Cell Membrane Functions

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Questions and Answers

What is the primary factor that influences the rate of diffusion, according to Fick's Law?

Surface area of the membrane

Molecular weight of the substance

Lipid solubility of the substance

Concentration gradient of the substance (correct)

Which of the following is NOT a characteristic of unassisted membrane transport diffusion?

It only occurs if the substance can cross the membrane

It is a passive mechanism

It always moves from an area of high to low concentration

It requires energy input (correct)

What type of hormones can move into cells passively?

Amino acid hormones

Peptide hormones

Protein hormones

Steroid hormones (correct)

What is the term for the movement of water down its own concentration gradient through a semipermeable membrane?

Osmosis Signup and view all the answers

What is the term for the difference in concentration of non-penetrating solutes between two solutions?

Tonicity Signup and view all the answers

What is the formula for the rate of diffusion, according to Fick's Law?

Rate = (SA x CG)/ TW Signup and view all the answers

What happens to a cell in a hypotonic solution?

It bursts Signup and view all the answers

What is the function of membrane-spanning proteins in carrier-mediated transport?

To bind and transport specific substances Signup and view all the answers

What is the maximum rate of transport by a carrier protein?

Tm Signup and view all the answers

Which type of transport involves the movement of a substance from high to low concentration?

Facilitated diffusion Signup and view all the answers

What happens to the carrier protein after the solute molecule binds to it in facilitated diffusion?

It changes conformation to release the solute Signup and view all the answers

What is the purpose of GLUT4 in adipose muscles?

To facilitate glucose uptake Signup and view all the answers

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

To separate the cell from its environment and prevent toxic waste buildup Signup and view all the answers

What is the main characteristic of the fluid mosaic model of the cell membrane?

A fluid structure with a dynamic arrangement of proteins and lipids Signup and view all the answers

What is the function of intrinsic proteins in the cell membrane?

To span the entire width of the membrane and function as self-identity markers Signup and view all the answers

What is the purpose of cholesterol in the cell membrane?

To provide fluidity and stability to the membrane Signup and view all the answers

What is the function of glycoproteins in the cell membrane?

To function as self-identity markers and help with cell differentiation Signup and view all the answers

What type of protein is aquaporin?

Water channel Signup and view all the answers

What is the function of cell adhesion molecules (CAMs) in the cell membrane?

To help with the adhesion of cells to each other Signup and view all the answers

What is the term for the entire structure of cells, tissues, organs, and systems that make up an organism?

Organism Signup and view all the answers

What is the term for the process of cells working together to provide signals on what needs to happen?

Cell signaling Signup and view all the answers

What is the function of the phospholipid bilayer in the cell membrane?

To form a barrier that separates the cell from its environment Signup and view all the answers

What is the effect of acetylcholine binding to its receptor on the voltage-gated ion channel?

It opens the channel, allowing Na+ flow in. Signup and view all the answers

What is the purpose of the Na+/K+ ATPase pump in generating the resting membrane potential?

To pump 3 Na+ out and 2 K+ in. Signup and view all the answers

What is the equilibrium potential of K+ (Ek+)?

-90 mV Signup and view all the answers

What is the general mechanism of second messenger pathways?

The first messenger binds to a receptor, releasing a second messenger, which then relays the signal. Signup and view all the answers

What is the primary mechanism by which sodium ions are transported out of the blood?

Active transport Signup and view all the answers

What is the purpose of leak channels for Na and K ions?

To passively allow diffusion down their concentration gradients. Signup and view all the answers

Which type of transport involves the movement of molecules down their concentration gradient?

Facilitated diffusion Signup and view all the answers

Why is the equilibrium potential for Na+ lower than for K+?

Because the concentration gradient for Na+ is smaller than for K+. Signup and view all the answers

What is the primary function of Na+/K+ ATPase in the kidney?

To regulate the concentration of sodium ions outside the cell Signup and view all the answers

Which type of vesicular transport involves the non-selective uptake of extracellular fluid?

Pinocytosis Signup and view all the answers

What is the primary function of exocytosis in the cell?

To secrete neurotransmitters and hormones Signup and view all the answers

Which type of cell communication involves the direct contact of plasma membranes between cells?

Juxtacrine signaling Signup and view all the answers

What is the primary function of lipid-soluble chemical messengers in signal transduction?

To cross the plasma membrane and affect gene transcription Signup and view all the answers

What is the primary function of ion channels in the cell?

To allow ions to move into the cell and affect physiological responses Signup and view all the answers

Which type of ion channel is always open and allows for the leakage of ions into and out of the cell?

Leak channel Signup and view all the answers

What is the primary function of ligand-gated ion channels in the cell?

To open and close in response to stimuli Signup and view all the answers

Study Notes

Passive Transport

Passive transport occurs without energy input, allowing substances to move from high to low concentration
Types of passive transport:
- Diffusion: movement of substances from high to low concentration
- Osmosis: movement of water molecules from high to low concentration

Facilitated Diffusion

Facilitated diffusion is a type of carrier-mediated transport
Carrier proteins bind to specific substances and transport them across the membrane
Characteristics:
- Specificity: each carrier protein binds to specific substances
- Saturation: finite number of carrier proteins, leading to saturation
- Competition: multiple substances competing for same carrier protein
Examples:
- GLUT4: facilitates glucose transport into adipose and muscle cells
- Insulin stimulates GLUT4 insertion into cell membrane

Active Transport

Active transport moves substances from low to high concentration, requiring energy input
Examples:
- Iodine uptake in thyroid gland cells
- Sodium-potassium pump (Na+/K+ ATPase) maintains ion balance

Cell Membrane Structure

Fluid mosaic model: flexible and dynamic structure with integral and peripheral proteins
Components:
- Phospholipids: amphipathic molecules forming bilateral layer
- Cholesterol: maintains fluidity and stability
- Carbohydrates: attached to lipids or proteins, functioning as identity markers
Functions:
- Physical barrier
- Homeostasis maintenance
- Mechanical barrier
- Adhesion between cells
- Cell signaling

Membrane Proteins

Types:
- Intrinsic (integral): spanning the membrane
- Extrinsic (peripheral): attached to one side of the membrane
Functions:
- Aquaporins: water channels
- Ion channels: selective ion transport
- Carrier molecules: facilitated diffusion
- Receptors: binding specific molecules
- Enzymes: performing physiological activities
- Cell adhesion molecules (CAMs): adhering cells together

Cell-Cell Adhesions

Cell-cell adhesions form tissues, organs, and systems
Extracellular matrix (ECM) components:
- Proteins
- Polysaccharides
- GAGs
Functions:
- Adhesion
- Signaling
- Mechanical support

Second Messenger Pathways

Second messenger relays signals inside the cell
Amplifies initial response through a signaling cascade
Two major pathways:
- Cyclic AMP
- Ca2+/DAG

Membrane Potential

Plasma membrane is polarized electrically, with a potential difference across the membrane
Generation of RMP (-70mV) due to unequal distribution of Na+, K+, and anions
Membrane potential is the capacity to do work, measured in millivolts (mV)

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Description

Learn about the crucial functions of the cell membrane, including its role as a physical barrier, maintaining homeostasis, and facilitating exchange of nutrients and wastes. Discover how it responds to environmental changes and signals, and how it knows when to produce an enzyme.