The Cell: A Comprehensive Overview PDF

THE CELL Cell Phospholipid Molecules - The basic morphological and func5onal unit of - Made 1 head and 2 tails linked by covalent all living things bonds...

THE CELL Cell Phospholipid Molecules - The basic morphological and func5onal unit of - Made 1 head and 2 tails linked by covalent all living things bonds - Smallest en5ty with the capacity to perform all Head life’s func5ons - Globular, polar, hydrophilic Zygote - Glycerol that is conjugated to a nitrogenous - Fer5lized ovum and star5ng point of humans compound by a phosphate bridge - Results from union of male sperm and female Tails egg cell - Slender, nonpolar, hydrophobic - Later undergoes mul5plica5on and - One straight-chain saturated faTy acid and differen5a5on to make organisms with another unsaturated faTy acid with a slight hundreds of cell types based on morphology kink and func5on Phospholipid Bilayer o Cells in adults: 100 trillion - Tails are in the inner region and heads in the Organiza4on outer region Cells Basic unit of life - Electron-lucent middle zone (tails; weak Tissues Cells with same general func5ons that intermolecular forces) are linked by some intercellular - Electron-dense outer zone (heads) material or cell-to-cell junc5on - Highly impermeable and only allows water, Organs Bonded 5ssues that form a more gases, and few nonpolar molecules to pass complex func5onal structure freely Organ Organs with interrelated func5ons - Acts as barrier that regulate entry and exit of Systems that group together substances Cell Varia4on Protein Molecules - Dictated by func5ons and state of ac5vity - Account for ½ the total mass of the cell Common Basic Structure of Cells membrane Cytoplasm 2 Types Cell Membrane – encases cytoplasm 1. Integral Proteins Nucleus – encased by nuclear envelope, - Also called integral membrane proteins or embedded in cytoplasm transmembrane proteins - Span the whole thickness of the cell and Cell Membrane projects to both surfaces of the membrane - Also called Plasma Membrane or 2. Peripheral Proteins Plasmalemma - Simply inserted or are loosely bound to the - 8–10 nm thick outer or inner surface - Can be seen in TEM: Func4ons o Trilaminar with 2 electron-dense - Transport substances sheets with a thin electron-lucent layer - Par5cipate in enzyma5c ac5vity, signal in the middle transduc5on, and cell-to-cell recogni5on Func4ons: Protects cells Cholesterol Molecules Regulates movement of substances in and out - Few to almost as many as the phospholipid molecules Provides aTachment for the cytoskeleton - Found in irregular spaces between Receives and sends s5muli phospholipids Provides binding sites and receptors for - S5ffens and strengthens membrane and makes enzymes and substances it less permeable to water-soluble substances Cell-to-cell recogni5on Forms specialized junc5ons with membranes Polysaccharide Molecules of adjacent cells or extracellular matrix - Glycolipids or glycoproteins Made up of: - Many project from the outer surface to form a 1. Phospholipids coa5ng called glycocalyx (cell coat) 2. Protein Molecules o 2–20 nm, amorphous electron-dense 3. Cholesterol o Cell-to-cell recogni5on and adhesion 4. Polysaccharides and immunological response  Organelles - Delimited by unit membranes except for ribosomes and centrosome - RBCs and lens fibers do not have organelles - Type and number of organelles are dictated by cell ac5vity and func5on 1. Mitochondria - Present in all cells except RBC and lens fibers - Hotdog-shaped, but can become rod-like, filamentous, or spherical Unit Membrane - 0.5–1.0 µm diameter; 10 µm long - Term used for the trilaminar en5ty of other - Visible in LM under special staining (Janus membrane-containing structures inside the green) and phase-contrast cells - Morphology can be appreciated in Electron - Varies in thickness depending on protein microscope molecules Specialized Junc4ons Formed by the Cell Membrane 1. Interdigita4on - Cells interlock or interdigitate like fingers with adjacent cells 2. Occluding Junc4ons - 1 form: zonula occludens 3. Adhesive Junc4ons - Zonula adherens, belt desmosome, fascia adherens, desmosome, hemidesmosome 4. For Communica4on Parts - Gap junc5ons, chemical synapses, motor Wall endplates (muscle) a. Outer Membrane/Leaflet Epithelium Zonula occludens and adeherens, o Delimits mitochondrion from desmosome, hemidesmosome, and cytoplasmic matrix gap junc5on b. Inner Leaflet Muscle Fascia adherens and motor endplate o In-folded