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Chapter 4

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BIOL 1000
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Chapter 4 – Energy and Enzymes - Energy detected through ability to do work (not measured or weighed) o Defined: capacity to do work - Heat, chemical, mechanical, electrical forms - Electromagnetic radiation (visible, infrared, and ultra-violet light) - Through photosynthesis – energy of light converted to chemical energy in the form of complex sugars & organic molecules - Kinetic energy energy posed by an object in motion o ex. Electricity (flow of electrons) / photons of light - potential energy stored energy (location/chemical structure) o Arrangement of atoms in a molecule of glucose/gasoline (chemical potential energy) - Thermodynamics study of energy and its transformations o System- object being studied  Isolated system – one that does not exchange matter/energy with surroundings • thermos  Closed system- can exchange energy but NOT matter with its surroundings • Green house  Open system – both energy and matter can move freely between system and surroundings • Ocean –absorbs and releases energy (hydrological cycle) evaporation and condensation o Surroundings – everything outside system o Universe - total system and surroundings - 1 law of thermodynamics –energy can be transformed (from one form to another or transferred) but NOT created or destroyed PRINCIPLE OF CONSERVATIO NOF ENERGY o Ex. Waterfalls – potential (top), kinetic (moving down), sound/heat (hits bottom) nd - 2 law of thermodynamics - energy transformations increase disorder o When energy transferred some is lost not 100% - heat o Entropy – measures the disorder (it takes energy to maintain low entropy) o Living things bring in energy and matter and use them to generate order out of disorder o Food – maintain cells in highly ordered state – supplies energy - Spontaneous reactions – a reaction will occur without an input of energy o 1. The change in energy content of a system 2. Change in entropy o Reactions tend to be spontaneous if products have LESS potential energy  Potential energy – enthalpy/H o Endothermic – reactions that absorb energy from surroundings = products having MORE potential energy than reactants o Exothermic – release energy = products have LESS potential energy than reactants- spontaneous o For a reaction to be spontaneous delta G = -ve (free energy (delta S) products must be less than reactants) products-reactants o High free energy = less stable - Chemical equilibrium – point at which there is no longer any overall change in concentration of products and reactants = free energy at lowest = no spontaneous = delta G = 0 - Metabolism – sum of all chemical reactions that take place within an organism - Exergonic – releases free energy =delta G = -ve = spontaneous - Endergonic – consumes free energy = delta G = +ve - Catabolic pathway – energy released by the breakdown of complex molecules to simpler compounds o Cellular respiration - Anabolic pathway – consumes energy to build complicated molecules from simpler ones (biosynthetic pathways) o Photosynthesis - ATP – includes 5-carbon sugar, ribose, nitrogenous base and chain of 3 phosphate groups. Breakdown –hydrolysis reaction = ADP o ATP releases large amounts of free energy upon hydrolysis o Energy coupling – the exergonic release of energy when ATP –ADP and P is i used to drive a endergonic reaction (requires enzyme based catalysis) –enzyme bringing a molecule of ATP and a reactant molecule into close contact ( the ATP transfers the Pi to reactant molecule = more unstable and reactive)  Hydrolysis prevented (not lost in heat) the enzyme where ATP and substrate react not accessible to water o ATP cycle – resynthesizes - Activation energy – initial energy investment required to start a reaction - Transition state – molecules that gain necessary activation energy (bonds unstable ready to be broken) - Catalysts – speed up reaction ex enzyme (reduce activation energy o Enzymes do not change delta G - Active site- specific site of an enzyme where catalysis takes place - Enzymes increase rate of reaction by increasing the number of substrate molecules that attain the transition state o 1. Bringing reactant molecules together (reactant molecules can assume transition state only when collided – binding brings reactants together) o 2. Exposing reactant molecule to altered changed environments that promote catalysis (+ve/-ve ions) alter substrate o 3. Change shape of substrate molecule –mimics transition state - Inhibitors – inhibit binding of substrate to active site of enzyme = slowing reaction rate - Competitive inhibition – concentration of inhibitor is high enough reaction could stop completely - Non-competitive inhibition - specific molecules inhibit enzyme activity BUT rather than binding at active site bind somewhere else on enzyme = decrease enzyme activity =changes conformation of enzyme which reduces ability of active site - Reversible inhibition - Irreversible inhibition – can only overcome by cell synthesizing more of particular enzyme - Allosteric site – enzyme activity controlled by reversible binding – non-competitive o Allosteric inhibition/activation (low affinity state/high affinity state) –respectively - Feedback inhibition – product of reactions acts to inhibit its own synthesis - Covalent modification – enzymes are made active or inactive o Proteolytic cleavage (pg. 88) - Enzymes have optimal pH where operates at peak efficiency o Pepsin – 1.5 pH / Trypsin – 8 pH - As temperature rises the rate a reactions increase (collision of molecules increase) (kinetic motion of amino acids chains of enzyme increase) = denature molecule - 0-40 degrees reaction rate doubles every 10 - 40 -50 denatures Chapter 5 – Cell membranes and signalling 5.3 - Membrane proteins separated into 4 major groups o Transport – protein provides hydrophilic channel allows movement of specific compound (change shape) o Enzymatic activity – many enzymes are membrane proteins o Signal transduction – membranes often contain receptor proteins on outer s
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