Chapter 2: Cells PDF

Chapter 2: Cells Cells: the basic living, structural and functional components of the body Compartmentalized Perform functions necessary for life Cytology: the study of the cellular structure & function Histology: microscopic study of structure of the tissues I. Cellular Diversity a. 100 trillion ce...

Chapter 2: Cells Cells: the basic living, structural and functional components of the body Compartmentalized Perform functions necessary for life Cytology: the study of the cellular structure & function Histology: microscopic study of structure of the tissues I. Cellular Diversity a. 100 trillion cells in human body b. 200 types of cells (making up 4 tissue types) c. Largest cell = oocyte (140µm) d. RBC = 10µm e. Hair = 100µm thick f. Shape (structure) determines fxn i. Sperm w/ flagellum to swim, RBC biconcave disc to ↑ SA and flex, microvilli to ↑ SA, ms fibers long spindles to contract, nerve axons II. Generalized cell a. Plasma membrane i. Flexible outer surface, separating internal & external environment ii. Selective barrier – key role in communication b/n cells & environment b. Nucleus i. Large organelle that houses most of the DNA ii. Chromosomes are strands of DNA associated with proteins containing genes which code for most cell processes & sx’s c. Cytoplasm i. All contents between plasma membrane and nucleus 1. Cytosol – intracellular fluid (water, dissolved solutes/suspended particles) 2. Organelles – characteristic shape & fxn III. Structures of the Plasma Membrane a. Fluid Mosaic Model – sea of lipids (fats) with mosaic of proteins that are free floating (iceberg) or anchored b. Lipid bilayer i. Phospholipids (75%) - hydrophilic heads, hydrophobic tails ii. Cholesterol (20%) - provides ion barrier, flexibility & strength to the membrane iii. Glycolipids (5%) – lipids attached to carbohydrates c. Membrane proteins i. Integral – extend into or through lipid bilayer 1. Transmembrane – span entire lipid bilayer extending from cytosol to extracellular fluid (ECF) ii. Peripheral – embedded on either internal or external surface 1. Glycoproteins = carbohydrates attached to outer surfaced. Glycocalyx = glycoproteins + glycolipids d. Functions of Membrane Proteins i. Ion channels (pores) – allow ions to pass through (K+, Na+) ii. Carriers/transporters for polar substances (hydrophilic) through hydrophobic membrane iii. Receptors – cellular recognition sites (ie. for insulin = ligand) iv. Enzymes – catalyze (speed up) chemical rxn’s in/out of cell v. Linkers – anchors to other cell membranes or protein filaments (peripheral) vi. Cell identity markers: glycocalyx = glycoproteins + glycolipids: molecular signature: recognition (immune), binding, protection 1. recognize other cells of same kind during tissue formation 2. recognize and respond to foreign invaders vii. Peripheral proteins also: provide membrane support, transport materials/organelles within cells, change shape of cells e. Membrane permeability i. Permeable = allows passage of substances through it. ii. Selective permeability = some substances pass more readily than others iii. Lipid bilayer is permeable to oxygen, CO2, & steroids (small, non-ions, hydrophobic) and water (aquaporins) 1. Transmembrane proteins – act as channels for ions, small-medium sized molecules 2. Endocytosis & Exocytosis – for macromolecules f. Fluid types i. Intracellular Fluid (ICF) – within cells ii. Extracellular Fluid (ECF) – outside of the cell 1. Interstitial fluid (ISF) / intercellular fluid – between cells 2. Blood plasma – in blood vessel 3. Lymph – in lymphatic vessels g. Transporting Substances in Fluids i. Passive Transport: [high] > [low], moves down concentration gradient using own kinetic energy (Brownian motion) 1. Diffusion: net movement of a substance until equilibrium is reached 2. Osmosis: net mvmt of water from [hi]>[low] across a semipermeable membrane a. H2O able to move through aquaporins (AQP’s) = integral proteins 3. Facilitated Diffusion: transmembrane proteins for large & insoluble (to