MHS1101-Lecture 2 - The Cell (Anatomy & Physiology I) Lecture Notes PDF

MHS1101 ANATOMY & PHYSIOLOGY 1 LECTURE 2 THE CELL Two hydrogen atoms walked into a room. The first hydrogen atom said to the second one, “I have lost my electron.” The second atom asked, “are you sure?” The first one answered, “I am positive.” LEARNING OUTCOMES By the end of today’s lecture, you sh...

MHS1101 ANATOMY & PHYSIOLOGY 1 LECTURE 2 THE CELL Two hydrogen atoms walked into a room. The first hydrogen atom said to the second one, “I have lost my electron.” The second atom asked, “are you sure?” The first one answered, “I am positive.” LEARNING OUTCOMES By the end of today’s lecture, you should be able to:  Describe the basic components of a typical cell  List the main organelles of a cell, describe their structure, and explain their functions  Describe the structure of the plasma membrane  Describe a second-messenger system & discuss its importance in human physiology  Describe the structure and functions of microvilli & cilia  Describe the cytoskeleton and its functions  The transport of substances across the plasma membrane THE CELL  all organisms are composed of cells  cells responsible for all structural & functional properties of living organisms  Important for understanding  workings of human body  mechanisms of disease  rationale of therapy CELL SHAPES & SIZES  ± 200 types of cells in human body  variable shapes  squamous - thin & flat  cuboidal - cube-shaped  columnar - taller than wide  fusiform - thick in middle, tapered toward ends  shape can appear different in different sections (e.g. longitudinal vs. cross section) Figure 3.1 Copyright © McGraw-Hill Education. Permission required for reproduction or display. CELL SHAPES & SIZES  Human cell size  most cells 10-5 micrometers (μm) in diameter  egg cells [ova] relatively large at 100 μm diameter  some nerve cells over 1 meter long  limit on cell size: overly large cells cannot support themselves & may rupture  for any given increase in diameter, volume increases more than surface area  volume proportional to cube of diameter  surface area proportional to square of diameter Basic Components of a Cell  Plasma (cell) membrane  surrounds cell & defines boundaries  made of proteins and lipids  Cytoplasm  organelles  cytoskeleton  inclusions (stored or foreign particles)  cytosol (intracellular fluid, ICF)  Extracellular fluid (ECF)  fluid outside of cells  includes tissue (interstitial) fluid LEARNING OUTCOMES By the end of today’s lecture you should be able to:  Describe the basic components of a typical cell  List the main organelles of a cell, describe their structure, and explain their functions  Describe the structure of the plasma membrane  Describe a second-messenger system & discuss its importance in human physiology  Describe the structure and functions of microvilli & cilia  Describe the cytoskeleton and its functions  The transport of substances across the plasma membrane STRUCTURE OF A REPRESENTATIVE CELL Figure 3.5 Copyright © McGraw-Hill Education. Permission required for reproduction or display. MEMBRANOUS & NON-MEMBRANOUS ORGANELLES  internal structures of a cell, carry out specialized metabolic tasks  Membranous organelles  nucleus, mitochondria, lysosomes, peroxisomes, endoplasmic reticulum & Golgi complex  Non-membranous organelles  ribosomes, centrosomes, centrioles, basal bodies Cytoplasm: Cytosol Cytosol vs. extracellular fluid  Cytosol [intracellular fluid] Extracellular fluid  higher K+ concentration  lower Na+ concentration  higher concentration suspended proteins (e.g. enzymes) Cytosol contains Cytoplasm  carbohydrates (energy)  amino acids (manufacture proteins)  lipids (energy) Plasma membrane The Nucleus  largest organelle (5 μm in diameter)  most cells have one nucleus – a few are anuclear or multinucleate  nuclear envelope - double membrane around nucleus  perforated by nuclear pores formed by rings of proteins  regulate molecular traffic through envelope & hold membrane layers together  Nuclear envelope is supported by nuclear lamina  web of protein filaments  provides