The Cellular Level of Organization Chapter 3 PDF
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San Pedro College
Dr. Allisa Mae A. Goneda, RMT
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This document provides a comprehensive overview of the cellular level of organization, including cell parts and their functions. It details the structure and function of plasma membranes, cytoplasm, and the nucleus.
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MLS 100 THE CELLULAR LEVEL OF ORGANIZATION CHAPTER 3 DR. ALLISA MAE A. GONEDA, RMT REFERENCE BOOK: Tortora's Principles of Anatomy and Physiology, 15th Edition CONTENTS 01 03 PARTS OF THE CELL CYTOPLASM...
MLS 100 THE CELLULAR LEVEL OF ORGANIZATION CHAPTER 3 DR. ALLISA MAE A. GONEDA, RMT REFERENCE BOOK: Tortora's Principles of Anatomy and Physiology, 15th Edition CONTENTS 01 03 PARTS OF THE CELL CYTOPLASM 02 04 PLASMA NUCLEUS MEMBRANE CONTENTS 05 07 CELLULAR DIVERSITY PROTEIN SYNTHESIS AND AGING 06 CELL DIVISION 01 PARTS OF THE CELL THE CELL PARTS OF THE CELL PLASMA MEMBRANE flexible outer surface Functions: ○ Selective barrier separates INTERNAL from EXTERNAL environment regulates flow of material in and out of the cell ○ Communication PARTS OF THE CELL CYTOPLASM consists of all the cellular contents between the plasma membrane and the nucleus. composed of: ○ CYTOSOL (aka intracellular fluid) fluid portion ○ ORGANELLES cytoskeleton ribosomes endoplasmic reticulum golgi complex lysosomes peroxisomes mitochondria PARTS OF THE CELL NUCLEUS houses the most of the cell’s DNA contains CHROMOSOMES that houses hereditary units (GENES) 02 THE PLASMA MEMBRANE PLASMA MEMBRANE Barrier that surrounds and contains the cytoplasm FLUID MOSAIC MODEL ○ The arrangement of resembles a continually moving sea of fluid lipids that contains a mosaic of different proteins Components ○ Membrane lipids ○ Proteins The plasma membrane is ASYMMETRIC PLASMA MEMBRANE FUNCTIONS Acts as barrier Control flow of substances in and out of the cell Helps identify the cell to other cells participates in intracellular signaling PLASMA MEMBRANE STRUCTURE LIPID BILAYER Basic structural framework of the plasma membrane Three types of lipid molecules ○ Phospholipid (75%) ○ Cholesterol (20%) ○ Glycolipid (5%) PLASMA MEMBRANE STRUCTURE LIPID BILAYER Lipids are AMPHIPATHIC (has polar and non-polar parts), hence they are arranged in a bilayer. “Like seeks like” ○ POLAR PART (hydroPHILIC) faces the extracellular fluid (ECF) and the cytosol ○ NON-POLAR part (hydroPHOBIC) faces towards another LIPIDS ARE AMPHIPATHIC PHOSPHOLIPID CHOLESTEROL GLYCOLIPID Phosphate containing POLAR PART head Tiny -OH (hydroxyl) group Carbohydrate group NON-POLAR Steroid rings of Fatty acid tail Fatty acid tail PART hydrocarbon Appears only in the NOTE membrane that faces the ECF LIPIDS ARE AMPHIPATHIC PLASMA MEMBRANE STRUCTURE MEMBRANE PROTEINS INTEGRAL PROTEINS PERIPHERAL PROTEINS - Extends INTO or THROUGH the lipid - Not firmly embedded to the plasma bilayer membrane - Mostly TRANSMEMBRANE proteins - May be attached to: (spans the entire bilayer) - Polar heads of lipid proteins - Amphipathic - Integral proteins - Many are glycoproteins PLASMA MEMBRANE STRUCTURE GLYCOCALYX Formed by the carbohydrate portions of glycoproteins and glycolipids Functions: ○ MOLECULAR SIGNATURE ○ Enables cells to adhere to one another ○ Protects cells from enzymatic degradation ○ Makes red blood cells slippery ○ Protects gastrointestinal and airway cells from drying out PLASMA MEMBRANE STRUCTURE FUNCTIONS OF MEMBRANE PROTEINS 1. Forms an Ion channel 2. Acts are carriers 3. Acts as receptors 4. Acts as Enzymes 5. Serves as linkers 6. Serves as cell-identity markers PLASMA MEMBRANE STRUCTURE PLASMA MEMBRANE STRUCTURE MEMBRANE FLUIDITY Fluidity depends on the NUMBER OF DOUBLE BONDS in the fatty acid tails ○ ↑double bond = ↑ fluidity Cholesterol - makes the membrane less fluid in normal temperature ○ ↓ temperature = ↑ fluidity Importance of membrane fluidity: ○ Decreases membrane rigidity → improves cell mobility ○ Enables cell processes (cell movement, growth, division, secretion, and cellular junction formation ○ Allows membrane to self-seal when punctured PLASMA MEMBRANE MEMBRANE PERMEABILITY