cellresp

cellresp - CELLULAR RESPIRATION Cellular respiration and...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
CELLULAR RESPIRATION Cellular respiration and fermentation are catabolic, energy-yielding pathways Organic compounds store energy in their arrangement of atoms. With the help of enzymes, a cell systematically degrades complex organic molecules that are rich in potential energy to simpler waste products that have less energy. Some of the energy taken out of chemical storage can be used to do work; the rest is dissipated as heat. As you learned in Chapter 6, metabolic pathways that release stored energy by breaking down complex molecules are called catabolic pathways. One catabolic process, fermentation, is a partial degradation of sugars that occurs without the help of oxygen. However, the most prevalent and efficient catabolic pathway is cellular respiration, in which oxygen is consumed as a reactant along with the organic fuel. In eukaryotic cells, mitochondria house most of the metabolic equipment for cellular respiration. Although very different in mechanism, respiration is in principle similar to the combustion of gasoline in an automobile engine after oxygen is mixed with the fuel (hydrocarbons). Food is the fuel for respiration, and the exhaust is carbon dioxide and water. The overall process can be summarized as follows: Although carbohydrates, fats, and proteins can all be processed and consumed as fuel, it is traditional to learn the steps of cellular respiration by tracking the degradation of the sugar glucose (C 6 H 12 O 6 ): This breakdown of glucose is exergonic, having a free-energy change of -686 kcal (-2,870 kJ) per mole of glucose decomposed (DG = -686 kcal/mol); recall that a negative DG indicates that the products of the chemical process store less energy than the reactants. Catabolic pathways do not directly move flagella, pump solutes across membranes, polymerize monomers, or perform other cellular work. Catabolism is linked to work by a chemical drive shaft: ATP. The processes of cellular respiration and fermentation are complex and challenging to learn. Therefore, as you study this chapter, it will help you to keep in mind your main objective: discovering how cells use the energy stored in food molecules to make ATP.
Background image of page 2
Cells recycle the ATP they use for work The molecule known as ATP, short for adenosine triphosphate, is the central character in bioenergetics. Recall from Chapter 6 that the triphosphate tail of ATP is the chemical equivalent of a loaded spring; the close packing of the three negatively charged phosphate groups is an unstable, energy-storing arrangement (because like charges repel each other). The chemical "spring" tends to "relax" by losing the terminal phosphate (see FIGURE 6.8). The cell taps this energy source by using enzymes to transfer phosphate groups from ATP to other compounds, which are then said to be phosphorylated. Phosphorylation primes a molecule to undergo some kind of change that performs work, and the molecule loses its phosphate group in the process (FIGURE 9.2). The price of most cellular work, then, is the conversion of ATP to ADP and inorganic
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 21

cellresp - CELLULAR RESPIRATION Cellular respiration and...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online