Post on 02-Jan-2016
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Energy, Metabolism, and Enzymes
Ch 6 BaboonCh 5.1-5.8 Bat
- Energy: the ability to do work
- Two major types of energy 1. Kinetic - energy of motion - EX: movement, heat, electrical, radiant
2. Potential - stored energy - EX: positional, chemical bonds, gravitational, charge potential (battery)
- Energy is constantly being transformed from one type to another
- EX: radiant energy from sunlight transformed into the energy of chemical bonds (kinetic to potential)
1st and 2nd Law of Thermodynamics
- 1st Law - Law of Conservation of Energy - Energy can be transformed or transferred but it can't be created or destroyed
- 2nd Law - Law of Entropy - When energy is is transformed or transferred, some will be "lost", usually as heat
- Every change in Energy results in the world becoming more disordered (chaotic)
- Entropy - the quantitative measure of disorder
Systems- Open - when energy and matter can be transferred back and forth between the system and its surroundings EX: human body
- Closed - when energy and/or matter can NOT be transferred back and forth between the system and its surroundings
Energy of Life- Living organisms require a constant supply of energy to
perform work that must take place in cells (powered by ATP)
- Mechanical work - cell division, muscle contraction, cilia movement, etc...
- Transport work - pumping substances across membranes
- Chemical work - breaking and forming chemical bonds
- Energy flows from the non-living world into living organisms and back
- Conversion of Radiant Energy to Chemical Energy - Photosynthesis (makes glucose) - Chemical Energy is transferred between organisms - Energy is "lost" as heat along the way
Metabolism
- Metabolism is the sum total of all chemical reactions in an organism (transformation of energy)
- Two types of reactions- 1. Catabolic reactions release energy by breaking chemical bonds (complex ⇒ simple) - also known as exergonic reactions because they release energy - EX: Cellular respiration
2. Anabolic reactions use energy to make chemical bonds (simple ⇒ complex) - also known as endergonic reactions because they require energy - EX: Photosynthesis
Exergonic vs. Endergonic (Catabolic) (Anabolic)
ΔG = amount of free energy in a system
ΔG is negative, energy is given off ΔG is positive, energy is absorbed
These reactions are usually coupled in living things - E released in exergonic is used to power endergonic
- Enzymes: proteins that act as catalysts for reactions without being permanently altered or destroyed - Catalyst: increases efficiency of reactions
- Enzymes frequently have the suffix "ase" - Substrate: substance the enzyme acts on - EX: enzyme salivary amylase breaks down starch
(substrate) in the food you eat - EX: enzyme glycogen synthase that builds glucose
into glycogen
Enzymes
- Enzyme - substrate relationships are specific
- Active site - point where substrate and enzyme interact (bind)
- Induced Fit Theory – active site is a crevice on the enzymes surface which interacts with the substrate. Enzyme folds around the substrate like a tight fitting glove
Enzyme - Substrate Relationships
- Reversibility - enzymes can break substances down (catabolic) or help put them together (anabolic)
Enzymes and Chemical Reactions
Enzymes and Chemical Reactions
- Catabolic (exergonic) - Enzymes weaken bonds of substrate so less energy is needed to break it down - lowers activation energy
- Anabolic (endergonic) - Enzymes chemically align angles of molecules to make bonding easier
Sucrose ----------------> Fructose + Glucose
Substrates ----------------> Products(reactants)
Enzyme
(sucrase enzyme)
Catabolic
- Activation energy: initial energy required to break chemical bonds during an exergonic (catabolic) reaction - i.e. Need to put a little E in before you can release some
Enzymes and Chemical Reactions
Enzymes and Chemical Reactions
- Enzymes act as catalysts - lower the activation energy required
Exergonic rx
Environmental Conditions
- Temperature - higher temperature result in increased molecular motion and higher kinetic energy. More collisions between molecules lead to faster reactions - in general an increase of 10°C doubles the rate of reactions - too much heat can, however, can cause denaturation
Environmental Conditions- pH
- most enzymes require a neutral pH - Exceptions:
- Pepsin (stomach) needs pH 2 - Trypsin (intestine) needs pH 7
- Concentration of substrate and product - Lots of substrate and little product = more product formed - Lots of product and little substrate = more substrate formed
- Non-protein molecules that are necessary for some enzymes to work - Usually vitamins that must be ingested by organisms because the body does not naturally produce them - EX: iron or zinc - Sometimes called co-enzymes
Cofactors
Enzyme Inhibitors
1. Competitive inhibitors - molecule binds to the active site, preventing substrate from binding - usually reversible - EX: pesticides, drugs
2. Non-competitive inhibitors - molecule binds to a region other than the active site causing a shape change in the enzyme - EX: penicillin - prevents enzymes used by bacteria to assemble the cell wall from working
- Cooperativity - Enzyme becomes more receptive to substrate molecules once one substrate molecule has attached
- EX: once one molecule of oxygen binds to hemoglobin it encourages the molecule to bind to several more molecules of oxygen
Cooperativity
- Allosteric enzymes - enzymes have 2 kinds of binding sites
1. one site for the substrate (the active site)
2. one site called the allosteric site that allows the enzyme to be controlled
- Allosteric inhibitors: bind to the allosteric site and stop the enzyme from functioning
- Allosteric activators: bind to the allosteric site and turn the enzyme on.
Allosteric Regulation