Cellular Respiration:
The Release of Energy in Cells
Cellular Respiration
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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 RespirationATP production • begins in the
cytoplasm• continues in
the mitochondria
Aerobic Respiration ReactionGlucose + Oxygen + 38 ADP + inorganic phosphate Yields
Carbon Dioxide + Water + 38 ATP
Formulas:
C6H12O6 + O2 + 38ADP + 38Pi
CO2 + H2O + 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 FADH2
What are the Steps in Aerobic Respiration?
There are four main phases:Glycolysis • glucose (6 C) splits into two 3-carbon moleculesPreparatory reaction • each 3-carbon molecule divides into a 2-carbon
molecule and CO2
Citric acid cycle (or Krebs cycle) • CO2, NADH, FADH2, 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: GlycolysisInvestment 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 ReactionsOccurs 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 (CO2) molecule is released
2. Electrons are picked up by NADNAD+ + H NADH
3. The acetyl group is attached to coenzyme A
producing acetyl CoA
Preparatory Reactions
Citric Acid CycleOccurs 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 CO2, 4 NADH, 6 FADH2, 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 FADH2 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 stepOccurs 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 FADH2 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 – O2 - 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
Stage Reactants Products
Glycolysis Glucose, 2 ATP, 4 ADP, NAD +
Pyruvate, 4ATP, NADH
Preparatory Reaction
Pyruvate, NAD, CoA Acetyl CoA, CO2, NADH
Citric Acid Cycle
Acetyl CoA, NAD, FAD+, ADP
CO2, NADH, FADH2, 2 ATP
Electron Transport
NADH, FADH2, O2 H2O, 34 ATP
How many ATP molecules are produced in each step?
Glycolysis Net 2Preparatory Reactions 0Citric Acid Cycle 2Electron Transport Chain 34
Anaerobic RespirationGlycolysis 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 O2 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 + CO2 + 2 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
