Chapter 3 Notes (pp.38-62)
Chapter 3 Notes (pp.38-62) BIOL 3040
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This 5 page Class Notes was uploaded by Min-Young Kim on Sunday January 10, 2016. The Class Notes belongs to BIOL 3040 at Clemson University taught by Christina Wells in Spring 2016. Since its upload, it has received 89 views. For similar materials see Biology of Plants in Biology at Clemson University.
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Date Created: 01/10/16
Chapter 3: The Plant Cell Characteristics of living organisms appear suddenly and specifically in form of living cell. -‐ Cell theory: cells are the basic unit of life. -‐ ~340 years ago, Robert Hooke noticed small cavities in cork/plant tissues -‐ 1838, Matthias Schleiden: all plant tissues consist of organized masses of cells. Theodor Schwann: all animal tissues made up of cells -‐ 1858, Rudolf Virchow: all cells arise from preexisting cells (continuity) -‐ Each cell is self-‐contained unit surrounded by plasma membrane, which controls passage of materials. -‐ Prokaryotes (e.g. archaea and bacteria): lack nuclei, nucleoid (large circular DNA chromosome with loose proteins), lack specialized organelles -‐ Eukaryotes’ chromosomes are surrounded by double membrane. DNA is linear, tightly bound to histones, and more complex than bacterial chromosomes Plant cell -‐ Plant cell consists of cell wall and protoplast (cytoplasm and nucleus) -‐ Cytoplasm made up of membrane-‐bound organelles (plastids, mitochondria), systems of membranes (endoplasmic reticulum, Golgi apparatus), nonmembranous entities (ribosomes, actin filaments, microtubules). The rest is cytosol. Cytoplasm surrounded by single plasma membrane. -‐ Plasma membrane: o Separates protoplast and external environment o Mediates transport of substances to and from protoplast o Coordinates synthesis and assembly of cellulose o Facilitates responses to environmental and hormonal signals (cell growth and differentiation) -‐ Plant cells develop vacuoles, surrounded my tonoplast (single membrane) -‐ Cytoplasm constantly moving: cytoplasmic streaming/cyclosis Nucleus -‐ The nucleus decides which and when protein molecules are being produced, and stores DNA (nuclear genome) -‐ Nuclear envelope: pair of membranes that surrounds nucleus. Nuclear pores provide passageway for exchange of materials -‐ Outer membrane of nuclear envelope may be continuous with endoplasmic reticulum (central in biosynthesis) -‐ Chromatin (DNA + histones) becomes more condensed until visible as chromosomes during nuclear division -‐ Haploid: single set, n, gametes (sex cells). Diploid: 2n, somatic cells. Polyploid: more than two sets of chromosomes (3n, 4n, 5n, etc.) -‐ Nucleoli: structures containing RNA, proteins, DNA. Ribosomal subunits are formed here, and then transported through the nuclear pores to the cytosol. -‐ Ribosomes consist of protein and RNA. Consist of large and small subunits, and are the site where amino acids are linked together. Both found free in cytoplasm and on endoplasmic reticulum -‐ Polysomes: clusters of ribosomes involved in protein synthesis; synthesize proteins in large quantities (found on endoplasmic reticulum, nuclear envelope) -‐ Plastids: in plant cells, concerned with photosynthesis and storage (chloroplasts, chromoplasts, leucoplasts). Double membrane with internal thylakoids and stroma (matrix). Reproduce by fission -‐ Chloroplasts: contain chlorophylls (green) and carotenoid pigments (yellow and orange). Found in plants and green algae. Sites of photosynthesis and synthesis of amino acids, fatty acids, and secondary metabolites. § Grana: stacks of thylakoids. Grana thylakoids are interconnected by stroma thylakoids. § Chloroplasts contain starch grains temporarily (accumulate during photosynthesis) and lipid droplets with proteins § Semiautonomous: contain nucleoids (clear regions of DNA), not associated with histones, have smaller ribosomes, and use binary fission. But have multiple DNA copies. -‐ Chromoplasts: pigmented plastids, variable shape, lack chlorophyll, and have carotenoids (yellow, orange, red). May develop from chloroplasts. May work as attractants for cross-‐pollination and dispersal of seeds -‐ Leucoplasts: lack pigments and elaborate system of inner membranes. § Amyloplasts: