Chapter 5 Structure & Function of Plasma Membranes

Flashcards covering the components, structure, function, and transport mechanisms of plasma membranes, including the fluid mosaic model, passive transport, active transport, and bulk transport.

Fluid Mosaic Model

A model stating that a membrane is a fluid structure with a 'mosaic' of various proteins embedded in it, consisting of phospholipids, cholesterol, proteins, and carbohydrates.

Plasma Membrane

The boundary that separates the living cell from its nonliving surroundings, exhibiting selective permeability and managing what enters and exits the cell.

Selective Permeability

The property of a membrane that allows some substances to cross it more easily than others.

Phospholipids

The main fabric of the plasma membrane, which are amphipathic molecules containing both hydrophobic and hydrophilic regions.

Amphipathic

A molecule possessing both hydrophilic (water-loving) and hydrophobic (water-fearing) properties.

Sterols

A type of lipid important for the fluidity of the plasma membrane, including cholesterol in animals.

Cholesterol

A sterol found in animal cell membranes that helps regulate membrane fluidity, increasing it at low temperatures and decreasing it at high temperatures.

Membrane Fluidity

The measure of the viscosity of the lipid bilayer, affected by temperature, fatty acid composition (saturated vs. unsaturated), and cholesterol.

Saturated Fatty Acids

Fatty acids in phospholipids that are straight and pack tightly, leading to less fluid membranes.

Unsaturated Fatty Acids

Fatty acids in phospholipids that have kinks, creating space and resulting in more fluid membranes.

Integral Proteins

Proteins integrated completely into the lipid bilayer, having one or more hydrophobic regions and others that are hydrophilic.

Peripheral Proteins

Proteins that occur only on the surfaces (exterior or interior) of the membrane, often functioning as enzymes or structural attachments.

Glycoproteins

Carbohydrates bound to proteins, located on the exterior plasma membrane surface for cell-cell recognition and attachment.

Glycolipids

Carbohydrates bound to lipids, located on the exterior plasma membrane surface for cell-cell recognition and attachment.

Asymmetric Membrane

A plasma membrane where the inner surface differs from the outer surface, with distinct compositions and functions for its components.

Endomembrane System

A group of membranes and organelles (ER, Golgi, nuclear envelope, plasma membrane, lysosomes) that synthesize, modify, package, and transport membrane proteins and lipids.

Passive Transport

The movement of molecules from areas of high concentration to areas of low concentration by diffusion, requiring no energy input.

Diffusion

The tendency for molecules of any substance to spread out evenly into the available space, moving down their concentration gradient.

Concentration Gradient

A difference in the concentration of molecules across a space, which drives diffusion; movement 'down' the gradient means from high to low concentration.

Simple Diffusion

A type of passive transport where molecules move directly across the lipid bilayer without energy or protein assistance.

Facilitated Diffusion

A type of passive transport that moves substances down their concentration gradients but requires the use of transmembrane proteins (channel or carrier proteins).

Channel Proteins

Transmembrane proteins with a hydrophilic core that allow specific ions and/or polar molecules to pass through the membrane; some are gated, opening only when a signal is received.

Aquaporins

Specific channel proteins that allow for the bulk transport of water across the hydrophobic plasma membrane.

Carrier Proteins

Transmembrane proteins specific to a single substance, which bind to that substance, change shape, and carry it to the other side of the membrane.

Osmosis

A special type of diffusion involving the movement of water across a semipermeable membrane, determined by solute concentration.

Water Potential

The tendency of water to move from one place to another, affected by solute concentration, pressure, and gravity.

Tonicity

The ability of a solution to cause a cell to gain or lose water, affecting the cell's volume by osmosis.

Isotonic Solution

A solution where the concentration of solute outside the cell is the same as inside, resulting in no net movement of water.

Hypotonic Solution

A solution where the concentration of solute outside the cell is lower than inside, causing the cell to gain water and potentially swell or burst.

Hypertonic Solution

A solution where the concentration of solute outside the cell is higher than inside, causing the cell to lose water and shrink.

Turgid

The firm and healthy state of plant cells, generally healthiest in a hypotonic environment due to water uptake balanced by the cell wall's elastic pressure.

