chapt04_lecture.ppt

CHAPTER 4 LECTURE SLIDES Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell Structure Chapter 4  Cells Cells were discovered in 1665 by Robert Hooke Early studies of cells were conducted by – Mathias Schleiden (1838)...

CHAPTER 4 LECTURE SLIDES Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell Structure Chapter 4  Cells Cells were discovered in 1665 by Robert Hooke Early studies of cells were conducted by – Mathias Schleiden (1838) – Theodor Schwann (1839) Schleiden and Schwann proposed the Cell Theory 3  Cell Theory 1. All organisms are composed of cells 2. Cells are the smallest living things 3. Cells arise only from pre-existing cells All cells today represent a continuous line of descent from the first living cells 4  Cell size is limited Most cells are relatively small due reliance on diffusion of substances in and out of cells Rate of diffusion affected by – Surface area available – Temperature – Concentration gradient – Distance 5 6  Surface area-to-volume ratio Organism made of many small cells has an advantage over an organism composed of fewer, larger cells As a cell’s size increases, its volume increases much more rapidly than its surface area Some cells overcome limitation by being long and skinny – like neurons 7  Microscopes Not many cells are visible to the naked eye – Most are less than 50 μm in diameter Resolution – minimum distance two points can be apart and still be distinguished as two separate points – Objects must be 100 μm apart for naked eye to resolve them as two objects rather than one 8  2 types Light microscopes – Use magnifying lenses with visible light – Resolve structures that are 200 nm apart – Limit to resolution using light Electron microscopes – Use beam of electrons – Resolve structures that are 0.2 nm apart 9  Electron microscopes – Transmission electron microscopes transmit electrons through the material – Scanning electron microscopes beam electrons onto the specimen surface 10  Basic structural similarities 1. Nucleoid or nucleus where DNA is located 2. Cytoplasm – Semifluid matrix of organelles and cytosol 3. Ribosomes – Synthesize proteins 4. Plasma membrane – Phospholipid bilayer 11  Prokaryotic Cells Simplest organisms Lack a membrane-bound nucleus – DNA is present in the nucleoid Cell wall outside of plasma membrane Do contain ribosomes (not membrane-bound organelles) Two domains of prokaryotes – Archaea – Bacteria 12 13  Bacterial cell walls Most bacterial cells are encased by a strong cell wall – composed of peptidoglycan – Cell walls of plants, fungi, and most protists different Protect the cell, maintain its shape, and prevent excessive uptake or loss of water Susceptibility of bacteria to antibiotics often depends on the structure of their cell walls Archaea lack peptidoglycan 14  Flagella Present in some prokaryotic cells – May be one or more or none Used for locomotion Rotary motion propels the cell 15 16  Eukaryotic Cells Possess a membrane-bound nucleus More complex than prokaryotic cells Hallmark is compartmentalization – Achieved through use of membrane-bound organelles and endomembrane system Possess a cytoskeleton for support and to maintain cellular structure 17 18 19  Nucleus Repository of the genetic information Most eukaryotic cells possess a single nucleus Nucleolus – region where ribosomal RNA synthesis takes place Nuclear envelope – 2 phospholipid bilayers – Nuclear pores – control passage in and out In eukaryotes, the DNA is divided into multiple linear chromosomes – Chromatin is chromosomes plus protein 20 21  Ribosomes Cell’s protein synthesis machinery Found in all cell types in all 3 domains Ribosomal RNA (rRNA)-protein complex Protein synthesis also requires messenger RNA (mRNA) and transfer RNA (tRNA) Ribosomes may be free in cytoplasm or associated with internal membranes 22  Endomembrane System Series of membranes throughout the cytoplasm Divides cell into compartments where different cellular functions occur One of the fundamental distinctions between eukaryotes and prokaryotes 23  Endoplasmic reticulum Rough endoplasmic reticulum (RER) – Attachment of ribosomes to the membrane gives a rough appearance – Synthesis of proteins to be secreted, sent