synthesize starch -‐ Proplastids: colorless, undifferentiated plastids in meristematic cells of roots and shoots. Precursors of chloroplasts, chromoplasts, or leucoplasts. § Prolamellar bodies: semicrystalline bodies composed of tubular membranes (when proplastid is arrested by absence of light) § Etioplasts: plastids containing prolamellar bodies. Grow in the dark -‐ Mitochondria: double membrane, generally smaller than plastids, sites of respiration (release of energy from organic molecules and its conversion to molecules of ATP). Also synthesize amino acids, vitamin cofactors, and fatty acids. § Cristae: in inner membrane; folds or tubules that increase surface area to proteins and reactions § Programmed cell death: genetically determined process that leads to death of cell. Mitochondria swells and releases cytochrome c, activate proteases and nucleases that degrade protoplast § Constantly in motion, fuse and divide, clustered where energy is required § Semiautonomous: inner membrane encloses matrix of proteins, RNA, DNA, ribosomes, and solutes. DNA in nucleoids -‐ Plant cells’ genetic information found in nucleus, plastid, and mitochondrion -‐ Mitochondria and chloroplasts originally bacteria engulfed by heterotrophic cells. -‐ Symbiosis: close association between two or more dissimilar organisms that may be beneficial to each -‐ Peroxisomes: spherical organelles with single membrane, granular interior. Self-‐replicating organelle, originating from endoplasmic reticulum. § Photorespiration: process that consumes oxygen and releases carbon dioxide. In green leaves, peroxisomes associated closely with mitochondria and chloroplasts § Glyoxysomes: peroxisomes that contain enzymes necessary for conversion of stored fats to sucrose during germination in seeds -‐ Vacuole: organelles surrounded by single membrane (tonoplast). May originate from endoplasmic reticulum, but may derive from Golgi apparatus § Many filled with cell sap: water, inorganic ions, sugars, organic acids, amino acids, crystals § Immature plant cell contains numerous small vacuoles that fuse into one (90% of cell space). Increased vacuole size develops internal pressure and maintains tissue rigidity § Can be storage compartments for primary metabolites (sugars, organic acids), can remove toxic secondary metabolites (nicotine, tannin), can breakdown molecules and recycle components in cell § Anthocyanins: dissolved in cell sap, responsible for red and blue pigments -‐ Endoplasmic reticulum (ER): complex membrane system within entire cytosol; communication system within cell; channel materials; lipid synthesis § Rough ER: cisternae (flattened sacs) with Polysomes on outer surface. Abundant in cells that store proteins § Smooth ER: lack ribosomes, abundant in cells that secrete lipids. Tubular form synthesizes lipids. § Cortical ER: ER inside plasma membrane in cortical cytoplasm. Regulate level of calcium ions, indicator of metabolic and developmental status of cell. Adjacent cells are connected by cytoplasmic strands (plasmodesmata) § Oil bodies: released into cytosol (abundant in fruits and seeds), provide energy and carbon to developing seedling -‐ Golgi apparatus: Golgi bodies (5-‐8 stacks of cisternae) of cell; dynamic, highly polarized membrane system. Involved in synthesis and secretion of noncellulosic polysaccharides (for cell wall). § Trans-‐Golgi network: maturing face of Golgi body § Also process and secrete glycoproteins via transition vesicles from rough ER to forming face. Transported across to maturing face by shuttle vesicles. § Coated vesicles: package vacuolar proteins at trans-‐Golgi network; covered with proteins (clathrin) § Glycoproteins and complex polysaccharides are not coated when prepared for secretion at cell surface, moved by actin filaments § Exocytosis: secretion of substances from cells in vesicles; vesicles fuse with plasma membrane and release contents into cell wall § Endocytosis: uptake of extracellular substances by infolding of plasma membrane and pinching off vesicle -‐ Endomembrane system: all cellular membranes (plasma membrane, nuclear envelope, endoplasmic reticulum, Golgi apparatus, tonoplast, vesicles). § ER is origin of membranes. o Transition vesicles from ER à Golgi apparatus. o Secretory vesicles from