The Cell and Cellular transport

Transcription

1 Cell theory (1838): The Cell 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 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) How many types of cells? Prokaryotic Unicellular organisms bacteria Eukaryotic Unicellular or (most of them) multicellular organisms Interior of the cell Only cytoplasm Interior of the cell Composed of Nucleus + Cytoplasm Only ribosomes, NO other organelles. Ribosomes are different in structure to those of eukaryotes Several specialized organelles 1

2 What is the size of a cell? Most of them smaller than 50µm ( inches) Why cells are not 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) Volume (4/3)πr 3 Ratio: Surface Area Volume Cell radius (r) Surface Area (4πr 2 ) 1cm cm cm 3 Increases with 1 2 Increases with cm 1,257 cm 2 4,189 cm times more volume! Cell membranes Two layers of phospholipids and proteins Extracellular side integral protein (inside the membrane) Also cholesterol and proteins phospholipids Fatty Acids tails (hydrophobic) Cholesterol Cytoplasm Peripheral protein (surface) Fluid-mosaic model Phospholipids heads (hydrophilic) Molecules in the membrane are able to flow and move around Interaction of molecules with its surroundings allows the membrane to maintains its forms 2

3 Cellular Organelles in Animal Cells (Eukaryotic cells) Ribosomes Endoplasmic reticulum (ER) Nucleus Mitochondria nucleolus Golgi apparatus Cytoskeleton Exclusive of animals cells Lysosomes Centrioles 1) Membrane organelles Inner membrane Mithocondrion cristae Aerobic cellular respiration Glu+O 2 CO 2 +H 2 O Energy conversion and release (in the form of ATP) vesicles Nuclear membrane: Protects the DNA inside the cell. nuclear membrane pores allow molecules to pass from one side to the other Nucleolus: site of ribosome manufacture Endoplasmatic reticulum (ER): folded membranes and tubes huge surface area many chemical reactions in a small place! Rough ER Ribosomes associated to the membrane proteins synthesis Smooth ER Lipids synthesis, destruction of toxic substances Golgi Apparatus: 5 to 20 membranous and smooth sacs modification of products (ex: activation of enzymes) from the ER, packing and export to the cytoplasm or extracellular space of certain molecules Lysosomes: Vesicles generated in the Golgi apparatus containing hydrolytic enzymes. Are use to degrade molecules 3

4 2) Protein organelles Cytoskeleton: Microtubules, microfilaments, and intermediate filaments proteins! Ribosomes: Interconnect and attach to the membrane cell Two subunits composed of RNA and proteins Responsible for proteins synthesis Associated to the Rough ER or free in cytoplasm Centrioles: Arrangement of two sets of microtubules (proteins!) at right angles Organize microtubules assembly for cell division (chromosomes attach to microtubules) flagella cilia Eukaryotic cilia and flagella Cilia and Flagella: hairlike structures used for locomotion Made of microtubules (two types of proteins in Eukaryotes and only one type in Prokaryotes) with a specific arrangement Energy is needed to move microtubules and cause movement Movement of particles across the cell membrane. allow the cell to carry out the metabolic processes needed to live Passive: NO energy is required Active: Energy is used (ATP) Cellular transport Diffusion:(passive) Movement of molecules down a concentration gradient from where are in higher concentration to where are in lower concentration. Higher concentration 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 can be only water 2) The regions of different concentrations are separated by a membrane permeable to water but not to the solute Equal Concentrations (dynamic equilibrium) Red blood cell (RBC) is Isotonic Hypotonic Hypertonic less solutes in the RBC more solutes in the RBC 4

5 Carrier Proteins controlled methods of transporting molecules Facilitated diffusion (passive) movement of molecules down a concentration gradient through the membrane by combining with specific carrier proteins. + concentration - 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: 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) 5

6 Enzymes Why do we need to speed up reactions using enzymes? Special proteins that acts as catalysts in chemical reactions between substances Speed up reactions but are not used in the reaction Energy is stored in covalent bonds of nutrients we incorporate with the food Molecules synthesis/breakdown and energy conversion require energy to initiate the breakdown of nutrients Energy of Activation (Ea) Extra energy required to destabilize existing chemical bonds and initiate a chemical reaction between two or more molecules (Products have less energy than reactants) Exergonic reaction Energy Energy Ea reactants product Do not occur spontaneously E stored time Endergonic reaction (Products have more energy than reactants) Ea reactants product Spontaneously would take millions of years! time E released Energy used Energy releases reactants product Ea No enzyme (uncatalyzed) Ea enzyme (catalyzed) Summary 1. Enzymes lower the energy of activation (Ea) Reactions occur very fast 2. Enzymes are substrate specific Only speed up the reaction of one type of molecule 3. Enzymes remain unchanged Because they are not used in the reaction 4. Enzymes can be reused billions of times One single enzyme can convert millions of substrate molecules per second! 6

7 How do enzymes speed reaction rates? Three-dimensional shape of the enzyme allows it to combine with reactants, lower the Ea and accelerate the reaction Ex: dipeptide (two amino acids) Ex:dehydration Ex: amino acid 1 Ex: hydrolysis Ex: amino acid 2 Enzyme-substrate complex ACTIVE SITE: Is the part of the ENZYME where the chemical reaction takes place, where the energy of activation is lowered by the enzyme so the reaction can happen Cofactors & coenzymes: enzyme helpers ions or molecules that attach to the enzyme and help to speed up the reaction 1) Cofactors help removing one of the end products or bring in part of the substrate 2) Enzymes are substrate specific but coenzymes can work with several different enzymes 3) Cofactors ARE inorganic ions (zinc, iron, magnesium). Coenzymes are organic molecules 4) As in the case of some fatty acids and amino acids, some coenzymes cannot be produced by the body and need to be obtained with the diet. Cells need vitamins in order to have coenzymes. 7

8 What environmental factors affect the enzymes activity? 1) Temperature Optimum (temperature range at which the speed of product generation is maximum) is around human body normal temperature The speed of the reaction, or the number of molecules of substrate that one enzyme can react with in a given time, decreases as temperature moves right or left of the optimum range. At higher or lower temperatures than the optimum, Enzymes can lose their configuration (be completely unfolded and only retain the primary structure) and be no longer active Denaturation Lost of the structures of a protein, only the primary structure remains Enzyme Denatured Enzyme (1ry structure = sequence of amino acids) 2) ph Is important in defining the final shape of proteins each enzyme reaches it maximum activity level at a given ph Changes in ph determine the number of H+ ions available in the enzyme environment these H+ may interact with exposed side-chains of the polar enzyme molecule enzyme activity changes Denaturation Lost of the structures of a protein, only the primary structure remains 8