Why do living organisms need energy? • To be able to carry out life’s functions such as growth, repair, movement, transport. • Living cells need a constant supply of energy for breaking and making molecules such as proteins.
What Can Cells Do with Energy? • Every time you acquire energy you can use it to do an energy requiring action • Cells do chemical work • Cells can do mechanical work
Kinetic energy is the energy of motion • Potential energy is stored energy • And can be converted to kinetic energy Figure 5.1A–C
Kinetic and Potential energy • Potential is stored energy. • Ex: A resting bird • Kinetic is the energy of motion • Ex: a bird in flight
Different forms of Energy • Forms of energy • Electrical • Mechanical • Chemical • Light • Heat
What is energy? • The capacity to do work, to cause change, to make things happen. We can measure it and experience its effects but we can’t see it. • What are the different forms of energy? • Two broad categories are • Potential energy stored, waiting to be released • Kinetic energy is energy associated with motion • Chemical energy (type of potential energy) is found in the chemical bonds of molecules such as a lump of coal, a steak, electricity, light.
How do we measure energy? • Calorie Usually in the form of HEAT because all forms ofenergycan be converted to heat. The Unit is : Calorie or Kilocalories (1000 calories). Unit of work is: Joule or Kilojoule
How do organisms obtain energy? • Green plants from the sun. Autotrophs • Animals, by eating the green plants or other animals. Heterotrophs • Where is the energy in food? • In the chemical bonds of its molecules. • The energy in food is in the electrons spinning around its atoms. The cells strip these electrons and use them to power their lives.
Energy can be converted from one form to another. • As the boy climbs the ladder to the top of the slide he is converting his kinetic energy to potential energy. • As he slides down, the potential energy is converted back to kinetic energy. • It was the potential energy in the food he had eaten earlier that provided the energy that permitted him to climb up.
Energy Flows in one direction • All energy for life comes from the sun • Producers trap energy from the sun and convert it into chemical bond energy Consumers are those that eat the producers • Allorganisms use the energy stored in the bonds of organic compounds to do work
Materials are recycled • While energy flows in one direction materials are used over and over again
What laws govern energy transformations? • All living things obey the laws ofthermodynamics. Thermo means heat • Thermodynamics is the study of heat transfers.
Thermodynamics • Thermodynamics is the study of energy transformations.All energy is transformed to heat energy. A closed systemis isolated from its surroundings. • Organisms are open systems. • They absorb energy - light or chemical energy in organic molecules - and release heat and metabolic waste products into the environment. • In an open system energy can be transferred between the system and surroundings.
First Law of Thermodynamics • The total amount of energy in the universe does not change, remains constant. We can say that energy cannot be created nor destroyed, it can only be transformed from one form to another. This is the “Law of Conservation of Energy” • Energy can undergo conversions from one form to another. The total energy in a closed system remains constant. Living organisms are open systems. Organisms can only convert energy from one form to another.
Second Law of Thermodynamics • During every energy transformations some energy is lost as heat.No energy conversion is 100 percent efficient. • The total amount of energy flows from high-energy forms to lower energy forms. Energy transfers increase disorder. • Example: as the chemical energy in gasoline is transformed into kinetic energy of motion in you car, heat is released.
The Second Law of Thermodynamics • The second law of thermodynamics • States that energy transformations increase disorder or entropy, and some energy is lost as heat Heat Chemical reactions Carbon dioxide + Glucose + ATP ATP water Oxygen Energy for cellular work Figure 5.2B
Entropy • Is the measurement of the degree of disorder in a system • The world of life can resist the flow toward maximum entropy only because it is getting more energy from the sun (plants) • Animals eat to get energy and fight entropy
ATP ATP shuttles chemical energy and drives cellular work • ATP powers nearly all forms of cellular work • ATP is made in the mitochondria of cells
Phosphategroups Adenosine diphosphate Adenosine Triphosphate H2O + P Energy P P P P P + Hydrolysis Adenine Ribose ATP ADP • The energy in an ATP molecule • Lies in the bonds between its phosphate groups Figure 5.4A
ATP Phosphorylation Hydrolysis Energy fromexergonicreactions Energy forendergonicreactions ADP + P • Cellular work can be sustained • Because ATP is a renewable resource that cells regenerate Figure 5.4C
Metabolism and energy coupling • Cells carry out thousands of chemical reactions • The sum of which constitutes cellular metabolism • Energy coupling • Uses exergonic reactions to fuel endergonic reactions
Exergonic reactions fuel endergonic reactions • Endergonic: Energy input required. Ex: photosynthesis • Product has more energy than starting substances • Exergonic reaction Ex: cellular respiration and wood burning _____________________________ • Endergonic= energy IN • Exergonic= energy OUT
Products Amount of energyrequired Energy required Potential energy of molecules Reactants Chemical reactions either store or release energy • Endergonic reactions • Absorb energy and yield products rich in potential energy Figure 5.3A
Reactants Amount of energyreleased Energy released Potential energy of molecules Products • Exergonic reactions • Release energy and yield products that contain less potential energy than their reactants Figure 5.3B
Exergonic reactions • Energy is released • Products have less energy than starting substance energy-rich starting substance ENERGY OUT products with less energy
ENZYMES • To survive organisms must obtain energy from nutrients in a short time. • Chemical reactions to break down a molecule could take along time. For example to break sucrose (table sugar) in a candy bar into glucose and fructose for the body to use could take a very long time. Living cells cannot wait that long. There is a way to speed up reactions without increasing the temperature. • What is a catalyst? A catalyst is a chemical that speeds the reaction but is not used up in the reaction.
