Cell Biology: Plasma Membrane and Transport Mechanisms

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Questions and Answers

What is the primary role of the plasma membrane in a cell?

Facilitates communication between cells

Stores energy in the form of ATP

Regulates the entry and exit of substances (correct)

Contains the genetic material of the cell

Which statement best describes the relationship between the extracellular fluid (ECF) and intracellular fluid (ICF) in cells?

The ECF and ICF are always in equilibrium.

They have identical compositions.

Their constituents and states are different. (correct)

The ICF acts as a waste disposal system for the ECF.

What does it mean for cells to have specialized functions in a multicellular organism?

Every cell can perform every task necessary for organism survival.

Some cells can replicate indefinitely while others cannot.

Specialized cells do not share any common functions.

Cellular functions are integrated through interactions among specialized cells. (correct)

Why might all cells have the same DNA, but not express all genes?

Cellular differentiation results in selective gene expression. Signup and view all the answers

Which mechanism is NOT involved in transport across the cell membrane?

Skeletal movement Signup and view all the answers

What percentage of body weight is constituted by Extra-cellular Fluid (ECF)?

20% Signup and view all the answers

Which compartment of ECF contains the largest volume of fluid?

Interstitial fluid Signup and view all the answers

What is the main cation found in the Extra-cellular Fluid (ECF)?

Na+ Signup and view all the answers

Which of the following best describes the role of the Na+-K+ pump?

Maintaining intracellular K+ levels Signup and view all the answers

Which anion primarily remains outside the cells due to the Donnan effect?

Cl- Signup and view all the answers

What percentage of body weight does Intra-cellular Fluid (ICF) represent?

40% Signup and view all the answers

What key factor leads to the distribution of solutes in body fluid compartments?

Electrochemical and osmotic activity Signup and view all the answers

Which transport mechanism requires energy to move substances across the cell membrane?

Active transport Signup and view all the answers

What is the main function of microtubules in a cell?

Maintenance of cell shape and enabling movement Signup and view all the answers

What is the structure of centrioles?

Nine sets of three fused microtubules Signup and view all the answers

Which type of granules is most common in cells?

Glycogen granules Signup and view all the answers

What is the primary role of the nuclear envelope?

Separating the nucleus from the cytoplasm Signup and view all the answers

What is chromatin composed of?

Coiled DNA and protein Signup and view all the answers

What is a characteristic of the nucleolus?

Composed of ribosomal RNA and granules Signup and view all the answers

Which components make up the cell membrane?

Phospholipids, cholesterol, and proteins Signup and view all the answers

What function do messenger RNA molecules serve in relation to the nuclear pores?

Passing from the nucleus to the cytoplasm Signup and view all the answers

What is a characteristic of positive feedback mechanisms?

They amplify responses and processes. Signup and view all the answers

How does a feed forward mechanism function in the body?

It senses disturbances and anticipates changes. Signup and view all the answers

What does allostasis emphasize in physiological responses?

The ability to maintain stability through adaptation. Signup and view all the answers

Which of the following is NOT an example of positive feedback?

Regulation of body temperature. Signup and view all the answers

What might be a consequence of an excessive positive feedback loop in biological systems?

Heightened risk of system failure. Signup and view all the answers

What is the main role of allostasis in the body?

To adapt to diverse and dangerous situations. Signup and view all the answers

What does allostatic load primarily refer to?

The cost of adapting to stress over time. Signup and view all the answers

Which of the following is a manifestation of allostatic load?

Increased risk for cardiovascular disease. Signup and view all the answers

How does overstimulation by frequent stress affect the body?

It results in excessive exposure to stress hormones. Signup and view all the answers

What could be a consequence of failing to inhibit allostatic responses when not needed?

Increased allostatic load. Signup and view all the answers

Which type of stress mediators is associated with allostatic regulation?

Catecholamines and cortisol. Signup and view all the answers

What may result from inefficient management of allostatic responses?

Accumulation of stress-related health issues. Signup and view all the answers

Which hormone is primarily involved in the body's stress response through allostasis?

Adrenaline. Signup and view all the answers

What characterizes pinocytosis in cellular transport mechanisms?

Formation of vesicles through membrane invagination Signup and view all the answers

Which statement correctly describes exocytosis?

It releases substances such as hormones and enzymes. Signup and view all the answers

What is the primary purpose of homeostasis within an organism?

To maintain a state of internal balance Signup and view all the answers

Which component is NOT part of the homeostatic regulation process?

Mitotic apparatus Signup and view all the answers

In negative feedback mechanisms, what occurs in response to a discrepancy from the set point?