points of attachment for chromatin  helps regulate cell life cycle  nucleoplasm - material in nucleus  chromatin (thread-like) composed of DNA & protein  nucleoli - masses where ribosomes are produced – protein synthesis DNA & RNA Nitrogen-containing bases: Adenine, Cytosine, Guanine, Thymine, Uracil DNA (deoxyribonucleic acid)  A, C, G, T  Double strand of nucleotides  genetic material in nucleus of the cell RNA (ribonucleic acid)  A, C, G, U  single strand of nucleotides  cytoplasm (outside nucleus)  carries out instructions for protein synthesis NUCLEUS Photos © McGraw-Hill Education NUCLEUS AS SEEN BY ELECTRON MICROSCOPE (a) Interior of nucleus (b) Surface of nucleus Figure 3.27a Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 3.27b a: © Richard Chao; b: © E.G. Pollock NUCLEAR PORES Photos © McGraw-Hill Education STRUCTURE OF THE NUCLEUS Figure 3.28 Copyright © McGraw-Hill Education. Permission required for reproduction or display. NUCLEOLUS Photos © McGraw-Hill Education MITOCHONDRIA  organelles specialized for synthesising ATP  continually change shape from spheroidal to thread-like  surrounded by a double membrane  inner membrane has folds called cristae  spaces between cristae called matrix  matrix contains ribosomes, enzymes used for ATP synthesis, small circular DNA molecule  mitochondrial DNA (mtDNA)  ‘Powerhouses’ of the cell  energy is extracted from organic molecules & transferred to ATP MITOCHONDRION Photos © McGraw-Hill Education CRISTAE OF MITOCHONDRION Photos © McGraw-Hill Education A MITOCHONDRION Figure 3.32 Copyright © McGraw-Hill Education. Permission required for reproduction or display. © Keith R. Porter/Science Source EVOLUTION OF MITOCHONDRIA  evolved from bacteria that invaded another primitive cell, survived in its cytoplasm & became permanent residents  bacterium provided inner membrane; host cell phagosome provided outer membrane  mitochondrial ribosomes resemble bacterial ribosomes  mtDNA resembles circular DNA of bacteria  mtDNA is inherited through the mother  mtDNA mutates more rapidly than nuclear DNA  responsible for hereditary diseases affecting tissues with high energy demands ENDOPLASMIC RETICULUM  system of channels (cisternae) enclosed by membrane Rough endoplasmic reticulum  parallel, flattened sacs covered with ribosomes  continuous with outer membrane of nuclear envelope  produces phospholipids & proteins of the plasma membrane  synthesizes proteins that are packaged in other organelles or secreted from cell ROUGH ENDOPLASMIC RETICULUM Photos © McGraw-Hill Education ENDOPLASMIC RETICULUM Smooth endoplasmic reticulum  lack ribosomes  cisternae more tubular and branching  cisternae thought to be continuous with rough ER  synthesises steroids and other lipids  detoxifies alcohol and other drugs  calcium storage  Rough & smooth ER are functionally different parts of the same network SMOOTH ENDOPLASMIC RETICULUM Photos © McGraw-Hill Education ENDOPLASMIC RETICULUM Figure 3.29c RIBOSOMES  small granules of protein & RNA  found in nucleoli, in cytosol, & on outer surfaces of rough ER, & nuclear envelope  ‘read’ coded genetic messages (messenger RNA) & assemble amino acids into proteins specified by the code MEMBRANE-BOUND RIBOSOMES Photos © McGraw-Hill Education FREE RIBOSOMES Photos © McGraw-Hill Education GOLGI COMPLEX  system of cisternae that synthesises carbohydrates & completes protein synthesis  receives newly synthesised proteins from rough ER  sorts proteins, splices some, adds carbohydrate moieties to some, & packages them into membrane-bound Golgi vesicles  some vesicles become lysosomes  some vesicles migrate to plasma membrane & fuse to it  some become secretory vesicles that store protein product for later release Figure 3.30 GOLGI COMPLEX Photos © McGraw-Hill Education CIS- & TRANS-FACE OF GOLGI COMPLEX cis-face Photos © McGraw-Hill Education trans-face SECRETORY VESICLE FROM GOLGI COMPLEX Photos © McGraw-Hill Education LYSOSOMES  package of enzymes bound by membrane  generally round, but variable in shape  Functions  intracellular hydrolytic digestion of proteins, nucleic