The plasma membrane is SELECTIVELY PERMEABLE LIPID BILAYER ○ Permeable to nonpolar molecules (oxygen, carbon dioxide, and steroids) ○ Moderately permeable - small uncharged molecules (water and urea) ○ impermeable to ions and large, uncharged polar molecules (glucose) TRANSMEMBRANE PROTEINS ○ Acts as channels or carriers Note: the more hydrophobic or lipid-soluble the substance is, the more it readily passes through the plasma membrane PLASMA MEMBRANE GRADIENT ACROSS THE PLASMA MEMBRANE CONCENTRATION GRADIENT ○ Difference in the concentration of a chemical from one place to another Concentrated in the extracellular fluid - oxygen and sodium ions Concentrated inside the cell - carbon dioxide and potassium ions ELECTRICAL GRADIENT aka MEMBRANE POTENTIAL ○ The difference of electrical charges in two different regions Due to the difference in distribution of positive and negatively-charged ions Inside the cell - NEGATIVELY CHARGED Outside the cell - POSITIVELY CHARGED ELECTROCHEMICAL GRADIENT - combination of concentration and chemical gradient ○ This contributes to the movement of substances across the plasma membrane TRANSPORT ACROSS THE MEMBRANE Transport of substances occur via ACTIVE OR PASSIVE PROCESS depending on the requirement of cellular energy. TRANSPORT ACROSS THE MEMBRANE ACTIVE TRANSPORT PASSIVE TRANSPORT Requires ATP? YES NO Movement of substances UPHILL DOWNHILL “Against” the concentration gradient Higher solute concentration → lower solute Lower SOLUTE concentration concentration → higher solute concentration Examples Active transport Diffusion - Primary - Simple - Secondary - Facilitated Vesicle transport Osmosis - Endocytosis - Exocytosis PASSIVE PROCESSES THE DIFFUSION PRINCIPLE DIFFUSION - a passive process in which the random mixing of particles in a solution occurs because of the particle’s kinetic energy. ○ SOLUTE - the dissolved particles ○ SOLVENT - liquid that does dissolving Rule: if a particular solute is present in high concentration in one area of solution and in love concentration in another area, the solute will diffuse towards the area of LOWER CONCENTRATION “Moves down their concentration gradient” FACTORS THAT INFLUENCE DIFFUSION RATE STEEPNESS OF THE Greater difference in concentration means higher CONCENTRATION GRADIENT rate of diffusion TEMPERATURE Higher temperature increases the rate of diffusion and vice-versa MASS OF THE DIFFUSING The larger the mass, the slower the diffusion rate SUBSTANCE SURFACE AREA The larger the surface area, the faster the diffusion rate DIFFUSION DISTANCE The greater the distance, the longer the diffusion rate TYPES OF PASSIVE DIFFUSION SIMPLE DIFFUSION FACILITATED OSMOSIS DIFFUSION Definition The substances passes freely Substances passes with Net movement of a through the lipid bilayer without the the help of an integral SOLVENT through a help of transport proteins membrane protein selectively permeable membrane Substances Nonpolar, hydrophobic molecules Channel mediated WATER - Oxygen - Ions (Sodium, - Carbon dioxide potassium, - Nitrogen gas chloride, calcium - Fatty acid ions) - Steroid - Fat-soluble vitamins (A,D,E,K) Carrier mediated - Glucose Small, uncharged polar molecules - Fructose - Water - Galactose - urea - vitamins FACILITATED DIFFUSION CHANNEL-MEDIATED Solute moves down the lipid bilayer CARRIER-MEDIATED through a membrane channel A carrier (transporter) moves a solute down its concentration gradient Most are ION channels Has transport maximum (upper limit of GATED Channel carriers available for transport) - When a part of the channel protein acts as a”plug” or “gate” OSMOSIS The net movement of SOLVENT through a selectively permeable membrane. In the context of the solvent: ○ Water (solvent) moves from an area of high water concentration to an area of low water concentration. In the context of the solute ○ Water moves from an area of low solute concentration to an area of high solute concentration. Water movement is through: ○ Simple diffusion ○ Through aquaporins (AQPs) OSMOSIS Osmosis occurs only when a membrane is permeable to water but impermeable to certain solutes. 