The Working Cell

Cool “Fires” Attract Mates and Meals Fireflies use light to send signals to potential mates instead of using chemical signals like most other insects They use a pattern on flashing lights to communicate with the opposite sex.

 The light comes from a set of chemical reactions  That occur in light-producing organs at the rear of the insect.  Light is a form of energy; it requires an enzyme controlled chemical reaction in the cells membrane.

◦ Females of some species  Produce a light pattern that attracts males of other species, which are then eaten by the female

ENERGY AND THE CELL  5.1 Energy is the capacity to perform work  All organisms require energy which is defined as: “the capacity to do work”  What kind of work does a cell do?  Breaks down polymers into monomers  Builds polymers  Transports nutrients

 Kinetic energy is the energy of motion.  Heat (thermal energy) is the kinetic energy associated with the movement of molecules.  Light is another kind of kinetic energy that can be harnessed to do work(photosynthesis).  Potential energy is stored energy that can be converted to kinetic energy. Figure 5.1A–C

Chemical Energy  Chemical energy is the potential energy of molecules: The arrangement of atoms and their charges provides potential energy that can do work for the cello. Life depends on the fact that energy can be converted from one form to another.

How Can An Object At Rest Have Energy ?  It can have potential energy as a result of its location.

5.2 Two laws govern energy transformations Thermodynamics. is the study of energy transformations

 The First Law of Thermodynamics According to the first law of thermodynamics: ○ Energy can be changed from one form to another ○ Energy cannot be created or destroyed Figure 5.2A

 The Second Law of Thermodynamics The second law of thermodynamics ○ Energy transformations increase disorder or entropy, and some energy is lost as heat. ○ Heat is a disordered form of energy, and its release makes the universe more random, more disorganized. Example the flow of energy in an ecosystem: Figure 5.2B Heat Chemical reactions ATP Glucose + Oxygen water Carbon dioxide + Energy for cellular work Web/CD 5A

Describe the energy transformation that occur when you climb to the top of a stairway.  You convert chemical energy (food that you have consumed) into Kinetic energy (climbing the stairs)  At the top of the stairs, some of the energy has been stored as Potential Energy (higher elevation).  The rest is converted to Heat

5.3 Chemical reactions either store or release energy Endergonic reactions requires input of energy. ○ Absorb energy and yield products rich in potential energy Figure 5.3A Potential energy of molecules Reactants Energy required Products Amount of energy required The energy gained Is stored in covalent bonds. e.g. Photosynthesis

Exergonic reactions - releases energy ○ Release energy and yield products that contain less potential energy than their reactants ○ Web/CD 5B Web/CD 5B Figure 5.3B Reactants Energy released Products Amount of energy released Potential energy of molecules

Cellular Respiration Cellular respiration uses oxygen to convert chemical energy (glycogen, fats, protiens,etc) to energy that does work for the cell. Cells carry out thousands of chemical reactions (endergonic and exergonic)the sum of which constitutes cellular metabolism. Energy coupling ○ Uses exergonic reactions to fuel endergonic reactions.

Cellular respiration is an exergonic process. Remembering that energy must be conserved, what becomes of the energy extracted from food during cellular respiration?  Some is stored as ATP  The rest is released as heat.

5.4 ATP shuttles chemical energy and drives cellular work ATP powers nearly all forms of cellular work

The energy in an ATP molecule lies in the bonds between its phosphate groups ○ By using HYDROLYSIS – the Phosphate bonds are broken and energy is released. (i.e. it is EXERGONIC). ○ Web/CD structure of ATP 5C Web/CD structure of ATP 5C Phosphate groups ATP Energy PPP P PP Hydrolysis Adenine Ribose H2OH2O Adenosine diphosphate Adenosine Triphosphate + + ADP Figure 5.4A * The three bonds in the phosphate group are unstable and can readily be broken by hydrolysis

ATP drives endergonic reactions by phosphorylation ○ Transferring a phosphate group to make molecules more reactive ○ ATP is a renewable resource that cell generate. Figure 5.4B ATP Chemical work Mechanical work Transport work P P P P P P P Molecule formedProtein moved Solute transported ADP + Product Reactants Motor protein Membrane protein Solute + There are three forms of work: Chemical Mechanical Transport

