Cool “Fires” Attract Mates and Meals Fireflies use light, instead of chemical signals, to send signals to potential mates Females can also use light flashes to attract males of other firefly species — as meals, not mates

The light comes from a set of chemical reactions, the luciferin-luciferase system Fireflies make light energy from chemical energy Life is dependent on energy conversions

Fireflies

Characteristics of organisms (light, pigment, sound, smell) are end products of chemical reactions Chemical reactions are for the purpose of energy transformations. All reactions equal some form of transformation.

Energy

ENERGY AND THE CELL Living cells are compartmentalized by membranes Membranes are sites where chemical reactions can occur in an orderly manner Living cells process energy by means of enzyme-controlled chemical reactions

5.1 Energy is the capacity to perform work Energy is defined as the capacity to do work All organisms require energy to stay alive Energy makes change possible

Kinetic energy is energy that is actually doing work Heat = randomly moving molecules Light, i.e. photosynthesis Figure 5.1A Potential energy is stored energy Chemical energy = energy stored in the arrangement of atoms in molecules Figure 5.1B

Laws of Thermodynamics

5.2 How is chemical energy “tapped” by organisms? Rearrangment of sugar molecules, releasing stored energy for cellular work What makes a living organism an open system (? Exchange of matter and energy with surrounds

5.2 Two laws govern energy conversion First law of thermodynamics (energy of conservation) Energy can be changed from one form to another However, energy cannot be created or destroyed, it is constant Gasoline to the right get ignited, where does chemical energy end up? Unspent chemical energy in unused gas KE of spinning engine Heat Figure 5.2A

Second law of thermodynamics (entropy increases) Energy changes are not 100% efficient Energy conversions increase disorder, or entropy Some energy is always lost as heat. See below: When gas is ignited PE is released causing flash of light and burst of heat, which heats up surrounding environment Figure 5.2B

5.2 Almost reactions produce heat, which is added to surroundings All energy transfers follow 2nd law -> production of heat.

5.3 Chemical reactions either store or release energy Cells carry out thousands of chemical reactions The sum of these endergonic and exergonic reactions constitutes cellular metabolism

Potential energy of molecules There are two types of chemical reactions: Endergonic reactions absorb energy and yield products rich in potential energy. Energy stored in covalent bonds of products. i.e. photosynthesis, energy of sunlight to form organic compounds. Products Amount of energy INPUT Potential energy of molecules Reactants Figure 5.3A

Amount of energy OUTPUT Potential energy of molecules Exergonic reactions release energy and yield products that contain less potential energy than their reactants Burning and cellular respiration, chemical energy of reactants released to form energy-poor products (heat and light) Reactants Amount of energy OUTPUT Potential energy of molecules Products Figure 5.3B

Difference between Burning and Cell Respiration? Burning = energy released all at once Cell Resp. = Multiple steps of energy release

5.4 ATP shuttles chemical energy within the cell Most endergonic cellular reactions require small amounts of energy, rather than large amounts food in food storage molecules. Food is like a $100 bill but you need $1’s. In cellular respiration, some energy is stored in ATP molecules = small change. Transfer amounts of energy from exergonic , food energy-releasing reactions to endergonic. ATP powers nearly all forms of cellular work ATP molecules are the key to energy coupling

Adenosine triphosphate Adenosine diphosphate (ADP) When the bond joining a phosphate group to the rest of an ATP molecule is broken by hydrolysis, the reaction supplies energy for cellular work (exergonic reaction) Adenine Phosphate groups Hydrolysis Energy Ribose Adenosine triphosphate Adenosine diphosphate (ADP) Figure 5.4A

Potential energy of molecules How ATP powers cellular work Phosphate group from ATP is one of the reactants and the energy source for endergonic reaction Reactants Products Potential energy of molecules Protein Work This energizing process is phosphorylation. ATP regeneration is the reverse process where ADP becomes ATP thru dehydration synthesis.

Dehydration synthesis The ATP cycle – note the order of the cycle, exergonic into endergonic Hydrolysis Dehydration synthesis Energy from exergonic reactions Energy for endergonic reactions Figure 5.4C

Energy conversations: Y or N PE -> KE Gas chem. E -> KE Photosynthesis = KE -> chem. E. Energy transformations = release heat E. YES Yes

HOW ENZYMES WORK 5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers Enzymes are large protein molecules that functional as biological catalysts, which speeds up reactions without being consumed. For a chemical reaction to begin, reactants must absorb some energy This energy is called the energy of activation (EA) This represents the energy barrier that prevents molecules from breaking down spontaneously Without this barrier, all ATP in your body could spontaneously combust.

