Chapter 6 magnification : ability to make an image larger than A - PDF document

7/21/2016 How We Study Cells Microscopes opened up the world of cells Characteristics of Microscopes Chapter 6 • magnification : ability to make an image larger than A Tour of the Cell actual size • resolution : power to show details clearly while enlarged (if poor, objects seem fuzzy) • constrast: accentuates different parts of the sample II. Electron Microscopes (1950’s) Types of Microscopes I. compound light - light passes through one or more lenses - limited by physical characteristics of light - object must be sliced thinly enough to be transparent - can magnify an image up to 200,000 X - upper limitation is 2000X or 0.5 microns (um) in diameter - resolution limitation: 0.2 microns - beams of electrons produces enlarged image - resolution limitation: 0.002 nm across object Types of Electron Microscopes 2. scanning electron microscope (SEM) - used to study surface structures 1. transmission electron microscope (TEM) - surface covered with thin film of gold - used to study internal structures - beam excites electrons on surface - produces three dimensional images - transmits a beam of electrons through very thinly sliced specimen stained with heavy metals - 100,000 X mag. - change density of cellular structures and electron transmission - dead specimens only - dead specimens - 200,000 X magnification - black and white only Plant Cell 1

7/21/2016 Isolating organelles CELL THEORY 1. Cell fractionation - take apart cells, separate major organelles 1. all living things are composed of cells 2. Ultracentrifuge - applies force 1 million times the force of gravity to separate further the cell organelles with the most dense 2. cells are basic units of structure and at the bottom function 3. all cells come from pre- existing cells Common features of all cells Activities of Life - plasma membrane (cell membrane) - cytosol: semi-fluid substance, holds cellular structures - cytoplasm: cystsol + organelles • Most everything you think of a whole - cytoskeleton: microscopic protein fibers that keep cells shape - ribosomes: make proteins organism needing to do, must be done at - DNA: controls all cell activities the cellular level… – reproduction – growth & development – energy utilization – response to the environment – homeostasis Prokaryote vs Eukaryote Cell Size - most cells are 5-50 microns DNA in nucleoid region, without chromosomes in nucleus, surface area ratio (limits size of cells) a membrane separating it from membrane-enclosed organelle rest of cell Cell Wall: made of Cellulose or inside of cell grows faster: cubed Cell Wall: Made of Chitin Peptidoglycans (V = L x W x H) Ribosomes: Larger, Free and Ribosome: Smaller, Free in Attached, Non-simultaneous outside of cell grows slower: squared cytoplasm, Simultaneous Transcription/Translation (A = L x W) 2

7/21/2016 Relationship of Surface Area to Volume Surface Area Example Cells must be small to maintain a large surface area to volume ratio Large S.A. allows  rates of chemical exchange between cell and environment LENGTH OF TOTAL TOTAL SURFACE SIDE SURFACE VOLUME AREA TO AREA (CM2) VOLUME (CM) (CM3) RATIO 1 (1X1X6)= 6 (1X1X1)=1 6:1 Small Intestine : highly folded surface to increase 24:8 2 (2X2X6)=24 (2X2X2)=8 3:1 absorption of nutrients Villi: finger-like projections on small intestine wall 54:27 3 (3X3X6)= 54 (3X3X3)=27 2:1 Microvilli: projections on each cell Limits to Cell Size Surface Area Example Root hairs increase surface area for water and mineral absorption • Metabolic requirements set uper limit of size – In large cell, cannot move material in and out fast enough to support life Cell Shape How to get Bigger - most spherical or cuboidal nerve cell • Become multi-cellular - different shapes reflect function dermal epidermal cells white blood cells goblet cell red blood cells 3

