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This 10 page Class Notes was uploaded by Shira Clements on Wednesday February 17, 2016. The Class Notes belongs to BSCI105 at University of Maryland taught by Norma Allewell in Fall 2015. Since its upload, it has received 56 views. For similar materials see Principles of Biology I in Biology at University of Maryland.
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Date Created: 02/17/16
Shira Clements BSCI105 Chapter 6 A Tour of the Cell- book has chart of everything Cell- simplest collection of matter that can be alive Microscopes are used to see the tiny things in life, like cells and their components, by using magnification (ratio of object’s image size to real size) and resolution (clarity of image) and contrast (accentuates difference parts of sample). - LM- light microscope- visible light passing through specimen then glass, which magnifies specimen - EM- Electron microscope- focuses on beam of electrons through specimen - SEM- Scanning Electron Microscope- detailed studies of topography - TEM- Transmission Electron Microscope- study on internal structure of cells Cell Fractionation- useful technique in studying cell structure and function - Takes cell apart and separates major organelles and subcellular structures - Uses centrifuge which spins different organelles to bottom at diff speeds Prokaryotes (bacteria and archaea) and Eukaryotes (protists, fungi, animals, and plants) - All have plasma membrane- selective barrier that binds cell and only lets certain things in and out. - All have cytosol- semifluid where subcellular components are suspended - All have chromosomes- carry genes in form of DNA - All have ribosomes- tiny complexes that make proteins according to instructions from genes Eukaryotic Cells Prokaryotic Cells DNA is in nucleus- bounded by DNA is in the nucleoid- not double membrane membrane bound Cytoplasm is only region between No membrane bound organelles- no nucleus and plasma membrane and nucleus within it (except for cytosol) are organelles Bigger, which allows for more Smaller but greater ratio of surface activity. More surface area and area to volume. volume. Microvilli- cell that have high ration of surface area to volume (exchange a lot of material with their surrounding cells). They are ting projections from surface that increase surface area without an appreciable increase in volume. Eukaryotic Cell- Nucleus (information central)- contains most genes in eukaryotic cell, while some are in mitochondria - Nuclear envelope- separates nucleus’s contents from cytoplasm with the help of nuclear lamina and nuclear matrix (protein fibers extending throughout interior) o Double membrane- each layer is a lipid bilayer with associated proteins Layers have pores and that’s where the inner and outer membranes are continuous. The protein pore complex is there and regulates the entry and exit of proteins and RNAs and large complexes of macromolecules. The nuclear side is lines with nuclear lamina, which is a protein that maintains the shape of nucleus by supporting the nuclear envelope. Chromosomes- DNA is organized into these structures that carry genetic information. Each chromosome contain one DNA molecules associated with many proteins, some may help coil which shortens the DNA so it can fit in nucleus. Can only be distinguished from one another once they start to divide. Humans have 46 in nucleus, except sex cells has 23 chromosomes. Chromatin- complex of DNA and chromosomes. Nucleolus- where ribosomal RNA is created from instructions in DNA Proteins imported from cytoplasm are assembled with rRNA into subunits of ribosomes, which then exit the nucleus through the pores to cytoplasm, where large and small subunit can assemble into ribosome. o Nucleus directs protein synthesis by making mRNA according to instruction of DNA. mRNA then foes to cytoplasm via pores and ribosomes translate the genetic message into primary structure of a polypeptide. Ribosomes (protein factories)- complexes made of ribosomal RNA and protein - Cellular components that carry out protein synthesis. - Free ribosomes- suspended in cytosol (enzymes that catalyzes sugar breakdown) - Bound ribosomes- attached to nuclear envelope or endoplasmic reticulum (usually make proteins that are destined for insertion into membranes or for export of cell=secretion) o Can alternate between free and bound Endomembrane System- includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and plasma membrane. - System takes care of many tasks- synthesizes proteins, transports things in or out of cell, metabolism and movement of lipids, and detoxification of poisons. - Vesicles- sacs made of membrane that help