ATP ADP + P Energy for endergonic reactions Energy from exergonic reactions Phosphorylation Hydrolysis Cellular work can be sustained ○ Because ATP is a renewable resource that cells regenerate Figure 5.4C

Explain how ATP transfers energy from exergonic to endergonic process in the cell By phosphorylation: 1. Exergonic reaction add (phosphorylates) a phosphate group to ADP (Adenosine Di- Phosphate) to make ATP (Adenosine Tri- Phosphat.e). 2. ATP transfers energy (Endergonic reaction) by releasing a phosphate (phosphorylating) to another molecule. (ATP → ADP)

5.5 HOW ENZYMES FUNCTION  Enzymes speed up the cell’s chemical reactions by lowering energy barriers  An enzyme is a protein molecule that functions as a biological catalyst, increasing the rate of a reaction without itself being changed into a different molecule.

For a chemical reaction to begin ○ Reactants must absorb some energy, called the energy of activation Figure 5.5A E A barrier Reactants Products 12 Enzyme

A protein catalyst called an enzyme ○ Can decrease the energy of activation needed to begin a reaction Figure 5.5B Reactants E A without enzyme E A with enzyme Net change in energy Products Energy Progress of the reaction

Why can’t an enzyme change an endergonic reaction into an exergonic reaction?  An enzyme has no effect on the reactants, it effects the rate of reaction by lowering the energy required to activate the reaction.

5.6 A specific enzyme catalyzes each cellular reaction  Enzymes have unique three-dimensional shapes that determine which chemical reactions occur in a cell. Enzymes are proteins with a unique three dimensional shape. ○ REVIEW: Reactants – the starting material in a chemical reaction Products – the ending material in chemical reaction ○ NEW TERM: Substrate – a specific substance (reactant) on which an enzyme reacts

Figure 5.6 Enzyme (sucrase) Glucose Fructose Active site Substrate (sucrose) H2OH2O 1 Enzyme available with empty active site 2 Substrate binds to enzyme with induced fit 4 Products are released 3 Substrate is converted to products The catalytic cycle of an enzyme: Web/CD 5DWeb/CD 5D

What is meant by induced fit? 1. The change in shape of the active site on an enzyme as the substrate attaches to the binding site. 2. This change in shape provides the right environment for the the reaction occur.

5.7 The cellular environment affects enzyme activity An enzymes structure and shape are essential to its function: ○ Its shape is effected by the changes in the environment Temperature Salt concentration pH influence enzyme activity Some enzymes require non-protein cofactors Such as metal ions or organic molecules called coenzymes

 Temperature: High temperatures denature the enzyme Optimal temperature 35° - 40° C  Salt Concentration Salt ions can interfere with some chemical bonds  pH Optimal range = 6 – 8 CONNECTION: lakes are influenced by acid precipitation which effect enzyme activity in organism that live there.

 Many Enzymes will not function without non- protein helpers: Cofactors (inorganic molecules) ○ Iron ○ Zinc Copper Coenzymes (organic molecules) ○ Vitamins

A few enzymes work best at very low pH, about 2. Where in the body do you think these enzymes are located?  The Stomach

5.8 Enzyme inhibitors block enzyme action.  Chemicals that interfere with an enzymes activity are called Inhibitors  Two types of Inhibitors: Competitive inhibitor Non-competitive inhibitor

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 Figure 5.8 Substrate Enzyme Active site Normal binding of substrate Enzyme inhibition Noncompetitive inhibitor Competitive inhibitor Inhibitors are not always harmful. Some act as feedback inhibition (i.e. the on and off switch)

What is the advantage of feedback inhibition to a cell?  It prevents the cell from wasting energy by synthesizing more of a product than is necessary

CONNECTION: 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors  Example Cyanide – inhibits an enzyme involved with the production of ATP during cellular respiration Serine – blocks the active site on acetylcholinesterase ( an enzyme vital to nerve transmission) Some antibiotics – inhibit enzymes necessary for bacteria to survive.

How does the antibiotic penicillin work? It interferes with an enzyme used in the making of cell wall in bacteria.