7/21/2016 Cell Structure Eukaryotic Cells Animal Plant Main components of eukaryotic cells 1. cell membrane (outer boundary) 2. nucleus (control center) 3. cytoplasm (material between nucleus Cytoplasmic channels- Connnect adjacent Cell’s cytoplasm and membrane) Structure: Nucleus - nuclear matrix - protein skeleton helps maintain nucleus shape • - control center of cell: directs all cell activities - nuclear envelope (double membrane) - contains chromatin : combination of strands of DNA and protein - contains DNA - nuclear pores: control substance movement - continuous with rough ER - nucleoplasm : dense, protein rich - site of DNA and RNA synthesis - nucleolus : region that forms ribosomal subunits - located in center of most cells Cytosol Organelles ( between membrane and nucleus) Organelle: tiny structure that performs - Cytoplasm = cytosol + organelles special functions in the cell – gel like material between to maintain life – contains water, salts, organic molecules – in constant motion (cytoplasmic streaming) – holds organelles animation amoeba animation 4

7/21/2016 Mitochondria Ribosomes • powerhouse of cell (cell respiration) • spherical structures which make proteins • provides energy for cell in form of ATP • membrane bound • not surrounded by membrane • double membrane: • composed of protein and rRNA • most numerous in cells which use a lot of energy (muscle) • self replicating, contain their own DNA • site of protein synthesis • free ribosomes : float in cytosol- make proteins used within cell • bound ribosomes : attached to rough ER- make proteins for export from cell (secretion) - cristae : folds of inner membrane greatly enlarge surface area of inner membrane (more area for chemical reactions of respiration) - matrix : fluid filled inner compartment Endoplasmic reticulum: (ER) Golgi Apparatus intercellular highway complex membrane system of folded sacs and tunnels regulates protein traffic and performs metabolic functions • flattened system of membranes and sacs piles on each other (like pancakes) Rough ER Smooth ER • very close to ER - ribosomes stuck to membrane - no ribosomes • processes, packages, and secretes proteins for transport (o other surface - also stores and acts as an parts of cell (vesicles) and produce lysosomes intercellular highway for proteins and - package proteins for secretion and inserted into ER enzymes - can be stored or exported to - involved in: – Cis face: receives vesicles smooth ER – Trans face : ships vesicles - synthesis of steroids in gland - prominent in cells that make a lot - cell regulation of Ca levels of protein in muscle - cells break down toxic animation substances in liver cells Steps of Protein Production and Lysosomes Transport • small round vesicles that contain digestive hydrolytic enzymes 1. ribosomes make proteins on the rough ER- packaged into vesicles • formed from Golgi Apparatus 2. vesicles transport the newly made proteins from the rough to the Golgi • digest and remove waste from cell (old organelles, byproducts, apparatus bact., viruses) 3. in Golgi, proteins are processed and then packaged into NEW vesicles 4. vesicles move thru Golgi to cell membrane and release contents outside cell animation 2 animation 5

7/21/2016 Vacuoles Peroxisomes • Storage of materials (food, water, minerals, pigments, poisons) • contain different oxidative enzymes than lysosomes • Membrane bound • break down toxic substances into H 2 O 2 • Ex: food vacuoles, contractile vacuoles (remove H from substances and transfer them to O 2 ) then converts H 2 O 2 to H 2 O - detox alcohol and drugs - break down fatty acids • formed from proteins in cytosol, not Golgi – Glyoxysomes (fat tissues of plant seeds) FA  sugar Cytoskeleton Structure Cytoskeleton (cell framework) • maintains shape and size of cell • composed of network of long protein strands located in cytosol • provides movement for organelles within cytosol • regulate biochemical activities A. Intermediate Filaments (medium size fibers) - protein fibers coiled into cables - maintain shape of cell - permanent fixtures - anchor nucleus and organelles Cytoskeleton Structure • flagella : long whip-like structures used for movement (motility) • cilia : short numerous hair like projections - movement - transport of substances across cell - signal receiving antenna for B. Microtubules (largest fibers) ex: ear drum: transmits sound waves - long hollow coiled protein tubes (tubulin) respiratory tract: moves mucus etc. - maintain shape and support cells - internal cell highways – move organelles thru cell Motility requires interaction Basal body- anchors of cytoskeleton fibers with cilia/flagella to cell - form centrioles, spindles (cell division) motor proteins . - motility (cilia and flagella) 6