Cell and its Functions PDF

CELL AND ITS FUNCTIONS PREPARED BY: JOHN MATTHEW C. REBUSTES, PTRP  ORGANIZATION OF THE CELL Protoplasm Water Electrolytes Proteins Lipids Carbohydrates  ORGANIZATION OF THE CELL Water Principal fluid medium of the cell Present...

CELL AND ITS FUNCTIONS PREPARED BY: JOHN MATTHEW C. REBUSTES, PTRP  ORGANIZATION OF THE CELL Protoplasm Water Electrolytes Proteins Lipids Carbohydrates  ORGANIZATION OF THE CELL Water Principal fluid medium of the cell Present in most cell, except fat cells 70 to 85% concentration Many cellular chemicals are dissolved in water Others are suspended in the water as solid particulates Chemical reaction takes place among the dissolved chemicals or at the surface of the suspended particles or membrane.  ORGANIZATION OF THE CELL Ions Important ions Provide inorganic for cellular K+ reactions Mg+2 Necessary for operation of some PO43- of the cellular control mechanisms SO42- HCO3 Na+ Cl- Ca+2  ORGANIZATION OF THE CELL Proteins Constitute 10 to 20% Structural vs. Functional Proteins Functional Proteins It has a direct contact with other substances in the cell fluid → catalyze specific intracellular chemical reactions  ORGANIZATION OF THE CELL Structural Proteins Functional Proteins Present in the cell in the form of Composed of combinations of a long filaments few molecules in tubular-globular Form the microtubules that form provide the cytoskeleton Main enzymes of the cell Extracellularly, fibrillar proteins Mobile in the cell fluid are found in collagen and elastin Many of these are adherent to fibers, blood vessel walls, membranous structures inside the tendons, ligaments cell  ORGANIZATION OF THE CELL Lipids Has a property of being soluble in fat solvents Phospholipids and cholesterol constitute only 2% of total cell mass Used to form the cell membrane and intracellular membrane barriers In fat cells, contains triglycerides; accounts 95% of cell mass  THREE PRINCIPAL PARTS OF A CELL Plasma membrane Cytoplasm Nucleus  PLASMA MEMBRANE Forms the cell’s flexible outer surface, separating the cell’s internal environment from the external environment Selective barrier It also play a role in communication among cells and between cells and their external environment  CYTOPLASM Consists of all the cellular contents between the plasma membrane and the nucleus Cytosol Fluid portion of cytoplasm Contains water, dissolved solutes, and suspended particles Organelles “little organs” within the cytosol Cytoskeleton, ribosomes, endoplasmic reticulum (ER), Golgi complex, lysosomes, peroxisomes, and mitochondria  NUCLEUS Houses most of a cell’s DNA Chromosomes Single molecule of DNA Contains thousands of hereditary units (genes) that control most aspects of cellular structure and function PLASMA MEMBRANE  PLASMA MEMBRANE Flexible yet sturdy barrier that surrounds and contains the cytoplasm of a cell The membrane lipids allow passage of several types of lipid-soluble molecules but act as a barrier to the entry or exit of charged or polar substances Some of the proteins in the plasma membrane allow movement of polar molecules and ions into and out of the cell  PLASMA MEMBRANE Other proteins can act as signal receptors or as molecules that link the plasma membrane to intracellular or extracellular proteins  LIPID BILAYER Basic structural framework of the plasma membrane Membrane lipid 75% are phospholipids 20% are cholesterol 5% are glycolipids Lipids are amphipathic molecules  LIPID BILAYER Phospholipid Head – hydrophilic Tail – hydrophobic Cholesterol molecules Weak amphipathic Interspersed among the other lipids -OH group – polar region Steroid rings and hydrocarbon tail - nonpolar  LIPID BILAYER Glycolipid Carbohydrate group – polar Fatty acid – nonpolar Appear only in the membrane layer that faces the ECF  MEMBRANE PROTEINS Integral protein Extend into or through the lipid bilayer among the fatty acid tails and are firmly embedded in it. Most integral proteins are transmembrane proteins. Peripheral protein Not as firmly embedded in the membrane Attached to the polar heads of membrane lipids or to integral proteins at the inner or outer surface  MEMBRANE PROTEINS Integral protein Many of these proteins are glycoproteins Glycocalyx Extensive sugary coat formed by carbohydrate portions of glycolipids and glycoproteins Pattern of carbohydrates in the