Cell Physiology PDF

The cell and its function Cell is the basic unit of the body Organization of the cell  Cell composition Water :70-85% Ions Proteins: 10-20% Lipids : 2-95% Carbohydrates : 1-6 % 1-Water: The principal fluid medium of the cell present in most cells except...

The cell and its function Cell is the basic unit of the body Organization of the cell  Cell composition Water :70-85% Ions Proteins: 10-20% Lipids : 2-95% Carbohydrates : 1-6 % 1-Water: The principal fluid medium of the cell present in most cells except fat cell 2-protiens : divided into two types : A- Structural proteins: Present in the cell mainly in the form of long filaments (mainly form microtubules that provide the cytoskeletons of such cellular organelles. b- functional proteins: Composed of combination of few molecules in tubular globular form (they are mainly the enzymes of the cell)  Lipids: Important lipids are : phospholipids and cholesterol constitute only about 2% of the total cell mass, they are mainly insoluble in water and therefore are used to form the cell membrane and intracellular membrane barriers that separate the different cell compartments. Neutral fat (triglycerides): in fat cell triglycerides account for 95% of the cell mass. The fat stored in theses cells represent the body’s main storehouse of energy-giving nutrients  Carbohydrates : Little structural function in the cell and play a major role in nutrition of the cell. Most human cells do not maintain large stores of carbohydrates , the amount usually averages about 1% of their total mass but increase to 3% in muscle cell and 6% in liver.  Membranous structure of the cell Cell membrane Nuclear membrane Membrane of the endoplasmic reticulum Membrane of mitochondria, lysosomes and Golgi apparatus.  Cell membrane Thin, pliable, elastic structure 7.5 – 10 nanometers thick Mainly composed of proteins and lipids. Protein 55% Phospholipids 25%  Cell Membrane Components: 1 - LIPIDS: barrier to water and water-soluble substances organized in a bilayer of phospholipid molecules CO2 O2 N2 ions glucose H2O urea halothane hydrophilic “head” hydrophobic FA “tail”  2- Proteins: provide “specificity” to a membrane defined by mode of association with the lipid bilayer – integral: channels, pores, carriers, enzymes, receptor, etc. – peripheral: enzymes, intracellular signal mediators, controllers of transport of substances through pores K+  3 - Carbohydrates: glycolipids (approximately 10%) glycoproteins (majority of integral proteins) proteoglycans (carbs bound to protein cores) Glycocalyx loose carbohydrate coat outside surface of the cell GLYCOCALYX  Carbohydrates (Cont.): important function for it: o negative charge of the carbo chains repels other o negative charges o involved in cell-cell attachments/interactions o play a role in immune reactions o Act as receptor substance for binding hormone such (-) (-) (-) as insulin (-) (-) GLYCOCALYX (-) (-)  Cytoplasm and its organelles Cytosol: clear fluid portion of the cytoplasm in which the particles are dispersed in. Particles Dispersed in cytoplasm are: 1- Neutral fat globules 2-Glycogen granules 3-Ribosomes 4-Secretory vesicles 5- the other organelles Cell Organelles 1 - The Endoplasmic Reticulum: Network of tubular and flat vesicular structures Membrane is similar to (and contiguous with) the plasma membrane Space inside the tubules is called the endoplasmic matrix  Rough or Granular ER outer membrane surface covered with ribosomes newly synthesized proteins are extruded into the ER matrix proteins are “processed” inside the matrix - cross-linked - folded - glycosylated (N-linked) - cleaved  Smooth ER (aGranular ER) Part of ER has no attached ribosomes. site of lipid synthesis - phospholipids - cholesterol growing ER membrane buds continuously forming transport vesicles, most of which migrate to the Golgi apparatus  The Golgi Apparatus: Membrane composition similar to that of the smooth ER and plasma membrane Composed of 4 or more stacked layers of flat vesicular Structures This apparatus is prominent in secretory cell, where its located on the side of the cell from which the secretory substance are extruded.  