Download Lecture 04 Notes

Lecture 4 Notes – Cell Structure and Function Questions • How is a cell more than simply the sum of its macromolecular parts? • What characteristics enable cells to be alive and allow them to self-­‐replicate? • How are cells able to metabolize and respond to environmental changes quickly? Intro – Art of Looking at Cells • Anton van Leeuwenhoek – Dutch microscopist – 1632 – 1723 – tiny “animalcules” in rainwater and other liquids 4.1 Cellular Level of Organization Cell = smallest unit of living matter 19th century scientists determined that plants and animals are composed of cells  Robert Brown – nucleus of cell  Matthais Schleiden – plant cells  Theodor Schwann – animal cells  Rudolph Virchow – cells reproduce and “every cell comes from pre-­‐existing cells” Unicellular organisms reproduce by dividing and becoming two new organisms Multicellular organisms grow, many cells divide Cell Theory – Schleiden, Schwann, and Virchow 1. All organisms composed of cells 2. Cells basic units of structure and function in organisms 3. Cells come only from preexisting cells because cells are self-­‐reproducing Most cells are microscopic • Cell sizes range from chicken egg (8 cm) to mycoplasmas (.2 micrometers) • Reason for small cell size o Surface area to Volume ratio greater for smaller cells – show example – limits sizes of cells o Need more surface area for diffusion (nutrients in and waste out) Microscopes • Resolution – measure of clarity of object • Human eye o Light passes through lens and focuses on retina o Resolution 0.1 mm (dust particle) o Magnification 1x • Light microscope o passes visible light through a specimen o magnifies 1000 times max o resolution 0.2 micrometer (some organelles) o Limitations to resolution  Wavelengths of visible light = 380 nm to 780 nm = .380 micrometers to .780 micrometers • Electron microscope (EM) o uses beam of electrons instead of light -­‐ vacuum chamber – air and liquid removed o magnifies about 100,000 times (large molecules) o resolution 2 nanometers o Limitations – cells killed in process o B&W initially -­‐ color added artificially to highlight and clarify • Scanning electron microscopes (SEM) o cell surfaces of cell or group of cells coated with thin metal film – image projected onto video screen – appear 3D o 10,000 – 20,000 x magnification Transmission electron microscope (TEM) o details internal cell structures – specimens cut into thin sections and stained with heavy metals such as gold – electron beam shot through a section and electromagnets bend electron beam to magnify and focus an image onto viewing screen or photographic film o 100,000 – 200,000 x magnifications • Light Microscopy (LM) – modifications improve resolution 1. Differential interference-­‐contrast microscopy 2. Fluorescence and confocal microscopy 4.2 Prokaryotes – no internal membrane bound organelles • Includes Bacteria and Archaea • Bacteria – tuberculosis, anthrax, tetanus, decomosers, genetically engineered to make insulin • Structures o Bacillus – rod-­‐shaped o Coccus – spherical-­‐shaped o Spirilla – rigid spirals o Spirochetes – flexible spirals • Parts o Cell envelope  Plasma membrane – phospholipid bilayer with embedded proteins  Mesosome – internal pouches in plasma membrane – increase surface area  Cell wall  Glycocalyx – layer of polysaccharides outside cell wall in some bacteria • Capsule – if well organized and not easily washed off • Slime layer if not well organized and washes easily o Cytoplasm region  Cytoplasm – semifluid solution composed of water, inorganic, and organic molecules  Nucleoid region – location of single, coiled chromosome  Plasmids – smaller circular pieces of DNA – used in biotechnology as a vector for inserting foreign DNA into different organisms  Ribosomes – sites of protein synthesis – contain RNA and protein in two subunits o Cyanobacteria – perform photosynthesis – and contain thylakoids – internal membranes that contain pigments that absorb solar energy for production of carbohydrates o Appendages – made of protein  Flagella – made of filament, hook, and basal body – for motion  Finbriae – hairlike bristles that allow adhesion to surfaces  Conjugation pili – rigid tubular structures used to pass DNA from cell to cell o Some have projections – pili, short projections, or flagella, longer projections – for movement • Size range = 1 to 20 micrometers or 1/10 a eukaryotic cell 4.3 Eukaryotic cells – cells with internal membrane bound structures • 10 -­‐100 micrometers • Origin – endosymbiotic theory by Lynne Margulis – Figure 4.5 o Infolding of plasma membrane creating endomembrane system o Nucleus forms from infolding around DNA or engulfing ancient archaea •
o Evolution of mitochondria from engulfed alpha-­‐proteobacteria o Evolution of chloroplasts from engulfed cyanobacteria o Evidence – p.337 (Ch. 18) • Organelles – compartments of eukaryotic cells with specialized functions – enclosed by membranes studded with proteins – cites of cellular metabolism – increase membrane surface area for biochemical reactions • Non-­‐membranous structures – centrioles, cytoskeleton made of microtubules (protein tubes), ribosomes • Includes plants, protists, fungi cells, animal cells • Animal cells 1. No cell wall 2. Often have flagella 3. Lysosomes and centrioles 4. Few or no vacuoles 5. No chloroplasts • Plant cells but not animal cells 1. Cell wall made of polysaccharide cellulose – rigid shape and protection 2. Chloroplasts – photosynthesis 3. Large central vacuole – stores water and chemicals 4. Usually no centrioles or lysosomes or flagella 5. (Only plant sperm may have flagella) 4.4 – 4.5 Nucleus and Ribosomes and Endomembrane system Organelles of the endomembrane system 1. Nucleus • Contains DNA – genetic material of cell • Controls cell activities by directing protein synthesis • Chromatin – long fibers of nuclear DNA