Osmoregulation

The control of water flow and solute concentrations to maintain water balance within a cell or organism.

Active Transport

The movement of molecules or ions against their concentration or electrochemical gradient, requiring energy input (usually ATP or an electrochemical gradient).

Pumps

Transmembrane, integral carrier proteins involved in active transport, categorized as Uniporters, Symporters, or Antiporters.

Uniporter

A type of carrier protein that carries one molecule or ion across the membrane.

Symporter

A type of carrier protein that carries two different molecules or ions in the same direction across the membrane.

Antiporter

A type of carrier protein that carries two different molecules or ions in different directions across the membrane.

Primary Active Transport

Active transport that directly moves an ion or molecule up its concentration gradient using energy from ATP hydrolysis.

Sodium-Potassium Pump

A primary active transport mechanism that moves 3 Na+ ions out of the cell and 2 K+ ions into the cell using 1 ATP, helping maintain resting potential.

Electrochemical Gradient

A gradient of ions across a membrane, arising from the combined effects of concentration and electrical gradients, critical for proper cell functioning.

Electrogenic Pump

A transport protein that generates voltage across a membrane, contributing to the membrane potential.

Membrane Potential

The voltage difference across a membrane, important in the maintenance and functioning of the nervous system.

Secondary Active Transport

Active transport that moves an ion or molecule up its concentration gradient, using energy from an electrochemical gradient produced by primary active transport.

Cotransport

A type of secondary active transport that utilizes a symporter to move two different molecules in the same direction, typically one down its gradient and one against.

Counter-transport

A type of secondary active transport that utilizes an antiporter to move two different molecules in different directions, typically one down its gradient and one against.

Bulk Transport

When cells import or export molecules/particles that are too large to pass through a transport protein, involving vesicles (Endocytosis and Exocytosis).

Endocytosis

A process of bulk transport where the cell takes in molecules by forming new vesicles from the plasma membrane; includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Exocytosis

A process of bulk transport where transport vesicles migrate to the plasma membrane, fuse with it, and release their contents into the extracellular environment.

Phagocytosis

A type of endocytosis commonly referred to as 'cellular eating,' where the cell engulfs large particles or whole cells.

Pinocytosis

A type of endocytosis commonly referred to as 'cellular drinking,' where the cell takes in extracellular fluid containing dissolved solutes by forming small vesicles.

Receptor-Mediated Endocytosis

A highly specific type of endocytosis where specific molecules (ligands) bind to receptors on the cell surface, triggering the formation of vesicles to internalize the receptor-ligand complex.

What is the primary energy source for Endocytosis?

ATP. Endocytosis is a form of bulk active transport, which requires direct energy input from ATP to form vesicles and move substances into the cell. Glucose is a fuel source, but not the direct energy molecule for transport.

What is the energy source for Facilitated Diffusion?

No energy needed. Facilitated diffusion is a type of passive transport, meaning it does not require metabolic energy (like ATP)

What is the energy source for Osmosis?

No energy needed. Osmosis is a type of passive transport, specifically the diffusion of water across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration. It does not require direct energy.

What is the primary energy source for Exocytosis?

ATP. Exocytosis is a form of bulk active transport, which requires direct energy input from ATP to fuse vesicles with the plasma membrane and release substances out of the cell.

A diagram shows molecules moving from high to low concentration through a gated channel protein activated by a hormone. What type of diffusion is this?

Facilitated Diffusion. The key indicators are:

• Movement from high to low concentration (down the concentration gradient) indicates passive transport.

• Requirement of a transport protein (gated channel) to move the molecules across the membrane. Simple diffusion does not use a protein, and active transport moves against the gradient.

Which type of protein is used to move water through the membrane rapidly?

Aquaporins, an integral channel protein. Aquaporins are specialized channel proteins that facilitate the rapid movement of water molecules (osmosis) across the cell membrane. They are integral proteins because they span the entire membrane.

Which molecule(s) are important in regulating animal cell membrane fluidity? (Choose all that apply)

Phospholipid tail and Cholesterol.

• The phospholipid tails (specifically their saturation and length) influence how tightly packed the membrane is.

• Cholesterol acts as a fluidity buffer, making the membrane less fluid at warmer temperatures and more fluid at colder temperatures, thus maintaining optimal fluidity.