The outputs work to oppose the deviation Signup and view all the answers

Which of the following is a form of intrinsic regulation in the body?

Local tissue adjustments Signup and view all the answers

What is the main role of receptors in homeostasis?

Detecting changes in the internal environment Signup and view all the answers

Which feedback mechanism amplifies responses rather than opposing them?

Positive feedback Signup and view all the answers

What mechanism is involved in the regulation of temperature as part of homeostasis?

Negative feedback mechanisms Signup and view all the answers

Which system is primarily responsible for rapid adjustments to changes in the body?

Nervous system Signup and view all the answers

In the context of physiological adjustments, allostasis refers to:

Changing to cope with new conditions Signup and view all the answers

Which structure assesses and discriminates transmitted signals in a homeostatic loop?

Integrating center Signup and view all the answers

What does the error signal represent in homeostatic regulation?

Deviations from measured values to the set point Signup and view all the answers

Which system is involved in long-lasting metabolic adjustments?

Endocrine system Signup and view all the answers

Study Notes

Introduction to Human Physiology

Human physiology integrates the functions of all the body's cells, tissues, and organs into a whole.
Separate organs and systems work together to maintain the body's proper function.
Feedback controls are crucial for maintaining necessary balances.

Cell Physiology

The Cell: The smallest, self-replicating unit of integrated physiological function.
- Specialized cells work together in a complex organism.
- Functional integration results from interactions between specialized cells.
Cell Components:
- Plasma membrane: Serves as a permeability barrier, determining what enters and leaves the cell.
- Extracellular fluid (ECF) and intracellular fluid (ICF) have different compositions.
- All cells have the same DNA, but not all genes are expressed equally.
- The organism is composed of cooperating cell types, each contributing unique functions to the whole.
Cell Composition:
- CHOS: ~3% of dry mass
- Lipids: ~40% of dry mass
- Proteins: ~50-60% of dry mass
- Nucleic acids: DNA + RNA
Cell Functions:
- Obtain food and oxygen from surroundings
- Eliminate waste products
- Perform various chemical reactions
- Synthesize materials for cellular structure, growth, and function
- Respond to changes in surroundings
- Reproduce (most cells, excluding nerve and muscle cells)
- Move materials in and out of the cell and within the cell to carry out cellular activities.
Cell Organelles:
- Non-membrane limited: Chromosomes, Nucleoli, Ribosomes, Microtubules, Microfilaments, Centrioles
- Membrane limited: Nucleus, Endoplasmic reticulum (ER), Golgi apparatus (GA), Lysosomes, Mitochondria, Peroxisomes
Plasma Membrane Details:
- 7.5nm thick
- Composed of a phospholipid bilayer and protein
- Selective barrier to ion/molecule movement
Mitochondria:
- Rod- or oval-shaped, double-membraned organelles
- Major site of ATP production, oxygen utilization, and CO2 formation
- Contain enzymes of the Krebs cycle and oxidative phosphorylation
Endoplasmic Reticulum:
- Interconnected cell organelle with two opposing membranes
- Granular ER: Ribosomal particles bound to ER membrane, synthesizes proteins meant for secretion.
- Agranular ER: No ribosomes, synthesizes fatty acids and steroid hormones, stores calcium in muscle cells
Golgi Apparatus:
- Cup-shaped membranous sacs and vesicles
- Modifies and concentrates proteins prior to secretion
Secretory Vesicles:
- Membrane-bound sacs with concentrated protein solutions
- Release proteins into the environment
Lysosomes:
- Density-staining oval bodies with hydrolytic enzymes
- Digest engulfed bacteria and damaged cell organelles
Peroxisomes:
- Play essential roles in metabolism and ROS (reactive oxygen species) detoxification
Free Ribosomes:
- 20nm particles of RNA and protein
- Assemble amino acids into proteins for intracellular use
Bound Ribosomes/Filaments:
- Attached to the granular endoplasmic reticulum
- Composed of protein threads, involved in protein synthesis for secretion and cell movements
- Support at cell junctions
Microtubules:
- Protein tubules with a hollow core (25nm diameter)
- Maintain cell shape (cytoskeleton)
- Associated with cilia, flagella, and the mitotic spindle
Centrioles:
- Two small cylindrical bodies with fused microtubules
- Form the spindle apparatus during cell division
- Involved in cilia formation and movement
Granules:
- Aggregates of chemical substance crystals
- Store specialized end products of metabolism, glycogen granules most common.
Fat droplets:
- Spherical globules of triacylglycerol
- Store fat
Nuclear Envelope:
- Surrounds the nucleus with two membranes
- Nuclear pores (50-70 nm) control molecule movement.
- Messenger RNA exits through pores.
Chromatin:
- Coiled DNA and protein threads
- 46 strands per human cell nucleus
- Stores genetic information
- Condenses into chromosomes during cell division
Nucleolus:
- Coiled filamentous structure containing granules
- Not membrane bound
- Site of ribosomal RNA (rRNA) synthesis

