Cellular Respiration Chapter 4.2

Objectives Describe Metabolism Describe the role of ATP and how it functions Understand what goes on during the three stages of aerobic cellular respiration that lead to the production of ATP: glycolysis, Krebs cycle, and the electron transport chain Recognize and explain the summary equation for aerobic cellular respiration

Objectives continued Describe the location and structure of mitochondria. Understand its function in cellular respiration Summarize the reactions of glycolysis (what goes on) Describe the role of Oxygen in the electron transport chain Be able to describe fermentation Recognize that multiple energy sources can “fuel” cellular respiration

Metabolism The sum of all the chemical processes occurring in an organism at one time Concerned with the management of material and energy resources within the cell Reactions can break down big molecules into smaller units or build larger molecules from smaller components

Anabolic (Biosynthetic) Pathways Pathways that consume energy to build larger, complicated molecules from simpler ones Polymerization Photosynthesis 6CO 2 +6H light  C 6 H O 2 Carbon dioxide, a low energy molecule, gets converted into carbohydrate, a high energy molecule

Catabolic Pathways Pathways that release energy by breaking down complex molecules into simpler compounds Cellular respiration C 6 H O 2  6CO 2 +6H ENERGY Carbohydrate, a high energy molecule, gets “digested” into carbon dioxide, a low energy molecule Cells use released energy to make ATP

ATP Energy molecule used to shuttle energy between catabolic and anabolic reactions Energy is released from ATP through the loss of phosphate groups Nucleotide with three phosphate groups attached to the ribose sugar

ATP Energy is released from ATP through the loss of phosphate groups

Phosphorylation When ATP gives a phosphate group to another molecule it is called phosphorylation Phosphorylated molecules have “more” energy and can do the work of the cell How do we make ATP? Cellular Respiration

What is cellular respiration? Cellular Respiration : the making of ATP through the breakdown of foods Aerobic Cellular Respiration Fermentation

Three Stages of Aerobic Cellular Respiration Aerobic cellular respiration has 4 steps –Glycolysis in cytosol –Kreb’s cycle in mitochondrial matrix –Electron Transport Chain at inner membrane of mitochondria C 6 H O 2  6CO 2 +6H ENERGY

Structure of the Mitochondria Organelle with an outer and inner membrane The Krebs cycle takes place in the matrix of the mitochondria –space bordered by the inner membrane Electron Transport Chain takes place across the inner membrane –between the matrix and intermembrane space This organelle produces the majority of ATP for the cell.

Glycolysis This part of cellular respiration takes place in the cell cytoplasm Each Glucose molecule gets converted into 2 pyruvate molecules Energy requiring and energy releasing steps Energy net yield is 2 ATP and 2 NADH Enzymes help along the way

Krebs Cycle Each pyruvate (carbohydrate) molecule is completely oxidized into carbon dioxide Energy released from these reactions results in the formation of 1 ATP molecule but 3 NADH molecules Collectively, 2 ATP and 6 NADH are made from the 2 pyruvates. NADH will be used in the electron transport chain.

Electron Transport Chain Uses NADH During the electron transport chain, H + is moved against a gradient. The energy needed to do this is supplied by electrons carried by NADH

What happens along the inner membrane of the mitochondria? The loss of electrons from NADH result in the addition of energy to protein pumps in the memebrane resulting in a H + being moved from the inside to the outside of the inner membrane This happens many times creating an imbalance (gradient) of H +. Oxygen pulls electrons to keep them moving.

What happens along the inner membrane of the mitochondria? ATP is made as H+ ions are allowed back into the matrix of the mitochondria by a different protein (ATP synthase). The energy released by the “rush” of H + is used by this enzyme to make ATP (kind of like a rush of water in a stream being used to turn a water wheel). Ultimately, aerobic respiration produces ~36 ATP molecules from each individual glucose molecule.

Why do we need oxygen? Oxygen is required by any organism that has mitochondria because it is used to keep the Electron Transport Chain running Oxygen pulls of electrons from the chain and combines with 2 H + to form H 2 0

What if we did not have oxygen? Without trees and bacteria to make oxygen, we would still be able to make ATP from sugar (just not as much) Modifications of glycolysis called fermentation reactions are used to release energy

Fermentation Reactions These reactions produce only 2 ATP per glucose molecule and must regenerate NAD + resulting in the formation of either: 1Ethanol and CO 2 or 2Lactic Acid.

What about other foods? Proteins, Carbs and Fats can all be utilized for energy following hydrolysis Amino Acids are converted to intermediates including pyruvate, 2-, and 4-carbon molecules Carbs enter glycolysis at the beginning or in the middle Fats components –glycerol enters as 3-carbon molecule –Fatty acids enter as 2-Carbon molecules