Lecture 6: Energy Flow
Covers 6.2-6.5
Some definitions and ground rules*
• Energy: the capacity to do work
• Work: transfer of energy from one place to another
...
Definitions & ground rules*
• Chemical reaction: a process that forms or
breaks chemical bonds.
• These reactions change m...
Reactants and End Products of Burning
Glucose
Fig. 6-5
energy
C6H12O6
(glucose)
6 O2
(oxygen)
+
6 CO2
(carbon
dioxide)
6 H...
Chemical Reactions can be EXERGONIC
or ENDERGONIC*
• Exergonic: the result of the reaction is that
reactants have been cha...
An Exergonic Reaction
Fig. 6-3
energy
reactants
products
+
+
An Endergonic Reaction
Fig. 6-4
reactants
products
+
+
energy
HERE IS THE KEY*
• Most organisms are powered by the breakdown of sugar into CO2
and H20.
• The energy that is released fr...
ATP*
• Recall that ATP is a nucleotide composed of a
nitrogen-containing base, a sugar, and three
phosphate groups.
• ADP ...
The Interconversion of ADP and ATP
Fig. 6-8
ADP
energy
(a) ATP synthesis: Energy is stored in ATP
(b) ATP breakdown: Energ...
Other types of energy carriers
• ATP is not the only molecule that carries
energy within its bonds:
– Electron carriers: s...
Reactions may need enzymes to make
them happen
• Some reactions (exergonic and endergonic) may
never actually happen unles...
ATP SYNTHASE
• This protein is an enzyme that makes these
reactions happen:
• ADP + Phosphate ATP
• ATP ADP + Phosphate
Structure of an enzyme*
• The function of an enzyme is determined by its structure.
• Every enzyme has an active site (cre...
The Cycle of Enzyme-Substrate Interactions
Fig. 6-11
The substrates, bonded
together, leave the enzyme;
the enzyme is read...
Regulation of reactions
• In the human body, reactions are SOMETIMES
linked in sequences called metabolic
pathways: an ini...
Simplified Metabolic Pathways
Fig. 6-12
PATHWAY 1
Initial reactant Intermediates Final products
enzyme 1 enzyme 2 enzyme 3...
Speed of reactions depends on
amount of substrate, enzymes
• The more substrate you have, the faster the given reaction wi...
Inhibition/Regulation of enzymes
• Competitive Inhibition: a substance that is not the normal
substrate for an enzyme can ...
(b) Competitive inhibition
A competitive inhibitor
molecule occupies the
active site and blocks
entry of the substrate
Fig...
noncompetitive
inhibitor molecule
(c) Noncompetitive inhibition
A noncompetitive
inhibitor molecule
causes the active site...
Allosteric Regulation of an Enzyme by
Feedback Inhibition
Fig. 6-14
enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5
isoleucin...
Example of allosteric
regulation/feedback inhibition
• Metabolic pathway that makes isoleucine
from threonine. 5 enzymes n...
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Lecture 6