acids, complex carbohydrates, phospholipids & other substances  autophagy - digestion of cell’s surplus organelles  autolysis - ‘cell suicide’ - digestion of a surplus cell by itself Photos © McGraw-Hill Education PEROXISOMES  resemble lysosomes but contain different enzymes & are produced by ER  Function - use molecular O2 to oxidise organic molecules  reactions produce hydrogen peroxide  catalase breaks down excess peroxide to &  neutralise free radicals, detoxify drugs & variety of blood-borne toxins  break down fatty acids into acetyl groups for use in ATP synthesis  In all cells, but abundant in liver & kidney Photos © McGraw-Hill Education LYSOSOMES & PEROXISOMES (a) Lysosomes Figure 3.31a Copyright © McGraw-Hill Education. Permission required for reproduction or display. (b) Peroxisomes Figure 3.31b (a-b): © Don Fawcett/Science Source PROTEASOMES  hollow, cylindrical organelles that dispose of surplus proteins  contain enzymes that break down tagged, targeted proteins into short peptides & amino acids Figure 3.32 CENTRIOLES  short cylindrical assembly of microtubules  arranged in 9 groups of 3 microtubules each  play important role in cell division  form basal bodies of cilia & flagella  each basal body is a centriole that originated in centriolar organising centre & then migrated to membrane Figure 3.34 © Educational Images LTD/Custom Medical Stock Photo/Newscom CENTRIOLES Photos © McGraw-Hill Education INCLUSIONS Two kinds of inclusions  Stored cellular products  glycogen granules, pigments, & fat droplets  Foreign bodies  viruses, intracellular bacteria, dust particles, & debris phagocytized by a cell  never enclosed in a unit membrane  not essential for cell survival FLAGELLA  tail of a sperm - only functional flagellum in humans  whip-like structure with axoneme identical to that of cilia  much longer than cilium  reinforced by coarse fibers that support the tail  movement is undulating, snake-like, corkscrew  no power stroke or recovery strokes PSEUDOPODS  continually changing extensions of cell  vary in shape & size  used for cellular locomotion, capturing foreign particles Figure 3.13 Copyright © McGraw-Hill Education. Permission required for reproduction or display. LEARNING OUTCOMES By the end of today’s lecture, you should be able to:  Describe the basic components of a typical cell  List the main organelles of a cell, describe their structure, and explain their functions  Describe the structure of the plasma membrane  Describe a second-messenger system & discuss its importance in human physiology  Describe the structure and functions of microvilli & cilia  Describe the cytoskeleton and its functions  The transport of substances across the plasma membrane STRUCTURE OF A REPRESENTATIVE CELL Figure 3.5 Copyright © McGraw-Hill Education. Permission required for reproduction or display. THE PLASMA [CELL] MEMBRANE  border of the cell - keeps internal & external cell environments separate  a selective, differentially, permeable lipid bilayer  controls entry & exit of ions, e.g., Na+, K+, Ca+  responds to extracellular fluid controls entry of substances into cell  (i) passively  (ii) actively a: © Don Fawcett/Science Source Figure 3.6a PLASMA MEMBRANE Photos © McGraw-Hill Education Plasma Membrane  Membrane lipids  Membrane proteins  Membrane carbohydrates Photos © McGraw-Hill Education THE PLASMA MEMBRANE Figure 3.6b Copyright © McGraw-Hill Education. Permission required for reproduction or display. MEMBRANE LIPIDS  98% of membrane molecules are lipids  Phospholipids  75% of membrane lipids are phospholipids  amphipathic molecules arranged in a bilayer  hydrophilic phosphate heads face H2O on each side of membrane  hydrophobic tails directed towards the centre, avoiding H2O  drift laterally, keeping membrane fluid Phospholipid Bilayer Outer Leaflet Photos © McGraw-Hill Education Inner Leaflet Phospholipid Molecules Fatty Acid Tails Polar Heads Photos © McGraw-Hill Education MEMBRANE LIPIDS  Cholesterol  20% of membrane lipids  holds phospholipids still & can stiffen membrane  Glycolipids  5% of membrane lipids  phospholipids