2 forces governing osmosis, maintaining equilibrium: ○ HYDROSTATIC PRESSURE Pressure exerted by the liquid ○ ONCOTIC PRESSURE Pressure exerted by impermeable solutes OSMOTIC PRESSURE - the amount of pressure needed to restore equilibrium OSMOSIS Under normal conditions: ○ osmotic pressure of the extracellular fluid is the same with the cytosol, therefore there is no change in the cell volume When a cell placed in a solution with different osmotic pressure → changes in cell size, shape, and volume ○ TONICITY - measure of the solution’s ability to change the volume of cells by altering the water content OSMOSIS - TONICITY ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION Concentration of equal The solutes are greater The solutes are lesser inside solutes inside vs inside than outside the cell than outside the cell outside the cell Movement of water Water enters in and out of OUTSIDE → INSIDE the INSIDE → OUTSIDE THE the cell without change in cell CELL cell size and shape Effect on cell Normal size and shape Cells may SWELL or Cell will shrink (crenated) BURST OSMOSIS - TONICITY ACTIVE PROCESS ACTIVE TRANSPORT are needed for: Solutes that are ○ POLAR or CHARGED molecules that needs to transported actively: move “uphill” or against the concentration - Sodium gradient - Potassium carrier proteins need energy to transport molecules - Hydrogen - Calcium across the membrane - Iodide ○ Two sources of cellular energy - Chloride PRIMARY ACTIVE TRANSPORT - - Amino acids energy is taken via HYDROLYSIS of ATP - Monosaccharides SECONDARY ACTIVE TRANSPORT - energy is taken from energy stored in an *some can be transferred via facilitated diffusion ionic concentration gradient ACTIVE TRANSPORT PRIMARY ACTIVE TRANSPORT Aka PUMPS - energy is derived from ATP hydrolysis that changes the shape of carrier protein → pumps the substance against its concentration gradient. ○ SODIUM-POTASSIUM PUMP (aka Na-K ATPase) Most prevalent primary active transport Maintains low concentrations of sodium (by pumping it out against its concentration gradient) and high concentration of potassium (by moving it inside against the concentration gradient) in the cytosol Importance: Maintains cell shape and volume Generate electrical signals for action potential ACTIVE TRANSPORT SECONDARY ACTIVE The TRANSPORT energy stored in a Na+ or H+ gradient is used to drive other substances across the membrane against the concentration gradient INDIRECTLY uses the hydrolysis of ATP (as Na+ and H+ gradient is established by primary active transport) A carrier protein simultaneously binds to Na+ and another substance and changes in shape so that both substances can cross the membrane at the same time. ACTIVE TRANSPORT SECONDARY ACTIVE TRANSPORT - TWO TYPES SYMPORTERS ANTIPORTERS Moves substances in the SAME direction Moves substances in the OPPOSITE DIRECTION More on absorption: More on regulation of ions and pH: - Na-glucose symport - Na-Ca++ antiport - Na-amino acid symport - Na-H+ antiport TRANSPORT IN VESICLES ENDOCYTOSIS EXOCYTOSIS TRANSCYTOSIS materials move into a cell in a vesicle Materials move OUT of a cell by fusion Movement of substance into, across, formed from the plasma membrane with the plasma membrane of vesicles and out of the cell formed within the cell Vesicles undergo endocytosis on one Three types: RECEPTOR-MEDIATED side, move across, then undergo PHAGOCYTOSIS exocytosis on the other side. BULK-PHASE ENDOCYTOSIS Occurs in: endothelial cells RECEPTOR-MEDIATED ENDOCYTOSIS Highly-selective type of endocytosis by which cells take up specific ligands Uses: ○ Uptake of LDL, transferrin, vitamins, antibodies and certain hormones STEPS: ○ Binding ○ Vesicle formation ○ Uncoating ○ Fusion with endosome ○ Recycling of receptors to plasma membrane ○ Degradation in lysosomes PHAGOCYTOSIS Aka CELL EATING A form of endocytosis in which the cell engulfs large solid particles (worn-out cells, whole bacteria, or viruses) PHAGOCYTES ○ Are cells capable of performing phagocytosis ○ Examples: Macrophages Neutrophils Undigested materials are excreted or turned into lipofuscin granules BULK-PHASE ENDOCYTOSIS Aka PINOCYTOSIS or cell-drinking A form of endocytosis in which droplets of extracellular fluid are taken up Mostly occurs in intestines and kidneys TRANSPORT ACROSS THE PLASMA MEMBRANE TRANSPORT ACROSS THE PLASMA MEMBRANE 