to form tubular cristae Nerves Chemical synapses mitochondriales Cristae Mitochondriales Cytoplasm o Project into the intercristal space - Refers to material within a living cell (excluding Intercristal Space nucleus) o Space or cavity nclosed by the wall - Consist of homogenous cytosol or cytoplasmic Intracristal Space matrix where formed elements are embedded o Empty space between loose inner and Formed Elements outer leaflets 1. Organelles Func4on - More or less permanent - Powerhouse of the cell 2. Inclusions - Contains enzymes for Kreb’s cycle that - Temporary lipids, pigments, or other degrades fat, carbohydrates, and proteins substances - Yields ATP 3. Fibrillar elements - Cells that do not have mitochondria rely on - Cytoskeleton Glycolysis - Increases the viscosity of cytoplasmic matrix Mitochondrial DNA - Mitochondrial matrix has DNA, mRNA, and Cytosol or Cytoplasmic Matrix tRNA - Viscid, translucent, and colloidal - Synthesize proteins and enzymes that it needs - 70% water - Only DNA found outside nucleus - Dissolved inorganic ions and organic molecules Loca4ons - Site of biochemical processes - Number depends on cell energy requirement - Hepatocyte “workhorse”: >2,000 mitochondria - Small lymphocyte: only a few  - Sperm: middle piece of tail to form sheath o Metabolism of carbohydrates, Replica4on detoxifica5on of metabolic products, - Binary fission alcohol, and drugs - Can only be produced from exis5ng ones o Plays a role in the transport of faTy - Mitochondria in all cells of the body are acids and lipids derived from female gamete o BeTer developed in hepatocytes 2. Ribosomes o Sarcoplasmic re5culum in striated - 15–30 nm muscles, storing and releasing calcium - Electron microscope ions - Electron-dense 4. Golgi Complex - Polyribosomes/Polysomes if clustered - Several layers of membrane-bound, smooth- o Ribosomes that are connected by fine surfaced, and flaTened tubes (cisternae) thread of mRNA, which they are - Cisternae have dilata5on (vesicles) on the ac5vely transla5ng lateral ends - Free or aTached to the surfaces of ER - Present in all cells - 2 subunits (small and large) - Can be seen as solid strands in LM with silver o Each called ribonucleoprotein salts or osmium and electron microscopy o Composed of rRNA and associated - Marked by a pale region (nega5ve Golgi image) proteins - 2 Surfaces: o Produced in nucleolus and exported to a. Convex or Cis or Forming Face the cytoplasm to form ribosomes b. Concave or Maturing or Trans Face - Present in all cells o Membrane is con5nually removed as - Many ribosomes = basophilic due to phosphate secretory vesicles (pinched off) in RNA - Dynamic Func4on Func4on - Sites for protein synthesis - Processes, concentrates, sorts, and packages - Amino acids are assembled into polypep5de proteins from the ER, and release them as chains secretory vesicles (membrane-wrapped) - Proteins from free ribosomes are used in the - Some proteins are used in the cell to make cell lysosomes or integral membrane proteins - Proteins from aTached ribosomes are - Some are exported processed in the ER and Golgi, and are either 5. Lysosome used in the cell or exported - Chemical containing pouches that float free in 3. Endoplasmic Re4culum cytoplasm - Most extensive membrane-bound structure - Contain hydroly5c enzymes (40 iden5fied - Consist of tubules, vesicles, and flaTened sacs ones) (cisternae) o Proteases, lipases, carbohydrases, o Fluid filled with unit membranes esterases, and nucleases - Present in all cells o Come from Golgi - Seen with fluorescent dyes and electron - Spherical or ovoid microscope - 0.05 to 0.8 µm - Dynamic, capable of remodeling and - Iden5fied through histochemical methods disassembling; interacts with organelles - Present in all cells 2 Regions Func4on a. Rough Endoplasmic Re4culum - Cons5tute intracellular diges5ve system o Rough because there are ribosomes - Degrades nearly all organic substances in the and polyribosomes aTached cell o Receives proteins from aTached - Enzymes act only in acidic environment and ribosomes, processes them, and inac5ve in cytosol (7.2 pH) passes them to the Golgi complex in - Heterophagy and autophagy the form of transfer vesicles Heterophagy o More extensive than sER in most cells - Lysosomal diges5on within the cell of materials b. Smooth Endoplasmic Re4culum that have been brought from the outside o Synthesis of lipids, phospholipids, through phagocytosis cholesterol, and steroids 5.1. Receptors on the cell surface