lipids) solutes (Glucose) ii. Active Transport: [low] > [high], move up its concentration gradient, requires ATP for energy 1. Ions make contact with transporter protein, ATP splits > conformational change 2. Important for maintaining ion concentrations within and outside of cell (ie. nerves – Na+/K+ pump) 3. Vesicle (little blister/bladder) – membranous sac, bud of membrane, transports substances a. Endocytosis – materials brought into a cell i. Phagocytosis – cell eating 1. Cell engulfs large solid particles (worn-out cells, bacteria, viruses) by extending pseudopods > phagosome (vesicle) > fuses with lysosome. Leftovers remain in residual body for exocytosis. 2. Carried out by macrophages & neutrophils ii. Pinocytosis (bulk-phase endocytosis) – cell drinking 1. Droplets of ECF are brought into cell, via vesicles, fuse with lysosomes 2. Occurs in most cells, especially intestines and kidneys iii. Receptor-mediated endocytosis – ligands bind to specific receptors 1. Binding 2. Vesicle formation 3. Uncoating 4. Fusion with endosome – separation of particles from receptors 5. Recycling of receptors to plasma membrane 6. Fusion with lysosome – enzymes break down the protein b. Exocytosis – releasing materials out of cells i. Secretory vesicles fuse with plasma membrane & release contents 1. Secretory cells producing enzymes, hormones, mucus, other secretions 2. Nerves > neurotransmitters 3. Wastes c. Transcytosis – vesicle brings substance from ECF into cell, moves across cell, then out other side i. Common in epithelial cells that line blood vessels, from blood plasma > ICF IV. Cytoplasm = all cellular components inside PM except nucleus a. Cytosol = fluid portion of cytoplasm surrounding organelles. i. 55% total cell volume ii. 75-90% water + various dissolved & suspended substances (ions, glucose, AA’s, fatty acids, proteins, lipids, ATP & wastes) iii. Organic molecules that aggregate for storage lipid droplets (triglycerides) and glycogen (glucose) iv. Inclusions – large storage aggregates (glycogen, melanin) v. Cytoskeleton – protein filaments contributing to sx of cell & organelles 1. Microfilaments (smallest)– actin & myosin, near cell membrane: movement & mechanical support: ms contraction, cell division & mvmt, anchor cytoskeleton to integral proteins in PM, support microvilli (sm tufts of hair) 2. Intermediate filaments (med size), several types of proteins, found in areas of mechanical stress, and/or organelles, attach cells 3. Microtubules (largest) – unbranched hollow tubes of tubulin, grow out from centrosome, migration of chromosomes during mitosis, move the cilia & flagella. b. Organelles - specialized structures within the cells with specific shape & fxn, own set of enzymes, #/type vary cell to cell depending on cell’s fxn. V. Organelles a. Non-membrane bound i. Centrosome: microtubule organizing center 1. 2 centrioles (9 clusters of 3 microtubules) perpendicular to each other 2. pericentriolar matrix (hundreds of ring-shaped complexes of tubulin ii. Cilia - hair like projections from cell surface, made of 20 microtubules (9 + 1 doublets) surrounded by PM, respiratory tract, uterine tube iii. Flagella – sx similar to cilia but much longer, able to move entire cell, sperm’s tail (only flagella in human body) iv. Ribosomes – sites of protein synthesis, packages of rRNA, made in nucleus and exit to begin producing proteins 1. Free: float in cytoplasm, produce proteins used within the cell 2. Membrane-Bound: attached to nuclear membrane & endoplasmic reticulum, make proteins for organelles, PM or exocytosis b. Membrane bound c. Endoplasmic Reticulum (ER): endo- = within/inside, -plasmic = cytoplasm, -reticulum = network; packaging/sorting site i. Rough ER: continuous with nuclear membrane, 1. lined with ribosomes 2. enzymes attach proteins to CHO’s → glycoproteins for PM, or to phospholipids 3. sends glycoprotein/phospholipids to organelle membranes, PM or secretes via exocytosis ii. Smooth ER: extends from RER, no ribosomes 1. Synthesizes fatty acids & hormones (not