03 CYTOPLASM Consists of all cellular contents between the plasma membrane and the nucleus 2 components: ○ CYTOSOL ○ ORGANELLES CYTOSOL Aka INTRACELLULAR FLUID The fluid portion of cytoplasm surrounding the organelles Constitutes 55% of cell volume Site of many chemical reactions (eg. Glycolysis) Composition: ○ 75-90% water, the remaining are dissolved and suspended components ○ Some have aggregations Examples (lipid droplets, glycogen granules) CYTOSOL - components ○ CYTOSKELETON Network of protein filaments that extends throughout the cytosol Contributes to the cytoskeleton and other organelle’s structure ○ Microfilaments, intermediate filaments, and microtubules Functions: Serves as scaffold that helps determine a cell’s shape and organize the cellular components Aids movement of organelles within the cell, of chromosomes during cell division, and of whole cells such as phagocytes. TYPES OF CYTOSKELETON MICROFILAMENT INTERMEDIATE MICROTUBULES S FILAMENTS Thinnest elements of the cytoskeleton Found in parts of cells subject to Largest of the cytoskeletal components mechanical stress Composed of ACTIN and MYOSIN Long, unbranched hollow tubes Helps stabilize the position of organelles composed mainly of TUBULIN Most prevalent at the cell edge Help attach cells to one another Begins in CENTROSOME → grows Functions: outward - Help generate movement - Muscle contraction, Functions: locomotion, cell division - Helps determine shape - Provide mechanical support - Helps in movement of organelles - responsible for strength - Secretory vesicles and shape of cells - Chromosomes during cell - microvilli division - Specialized cell projections (CILIA and FLAGELLA) TYPES OF CYTOSKELETON ORGANELLES Are specialized structures within the cell Performs different functions with one goal: PROMOTE HOMEOSTASIS within the cell CENTROSOME Aka MICROTUBULE ORGANIZING CENTER Located near the nucleus Components: two centrioles Nine clusters of three microtubules arranged in a circular pattern One pericentriolar matrix Surrounds the centrioles Composed of ring-shaped complexes (tubulin) Function: Builds microtubules in non-dividing cells Forms the mitotic spindle during cell division CILIA AND FLAGELLA Motile projections of the cell surface Made up of microtubules CILIA ○ Numerous, short, hair-like projections that extend from the surface of the cell ○ Function - moves fluids along a cell’s surface Found in: respiratory tract FLAGELLA ○ Longer than cilia ○ Usually moves an entire cell Generates a forward motion along its axis by rapidly wriggling in a wavelike pattern Example: SPERM RIBOSOMES Site of protein synthesis Contains high content of rRNA (ribosomal RNA) Consists of 2 subunits Types of ribosomes and their function: ○ attached to the nuclear membrane and to the endoplasmic reticulum Synthesizes proteins destined for insertion in the plasma membrane or secretion ○ Free ribosomes Synthesizes proteins used in the cytosol ENDOPLASMIC RETICULUM Network of membranes in the form of flattened sacs or tubules. ROUGH ENDOPLASMIC RETICULUM SMOOTH ENDOPLASMIC RETICULUM Continuous with the nuclear membrane Not studded with ribosomes Outer surface is studded with RIBOSOMES Produces PROTEINS: Produces: - Secretory proteins - Fatty acids and steroids - Membrane proteins - Organellar proteins Synthesizes glycoproteins and phospholipids → Other functions: transferred to cellular organelles → inserted to - Releases glucose in liver cells plasma membrane or secreted - Inactivate or detoxify lipid-soluble drugs - Releases calcium during muscular contraction (sarcoplasmic reticulum) ENDOPLASMIC RETICULUM Network of membranes in the form of flattened sacs or tubules. GOLGI COMPLEX More extensive in cells that secrete proteins Consists of 3-20 cisterns (small, flattened membranous sacs with bulging edges) ○ Entry (cis) face - cistern that faces the ER; convex May be formed from transport vesicles ○ Exit (trans) face - faces the plasma membrane ○ Medial cisterns - sacs between entry and exit faces Functions ○ Modifies, sorts, packages, and transports proteins received from the ER ○ Forms secretory vesicles - discharges substances via exocytosis ○ Forms membrane vesicles - carries new molecules to the