NURS 207 (01) Cellular level of organization Sept 9-20234.pdf
Transcript
NURS 207 (N01) Cellular level of organization Structure of the plasma membrane, categories of membrane transport Tortora, 16th ed., Ch. 3 & Ch. 12 September 9, 2024 Dr. P. Lee Objectives 1) Describe the main p...
NURS 207 (N01) Cellular level of organization Structure of the plasma membrane, categories of membrane transport Tortora, 16th ed., Ch. 3 & Ch. 12 September 9, 2024 Dr. P. Lee Objectives 1) Describe the main parts of the cell 2) Distinguish between cytoplasm and cytosol 3) Study the properties of plasma membrane 4) Know the six basic transport mechanisms across the plasma membrane 5) Know the first two of the 4 main categories of transport processes Cell - Introduction ❖ A cell is defined as a single basic living, structural, and functional unit enclosed by a membrane With various shapes and forms that are adapted to serve in diverse physiological capacities → The architectural diversity of living cells are the reflection of their unique individual physiological function 3 main parts of a cell 1) Plasma membrane A highly selective permeable membrane enclosing all the internal contents of a living cell ❖ Selective permeability is one of the important properties of a membrane (meaning that each individual substance has its own unique permeability through a specific type of membrane) ✓ Allows the creation of an intracellular condition to be very different from that of its surroundings ✓ Cellular function requires the maintenance of a very precisely regulated intracellular and extracellular environment Figure 1.6 The body compartments are in a dynamic steady state but are not at equilibrium 140 ECF ICF 120 Concentration (mmol/L) 100 80 60 40 20 Na+ Cl- K+ Na+ Cl- K+ 3 main parts of a cell 1) Plasma membrane → Forms the cell’s flexible outer surface → Hold the interior structural Cytoskeleton scaffolding Microvilli increase cell (cytoskeleton) in surface area. They are supported by microfilaments. place to maintain Microfilaments form a network just inside the cell membrane. cell shape Microtubules are the largest cytoskeleton fiber. Intermediate filaments include myosin and keratin. 3 main parts of a cell 2) Cytoplasm → Consists of all the cellular contents inside the cell between the plasma membrane and the nucleus i.e. excluding the cell nucleus 3 main parts of a cell 2) Cytoplasm → With 2 main components: a) Cytosol ▪ Fluid portion of the cytoplasm ▪ Also known as intracellular fluid ▪ With water, dissolved solute (e.g. electrolytes) and suspended particles such as proteins and nucleic acids 3 main parts of a cell 2) Cytoplasm b) Organelles ▪ Structures enclosed with discrete intracellular membrane in various shapes, sizes, & functions 3 main parts of a cell 2) Cytoplasm b) Organelles → some of the major structures: ▪ Mitochondria ✓ For energy production in the form of adenosine triphosphate (ATP) ▪ Endoplasmic reticulum (ER) → 2 forms (smooth & rough) ✓ Smooth ER → sites for lipids, phospholipids, and steroids synthesis ✓ Rough ER → With ribosomes as the sites for protein synthesis 3 main parts of a cell 2) Cytoplasm → 2nd Components: b) Organelles ▪ Golgi complex ✓ A processing station that participates in protein maturation and targets newly synthesized proteins to their appropriate subcellular destinations ▪ Lysosome ✓ Cell’s digestive organelle 3 main parts of a cell 3) Nucleus Structure associated with gene expression and cell division Serves as a cell’s depot for its complement of chromosomal DNA (site where genetic information are stored) i.e. the control center of a cell ✓ The uniqueness in a cell’s architectural feature and its associated function is regulated by gene expression Functions of the plasma membrane Plasma membrane 4 general functions of the plasma membrane: 1) Structural support → Through a network of cytoskeleton 2) Physical isolation → Separates its internal contents (intracellular) from the external environment (extracellular) 3) Regulation of exchange → As a barrier that can regulate the flow of materials into and out of the cell 4) Communication → Establishes communication between cells and its external environment Structure of the plasma membrane Plasma membrane Compartments Are Separated by Membranes Pericardial Tissue membranes Phospholipid bilayers membrane have many cells. create cell membranes Cell Heart Loose connective tissue The pericardial sac is Seen magnified, the pericardial Each cell of the The cell membrane a tissue that surrounds membrane is a layer of pericardial membrane is a phospholipid the heart. flattened cells supported by has a cell membrane bilayer. connective tissue. surrounding it. Plasma membrane Common characteristics of plasma membrane : → “Fluid mosaic model” is often use to describe the structural model of the plasma membrane i.e. Plasma membrane is a mosaic of lipids with various proteins as part of the fabrics Plasma membrane Structure of the plasma membrane: The basic structural framework of the plasma membrane is the lipid bilayer Layer facing exterior of the cell Layer facing interior of the cell Plasma membrane Structure of the plasma membrane: → Plasma membrane are mostly Head phospholipids → Phospholipids are amphipathic molecules Tails i.e. They have both polar & nonpolar parts → Polar region is the “head” region containing phosphate – which is hydrophilic (water loving) → Nonpolar region is the “tails” region containing 2 long chains of fatty acid – which is hydrophobic (water fearing) Plasma membrane Structure of the plasma membrane: → “Like seeks like” → Head region (hydrophilic) with the phosphate faces the watery fluid on either side of the plasma membrane - cytosol (intracellular) and extracellular → Hydrophobic fatty acid tails in each phospholipid points toward each other and form a nonpolar region in the membrane’s interior i.e. Forming a single structure with bilayer Plasma membrane Membrane proteins ❖ In general, the more metabolically active a membrane is, the more proteins it contains 2 main categories: 1) Integral membrane proteins → Tightly attached to the membrane 2) Peripheral membrane proteins → Loosely attached to the membrane First category (integral)of membrane proteins a) Lipid-anchored proteins → Membrane proteins that insert themselves into either side of the cell membrane → Covalently bounded to lipid tail within the lipid bilayer The Fluid Mosaic Model of Biological Membranes Peripheral proteins Glycoprotein can be removed This membrane- Transmembrane Lipid- without disrupting the integrity of the proteins cross the spanning protein lipid bilayer. crosses the membrane anchored membrane. seven times. Carbohydrate proteins Phospholipid heads face the aqueous Extracellular fluid COOH intracellular and extracellular compartments. Lipid-anchored Lipid tails proteins Peripheral form the protein interior Cytoplasm Cytoskeleton layer of the membrane. proteins. Phosphate Cholesterol molecules insert Cell Intracellular NH2 membrane fluid Cytoplasmic loop themselves into the lipid layer. First category (integral)of membrane proteins b) Transmembrane proteins → Span the entire lipid bilayer and protrude into both the cytosol and extracellular fluid (also known as membrane-spanning proteins) → Function as a channel for the transport of specific substances across the biological membrane The Fluid Mosaic Model of Biological Membranes Glycoprotein This membrane- Peripheral proteins spanning protein can be removed Transmembrane crosses the membrane without disrupting proteins cross the seven times. the integrity of the lipid bilayer. Phospholipid heads membrane. Carbohydrate Extracellular face the aqueous COOH fluid Transmembrane intracellular and extracellular Lipid-anchored Lipid tails Peripheral proteins compartments. form the Cytoplasm proteins protein Cytoskeleton interior layer of the proteins. Phosphate Cholesterol molecules insert Cell Intracellular NH2 membrane. fluid Cytoplasmic loop themselves into the lipid layer. membrane Second category (peripheral) of membrane proteins → Peripheral membrane proteins are those membrane protein that are loosely attached to either the polar head or other membrane proteins The Fluid Mosaic Model of Biological Membranes Peripheral proteins Glycoprotein can be removed This membrane- without disrupting Transmembrane proteins cross the spanning protein the integrity of the crosses the membrane lipid bilayer. Peripheral membrane. Carbohydrate seven times. Phospholipid heads Extracellular proteins face the aqueous COOH fluid intracellular and extracellular compartments. Lipid-anchored Lipid tails proteins Peripheral form the protein interior Cytoplasm Cytoskeleton layer of the proteins. membrane. Phosphate Cholesterol molecules insert Cell Intracellular NH2 membrane fluid Cytoplasmic loop themselves into the lipid layer. Summary Basic category of the plasma membrane proteins: Plasma membrane proteins Integral proteins Peripheral proteins Transmembrane Lipid-anchored proteins proteins Plasma membrane General functions of membrane proteins: 1) Ion channels → Form pores that allow a specific ions pass through 2) Receptors → Serve as cellular recognition sites with each type of receptor recognizes and binds a specific type of molecule 3) Carriers/transporters → Selectively moving a molecule or ion across the membrane Plasma membrane General functions of membrane proteins: 4) Enzymes → Catalyze specific biological reactions either inside or outside the cell 5) Linkers → Anchor plasma membrane of neighboring cells to one another 6) Cell-identity markers → To identify a cell whether it is one of its own or foreign Six basic transport mechanisms across the plasma membrane 6 basic transport mechanisms i) Diffusion ❖ Movement of solute within a medium and membrane in biological system ❖ By concentration gradient (from concentrated to dilute) 6 basic transport mechanisms ii) Osmosis ❖ Movement of solvent through a membrane ❖ By means of concentration gradient ❖ Water moves from dilute (low osmolality) to concentrated (high osmolality) ❖ Requires water channels (aquaporins) 6 basic transport mechanisms iii) Facilitated diffusion ❖ Carrier-mediated transport (carrier proteins) ❖ From higher to lower concentration ❖ Transport of large or electrically charged molecules e.g. glucose, amino acids, HCO3- etc 