proteins), ie. testosterone, estrogen, releases glucose from liver, Ca2+ released from SR d. Golgi Complex: 3-20 cisternae (cavities) resembling curved stack of pita bread i. Transport vesicles move proteins from RER to entry face of Golgi ii. Enzymes in Golgi medial cisternae modify proteins to form glycoproteins, glycolipids and lipoproteins iii. Transfer vesicles move enzymes back to entry face and modified proteins to exit face of Golgi iv. Further sorting, packaging and modification occurs. v. Exit Golgi 1. Secretory vesicles are secreted through PM via exocytosis (ie. insulin released by pancreatic cells) 2. Membrane vesicles deliver contents to PM and stay there 3. Transport vesicles deliver to other cell sx’s (ie. digestive enzymes sent to lysosomes) e. Lysosomes i. Membrane enclosed vesicles from Golgi ii. Contain enzymes which can help to break down/digest nutrients into sugars, AA, fatty acids & microbes (bacteria and viruses) iii. Autophagy: digestion of worn out organelles iv. Autolysis: lysosome destroys entire cell that contains them (pathological conditions or postmortem) v. Tay-Sachs dz in Ashkenazi Jews: lack lysosomal enzyme Hex A which normally breaks down glycolipid in nerve cells. f. Peroxisomes (microbodies or oxidases): peroxi = peroxide, -somes = bodies i. Similar but smaller than lysosomes ii. Used to oxidize and break down chemicals such as alcohol (abundant in liver) iii. Release H2O2 and superoxides which can be toxic iv. Also contains catalase → degrades H2O2 and other enzymes to destroy superoxides to detoxify products of metabolism g. Proteasomes – break down unneeded, damaged or faulty proteins i. Contain proteases ii. Very small, recently discovered iii. Failed proteasomes may contribute to Alzheimer’s & Parkinson’s h. Mitochondria – generate ATP through aerobic respiration (mito- = thread, -chondria = granules) i. Powerhouse of the cell ii. 100 – several thousand per cell iii. Structure 1. External mitochondrial membrane 2. Internal mitochondrial membrane 3. Mitochondrial cristae – folds of internal mitochondrial membrane, ↑ SA for cellular respiration 4. Mitochondrial matrix – central fluid filled cavity iv. Apoptosis – programmed cell death 1. Mitochondrion releases cytochrome c and others when ↑ free radicals, DNA damage, ↓ growth factor, ↓ O2/nutrients v. Self-replicate (like peroxisomes) on demand vi. Contain own DNA molecule with 37 genes vii. Mitochondria (and their DNA) passed down through mother only from oocyte (egg) – sperm has no organelles that survive VI. Nucleus a. Most prominent spherical/oval shaped sx b. Most cells have only one, a few (ms., WBC) have a few, some have none c. Sx i. Nuclear envelope – double membrane separating nuclear contents from cytoplasm, lipid bilayer, outer is continuous with RER ii. Nuclear pores – large holes in nuclear envelop, 1. Sm molecules & ions passively transported, RNA lg molecules actively transported iii. Nucleoli – produce ribosomes 1. Cluster of DNA, RNA & proteins 2. No membrane iv. Chromosomes – long molecule of DNA + coiled around several proteins 1. Genes = hereditary units of DNA (genome = all of the genetic info in a cell, 30,000 genes, 3.2B nucleotides) v. Chromatin = DNA + proteins + RNA vi. Histones = core of 8 proteins wrapped twice around by double stranded DNA VII. Cell Division a. 2 Types i. Somatic 1. all cells except gametes (sperm & egg/oocyte) 2. Mitosis (nuclear division) + cytokinesis (cytoplasmic division) 3. Replaces dead/injured cells, adds new cells ii. Reproductive 1. Produces gametes (haploid cells: sperm & oocytes, needed for producing new organisms) 2. Meiosis – two step cell division, # of chromosomes cut in half b. Somatic Cell Division i. 23 pairs of homologous chromosomes (46 total) in human – 22 pairs are autologous, meaning they code for the same type of proteins. ii. Sex chromosomes (23rd pair) XX (female) & XY (male), with Y being much smaller iii. Diploid (2n) = must maintain diploid status upon division iv. 2 Major Phases of Cell Life 1. Interphase – high metabolic