The Cell Cell theory (1838): 1. All organisms are composed of one or more cells, and the life processes of metabolism and heredity occur within these cells. 2. Cells are the smallest living things, the basic units of organization of all organisms. 3. Cells arise only by division of a previously existing cell. Enzymes (for metabolic reactions) Ribosomes (for protein synthesis) DNA for the genetic code RNA for transcription of the code during protein synthesis Common to ALL types of cells ATP ATP A tour of the cell First discovered in 1665 since then every organism observed with microscopes shows cells Cell membrane (controls the movement of things in and out of the cell) Cytoplasm or cytosol (intracellular fluid) Energy currency (to provide energy for metabolic processes) Observation was originally made with light microscopes But it greatly improved by the 1950 s with the electron microscopes SEM = scanning electron microscope (cells surface) TEM = transmitted electron microscope (cells internal structure) 1
How many types of cells? Prokaryotic Unicellular organisms bacteria Eukaryotic Unicellular or (most of them) multicellular organisms Interior of the cell Only cytoplasm DNA in the cytoplasm Only ribosomes, NO other organelles. Ribosomes are different in structure to those of eukaryotes Interior of the cell Composed of Nucleus + Cytoplasm DNA in the nucleus Many specialized membrane organelles... Compartimentalization! What is the size of a cell? Most of them smaller than 50µm (0.0020 inches) Why are not cells bigger? Practical reasons! communication the different regions of a cell need to communicate with one another for the cell as a whole to function effectively Cell surface responsible for the interaction with the environment small cells have bigger surface area per unit of volume than large ones control is more effective (ex: 3 vs. 0.30) Ratio: Surface Area Volume Cell radius (r) Surface Area (4πr 2 ) Volume (4/3)πr 3 1cm 12.57 cm 2 4.189 cm 3 Increases with 1 2 Increases with 1 3 10cm 1,257 cm 2 4,189 cm 3 1000 times more volume! 2
Cell membrane In all living things, from bacteria to blue whales, is composed of Two layers of phospholipids Also cholesterol and proteins Extracellular side integral protein (inside the membrane) phospholipids Fatty Acids tails (hydrophobic) Phospholipids heads (hydrophilic) Cholesterol Fluid-mosaic model Cytoplasm Peripheral protein (surface) Molecules in the membrane are able to flow and move around Interaction of molecules with its surroundings allows the membrane to maintains its forms Cellular Organelles (in Eukaryotic cells) Common to both types chloroplasts cell wall (cellulose) central vacuole Ribosomes Nucleus nucleolus Endoplasmic reticulum (ER) Golgi apparatus Mitochondria Cytoskeleton Chloroplasts Cell wall Central vacuole Exclusive of plants Exclusive of animals Lysosomes Centrioles 3
1) Membrane organelles: All made of phospholipids! Nucleus: the phospholipids layers that make up the nuclear membrane protect the DNA inside the cell. Nucleolus: is the site for ribosomes manufacture Nuclear membrane Nuclear pore DNA Nuclear pores allow molecules to pass from one side to the other Chloroplast Photosynthesis takes place here, where the chlorophyll is present in the granum Light+CO 2 +H 2 O Glu+O 2 Energy conversion (light to chemical) and storage (in the form of glucose) Mitochondria Aerobic cellular respiration Glu+O2 CO 2 +H 2 O + ATP Energy conversion (chemical to chemical) and release (in the form of ATP for metabolic reactions) The Endomembrane System Includes the endoplasmic reticulum, golgi, vacuoles, lysosomes, and the nuclear membrane, all involved in producing and manufacturing cellular products All these organelles communicate with each other Rough Endoplasmic Reticulum (RER) With ribosomes associated to the membrane The Rough ER secretes proteins in vesicles Smooth Endoplasmic Reticulum (SER) Synthesis of lipids (including steroids) Destruction of antibiotics and toxic substances like drugs 4
Golgi Apparatus: Works as a refinery, warehouse and shipping center Modification of products (ex: activation of enzymes) from the ER, packing and export to the cytoplasm or extracellular space of diverse molecules Lysosomes: Vesicles generated in the Golgi apparatus containing digestive enzymes. Are used to degrade molecules The stomach of the cell Vacuoles: Any sac or vesicle that buds from Golgi, the ERs or the cell membrane 2) Protein organelles Ribosomes: Two subunits composed of RNA and proteins Are the site for proteins synthesis Can be associated to the Rough ER or free in cytoplasm Centrioles: Arrangement of two sets of microtubules (proteins!) at right angles Organize spindle fibers during cell division in animal cells (absent in plant cells) for chromosomes separation Chromosome Spindle fibers 5
2) Protein organelles Cytoskeleton: Provides shape and helps in movement. Is also used as tracks that carry vesicles form place to place. Serves as both skeleton and muscles for the cell Composed of protein fibers called microtubules and microfilaments Interconnects and attaches to the membrane of the cell flagella Cilia and Flagella: Hair like structures used for locomotion, they serve as the limbs for the cell Made of two types of proteins in Eukaryotes and only one type in Prokaryotes) with a specific arrangement Energy (ATP) is needed to produce movement cilia Ch.5 The Working Cell Cellular Transport Movement of particles or molecules across the cell membrane, allows the cell to carry out the metabolic processes needed to live. It is called Passive: NO energy is required (HIGH to LOW concentration movement) Active: Energy is used (ATP) (LOW to HIGH concentration movement) Diffusion:(passive) Movement of molecules down a concentration gradient from higher concentration to lower concentration. Osmosis: (passive) Net movement of water through a selectively permeable membrane. 1) Osmosis is a special type of diffusion in which the diffusing substance is water 2) The regions of different concentrations are separated by a membrane permeable to water but not to the solute 6
So what happens to cells when exposed to different concentrations outside? (Hypertonic solution) (Hypotonic solution) 80% H 2 O 99% H 2 O 100% H 2 O Water moves out and the cell shrinks Water moves in and out (dynamic equilibrium) Water moves in and the cell swells Carrier Proteins controlled method of transporting molecules Facilitated diffusion (passive) Movement of molecules down a concentration gradient through the membrane by combining with specific carrier proteins. (+) (-) 7
Active transport (active) Movement of molecules up a concentration gradient. An input of energy (ATP) is needed to move the molecule against its concentration gradient. ATP ADP+Pi Endocytosis & Exocytosis: (active) Transport of materials into and out of the cell by formation of vesicles of cell membrane containing the particles, food, or materials Pinocytosis: molecules engulfed are dissolved in water liquids Phagocytosis: solid materials, the sac is named phagosome (ex: viruses, food, bacteria, lipoproteins) 8