glycocalyx varies from one cell to another Enables cells to adhere to one another in some tissues and protect cells from being digested by enzymes in the ECF  FUNCTIONS OF MEMBRANE PROTEINS Ion channels Specific ions, such as potassium ions, can flow through to get into or out of the cell Selective  FUNCTIONS OF MEMBRANE PROTEINS Carriers Transporters Selectively moving a polar substance or ion from one side of the membrane to the other  FUNCTIONS OF MEMBRANE PROTEINS Receptors Serve as cellular recognition sites Each type of receptor recognizes and binds a specific type of molecule Ligand Specific molecule that binds to a receptor  FUNCTIONS OF MEMBRANE PROTEINS Enzymes Catalyze specific chemical reactions at the inside or outside surface of the cell  FUNCTIONS OF MEMBRANE PROTEINS Linkers Anchor proteins in the plasma membranes of neighboring cells to one another or to protein filaments inside and outside th cell  FUNCTIONS OF MEMBRANE PROTEINS Cell identity markers Membrane glycoproteins and glycolipids Recognize other cells of the same kind during tissue formation Recognize and respond to potentially dangerous foreign cells  FUNCTIONS OF MEMBRANE PROTEINS Peripheral proteins Help support the plasma membrane Anchor integral proteins Moving of materials and organelles within the cells Changing cell shape in dividing and muscle cells Attaching cells to one another CYTOPLASM  CYTOSOL Fluid portion of the cytoplasm that surrounds organelles Constitutes about 55% of total cell volume It varies from one part of a cell to another, 75-90% water plus various dissolved and suspended components Site of many chemical reactions required for a cell’s existence  CYTOSOL Cytoskeleton Network of protein filaments extended throughout the cytosol Three types: Microfilaments Intermediate filaments Microtubules  MICROFILAMENTS Thinnest Functions: Composed of actin and myosin Generate movement protein Mm contraction Cell division, locomotion Most prevalent at the edge of the Provide mechanical support cell Anchor the cytoskeleton to integral proteins Support to microvilli MICROFILAMENTS  INTERMEDIATE FILAMENTS Thicker than microfilaments Function: Composed of several different Help stabilize the position of organelles proteins that are exceptionally strong Help attach cells to one another Found in parts of cells subject to mechanical stress INTERMEDIATE FILAMENTS  MICROTUBULES Largest of the cytoskeletal Function: components Determine the cell shape Long, unbranched hollow tubes Movement of organelles Secretory vesicles Composed mainly by tubulin Chromosomes protein Cilia and flagella MICROTUBULES  RIBOSOMES Site of protein synthesis High context of ribosomal RNA (rRNA) Consists of two subunits, made separately in the nucleolus Some ribosomes are attached to the outer surface of nuclear membrane, ER, and mitochondria Some are “free” or unattached to other cytoplasmic structures  ENDOPLASMIC RETICULUM Network of membranes in the form of flattened sacs or tubules Extends from the nuclear envelope Constitute more than half of the membranous surfaces within the cytoplasm of most cells  ROUGH ENDOPLASMIC RETICULUM Continuous with the nuclear membrane and usually is folded into a series of flattened sacs Ribosomes are attached to the outer surface of rough ER Protein synthesized by ribosomes attached to rough ER enter spaces (endoplasmic matrix) within the ER for processing and sorting Produces secretory proteins, membrane proteins, and many organellar proteins  SMOOTH ENDOPLASMIC RETICULUM Extends from the rough ER to form a network of membrane tubules Absent ribosomes on the outer surfaces of its membrane Synthesize fatty acids and steroids, such as estrogens and testosterone Inactivate or detoxify lipid-soluble drugs or harmful substances Removes the phosphate group from glucose-6-phosphate Stores and release calcium ions that trigger contraction in muscle cells  GOLGI COMPLEX Transport pathway Proteins synthesized by ribosomes to rough ER are transported to the other regions of the cell through this organelle Modifies, sorts, packages, and transport proteins received from rough ER Consists of 3 to 20 cisternae Convex entry or cis face – faces the rough ER Concave exit or trans face – faces the plasma membrane  GOLGI COMPLEX Medial cisternae Sacs between the entry and exit faces Add carbohydrates to proteins → glycoproteins, and lipids to proteins → lipoproteins Entry face Receives and modifies proteins produced by rough ER Exit face Modifies the molecules further and then sorts and packages for transport to their destinations  GOLGI COMPLEX Transport vesicles from rough ER → entry face, releases the proteins into its lumen → medial cisternae, modify the proteins using enzymes to form glycoproteins, glycolipids, and lipoproteins → exit face, further modified and are sorted and packaged → secretory vesicles → membrane vesicles → transport vesicles  LYSOSOMES Membrane-enclosed vesicles that form from the Golgi complex Contain as many as 60 kinds of powerful digestive and hydrolytic enzymes Lysosomal interior has a pH of 5  LYSOSOMES Autophagy Digestion of entire worn-out organelles Autophagosome Vesicle derived from ER, fuses with lysosome to enclosed the organelle Autolysis Destruction of entire cell that contains lysosomal enzymes  PEROXISOMES AKA Microbodies Contain several oxidases and catalase Abundant in the liver Can self-replicate  PROTEASOMES Tiny barrel-shaped Destroys the unneeded, damaged, or faulty proteins Contain myriad proteases  MITOCHONDRIA Powerhouse of the cell Generate most of the ATP through aerobic respiration Large number of mitochondria are found in muscles, liver, and kidneys Two lipid bilayer Outer membrane Inner membrane Shelves/cristae Oxidative enzymes Matrix  MITOCHONDRIA Able to self-replicate It has its own DNA, in the form of multiple copies of circular DNA molecule that contains 37 genes 2 ribosomal RNA 22 transfer RNA 13 proteins that build mitochondrial components Mitochondrial genes are inherited only from the mother Mitochondrial DNA can be used to trace maternal lineage NUCLEUS  NUCLEUS Spherical or oval-shaped Control center of the cell Controls cellular structure Directs cellular activities Produces ribosomes in nucleoli It contains large quantities of DNA Determine the characteristics of the cell’s protein and intracellular enzymes Control and promote reproduction of the cell itself  NUCLEAR MEMBRANE AKA Nuclear Envelope Separates the nucleus from the cytoplasm Lipid bilayer Outer membrane is continuous with rough ER  NUCLEAR MEMBRANE Nuclear pores extend through the nuclear membrane Control the movement of substances between the nucleus and the cytoplasm Small molecules and ions move through the pores in contrast to large molecules Each nuclear pore consists of a circular arrangement of proteins surrounding a large central opening  NUCLEOLI Located inside the nucleus Produces ribosomes Sites of synthesis of rRNA and assembly of rRNA and protein into ribosomal subunits  GENE Cell’s hereditary unit Control cellular structure and direct cellular activities Arranged along chromosomes FUNCTIONAL SYSTEMS OF THE CELL  VESICLES A variety of substances are transported in vesicles from one structure to another within cells Import materials and release materials into ECF Endocytosis Materials move into a cell in a vesicle formed from the plasma membrane Pinocytosis Phagocytosis Receptor-mediated endocytosis Exocytosis Materials move out of a cell by the fusion with the plasma membrane of vesicles formed inside the cell.  PINOCYTOSIS Process by which macromolecules like bacteria and antigens are taken into the cell AKA “cell drinking” – 100 to 200nm in diameter The only way by which most large macromolecules can enter cells  PHAGOCYTOSIS Process by which particles larger than the macromolecules, such as larger bacteria, larger antigens and other larger foreign bodies are engulfed into the cells. AKA “cell eating” Only few cells in the body like neutrophils, monocytes, and the tissue macrophage (largest phagocytic cells) show phagocytosis.  RECEPTOR-MEDIATED ENDOCYTOSIS It is a process transporting the macromolecules with the help of a receptor protein. Surface of cell membrane has some pits which contain a receptor protein (clathrin).  EXOCYTOSIS A process by which the substances are expelled from the cell. In this process, the substances are extruded from cell without passing through the cell membrane. LOCOMOTION OF CELLS  AMEBOID MOVEMENT Movement of an entire cell in relation to its surroundings. Begins with protrusion of a pseudopodium from one end of the cell. The pseudopodium projects away from the cell body and partially secures itself in a new tissue area, and then the remainder of the cell is pulled toward the pseudopodium.  