connect membranes. - Endoplasmic Reticulum (ER)- extensive network of membranes that it accounts for more than half the total membrane in eukaryotic. Has network of membrane tubules and sacs called cisternae. ER separates the ER lumen (internal compartment of ER) from the cytosol - Smooth ER- outer surface lacks ribosomes o Synthesis of lipids (oils, phospholipids, steroids)- sex hormones- testes and ovaries have a lot of smooth ER o Detoxify drugs and poisons esp in liver by adding OH to the drug molecules to help make them more soluble and easier to flush from body. o Stores calcium ions- muscle cells, the smooth ER pumps calcium from cytosol to ER lumen, but come back after a muscle is stimulated by nerve impulse. - Rough ER- studded with ribosomes on outer surface of membrane, continuous with the cytoplasmic side of nuclear membrane o many cells produce proteins produced by ribosomes attached to rough ER- pancreatic cells produce insulin and then secrete hormone into bloodstream o polypeptide chain grows from ribosome and is threaded into ER lumen through a pore formed by a protein complex in ER membrane- as the chain enters the ER lumen, it folds into native shape. o Glycoproteins are proteins that secrete- have carbohydrates bonded to them. These proteins are kept separate from proteins that are produced by free ribosomes and ones that remain in cytosol. They depart from ER wrapped in membrane of vesicles that bud like bubbles from region called transitional ER. o Vesicles in transit from one part of cell to other are called transport vesicles. o Membrane factory for cells- grows by adding membrane proteins and phospholipids to own membrane- some of it is transferred by transport vesicles to other parts of ER. o Makes membrane phospholipids - Golgi Apparatus- shipping and receiving center- modify, store, leave o From ER, many transport vesicles come here o Has cisternae- flattened membranous sacs- separates internal from cytosol Distinct structural directionality- membranes of cisternae on opposite sides which gives it thickness and molecular composition. Two sides: cis (near ER and transport vesicles bring material to it and has ability to fuse with ER) and trans face (allows material to travel to other sites). Between cis and trans- fix the materials that come in- manufactures some macromolecules Cisternae progress from cis to trans face- modifying their cargo as they go “Labels” each material with the function they have so can go to right place - Lysosome- digestive compartment o Membranous sac of hydrolytic enzyme that an animal uses to digest or hydrolyze molecules o Enzymes work best in acidic environments in lysosomes, so if the lysosome break, the enzymes wont work in the cytosol because it has a neutral pH o Hydrolytic enzymes and lysosome membrane are made by rough ER and transferred to golgi apparatus for processing o The 3D shape of these proteins protect vulnerable bonds from enzymatic attack o Intracellular digestion-enzyme digests food, along with sugars and amino acids, pass through cytosol and become nutrients for cell. o Phagocytosis- eats other organisms. Enzymes helps recycle cells own organic material- autophagy- lysosome fuses with damaged organelle or small amount of cytosol and surrounds with a double membrane and dismantle the enclosed material, so the monomers are returned to cytosol for reuse. Helps cell renew itself - Vacuole- diverse maintenance compartments- (bigger in plants than in animal cell) o Large vesicles derived from ER and golgi apparatus o Food vacuoles- help with phagocytosis o Contractile vacuoles- pump excess water out of cell o Some do enzymatic enzymatic hydrolysis, but some people call this part of the lysosome o Hold reserves for some compounds for proteins o Stores poisonous compounds to animals for protection of plant o Plant vacuoles contain pigment of petals for pollination o Central vacuole- contains cell sap- cell’s main repository of inorganic ions o Helps with growth of cell- when absorbs water, cell gets bigger Changing Energy (convert solar energyto chemical energy by getting sunlight which drives synthesis of organic compounds from CO and w2ter)- Mitochondria-chemical energy conversion - Sites of cellular respiration- uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels - All eukaryotic cells- most have hundreds of mitochondria- correlates with cell’s metabolic activity - Enclosed by two membranes- each with phospholipid bilayer and proteins (ones that help with cellular respiration)- outer is smooth and inner is convoluted, with infoldings called cristae, which divides the mitochondrion into two internal compartments and enhances productivity of cellular respiration