Cell Membranes
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Questions and Answers

What is the primary function of the cell membrane as a selective barrier?

  • To regulate the flow of material in and out of the cell (correct)
  • To store genetic information
  • To provide structural support to the cell
  • To facilitate communication between cells only

Which of the following statements about phospholipids is true?

  • They can only be saturated fatty acids.
  • They have a hydrophobic head and a hydrophilic tail.
  • They are exclusively found in the nucleus of the cell.
  • Their structure influences the fluidity of the cell membrane. (correct)

How does the nature of fatty acids influence cell membrane fluidity?

  • Short, unsaturated fatty acids decrease fluidity.
  • Long, saturated fatty acids increase fluidity.
  • All fatty acids have the same effect on fluidity.
  • The presence of double bonds in fatty acids affects their melting temperatures. (correct)

What type of fats are considered 'bad' according to the content?

<p>Trans fats and fats with altered affinities (D)</p> Signup and view all the answers

What are eicosanoids derived from?

<p>Arachidonic acid and other polyunsaturated fatty acids (A)</p> Signup and view all the answers

Which transmembrane proteins are involved in the fluidity of the cell membrane?

<p>Ion channels that require shape changes (A)</p> Signup and view all the answers

What is the significance of glycolipids in cell membranes?

<p>They contribute to membrane structure and cellular recognition. (A)</p> Signup and view all the answers

Which type of junction is primarily responsible for cell-cell communication?

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

What is the main role of the sodium-potassium pump in neurons?

<p>To create resting membrane potential (A)</p> Signup and view all the answers

What effect does depolarization have on the membrane potential?

<p>Reduces charge separation (D)</p> Signup and view all the answers

Which of the following correctly describes the action of the sodium-potassium pump?

<p>Uses ATP hydrolysis to actively transport ions against their gradients (C)</p> Signup and view all the answers

In which scenario does calcium primarily move into the cell?

<p>When extracellular calcium concentration is significantly lower (C)</p> Signup and view all the answers

What charge is typically associated with the inside of a cell relative to the outside?

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

Which type of transport protein is characterized by high capacity for transporting inorganic ions?

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

What primarily determines the resting membrane potential of excitable cells?

<p>Equilibrium potentials of potassium (C)</p> Signup and view all the answers

Which mechanism allows potassium ions to move out of the cell at rest?

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

In carrier proteins, what is the key process that allows the transport of specific substances across the membrane?

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

What is the characteristic of membrane proteins in terms of selective permeability in a typical mammalian cell?

<p>Allow selective permeability mostly to potassium ions (D)</p> Signup and view all the answers

Which type of carrier protein transports two different ions in the same direction?

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

Which condition is true for ion movements during resting potential?

<p>Potassium efflux primarily causes the negative charge inside the cell (C)</p> Signup and view all the answers

What distinguishes ion channel proteins from carrier proteins in the context of transport?

<p>Ion channels transport molecules at a higher rate than carrier proteins (D)</p> Signup and view all the answers

What is the term for the state where electrochemical forces are balanced within a cell membrane?

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

What drives the efflux of potassium ions out of a resting excitable cell?

<p>Concentration gradient favoring the efflux (A)</p> Signup and view all the answers

Which ions are primarily involved in establishing the resting membrane potential of an excitable cell?

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

What role do active ion transporters play in a cell membrane?

<p>They maintain concentration gradients against the flow (A)</p> Signup and view all the answers

The resting membrane potential of a mammalian cell is primarily close to which equilibrium potential?

<p>-80mV (D)</p> Signup and view all the answers

Which of the following best describes how the sodium-potassium pump contributes to membrane potential?

<p>Moves potassium ions into the cell and sodium ions out, depleting energy (C)</p> Signup and view all the answers

What is the expected effect of increased Cl- permeability on muscle contractility?

<p>Reduce muscle contractility (D)</p> Signup and view all the answers

Which fatty acid would typically have the lowest melting temperature?

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

What is the role of membrane lipids in relation to bioactive signaling molecules?

<p>Serve as a store of bioactive signaling molecules (C)</p> Signup and view all the answers

How do w-6 and w-3 fatty acids differ in terms of their eicosanoid profiles?

<p>w-6 fatty acids generally produce pro-inflammatory eicosanoids (D)</p> Signup and view all the answers

What does the term 'electrochemical gradient' define?

<p>The difference in concentration and charge across the membrane (D)</p> Signup and view all the answers

What physiological effects do eicosanoids primarily influence?

<p>Inflammatory and immune responses (C)</p> Signup and view all the answers

Which of the following ion concentrations is typically higher outside the cell than inside?

