Bio week 5 notes
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This 9 page Class Notes was uploaded by Mary Notetaker on Sunday September 11, 2016. The Class Notes belongs to BIO 101 at University of South Carolina taught by Mihaly Czako in Fall 2016. Since its upload, it has received 4 views.
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Date Created: 09/11/16
Chapter 5 Continued: Genomics and proteomics – transformed bio inquiry and applications o Once structure of DNA and relationship to amino acid sequence = understood, biologists wanted to decode genes through base sequences o First chemical techniques for DNA sequencing developed in 1970s and refined o Enlightening to sequence full DNA of organism’s genome o Rapid development of faster and less expensive mapping methods = side effect of Human Genome project o Many genomes sequenced = lots of data o Bioinformatics – uses computer software/computational tools DNA and Proteins = tape measure of evolution o Gene sequences and protein products document hereditary background of an organism o Linear sequences of DNA molecules passed from parent to offspring o We can extend concept of molecular genealogy to relationships between species o Molecular biology added new measure to toolkit of evolutionary biology SickleCell Disease o Slight change in primary structure can affect protein’s structure and ability to function o Sickle cell disease – inherited blood disorder results from single amino acid substitution in protein hemoglobin Unit 2: The Cell Chapter 6 – Tour of the Cell Basic unit of life o All organisms made of cells From single to multi celled o Simplest living collection of matter o Cells related by descent from earlier cells Modified over time Can differ but share common features Microscopy – cells usually too small to be seen with naked eye o Development of technology allowed discovery/study of early cells 1590 – microscopes invented, refined in 1600s Robert Hooke 1665 – first to see cell walls (oak tree bark) Visualize living cells possible by Antoni van Leeuwenhoek’s lenses o Early and current lab microscopes are light microscopes Visible light passed through specimen then glass lenses that refract the light to magnify image and project to eye or camera Magnify about 1000x o 3 parameters in microscopy magnification – ratio of an object’s size to actual size resolution – measure of clarity of an image minimum distinguishability at separate points contrast – difference in brightness between light and dark areas image enhanced through staining or labeling o Organelles not visible until 1950s Electron microscope – focuses beam of electrons through specimen or on surface Resolution inversely related to wavelength of light that a microscope uses for imaging Electron beams – much shorter than visible light o Scanning electron microscope Used for detailed study of specimen topography Electron beam scans sample surface (usually coated thinly w/ gold) Excites electrons on surface then secondary electrons are detected by a device that translates electron patterns into electronic signal on video screen Result = 3D surface image Uses electromagnets as lenses to bend electron paths and focus image on monitor o Transmission electron microscope Studies internal structure of cells Aims electron beam through thin section of specimen – similar to light microscope with light on a slide Specimen has been stained w/ atoms of heavy metals (attach to certain cell structures and enhance electron density of specific parts of cell) Electrons pass through specimen and scattered to dense regions (fewer are transmitted) Image displays pattern of transmitted electrons Uses electromagnets as lenses to bend electron paths and focus image on monitor o Electron mics vs light mics Electron Revealed many subcellular structures Cells are dead Light Advantages – living cells Recently revitalized by technological advances o Labeling with fluorescent markers gives more detail o Confocal and deconvolution provide sharper 3D images of tissue/cell o Super resolution microscopy Allows subcellular structures distinguished as small as 1020 nm Allowed researchers to break resolution barrier o Cell Fractionation Takes cells apart and separates major organelles and other subcellular structures Centrifuge – equipment that spins test tubes with mixtures of disrupted cells at increasing speeds that causes a subset of cell components to settle at bottom and form a pellet o Lower speeds – pellet has larger components o Higher speeds – pellet with smaller components Enables researchers to create specific cell components in bulk and identify functions Example: tests showed presence of enzymes in cellular respiration while electron microscopy showed large numbers of mitochondria o Helped determine mitochondria were sites of cellular respiration o Biochemistry