Receives transport vesicles from smooth ER Substances formed in the ER are “processed” - phosphorylated - glycosylated Substances are concentrated, sorted and packaged for secretion. Transported substance are then processed in Golgi apparatus to form : - Lysosomes - Secretory vesicle - Cytoplasmic component  Lysosomes: vesicular organelle formed from budding Golgi Lysosome provide an intracellular digestive system that allows the cell to digest: -damaged cellular structure -food particles that have been ingested by cell -unwanted matter such as bacteria contain hydrolytic enzymes (acid hydrolases) - phosphatases - nucleases - proteases - lipid-degrading enzymes - lysozymes digest bacteria fuse with pinocytotic or phagocytotic vesicles to form digestive vesicles  Peroxisomes: similar physically to lysosomes two major differences: formed by self-replication they contain oxidases (hydrogen peroxide and catalase) Function: oxidize substances (e.g. alcohol) that may be otherwise poisonous Secretory Granules Secretory vesicle in acinar cells of the pancreas  Secretion: secretory vesicles containing proteins synthesized in the RER bud from the Golgi apparatus These vesicle store protien proenzyme (enzymes that are not yet activated) fuse with plasma membrane to release contents - constitutive secretion - happens randomly - stimulated secretion - requires trigger  Exocytosis: Secretory vesicles diffuse through the cytosol and fuse to the plasma membrane Lysosomes fuse with internal endocytotic vesicles  Mitochondria (powerhouse) : Primary function: extraction of energy from nutrients Mitochondria are self-replicative Matrix: contain large amount of dissolve enzymes  Cytoskeleton Fibrillar protein originated as precursor protein molecules synthesized by ribosomes in the cytoplasm. The precursor molecules then polymerize to form filaments The primary function of microtubules is to act as cytoskeleton, providing rigid physical structure The Nucleus: “Control Center” of the Cell Nucleus contains large quantities of DNA ,which are the genes  The Nucleus: “Control Center” of the Cell Nuclear membrane is two separated bilayer membrane, the outer membrane is continuous with the endoplasmic reticulum. Nuclear membrane penetrated by several thousand nuclear pores The nuclear membrane is permeated by thousands of nuclear pores 100 nm in diameter (selectively) permeable to molecules Chromatin (condensed DNA) is found in the nucleoplasm o Nucleolus one or more per nucleus contains RNA and proteins not membrane delimited functions to form the granular “subunits” of ribosomes Ingestion by the cell Receptor-mediated endocytosis: Pinocytosis and phagocytosis molecules attach to cell- surface receptors concentrated in clathrin-coated pits receptor binding induces invagination also ATP-dependent and involves recruitment of actin and myosin Digestion of Substances in Pinocytotic or Phagocytic Vesicles Pinocytosis: ingestion of minute particles that form vesicles of extracellular fluid in the cytoplasm (“Cell Drinking”) Digestion of Substances in Phagocytosis Phagocytic Vesicles Phagocytosis: the same as pinocytosis except that it involve large particles rather than molecule like macrophages and WBC (“Cell Eating”). Phagocytosis occur in the following steps : 1- The cell membrane receptors attach to the surface ligands of the particles. 2- The edge of the membrane around the points of attachment evaginate outward. 3- Action and other contractile fibrils in the cytoplasm surround the phagocytic vesicle and contract around its outer edge. 4- The contractile proteins then pinch the stem of the vesicle so completely that the vesicle separates from the cell membrane.  Digestion of pinocytosis and phagocytic foreign substance inside the cell Function of the lysosomes: -lysosome attached to the vesicle and empty their acid hydrolases to the inside of the vesicle -digestive vesicle is formed inside the cell cytoplasm and hydrolyzing just begin, the products of digestion are small molecules of amino acid, glucose, phosphate, then diffuse through membrane of the vesicle into the cytoplasm. Residual body is left from digestive vesicle which represent indigestible substances, and this is excreted by exocytosis. Digestive organ is Pinocytic and phagocytic vesicle containing lysosomes.  Regression of the tissue and autolysis of cells Tissue of the body often regress to a smaller size and the lysosomes are responsible for much of this regression Lysosomes also remove damaged cells (autolysis) Lysosomes also contain bactericidal agents that can kill phagocytized bacteria before they can cause cellular damage. -Lysozyme: dissolve the bacterial cell membrane -Lysoferrin: bind iron and before they can promote bacterial growth -acid at a pH 5, which activate the hydrolase and inactivate bacterial metabolic system.  