1	THE WORKING CELL CHAPTER 5 Energy, Enzymes and Membranes
2	ENERGY Energy is the capacity to do work. Energy moves matter in some direction it could not go if left alone. All organisms need energy to: move from place to place move fluids throughout the cell/organism move molecules
3	ENERGY Two forms of energy: 1. kinetic – energy that is actually doing something….energy in motion 2. potential – energy that is stored…. Chemicals store energy in the bonds that hold the atoms together = chemical energy. The energy involved in a chemical reaction will either be endergonic or exergonic
4	ENERGY Endergonic reactions require an input of energy. The products will contain more potential energy than the reactants. Photosynthesis is a good example of this. CO₂ and H₂O have relatively low amounts of energy within their molecules but when combined with sunlight, they form glucose, C₆H₁₂O₆, a high energy sugar.
5	ENERGY Exergonic reactions release the energy in the chemical bonds. The products have less energy than the reactants. Cellular respiration is the energy-releasing chemical breakdown of glucose.
6	CELLULAR METABOLISM Is the sum of thousands of endergonic and exergonic reactions. To move, find, eat and digest food, escape predators, repair damage to the body, grow and reproduce requires energy. All of these processes maintains an organism’s metabolism.
7	ATP Adenosine triphosphate is the molecule that powers nearly all forms of cellular work. Energy coupling is the using of energy released form an exergonic reactions to drive essential endergonic reactions. All cells use this energy coupling and ATP is the key to energy coupling. The usable energy released by most exergonic reaction is stored in ATP. And the energy used in most endergonic reactions comes from ATP.
8	ATP ATP has 3 parts: 1. adenine – a nitrogeneous base 2. ribose – a 5 carbon sugar 3. a chain of 3 phosphates The covalent bonds connecting the 2^nd and 3^rd phosphates are not stable. Hydrolysis breaks these bonds.
9	ATP 3 things happen when ATP’s 3^rd bond is broken: 1. a phosphate is removed 2. ATP becomes ADP 3. energy is released. The 3^rd phosphate is an energy shuttle that powers a cellular process. The transfer of a phosphate group to another molecule is called phosphorylation.
10	ATP The cellular respiration process will regenerate the ADP to ATP by adding a phosphate through dehydration synthesis. This is a recurring process within a cell that maintains its metabolism. The entire cell’s pool of ATP is renewed about once each minute.
11	ENZYMES An enzyme is a protein molecule that acts as a biological catalyst. It speeds up the rate of a reaction without being changed into a different molecule. An enzyme lowers the E_A (energy of activation). It does not add energy to the reaction.
12	ENZYMES Because an enzyme is a protein, it has a unique 3-dimensional shape (quaternary structure) that will determine which chemical reaction the enzyme can catalyze. A substance that an enzyme acts on is call the enzyme’s substrate. Each enzyme can recognize only one specific substrate. It takes many enzymes to catalyze all the reactions in a cell
13	ENZYMES The part of the enzyme that binds to the substrate is called the active site. It is a very small pocket or groove that only fits one kind of substrate.
14	ENZYMES The cellular environment affects enzyme activity: 1. temperature – molecular motion allows substrate to come in contact with enzyme more often if there is a slight increase in temp. Optimal temp is, of course, body temp 35-40 °C. Too high a temp will denature the enzyme. 2. Salt concentration and pH – salt ions and H⁺ ions interfere with some of the chemical bonds that maintain protein structure.
15	ENZYMES 3. Cofactors – are non-protein helpers such as Zn, Fe, or Cu. Organic cofactors are called coenzymes. Many enzymes require these cofactors to perform their function. Many vitamins are cofactors
16	ENZYMES INHIBITORS Enzyme inhibitors are chemicals that interferes with an enzyme’s activity. A competitive inhibitor resembles the enzyme’s normal substrate and competes with the substrate for the active site on the enzyme. This prevents the enzyme from acting. A noncompetitive inhibitor does not enter the active site. Instead, it binds to the enzyme somewhere outside the active site. Its binding changes the shape of the enzyme so that the active site no longer fits the substrate.
17	ENZYMES INHIBITORS When covalent bonds form between the enzyme and inhibitor, the actions is irreversible. When weak hydrogen bonds form, it can be reversed. These enzyme inhibitors are important regulators of cell metabolism. They can act as a negative feedback system, meaning when too many products are produced, they become the noncompetitive inhibitors.
18	CELL MEMBRANES Because so many reactions occur simultaneously in a cell, the cell must be highly organized. Some of the organization comes from teams of enzymes that function like an assembly line. A product from one enzyme-catalyzed reaction becomes the substrate for a neighboring enzyme and so on until the final product is made.
19	CELL MEMBRANES For a cell’s assembly lines to operate, the right enzymes have to present at the right time and in the right place. Plasma membranes provide a structural basis for metabolic order. These membranes partition the cell into compartments called organelles, that contain enzymes necessary for a particular function. Plasma membrane forms a boundary between the cell and its surroundings and controls the traffic of molecules into and out of the cell.
20	CELL MEMBRANE STRUCTURE All cell membranes are selectively permeable, meaning they allow some substances to cross more easily than others and block passage of certain other substances.
