Podcast
Questions and Answers
What is the primary function of the cell membrane?
What is the primary function of the cell membrane?
Which component is responsible for the toughness of the cell membrane?
Which component is responsible for the toughness of the cell membrane?
Which type of membrane protein penetrates the entire thickness of the membrane?
Which type of membrane protein penetrates the entire thickness of the membrane?
How is the structure of the cell membrane primarily organized?
How is the structure of the cell membrane primarily organized?
Signup and view all the answers
What role do peripheral proteins play in the cell membrane?
What role do peripheral proteins play in the cell membrane?
Signup and view all the answers
What role do adhesion molecules play in cells?
What role do adhesion molecules play in cells?
Signup and view all the answers
Which statement correctly describes the composition of the cell membrane?
Which statement correctly describes the composition of the cell membrane?
Signup and view all the answers
Which type of transport across the cell membrane is characterized by requiring no energy?
Which type of transport across the cell membrane is characterized by requiring no energy?
Signup and view all the answers
What characterizes the intracellular fluid in terms of ion concentrations compared to extracellular fluid?
What characterizes the intracellular fluid in terms of ion concentrations compared to extracellular fluid?
Signup and view all the answers
How do ions typically pass through the cell membrane given their charge?
How do ions typically pass through the cell membrane given their charge?
Signup and view all the answers
Study Notes
General Physiology
- Topic: General Physiology
- Presenter: Dr. Shaimaa M. Abdelghany, Assistant Professor of Physiology
Structure of the Cell
- Cells are the smallest structural units in the human body.
- A cell is a mass of protoplasm, consisting of:
- Cytoplasm
- Cell organelles
- Nucleus
- Cell membrane
The Cell Membrane
- Also known as the plasma membrane.
- A double layer of lipids and proteins.
- Separates the cytoplasm from the surrounding environment.
- Contains:
- Phospholipids (41%)
- Proteins (55%)
- Carbohydrates (4%)
Function of the Cell Membrane
- Protects the cell and gives it shape.
- Controls movement of substances in and out of cells and organelles.
- Selectively permeable to ions and organic molecules.
- Contains receptors for chemical substances that stimulate or inhibit cell functions.
Lipids
- Mostly a mixture of phospholipids and cholesterol.
- Phospholipids are arranged in a bilayer with hydrophilic heads on the inner and outer surfaces and hydrophobic tails in the center.
- Cholesterol contributes to the membrane's toughness and solidity. The solidity is proportional to the cholesterol/phospholipid ratio.
Proteins
- Embedded in the phospholipid bilayer.
- Some are combined with lipids (lipoproteins).
- Some are combined with carbohydrates (glycoproteins).
- Types:
- Peripheral proteins
- Transmembrane/integral proteins
- Associated / anchored proteins
Peripheral Proteins
- Attached to the cell membrane surface (both inside and outside).
- Primarily act as enzymes.
- Bind to substances to be transported.
- Example: hormone receptors
Transmembrane/Integral Proteins
- Occupy the entire thickness of the membrane.
- Located on both the outer and inner surfaces.
- Form channels (pores)
- Act as carrier proteins.
Membrane Proteins: Functions
- Membrane receptors: relay signals between the cell and the external environment.
- Transport proteins: move water and ions.
- Membrane enzymes: catalyze reactions on the membrane surfaces.
- Adhesion molecules: give cells identity and allow interaction (e.g., in immune responses).
- Structural proteins: maintain membrane integrity.
Carbohydrates
- Present in small amounts (less than 10% of the cell membrane mass).
- Combined with proteins or lipids as glycoproteins or glycolipids (respectively).
- Found on the outer surface of the cell membrane.
- Functions include:
- Cell adhesion
- Acting as receptor substances
- Role in immune reactions
- Contributing to the cell's negative surface charge, interacting with regulatory molecules.
Transport of Substances Across Cell Membranes - Overview
- The cell membrane is described as partially/semi-permeable.
- Phospholipids form a barrier to polar ions and water-soluble substances.
- This transport occurs via membrane proteins.
- Concentration differences exist between extracellular and intracellular fluids.
Passive Transport
- Movement is due to a concentration gradient, requires no energy.
- Can occur through the lipid bilayer, or through membrane proteins/channels/pores.
- Types include:
- Simple diffusion
- Facilitated diffusion
- Osmosis
Simple Diffusion
- Net movement of substances from higher to lower concentration, toward equilibrium.
- No energy needed.
Facilitated Diffusion
- Movement from higher to lower concentration with the help of proteins (proteins may assist with their hydrophobic tails, or creating a water-filled pore).
- No energy needed.
- Larger molecules or substances not readily soluble in lipids, such as glucose may use this method.
Osmosis
- Movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration, to equalize the solute concentration on both sides of the membrane.
- Requires no energy.
Types of Protein Channels
- Non-gated (leak) channels: always open, slow diffusion.
- Gated channels: open or close in response to stimuli (e.g., voltage-gated, ligand-gated, or stretch-activated).
Additional Transport Mechanisms
- Active Transport
- Endocytosis
- Exocytosis
Transport: Characteristics of Carrier Proteins
- Specificity: a protein is specific to a certain substance.
- Saturation: the maximum number of substances are carried at a time, determined by the number of available carriers.
- Competition: similar substances can compete for a specific carrier.
Factors Affecting the Rate of Diffusion
- Concentration difference
- Surface area
- Temperature
- Distance
- Molecular weight
Osmotic Pressure
- Pressure needed to prevent solvent movement across a semipermeable membrane due to different osmolarity.
- Dependent on the number of particles in the solution, not particle type.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz covers fundamental concepts in general physiology focusing on the structure of the cell and the cell membrane. It addresses key components such as organelles, phospholipids, and the functions of the plasma membrane. Test your knowledge on how cells protect and regulate their internal environments!