Syntheses and formation of cellular structure by endoplasmic reticulum and Golgi apparatus Proteins are formed by the granular endoplasmic reticulum within the structure of the ribosomes Lipids are formed by the smooth endoplasmic reticulum especially (phospholipids and cholesterol). -This process cause the ER to grow more extensive and to keep it normal small vesicle called ER, vesicles continually break away from the smooth reticulum and then migrate to Golgi apparatus.  ATP production (function of the mitochondria) Step 1. Carbohydrates are converted into glucose Proteins are converted into amino acids Fats are converted into fatty acids Step 2. Glucose, AA, and FA are processed into Acetyl-CoA Step 3. A maximum of 38 molecules of ATP Acetyl-CoA reacts with O2 to are formed per molecule of glucose produce ATP degraded.  Locomotion of cell 1-Ameboid movement 2-Cilia and ciliary movements (cilium and flagellum)  Ameboid movement It is the movement of an entire cell in relation to its surroundings. It begins with protrusion of pseudopodium from one end of the cell ,then projects far out from the cell body and partially secure itself in a new tissue area Then the remainder of the cell is pulled toward the pseudopodium  Ameboid Locomotion: Mechanism is result from continual formation of new cell membrane at the leading edge of the pseudopodium and continual absorption of the membrane in mid and rear portion of the cell. continual endocytosis at the “tail "and exocytosis at the leading edge of the pseudopodium attachment of the pseudopodium is facilitated by receptor proteins carried by vesicles forward movement results through interaction of actin and myosin (ATP-dependent)  Ameboid locomotion Types of cells exhibits ameboid locomotion: 1-WBCs 2-fibroblast which move into damaged area 3- its especially important in development of the embryo and fetus after fertilization of an ovum. Cell movement is influenced by chemical substances… chemotaxis is the most important initiator of ameboid locomotion by chemotactic substance Chemotaxis Low concentration high concentration (negative) (positive)  Cilia and Ciliary Movements: Occurs only on the inside surfaces of the human airway (cause a layer of mucus to move at a rate of about 1cm\min toward the pharynx) and fallopian tubes(to transport the ovum from ovary to uterus) Each cilium is comprised of 11 microtubules 9 double tubules axoneme 2 single tubules Each cilium is an outgrowth of the basal body and is covered by an outcropping of the plasma membrane. Ciliary movement is ATP-dependent (also requires Ca2+ and Mg2+)  Flagellum Is much longer than cilium and its moves in quasi- sinusoidal waves instead of whip like movements.  TRANSPORT ACROSS CELL MEMBRANES 1-Simple diffusion 2-Carrier mediated transport 3-Facilated diffusion 4-Primary active transport 5-Co transport 6-Counter transport  TRANSPORT ACROSS CELL MEMBRANES A. Simple diffusion 1. Characteristics of simple diffusion is the only form of transport that is not carrier- mediated. occurs down an electrochemical gradient (“downhill”). does not require metabolic energy and therefore is passive.  Permeability Describes the ease with which a solute diffuses through a membrane. Depends on the characteristics of the solute and the membrane. A- Factors that increase permeability: ↑ Oil/water partition coefficient of the solute increases solubility in the lipid of the membrane. ↓ Radius (size) of the solute increases the diffusion coefficient and speed of diffusion. ↓ Membrane thickness decreases the diffusion distance.  CARRIER MEDIATED TRANSPORT Includes facilitated diffusion and primary and secondary active transport. The characteristics of carrier-mediated transport are: 1. Stereospecificity, for example, D-glucose (the natural isomer) is transported by facilitated diffusion, but the L-isomer is not. 2. Saturation: the transport rate increases as the concentration of the solute increases, until the carriers are saturated. 