plasma membrane ○ Forms transport vesicles - carries molecules to other organelles Proteins synthesized from the RER are surrounded by ER membrane → buds off to form TRANSPORT VESICLES GOLGI COMPLEX Transport vesicles move towards the entry face of golgi complex GOLGI COMPLEX Fusion of several transport vesicles creates the entry face of golgi complex → release of substances to the lumen GOLGI COMPLEX Proteinsofmove Transport Fusion synthesized several vesicles from from the move transport entry phase towards RER vesicles →are the surrounded entry creates medial face cisterns theofentry by golgi ER membrane complex face of golgi→ buds off to form→ complex Enzymes modify releasethe TRANSPORT of proteins, substances forming to the VESICLES lumen glycoproteins, glycolipids, and lipoproteins Transfer vesicles move enzymes back to the entry face and modified proteins to the exit face GOLGI COMPLEX Products of the medial cisterns move into the lumen of the exit face GOLGI COMPLEX Products are further modified, sorted, and packaged at the exit face GOLGI COMPLEX Some of the process proteins leave the exit face and stored in secretory vesicles → proteins are delivered to plasma membrane and discharged via exocytosis Ex. release of insulin hormone from the pancreatic cell GOLGI COMPLEX Others leave in MEMBRANE VESICLES → plasma membrane → incorporated to the membrane GOLGI COMPLEX Some will exit in TRANSPORT vesicles that will carry the proteins to another cellular destination. Ex. transport of enzymes to lysosomes GOLGI COMPLEX LYSOSOME Membrane-enclosed vesicles that form from the golgi complex Contains as many as 60 kinds of powerful digestive and hydrolytic enzymes (lysosomal enzymes) ○ Lysosomal enzymes works best in acidic pH (lysosome pH = 5; cytosol pH = 7) Components: ○ Transport pumps (imports H+) ○ Transporters that moves products of digestion (glucose, fatty acids, and amino acids) into the cytosol functions: ○ Digest substances that enter the cell via endocytosis and transport final products of digestion into the cytosol ○ AUTOPHAGY - digestion of worn-out organelles ○ AUTOLYSIS - digestion of entire cell ○ Extracellular digestion PEROXISOME PROTEASOME Aka microbodies Function: Contains OXIDASES - Destroys unneeded, damaged, or faulty - Enzymes that oxidize (remove H+ atoms) proteins various organic substances - By-products: H2O2 and superoxide Contains PROTEASES - H2O2 - decomposed by - Enzymes that cut proteins into small CATALASE peptides - Superoxide - decomposed by other enzymes Capable of self-replications Functions: - Detoxification of alcohol and other damaging substances - Prevents accumulation of by-products of MITOCHONDRIA Functions: ○ “POWERHOUSE” of the cell Generates most of the ATP through AEROBIC (oxygen-requiring) respiration ○ Plays a role in APOPTOSIS Aka programmed cell death In response to stimuli, mitochondria releases chemicals (cytochrome c) to the cytosol initiating cascade of activation of protein-digesting enzymes → cell death Capable of self-replication Has ribosomes attached in the mitochondrial matrix Has their own DNA (multiple copies of circular DNA that contains 37 genes) ○ For synthesis of 2 rRNA, 22 tRNA, 13 proteins Mitochondrial genes are inherited from the MOTHER ONLY MITOCHONDRIA - PARTS 04 THE NUCLEUS NUCLEUS Contains most of the cell’s GENES. Functions: - Controls cellular structure - Directs cellular activities - Produces ribosomes in nucleoli NUCLEAR ENVELOPE - Double membrane - Separates the nucleus from the cytoplasm - Lipid bilayer - Outer envelope is continuous with the RER NUCLEUS - PARTS NUCLEAR PORE ENVELOPE - Consistsmembrane Double of a circular arrangement of proteins - Separates the surrounding a large nucleus central fromopening the cytoplasm - Lipid bilayer Controls the movement of substances between - Outer the nucleus envelope and iscytoplasm continuous with the RER NUCLEUS - PARTS NUCLEOLI/NUCLEOLUS NUCLEAR PORE ENVELOPE - - Located Doubleinside Consists membrane of athe circular nucleusarrangement of proteins - - Produces Separates surrounding ribosomes the a large nucleus (site central from of synthesis opening the cytoplasm and assembly of - rRNA Lipid Controls and bilayer proteins) the movement of