly involved in the transport.
- Na-K ATPase pump
Secondary active transport- Energy harnessed from the concentration gradient of a different substance to move another. - SGLT (sodium-glucose cotransporter)

Vesicular Transport

Large molecules and materials are transported in vesicles.
Two types
- Endocytosis- into the cell
- Exocytosis- Out of the cell
Includes pinocytosis, receptor-mediated endocytosis, and phagocytosis.

Cell-Cell Communication

Mechanisms for cells to communicate with each other.
Direct: (Gap junctions, Tunneling nanotubes, Juxtacrine)
Indirect: (Paracrine, Autocrine, Endocrine, Neuronal)

Signal Transduction

The process by which a signal from outside the cell changes a signal inside the cell.
Extracellular messengers- Lipid and water soluble, can be molecules that trigger this transduction..
Signal transduction process- "Transduction"- converting in one form of energy to another (e.g., radio waves to sound).
Pathways: First messengers-bind to receptors (e.g., hormones). Second messengers- Activate intracellular pathways.
Lipid soluble and water soluble messengers bind in different ways and initiate different processes.

Ion Channels

Proteins forming channels in the plasma membrane allowing regulated passage of ions, water soluble substances.
- Leak channels - Always open
- Gated channels- Open or close in response to stimuli (Ligand-gated, voltage-gated).
Ion movement across these channels initiates a response in the cell.

Second Messenger Pathways

Relaying of messages within the cell.
Main mechanisms- Cyclic AMP, Ca2+/DAG.
Disturbances can lead to disease.

Membrane Potential

Electrical difference across the plasma membrane.
Separation of charges (ions).
Generated by differences in ion concentrations and permeability.
Resting membrane potential (RMP): The charge difference when the cell is at rest.
Types of potentials-Graded potentials, and action potentials.

Changes in RMP

Depolarization, Repolarization, Hyperpolarization.
Important for nerve and muscle cell function.

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Description

Test your understanding of cell membranes with this quiz. Explore topics such as the fluid mosaic model, cell junctions, and the extracellular matrix. Challenge yourself with questions about the structure and functions of the cell membrane.