Ch 3.pdf

Cells Chapter 3 Outline Introduction to Cells Cells History Modern Microscopes Eukaryotic versus Prokaryotic Cells Cell Structure and Communication Cellular components Cell Reproductions Higher plants Cells versus animal cells Introduction to Cells All living things are a...

Cells Chapter 3 Outline Introduction to Cells Cells History Modern Microscopes Eukaryotic versus Prokaryotic Cells Cell Structure and Communication Cellular components Cell Reproductions Higher plants Cells versus animal cells Introduction to Cells All living things are are composed of cells. All living things began life as a single cell. Differentiation occurs in structure and function. Some specializations allow transport of food and water. Cells have varying life spans. Cells share common features. Cells: History 1665 - Cells discovered by Robert Hooke. 1670s - Marcello Malpighi and Nehemiah Grew described single- celled organisms Referred to them as “animacules” 1809 – Jean Baptiste de Lamarck said “No body can have life if its constituent parts are not cellular tissue.” Modern Microscopes: Light Light Microscopes Increase magnification Microscopes as light passes through a series of transparent lenses Can distinguish organelles 2 micrometers or larger in diameter Include compound microscopes and dissecting microscopes, or stereomicroscopes  Electron Microscopes Use a beam of electrons produced when high- voltage electricity is passed through a wire Include transmission and scanning electron microscopes. Transmission- Up to 200,000x Scanning- Up to 10,000x magnification magnification, but material Surface detail can be observed on thick must be sliced extremely thin objects. Eukaryotic versus Prokaryotic Cells Prokaryotic - Cells lack a nucleus. Lack membrane bound organelles Bacteria Eukaryotic - Cells contain a nucleus. Unicellular eukaryotes, fungi, plants, and animals Organelles - Membrane-bound bodies found within eukaryotic cells Both can have cells walls Cell Structure and Cell Wall surrounds plasma membrane. Communication Cellular components bound by plasma membrane Cytoplasm consists of all cellular components between the plasma membrane and the nucleus. Cytosol - Fluid within cytoplasm containing organelles  Cell Wall Main structural component of cell walls is cellulose (long chains of glucose monomers). Cellulose Microfibrils Secondary Walls Secondary walls produced inside primary walls. Derived from primary walls by thickening and inclusion of lignin Cellulose microfibrils embedded in lignin for strength. Communication Between Cells Fluids and dissolved substances can pass through walls of adjacent cells via plasmodesmata. Plasmodesmata are cytoplasmic strands that extend between cells through minute openings.  Plasma membrane Cellular components Nucleus Describe the structure and function of each Endoplasmic reticulum Ribosomes Dictyosomes Plastids Mitochondria Microbodies Vacuoles Cytoskeleton Plasma Membrane The semipermeable outer boundary of the living part of the cell. Regulates movement of substances into and out of cell Composed of phospholipid bilayer, with proteins Fluid mosaic model – This is a dynamic structure Nucleus Control center of cell - DNA Bound by two membranes, which together constitute the nuclear envelope Nuclear pores - channels Nucleoli - Composed primarily of RNA- makes ribosomes  Endoplasmic Reticulum (ER) Endoplasmic reticulum is enclosed space consisting of a network of flattened sacs and tubes forming channels throughout the cytoplasm. Facilitates cellular communication and channeling of materials Synthesizes membranes for other organelles and modifies proteins Rough ER - Ribosomes distributed on outer surface of ER. Associated with protein synthesis and storage Smooth ER - Devoid of ribosomes and associated with lipid secretion Ribosomes Link amino acids to construct complex proteins May occur on outside of rough ER, or in cytoplasm, chloroplasts or other organelles Dictyosomes Dictyosomes (Golgi bodies in animals) - Stacks of flattened discs or vesicles To modify carbohydrates attached to proteins that are synthesized and packaged in the ER. To assemble polysaccharides and collect them in small vesicles. Vesicles migrate to plasma membrane, fuse with it, and secrete contents to the outside of cell. Contents may include cell wall polysaccharides, floral nectars, and essential oils in herbs. Plastids Chloroplasts are the most conspicuous plastids. Bound by double membrane and contain: Grana made up of thylakoids Thylakoid membranes contain chlorophyll. First steps of photosynthesis occur in thylakoid membranes. Stroma - Matrix of enzymes involved in photosynthesis Other Plastids Chromoplasts Synthesize and accumulate carotenoids (yellow, orange, red) Leucoplasts Colorless May synthesize starches (amyloplasts) Or oils (elaioplasts) Mitochondria Site of cellular respiration (ATP). Bound by two membranes Inward membrane forms numerous folds = cristae. Microbodies Microbodies are small, spherical bodies distributed throughout the cytoplasm that contain specialized enzymes. Bound by a single membrane Peroxisomes - Serve in photorespiration Glyoxisomes - Aid in conversion of fat to carbohydrates Vacuoles In mature cells, 90% of volume may be taken up by central vacuoles. Filled with watery fluid called cell- sap Contains dissolved substances, such as salts, sugars, organic acids and small proteins Functions: maintenance of cell pressure and pH, storage of numerous cell metabolites and waste products.  Cytoskeleton - Movement within cell and in cell’s architecture The Form network Cytoskeleton Microtubules: Are thin, hollow, tubelike and composed of tubulins (proteins) Control addition of cellulose to cell wall Involved in movement of flagella and cilia  Cellular Reproduction Cell cycle - Orderly series of events when cells divide Divided into interphase and mitosis Interphase Occupies up to 90% of cell cycle Period when cells are not dividing G1 - Cell increases in size. S - DNA replication takes place. G2 - Mitochondria and other organelles divide, and microtubules are produced.  Mitosis refers to the process of cellular division. Produces 2 identical daughter cells Mitosis occurs in meristems. Although mitosis is a continuous process, it is divided into 4 phases: prophase, metaphase, anaphase and telophase. Chromosomes in Prophase Chromosomes condense by coiling and tightening to become shorter and thicker. Chromosomes made of two identical chromatids held together by centromeres. Kinetochore (protein complex) is located on the outer surface of each centromere. Prophase Spindle fibers (microtubules) become attached to the kinetochore and anchored to two poles of the cell. Nuclear envelope dissociates Nucleolus disintegrates Metaphase Chromosomes align between the poles around the circumference of the spindle at the cell’s equator. Spindle fibers collectively referred to as the spindle. At the end of metaphase, centromeres holding each sister chromatid separate lengthwise. Anaphase Sister chromatids separate in unison and are pulled to opposite poles, with centromeres leading the way. Spindle fibers gradually shorten as material is continuously removed from the polar ends. Chromatids after separation are called daughter chromosomes. Telophase Each group of daughter chromosomes become surrounded by a nuclear envelope. Daughter chromosomes become longer and thinner and eventually, indistinguishable. Nucleoli reappear. Spindle fibers disintegrate. Cell Plate Formation Phragmoplast develops between daughter cell nuclei. This is where the cell plate forms Vesicles fuse to form cell plate. Cell plate grows outward toward mother cell walls. Higher Plant Cells Versus Animal Cells Plants: Cell walls Cell plate and plasmodesmata Plastids and vacuoles Animals: Internal or external skeletons; no cell walls Plasma membrane called cell membrane. Divide by pinching in two; no cell plate nor plasmodesmata Centrioles present during cell division. No plastids nor vacuoles