___ are used to pump molecules from a low concentration to a high concentration utilizing an __ gradient through the process of __.

Carrier proteins are used to pump molecules from a low concentration to a high concentration utilizing an electrochemical gradient through the process of Secondary Active Transport.

A patient (experiencing blood loss) receives an intravenous drip of Dead Sea salt water (super salty). What is the most likely result for the red blood cells?

The red blood cells are in danger of shrinking because they were subjected to a hypertonic environment. The Dead Sea water has a much higher solute concentration than the blood cells. Due to osmosis, water will move out of the red blood cells and into the surrounding hypertonic solution to try and equalize solute concentrations, causing the cells to shrivel (crenation).

On the basis of energy requirement, which does NOT belong to the group: "Pure water rushing into celery stalks and bulking them up," "GLUTS moving glucose molecules from the bloodstream, which has a high blood glucose concentration, into cells," "Spraying lysol in one room and over time smelling it in a room where is wasn't sprayed," "The Na/K pump."

The Na/K pump. This is a form of Primary Active Transport, which requires ATP to move ions against their concentration gradients. The other examples (water rushing into celery, glucose transport by GLUTS, and Lysol spreading) are all forms of passive transport (osmosis, facilitated diffusion, and simple diffusion, respectively) and do not directly require metabolic energy.

Arrange the following molecules according to increasing rate of diffusion across a lipid bilayer without the aid of any membrane protein: H2O, CO2, sucrose, Na+.

Hardest to move through the membrane (lowest diffusion rate):

1. Na+ (Charged ion - cannot pass hydrophobic core)

2. sucrose (Large polar molecule - too big and polar)

3. H2O (Small polar molecule - can pass slowly)

4. CO2 (Small nonpolar molecule - passes easily)
   Easiest to move through the membrane (highest diffusion rate):

General rule of diffusion rate

Small, nonpolar molecules pass most easily. Large, polar, or charged molecules have the hardest time and usually require transport proteins.

Of the following cell components, which group comprises the endomembrane system?
(Incorrect choices: Lysosome, vacuole, peroxisomes; Vacuole, plasma membrane, mitochondria; Peroxisomes, mitochondria, endoplasmic reticulum; Nuclear membrane, chloroplasts, Golgi apparatus)

Lysosomes, nuclear envelope, endoplasmic reticulum, Golgi apparatus, vacuoles, and the plasma membrane. The endomembrane system includes a variety of organelles that work together to synthesize, modify, package, and transport proteins and lipids. Mitochondria and chloroplasts are not part of the endomembrane system.

Why can someone caught adrift in the ocean not drink ocean water or they will die?

The ocean water has a higher salt concentration than the body, so due to osmosis, it will pull water from the body and dehydrate the person more. Ocean water is a hypertonic solution relative to human body fluids. If ingested, the high salt concentration in the digestive tract and bloodstream would draw water out of the body's cells (including red blood cells) into these areas, leading to severe dehydration and cell crenation.

In a typical cell membrane diagram, match the following labels (A, B, C, D, E, F, G, H) to their correct components: integral protein, channel protein, glycoprotein, peripheral protein, fatty acid hydrophobic tail, phosphate hydrophilic head.

• Integral proteins: Span the entire membrane (e.g., B, D, E).

• Peripheral proteins: Located on the surface of the membrane (e.g., F).

• Channel proteins: A type of integral protein that forms a pore for molecules to pass through (e.g., a specific integral protein like D or E).

• Glycoprotein: A protein with attached carbohydrate chains, usually on the exterior surface (e.g., A or C).

• H: Represents the fatty acid hydrophobic tail of a phospholipid.

• G: Represents the phosphate hydrophilic head of a phospholipid.

A virus binds to receptors on the outside of a cell. The cell then proceeds to form a vesicle around the virus and bring it into the cell.

Receptor-Mediated Endocytosis

A white blood cell engulfs a pathogen in your blood stream and degrades it.

Phagocytosis

An amoeba creates a vesicle to bring water and dissolved nutrients in.

Pinocytosis

Pancreatic cells package digestive enzymes into vesicles and expel them from the cells.

Exocytosis