What are the main components of the cell membrane, and what is their approximate percentage composition?

Lipids (40%), Proteins (55%), Carbohydrates (3%)

In the fluid mosaic model, how do integral proteins interact with the lipid bilayer?

Integral proteins are embedded in the membrane via hydrophobic interactions and may span the membrane.

What is the role of cholesterol in the cell membrane?

Cholesterol stabilizes the membrane at 37°C, maintaining permeability and fluidity.

Describe the structure and function of lysosomes.

Lysosomes digest cellular waste materials.

• Contain acid hydrolases.

• Degrade worn-out organelles.

• Involved in intracellular digestion.

What distinguishes rough endoplasmic reticulum (RER) from smooth endoplasmic reticulum (SER)?

RER has ribosomes on its surface, while SER is agranular and involved in lipid synthesis and detoxification.

How does the Na⁺-K⁺ ATPase pump contribute to resting membrane potential?

It pumps 3 Na⁺ out and 2 K⁺ in per ATP hydrolyzed, establishing concentration gradients that contribute to RMP.

What is the significance of the Gibbs-Donnan equilibrium in cellular physiology?

It describes the distribution of permeant ions across a membrane due to the presence of impermeant ions, leading to electroneutrality.

Which type of transport requires energy and moves substances against their concentration gradient?

Active transport requires energy and moves substances against their concentration gradient.

What factors influence membrane fluidity according to the fluid mosaic model?

Temperature, lipid composition (unsaturated vs. saturated fatty acids), and cholesterol content influence membrane fluidity.

Describe the composition and function of microtubules.

Microtubules are polar structures made of α- and β-tubulin, involved in intracellular transport and the formation of cilia and the mitotic spindle.

What is the primary role of ribosomes within the cell?

Ribosomes are responsible for protein synthesis.

How does the permeability of cell membranes vary among different ions?

Cell membranes vary in ion permeability.

• K⁺ is most permeable.

• Na⁺ permeability is lower.

• Cl⁻ has minimal permeability.

What mechanism allows for the rapid diffusion of ions through the cell membrane?

Channel proteins facilitate the rapid diffusion of ions through selective pores in the membrane.

What distinguishes primary active transport from secondary active transport?

Primary transport uses ATP directly.

• Direct ATP usage for movement.

• Secondary relies on gradients.

• Key in cellular transport processes.

Explain the function of desmosomes in cellular structure.

Desmosomes provide structural support by anchoring intermediate filaments between adjacent cells.

What types of junctions allow for intercellular communication?

Gap junctions allow for the passage of ions and small molecules between cells, facilitating intercellular communication.

What role do peroxisomes play in cellular metabolism?

Peroxisomes break down fatty acids, detoxify hydrogen peroxide, and participate in gluconeogenesis.

In terms of ion equilibrium potentials, what is the typical value for K⁺?

The equilibrium potential for K⁺ is approximately -90 mV.

How does hyperkalemia affect resting membrane potential?

Hyperkalemia decreases resting membrane potential, making it less negative due to reduced K⁺ efflux.

What is the function of the Golgi apparatus in cellular processes?

The Golgi apparatus processes and packages proteins and lipids for secretion or delivery to other organelles.

Describe the primary characteristic of graded potentials.

Graded potentials have variable amplitude and are conducted decrementally over short distances without a threshold.

What is the primary function of the centrosome during cell division?

The centrosome organizes microtubules and facilitates chromosome movement during cell division.

What is the effect of temperature on membrane fluidity?

Higher temperatures increase membrane fluidity by transitioning the state of lipids from ordered to disordered.

What is the reflection coefficient, and how does it modify osmotic pressure?

Reflection coefficient affects osmotic pressure.

• Quantifies membrane permeability.

• σ = 0 is freely permeable.

• σ = 1 is impermeable.

Explain the role of aquaporins in cellular water transport.

Aquaporins are channel proteins that facilitate rapid water transport across the cell membrane.

What defines the resting membrane potential (RMP) in neurons?

RMP is defined as the voltage difference across the membrane at rest, typically around -70 mV.

How do Na⁺ channel mutations affect neuronal excitability?

Na⁺ channel mutations can alter the threshold for action potential generation, impacting neuronal excitability and signal propagation.

What types of molecules can diffuse through the lipid bilayer without assistance?

Small nonpolar molecules such as O₂ and CO₂ can diffuse rapidly through the lipid bilayer.

Identify the primary factors that contribute to the maintenance of resting membrane potential.

The concentration gradients of ions, particularly Na⁺ and K⁺, and the activity of the Na⁺-K⁺ ATPase pump are primary factors.

How does the presence of impermeant ions affect osmotic pressure across a membrane?

The presence of impermeant ions increases osmotic pressure on the side of the membrane containing these ions, affecting water movement.

Which organelle is responsible for ATP synthesis, and how does its structure facilitate this function?

Mitochondria are responsible for ATP synthesis; their inner membrane contains cristae that increase surface area for oxidative phosphorylation.

What distinguishes constitutive exocytosis from regulated exocytosis?

Constitutive exocytosis involves rapid transport with minimal processing, while regulated exocytosis requires specific signals for vesicle release.

What is the primary mechanism by which clathrin-mediated endocytosis occurs?

Clathrin-mediated endocytosis occurs through the formation of clathrin-coated pits that internalize receptors and ligands.

Describe the impact of hypokalemia on resting membrane potential.

Hypokalemia increases resting membrane potential, making it more negative due to reduced extracellular K⁺ concentration.

What is the function of the smooth endoplasmic reticulum in a cell?

The smooth endoplasmic reticulum is involved in lipid synthesis, steroid hormone production, and detoxification processes.

What is the primary role of the Na⁺-K⁺ ATPase pump in cellular physiology?

Maintains concentration gradients for Na⁺ and K⁺ by pumping 3 Na⁺ out and 2 K⁺ in per ATP hydrolyzed.

Which type of transport mechanism allows glucose to move across the cell membrane against its concentration gradient?

Secondary Active Transport, such as sodium-linked glucose transport (SGLT).

How does the presence of cholesterol influence membrane fluidity at temperatures above the transition temperature (Tm)?

Cholesterol decreases membrane fluidity by stabilizing the membrane structure.

What is the significance of the Gibbs-Donnan equilibrium in relation to ion distribution across a semipermeable membrane?

Gibbs-Donnan equilibrium affects ion distribution.

• Non-diffusible ions influence balance.

• Creates ion concentration gradients.

• Essential for cellular functions.

In the context of action potentials, what does depolarization refer to?

It refers to the process where the membrane potential becomes less negative, moving from a resting value (e.g., -70 mV) towards a more positive value.