MECHANISM OF AMEBOID LOCOMOTION Results from continual formation of new cell membrane at the leading edge of the pseudopodium Attachment of pseudopodium to surrounding tissues effected by receptor proteins Provide energy required to pull the cell body in the direction of the pseudopodium  AMEBOID MOVEMENT: TYPE OF CELL White blood cells → tissue macrophages Fibroblasts Development of embryo and fetus after fertilization of an ovum  CONTROL OF AMEBOID LOCOMOTION Chemotaxis Process that initiates ameboid locomotion Chemotactic substance Any chemical substance that causes chemotaxis to occur Positive Chemotaxis Cells that exhibit ameboid locomotion move toward the source of a chemotactic substance Negative Chemotaxis Some cells move away from the source  CILIA AND CILIARY MOVEMENT Whip-like movement of cilia on the surface of cells Occurs only in two places in the human body: Respiratory airways Inside surfaces of the uterine tubes  CILIA AND CILIARY MOVEMENT Cilium has the appearance of sharp- pointed straight or curved hair that projects 2 to 4 micrometers from the surface of the cell As many as 200 cilia project from a single cell Cilium is covered by an outcropping of the cell membrane, and it is supported by 11 microtubules 9 double tubules in the periphery 2 single tubules in the center  CILIA AND CILIARY MOVEMENT Cilium moves forward with a sudden, whiplike stroke 10 to 20 times per second It move fluids from one part of the surface to another Axoneme – protein cross-linkages that linked the nine double tubules and the two single tubules Even after removal of the membrane and destruction of other elements of the cilium besides the axoneme, the cilium can still beat under appropriate conditions  CILIA AND CILIARY MOVEMENT: MECHANISM There are two necessary conditions for continued beating of the axoneme after removal of the other structures of the cilium Availability of ATP Appropriate ionic condition During forward motion of the cilium, the double tubules on the front edge of the cilium slide outward toward the tip of the cilium while those on the back edge remain in place  CILIA AND CILIARY MOVEMENT: MECHANISM Multiple protein arms composed of the protein dynein, which has ATPase enzymatic activity, project from each double tubule toward an adjacent double tubule. CELL TRANSPORT MECHANISMS  TRANSPORT MECHANISMS Basic Mechanism of Transport Two types of basic mechanisms are involved in the transport of substances across the cell membrane: Passive transport mechanism Active transport mechanism  PASSIVE TRANSPORT AKA diffusion or downhill movement. Transport of substances along the concentration gradient or electrical gradient or both (electrochemical gradient). It does not need energy to transport substances from one place to another. The substances move from region of higher concentration to the region of lower concentration. Two types of diffusion: a. Simple diffusion: occurs either through lipid bilayer or protein layer of the cell membrane b. Facilitated diffusion occurs with the help of the carrier proteins of the cell membrane.  SIMPLE DIFFUSION THROUGH LIPID BILAYER Lipid layer of the cell membrane is permeable only to lipid-soluble substances like oxygen, carbon dioxide, and alcohol. The diffusion through the lipid layer is directly proportional to the solubility of the substances in lipids.  SIMPLE DIFFUSION THROUGH PROTEIN LAYER Protein layer of the cell membrane is permeable to water-soluble substances Mainly, electrolytes diffuse through the protein layer Protein Channels or Ion Channels These pores form the channels for the diffusion of water electrolytes, and other substances, which cannot pass through the lipid layer. Selectively permeable each channel can permit only one type of ion to pass through it Some of the protein channels are continuously opened (ungated channels) and most of the channels are always closed (gated channels)  GATED CHANNELS Voltage-gated channels Channels which open whenever there is a change in the electrical potential (action potential). Ligand-gated channels Types of channels which open in the presence of some hormonal substances. Mechanically gated channels These are the channels which are opened by some mechanical factors.  