SBU1053_Chapter 3_Part II.pdf

Modifications of Cell Surfaces ✘ Cells live and interact with external environment. ✘ Extracellular environment is made of large molecules produced by nearby cells. ✘ Materials are deposited by secretion. ✘ Plants, prokaryotes, fungi are surrounded by cell walls. ✘ Animals have mor...

Modifications of Cell Surfaces ✘ Cells live and interact with external environment. ✘ Extracellular environment is made of large molecules produced by nearby cells. ✘ Materials are deposited by secretion. ✘ Plants, prokaryotes, fungi are surrounded by cell walls. ✘ Animals have more varied extracellular environments that can change.  Cell Surfaces in Animals ✘ Animal cells have two different types of cell surfaces. ✗ Extracellular matrix outside of cells A m eshwork of prot eins a nd polysa ccha rides closely a ssocia t ed wit h cells t ha t produced t hem Com m on st ruct ura l prot eins in ECM Colla gen resist s st ret ching Ela st in provide resilience (st ret cha ble) t o ECM Fibronect in is a n a dhesive prot ein t ha t links int egrin The st rengt h a nd flexibilit y of ext ra cellula r m a t rix va ries The ext ra cellula r m a t rix of ca rt ila ge ca n be very flexible The ext ra cellula r m a t rix of bone is ha rd beca use m inera l sa lt s a re deposit ed out side t he cell ✗ Junctions t ha t occur bet ween cells ✘ Bot h ca n a ssocia t e wit h t he cyt oskelet on a nd cont ribut e t o cell- t o- cell com m unica t ion.  Junctions Between Cells ✘ Cell surfaces in certain tissues of animals ✗ Junctions Between Cells Adhesion Junct ions: Int ercellula r fila m ent s bet ween cells Tight Junct ions : Form im perm ea ble ba rriers bet ween cells Ga p Junct ions : Pla sm a m em bra ne cha nnels a re joined (a llows com m unica t ion)  Plant Cell Walls ✘ All plant cells have a cell wall. ✗ It contains celluloseas the main component. ✗ Pectins allow the walls to stretch as cells grow. ✗ Noncellulosepolysaccharides harden the wall as the cell matures. ✗ Pectin is abundant in the middle lamella, a layer ofadhesive substances that holds cells together. ✘ Plasmodesmata are narrow channels that penetrate the cell wall to connect adjacent cells. ✘ Each channel contains a strand of cytoplasm. ✘ Cytoplasm allows exchange of materials between cells. ✗ Only water and small solutes pass freely. ✘ Cytoplasm connects all the cells within a plant.  Nucleus nuclear ✘ envelope Nucleoplasm, a semifluid medium nucleolus in the nucleus ✘ Nucleolus Nuclear envelope: nuclear pore ✗ Where ribosomal RNA inner membrane outer membrane chromatin nucleoplasm nuclear pore (rRNA) is made ✘ Nuclear Envelope—a double membrane that separates the nucleus from the cytoplasm ✘ Nuclear pores—openings that permit transport of protein and ribosomal subunits phospholipid Nucleus ✘ The nucleus of the eukaryotic cell containschromatin within a semifluid nucleoplasm. ✘ Chromatin, which is composed ofDNA, protein, and some RNA, is usually a network of fine strands. ✘ The strands condense during cell divisionto form chromosomes.  Ribosomes ✘ Site of protein synthesis ✗ Use messenger RNA (mRNA) as template ✘ Composed of two subunits (large and small) ✗ Subunits consist of rRNA and protein molecules ✘ Where found ✗ In groups ofpolyribosomes, several ribosomes associated with a single mRNA ✗ attached to endoplasmic reticulum ✗ free in cytoplasm  Endomembrane System ✘ The endomembrane system has 4 components: ✗ The nuclear envelop (membrane) ✗ The endoplasmic reticulum (ER) ✗ The Golgi apparatus ✗ Membranous sacs called vesicles ✘ This system compartmentalizes the cell and carries molecules between components of the system.  