Cellular Respiration: The Release of Energy in Cells

Cellular Respiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cells need energy to carry out activities Muscles need energy to contract (or to relax) Neurons need energy to transmit impulses Cells get their energy from breaking down absorbed molecules in a process called: CELLULAR RESPIRATION

How do Cells Get Energy? Cells obtain energy by breaking the chemical bonds of glucose Covalent bonds between atoms = stored energy One glucose molecule yields as many as 38 ATP molecules

What is ATP? Adenosine Tri Phosphate A nucleotide A molecule that serves as an energy carrier – Carries energy in useable amounts – Is transported to wherever energy is needed to perform reactions in cell High energy bonds between phosphates store chemical energy

How Does ATP Store and Release Energy? Energy is stored when a third phosphate is attached to ADP – adenosine di phosphate, forming ATP Energy is released when the bond between the last two phosphates is broken, making ADP The ADP can be used to make another ATP ADP

ADP + Phosphate  ATP stores energy ATP  ADP +Phosphate releases energy

Two ways to Release Chemical Energy from Molecules Series of reactions called metabolic pathways Aerobic Respiration – Requires oxygen – Makes as many as 38 ATP Anaerobic Respiration – Does not require oxygen – Makes only 2 additional ATP

Aerobic Respiration ATP production begins in the cytoplasm continues in the mitochondria

Aerobic Respiration Reaction Glucose + Oxygen + 38 ADP + inorganic phosphate Yields Carbon Dioxide + Water + 38 ATP Formulas: C 6 H 12 O 6 + O ADP + 38Pi CO 2 + H 2 O + 38 ATP Reactants Products Pi = inorganic phosphate

Oxidation - removal of electrons from a molecule Reduction - addition of electrons to a molecule a hydrogen atom is usually also transferred The breakdown of glucose is an Oxidation- Reduction reaction Oxidation-Reduction Reactions

Coenzymes Carry Electrons Two Coenzymes are used to carry electrons from one part of the reaction to another: – NAD+ (nicotinamide adenine dinucleotide) – FAD+ (flavine adenine dinucleotide) They receive the hydrogen atoms removed from glucose along with the electrons –NAD + becomes NADH –FAD + becomes FADH 2

What are the Steps in Aerobic Respiration? There are four main phases:Glycolysis glucose (6 C) splits into two 3-carbon molecules Preparatory reaction each 3-carbon molecule divides into a 2-carbon molecule and CO 2 Citric acid cycle (or Krebs cycle) CO 2, NADH, FADH 2, and ATP produced Electron transport chain + Oxidative Phosphorylation largest amount of ATP produced

Step 1: Glycolysis Occurs in the cytoplasm Glucose is broken into two three carbon molecules called pyruvate No oxygen is required Occurs in aerobic and anaerobic respiration Glucose (6 C)  2 Pyruvate (3 C)

Step 1: Glycolysis Investment Stage: Two ATP are used to begin the reaction NADH is made from NAD by transfering electrons from glucose Payoff Stage: Four ATP are Produced (NET of 2 ATP)

Step 2: Preparatory Reactions Occurs in the MATRIX of a Mitochondria Pyruvate enters the mitochondria matrix 1. Pyruvate (C3) is oxidized into an acetyl group (C2) and one carbon dioxide (CO 2 ) molecule is released 2. Electrons are picked up by NAD NAD + + H  NADH 3. The acetyl group is attached to coenzyme A producing acetyl CoA

Preparatory Reactions

Citric Acid Cycle Occurs in mitochondria matrix. Final steps to break down glucose Acetyl CoA attaches to a 4 carbon molecule then is broken down Krebs Cycle Products: 2 CO 2, 4 NADH, 6 FADH 2, and 2 ATP

Each NADH is converted to 3 ATPs 2 from glycolysis, 2 from preparatory reaction, 6 from Krebs cycle 10 x 3 = 30 Each FADH 2 is converted to 2 ATPs 2 x 2 = 4 A total of 34 ATP’s will be produced in this step Electron Transport Chain Most of the ATP is created in this step Occurs on the cristae (inner membrane) of the mitochondria

Intermembrane space How Does the Electron Transport Chain Work? H+ from the matrix is actively transported into the intermembrane space, creating a concentration gradient The H+ ions are then allowed to diffuse back across the membrane turning an ATP generator

High energy electrons released by NADH or FADH 2 are transported from carrier to carrier in the membrane. Each transfer releases enough energy to pump H+ across the membrane. Finally electrons are handed off to – O 2 - the final electron carrier (this is the aerobic part) The oxygen combines with H+ to make - (ta da!) Water

The concentration gradient of H + will be used to produce ATP Passive transport (diffusion) activates ATP synthase for ATP synthesis

What are the reactants and products of each step? Recap of Reactants and Products StageReactantsProducts Glycolysis Glucose, 2 ATP, 4 ADP, NAD + Pyruvate, 4ATP, NADH Preparatory Reaction Pyruvate, NAD, CoAAcetyl CoA, CO 2, NADH Citric Acid Cycle Acetyl CoA, NAD, FAD+, ADP CO 2, NADH, FADH 2, 2 ATP Electron Transport NADH, FADH2, O2H2O, 34 ATP

How many ATP molecules are produced in each step? GlycolysisNet 2 Preparatory Reactions 0 Citric Acid Cycle 2 Electron Transport Chain 34

Anaerobic Respiration Glycolysis will occur (it’s anaerobic) in the cytoplasm Only 2 ATPs generated Pyruvate is broken down by fermentation Fermentation does not generate more ATP Two main types of fermentation: lactic acid fermentation alcohol fermentation

Lactic Acid Fermentation : Glucose + 2 ADP  Lactic Acid + 2 ATP Occurs: In certain bacteria Human muscle cells: when used strenuously, not enough O 2 can be supplied cells switch from aerobic to anaerobic to keep working; lactic acid buildup causes fatigue, cramps Anaerobic Respiration

Alcoholic fermentation: Glucose + 2 ADP  Ethyl alcohol + CO ATP Performed by yeasts (kind of fungi) in bread making, alcohol brewing Anaerobic respiration

Aerobic vs. Anaerobic Respiration Aerobic Anaerobic Needs Does not need 38 2 More steps Faster energy CO2 + H2O Lactic acid or alcohol and CO2 Oxygen ATP Produced Processing End products Location Cytoplasm & Mitochondria Cytoplasm