with short carbohydrate chains on extracellular face  contributes to glycocalyx - carbohydrate coating on cell surface MEMBRANE LIPIDS Cholesterol Photos © McGraw-Hill Education Glycolipid Photos © McGraw-Hill Education MEMBRANE PROTEINS  2% of molecules but 50% of weight of membrane  integral (part of membrane)  peripheral (bound to membrane) Functions  anchoring proteins (support)  recognition proteins (self)  enzymes (catalyse reactions)  receptor proteins (binding)  carrier proteins (transport)  channels (water soluble passage) MEMBRANE PROTEINS Integral proteins - penetrate membrane  transmembrane proteins pass right through  hydrophilic regions contact cytoplasm, extracellular fluid  hydrophobic regions pass through lipid of membrane  some drift in membrane  others anchored to cytoskeleton Peripheral proteins  adhere to one face of membrane  do not penetrate membrane  usually tethered to cytoskeleton Photos © McGraw-Hill Education Transmembrane Proteins Photos © McGraw-Hill Education Peripheral Protein TRANSMEMBRANE PROTEINS Figure 3.7 Copyright © McGraw-Hill Education. Permission required for reproduction or display. SOME FUNCTIONS OF MEMBRANE PROTEINS (a) Receptor A receptor that binds to chemical messengers such as hormones sent by other cells (b) Enzyme An enzyme that breaks down a chemical messenger and terminates its effect (d) Gated channel (c) Channel A channel protein that is constantly open and allows solutes to pass into and out of the cell A gate that opens and closes to allow solutes through only at certain times Figure 3.8 Copyright © McGraw-Hill Education. Permission required for reproduction or display. (e) Cell-identity marker A glycoprotein acting as a cell-identity marker distinguishing the body's own cells from foreign cells (f) Cell-adhesion molecule (CAM) A cell-adhesion molecule (CAM) that binds one cell to another MEMBRANE PROTEINS Function as:  receptors - bind chemical signals  second messenger systems - communicate within cell receiving chemical message  enzymes - catalyze reactions including digestion of molecules, production of second messengers  channel proteins - allow hydrophilic solutes & water to pass through membrane  some are always open, some are gated  ligand-gated channels - respond to chemical messengers  voltage-gated channels - respond to charge changes  mechanically-gated channels - respond to physical stress on cell  crucial to nerve & muscle function Channel Pore Photos © McGraw-Hill Education MEMBRANE PROTEINS  carriers - bind solutes & transfer them across membrane  pumps - carriers that consume ATP  cell-identity markers - glycoproteins acting as identification tags  cell-adhesion molecules - mechanically link cell to extracellular material SECOND MESSENGERS  chemical first messenger (e.g., epinephrine) binds to a surface receptor  receptor activates G protein - an intracellular peripheral protein that obtains energy from guanosine triphosphate (GTP)  G protein relays signal to adenylate cyclase which converts ATP to cAMP (second messenger)  cAMP activates cytoplasmic kinases  kinases add phosphate groups to other enzymes turning some on & others off  up to 60% of drugs work through G proteins & second messengers A SECOND-MESSENGER SYSTEM 1) A messenger [e.g. epinephrine] (red triangle) binds to a receptor in plasma membrane. 2)Receptor releases a G protein travels freely in cytoplasm & can go on to step 3 or have various other effects on the cell. 3)The G protein binds to an enzyme, adenylate cyclase, in the plasma membrane. Adenylate cyclase converts ATP to cyclic AMP (cAMP), the second messenger. 4)cAMP activates a cytoplasmic enzyme called a kinase. 