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Transcript
Faculty of Science, School of Sciences, Lautoka Campus BIO509 Botany Lecture 4: Cells and cell components The Three Domain System is based on molecular studies Prokaryote Eukaryote Before we learn more about the three domain system lets divert a little bit and lets first look at what are cells? Cells • Cells are the basic functional units of life. • Cells make up the entire structure for an organism, some organisms, such as bacteria, are unicellular while other organisms are multicellular. • Cells can take in nutrients, convert those nutrients into energy, and carry out specialized functions. • Cells also contain the organisms hereditary material and can make copies of themselves. Onion cells Common cell components • • • • • • • • • • Plasma membrane Cytoplasm Nucleus Nuclear Membrane Endoplasmic Reticulum Ribosomes Golgi Bodies Mitochondria Lysosomes Vacuoles Some organelles are found only in Plant cells. These organelles are: • Cell Wall • Chloroplasts Plasma membrane • Composed of two layers of phospholipids. • The two layers of phospholipids are arranged with the “heads” on the outside and the “tails” on the inside. (Attracts water) (Repels water) 7 Plasma membrane continued … • Proteins molecules are interspread, some going all the way to both sides, some not. • Proteins passing all the way through aid in passage of certain ions. • Molecules of cholesterol are also found imbedded in it. Functions of a plasma membrane • Serves as an envelope enclosing the cytoplasm. • Controls passage of molecules into and out of the cell, preventing some and promoting others. 9 Nucleus • Contains the genetic material and is the control center of the cell and sends coded messages via DNA. • Stores the cell’s hereditary information and controls all cell activities. • Bounded by a double membrane (=nuclear envelope) which is sometimes continuous with endoplasmic reticulatum. 10 • Inside the nucleus there is one or more nucleoli, roughly spherical shape. • Made of protein and ribosomal DNA. • Serve in the production and assembly of ribosomes components. • The rest of the nucleus comprises the granular nucleoplasm packed with chromatin, the resting-cell form of DNA. • Chromatin forms chromosomes when cell is dividing. 11 Endoplasmic reticulum (ER) • Three dimensional membrane system within the cell. • Network of flattened sacs and tubes that form channels, creating subcompartments. • Two kinds of ER • Rough ER is covered with ribosomes - Functions in synthesis, secretion, and storage of proteins - Predominates in cells storing proteins • Smooth ER is mostly without ribosomes - Functions in making lipids - Predominates in cells that secrete lipids 12 Ribosomes • Small ellipsoidal particles 17—23 nm in diameter. • About 60% of mass is RNA, the rest mostly protein. • Considered an organelle, but not membrane bounded. • Located floating in the cytoplasm, on the rough ER, in other organelles, and on the nuclear membrane. • Comprise two subunits made of RNA and proteins. • The two parts function in assembling proteins by reading (transcribing) messenger RNA and putting the amino acids in the correct order 13 Lysosomes • Functions in digesting food or cellular invaders. • Recycling cellular components • (The lysosome is not found in plant cells) Golgi apparatus • Golgi apparatus collective term for golgi bodies, roundish flattened sacs scattered in cytoplasm. • Polarized membrane system with one side facing the nucleus (cis) & the other (trans) the plasma membrane. • Often 5 to 8 in a stack, but 30+ in simpler organisms. • Produce and secrete non-cellulose polysaccharides sent to the cell wall. • Involved in the transport of lipids around the cell, as well as creating lysosomes 15 Mitochondria • Double membrane organelle, that is involved in cells energy generation. • Inner membrane forms cristae (partitions). These increase surface area for enzymes to work. • Matrix also contains DNA, RNA, ribosomes, proteins, and dissolved substances. • Energy released in cellular respiration inside them 16 Chloroplast in plant cells • They are organelles bound by a double membrane. • Several kinds concerned with storage and photosynthesis. • Usually 75 to 125 per cell is common, more than that in algae, and up to several hundred in some plants. • Usually 4–6 (2–10 ) microns in diameter. • Function to capture light energy in photosynthesis and convert it to energy used in cell—virtually all of world’s food. Vacuoles in plant cells • Makes up to 90% of cell contents. • Bounded by vacuolar membranes (tonoplast) single, and similar to cell membrane. • Filled with cell sap, slightly to moderately acidic, contains inorganic ions, sugars, acids, and amino acids. • Functions mainly to maintain turgor pressure. flaccid turgid 19 A typical bacterial cell A typical animal cell A typical plant cell Animal vs Plant cell Study of cells • The invention of the microscope made it possible for people to discover and learn about cells. • Cell structure and function can be studied provided by preparing tissues of study in different ways. Modern microscopes Light microscopes • Provide basic information about cell structure and some organelles within the cells. • Form an image when light passes through one or more lenses to produce an enlarged image of a specimen • Two basic types - compound microscopes (a) - stereo or dissecting microscopes (b) a b Electron microscopes • Reveal detailed images of tiny structures within the cells. • Form an image of a specimen using a beam of electrons rather than light. • Two types – Transmission electron microscope (a) – Scanning electron microscope (b) a b Readings • Chapter 3, Stern’s Introductory Plant Biology. Questions are welcome???