The Working Cell Chemical Energy ATP & Cellular Work Enzymes Membrane Function

Chemical Energy Where do our muscles get energy to perform work? From food we eat When body breaks down food molecules what happens? Energy from food molecules is stored Potential energy

When, how is stored energy released? During the process of cellular respiration What does cell respiration do? Converts chemical energy (food) To another form of energy: ATP What is the significance of ATP? Can be converted to kinetic energy Or, muscle activity More cellular respiration and ATP in Chapter 6

Cell respiration Food ? ? ? ? ? Energy for cellular work Muscle work

How much energy do we get to use for cellular work? The diagram gives us a clue What percent is given off as heat? ~60% What is the ~60% heat converted to? ~40% What percent is captured as ATP?

Food Calories What is a calorie? And, how is it measured? A unit of energy And, how is it measured? is the amount of energy that raises the temperature of one gram (g) of water by one degree (1o) Celsius How much energy is in this handful of peanuts? Enough to boil a quart of water!

The kilocalorie (Kcal or C) is 1,000 calories (in kilocalories) (as fuel for energy) The kilocalorie (Kcal or C) is 1,000 calories The unit used to measure the energy in food

Pizza! You’d have to run about 14 miles! What would you have to do to burn off the calories from this pizza? You’d have to run about 14 miles!

ATP What is ATP? Why is ATP so important? How? (adenosine triphosphate) What is ATP? It is a nucleotide that performs many essential roles in the cell Why is ATP so important? It ‘powers’ all cellular work How? It releases ‘free’ energy When its phosphate bonds are hydrolyzed (or, broken down)

What does the ATP structure look like? Adenosine Phosphate ‘tail’ Ribose sugar + ADP? ATP is broken down to ADP (adenosine diphosphate) Accompanied by release of energy

Where’s the power in ATP? In the phosphate tail Release of last P makes energy available Unstable. Why? (adenosine diphosphate) Repulsion between negatively charged phosphate groups

What about that ‘leftover’ phosphate? Its used to energize other molecules What do these other molecules do? Help cells do 3 main types of work Mechanical Transport Chemical

ATP and Mechanical Work? Phosphate transferred to special motor proteins (muscles) What happens then? Proteins change shape Muscle cells contract Perform mechanical work

ATP and Transport Work? What happens then? Phosphate transferred to brain cells What happens then? Ions pumped across membranes

ATP and Chemical Work? What happens then? Make cell’s giant molecules Reactants Products What happens then? Amino acids are linked to make a protein Via a dehydration reaction

What is the ATP cycle? Our cells need energy (ATP) all the time! Its recyclable! Our cells need energy (ATP) all the time! Food Energy out… Cellular respiration For cellular work Energy in… The 3rd phosphate To regenerate ATP Acts as an energy shuttle

Learning check 1. What is the source of energy for regenerating ATP from ADP? 2. A kilocalorie is equal to _______? 3. Most cellular work is accomplished by _____ energizing molecules by _____ them. a. enzymes ... activating b. diffusion ... activating c. substrates ... transferring a phosphate group to d. ATP ... transferring a phosphate group to

Enzymes What is the barrier for reactions to occur? Energy must be added What is this energy called? Energy of activation EA How does the cell overcome the barrier? Uses a specialized protein, an enzyme

What does the enzyme do? Serves as a biological catalyst Increases the rate of the reaction ‘lowers the energy barrier’ Reduces activation energy

What are the details? Enzyme very selective Binds to specific molecules (substrates) At the enzymes active site Puts them under physical or chemical stress Which makes it easier to break bonds And start a reaction

Induced fit? Identify the steps? Substrate ? Sucrose What is this site? sucrase What are these molecules? Identify the steps? 1. Enzyme available with empty active site 2. Substrate binds to enzyme 3. Substrate converted to products 4. Products are released

What are enzyme inhibitors? ‘Imposters’ that plug up the active site Or at some remote site How do they function? Binding changes the shape of the enzyme Active site no longer receptive

Examples of enzyme inhibitors? Poisons e.g., malathion Inhibits an enzyme required for normal function of the insect nervous system Antibiotics e.g., penicillin Inhibits an enzyme bacteria use to make cell walls

Membrane Function 1. Endocytosis moves materials _____ a cell via _____. a. into ... facilitated diffusion b. into ... membranous vesicles c. into ... a transport protein d. out of ... diffusion e. out of ... membranous vesicles

3. Active transport ______. 2. What name is given to the process by which water crosses a selectively permeable membrane? a. diffusion b. passive transport c. phagocytosis d. pinocytosis e. osmosis 3. Active transport ______. Can move solutes against their concentration gradient Can involve the transport of ions Requires the cell to expend energy Uses ATP as an energy source All of the above

2. A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mothers milk. These molecules probably enter the cells lining the baby’s digestive tract via ____________? a. osmosis b. passive transport c. exocytosis d. active transport e. endocytosis

Hydrolysis Decomposition of a substance by the insertion of water molecules between certain of its bonds. Food is digested by hydrolysis. protein A three-dimensional biological polymer constructed from a set of 20 different monomers called amino acids. enzyme A protein serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction. substrate The reactant on which an enzyme works. active site The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.