5.10 MEMBRANE STRUCTURE AND FUNCTION Membranes organize the chemical activities of cells Membranes provide structural order for metabolism Membranes form most of the cell’s organelles, partitioning the cell into functional compartments that contain specific enzymes.

A. Membranes separate cells from the outside environments, including, in multi-cellular organisms, the environment in other cells that perform different functions. B. Membranes control the passage of molecules from one side of the membrane to the other. C.In eukaryotes, membranes partition function into organelles D. Membranes provide reaction surfaces, and organize enzymes and their substrates. E.Membranes are selectively permeable, which means some substances can pass through a membrane more easily than other substances. Compare ethanol (as a fixative) to glucose.

The plasma membrane of the cell is selectively permeable ○ It controls the flow of substances into or out of the cell Figure 5.10 Cytoplasm Outside of cell TEM 200,000 

5.11 Membrane phospholipids form a bilayer phospholipids ○ Have a hydrophilic head and two hydrophobic tails ○ Are the main structural components of membranes Figure 5.11A CH 2 CH 3 CH 2 CH CH 2 CH 3 CH 2 CH 3 N + O O O–O– P O CH 2 CH CH 2 C O C O O O Phosphate group Symbol Hydrophilic head Hydrophobic tails

Phospholipids form a two-layer sheet ○ Called a phospholipid bilayer, with the heads facing outward and the tails facing inward Figure 5.11B Water Hydrophilic heads Hydrophobic tails

Why do phospholipids tend to organize into a bilayer in an aqueous environment?  This structure shields the hydrophobic tail from water, while exposing the hydrophilic heads to water, making the membrane selectively permeable.

5.12 The membrane is a fluid mosaic of phospholipids and proteins A membrane is a fluid mosaic with proteins and other molecules embedded in a phospholipid bilayer. Web Activity 5E Figure 5.12 Fibers of the extracellular matrix Carbohydrate (of glycoprotein) Glycoprotein Microfilaments of cytoskeleton Phospholipid Cholesterol Proteins Plasma membrane Glycolipid Cytoplasm

Why are cellular membranes described as a fluid mosaic?

5.13 Proteins make the membrane a mosaic of function 1. Membrane proteins have a variety of diverse functions. 2. Different cells have different sets of membrane proteins 3. Many membrane proteins function as enzymes Enzymes: catalyzing intracellular and extracellular reactions Figure 5.13A

4. Other membrane proteins function as receptors for chemical messages from other cells: Receptors trigger cell activity when a messenger molecule attaches. This is also known as Signal Transduction. Figure 5.13B Messenger molecule Receptor Activated molecule Example: hormones Web/CD Activity 5F

Membrane proteins also function in transport ○ Moving substances across the membrane Figure 5.13C ATP. CO 2 & O 2 are small non-polar And molecules that can pass freely through the lipid bi-layer; Other essential molecules such as glucose and water cannot pass freely, they need assistance. Example: Transporters of hydrophilic molecules 5G

5.14 Passive transport is diffusion across a membrane ◦ In passive transport, substances diffuse through membranes without work by the cell  Spreading from areas of high concentration to areas of low concentration  Web/CD Activity 5H Web/CD Activity 5H EquilibriumMembraneMolecules of dye Equilibrium Figure 5.14B Figure 5.14A Different molecules diffuse independently of one another

Small nonpolar molecules such as O 2 and CO 2 ○ Diffuse easily across the phospholipid bilayer of a membrane ○ Ions (charged atoms) and polar molecules (water, glucose) can diffuse if they move down their concentration gradients and if they have a transport protein to escort them into the cell. ○ Passive transport is an extremely important way for small molecules to get into and out of cells. For example, O 2 moves into red blood cells and CO 2 moves out of these cells by this process in the lungs. The reverse process takes place in the tissue because the concentration gradients have reversed.

5.15 Facilitated Diffusion A.Facilitated diffusion occurs when a pored protein, spanning the membrane bilayer, allows a solute to diffuse down a concentration gradient. B.The cell does not expend energy. C.The rate of facilitated diffusion depends on the number of such transport proteins, in addition to the strength of the concentration gradient.