Endoplasmic Reticulum ✘ Rough ER ✗ Studded with ribosomes ✗ Processing, folding and modification of proteins ✘ Smooth ER ✗ Has no attached ribosomes ✗ Synthesizes phospholipids and steroids ✗ Stores calcium ions ✗ Various other functions, depending on cell type  Golgi Apparatus ✘ Consists of a stack of three to twenty slightly curved sacs. ✘ In animal cells,one side is directed toward the ER, and other side is directed toward the plasma membrane. ✘ Often referred to as the shipping center of the cell. ✘ Apparatus collects, sorts, packages, and distributes materials such as proteins and lipids. ✘ Apparatus receives proteins and also lipid- filled vesicles that bud from the ER. ✘ Proteins made in rough ER have tags that serve as “zip codes” to direct Golgi apparatus where to send them. ✘ Lipids and proteins are modified in transit through the Golgi before being repackaged into secretory vesicles ✘ Contents are discharged out of the cell by secretion.  secretion plasma membrane incoming vesicle secretory vesicle brings substances into fuses with the plasma the cell that are digested membrane as secretion when the vesicle fuses occurs with a lysosome enzyme Golgi apparatus modifies lipids and proteins lysosome from the ER; sorts them contains digestive enzymes and packages them in that break down worn - out vesicles cell parts or substances entering the cell at the plasma membrane protein transport vesicle shuttles proteins to transport vesicle various locations such as shuttles lipids to various the Golgi apparatus locations such as the Golgi apparatus lipid rough endoplasmic reticulum smooth endoplasmic folds and processes proteins reticulum and packages them in vesicles; synthesizes lipids and vesicles commonly go to also per forms various the Golgi apparatus other functions ribosome Nucleus  A Variety of Vesicles ✘ Small, membrane-enclosed, saclike vesicles form in a variety of types, either on their own or by budding ✘ Many vesicles transport substances from one organelle to another ✘ Other vesicles include peroxisomes, lysosomes, and vacuoles (including central vacuoles)  Lysosomes ✘ Membrane- enclosed vesicles formed by Golgi ✗ Contain hydrolytic digestive enzymes ✗ Act as garbage disposals of the cell ✗ Break down unwanted, foreign substances or worn- out parts of cells ✗ Bring macromolecules into the cell  Vacuoles ✘ Large membranous sacs ✘ Larger than vesicles ✘ More prominent in plants ✗ Central vacuole provides Nucleus: nuclear envelope nucleolus central vacuole* cell wall of adjacent cell added support chromatin nuclear pore ✘ ribosomes centrosome Store substances Endoplasmic chloroplast* Reticulum: rough ER ✗ Water smooth ER mitochondrion peroxisome Golgi apparatus ✗ Pigments microtubules cytoplasm actin filaments plasma membrane ✗ Toxins granum* cell wall* *not in animal cells  Peroxisomes ✘ Membrane- bound vesicles peroxisome containing enzymes derived from cytoplasmic ribosomes ✗ Actions of enzymes lead to hydrogen peroxide (H2O2) ✗ H2O2 quickly broken down into water and oxygen by the enzyme catalase ✗ Functions vary amongst cells In liver cells, t hey m et a bolize fa t s or produce bile. In germ ina t ing pla nt cells, t hey oxidize fa t t y a cids.  