A protein catalyst called an enzyme can decrease the energy barrier EA barrier Enzyme Reactants 1 Products 2 Figure 5.5A

EA without enzyme EA with enzyme Reactants Net change in energy Products Figure 5.5B

6 facts about enzymes Protein molecule Biological catalyst Increases reaction rate Not being used up Does not add energy – lowers energy barrier Speeds up metabolism for life processes

5.6 A specific enzyme catalyzes each cellular reaction Enzymes are selective This selectivity determines which chemical reactions occur in a cell Enzymes are specific and catalyze specific cellular reactions.

Reactant = the substrate How an enzyme works Reactant = the substrate Active site = part of the enzyme that binds to substrate and facilitates reaction. Substrate turns to product Active site Enzyme (sucrase) Substrate (sucrose) Glucose Fructose 1 4 Enzyme available with empty active site Products are released 3 2 Substrate is converted to products Substrate binds to enzyme with induced fit Figure 5.6 The enzyme is unchanged and can repeat the process

5.7 The cellular environment affects enzyme activity Enzyme activity is influenced by temperature – some temp. speeds up reaction, but too much = denatures -> changes shape, and structure related to function salt concentration – salt ions interfere with bonds pH – extra H+’s interfere Some enzymes require nonprotein cofactors inorganic like metals, i.e. Magnesium for chlorophyll) Some cofactors are organic molecules called coenzymes (vitamins)

5.8 Enzyme inhibitors block enzyme action Inhibitors interfere with enzymes A competitive inhibitor takes the place of a substrate in the active site A noncompetitive inhibitor alters an enzyme’s function by changing its shape Substrate Active site Enzyme NORMAL BINDING OF SUBSTRATE Competitive inhibitor Noncompetitive inhibitor ENZYME INHIBITION Figure 5.8

Irreversible inhibition/Negative Feedback Inhibition is irreversible when there are covalent bonds but are reversible when there are Hydrogen bonds. Think of bond strength Type of inhibition whereby enzyme activity is blocked by one of the products of the reaction it catalyzes Too much of something, machine turns off, but once depleted, machine turns back on

5.9 Connection: Some pesticides and antibiotics inhibit enzymes Certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system Pesticide Malathion inhibits the enzyme acetylcholinesterase, involved in nerve transmission. Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria Penicillin inhibits an enzyme that bacteria use in making cell walls

5.10 Membranes organize the chemical activities of cells MEMBRANE STRUCTURE AND FUNCTION 5.10 Membranes organize the chemical activities of cells Membranes organize the chemical reactions making up metabolism   Cytoplasm Figure 5.10

Membranes are selectively permeable Membranes separate cells from outside environment, including the environment of other cells that perform different functions. Membranes are selectively permeable They control the flow of substances into and out of a cell In eukaryotes partition function into organelles Membranes can hold teams of enzymes that function in metabolism

5.11 Membrane phospholipids form a bilayer Phospholipids (are like fats) are the main structural components of membranes They each have a hydrophilic (polar) head and two hydrophobic (nonpolar) tails Head Symbol Tails Figure 5.11A

B. Structure (Fluid mosaic model) (10nm.) A. Functions 1. Regulates the movement of molecules into and out of the cell 2. Site of cell recognition and communication B. Structure (Fluid mosaic model) (10nm.) 1. Phospholipids a. 5 - 10 different types b. Most common = phosphotidylcholine c. Membrane fusion easily accomplished d. Movement - 2 mm./sec. 2. Cholesterol - decreases fluidity of membrane

In water, phospholipids form a stable bilayer The heads face outward and the tails face inward Water Hydrophilic heads Hydrophobic tails Water Figure 5.11B

Plasma Membrane - all cells have them - complex, dynamic structures, not passive - differentially permeable

Going thru the membrane If soluble in lipids, can pass = non-polar If unsoluble in lipids, can’t pass without protein molecule help, = polar

5.12 The membrane is a fluid mosaic of phospholipids and proteins Phospholipid molecules form a flexible bilayer Cholesterol and protein molecules are embedded in it Carbohydrates act as cell identification tags Mosaic = proteins Fluid = individual molecules can more or less move freely laterally Two sides with different proteins: glycoproteins and glycolipids. Some proteins extend thru membrane and bind to cytoskeleton or extracellular matrix