bind the o Have aTached enzymes phagocy4c material  5.2. Pseudopodia is formed at the area of - Made of a pair of centrioles surrounded by binding centriolar satellites 5.3. Pseudopodia membranes fuse and envelop - Seen in TEM the phagocy5c material, becoming a Func4on phagosome or phagocy4c vacuole - Where microtubules are assembled 5.4. Phagosome is pinched off and drawn inside o Cytoskeleton, centrioles, mito5c 5.5. Primary Lysosome fuses with the spindles, and core (axoneme) of cilium membrane of the phagosome and digest and flagellum the material and becomes secondary Centrioles lysosome or phagolysosome - The 2 centrioles are referred to as diplosome 5.6. Nutrients from the phagocy5c material are - Perpendicular recycled. - 0.5–0.7 µm in length 5.7. Undigested material become residual - Electron-dense wall surrounding electron- bodies lucent space - Residual bodies are some5mes released by - Walls are made up of 9 groups of microtubules exocytosis, or kept in the cytoplasm o Each group is called a triplet of o Short-lived cells: dispersed when cell microtubule dies o Innermost microtubule in the triplet is o Long-lived cells: lipochrome or circular, while others are C-shaped lipofuschin pigments Phagocytosis - Neutrophils and macrophages - Phagocytes have numerous lysosomes Autophagy - Diges5on of unneeded or senescent organelles - Similar process to heterophagy - Structural renewal of cell - Lysosomes are numerous in cells with high turnover of organelles, like exocrine glands Osteoclasts - Cells that release their lysosomal enzymes extracellularly Centriole Replica4on - Bone resorp5on - 2 centrioles replicate prior to mitosis 6. Peroxisomes - Procentriole grows out of the lateral surface, - Membrane-bound, spherical elongate to form daughter centrioles - Oxidases and catalases - Sources of mito5c spindles - Enzymes come from cytoplasmic matrix, from o Pulls sister chroma5ds free ribosomes o Disintegrate during telophase - 0.5–1.2 µm - Sources of cilia and flagellum of sperm - Dis5nguished through histochemical o Remains aTached to parent centriole techniques or basal body - Present in all cells, numerous in hepatocytes Oxidases Inclusions - Oxida5on for detoxifica5on and catabolism of - Temporary and inert, useful and harmful phospholipids, faTy acids, ethanol, and - Fat droplets, glycogen, zymogen granules, formaldehyde taken into the cell pigment granules, crystals, and dust par5cles - Oxida5on generated H2O2, which are used by 1. Fat or Lipid Droplets phagocytes - Adipose cell is specialized to store this; 90% of Catalases the cell - Catalyze conversion of H2O2 to water and - In direct contact with cytoplasmic matrix oxygen because it may be toxic in large - Gray- or black-staining globules amounts (glutaraldehyde and osmic acid) 7. Centrosome 2. Glycogen - Microtubule Organizing Center - Storage of carbohydrates - Near nucleus and surrounded by Golgi - Abundant in liver and muscle - Present in all cells  - Periodic Acid Schiff Method, seen as purple or - Responsible for contrac5lity of muscle and magenta myoepithelial cells - Electron-dense, not enveloped by membrane 2. Intermediate Filaments - Large (alpha) and small (beta) par5cles - 10–12 nm - 90 nm and 20–30 nm in diameter - Do not undergo frequent assembly and 3. Zymogen Granules disassembly - Secretory epithelial cells - cytoplasm and nucleus - Synonymous with secretory granules - Cytoplasmic: kera5n, desmin, vimen5n, 4. Pigments neurofilament, and glial filament a. Melanin - Nuclear: lamins o Brown to black a. Kera5n o Permanent inclusions of kera5nocytes o Only in epithelial cells; kera5nocytes (epidermis) o Protect cells from mechanical and non- o Substan5a nigra and locus coeruleus mechanical stress (nerve cells) o Cell-to-cell aTachment (inner surface o Pigment epithelium of re5na of cell membrane) (produced by sER) b. Desmin b. Hemosiderin o Muscle cells o Brown o Numerous in smooth than striated o Lysosomal diges5on of hemoglobin o Form bundles in smooth muscle o Spleen o Around myofibrils in striated muscles, o Residual bodies; membrane-bound especially in Z-lines (discs) o Prussian blue o Cell architecture and structure c. Lipochrome or Lipofuschin Pigments (connect or anchor cytoplasmic o Coalesced residual bodies components) o Yellowish-brown c. Vimen5n o Long-lived cells: cardiac muscle cells o Cells differen5ated from mesenchyme and Sertoli cells in testes o Fibroblasts and muscle cells 5. Crystals o ScaTered in cytoplasm - Inters55al