CELLULAR RESPIRATION

(The process of converting glucose into ATP)

I. Overview Both autotrophs and heterotrophs break

down glucose to get energy. This energy is used to fuel life processes.

Review and be familiar with the following terms: Autotrophs Heterotrophs

1. ATP (adenosine triphosphate) ATP: A modified nucleotide molecule that

powers all cellular work directly. Its structure: adenine, ribose and three

phosphates are combined by dehydration synthesis

ATP molecules release phosphate groups to various other molecules. These molecules take in the phosphate by phosphorylation and get excess energy to perform various processes.

When ATP releases a phosphate + energy it produces ADP (adenosine diphosphate)

ADP can turn back to ATP by taking in a phosphate and energy by phosphorylation

2. Electron Carrier Molecules There are two different molecules that are

used to carry electrons and hydrogen ions to the last step cellular respiration.

NAD+ carries 2 electrons and a hydrogen ion at a time – NADH

FAD carries 2 electrons and two hydrogen ions at a time -- FADH

3. The Basics of Cellular Respiration Cellular respiration – releases energy by

breaking down glucose and other food molecules in the presence of oxygen.

6 O2 + C6H12O6 → 6 CO2 + 6 H2O + Energy Cellular respiration takes place in small steps to

minimize the loss of energy in the form of heat or light.

Processes that require oxygen to take place are called aerobic.

Processes that do not require oxygen to take place are anaerobic.

Cellular respiration consists of three major steps if oxygen is present: Glycolysis – in the cytoplasm The Krebs cycle (citric acid cycle) – in the

mitochondrion Oxidative phosphorylation – in the mitochondrion

Cellular respiration is a collection of enzyme catalyzed reactions of oxidation (the loss of electrons or hydrogen from an element, or the gain of oxygen) and reduction (the gaining of an electron, or hydrogen or losing oxygen by an element)

ATP molecules can be produced in two ways: Substrate level phosphorylation -- when

enzymes directly transfer phosphate to ADP during chemical reactions.

Oxidative phosphorylation – When ATP synthesis is fueled by creating a concentration difference of H ions between two sides of a membrane.

II. The Steps of Cellular Respiration – Glycolysis The process in which one molecule of glucose is

broken in half, producing two molecules of pyruvic acid.

This process will also produce 2 ATP and 2 NADH molecules.

ATP is used in other life processes NADH moves 2 electrons and 1 H+ per molecule

to the last step of cellular respiration The initial investment of 2 ATP molecules are

needed http://programs.northlandcollege.edu/biology/Biology1111/animations/glycolysis.html http://www.wwnorton.com/college/biology/discoverbio4/animations/main.aspx?chno=ch08p02a

III. Fermentation (an alternative if oxygen is not present) After glycolysis fermentation will take place if

oxygen is not present in the organism. Fermentation will recycle the used NADH into

NAD+. Fermentation forms a total of 2 ATP

molecules from one glucose.

Types of fermentation: Alcoholic fermentation – Yeast and other

organisms form alcohol and CO2 by the following process:

Pyruvic acid + NADH2 → CO2 + ethanol + NAD+

Lactic acid fermentation – Skeletal muscle cells of mammals and some bacteria produce lactic acid. Lactic acid is a harmful chemical than needs to be removed from the muscle cells:

Pyruvic acid + NADH2 → lactic acid + NAD+

http://www.wwnorton.com/college/biology/discoverbio4/animations/main.aspx?chno=ch08p02d

IV. The Krebs Cycle – The Second Step of Cellular Respiration Aerobic process that takes place in the matrix

of the mitochondrion. During this process, pyruvic acid is broken

down into carbon dioxide and ATP in a series of reactions.

Requirements: Electron carriers (NAD+, FAD) ADP molecules Enzymes

The first step of this process is to break down pyruvic acid into an acetyl group that binds with a Coenzyme-A the complex that is formed is called Acetyl-CoA. – This is called the intermediate step. This is not part of the citric acid cycle but comes before it.

Acetyl-CoA starts the Krebs cycle that will extract energy and electrons from organic molecules.

During the citric acid cycle, the carbon atoms from Acetyl – CoA form CO2 – released into the atmosphere

Hydrogen ions and electrons bind to NAD+ and FAD and move to the oxidative phosphorylation

1 ATP per cycle is also produced. The cycle takes place twice per glucose

V. Oxidative Phosphorylation NADH and FADH2 molecules from the Krebs

cycle pass their electrons through an electron transport chain. This uses the high energy electrons to convert ADP into ATP.

This process takes place on the inner membrane of the mitochondrion (cristae).

Requirements: 10 NADH, 2 FADH2 Enzymes 32 ADP Oxygen (from breathing)

Products: 6 H2O 32 ATP molecules

The movement of hydrogen ions from the matrix to the intermembrane space of the mitochondrion fuels the movement of high energy electrons and the production of ATP.

We are going to look at the picture on the next slide together and form the steps of the electron transport chain and oxidative phosphorylation together

http://vcell.ndsu.nodak.edu/animations/etc/movie.htm http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

VI. Comparing Aerobic Respiration and Fermentation While fermentation can take place without

oxygen and is a simpler process, it produces only 2 ATP molecules from glucose. It also produces some harmful chemicals (ethanol or lactic acid) that the body needs to break down.

Cellular respiration produces a total of 36 ATP molecules from one glucose. Other producs include CO2 and H2O that are released into the environment.

VII. Energy and Exercise When the body needs energy quickly, it starts

to break down the available ATP molecules, than glucose. If oxygen is not present fermentation will take place. If enough oxygen is present in the cell, cellular respiration takes place.

If enough glucose is not available, the body starts to break down the stored glycogen than fats finally proteins.