Cell Membrane

Composition:
- Lipids: Phospholipids and cholesterol
- Proteins: Peripheral and integral
- Carbohydrates: Polysaccharides
Lipids:
- Phospholipids: Amphipathic molecules, glycerol backbone, hydrophobic tails, hydrophilic head; form a bilayer.
Proteins:
- Peripheral: hydrophilic, loosely attached, regulate cell function
- Integral: partly hydrophillic and hydrophobic, embedded, transport molecules, receptors.
Carbohydrates:
- Hydrophilic polysaccharides bound to proteins or lipids ( glycoproteins and glycolipids)
Ion Channels:
- Leak: continuously open
- Voltage-gated: regulated by membrane potential changes
- Ligand-gated: regulated by chemical signals

Cellular Connections

Tight junctions (zonula occludens): Intercellular complexes controlling paracellular permeability, forming borders between apical and basolateral domains in polarized epithelia.
Gap junctions: Clusters of intercellular channels facilitating direct ion and small molecule diffusion between adjacent cells, formed by connections (connexons) of trans-membrane proteins (connexins).
Desmosomes: Intercellular junctions anchoring intermediate filaments to the plasma membrane, critical for stable cell-cell adhesion in tissues experiencing structural stress.
Adherence junctions (zonula adherens): Cell-cell adhesion complexes allowing for responses to forces and changes in the microenvironment and providing strong mechanical attachments

Cellular Communication

Cells detect environmental changes by using membrane-embedded receptors.
Mechanisms of chemical signaling include autocrine, paracrine, synaptic, endocrine, and neuroendocrine mechanisms

Body Fluid Composition and Electrolyte Balance

**Body Fluid Compartments:**Plasma membrane separates ICF and ECF
- ECF (extracellular fluid): fluids in blood vessels, interstitial fluid, and transcellular fluid.
- ICF (intracellular fluid): fluid inside cells
Fluid composition: Main cations in ECF = Na+; ICF = K+
- Na(+)-K(+)-ATPase is crucial in maintaining these different concentrations.
- Main anions in ECF = Cl-, HCO3-; Anions in ICF = proteins and phosphates.
Distribution of solutes: based on electrochemical activity and osmotic activity.

Transport Across the Cell Membrane

Passive transport: Does not require metabolic energy.
- Simple diffusion: Movement of a substance from higher concentration to lower.
- Facilitated diffusion: Movements of molecules with assistance from membrane proteins.
- Osmosis: Passive movement of water across a membrane from high to low concentrations.
- Filtration: Fluid forced across a membrane due to pressure differences.
Active transport: Needs metabolic energy.
- Primary active transport: moving substances against concentration gradients using ATP directly.
  - Examples: Na(+)-K(+)ATPase, Ca(2+)ATPase, H(+)-K(+)ATPase.
- Secondary active transport: Couples downhill movement of one substance to uphill movement of another.
  - Examples: Na(+)-glucose cotransporter, Na(+)-Ca(2+) exchanger, Na(+)-K(+)-2Cl- cotransporter
Bulk transport: Transporting large molecules.
- Endocytosis: engulfing material into the cell through invagination of the membrane.
  - Phagocytosis: Large molecules, such as bacteria, are engulfed
  - Pinocytosis: Liquid is engulfed
- Exocytosis: releasing material from the cell through fusion of secretory vesicles.

Physiological Adjustment

Homeostasis: Maintaining a more or less constant internal environment.
- Intrinsic regulation: cells, tissues, and organs self-regulate based on their local conditions.
- Extrinsic regulation: nervous and endocrine systems coordinate long-distance adjustments.
Allostasis: Maintaining stability via acute changes. Adapting to and coping with stress.
Allostatic load: The cost of prolonged adaptation to stress.
Heterostasis (Adaptation): Long-term changes to adapt or cope with the environment (e.g., adjusting to high altitude, cold, or heat).

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Description

This quiz explores essential concepts in cell biology, focusing on the plasma membrane's role and transport mechanisms across the cell membrane. It also examines the relationship between extracellular and intracellular fluids, cell specialization, and the distribution of solutes. Test your knowledge on these fundamental topics in cellular structure and function.