Transfer of Energy and Materials in an Ecosystem

Complete oxidation of glucose in aerobic conditions yields large quantities of energy Reaction takes place in a series of small, energy yielding steps Each step releases a small quantity of total available energy Multi-step reactions allow precise control –Feedback mechanisms One cell would be unable to harness all energy (explosive!) made in the oxidation of glucose if it were all released at one Cellular Respiration Full “oxidation of glucose” yields carbon dioxide and water has a very high energy yield

Very stable High activation energy…. –What does this mean? Large amount of energy required to begin breaking up glucose… How do living things over come this obstacle? Two ways: 1.Enzymes help LOWER activation energy (sound familiar???) that it takes to break down glucose (initially) 2.Energy level of glucose is RAISED by phosphorylation (adding a phosphate from ATP to glucose) A little bit about Glucose…. OXIDATION of Glucose

Phosphorylation is a chemical process in which a phosphate group (PO 4 3- ) is added to a compoundchemical process process involved in : –protein synthesis –production of adenosine triphosphate (ATP) Plays crucial role in various chemical signaling and regulatory mechanisms within the cell –modifies the structure of various proteins and altering their activities Phosphorylation

Oxidative-phosphorylation –Metabolic pathway in which the mitochondria in cells use their structure, enzymes, and energy released by the oxidation of nutrients to reform ATP –Electron transport chain –Chemosmosis Substrate-level phosphorylation – type of metabolic reaction –results in the formation of adenosine triphosphate (ATP) or guanosine triphosphate (GTP) by the direct transfer and donation of a phosphoryl (PO 3 ) group to adenosine diphosphate (ADP) or guanosine diphosphate (GDP) from a phosphorylated reactive –the synthesis of ATP by reactions in which ADP is one of several substrates and ATP is one of several products of an enzyme catalyzed reaction Types of Phosphorylation

Theoretically: –Energy released from each step of cell resp. could be harnessed for the cell to perform “WORK” Realistically: –Flexible system –Energy released from each step of cell resp. is used to make intermediary molecule ATP What does this stored energy in Glucose tell us?

ATP: Adenosine Triphosphate

Adenosine Triphosphate (ATP) –Remove a Phosphate group –Releases energy (30.5kJmol -1 ) and makes… Adenosine diphosphate (ADP) –Remove a Phosphate group –Releases energy (30.5kJmol -1 ) and makes… Adenosine monophosphate (AMP) –Remove last Phosphate group –Releases energy (14.2kJmol -1 ) and leaves only adenosine (adenine and nitrogenous base) ATP

Bonds attaching two OUTER phosphates are HIGH-ENERGY bonds –More Energy is released when broken than the last phosphate –Not a good description though (i.e. do not use on exam) –“Energy does not simply come from breaking those bonds but rather from changes in chemical potential energy of all parts of the system” –Cambridge Biology Course Book 4 th Edition ATP

Interconversion of ATP and ADP is the most important part of providing energy in the cell Rate of Interconversion (turnover) –Enormous –Human at rest uses 40 kg of ATP in 24 hours –At any given time, there is only 5 g of ATP (b/c it is being constantly converted into ADP…it’s being used) –Strenuous exercise: –ATP breakdown as much as 0.5 kg per minute

ATP is the universal intermediary molecule between energy=-yielding and energy- requiring reactions in a cell “Energy currency” of cell Why is ATP a good molecule to use in comparison to other intermediates? 1.Readily hydrolyzed 2.Easily transported –Small –Water soluble

Inefficient Some energy during E transfer is always converted to thermal energy Thermal energy is lost Energy made available does NOT always correspond with the energy needed to make ATP Excess energy converted to thermal energy Some reactions in cell use less energy than what is released by hydrolysis of ATP to ADP Energy Transfer in living organisms

These molecules are short-term or long-term storage of CHEMICAL POTENTIAL ENERGY –Glucose/Sucrose (short) –Glycogen/Starch/Triglycerides (long) Molecules used as ENERGY STORAGE This molecule acts as immediate DONOR of ENERGY to the cells’ energy-requiring reactions Molecules used as ENERGY CURRENCY Important Distinction!

Most ATP generated this way This energy is harnessed from the transfer of electrons by electron carriers in the mitochondria and chloroplast Stored as difference in proton (H+ ion) concentration across phospholipid membranes in mit. & chlorp. –Phospholipid membrane is impermeable to hydrogen ions –How do they move across??? Electrical Potential Energy (ETC) Some ATP generated this way The process of glycolysis and Krebs cycle involve rearrangement of chemical bonds –Chemical potential energy Rearrangement results in production of ATP Glycolysis and Krebs Cycle (The Citric Acid Cycle…TCA) Energy for ATP Synthesis

Chemosmosis (proposed by Peter Mitchell 1961) Facilitated diffusion Move from high concentration of H+ ions to low concentration of H+ ions through a transmembrane protein –Part of protein acts as enzyme, synthesizing ATP –“ATP Synthase” –Transfer of 3 protons = production of 1 ATP molecule –ATP is only made if ADP and inorganic phosphate is available inside organelle How Protons (H+) Move Across Membrane

Three binding sites for protons (H+ ions) Rotating portion, gamma ( γ) –Rotates as hydrogen ions pass through –Results in structural changes in binding sites –Allow binding sites to pass through 3 sequential phases: 1.Binding ADP to Pi 2.Forming tightly bound ATP 3.Releasing ATP ATP Synthase

Role of ATP in Active Transport Active transport –Movement of molecules or ions across a partially permeable membrane AGAINST a concentration gradient –Energy needed –ATP required –Counteracts tendency of molecules to want to move down the concentration gradient

Evident in ALL cells 50% of ATP in resting animal is used to maintain ionic contents of cell via sodium-potassium pump (  click for video) sodium-potassium pump Especially in concentration of sodium (Na+) ions and potassium (K+) ions, inside the cell with respect to the surrounding solution Sodium-Potassium Pump –Transmembrane protein that acts as an ATPase –Catalyzes the hydrolysis of ATP to ADP and an inorganic phosphate –Releases energy to drive the Na-K pump Differences in Ion Concentration

 Found on Cell surface membranes  Pump sodium OUT of the cell  Coupled with ability to pump potassium INTO cell from surrounding solution  Binding sites for sodium ions AND for ATP on inner side  Binding site for potassium ions on the outside  When ATP attaches, it results in changes in the shape of the protein  This change moves Na and K ions across membrane in OPPOSITE directions  1 ATP used moves 2 potassium ions INTO cell and 3 sodium ions OUT of cell  This unequal movement of ions creates a potential difference across the membrane  The inside of the cell membrane is negative with respect to the outside  Sodium and potassium ions leak back across membranes, down concentration gradients  increase potential difference across membrane  More potassium channels than sodium channels so Potassium diffuses out of cell much faster than sodium diffusing into the cell Sodium-Potassium Pump

Resting potential of nerve cells –Difference between electric potential inside the nerve cell compared to the outside Specialized to have exaggerated potential difference across cell membrane This is how nerve cells relay signals Large resting potential (potential difference) is due to Sodium- Potassium Pumps Nerve Cells

Work with a partner Create a 2D model (ie on poster) of adenine and each of the following: –ATP –ADP –DNA –RNA Create a 3D model of each of the above structures –Create a color coded key for each atom in your molecule –Use marshmellows, markers, dry erase boards Create a Flipagram showing hydrolysis of ATP to ADP using 3D model ATP Activity