3. Competition. Structurally related solutes compete for transport sites on carrier molecules ( galactose is a competitive inhibitor of glucose transport in the small intestine)  Facilitated diffusion Characteristics of facilitated diffusion: Occurs down an electrochemical gradient (“downhill”), similar to simple diffusion. does not require metabolic energy and therefore is passive is more rapid than simple diffusion. is carrier-mediated and therefore exhibits stereospecificity, saturation, and competition. Example of facilitated diffusion Glucose transport in muscle and adipose cells is “downhill,” is carrier-mediated, and is inhibited by sugars such as galactose; therefore, it is categorized as facilitated diffusion. In diabetes mellitus, glucose uptake by muscle and adipose cells is impaired because the carriers for facilitated diffusion of glucose require insulin.  Primary active transport Characteristics of primary active transport: Occurs against an electrochemical gradient (“uphill”). requires direct input of metabolic energy in the form of adenosine triphosphate (ATP) and therefore is active. is carrier-mediated and therefore exhibits stereo specificity, saturation, and competition. Examples of primary active transport a. Na+, K+-ATPase (or Na+–K+ pump) in cell membranes transports Na+ from intracellular to extracellular fluid and K+ from extracellular to intracellular fluid; it maintains low intracellular [Na+] and high intracellular [K+].  Both Na+ and K+ are transported against their electrochemical gradients. Energy is provided from the terminal phosphate bond of ATP. The usual stoichiometry is 3 Na+/2 K+. Specific inhibitors of Na+, K+-ATPase are the cardiac glycoside drugs ouabain and digitalis. b. Ca2+-ATPase (or Ca2+ pump) in the sarcoplasmic reticulum (SR) or cell membranes transports Ca2+ against an electrochemical gradient. Sarcoplasmic and endoplasmic reticulum Ca2+-ATPase is called SERCA. c. H+,K+-ATPase (or proton pump) in gastric parietal cells transports H+ into the lumen of the stomach against its electrochemical gradient. It is inhibited by proton pump inhibitors, such as omeprazole  SECONDARY ACTIVE TRANSPORT Characteristics of secondary active transport : a. The transport of two or more solutes is coupled. b. One of the solutes (usually Na+) is transported “downhill” and provides energy for the “uphill” transport of the other solute(s). c. If the solutes move in the same direction across the cell membrane, it is called co-transport, or symport. (Examples are Na+–glucose cotransport in the small intestine and Na+–K+– 2Cl– co-transport in the renal thick ascending limb) d. If the solutes move in opposite directions across the cell membranes, it is called counter-transport, exchange, or anti-port (Na+–Ca2+ exchange and Na+–H+ exchange)  SECONDARY ACTIVE TRANSPORT Example of Na+–glucose co-transport a. The carrier for Na+–glucose co transport is located in the luminal membrane of intestinal mucosal and renal proximal tubule cells. b. Glucose is transported “uphill”; Na+ is transported “downhill.” c. Energy is derived from the “downhill” movement of Na+. The inwardly directed Na+ gradient is maintained by the Na+–K+ pump on the basolateral (blood side) membrane. Poisoning the Na+–K+ pump decreases the transmembrane Na+ gradient and consequently inhibits Na+–glucose cotransport.  Osmosis A. Osmolarity is the concentration of osmotically active particles in a solution. is a colligative property that can be measured by freezing point depression. can be calculated using the following equation: Osmolarity = g x C where: Osmolarity = concentration of particles (osm/L) g = number of particles in solution (osm/mol) C = concentration (mol/L)  Two solutions that have the same calculated osmolarity are isosmotic If two solutions have different calculated osmolarities, the solution with the higher osmolarity is hyper-osmotic the solution with the lower osmolarity is hyposmotic.  Osmosis is the flow of water across a semipermeable membrane from a solution with low solute concentration to a solution with high solute concentration. 1. Example of osmosis: a. Solutions 1 and 2 are separated by a semipermeable membrane. Solution 1 contains a solute that is too large to cross the membrane. Solution 2 is pure water. The presence of the solute in solution 1 produces an osmotic pressure b. The osmotic pressure difference across the membrane causes water to flow from solution 2 (which has no solute and the lower osmotic pressure) to solution 1 (which has the solute and the higher osmotic pressure). c. With time, the volume of solution 1 increases and the volume of solution 2 decreases Thank you