substances between - - Prominent Outer the nucleus envelope in cells andthat iscytoplasm continuous synthesize with large theamount RER of proteins NUCLEUS - PARTS THE CHROMOSOMES The GENES housed within the nucleus controls cellular structure and direct cellular activities. ○ Arrange along CHROMOSOMES ○ Somatic cells - 46 chromosomes GENOME - the total genomic information carried in a cell/organism DNA helix + Histones → nucleosome → further coiling → chromatin → 2 chromatids + centromere → chromosome Nucleosome - Double stranded DNA wrapped twice around histone (core of eight proteins) CELL PARTS AND THEIR CELL PARTS AND THEIR 05 PROTEIN SYNTHESIS PROTEIN SYNTHESIS GENE EXPRESSION - A gene’s DNA is used as a template for protein synthesis - process: 1. TRANSCRIPTION (nucleus) 2. TRANSLATION (cytoplasm) - Genetic expression are stored in sets of three nucleotides - Base triplets - three set of nucleotides in DNA - Codon - complementary sequence of base triplets; it codes for a specific amino acid TRANSCRIPTION Occurs inside the nucleus The sequence of base triplets in DNA is copied to produce a complementary sequence of RNA (codons) Three types of RNA are made: ○ Messenger RNA (mRNA) Directs protein synthesis ○ Ribosomal RNA (rRNA) Joins with ribosomal proteins to form ribosomes ○ Transfer RNA (tRNA) Binds to amino acids and incorporates it into the protein during translation TRANSCRIPTION PROCESS RNA polymerase DNA RNA ○ Enzyme that catalyzes the transcription of DNA Adenine (A) Uracil (U) TRANSCRIPTION PROCESS: ○ INITIATION Thymine (T) A RNA polymerase binds to a PROMOTER Guanine (G) C Bases pair in a complementary manner Cytosine (C) G ○ ELONGATION ○ TERMINATION Transcription stops when a TERMINATOR sequence is reached RNA polymerase detaches to the DNA strand pre-mRNA - product of transcription ○ Contains INTRONS (non-coding) and EXONS (codes proteins) TRANSLATION Occurs in CYTOPLASM The nucleotide sequence of mRNA is translated into a sequence of amino acids, forming a new protein molecule Ribosomes: organelle responsible ○ Small binding site - binds to mRNA ○ Large binding site - binds to tRNA A (aminoacyl) site - binds the tRNA carrying the next amino acid to be added P (peptidyl) site - binds to tRNA carrying the growing peptide chain E (exit) site - binds to tRNA before release to ribosome TRANSLATION PROCESS 06 CELL DIVISION CELL DIVISION The process by which cells reproduce themselves TWO TYPES: ○ SOMATIC CELL DIVISION Somatic cells (any cell of the body except the gametes/ germ cell) Undergoes MITOSIS Product: DIPLOID CELL ○ normal number of chromosomes (46) ○ Has both members of the chromosome pair ○ REPRODUCTIVE CELL DIVISION Production of germ cells/gametes (egg cell and sperm cell) Undergoes MEIOSIS (two-step nuclear division) Product: HAPLOID CELL ○ half the number of chromosomes (23) ○ Only one member of the chromosome pair SOMATIC CELL DIVISION CELL CYCLE - An orderly sequence of events in which a somatic cell duplicates its contents and divides in two. - Homologous chromosomes - Two chromosomes that make up one pair of chromosomes - Human cells (except gametes) contain 23 pairs of chromosomes - One member of each pair is inherited from each parent - Diploid (2n) cell - contains two sets of chromosomes - Haploid (n) cell - contains only one set of chromosomes SOMATIC CELL DIVISION CELL CYCLE - Consists of two major periods: - INTERPHASE - The cell is not dividing - MITOTIC (M) PHASE - The cell is dividing Summary of sequence of events in cell cycle: G1 → S PHASE → G2 → MITOSIS → CYTOKINESIS SOMATIC CELL DIVISION INTERPHASE - A state of “high metabolic activity” - The cell undergoes growth - The cell replicates DNA in preparation for cell division - Undergoes production of additional organelles and cytosolic proteins - Three phases: - G1,S, and G2 SOMATIC CELL DIVISION INTERPHASE - G1 (GAP) PHASE (46 chromosomes) - Cell is metabolically active - The cell replicates most of its organelles EXCEPT DNA - G0 PHASE - Cells that remain in G1 for a long time or does not divide - Example: nerve cell and skeletal muscle SOMATIC CELL DIVISION INTERPHASE - S PHASE (92 chromosomes) - Cell undergo DNA REPLICATION - DNA uncoils, the old DNA strand pairs with