Transport proteins may facilitate diffusion across membranes Many kinds of molecules do not diffuse freely across membranes For these molecules, transport proteins provide passage across membranes through a process called facilitated diffusion. Figure 5.15 Solute molecule Transport protein Web 5I Facilitated diffusion occurs when a pored protein, spanning the membrane bi-layer, allows a solute to diffuse down a concentration gradient.

Daily Planner

5.16 Osmosis is the diffusion of water across a membrane. In osmosis water travels from a solution of lower solute concentration to one of higher solute concentration Figure 5.16 Lower concentration of solute Higher concentration of solute Equal concentration of solute H2OH2O Solute molecule Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Net flow of water

Osmosis Cont., A. Water travels from area of low solute concentration to area of high solute concentration. B.The direction of osmosis is determined only by the difference in total solute concentrations. C.Two solutions equal in solute concentrations are isotonic to each other; therefore, osmosis does not occur. D.However, even in isotonic solutions separated by a selectively permeable membrane, water molecules are moving in both directions at equal rates.

5.17 Water balance between cells and their surroundings is crucial to organisms. ◦ Cell membranes act as selectively permeable membranes between the cell contents and its surroundings (Figure 5.17). The propensity of a cell to gain or lose water with its surroundings is referred to as tonicity. Figure 5.17 Plant cell H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Plasma membrane (1) Normal (2) Lysed (3) Shriveled (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed) Isotonic solution Hypotonic solution Hypertonic solution Animal cell

Tonicity ◦ Osmosis causes cells to: ◦ shrink in hypertonic solutions ◦ swell in hypotonic solutions ◦ In isotonic solutions Animal cells are normal, but plant cells are limp. The control of water balance ○ Is called osmoregulation ◦ WEB 5J Osmosis and Water Balance in Cells WEB 5J Osmosis and Water Balance in Cells

Explain the function of the contractile vacuole in the Paramecium cell in Fig. 4.12B in terms of what you have learned about water balance in cells. LM 650  Nucleus Contractile vacuoles Pond water is HYPOTONIC to the Paramecium; therefore water moves Into the vacuole. The ability of the Vacuoles to contract, expels the water so the cell does not explode.

P P P Protein changes shape Phosphate detaches ATP ADP Solute Transport protein Solute binding 1 Phosphorylation 2 Transport 3 Protein reversion Cells expend energy for active transport ◦ Transport proteins can move solutes against a concentration gradient  Through active transport, which requires ATP  Web 5K (optional) Web 5K Figure 5.18

Fluid outside cell Cytoplasm Protein Vesicle  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) ○ Web 5L Exocytosis and Endocytosis Web 5L Figure 5.19A

Membranes may fold inward ○ Enclosing material from the outside (endocytosis) Figure 5.19B Vesicle forming

Endocytosis can occur in three ways ○ Phagocytosis – taking in food particles ○ Pinocytosis – cellular drinking ○ Receptor-mediated endocytosis – highly specific, the cell forms a pit and forms a vesicle that will carry the molecule to the cytoplasm. Pseudopodium of amoeba Food being ingested Phagocytosis Pinocytosis Receptor-mediated endocytosis Material bound to receptor proteins PIT Cytoplasm Plasma membrane TEM 54,000  TEM 96,500  LM 230  Figure 5.19C

CONNECTION A.Cholesterol is carried in the blood by low-density lipoprotein (LDL) particles. B.In people with normal cholesterol metabolism, excess LDL-bound cholesterol in the blood is eliminated by receptor-mediated endocytosis by liver cells. C. In people with a genetic condition that results in increased levels of cholesterol (hypercholesterolemia), fewer or no such receptor sites exist, and the people accumulate LDL-bound cholesterol. These people are at high risk for developing heart disease.

5.20 CONNECTION Faulty membranes can overload the blood with cholesterol Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors LDL particle Protein Phospholipid outer layer Cytoplasm Receptor protein Plasma membrane Vesicle Cholesterol Figure 5.20

5.21 Chloroplasts and mitochondria make energy available for cellular work Chloroplasts carry out photosynthesis ○ Using solar energy to produce glucose and oxygen from carbon dioxide and water Mitochondria consume oxygen in cellular respiration ○ Using the energy stored in glucose to make ATP Web 5M Build a Chemical Cycling System