and cytology complement each other in correlation with cell structure and function Prokaryotic VS Eukaryotic cells All cells have basic features o Bound by selective barrier – plasma membrane o Filled with jelly, semifluid – cytosol In which subcellular components are suspended o Contain chromosomes – carry genes in form of DNA o Have ribosomes – complexes that make proteins from gene instructions Major difference – DNA location o Eukaryotic cell – most DNA stored in nucleus (bound by double membrane) Means true nucleus o Prokaryotic cell – DNA in concentrated region not membrane enclosed – nucleoid Means before nucleus Eukaryotic o Inside called cytoplasm – refers to only region between nucleus and plasma membrane Suspended in cytosol of cytoplasm are organelles with specialized form and function Has membrane bound organelles that prokaryotic doesn’t Prokaryotic o Cytoplasm not formless soup – organized into regions and bound by plasma membrane o No nucleus o DNA unbound in nucleoid Cell Size o Eukaryotic Larger than prokaryotic cells o Size = general part of cell structure that relates to function Carrying out metabolism limits cell size o Cell boundary – plasma membrane Selective barrier that allows passage of enough oxygen, nutrients, and wastes to service cell Limited # of substance can cross/second so SA to V ration = crucial as cell increases in size, surface area grows less than volume this explains elongated shape of certain cells (nerve) microvilli projections – increase surface area without an appreciable increase in volume The Eukaryotic Cell o Elaborate internal membranes that create sections of the cell – organelles Provide local environments and support certain functions Plasma and organelle membranes contribute to metabolism – many enzymes built into membranes o Basic biological membrane – double layer of phospholipids and other lipids o Plant/animal cells – most of the same organelles o Nucleus contains most of DNA Ribosomes use information from DNA to make proteins Nucleus – contains most of cell genes and is usually most conspicuous organelles o Enclosed by nuclear envelope – separated from cytoplasm Double membrane with lipid bilayer Lined by nuclear lamina – proteins that maintain nucleus shape o Pores regulate coming/going of molecules from nucleus o DNA organized into chromosomes Each contains single DNA molecule with proteins Combo of DNA and proteins = chromatin Condenses to form discrete chromosomes as cell preps for division o Nucleolus – located in nucleus, site of ribosomal RNA synthesis Ribosomes – complexes made of ribosomal RNA and protein o Carry out protein synthesis in 2 locations In cytosol Outside endoplasmic reticulum or nuclear envelope o Endomembrane system – regulates protein traffic and does metabolic functions in cell Consists of: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane Either continuous or connected by transfer by vesicles Endoplasmic reticulum – accounts for > half of total membrane in eukaryotic cells Continuous with nuclear envelope 2 distinct regions: o smooth ER – lacks ribosomes synthesizes lipids, metabolizes carbohydrates, detoxifies drugs and poisons, stores calcium ions o rough ER – surface covered in ribosomes has bound ribosomes that secrete glycoproteins – proteins covalently bonded to carbs distributes transport vesicles secretory proteins surrounded by membranes membrane factory for cell Golgi apparatus – consists of flattened membrane sacs – cisternae Functions: o Modifies products of ER o Manufactures certain macromolecules o Sorts and packages materials in transport vesicles Lysosomes – digestive compartments, membranous sac of hydrolytic enzymes that can digest macromolecules Lysosome Enzymes Work best in acidic environment of lysosome Hydrolytic enzymes & lysosomal membranes – made by rough ER then transferred to Golgi apparatus Some cells absorb another by phagocytosis – forms food vacuole o Fuses with lysosome and digests molecules Lysosomes use enzymes to recycle own organelles/macromolecules – autophagy Vacuoles – diverse maintenance compartments Large vesicles derived from ER and Golgi apparatus Perform variety of functions in different cells Food vacuoles formed by phagocytosis Contractile vacuoles – found in many freshwater protists, remove excess water from cells Central vacuoles – found in mature plant cells, hold organic compounds and water o Mitochondria and Chloroplasts Mitochondria – sites of cellular respiration, metabolic process that uses oxygen to generate ATP Chemical energy conversion In nearly all eukaryotic cells Smooth outer membrane and inner membrane folded into cristae Inner membrane – two compartments intermembrane and mitochondrial matrix o Some metabolic steps of cell respiration catalyzed in mitochondrial matrix o Cristae – large surface area for enzymes that