the newly formed DNA strand - G2 PHASE (92 chromosomes) - Cell growth continues - Replication of centromere is completed EARLY PROPHASE (92 CHROMOSOMES) - Chromatin fibers condense and shorten into chromosomes - Each chromosomes contain chromatids held together by centromere LATE PROPHASE - Pericentriolar material of centrosomes start to form mitotic spindle SOMATIC CELL DIVISION - M PHASE METAPHASE EARLY PROPHASE(92 CHROMOSOMES) (92 CHROMOSOMES) - Microtubules of the Chromatin fibers mitotic spindle condense and align theinto shorten centromeres chromosomes of the chromatid - Eachpairs at the center chromosomes contain chromatids held together by - METAPHASE PLATE (equatorial centromere plate) LATE PROPHASE - - Plane of Pericentriolar alignment material of of the centromeres centrosomes start to form mitotic spindle SOMATIC CELL DIVISION - M PHASE ANAPHASE METAPHASE EARLY PROPHASE(46 (92CHROMOSOMES/CELL) CHROMOSOMES) (92 CHROMOSOMES) - Microtubules The centromeres Chromatin of the fibers split, mitotic condense separating spindle and align each shortenthe chromatid centromeres into pair, moving chromosomes of the towards chromatid the- opposite Each pairs poles at the of the chromosomes center cell contain chromatids held together by - METAPHASE Each chromatid centromerePLATE are now (equatorial termed as plate) CHROMOSOMES LATE PROPHASE - - Plane of Pericentriolar alignment material of of the centromeres centrosomes start to form mitotic spindle SOMATIC CELL DIVISION - M PHASE METAPHASE ANAPHASE EARLY PROPHASE TELOPHASE (46 (92CHROMOSOMES/CELL) (46 CHROMOSOMES) (92 CHROMOSOMES) CHROMOSOMES/CELL) - Microtubules The Beginscentromeres Chromatin of the afterfibers split, mitotic condense chromosomal separating spindle and movement align each shorten stops the chromatid centromeres into pair, moving chromosomes of the towards - chromatid the- opposite Each Chromosomes pairs poles at the of the chromosomes uncoil center and cell contain revert to chromatinchromatids form held together by - METAPHASE Each nuclear chromatid centromere envelope PLATE are now forms (equatorial termed as LATE plate) reappear CHROMOSOMES - PROPHASE Nucleoli - - Mitotic Plane spindleof Pericentriolar alignment material breaks of of the up - centromeres centrosomes Cytokinesis start to form mitotic starts spindle SOMATIC CELL DIVISION - M PHASE CYTOKINESIS AKA CYTOPLASMIC DIVISION ○ Division of cell’s cytoplasm and organelles into separate and equal portions ○ Usually begins in LATE ANAPHASE with the formation of cleavage furrow CLEAVAGE FURROW ○ Appears midway between centrosomes ○ Always perpendicular to the mitotic spindle ○ Actin microfilaments form a contractile ring that pulls the plasma membrane inward Interphase begins once cytokinesis is complete CONTROL OF CELL DESTINY THREE (3) POSSIBLE DESTINIES OF THE CELL: 1. To remain alive and functioning without dividing 2. To grow and divide 3. To die Various signals tell a cell when to exist in the G0 phase, when to divide and when to die ○ CYCLIN-DEPENDENT PROTEIN KINASES (CDK’s) Crucial in the regulation of DNA replication, mitosis, and cytokinesis Regulated by CYCLINS (activates or deactivates CDKs) ACTIVATED by transfer of a phosphate group from ATP to protein DEACTIVATED by removing of phosphate group CLASSIFICATION OF SOMATIC CELL BASED ON THEIR MITOTIC ACTIVITY STATIC CELL Composed of cells no longer dividing Cells of the CNS POPULATION *some cells may enter mitosis Cardiac Myocytes STABLE CELL Cells may divide episodically and Periosteal and perichondrial cells POPULATION slowly to maintain normal tissue Smooth muscle clueless structure Endothelial cells fibroblasts RENEWING CELL Displays regular mitotic activity, but Stem cells POPULATION may be slowly or rapidly dividing SLOWLY Displays regular mitotic activity but are Smooth muscle cell of hollow organs RENEWING slowly dividing Fibroblast of uterine wall POPULATION RAPIDLY Displays regular mitotic activity but are Blood cells RENEWING rapidly dividing Epithelial cells and Dermal fibroblasts (skin) Epithelial cells of the gastrointestinal tract POPULATION REPRODUCTIVE CELL DIVISION MEIOSIS The reproductive division that occurs in the gonads (ovaries and testes), that produces