21	CELL MEMBRANE STRUCTURE Membranes are composed mainly of phospholipids that form a bilayer. The hydrophilic head faces outward exposed to the water and their hydrophobic tails point inward, shielded from the water. Nonpolar, hydrophobic molecules are soluble in lipids and they can easily pass through the membrane. Polar hydrophilic molecules are not soluble in lipids. And whether they pass through the membrane depends on the type of protein molecules in the phospholipid bilayer
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23	CELL MEMBRANE STRUCTURE This type of structure is called a fluid mosaic. ‘Mosaic’ denotes a surface made of small fragments – protein molecules. ‘Fluid’ refers to the floating of many proteins and lipids laterally within the phospholipid. The steroid, cholesterol, is wedged into the bilayer to help stabilize the phospholipids. The outside surfaces of the membranes has carbohydrates bonded to proteins and lipids in the membrane.
24	CELL MEMBRANE STRUCTURE Protein attached to a sugar is called a glycoprotein. A lipid attached to a sugar is called a glycolipid. Glycoprotein and glycolipids are specific to a species and to an individual. They are used as identification tags so the cell can be recognized as its own or as foreign.
25	CELL MEMBRANE FUNCTIONS Attachment to the cytoskeleton, identification tags, forming junctions between adjacent cells, enzymes for a molecular pathway, receptors for chemical messengers from other cells, signal transduction Move substances across the membrane.
26	CELL MEMBRANE – PASSIVE TRANSPORT Diffusion is the tendency for molecules to move from an area of higher concentration to a lower concentration. Even though a transport molecule may be needed in the cell membrane, no work is involve in diffusion. It is the result of kinetic energy and entropy. The molecules will flow down a concentration gradient. Higher to lower until equilibrium is reached.
27	CELL MEMBRANE – PASSIVE TRANSPORT Examples: in the lungs, O₂ and CO₂ flow with the concentration gradient in and out of the red blood cells. H₂O flows in and out of all cells through passive transport
28	CELL MEMBRANE – PASSIVE TRANSPORT - OSMOSIS H₂O flows in and out of all cells through passive transport. Diffusion of water across a selectively permeable membrane is a special case of passive transport called Osmosis.
29	CELL MEMBRANE – PASSIVE TRANSPORT-OSMOSIS The ideal solution for a cell to be immersed in is when the flow of H₂O in and out of the cell is at equilibrium- isotonic solution. If the cell is immersed in a solution with more solute particles on the outside of the cell, the water inside the cell will rush out to create and equilibrium outside the cell. The cell has lost most of its water so it shrivels up. The solution is called hypertonic and the cell can die for lack of water.
30	CELL MEMBRANE – PASSIVE TRANSPORT-OSMOSIS In the opposite situation, when the solution the cell is immersed in has fewer solute particles than the cell, the water will rush into the cell, filling it up and expanding the cell membrane like a balloon. This is called hypotonic solution and the cell can expand until it pops (lyses) and dies.
31	CELL MEMBRANE – PASSIVE TRANSPORT-OSMOSIS Osmoregulation is the control of water balance in an organism. In plant cells, the contractile vacuoles’ function is to maintain the cell’s turgid (water balance). In animals, the kidneys excrete the excess water.
32	CELL MEMBRANE – PASSIVE TRANSPORT -FACILITATED DIFFUSION Many molecules move across a membrane with the help of specific transport proteins in the membrane. Because no energy is expended, it is a form of passive transport. The crossing molecules follow the concentration gradient. The transport protein molecules spans the membrane and provides a pore for the solute.
33	CELL MEMBRANE – PASSIVE TRANSPORT -FACILITATED DIFFUSION Examples of molecules that use facilitated diffusion include some sugars, amino acids, some ions and water. Water is included because it needs help getting through the nonpolar portion of the phospholipid bilayer.
34	CELL MEMBRANE –ACTIVE TRANSPORT Active transport requires energy for the cell to move molecules across a membrane because the solute is flowing against the concentration gradient. ATP is the usual energy source. Example: Na⁺ and K⁺pump that help nerve cells generate nerve signals
35	CELL MEMBRANE –ACTIVE TRANSPORT Active transport process: 1. solute binds to transport protein 2. PO₄ group is transferred from ATP to protein 3. energy surge form the phosphorylation makes the protein change shape and release the solute molecule on the other side of the membrane
36	CELL MEMBRANE –ACTIVE TRANSPORT 4. As the protein releases the first solute, its shape and position allows the second solute to bind to it 5. the PO₄ group is released causing the protein to return to its original shape 6. releasing the second solute on the opposite side of the membrane.
37	CELL MEMBRANE –ACTIVE TRANSPORT-EXOCYTOSIS A cell uses the process of exocytosis to export large materials. 1. a membrane-enclosed vesicle filled with macromolecules move to the plasma membrane. 2. the vesicle fuses with the plasma membrane 3. the vesicle’s contents spill out of the cell. Examples: insulin excretion into blood, tears
38	CELL MEMBRANE –ACTIVE TRANSPORT-ENDOCYTOSIS The plasma membrane forms a vesicle around the particle. Phagocytosis is the membrane enclosing around a prey and packaging it within a vacuole. The vacuole fuses with a lysosome to allow the hydrolytic enzymes to digest the contents. Pinocytosis is the taking in of droplets of fluid for the surrounding into tiny vesicles.
39	CELL MEMBRANE –ACTIVE TRANSPORT-ENDOCYTOSIS Receptor-mediated endocytosis is highly specific. The plasma membrane forms a pit that is lined with receptor proteins that have picked up particular molecules from the surroundings. The pit will pinch close to form a vesicle that will carry the molecules into the cytoplasm.