cells (of Leydig) and Sertoli cells o Cell shape and integrity of cytoplasm - Not membrane-bound and free and stabilizing cytoskeletal - Common in cells of older people interac5ons 6. Dust Par4cles o Anchor cytoplasmic organelles - Brown to black d. Neurofilaments - Membrane-bound o Nerve cells - Phagocytes of lungs (pulmonary alveolar o Internal support macrophage or dust cells); smokers and city o Cell body and processes of neurons dwellers (run parallel to the long axis) e. Glial Filaments Cytoskeleton o Suppor5ve cells in nervous system - Fibrillar elements that form the structural o Cell body and processes of neurons framework o Internal support - Electron microscopy f. Lamins 1. Microfilaments o 2 major subtypes - All cells o Form part of the nuclear lamina - 5–7 nm in diameter o Shape of the nucleus and anchor - Made up of F-ac5n nucleus to the endoplasmic re5culum o Formed when 2 strands of G-ac5n coil 3. Microtubules around each other - Hollow pipes - Assembled and disassembled for changes in - 25 µm diameter shape and movement - Assembled and disassembled - Peripheral areas of cells beneath the - Wall is formed by 13 tubulin molecules membrane arranged around a lumen - Involved in endocytosis and exocytosis - Tubulin – small family of minute globular - ScaTered in the center of the cell proteins - Involved in moving organelles o Formed by alpha-tubulin and beta- tubulin - Assembled in centrosome - One chromosomes of each pair is inherited - Comprise the walls of centrioles, mito5c from on parent spindles, core of cilia, and flagellum of sperm - 2 chromosomes in each pair are homologous - Surrounded by microtubule-associate proteins (similar in length, gene posi5on, and loca5on o Strengthen and stabilize their wall of centromere, but have different alleles) o Involved in movement of substances - Consists of DNA molecule and nucleoproteins over surfaces of microtubules (histones and nonhistones) o Bending of cilia and flagella - Chromosomes are stretched out in interphase, o Movement of mito5c spindle called chroma5ns o Euchroma5n Nucleus § Extended - Largest structure in a cell § Do not stain - 3–10 nm § Ac5vely producing rRNA, - Round or spherical, forms lobes in WBCs tRNA, and mRNA - Present in all cells except RBCs and lens fibers o Heterochroma5n - Delimited by nuclear envelope § Condensed - Chromosomes are embedded in the § Stains and forms chroma5n nucleoplasm (similar to cytoplasm) granules - Contains genes for proteins and nucleic acids § Not ac5vely producing RNA - Site for produc5on of RNAs - Star5ng mitosis, chromosomes condense and - Interphase are seen as basophilic under LM o Chromosomes become chroma5n o 0.5–0.8 µm in diameter; 3–6 µm in o Nucleoli are seen in nucleoplasm length - Framework is formed by the nuclear matrix o Rod-like o Stretch out again at the end of mitosis Nuclear Envelope - TEM Human Genome - Outer and inner nuclear membranes - Total amount of DNA present in the o 7–8 nm thick, separated by a 10–30 chromosomes (chromosomal genome) nm fluid-filled perinuclear space - Includes mitochondrial genome - Regarded as specialized por5on of rER because - 3 billion base pairs the perinuclear space is con5nuous with its - Genes – segment of DNA that code for a cavity and the outer nuclear membrane with its par5cular protein membrane; also studded with ribosomes - 19,000–20,000 genes - Fibrous Lamina – fibrillar protein layer that is - 5% of DNA molecules in chromosomes code for part of the nuclear matrix genes o 30–100 nm thick - Some exist for structure, regula5ng the use of o Consists of intermediate filaments gene5c informa5on, and some for no aparrent called lamins and nuclear lamin- reason associated membrane proteins o Mechanical support to nucleus Nucleolus - Clumps of chroma5n are aTached to the - Spherical, highly basophilic, eccentrically fibrous lamina located in the nucleus o Basophilic; outlines the inner surface - Not membrane enveloped and present only at of the nuclear envelope interphase - Nuclear Pores - Disappears during prophase and reappears late o Circular openings in nuclear envelop telophase, the same 5me nuclear membrane o 70–75 nm in diameter disappears and reappears o Stabilized by fibrous lamina - Can be more than two in protein synthesizing o Ringed by nuclear pore complex, that cells, like muscle cells form a thin film called pore diaphragm - Synthesizes ribosomal units o Exchange of substances between - Electron microscope cytoplasm and nucleus 3 Areas