Chapter 9 Cellular Respiration: Harvesting Chemical Energy
MST Biology Notes Janet Li 1/24/2005
~ Energy enters most ecosystems in the form of sunlight
~ Cells harvest energy stored in cells:
• W/ help of enzymes – cell degrades molecules rich in potential energy to simpler waste products that have less energy
• Energy taken out of chemical storage can be used to do work; rest is dissipated with heat
~ catabolic process – fermentation – partial degradation of sugars that occurs without the help of oxygen.
~ Cellular respiration – oxygen is consumed as a reactant along with the organic fuel.
• In eukaryotic cells, mitochondria houses metabolic equipment for ^.
• Food is fuel for respiration – the exhaust is carbon dioxide and water:
Organic + Oxygen Carbon + Water + Energy
~ carbohydrates, fats, and proteins call be processed & consumed as fuel. Traditional to track down degradation of glucose (C6H12O6) to learn steps of cellular respiration:
C6H12O6 + 6 CO2 6 CO2 + 6 H2O + Energy (ATP + Heat)
~ Catabolic pathways don’t directly move flagella, pump solutes, polymerize monomers…
ATP & CELLULAR WORK: A REVIEW
~ ATP – adenosine triphosphate – central character in cellular energetics.
CHEMICAL BACKGROUND: RESPIRATION AS AN OXIDATION-REDUCTION PROCESS
~ In many chemical reactions, there is a transfer of one or more electrons from one reactant to another which is call oxidation-reduction reactices, or redox reactions.
• the loss of electrons from one substance is called oxidation
• addition of electrons to another substance is known as reduction
• electron donor – reducing agent
• electron acceptor – oxidizing agent
~ Some reactions change the degree of electron sharing in covalent bonds.
~ Energy must be added to pull an electron away from an atom
~ ^ electronegative the atom, ^ more energy is required to keep electron away from it.
~ electron loses potential energy when it shifts from a less electronegative atom toward a more electronegative one
~By oxidizing glucose, respiration takes energy out of storage; for ATP synthesis
~Electrons extracted from food are usually transferred first to NAD+, then reducing the compound to NADH
~NADH passes these electrons to an electron transport chain. The chain conducts the electrons to oxygen in a series of steps that release energy.
- oxidative phosphorylation uses this energy to make ATP
~ NAD+ traps electrons from glucose and other fuel molecules:
1) dehydrogenases (enzymes) remove a pair of hydrogen atoms from the substrate
2) Removal of two electrons and two protons. The enzyme delivers the two electrons and one proton to NAD+… the other proton is released as a hydrogen ion (H+)
| Dehydrogenase |
H –C – OH + NAD+ ________________________> C = O + NADH + H+
~Electrons lose little potential energy when transferred by dehydrogenases from food to NAD+…. Thus, NADH molecule fromed during repirations represents stored energy
~ In cellular respiration, an electron transport chain breaks the “fall” of electrons in this reaction into a series of smaller steps and stores some of the released energy in a form that can be used to make ATP (the rest of the energy is released as heat).
- the chain consists of mostly proteins built into inner membranes of mitochondria
- small steps until the carrier molecules cascade down the change to oxygen, the terminal electron acceptor.
- What keeps the electrons moving? Each carrier has a greater affinity for electrons than its “uphill” neighbor. At the bottom of the chain is oxygen which has a great affinity for electrons.
AN OVERVIEW OF cELLLULAR RESPIRATION
> glycolysis – occurs in the cytosol – begins degradation by breaking glucose into two molecules of pyruvate:
- glycolysis – “splitting of sugar” - glucose, a six-carbon sugar is split into two three-carbon sugars.
~ The cell spends ATP to phosphorylate the fuel molecules.
- consists of ten steps that occurs right outside of mitochondria.
- Two molecules of ATP are consumed as glucose is split into two molecules of glyceraldehydes phosphate.
- the conversion of these molecules to pyruvate produces two NADH and four ATP by substrate-level phosphorylation.
~ For each molecule of glucose, glycolysis yields a net gain of two ATP and two NADH
lub you all... hope this is helpful in a way.