because it gives it more surface area o Intermembrane space- narrow region between inner and outer membranes o Mitochondrial matrix- enclosed by inner membrane. Contains enzymes (catalyze steps in cellular respiration) and mitochondrial DNA and ribosomes Chloroplasts- capture of light energy- found in plants (leaves) - Sites of photosynthesis - Contain green pigment- chlorophyll- and enzymes that help with photosynthetic production of sugar - Two membranes to separated by small intermembrane space to partition it from cytosol o Intermembrane space, stroma, thylakoid= 3 compartments of chloroplast - Thylakoids- interconnected sacs in the chloroplast, flattened membrane o Stacked like poker chips- each stack is granum - Fluid outside thylakoids is stroma- contains chloroplast DNA, ribosomes, and enzymes - Shape is changeable, grow occasionally and can reproduce itself if it grows (pinches in 2) - Can move around cell along cytoskeleton - Part of plastid family Peroxisomes- oxidation - Specialized metabolic compartment bounded by single membrane. - Have enzymes that remove H atoms from substrates and gives them to O2to make H O 2 h2drogen peroxide - Use O 2o break fatty acids down into molecules that go to the mitochondria and used for cellular respiration - In liver- detoxify alcohol and other poisonous compounds by transferring H to O - H2O 2s toxic itself but it has enzyme to make it into water- the cell components that make hydrogen peroxide are separated from other parts of cell, so it doesn’t damage - Glyoxysomes- specialized peroxisomes in fat storing tissues of plant seeds o Have enzyme to make fatty acid a sugar, which is source of energy and C - Grow larger by incorporating proteins made in the cytosol and ER and within itself Cytoskeleton- network of fibers in cytoplasm that organize structures and activities in cell - Support and mobility (esp in animal cells which lack a cell wall) o Stabilized by opposing forces exerted by elements o Can be dismantled in one part of cell and resembled in new location- changing shape of cell o Cell motility- changes in cell location and limited movements in parts of cell Requires interaction with motor proteins (bend cilia and flagella by gripping microtubules within those organelles and sliding them against each other)- work together to allow complete cells to move along fibers outside the cell o Manipulates plasma membrane by bending it inwards to form food vacuoles (other phagocytosis vesicles) - Microtubules- hollow rods- walls are constructed of many tubulin, globular protein that is a dimer (has two subunits)- alpha tubulin and beta tubulin, so the two ends are slightly different- one can release or gather tubulin dimers much faster than other. o shape and support the cell o serve as the track that organelles with motor proteins can move. Guide secretory vesicles from Golgi apparatus to plasma membrane o Helps with separation of chromosomes in cell division o Grow out from centrosome- located near nucleus and organize microtubules Centrioles-in centrosome and composed of 9 sets of triplet microtubules arranged in a ring (like a star). Before dividing, they replicate- but are not needed in all eukaryotes (plant and fungi don’t have), but they help organize microtubules o Specialized arrangement of microtubules is responsible for beating of flagella and cilia (extensions that contain microtubules that project from cell). Act as engine for unicellular eukaryotes Can move fluid over surface of tissue when extend from cells in tissue layer Flagella- works like tail of fish- same direction as axis Cilia- works like oars of boat (alternate, against axis) Signal receiving antenna for cell, so can’t move spontaneously, which is called primary cilium- transmit signals from outside to inside cell that will trigger activity in cell Both have microtubules enclosed in an extension in plasma membrane 9 doublets of microtubules in ring and in center- 2 microtubules = 9+2 pattern, but ones that cant move spontaneously don’t have the 2 on the inside the ring is known as basal body- microtubule triplets, similar to centriole, sometimes it becomes a centriole flexible cross linking proteins connect the outer doublets to one other and to the two central microtubules. Each doublet has pairs of protruding proteins spaced alone its length to get the other doublet, which are large motor proteins called dyneins-bend the organelles, and ATP gives energy for them to bend organelles- kinds of like walking- two feet that walk along microtubules of adjacent doublet, so it has a pull (the back foot) which helps bend an cant slide past each other because of the cross linking proteins, so it curves instead. - Microfilaments- solid