Cellular RespirationHarvesting Energy From Food

Chapter 7

Obtaining FoodAll organisms need food for energy and building materials. Biologists classify organisms according to how they obtain food.

Autotrophs are organisms such as a plant that makes its own food. For example, during photosynthesis plants use the sun's energy to convert water and carbon dioxide into sugars. Autotrophs are also called producers.

Heterotrophs are organisms that cannot make their own food, such as humans, meaning "other eaters." Heterotrophs are also called consumers.

Energy flow occurs through the ecosystem

The products of photosynthesis are the chemical ingredients for cellular respiration, while the products of cellular respiration are the chemical ingredients for photosynthesis.

Principles of Energy Harvest

Chemical Energy

Just like the molecules in gasoline and other fuels, organic compounds are a form of potential energy called chemical energy.

The stored chemical energy of foods such as peanuts can be released through cellular respiration.

Introduction to Energy

Energy is the ability to do work.

Can you identify examples of these forms of energy?

kinetic energy: energy of motion

potential energy: energy stored due to an object's position or arrangement

Putting Chemical Energy to Work

Potential energy is converted to Kinetic energy

Calories: Units of Energy

calorie: amount of energy required to raise the temperature of 1 g of water 1°C.

The "calories" shown on a food label are actually kilocalories. One kilocalorie (kcal) equals 1,000 calories.

What factors contribute to the energy (calorie) needs of a person?

ATP provides the energy for cellular work

ATP: (adenosine triphosphate) main energy source that cells use for most of their work

An ATP molecule contains potential energy, much like a compressed spring. When a phosphate group is pulled away during a chemical reaction, energy is released.

The ATP Cycle

ATP is constantly recycled in your cells. A working muscle cell recycles all of its ATP molecules about once each minute. That's 10 million ATP molecules spent and regenerated per second!

ATP powers cellular work by coupling energy releasing to energy using reactions

ATP + H2O ADP + P

ATP and Cellular Work

Cells perform three main types of work: chemical work, mechanical work, and transport work.

The transfer of the phosphates from ATP forming ADP provides the energy.

Relationship of Cellular Respiration to Breathing

Cellular respiration is an aerobic process, meaning that it requires oxygen

Breathing supports cellular respiration by providing the body with oxygen and removing carbon dioxide.

Overall Equation for Cellular Respiration

In cellular respiration, the atoms in glucose and oxygen are rearranged, forming carbon dioxide and water. The cell uses the energy released to produce ATP.

Cellular respiration breaks down organic molecules to yield energy.

Energy stored in organic compounds is released in a series of enzymes controlled reactions. Similar to burning but…

"Falling" Electrons as an Energy Source

Food represents a source of high energy electrons similar to the potential energy of being on top of a slide.

When the electrons pass from the high potential state of food to oxygen, released energy is converted to other forms of energy.

How does burning compare to cellular respiration?

When sugar is burned, oxygen atoms pull electrons from carbon and hydrogen, forming new chemical bonds. Burning releases energy in the form of heat and light.

Burning Compared to Cell Respiration: The energy release is controlled by enzymes and carrier molecules in a series of steps.

Electron Transport Chains

Compared with burning, cellular respiration is a more controlled. Energy is released from glucose in small amounts that cells can put to productive use—the formation of ATP molecules.

In Eukaryotic Cells, the reaction of Aerobic Respiration occur Inside MITOCHONDRIA.

Structure of Mitochondria

Mitochondria are found in almost all eukaryotic cells. Its structure is key to its role in cellular respiration.

Its complex folding pattern of membranes and spaces allows for many sites where reactions can occur.

Respiration involves glycolysis, the Krebs cycle, and electron transport

Stage I: Glycolysis

The first stage in breaking down a glucose molecule, called glycolysis (splitting sugar), takes place outside the mitochondria in the cytoplasm of the cell.

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

The energy input and output of glycolysis.

Concentrate on the totals, not the details!

Glycolysis movie

Stage 2: The Krebs Cycle

The Krebs cycle finishes the breakdown of pyruvic acid molecules to carbon dioxide, releasing more energy in the process. The enzymes for the Krebs cycle are dissolved in the fluid matrix within a mitchondrion's inner membrane.

Kreb’s Cycle:

Where does this occur?

Identify the products.

Kreb’s Cycle movie

Stage 3: Electron Transport Chain and ATP Synthase ActionThe final stage occurs in the inner membranes of mitochondria. This stage has two parts: an electron transport chain and ATP production by ATP synthase

 The inner mitochondrial membrane couples electron transport to ATP synthesis.

The Pathway of Electron Transport

This energy change is used to “pump” hydrogen to the inner membrane space creating a gradient which can power cell processes.

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Chemiosmosis couples the electron transport chain to ATP synthesis

Chemiosmosis: The Energy-Coupling Mechanism

ATP synthase protein complex functions as a mill, powered by the flow of hydrogen ions.

This complex resides in mitochondrial and chloroplast membranes of eukaryotes and in the plasma membranes of prokaryotes..

The gradient of hydrogen ions “pushes” the ATP synthesis.

Animation of ATP synthesis in Mitochondria

Copyright 1997. Thomas M. Terry, The University of Connecticut

Cellular respiration generates many ATP molecules for each sugar molecule it oxidizes

During respiration, most energy flows in this sequence:

Glucose NADH electron transport chain protonmotive force ATP

Harvesting Energy without Oxygen

Fermentation in Human Muscle Cells

When your lungs and bloodstream can't supply oxygen fast enough to meet your muscles' need for ATP. Your muscle cells use fermentation, to make ATP without using oxygen.

How does the energy production of Lactic Acid fermentation compare to aerobic respiration?

Lactic Acid fermentation occurs in animal cells deficient in oxygen

Lactic Acid Fermentation movie

Fermentation in Microorganisms

Yeast (a microscopic fungus) is capable of both cellular respiration and fermentation.

Fermentation in yeast produces ethyl alcohol. The carbon dioxide that is released during fermentation creates bubbles and pockets that make bread rise. The alcohol evaporates during baking.

Fermentation enables some cells to produce ATP without the help of oxygen. Alcoholic fermentation occurs in yeast.

Alcoholic Fermentation movie

Pyruvate as a key juncture in catabolism. Glycolysis is common to fermentation and respiration.

How does the net gain of ATP compare in aerobic vs. fermentation?

The catabolism of various food molecules. Carbohydrates, fats, and proteins can all be used as fuel for cellular respiration.