<p>Na+ (Sodium) (D)</p> Signup and view all the answers

What is the primary mechanism for actively transporting ions across the cell membrane?

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

What structural aspect of the cell membrane contributes to its designation as a 'fluid mosaic'?

<p>It is a flexible layer of lipids with proteins interspersed throughout. (A)</p> Signup and view all the answers

How do fatty acids in the cell membrane influence its fluidity?

<p>Through their length and degree of saturation affecting membrane characteristics. (B)</p> Signup and view all the answers

Why is membrane fluidity important for ion channels?

<p>It facilitates shape changes of ion channels for easier ion movement. (B)</p> Signup and view all the answers

What is the role of eicosanoids in cellular function?

<p>To act as bioactive signaling molecules affecting cellular activities. (B)</p> Signup and view all the answers

What does the selective permeability of cell membranes enable?

<p>Regulation of ion concentrations and responses to environmental changes. (B)</p> Signup and view all the answers

Which process primarily establishes an electrical potential across the cell membrane?

<p>Selectively moving ions through channels and transporters. (A)</p> Signup and view all the answers

What effect does an influx of Na+ ions have on a nerve cell?

<p>It initiates depolarization, promoting an action potential. (D)</p> Signup and view all the answers

What defines the role of selective channels in cell membranes?

<p>They specifically regulate the movement of certain ions based on concentration gradients. (A)</p> Signup and view all the answers

Flashcards

Lipid bilayer

The basic structure of a cell membrane, made up of two layers of phospholipids.

Phospholipid structure

Has a hydrophilic head (attracts water) and two hydrophobic tails (repel water).

Membrane fluidity

The ability of the cell membrane to change shape; affected by fatty acid structure.

Fatty acid type effect

Different fatty acids (saturated vs. unsaturated) affect membrane fluidity and melting points.

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Transmembrane proteins

Proteins that span the cell membrane, performing various functions.

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Cell membrane function

Regulates what enters and exits the cell, enabling communication.

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Glycolipids

Lipids with attached carbohydrate chains; involved in cell communication

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Eicosanoids

Hormone-like molecules derived from fatty acids.

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Sodium-potassium pump

A protein that actively transports sodium ions out of the cell and potassium ions into the cell using ATP.

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Electrogenic pump

A pump that contributes to the resting membrane potential by creating an imbalance of charge across the cell membrane.

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Resting membrane potential

The difference in electrical charge across the cell membrane when the cell is not actively transmitting a signal.

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Depolarization

A reduction in the difference in electrical charge across the cell membrane, making it more positive.

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Hyperpolarization

An increase in the difference in electrical charge across the cell membrane, making it more negative.

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Plasma Membrane Barrier

The lipid bilayer of the cell membrane acts as a barrier, preventing most water, ions, and hydrophilic molecules from passing through. However, it allows hydrophobic materials and gases to cross.

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Membrane Transport Proteins

These proteins embedded within the plasma membrane facilitate the movement of water, ions, and hydrophilic molecules across the membrane, overcoming the barrier created by the lipid bilayer.

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Ion Channel

A type of membrane transport protein that forms pores across the membrane, allowing specific inorganic ions, like sodium (Na+), potassium (K+), and chloride (Cl-), to pass through.

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Carrier Protein

Another type of membrane transport protein that binds to specific molecules, such as glucose, amino acids, or ions, undergoes a conformational change, and then releases the molecule on the other side of the membrane.

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Ion Channel Capacity

Ion channels can transport a very high number of ions per second (up to 10^8 ions/second).

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Carrier Protein Capacity

Carrier proteins have a lower transport capacity compared to ion channels, moving 10^2-10^3 molecules per second.

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Uniport

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

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Symport

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

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Antiport

A carrier protein that transports two different molecules or ions in opposite directions across the membrane.

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Concentration Gradient

The difference in concentration of a substance between two regions, such as inside and outside the cell.

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Ionic Gradient

The difference in concentration of ions across the cell membrane, influenced by factors such as active pumps and membrane permeability.

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K+ Efflux

The movement of potassium ions (K+) out of the cell, driven by the concentration gradient and contributing to the establishment of the resting membrane potential.

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Selective Permeability

The cell membrane allows some substances to pass through more easily than others, contributing to the establishment of the membrane potential.

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Equilibrium Potential (Eion)

The membrane potential at which the electrical and concentration gradients for a specific ion are balanced, so there is no net movement of that ion across the membrane.

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Fluid Mosaic Model

Describes the cell membrane as a flexible structure with various proteins embedded within a lipid bilayer.