trans-‐Golgi network à plasma membrane. o Vesicles from trans-‐Golgi network à tonoplast à vacuoles -‐ Cytoskeleton: dynamic, 3-‐D network of protein filaments extending throughout cytosol. Involved with cell division, growth, differentiation, and movement of organelles. Contain microtubules, actin filaments, and intermediate filaments. -‐ Microtubules: cylindrical structures made of protein, tubulin. Arranged in helix of 13 rows (protofilaments). o Positive end (+): fast-‐growing. Negative end (-‐): slow-‐growing o Dynamic instability: regular sequences of breakdown, reformation, rearrangement. o Assembled in microtubule organizing centers o Inside plasma membrane, allow orderly growth of cell wall. Direct secretory Golgi vesicles toward developing wall. Make of spindle fibers during cell division. Also part of flagella and cilia -‐ Microfilaments: polar structures composed of protein, actin. o Cell wall deposition, tip growth of pollen tubes, movement of nucleus for cell division, organelle movement, vesicle secretion, organization of ER, cytoplasmic streaming -‐ Filaments and cilia are hair-‐like structures extending from surface of eukaryotic cells (flagella usually longer and found alone) o Flagella only found in gametes plants with motile sperm o Outer ring of 9 pairs microtubules around 2 additional microtubules (9+2). Pairs slide past each other to create movement -‐ Basal bodies: cylinder shaped structures in cytoplasm where flagella grow out -‐ Cell wall: constrains expansion of protoplast and prevents rupture of plasma membrane. Determines size and shape of cell and texture of tissue. Contain enzymes and involved in absorption, transport, and secretion. Defense against fungal and bacterial pathogens. -‐ Cellulose: principal component of cell walls. Made of repeating monomers of glucose. Cellulose polymers bundled into microfibrils. Crosslinked by matrix of molecules, including hemicelluloses and pectins. -‐ Hemicelluloses: vary greatly. Hydrogen bonded to cellulose microfibrils, limit the extensibility of cell wall by tethering; regulate cell enlargement -‐ Pectins: characteristic of primary cell wall layers and middle lamella that cements the walls of contiguous cells. Highly hydrophilic, attract water that allows wall to be plastic -‐ Callose: composed of spirally wound chains of glucose residues, widely distributed cell wall polysaccharide. Associated with sieve elements of angiosperm phloem. Deposited rapidly in response to mechanical wounding and stress. -‐ Glycoproteins: structural proteins. Extensins: hydroxyproline rich proteins, strengthen wall -‐ Lignin: adds compressive strength and rigidity to cell wall -‐ Cutin (walls of epidermis), suberin (cork), and waxes: fatty substances commonly found in walls of outer protective tissues. Reduce water loss -‐ Primary wall: cellulosic layers formed first. Deposited before and during growth of plant cell. Composed of cellulose, hemicelluloses, pectins, proteins, water (sometimes lignin, suberin, cutin) o Primary pit fields: thin areas in primary walls -‐ Middle lamella: region of union of primary walls of adjacent cells. Composed mainly of pectins. (Compound middle lamella: two adjacent primary walls, middle lamella, first layer of secondary wall) -‐ Secondary wall: additional wall layers laid down by protoplast on inner surface of primary wall, mostly after cell has stopped growing. Cellulose is more abundant, and pectin may be lacking. Rigid. Matrix composed of hemicellulose. Structural proteins and enzymes are not present. o S1, S2, S3 layers (outer, middle, inner) o Pits: interruptions in secondary wall. Pit membrane: middle lamella and two primary walls between two pits. Pit-‐pair: two opposite pits and membrane. Simple pits: no overarching. Bordered pits: secondary wall arches over pit cavity. -‐ Expansins: wall proteins that loosen up primary wall structure to grow. -‐ Cellulose synthase: synthesize cellulose microfibrils in plasma membrane. -‐ Matrix substances (hemicelluloses, pectins, glycoproteins) carried via secretory vesicles to cell wall (amount secreted depends on development). -‐ Plasmodesmata: connect protoplasts of adjacent plant cells. Found in cell wall, primary pit-‐fields, or pit membranes.
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