synthesize ATP Chloroplasts – found in plants and algae, sites of photosynthesis Capture light energy Contain green pigment – chlorophyll Contain enzymes and other molecules involved in photosynthesis Found in leaves and other green organs of plants and in algae Structure: o Thylakoids – membrane sacs stacked to form a granum o Stroma – internal fluid Group of plant organelles called plastids Peroxisomes – oxidative organelles Specialized metabolic partitions bound by single membrane Produce hydrogen peroxide and convert to water Perform reactions with different functions Unknown relation to other organelles Evolution of Mitochondria/chloroplasts Similarities with bacteria o Enveloped by double membrane o Contain free ribosomes and circular DNA molecules o Grow/reproduce marginally independently Similarities sparked endosymbiont theory o Suggests early eukaryotic ancestor with endomembrane system engulfed oxygenusing nonphotosynthetic prokaryotic cell o Engulfed cell made relationship with host cell – endosymbiont Evolved into mitochondria One of these cells may have taken up photosynthetic prokaryote and became chloroplast o Cytoskeleton – network of fibers that organize cell structure and activity Organizes cell structure and activities – anchors organelles Composed of three molecular structures: Microtubules – thickest o Hollow rods 25 nm in diameter and 200 nm25 microns long Shape cell Guide movement of organelles Separate chromosomes during cell division o Animal cells: microtubules grow from centrosome near nucleus Centrosome has centriole pair – nine triplets of microtubules arranged in ring o Control beating of flagella and cilia – microtubule containing extensions of some cells Common structure – microtubule core sheathed by plasma membrane Basal body anchors cilium/flagellum Motor protein dynein – drives bending movements o Dynein Arms alternately grab/move/release out microtubules o Protein crosslinks limit sliding o Forces of dynein arms bend cilium/flagellum Microfilaments – actin filaments, thinnest o Solid rods 7nm in diameter, built as twisted double chain of actin subunits o Bear tension – resist pulling forces in cell o From 3D network called cortex inside plasma membrane to support cell shape o Bundles make up core of microvilli of intestinal cells o Those involved in cellular motility contain myosin protein o In muscle cells – 1000s actin filaments parallel to each other o Thicker filaments of myosin interdigitate with thinner actin fibers o Actin and myosin cause contraction – drives amoeboid movement Cells move on a surface by using pseudopodia and moving toward them o Cytoplasmic streaming – circular flow of cytoplasm in cell Quickens material distribution Actinmyosin and solgel transformations drive cytoplasmic streaming Intermediate filaments – midrange diameter o Range from 812 nm o Support cell shape and anchor organelles o More permanent cytoskeleton fixtures Role – support and motility Supports cell and maintains shape Interacts with motor proteins to produce motility Inside cell – vesicles travel along tracks of cytoskeleton o Extracellular components and cell connections Help coordinate cellular activities Most cells create materials outside plasma membrane These structures involved in cell functions Plant cell walls Extracellular structure that distinguishes plant from animal cells Prokaryotes, fungi, and unicellular eukaryotes also have cell walls Protects plant cell, maintains shape, and prevents too much water absorption Made of cellulose fibers inside polysaccharides and protein Multiple layers o Primary cell wall – relatively thin and flexible o Middle lamella – thin layer between primary walls of adjacent cells o Secondary cell wall – (some cells) between plasma membrane and primary cell wall Plasmodesmata – channels between adjacent plant cells Extracellular matrix (animal cells) ECM made of glycoproteins – collagen, proteoglycans, and fibronectin ECM proteins bind to receptor proteins in plasma membrane (integrin) Influential in cell lives o Regulates cell behavior by communication through integrins o Influences activity of gene in nucleus o Mechanical signaling can trigger chemical signals in cell Cell junctions Close cells in tissue, organ, or organ systems can interact through physical contact Plasmodesmata (plant cells) Channels that perforate cell walls o Water and small solutes pass through Tight junctions, desmosomes, gap junctions (animal cells) 3 types of cell junctions in epithelial tissue o tight junctions – close cell membranes press together – no leakage of extracellular fluid o desmosomes – fasten cells in strong sheets o gap junctions – provide cytoplasmic channels between close cells o Cell – greater than sum of parts Rely on integration of structures/organelles
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