gametes (egg cell and sperm cell) in which the number of chromosomes is reduced by half. ○ Produced HAPLOID (n) cells - single set of 23 chromosomes Occur in two successive stages: ○ Meiosis I (REDUCTIONAL division) Begins with diploid cells, ending with two daughter haploid cells ○ Meiosis II (EQUATORIAL division) Similar to process to mitosis Note: Begins with two haploid cells, ending with four haploid daughter cells PROPHASE I (92 CHROMOSOMES) - Chromosomes shorten and thicken, nuclear envelope and nucleoli disappear, mitotic spindle forms - SYNAPSIS - two sister chromatids of each pair of homologous chromosome pair of, forming a TETRAD - CROSSING-OVER - an exchange of parts between chromatids occurs - This results to GENETIC RECOMBINATION - formation of new sets of genes leading to genetic variation METAPHASE I (92 CHROMOSOMES) - Tetrads formed by the homologous pairs of chromosomes line up along the metaphase plate REPRODUCTIVE CELL DIVISION (MEIOSIS I) ANAPHASE I (46 CHROMOSOMES/CELL) - Members of each homologous pairs of chromosomes separate - Note: the chromatid pairs are still held together by centromere - Result: haploid number of chromosomes TELOPHASE I and CYTOKINESIS (46 CHROMOSOMES/CELL) - Same with mitosis - Product: - HAPLOID cell (two daughter cells) REPRODUCTIVE CELL DIVISION (MEIOSIS I) NO INTERPHASE (46 CHROMOSOMES) - No DNA replication PROPHASE II (46 CHROMOSOMES) METAPHASE I (46 CHROMOSOMES) - chromosomes line up along the metaphase plate ANAPHASE II (23 CHROMOSOMES/CELL) - Members of each homologous pairs of chromosomes separate TELOPHASE II and CYTOKINESIS (23 CHROMOSOMES/CELL) - Same with mitosis - Product: - HAPLOID cell (four daughter cells) REPRODUCTIVE CELL DIVISION (MEIOSIS II) COMPARISON - MITOSIS V. MEIOSIS CONTROL OF CELL DESTINY TYPES OF CELLULAR DEATH APOPTOSIS NECROSIS Definition Orderly, genetically programmed cell death Cell death resulting from a tissue injury Normal process Pathologic (abnormal) type of cell death Process A triggering event causes “cell suicide: Adjacent cell swell, burst, and spill their genes to activate and produce enzymes cytoplasm into the interstitial fluid that damage the cells → nuclear fragments (plasma membrane is not intact) → and cytoplasm shinks (plasma membrane stimulation of inflammatory response intact) → cell is phagocytosed by phagocytes (no inflammatory response) Function/ Removes unneeded cells example - Fetal development - removal of webbing between digits - Eliminates potential dangerous cells 07 CELL AGING CELLULAR DIVERSITY Cells vary considerably in size ○ Micrometers - unit of measure of cells Largest cell: oocyte (140 um) Cells also vary considerably in shape ○ This relates to its function in the body examples: Sperm - has whip-like tail for locomotion Red blood cell - disc shape to enlarge its surface area Smooth muscle cell - spindle-shape to increase muscle shortening during contraction Nerve cells - have long extensions to permit conduction of nerve in long distances AGING AND CELLS AGING ○ A normal process accompanied by progressive alteration of the body’s homeostatic responses ○ Produces observable changes in structure and function, and increases vulnerability to environmental stress and disease GERIATRICS ○ Branch of medicine that deals with medical problems and care of elderly person GERONTOLOGY ○ Scientific study of the process and problems associated with aging AGING AND CELLS Factors relating to cell aging: - “Aging genes” as part of the genetic blueprint - Cells have only limited capacity to divide - Cessation of mitosis is normal, genetically programmed event - Erosion/shortening of telomeres - TELOMERES - DNA sequences found at the tip of the chromosome - Protects the tip of the chromosome from erosion - Each cellular division leads to shortening of telomeres → functional chromosome material may be lost → cell death - Glucose - May be haphazardly added to proteins in the cells, forming irreversible cross-links between adjacent protein molecules → stiffening and loss of elasticity - Autoimmune response - Changes in cell-identity markers while aging leads to autoimmune response, attacking cells leading to destruction. 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