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Lecture 6

  1. 1. Lecture 6: Energy Flow Covers 6.2-6.5
  2. 2. Some definitions and ground rules* • Energy: the capacity to do work • Work: transfer of energy from one place to another • Chemical energy: energy contained in molecules and released through chemical reactions. • Sugar, glycogen and fat are the molecules in our bodies that can store chemical energy. • ATP is the molecule that can accept the energy and transfer it from one chemical reaction to another. • This energy allows us to move and grow. EX: muscle contraction results from the interaction of proteins that are fueled by ATP.
  3. 3. Definitions & ground rules* • Chemical reaction: a process that forms or breaks chemical bonds. • These reactions change molecules from one form to another: • Reactants (name for molecules BEFORE reaction) go through a chemical reaction. At the end of the reaction, the reactants have become the products (name for molecules AFTER the chemical reaction.)
  4. 4. Reactants and End Products of Burning Glucose Fig. 6-5 energy C6H12O6 (glucose) 6 O2 (oxygen) + 6 CO2 (carbon dioxide) 6 H2O (water) +
  5. 5. Chemical Reactions can be EXERGONIC or ENDERGONIC* • Exergonic: the result of the reaction is that reactants have been changed to products AND energy is RELEASED. • Endergonic: the result of the chemical reaction is that reactants have been changed to products BUT ENERGY IS REQUIRED TO MAKE THE REACTION HAPPEN.
  6. 6. An Exergonic Reaction Fig. 6-3 energy reactants products + +
  7. 7. An Endergonic Reaction Fig. 6-4 reactants products + + energy
  8. 8. HERE IS THE KEY* • Most organisms are powered by the breakdown of sugar into CO2 and H20. • The energy that is released from this reaction does all of the work that a cell needs to do: make proteins, move materials around, muscle contraction, etc. • But the energy from this reaction must be carried from the place the glucose is broken down to the place that the energy is needed. • ATP IS THE CARRIER MOLECULE OF CHEMICAL ENERGY IN OUR BODIES. IT CANNOT STORE THE ENERGY FOR LONG PERIODS, ONLY ENOUGH TIME TO CATCH THE ENERGY FROM AN EXERGONIC REACTION AND MOVE IT TO A PLACE WHERE ENERGY IS NEEDED IN ANOTHER PART OF THE CELL. (LATER IT CAN PICK UP MORE ENERGY AND DELIVER IT TO OTHER AREAS OF THE CELL.) • AND FINALLY, THE ENERGY FROM EXERGONIC REACTIONS OFTEN FUELS ENDERGONIC REACTIONS. (called coupled reactions)
  9. 9. ATP* • Recall that ATP is a nucleotide composed of a nitrogen-containing base, a sugar, and three phosphate groups. • ADP (the base, sugar and TWO phosphates) is a stable molecule. It gets unstable when energy from a reaction causes another Phosphate to be added to ADP and ATP is formed. ATP will then deliver the ENERGY CONTAINED IN THE LAST PHOSPHATE BOND to a place where it is needed. • When it “drops off” the energy, ATP is converted back to ADP BECAUSE THE ENERGY IS IN THE PHOSPHATE BOND.
  10. 10. The Interconversion of ADP and ATP Fig. 6-8 ADP energy (a) ATP synthesis: Energy is stored in ATP (b) ATP breakdown: Energy is released ATP ATP ADP phosphate phosphate energy P P P P P P +P P P P P P+
  11. 11. Other types of energy carriers • ATP is not the only molecule that carries energy within its bonds: – Electron carriers: some energy in exergonic reactions is transferred to electrons within special molecules called electron carriers. When the carriers reach their destination, the electrons (and the energy they carry) can be released. • NADH & FADH2 are electron carriers
  12. 12. Reactions may need enzymes to make them happen • Some reactions (exergonic and endergonic) may never actually happen unless an catalyst is present. • A catalyst is a molecule that speeds up a reaction without the catalyst itself being changed. • ENZYMES are catalysts that make reactions in the body happen. They are proteins. • Each enzyme can only catalyze ONE (or a small number of) reactions.
  13. 13. ATP SYNTHASE • This protein is an enzyme that makes these reactions happen: • ADP + Phosphate ATP • ATP ADP + Phosphate
  14. 14. Structure of an enzyme* • The function of an enzyme is determined by its structure. • Every enzyme has an active site (created as a byproduct of it’s quartenary structure) • The molecule to be changed (the reactant, called the substrate in the case of enzymes) in the reaction enters the active site • Active site is altered once the substrate is attached (aa’s within the active site may bond with atoms of the substrate) • The reaction occurs, and the products of the reaction are released from the active site along with the enzyme.
  15. 15. The Cycle of Enzyme-Substrate Interactions Fig. 6-11 The substrates, bonded together, leave the enzyme; the enzyme is ready for a new set of substrates The substrates and active site change shape, promoting a reaction between the substrates substrates active site of enzyme Substrates enter the active site in a specific orientation enzyme 1 3 2
  16. 16. Regulation of reactions • In the human body, reactions are SOMETIMES linked in sequences called metabolic pathways: an initial reactant molecule is modified by one enzyme, that product is then modified by another enzyme and so on. • EX: Glycolysis is the initial stage of the breakdown of glucose. Photosynthesis is a metabolic pathway that plants use to change H20 and CO2 into glucose.
  17. 17. Simplified Metabolic Pathways Fig. 6-12 PATHWAY 1 Initial reactant Intermediates Final products enzyme 1 enzyme 2 enzyme 3 enzyme 4 PATHWAY 2 enzyme 5 enzyme 6 A B D E F C G
  18. 18. Speed of reactions depends on amount of substrate, enzymes • The more substrate you have, the faster the given reaction will occur until all available enzymes are being used. • HOWEVER, our bodies can regulate the speed of a reaction (it’s not just substrate in, reaction happens)…HOW? By changing the rate at which enzymes are produced. (if our body doesn’t make enzymes, all of the substrate in the world doesn’t matter. The enzymes are required for the reaction to occur.) • WE MAKE ENZYMES (PROTEINS) VIA PROTEIN SYNTHESIS. MORE LATER. • So, our cells can actually “turn on” the production of enzymes when there is a lot of substrate, and “turn off” the production of enzymes when there is less substrate around. • Our bodies can also synthesize enzymes in an inactive form, so they will only “turn on” when they are activated. • We can also inhibit enzymes from catalyzing reactions.
  19. 19. Inhibition/Regulation of enzymes • Competitive Inhibition: a substance that is not the normal substrate for an enzyme can “sit” in the active site, thus inhibiting the normal substrate to enter • Noncompetitive inhibition: a substance binds to the enzyme (BUT NOT IN THE ACTIVE SITE) and the presence of this substance will cause the enzyme to not bind its normal substrate • Allosteric regulation: an enzyme can have 2 different configurations: an active and an inactive configuration depending on the presence of molecules that activate or inhibit the enzyme. These activators/inhibitors are often either the end product in the reaction OR intermediate products in a metabolic pathway.
  20. 20. (b) Competitive inhibition A competitive inhibitor molecule occupies the active site and blocks entry of the substrate Fig. 6-13b
  21. 21. noncompetitive inhibitor molecule (c) Noncompetitive inhibition A noncompetitive inhibitor molecule causes the active site to change shape, so the substrate no longer fits Fig. 6-13c
  22. 22. Allosteric Regulation of an Enzyme by Feedback Inhibition Fig. 6-14 enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5 isoleucine (end product) threonine (initial reactant) A B C D As levels of isoleucine rise, it binds to the regulatory site on enzyme 1, inhibiting it isoleucine enzyme 1 intermediates
  23. 23. Example of allosteric regulation/feedback inhibition • Metabolic pathway that makes isoleucine from threonine. 5 enzymes needed for this pathway, with 4 intermediate products. As amount of isoleucine increases, it will actually inhibit the first enzyme in the pathway. • EX #2: ATP can inhibit enzymes in the metabolic pathways that create it. (if too much ATP, no need to make more at the moment.)

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