a. Nucleolar Organizing Region Chroma4n o Circular pale area surrounded by - 46 chromosomes (22 pairs soma5c; 1 pair sex) electron-dense filaments (pars fibrosa) - XY: males, XX: Females o Can be several per nucleolus  o Place where nuclear organizers gather complementary an5codon to pair up § Gene that codes for rRNA with the codon in the mRNA. The tRNA § Five chromosomes with is then released auer a chain is formed. nucleolar organizers o This process con5nues un5l a stop o Nuclear organizers are transcribed and codon is reached rRNA is produces - More than 1 ribosome can translate mRNA at o mRNA and tRNA are produced in the the same 5me euchroma5n - Proteins produced by free ribosomes are b. Pars Fibrosa released in the cell to be used or become part o Formed by rRNA produced in the of the membranes nucleolar organizing region - Proteins produced in aTached ribosomes go to c. Pars Granulosa the rER where they are processed and specific o Formed by ribosomal subunits chemical groups are added. They are then o Grainy area released as transfer vesicles going to the Golgi o Ribosomal subunits or complex ribonucleoprotein are newly formed - They travel to the forming face of the Golgi and rRNA that are linked to proteins are released into the lumen of the cisternae. imported from the cytoplasm Moving towards the maturing face, they are o Large and small ribosomal units form a further processed and then condensed, sorted, ribosome in the cytoplasm at the start packaged, and chemically labeled, and then of protein synthesis released to the cytoplasmic matrix as secretory vesicles Protein Synthesis o some are used within the cell as Proteins lysosomes or integral membrane - Make up parts of cells and 5ssues, enzymes, proteins and hormones and are important in the o some are exported by the cell through immune response and cell mul5plica5on exocytosis - A polypep5de chain composed of amino acid linked pep5de bonds Movement of Materials Across the Cell Membrane - Range from 50–5,000 amino acids - Simple molecules cross through diffusion, ion - Each has par5cular amino acid sequence channels, carrier transport, and ac5ve Amino Acids transport (with aid of pumps) - 20 kinds - Bigger substances like bacteria, secretory - Non-essen5al products, and other macromolecules are o Can be synthesized in the body transported (bulk transport) via endocytosis, - Essen5al exocytosis, and transcytosis o Cannot be synthesized in the body and 1. Endocytosis only acquired from diet - Bulk transfer from the extracellular matrix into Protein Synthesis the cell - Occurs in the cytoplasm a. Phagocytosis – solid substances (bacteria or - Code for a specific protein is transcribed from dust) the chromosome to an mRNA b. Pinocytosis – liquid substances o Transcribed pre-mRNA undergoes o Common in all cells post-transcrip5onal modifica5on and o Does not require receptors and becomes mRNA, going to the pseudopodia cytoplasm o Involves invagina5on of the cell - Codon – 3 consecu5ve amino acid code membrane to enclose the fluid and - tRNA – has two ends then pinching off of the pinocy4c o one where amino acid gets aTached vesicle Macrok) o the other where an an5codon o Micropinocytosis (large amounts of complementary to the codon is liquid) aTached o Micropinocytosis (small amounts of - mRNA aTracts ribosomes in the cytoplasm, liquid) which translate the mRNA and assemble amino o ATacked by lysosomes acids into polypep5de chains 2. Exocytosis o As the ribosome scans the mRNA for a - Transport from inside the cell to the outside codon, it allows the tRNA with the - Mostly secretory products (secretory vesicles) - Involves fusion of the vesicular membrane with cell membrane auer the release of its contents - Generates extra cell membrane, but is later brought back through phagocytosis and endocytosis - Exocyto5c release of secretory products can be: o Regulated secre4on § Occurs in pancrea5c acinar and major salivary glands § Secretory vesicles are first stored in the apical por5on of the cell where they accumulate and get dehydrated (appear as granules in TEM) § Content are released auer specific signal from neural or hormonal s5mulus o Cons4tu4ve secre4on § Occurs in fibroblasts and chondroblasts § Released from the cells as soon as they are formed § Do not have visible secretory granules 3. Transcytosis - Endocytosed macromolecules are not aTacked by lysosomes but are transported across the cell and released at the opposite cell surface through exocytosis