5) Kinases add phosphate groups 𝐏𝐢 to other cytoplasmic enzymes. This activates some enzymes and deactivates others, leading to varied metabolic effects in the cell. Figure 3.9 Copyright © McGraw-Hill Education. Permission required for reproduction or display. THE GLYCOCALYX  fuzzy coat external to plasma membrane  carbohydrate moieties of glycoproteins & glycolipids  unique in everyone except identical twins  Functions  protection  immunity to infection  defense against cancer  transplant compatibility MEMBRANE CARBOHYDRATES: GLYCOCALYX Photos © McGraw-Hill Education Glycoprotein Photos © McGraw-Hill Education LEARNING OUTCOMES By the end of today’s lecture, you should be able to:  Describe the basic components of a typical cell  List the main organelles of a cell, describe their structure, and explain their functions  Describe the structure of the plasma membrane  Describe a second-messenger system & discuss its importance in human physiology  Describe the structure and functions of microvilli & cilia  Describe the cytoskeleton and its functions  The transport of substances across the plasma membrane NON-MEMBRANOUS ORGANELLES MICROVILLI  made of microfilaments - provide strength & anchor microvilli to cell  increase surface area  increase exposure to extracellular fluid  absorb materials from extracellular fluid  often seen as a block [‘brush border’] NON-MEMBRANOUS ORGANELLES MICROVILLI a: © Don W. Fawcett/Science Source; b: © Biophoto Associates/Science Source Figure 3.10a Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 3.10b NON-MEMBRANOUS ORGANELLES CILIA made of microtubules - function in movement hair-like processes 7 - 10 μm long single, nonmotile cilium found on most cells monitor nearby conditions balance in inner ear; light detection in retina multiple nonmotile cilia on sensory cells of nose motile cilia - respiratory tract, reproductive tract, ventricles of brain beat in waves to sweep material across surface in one direction Photos © McGraw-Hill Education NON-MEMBRANOUS ORGANELLES: CILIA  axoneme - core of motile cilium  9 + 2 structure of microtubules  2 central microtubules surrounded by ring of nine pairs  pairs anchor cilium to cell as part of basal body  dynein arms ‘crawl’ up adjacent microtubule, bending cilium  uses energy from ATP a: © SPL/Science Source; c: © Don Fawcett/Science Source Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 3.11 NON-MEMBRANOUS ORGANELLES: CILIA  cilia beat freely within a saline layer at cell surface  Chloride pumps move  & into ECF follow  mucus floats on top of saline layer Figure 3.12 Copyright © McGraw-Hill Education. Permission required for reproduction or display. CYSTIC FIBROSIS  hereditary disease  cells make chloride pumps, but fail to install them in plasma membrane  chloride pumps fail to create adequate saline layer on cell surface  Thick mucus plugs pancreatic ducts & respiratory tract  inadequate digestion of nutrients & absorption of oxygen  chronic respiratory infections  lowered life expectancy THE CYTOSKELETON  network of protein filaments & cylinders  determines cell shape  supports structure  organises cell contents  directs movement of materials within cell  contributes to movements of cell as a whole  composed of microfilaments, intermediate fibers, microtubules LEARNING OUTCOMES By the end of today’s lecture, you should be able to:  Describe the basic components of a typical cell  List the main organelles of a cell, describe their structure, and explain their functions  Describe the structure of the plasma membrane  Describe a second-messenger system & discuss its importance in human physiology  Describe the structure and functions of microvilli & cilia  Describe the cytoskeleton and its functions  The transport of substances across the plasma membrane THE CYTOSKELETON Copyright © McGraw-Hill Education. Permission required for reproduction or display. b: © Dr. Torsten Wittmann/Science Source Figure 3.25 THE CYTOSKELETON  Microfilaments  6 nm thick, made of actin protein  forms terminal web  Intermediate filaments  8-10 nm thick, within skin cells, made of protein keratin  give cell shape, resist stress  Microtubules  25 nm thick, consist of protofilaments made of protein tubulin  radiate from centrosome  maintain cell shape, hold organelles, act as ‘railroad tracks’ for walking motor proteins; make axonemes of cilia & flagella; form mitotic spindle THE CYTOSKELETON Microfilaments Photos © McGraw-Hill Education Intermediate Filaments Microtubules MICROTUBULES Figure 3.26 Copyright © McGraw-Hill Education. Permission required for reproduction or display. LEARNING OUTCOMES By the end of today’s lecture, you should be able to:  Describe the basic components of a typical cell  List the main organelles of a cell, describe their structure, and explain their functions  Describe the structure of the plasma membrane  Describe a second-messenger system & discuss its importance in human physiology  Describe the structure and functions of microvilli & cilia  Describe the cytoskeleton and its functions  The transport of substances across the plasma membrane MEMBRANE TRANSPORT  plasma membrane is selectively permeable  allows some things through, but prevents others from passing  Passive mechanisms require no ATP  random molecular motion of particles provides necessary energy  filtration, diffusion, osmosis  Active mechanisms consume ATP  active transport and vesicular transport  carrier-mediated mechanisms use a membrane protein to transport substances across membrane FILTRATION  particles driven through membrane by physical pressure  e.g., filtration of water & small solutes through gaps in capillary walls  allows delivery of water & nutrients to tissues  allows removal of waste from capillaries in kidneys FILTRATION THROUGH WALL OF BLOOD CAPILLARY Blood pressure in capillary forces H2O & small solutes such as salts through narrow clefts between capillary cells. Clefts hold back larger particles such as red blood cells. Figure 3.14 Copyright © McGraw-Hill Education. Permission required for reproduction or display. SIMPLE DIFFUSION  net movement of particles from high concentration to lower concentration  due to constant, spontaneous molecular motion  molecules collide & bounce off each other  substances diffuse down their concentration gradient  does not require a membrane  substance can diffuse through membrane if membrane is permeable to the substance SIMPLE DIFFUSION Factors affecting diffusion rate through a membrane  temperature:  temperature results in  motion of particles  molecular weight: larger molecules move slower  steepness of concentrated gradient: difference leads to  rate  membrane surface area:  in surface area leads to  rate  membrane permeability:  permeability results in  rate OSMOSIS  net flow of H20 through selectively permeable membrane  H20 moves from more concentrated to less concentrated  solute particles that cannot pass through membrane ‘draw’ H20 from other side  crucial consideration for I.V. fluids - osmotic imbalances underlie diarrhea, constipation, edema  H20 can diffuse through phospholipid bilayers, but osmosis is enhanced by aquaporins - channel proteins in membrane specialized for H20 passage  cells can speed osmosis by installing more aquaporins OSMOSIS (a) Start (b) 30 minutes later Figure 3.15 Copyright © McGraw-Hill Education. Permission required for reproduction or display. CARRIER-MEDIATED TRANSPORT  transport proteins in membrane carry solutes into or out of cell (or organelle)  Specificity  transport proteins are specific for particular solutes  solute (ligand) binds to receptor site on carrier protein  solute is released unchanged on other side of membrane  Saturation  as solute concentration rises, the rate of transport rises, but only to a point - transport maximum (Tm)  transport maximum - rate at which all carriers are occupied CARRIER SATURATION & TRANSPORT MAXIMUM Figure 3.17 Copyright © McGraw-Hill Education. Permission required for reproduction or display. CARRIER-MEDIATED TRANSPORT Three kinds of carriers  uniport - carries one type of solute - e.g., Ca+ pump  symport - carries two or more solutes simultaneously in same direction (cotransport) - e.g., sodium-glucose transporters  antiport - carries two or more solutes in opposite directions (countertransport) - e.g., Na+-K+ pump removes Three mechanisms of carrier-mediated transport  facilitated diffusion  primary active transport  secondary active transport brings in FACILITATED DIFFUSION 1) A solute particle enters channel of a membrane protein (carrier). 