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?

Trans fats and fats with altered affinities Signup and view all the answers

What are eicosanoids derived from?

Arachidonic acid and other polyunsaturated fatty acids Signup and view all the answers

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

Ion channels that require shape changes Signup and view all the answers

What is the significance of glycolipids in cell membranes?

They contribute to membrane structure and cellular recognition. Signup and view all the answers

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

Gap junctions Signup and view all the answers

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

To create resting membrane potential Signup and view all the answers

What effect does depolarization have on the membrane potential?

Reduces charge separation Signup and view all the answers

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

Uses ATP hydrolysis to actively transport ions against their gradients Signup and view all the answers

In which scenario does calcium primarily move into the cell?

When extracellular calcium concentration is significantly lower Signup and view all the answers

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

Negative Signup and view all the answers

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

Ion channels Signup and view all the answers

What primarily determines the resting membrane potential of excitable cells?

Equilibrium potentials of potassium Signup and view all the answers

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

Simple diffusion Signup and view all the answers

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

Conformational change Signup and view all the answers

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

Allow selective permeability mostly to potassium ions Signup and view all the answers

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

Symport Signup and view all the answers

Which condition is true for ion movements during resting potential?

Potassium efflux primarily causes the negative charge inside the cell Signup and view all the answers

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

Ion channels transport molecules at a higher rate than carrier proteins Signup and view all the answers

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

Equilibrium potential Signup and view all the answers

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

Concentration gradient favoring the efflux Signup and view all the answers

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

Potassium and Sodium Signup and view all the answers

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

They maintain concentration gradients against the flow Signup and view all the answers

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

-80mV Signup and view all the answers

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

Moves potassium ions into the cell and sodium ions out, depleting energy Signup and view all the answers

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

Reduce muscle contractility Signup and view all the answers

Which fatty acid would typically have the lowest melting temperature?

Docosahexaenoic acid Signup and view all the answers

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

Serve as a store of bioactive signaling molecules Signup and view all the answers

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

w-6 fatty acids generally produce pro-inflammatory eicosanoids Signup and view all the answers

What does the term 'electrochemical gradient' define?

The difference in concentration and charge across the membrane Signup and view all the answers

What physiological effects do eicosanoids primarily influence?

Inflammatory and immune responses Signup and view all the answers

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

Na+ (Sodium) Signup and view all the answers

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

Active transport Signup and view all the answers

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

It is a flexible layer of lipids with proteins interspersed throughout. Signup and view all the answers

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

Through their length and degree of saturation affecting membrane characteristics. Signup and view all the answers

Why is membrane fluidity important for ion channels?

It facilitates shape changes of ion channels for easier ion movement. Signup and view all the answers

What is the role of eicosanoids in cellular function?

To act as bioactive signaling molecules affecting cellular activities. Signup and view all the answers

What does the selective permeability of cell membranes enable?

Regulation of ion concentrations and responses to environmental changes. Signup and view all the answers

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

Selectively moving ions through channels and transporters. Signup and view all the answers

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

It initiates depolarization, promoting an action potential. Signup and view all the answers

What defines the role of selective channels in cell membranes?

They specifically regulate the movement of certain ions based on concentration gradients. Signup and view all the answers

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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