attached to proteins • Chromosome – coiled up chromatin visible prior to cell division • Genes – hereditary units – segments of DNA that code for proteins • Nuclear envelope – a double membrane with pores that control flow of material into and out of nucleus • Nucleolus – ribosomes made here – “little nucleus” • Ribosomes – sites of protein synthesis – made of rRNA and proteins 2. Endomembrane system – a collective system of interrelated membranes and membrane segments • Vesicles – membrane segments • Function – work together in synthesis, storage, and export of molecules • Includes endoplasmic reticulum (ER) – continuous with nuclear envelope – divides cell into compartments 3. Smooth endoplasmic reticulum • Smooth because it lacks ribosomes • Synthesis of lipids – fatty acids, phospholipids, steroids • Sex cells (ovaries and testes) – production of sex hormones • Liver cells – large amounts of smooth ER – help process drugs and other harmful substances – barbiturates, alcohol – smooth ER increases with drug use – other medicines lose effectiveness • Storage of calcium ions – in muscle cells, calcium ions leak out of smooth ER to trigger contraction of cell 4. Rough endoplasmic reticulum • Rough because ribosomes stud the membrane Two functions a. Makes more membrane – some used by other organelles b. Modifies proteins that will be transported to other organelles or secreted by cell • Secretory protein – a protein secreted by a cell • Steps of secretory protein production a. Polypeptide synthesized by attached ribosome enters ER and folds into 3D shape b. Short chains of sugars are linked to protein making glycoprotein c. Molecule is packaged in a transport vesicle d. Vesicle buds off from ER and goes to Golgi apparatus for further processing e. Transport vesicle with finished molecule goes to plasma membrane and exits cell 5. Golgi apparatus • Receives and modifies substances manufactured by the ER • Chemically marks and sorts molecules into different batches for different destinations. 6. Lysosomes • Contains digestive (hydrolytic) enzymes enclosed in membranous sac • Formation of lysosomes a. Rough ER packages the enzymes into transport vesicles b. Golgi apparatus chemically refines enzymes and releases mature lysosomes • Various functions a. Protists engulf food particles into tiny cytoplasmic sacs (food vacuoles) and lysosomes break down food releasing nutrients into cell. b. White blood cells ingest bacteria into vacuoles and lysosomal enzymes empty into vacuoles and rupture bacterial cell walls c. Damaged organelles and small amounts of cell fluids get digested d. Destroy cells of webbing in early embryo or tadpole’s tail • Abnormal lysosomes o One or more hydrolytic enzymes is missing – indigestible substances build up – fatal childhood diseases o Pompe’s disease – polysaccharide glycogen accumulates in muscle and liver cells due to lack of glycogen digesting enzyme o Tay-­‐Sachs disease – lipids build up in nerve cell membranes – destroys nerve cells in brain 4.6 Other Vesicles and Vacules – not part of endmembrane system Peroxisome • vesicle that is involved in fatty acid metabolism • contain enzymes that result in hydrogen peroxide (H2O2) • RH2 +O2  R + H2O • ALD – adrenoleukodystrophy – Peroxisome malfunction disorder Vacuoles • Membranous sacs • Food vacuoles • Plant’s central vacuole a. Can function as large lysosome b. Helps plants grow by absorbing water c. Stores vital chemicals and waste products d. May contain pigments in flowers to attract pollinators e. May contain poisons that protect against plant-­‐eating animals f. 90% volume of plant cell • In protists – helps maintain internal environment •
4.7 Energy-­converting organelles 1. Chloroplasts – convert solar energy into chemical energy of sugar molecules • Photosynthesis – solar energy + carbon dioxide + water  carbohydrates + oxygen • Parts o Outer and inner membrane – between is intermembrane space o Stroma – thick fluid enclosed by inner membrane space o Granum – stacks of disks 2. Plastids – plant organelles surrounded by double membrane with varied functions  Chromoplasts – responsible for fall colors and colors in carrots, flowers, and so on  Leucoplasts – colorless plastids that synthesize and store starches and oils (potato tissue) 3. Mitochondria – convert chemical energy of foods such as sugars to chemical energy of a molecule called ATP • Cellular respiration – carbohydrates + oxygen  carbon dioxide + water + energy • ATP = adenosine triphosphate – main energy source for cellular work • Structure – two membranes = two compartments o Intermembrane space forms one fluid filled compartment o Highly folded inner membrane encloses second compartment-­‐ mitochondrial matrix – site of cellular respiration – ATP molecules embedded in inner membrane o Cristae – folds in inner membrane • Diseases – more than 40 related to mitochondria malfunction – unable to metabolize organic molecules to produce ATP 4.8 Cytoskeleton and movement • Cytoskeleton – meshwork of protein fibers provide structural support and involved in cell movement, may regulate cellular activities by mechanically transmitting signals from cell surface to interior • Parts of cytoskeleton: o Microfilaments -­‐ Actin filaments – thinnest type of fiber – sold rods composed of globular proteins – cell movement, inc. muscle contraction o Microtubules – thickest fibers – hollow tubes of globular proteins – guide movement of organelles through cell and basis of ciliary and flagellar movement  centrosomes o Intermediate filaments – ropelike strands of fibrous proteins – tension bearing & anchoring organelles • Movement o Cilia – short numerous hairlike projections – 9+2 o Flagellum – long and few – 9+2 o Aid in movement of whole cell or movement of materials across surface of cell o Centrioles – 9+0 o Basal body – anchoring structure – identical to centrioles