activity, most growth (time periods would be if the cell had taken 24 hours to divide) a. G1 – metabolically active, replicates most organelles, cytosolic components but not DNA, 8-10 hrs b. S – DNA replication, 8 hrs c. G2 – cell growth continues, enzymes prepare for cell division, centrosomes replicate, 4-6 hrs d. Microscope shows clear nuclear envelope, nucleolus, chromatin mass 2. Mitosis (M) Phase – results in two identical cells a. Nuclear division i. Prophase – 1. Chromatin fibers condense & shorten 2. Chromatids (duplicate/sister strands of DNA from interphase) now visible, held by centromere 3. Mitotic spindles form out of tubulin from centrosomes, pushing centrosomes to opposite poles 4. Spindles attach to kinetochore (protein complex) on centromere 5. Nucleolus disappears ii. Metaphase 1. Microtubules of mitotic spindles line up chromosomes on metaphase plate iii. Anaphase 1. Centromeres split 2. Chromatid pairs separate (now chromosomes), moving toward opposite poles 3. Chromosomes v-shape, as pulled from centromere 4. Cleavage furrow begins iv. Telophase 1. Chromosomal mvmt stops 2. Chromosomes uncoil to become chromatin 3. Nuclear envelop reforms 4. Nucleolus reappears 5. Mitotic spindles break up 6. Deep cleavage furrow b. Cytoplasmic Division i. Cytokinesis (not technically a phase of mitosis) 1. Cleavage furrow completes division – indentation of plasma membrane, perpendicular to mitotic spindles 2. Actin myofilaments form a contractile ring (like tightening a belt around the cell from inside) 3. Cell Destiny a. Cyclins are proteins responsible for enzymes that regulate G1>G0 or S>G2>Mitosis b. Apoptosis – preprogrammed cell death > enzymes destroy cytoskeleton or nuclear envelope i. Important during fetal development (removes webbing between fingers), regulates growth/cancer) c. Necrosis – pathological type of cell death from injury (cells swell > burst > spill cytoplasm into ISF) c. Reproductive Cell Division / Sexual Reproduction = Meiosis: (Mei- = lessening, -osis = condition of) i. Occurs in gonads (ovaries & testes) ii. Results in haploid (1n) cells (hapl- = single) iii. Occurs in 2 stages: Meiosis I & Meiosis II 1. Meiosis I - Begins once sister chromatids formed during interphase a. Prophase I: chromosomes shorten & thicken, nuclear envelope & nucleoli disappear, mitotic spindles i. Synapsis – homologous chromosomes pair off into a tetrad (2 pairs of sister chromatids) ii. Crossing over – exchange of genetic info b/n non-sister homologous chromosomes b. Metaphase I - Tetrads formed line up along metaphase plate (independent assortment) c. Anaphase I – homologous chromosomes are separated, centromeres keep chromatids together d. Telophase I – just like mitosis Each of the 2 new cells have ½ the number of chromosomes (haploid, 1n, 23C) 2. Meiosis II a. Prophase II, Metaphase II, Anaphase II, Telophase II and Cytokinesis II similar to mitosis Results in 4 genetically different cells from the parent cell due to: i. Crossing over (Prophase I) – homologous chromosomes exchange genes ii. Independent assortment (Metaphase I)– order of alignment on metaphase plate VIII. Cell Aging a. Aging is a normal process, progressive alteration of body’s homeostatic responses to maintain normal conditions b. Geriatrics is branch of medicine dealing with care of elderly persons c. Gerontology is the study of process/problems associated with aging. d. Some cells don’t/rarely divide, stuck in G0 (after G1) – skeletal muscle & nerve cells e. Telomeres – DNA sequence at tips of chromosomes i. Protect the chromosomes from erosion and sticking to each other. ii. Each cell division shortens the telomeres, resulting in loss of DNA, contributing to cell aging iii. Individuals with high stress have shorter telomere length f. Glucose can be added to proteins inside & outside of the cell i. Forms cross-links b/n proteins causing stiffness / loss of elasticity that occurs with aging g. Autoimmune response – may be associated with cell markers at cell surface (glycoproteins, glycolipids)