What are enzymes? • Enzymes are organic proteins that speed up the rate of chemicals reactions without changing the temperature. • How do enzymeswork? By lowering the activation energy, which means lowering the amount of energy needed to get a reaction going.
Chloroplasts and mitochondria make energy available for cellular work • Enzymes are central to the processes that make energy available to the cell
HOW ENZYMES FUNCTION? • Enzymes speed up the cell’s chemical reactions by lowering energy barriers In other words enzymes work by lowering the activation energy, which means lowering the amount of energy needed to get a reaction going.
EA barrier Enzyme Reactants Products 1 2 • For a chemical reaction to begin • Reactants must absorb some energy, called the energy of activation Figure 5.5A
The Induced-Fit model. • The Induced-Fit model. It almost (but not quite) fit precisely in the active site.
1 Enzyme availablewith empty activesite Substrate binds to enzyme with induced fit 2 4 Products arereleased 3 Substrate is converted to products • THIS IS HOW ENZYMES WORK Active site Substrate(sucrose) Enzyme(sucrase) Glucose Fructose H2O Figure 5.6
Definitions: • Active site: crevice , groove pocket where the substrate molecule fits and is changed. • Substrate: molecule acted upon, changed in some way by the enzyme • End product: final result of reaction
Theory of enzyme action • The Induced-Fit model. It almost (but not quite) fit precisely in the active site.
ENZYMES ARE HYGHLY SPECIFIC • A specific enzyme catalyzes each cellular reaction.There is a different enzyme for each reaction. • Enzymes have unique three-dimensional shapes that determine which chemical reactions occur in a cell
Characteristics of enzymes. • are proteins • are reusable • reactions are reversible. Work forward and backward • highly specific structure that matches the structure of the substrate molecule • the ending –“ase” tells you it is an enzyme. Ex: polymerase, amylase, DNAse, sucrase
Factors that affect enzyme action: • A protein (enzyme) gets DENATURED in these conditions.(Denatured means: Its three dimensional SHAPE is disrupted). • extreme temperatures • pH above 8 or below 6 • extreme salinity ( high salt concentrations) • The cellular environment affects enzyme activity • Some enzymes require non -protein cofactors • Such as metal ions or organic molecules called coenzymes • NAD+, FAD, zinc, some vitamins.
Chemical factors that control enzymes cofactors Small molecules that help enzymes catalyze reactions. How? Usually binds to the active site. Many are vitamins (called coenzymes) and others are inorganic metals such as zinc, iron or copper. All are “enzyme helpers”.
Enzyme inhibitors block enzyme action • Inhibitors interfere with an enzyme’s activity • There are competitive and non-competitive inhibitors
enzyme inhibitors • How? Certain chemicals can inhibit enzyme activity and it can be irreversible in many cases. • These can be competitive and non-competitive • Competitive inhibitors are chemicals that resemble the enzymes normal substrate and compete for its active site. They can block the active site from the substrate. • Noncompetitive inhibitors are substances that do not enter the enzyme’s active site but bind toanother part of the enzymecausing the enzyme tochange its shape. Many metabolic poisons as well as some antibiotics work this way.
Active site Substrate Enzyme Normal binding of substrate Competitiveinhibitor Noncompetitiveinhibitor Enzyme inhibition • 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
Allosteric regulation How? • Most enzymes have a receptor site on some other part of the enzyme molecule that is not the active site. • Allosteric enzymes can change back and forth between an active and an inactive form. • When there is an “activator” binding to the allosteric site, the enzyme enters reactions. • When there is an “inhibitor” binding to the allosteric site, the enzyme becomes inactive. • The activator or inhibitor at the active site changes the shape of the active site.
How is enzyme action controlled? • By a feedback mechanism. • This is ALLOSTERIC CONTROL. The molecule binds to the enzyme at a different site changing its shape.
Web sites to check : • http://programs.northlandcollege.edu/biology/Biology1111/animations/enzyme.html • http://resources.ed.gov.hk/biology/english/virtual_lab/flash/enzyme_lab.html
TRANSPORT ACROSS THE MEMBRANE • Cell membranes are semi-permeable, membranes show “SELECTIVE PERMEABILITY” which means some substances can pass through but others cannot. This is because it is a phospholipid bilayer. • The size of a molecule, its concentrationand its electrical charge determine how it passes across.
Transport across cell membranes Passive transport Diffusion and Osmosis Active transport Endocytosis Exocytosis
Check these: • http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm • http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm • http://www2.nl.edu/jste/osmosis.htm#Osmosis
What is “concentration gradient”? • Concentration gradient means that the number of molecules in one area is different than the number in another area • A substance moves from a region where it is more concentrated to one one where it is less concentrated - “down” gradient