The plasma membrane of an animal cell Glycoprotein Carbohydrate (of glycoprotein) Fibers of the extracellular matrix Glycolipid Phospholipid Cholesterol Microfilaments of the cytoskeleton Proteins CYTOPLASM Figure 5.12

5.13 Proteins make the membrane a mosaic of function Some membrane proteins form 1) cell junctions, 2) either attachment to other cells or internal cytoskeleton Others 3) transport substances across the membrane (hydrophilic molecules) Figure 5.13 Transport

Many membrane proteins are4) enzymes, catalyzing reactions Some proteins function as 5) receptors for chemical messages from other cells The binding of a messenger to a receptor may trigger signal transduction Messenger molecule Receptor Activated molecule Figure 5.13 Enzyme activity Signal transduction

6) Identification tags: particularly glycoproteins

5.14 Passive transport is diffusion across a membrane In passive transport, substances diffuse through membranes without work by the cell They spread from areas of high concentration to areas of lower concentration At equilibrium, molecules diffuse back and forth, but no net change in concentration PE = concentration gradient KE = movement of molecules Molecule of dye Membrane EQUILIBRIUM EQUILIBRIUM Figure 5.14A & B

Different molecules diffuse independently of each another Passive transport is an extremely important way for small molecules to get into and out of cells. For example, O2 moves into red blood cells and CO2 moves out of these cells by this process in the lungs.

5.15 Osmosis is the passive transport of water Hypotonic solution Hypertonic solution In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Osmosis can cause a physical force to be applied to the hypertonic solution. Force raises level of solution against force of gravity until weight difference in levels equals the osmotic force Selectively permeable membrane Solute molecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectively permeable membrane Solute molecule with cluster of water molecules NET FLOW OF WATER Figure 5.15

The direction of osmosis is determined only by the difference in total solute concentrations Two solutions equal solute concentrations are isotonic to each other; therefore osmosis does not occur. However, even in isotonic solutions separated by selectively permeable membrane, water molecules are moving at equal rates in both directions.

5.16 Water balance between cells and their surroundings is crucial to organisms Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution The control of water balance (osmoregulation) is essential for organisms Know terminology for plant/animal cells ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION ANIMAL CELL (1) Normal (2) Lysing (3) Shriveled Plasma membrane PLANT CELL Figure 5.16 (4) Flaccid (5) Turgid (6) Shriveled

Real life water issues Drinking too much saltwater = ? Drinking too much fresh water = ? High concentration in solution, water leaves cells = dehydrated Low concentration in solution, water rushes into cells = lyses

5.17 Transport proteins facilitate diffusion across membranes Small nonpolar molecules diffuse freely through the phospholipid bilayer Many other kinds of molecules pass through selective protein pores by facilitated diffusion . A pored protein, spanning the membrane bilayer, allows solute to go down concentration gradient. Solute molecule Transport protein Figure 5.17

The cell does not expend energy The rate of facilitate diffusion depends on the number of such transport proteins, in addition to the strength of the concentration gradient. Water is a polar membrane and therefore needs the assistance of transport proteins when crossing membranes.

5.18 Cells expend energy for active transport Transport proteins can move solutes across a membrane against a concentration gradient This is called active transport Active transport requires ATP to help the protein change its structure and thus move the solute molecule. Active transport molecules often couple the passage of two solutes in opposite directions across the membranes.

Active transport in two solutes across a membrane FLUID OUTSIDE CELL Phosphorylated transport protein Active transport in two solutes across a membrane Transport protein First solute 1 First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell Second solute 4 Second solute binds to protein 5 Phosphate detaches from protein 6 Protein releases second solute into cell Figure 5.18

5.19 Exocytosis and endocytosis transport large molecules To move large molecules or particles through a membrane a vesicle may fuse with the membrane and expel its contents (exocytosis) FLUID OUTSIDE CELL CYTOPLASM Figure 5.19A

or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

Material bound to receptor proteins Three kinds of endocytosis Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm Figure 5.19C Cell mediated – receptors sense molecule and pinch around it

Chloroplasts and Mitochondria The two are linked Solar energy is used to build energy-rich molecules in endergonic reactions in chloroplasts. Energy-rich molecules release their energy to form aTP in mitochondria Chemicals involved as the reactants in chloroplasts are the products in mitochondria and vice-versa. Energy in the form of heat is lost to the environment thus a constant supply of energy must be supplied to all organisms.