2) Solute binds to receptor site on the carrier & the carrier changes conformation. Figure 3.18 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 3) The carrier releases the solute on other side of the membrane. Does not require ATP. CARRIER-MEDIATED TRANSPORT  primary active transport - carrier moves solute through membrane up its concentration gradient  carrier protein uses ATP for energy  Examples:  Ca+ pump (uniport) uses ATP while expelling Ca+ from cell to where it is already more concentrated − pump (antiport) uses ATP while expelling  −     & importing into cell pump functions maintains concentration gradient allowing for secondary active transport regulates solute concentration & thus osmosis & cell volume maintains negatively charged resting membrane potential produces heat THE SODIUM–POTASSIUM PUMP ( –  Each pump cycle consumes one ATP & exchanges 3 for 2  Keeps concentration higher & concentration lower within cell than in ECF  Necessary because & constantly leak through membrane  Half of daily calories utilized for − pump Copyright © McGraw-Hill Education. Permission required for reproduction or display. Figure 3.20 ATPASE) SECONDARY ACTIVE TRANSPORT  carrier moves solute through membrane but only uses ATP indirectly  e.g., sodium-glucose transporter (SGLT) (symport)  moves glucose into cell while simultaneously carrying down its gradient  depends on primary transport performed by pump  does not itself use ATP  SGLTs work in kidney cells that have − pump at other end of cell  prevents loss of glucose to urine Figure 3.19 Copyright © McGraw-Hill Education. Permission required for reproduction or display. VESICULAR TRANSPORT  moves large particles [fluid droplets, molecules] through membrane in vesicles - enclosures of membrane  endocytosis - processes that bring material into cell  phagocytosis - ‘cell eating’, engulfing large particles  pseudopods; phagosomes; macrophages  pinocytosis [‘cell drinking’] - takes in ECF containing molecules useful to cell  membrane caves in then pinches off pinocytic vesicle  receptor-mediated endocytosis - particles bind to specific receptors on plasma membrane  exocytosis - discharging material from the cell  utilizes motor proteins energized by ATP PHAGOCYTOSIS, INTRACELLULAR DIGESTION & EXOCYTOSIS 1) A phagocytic cell encounters a particle of foreign matter. 7) The indigestible residue is voided by exocytosis. 2) The cell surrounds the particle with its pseudopods. 6) The phagolysosome fuses with the plasma membrane. 3) The particle is phagocytized and contained in a phagosome. 5) Enzymes from the lysosome digest the foreign matter. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 4) The phagosome fuses with a lysosome and becomes a phagolysosome. Figure 3.21 RECEPTOR-MEDIATED ENDOCYTOSIS 1) Extracellular molecules bind to receptors on plasma membrane; receptors cluster together. 2) Plasma membrane sinks inward, forms clathrin-coated pit. Figure 3.22 Copyright © McGraw-Hill Education. Permission required for reproduction or display. 3) Pit separates from plasma membrane, forms clathrin-coated vesicle containing concentrated molecules from ECF. (1-3): Courtesy of the Company of Biologists, Ltd. EXOCYTOSIS 1) A secretory vesicle approaches plasma membrane & docks on it by means of linking proteins. Plasma membrane caves in at that point to meet the vesicle. 2) Plasma membrane & vesicle unite to form fusion pore through which the vesicle contents are released. Figure 3.24 Copyright © McGraw-Hill Education. Permission required for reproduction or display. b: Courtesy of Dr. Birgit Satir, Albert Einstein College of Medicine LEARNING OUTCOMES And this is what we covered today:  Describe the basic components of a typical cell  List the main organelles of a cell, describe their structure, and explain their functions  Describe the structure of the plasma membrane  Describe a second-messenger system & discuss its importance in human physiology  Describe the structure and functions of microvilli & cilia  Describe the cytoskeleton and its functions  The transport of substances across the plasma membrane NEXT LECTURE CELLULAR RESPIRATION & ATP PRODUCTION