to lysosomes or plasma membrane Smooth endoplasmic reticulum (SER) – Relatively few bound ribosomes – Variety of functions – synthesis, store Ca2+ , detoxification Ratio of RER to SER depends on cell’s function 24 25  Golgi apparatus Flattened stacks of interconnected membranes (Golgi bodies) Functions in packaging and distribution of molecules synthesized at one location and used at another within the cell or even outside of it Cis and trans faces Vesicles transport molecules to destination 26 27 28  Lysosomes Membrane-bounded digestive vesicles Arise from Golgi apparatus Enzymes catalyze breakdown of macromolecules Destroy cells or foreign matter that the cell has engulfed by phagocytosis 29 30  Microbodies Variety of enzyme- bearing, membrane- enclosed vesicles Peroxisomes – Contain enzymes involved in the oxidation of fatty acids – H2O2 produced as by- product – rendered harmless by catalase 31  Vacuoles Membrane-bounded structures in plants Various functions depending on the cell type There are different types of vacuoles: – Central vacuole in plant cells – Contractile vacuole of some protists – Storage vacuoles 32 33  Mitochondria Found in all types of eukaryotic cells Bound by membranes – Outer membrane – Intermembrane space – Inner membrane has cristae – Matrix On the surface of the inner membrane, and also embedded within it, are proteins that carry out oxidative metabolism Have their own DNA 34 35  Chloroplasts Organelles present in cells of plants and some other eukaryotes Contain chlorophyll for photosynthesis Surrounded by 2 membranes Thylakoids are membranous sacs within the inner membrane – Grana are stacks of thylakoids Have their own DNA 36 37  Endosymbiosis Proposes that some of today’s eukaryotic organelles evolved by a symbiosis arising between two cells that were each free- living One cell, a prokaryote, was engulfed by and became part of another cell, which was the precursor of modern eukaryotes Mitochondria and chloroplasts 38 39  Cytoskeleton Network of protein fibers found in all eukaryotic cells – Supports the shape of the cell – Keeps organelles in fixed locations Dynamic system – constantly forming and disassembling 40  3 types of fibers Microfilaments (actin filaments) – Two protein chains loosely twined together – Movements like contraction, crawling, “pinching” Microtubules – Largest of the cytoskeletal elements – Dimers of α- and β-tubulin subunits – Facilitate movement of cell and materials within cell Intermediate filaments – Between the size of actin filaments and microtubules – Very stable – usually not broken down 41 42  Centrosomes Region surrounding centrioles in almost all animal cells Microtubule-organizing center – Can nucleate the assembly of microtubules Animal cells and most protists have centrioles – pair of organelles Plants and fungi lack centrioles 43  Cell Movement Essentially all cell motion is tied to the movement of actin filaments, microtubules, or both Some cells crawl using actin microfilaments Flagella and cilia have 9 + 2 arrangement of microtubules – Not like prokaryotic flagella – Cilia are shorter and more numerous 44 45  Eukaryotic cell walls – Plants, fungi, and many protists – Different from prokaryote – Plants and protists – cellulose – Fungi – chitin – Plants – primary and secondary cell walls 46  Extracellular matrix (ECM) Animal cells lack cell walls Secrete an elaborate mixture of glycoproteins into the space around them Collagen may be abundant Form a protective layer over the cell surface Integrins link ECM to cell’s cytoskeleton – Influence cell behavior 47 48 49  Cell-to-cell interactions Surface proteins give cells identity – Cells make contact, “read” each other, and react – Glycolipids – most tissue-specific cell surface markers – MHC proteins – recognition of “self” and “nonself” cells by the immune system 50  Cell connections 3 categories based on function 1. Tight junction – Connect the plasma membranes of adjacent cells in a sheet – no leakage 2. Anchoring junction – Mechanically attaches cytoskeletons of neighboring cells (desmosomes) 3. Communicating junction – Chemical or electrical signal passes directly from one cell to an adjacent one (gap junction, plasmodesmata) 51 52