Energy- Related Organelles ✘ Two types of membranous organelles that specialize in energy conversion are the chloroplasts and mitochondria. ✘ Chloroplasts use solar energy to synthesize carbohydrates via photosynthesis. ✘ Mitochondria break down carbohydrates to produce adenosine triphosphate (ATP). ✘ Chloroplasts and Mitochondria are organelles that specialize in converting energy into useable forms for cells. ✗ Chloroplasts use solar energy to synthesize carbohydrates. ✗ Mitochondria use the breakdown of carbohydrates to produce ATP 18 solar energy + carbon dioxide + water carbohydrate + oxygen ✘ Photosynthesis ✗ Plants, algae, and cyanobacteria have this ability. ✗ Solar energy is the ultimate source of energy for most cells. carbohydrate + oxygen carbon dioxide + water + energy ✘ Cellular respiration ✗ All organisms convert chemical energy into ATP. ✗ ATP is used for all energy - requiring processes in cells.  Chloroplasts Site of photosynthesis in plants and algae Structure: ✗ Double membrane ✗ Ma ke m ost of t heir own prot eins ✗ Stroma – fluid- filled spa ce bounded by double m em bra nes Cont a ins single circula r DNA m olecule a nd ribosom es ✗ Grana– st a cks of t hyla koids Chlorophyll loca t ed in t hyla koid m em bra nes  Mitochondria ✘ Found in all eukaryotic cells ✗ Including plants and algae ✘ Site of cellular respiration ✘ Structure ✗ Bounded by double membrane ✗ Matrix—the inner fluid- filled space ✗ Cristae—formed by invaginations of the inner membrane Inva gina t ions increa se surfa ce a rea ✘ Cont a in t heir own DNA  Cytoskeleton ✘ Consists of three interconnecting proteins ✗ Actin filaments ✗ Intermediate filaments ✗ Microtubules ✘ Maintains cell shape ✘ Assists in movement of cell and organelles ✘ Dynamic—assembled and disassembled as needed  Actin Filaments ✘ Two long, thin, flexible actin chains twisted in helix ✘ Roles ✗ Provide structure as dense web under plasma membrane ✗ Form projections in intestinal cells as microvilli ✗ Allow for formation of pseudopods in amoeboid movement ✘ Actin interacts with motor molecules for movement ✗ Example: muscle cells ✘ In the presence of ATP,myosin pulls actin along  Intermediate Filaments ✘ Intermediate in size between actin filaments and microtubules ✘ Functions: ✗ Support nuclear envelope ✗ Help form cell- to - cell junctions, such as those holding skin cells tightly together ✗ Strengthen human hair Microtubules ✘ ✘ Hollow cylindersmade of globular tubulin (α a nd β) Assem bly ✗ Cont rolled by Microt ubule Orga nizing Cent er (MTOC) ✗ Most im port a nt MTOC is centrosome ✘ Roles ✗ Help m a int a in cell sha pe ✗ Int era ct wit h m ot or m olecules kinesin a nd dynein t o ca use m ovem ent of orga nelles ✗ Form spindle a ppa ra t us during cell division  Centrioles ✘ Found in centrosomes of animal cells ✘ May be involved inmicrotubule assembly and disassembly ✘ Short cylinders with a 9 + 0 pattern of microtubule triplets one microtubule triplet Cilia and Flagella ✘ Ha irlike project ions t ha t a id in cell m ovem ent ✗ In euka ryot es, cilia a re m uch short er t ha n fla gella. ✗ Bot h a re m em bra ne- bound cylinders. 9 + 2 pa t t ern of m icrot ubules ✗ Exa m ples of cilia : Pa ra m ecia m ove by m ea ns of cilia. Cells of t he upper respira t ory t ra ct use cilia t o sweep debris t ra pped wit hin m ucus. ✗ Exa m ple of fla gella : Sperm ht t ps:/ / www.yout ube.com / wa t ch?v=QGAm 6hMysTA  outer microtubule doublet radial The shaft of the spoke flagellum has a ring of nine microtubule central doublets anchored microtubules to a central pair of microtubules. dynein flagellum side arm Flagellum cross section 25 nm Sperm Flagellum The side arms of each doublet dynein are composed side arms shaft of dynein, a motor molecule. ATP In the presence of ATP, the dynein side plasma arms reach out to membrane their neighbors, and bending occurs. Cilia Cilia and Flagella