6 basic transport mechanisms iv) Active transport ❖ Move against concentration gradient ❖ Energy dependent carrier mediated, requires adenosine triphosphate (ATP) 6 basic transport mechanisms v) Cotransport (symport) ❖ Carrier mediated simultaneous movement of 2 or more solutes in the same direction ❖ Type of secondary active transport (e.g. moving K+ from extra into intracellular space by NKCC channels → against conc. gradient) 6 basic transport mechanisms vi) Countertransport (antiport) ❖ Similar to cotransport ❖ But the transported molecules are moving in the opposite direction 4 main categories of transport processes 4 main categories of transport processes → Bulk flow; diffusion; protein-mediated transport; and vesicular transport 1st category of transport processes 1) Bulk flow → Requires pressure gradient → Flow from high pressure to low e.g. - Blood flow within a blood vessel - Air moving in and out of the lungs 2nd category of transport processes 2) Diffusion → Requires concentration gradient such as chemical, electrical, or both (electrochemical gradient) - Gradient is the difference in the driving force required for the movement of a substance between 2 regions → Flow from high concentration to low - could take place in an open system or through a plasma membrane 2) Diffusion → Passive process which requires no input of energy → Finish when dynamic equilibrium is established i.e. Equal gradient (electrochemical – electrical and chemical gradients combined) in both regions Rate of diffusion through membrane Outside the cell Membrane Lipid Molecular size surface area Solubility Concentration Gradient Membrane Composition Inside the cell Rate of diffusion through membrane is a function of: Membrane Molecular Concentration Membrane Lipid surface area size gradient composition solubility → High cholesterol content decrease the membrane permeability to a substance by decreasing the space between the fatty acid tails Rate of diffusion through membrane by Fick's law V = D (A ⁄ T) (P1 – P2) Where: V = rate of diffusion D = diffusion constant (related to membrane permeability) A = area of the membrane T = thickness of the membrane (P1 – P2) = difference in concentration Rate of diffusion through membrane by Fick's law Also: D α Solubility ⁄ √ (Mol. wt.) Because: V = D (A ⁄ T) (P1 – P2) Therefore: V α (A ⁄ T) (P1 - P2) Solubility ⁄ √ (Mol. wt.) Lipid solubility → Plasma membranes are selectively permeable to molecules and ions i.e. Some can cross (permeable) and other cannot (impermeable) → Permeability of the membrane to a substance is a property of the membrane and the substance Lipid solubility Ability of a molecule to dissolve into the lipid bi-layer plasma membrane depends upon: a) Chemical nature of the molecule → Only non-polar lipophilic (lipid soluble) molecule can dissolve in the central lipid region of the membrane e.g. Lipids, steroids, and small lipophilic molecules can move across membrane by simple diffusion b) Cholesterol content within the membrane → High cholesterol content decrease the membrane permeability to a substance by decreasing the space between the fatty acid tails Sample questions 1) The main structural component of the plasma membrane is: a) Proteins b) Cholesterol c) Single layer of phosphate and free fatty acids d) Phospholipid bilayers 2) What are the nonpolar parts of phospholipids? a) phosphate-containing head groups b) fatty acid tail groups c) both the head and tail groups are nonpolar d) neither the head nor tail groups are nonpolar Sample questions 3) The more metabolically active a membrane is, the more ______ it contains? a) phospholipids b) proteins c) lipoprotein d) fatty acids 4) Plasma membranes are _____, which means that some chemicals move easily through plasma membrane while other chemicals do not. a) good chemical insulators b) highly selective permeable membranes c) poor chemical conductors d) semi-permeable membranes Sample questions 5) Which of the following(s) can influence the rate of diffusion of a chemical across a plasma membrane? a) concentration gradient of the chemical across the membrane b) mass of the diffusing chemical c) distance that the chemical has to diffuse d) all of the above 6) Which type of membrane protein extends across the entire lipid bilayer of the plasma membrane touching both intracellular fluid and the extracellular fluid? a) transmembrane protein b) peripheral protein c) lipoprotein d) all of these choices are correct Sample questions 7) In this type of transport process, a solute binds to a specific carrier protein on one side of the membrane. This binding induces a conformational change in the carrier protein that results in the other type of solute moving down its concentration gradient to the other side of the membrane. a) osmosis b) diffusion c) primary active transport d) facilitated diffusion 8) In this transport process, the energy from hydrolysis of ATP is used to drive substances across the membrane against their own concentration gradients. a) primary active transport b) facilitated diffusion c) secondary active transport d) osmosis Answer to sample questions 1) d 2) b 3) b 4) b 5) d 6) a 7) d 8) a