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Electrical Potential Difference

The difference in electrical charge across the cell membrane, established by the uneven distribution of ions.

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How does membrane fluidity affect ion channels?

A more fluid membrane allows ion channels to change shape more easily, enabling the passage of ions.

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Fatty Acid Structure

A long chain of carbon atoms with a carboxyl group at one end. The number and position of double bonds determine its properties.

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Double Bond Effect

Presence of a double bond in a fatty acid makes it unsaturated, lowering its melting point and increasing membrane fluidity.

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Eicosanoid Pathway

A series of enzymatic reactions that convert arachidonic acid into various bioactive signaling molecules.

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Electrochemical Gradient

The combined influence of concentration differences and electrical potential across a membrane on the movement of ions.

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Passive Transport

Movement of substances across a membrane without energy expenditure, driven by concentration or electrochemical gradients.

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Facilitated Transport

Movement of substances across a membrane with the assistance of proteins, but still driven by concentration or electrochemical gradients.

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Active Transport

Movement of substances across a membrane against their concentration or electrochemical gradients, requiring energy expenditure.

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Study Notes

Cell Membranes 1

  • Cell membranes, though diverse, share a basic structure
  • These membranes are formed by a lipid bilayer
  • The lipid bilayer also includes proteins and glycolipids
  • The structure is a selective barrier for material flow

Phospholipids

  • Phospholipids are the fundamental components of the lipid bilayer
  • Phospholipids consist of a hydrophilic head and hydrophobic tails
  • These molecules arrange themselves in a bilayer in the cell membrane
  • The hydrophilic heads face the aqueous environments inside and outside the cell
  • The hydrophobic tails cluster together within the membrane

The Lipid Bilayer

  • The arrangement of fatty acids dictates fluidity
  • The fluidity of the bilayer impacts electrical activity within the cell
  • Shapes and melting points of lipids are critical
  • Differences in lipid structure explain the various "good" and "bad" fats

Stearic Acid

  • Stearic acid, a saturated fatty acid, is a key component of animal fats like lard.
  • Its melting point of 69°C makes it solid at room temperature
  • Characterized by distinct α, β, and ω carbon atoms

Oleic Acid

  • Oleic acid is a monounsaturated fatty acid—having one double bond
  • It is a cis isomer, which leads to a "bent" shape and different fluid properties, compared to its trans isomer
  • Many naturally occurring fats are oleic acid ligands.
  • The shape and properties can influence how these substances interact with cellular processes, potentially impacting health in ways like their effect on affinities

Polyunsaturates

  • Arachidonic acid (ω-6) is a part of this category, other fats can be processed into Arachidonic Acid
  • These fats are sources for Eicosanoids
  • Docasahexanoic acid (DHA) and Eicosapentaenoic acid (EPA) are omega-3 fatty acids, including double bonds, common in fish oils
  • These fatty acids have lower melting points compared to saturated fats
  • They are stored within cellular membranes and involved in the production of eicosanoids

Fluidity

  • The fluidity of the membrane greatly correlates with ion channel activity.
  • Ion channels are transmembrane proteins
  • Changes in membrane fluidity affect the shape and functioning of these proteins
  • Fluidity can influence the enhancement of conduction across the membrane

Eicosanoids

  • Bioactive lipids, including prostaglandins, leukotrienes, and thromboxanes are Eicosanoids.
  • They are involved in various processes including inflammation and cardiovascular function
  • They play vital roles in controlling blood pressure, blood clotting, immune response, and other bodily processes like sleep cycles
  • These molecules are involved in various physiological functions within the body

Cyclic and Linear Pathways

  • Eicosanoids are formed through cyclic and linear pathways.
  • The pathways involve enzymes like cyclooxygenase and lipoxygenase
  • These enzymes catalyze the reactions that produce different kinds of eicosanoids
  • Various pathways result in a diverse range of eicosanoid molecules involved in cellular processes

Important Eicosanoids

  • Prostacyclin and TXA2 are important eicosanoids in cardiovascular health
  • The balance between these two influences vascular health
  • TXA2's role in vasoconstriction and platelet activation can contribute to thrombosis
  • Prostacyclin is an antagonistic molecule, inhibiting platelet activity and promoting vessel relaxation

Receptors

  • Various signaling molecules interact with membrane receptors (e.g., COX1, COX2) to produce certain eicosanoids
  • The pathways involved in the production of eicosanoids can involve several steps
  • Receptors play important roles in mediating cellular responses to a variety of stimuli

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PL1003 Cell Membranes Learning Outcomes PDF

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