rods, built from molecules of actin, twisted double chain of actin subunits o Structural networks when certain proteins bind along actin filament so it would extend like a branch o Role is to bear tension (pulling forces) o 3D network of it in plasma membrane- cortial microfilaments- helps with shape gives outer cytoplasmic layer of cell a gel texture- cortex o Make up core of specialized materials across plasma membrane o Cell motility- esp in contractile apparatus of muscle cells Actin filaments are parallel to one another along muscle cells, interlocked with thicker filaments made of protein myosin. When it interacts with microtubules, myosin acts like a motor protein and walk the actin filaments, but it slides this time which make cell shorter, which cause contradictions in cell, which can lead to dividing cell. Amoeba crawls along surface by extending pseudopodia (false foot) and moving towards them- they extend by assembly of actin subunits into microfilaments that convert cytoplasm from sol (liquid) to gel- this helps make strong attachments. The trailing end of the interaction of microfilaments and myosin causes contradiction which loosens ell surface attachments and pulls it forward toward pseudopodia- forward movement is slowed down. Actin-myosin and sol-gel interactions in plant cells may be involved in cytoplasmic streaming- circular flow of cytoplasm within cell- speeds up distribution within cell. - Intermediate Filaments- bigger than microfilaments but smaller than microtubules in size o Specialized for bearing tension (like microfilaments)- help with shape and reorganizing organelles when needed o Each type is constructed from particular molecular subunit of proteins containing keratin- varies in diameter o More permanent than other two- do not dissemble-help retain shape even after microtubules and microfilaments are gone Extracellular components and connections between cells- help coordinate cellular activities - Cell walls- extracellular structure of plant cells o protects, maintains shape, and prevents excess water from getting in o hold of plant against force of gravity together o Microfibrils made of cellulose are made by enzyme cellulose synthase and embedded in a matrix of other polysaccharides and proteins in extracellular space- basic architectural design of cell wall (strong fibers) young plant cell- secretes tin and flexible wall- primary cell wall cellulose fibers are oriented at right angles to expand cell microtubules guide cellulose synthase since it makes and deposits cellulose fibrils, so it affects growth pattern of cell Middle lamella- between primary and adjacent cells, thin layer of rich and sticky polysaccharides called pectins. It glues adjacent cells together, and when it stops growing, the wall is strengthened. Secondary cell wall- between plasma membrane and primary cell wall. Several laminated layers are strong for protection and support - Extracellular Matrix (ECM)- animal cells’ version of cell wall. o Glycoproteins and other carbohydrate- containing molecules secreted by cell Collagen- most abundant glycoprotein- forms strong fibers outside cell Embedded in network woven out of proteoglycans secreted by cell. Small core proteins with carbohydrate chains covalently attached. Fibronectin- ECM glycoprotein that attaches cells to ECM, and bind to integrins, surface cell receptor protein in plasma membrane and bind on the cytoplasmic side to associated proteins attached to microfilaments of cytoskeleton, and can transmit signals between ECM and cytoskeleton. Can regulate cells’ behaviors and can influences genes in nucleus through some pathways and can help coordinate cell’s behavior by triggering chemical signaling pathways in cell Cell Junctions- - Plasmodesmata- cell walls are perforated by this o Membrane-lined channels filled with cytoplasm o Cytosol passes through and joins internal chemical environments of adjacent cells, unifying plant- plasma membrane of cell line channel of each plasmodesma and thus are continuous - Tight junctions, desmosomes, and gap junctions- cell junctions, common in epithelial tissue- lines external and internal surface of body o Tight junctions- plasma membranes of neighboring cells are tightly pressed against each other through proteins, prevent leakage of fluid o Desmosomes- fasten cells together like a sheet, made of intermediate filaments, attach muscle cells to each other o Gap Junctions- provide cytoplasmic channels from one cell to adjacent cell- kind of like plasmodesmata, consist of membrane proteins that surround a pore through small compounds may pass. Necessary for communication between cells
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