FACILITATED OR CARRIER-MEDIATED DIFFUSION Type of diffusion by which the water-soluble substances having larger molecules are transported through the cell membrane with the help of a carrier protein. Faster than transport by simple diffusion Example: Glucose and amino acids molecules are larger molecules which cannot diffuse through the channels because of their size.  FACTORS AFFECTING RATE OF DIFFUSION 1. Permeability of the Cell Membrane 2. Temperature 3. Concentration Gradient or Electrical Gradient of the Substances across the Cell Membrane 4. Solubility of the Substance 5. Thickness of the Cell Membrane 6. Size of the molecules 7. Charge of the Ions  ACTIVE TRANSPORT AKA uphill transport Movement of substances against the chemical or electrochemical gradient. They require energy, which is obtained mainly by breakdown of ATP, Two types of carrier proteins in active transport: Uniport – Carrier protein that carries only one substance in a single direction Symport or Antiport - Carrier protein that transports two substances at a time Symport pump: Carrier protein that transports two different substances in the same direction Antiport pump: Carrier protein that transport two different substances in opposite direction.  ACTIVE TRANSPORT Primary active transport Secondary active transport  PRIMARY ACTIVE TRANSPORT Type of transport mechanism in which the energy is liberated directly from the breakdown of ATP. By this method, the substances like sodium, potassium, calcium, hydrogen, and chloride are transported across the cell membrane.  SODIUM POTASSIUM PUMP Three receptor sites for sodium ions on the inner (towards cytoplasm) surface of the protein molecule. Two receptor sites for potassium ions on the outer (towards ECF) surface of the molecule. One site for enzyme ATPase, which is near the sites for sodium.  TRANSPORT OF CALCIUM IONS Calcium is actively transported from inside to outside the cell by calcium pump. Calcium pump is operated by a separate carrier protein. Energy is obtained from ATP by the catalytic activity of ATPase.  TRANSPORT OF HYDROGEN IONS Hydrogen ions is actively transported by the carrier protein hydrogen pump. It also obtains energy from ATP by the activity of ATPase. The hydrogen pumps that are present in two important organs have some functional significance: Stomach: hydrogen pumps in parietal cells of the gastric glands are involved in the formation of hydrochloric acid. Kidney: hydrogen pump in epithelial cells of distal convoluted tubules and collecting ducts are involved in the secretion of hydrogen ions from blood into urine.  SECONDARY ACTIVE TRANSPORT Transport of a substance with sodium ion, by means of a common carrier protein. When sodium is transported by a carrier protein, another substance is also transported by the same protein simultaneously either in the same direction (of sodium movement) or in the opposite direction. Two types of Secondary Active Transport a. Cotransport b. Counter transport  SODIUM COTRANSPORT It is the process in which, along with sodium, another substance is transported by a carrier protein (symport). Substances carried by sodium cotransport are glucose, amino acids, chloride, iodine, iron, and urate. Carrier protein for sodium cotransport Carrier protein for the sodium cotransport has two receptors sites on the outer surface. One is for binding of sodium, and another site is for binding of other substance.  SODIUM COUNTER TRANSPORT It is the process by which the substances are transported across the cell membrane in exchange for sodium ions by carrier protein (antiport). Sodium-calcium counter transport Sodium-hydrogen counter transport Other counter transport systems: sodium-magnesium counter transport sodium-potassium counter transport calcium-magnesium counter transport calcium-potassium counter transport chloride-bicarbonate counter transport chloride-sulfate counter transport Sodium cotransport Sodium counter transport SUMMARY OF CELL TRANSPORT MECHANISMS A. Passive Transport 1. Simple Diffusion a. Simple Diffusion Through Lipid Bilayer b. Simple Diffusion Through Protein Bilayer i. Ungated ii. Gated Voltage-gated Channels Ligand-gated Channels Mechanically-gated channels 2. Facilitated Diffusion B. Active Transport 1. Primary Active Transport 2. Secondary Active Transport a. Sodium Cotransport b. Sodium Counter Transport  END Any questions?