Cellular Respiration How do living things release energy from the foods they consume or produce?

Cellular Respiration

How do living things release energy from the foods they consume or

produce?

Objectives

Compare the reactants and products of photosynthesis and cellular respiration in terms of energy and matter (TEKS 9B)

• What is cellular respiration?• Describe what happens during the process of

glycolysis.• Describe what happens during the Krebs cycle• Explain how high-energy electrons are used by the

electron transport chain• Compare photosynthesis and cellular respiration

Cellular Respiration

Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.

Cellular Respiration-Overview

There are 3 major steps to cellular

respiration:

1. Glycolysis2. Krebs cycle3. Electron

Transport Chain

Objectives





Chemical Energy and Food

How much energy is actually present in food?

Quite a lot. 1 gram of glucose when burned in the presence of oxygen can release 3811 calories of heat energy

A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius.

The “Calorie” used on food labels is actually a kilocalorie or 1000 calories.

Cellular Respiration- Glycolysis

• Cells don’t “burn” glucose. They gradually release the energy from glucose and other food compounds.

• This process begins with glycolysis.• Glycolysis is the process in which 1 molecule of

glucose (a 6-carbon compound) is broken in half, producing 2 molecules of pyruvic acid (a 3-carbon compound).

Cellular Respiration- Glycolysis

• Glycolysis occurs in the cytoplasm of a cell.• 2 ATP molecules are used to get the process

going.• 4 ATP molecules are produced at the end of

glycolysis This means the cell, overall, gains 2 ATP

molecules from this process.• NAD+ is an electron carrier used to carry 4

high-energy electrons (turns into NADH) to the electron transport chain

• Glycolysis is very fast. Cells can produce thousands of ATP molecules in just a few milliseconds.

• No oxygen is needed (Anaerobic). This means that cells can supply chemical

energy to cells even when oxygen isn’t available

Glycolysis-FermentationIf oxygen is NOT present, glycolysis is followed by a process called fermentation instead of the Krebs cycle and the electron transport chain.

Fermentation releases energy from food molecules by producing ATP in the absence of oxygen.

Produces much less ATP than if oxygen were present; only 2 ATP total, whereas aerobic cellular respiration can produce up to 38 ATP molecules.

It is an anaerobic process because it does not require oxygen.

Glycolysis-Fermentation

Two types of fermentation:

Lactic acid fermentation – Occurs in muscle cells (makes muscles tired)

Alcohol fermentation - Occurs in yeast and a few other microorganisms to

make ethyl alcohol

Objectives





Cellular Respiration – The Krebs Cycle

• At the end of glycolysis, about 90% of the chemical energy available in glucose is still unused.

• Oxygen is one of the most powerful electron acceptors.

• Since the remaining pathways of cellular respiration require oxygen, they are aerobic.

• The Krebs cycle (also called the citric acid cycle) is the step that follows glycolysis when oxygen is present.

• During the Krebs cycle, pyruvic acid is broken down into CO2 in a series of energy-extracting reactions.

The Krebs Cycle - Summary

• Takes place in matrix of mitochondria

• Requires Oxygen (Aerobic)• Cyclical series of oxidation

reactions that give off CO2 and produce one ATP per cycle

• Turns twice per glucose molecule

• Produces two ATP • Each turn of the Krebs Cycle

also produces 3NADH, 1FADH2, and 2CO2

• Therefore, For each Glucose molecule, the Krebs Cycle produces 6NADH, 2FADH2, 4CO2, and 2ATP

Pyruvic acid enters the

mitochondrion1 carbon atom from

pyruvic acid becomes part of a CO2 molecule

The other 2 carbons combine with coenzyme A to form acetyl-CoA Acetyl-CoA then

combines with a 4-carbon

compound to form citric acid

Citric acid is broken down , releasing more CO2, and electrons are transferred to energy carriers (NAD+ and FAD)

All the high-energy electrons in carriers

(NADH and FADH2) are then transported to

the electron transport chain where huge

amounts of ATP can be made.

2 ATP molecules are produced during the Krebs cycle

Objectives





Cellular Respiration- The Electron Transport

ChainThe electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.

Overview:• Occurs Across Inner

Mitochondrial membrane• 34 ATP Produced• H2O Produced• Uses coenzymes NAD+ and

FAD+ to accept e- from glucose• NADH = 3 ATP’s• FADH2 = 2 ATP’s

A. High-energy electrons from NADH and FADH2 are passed along the electron transport chain.

At the end of the chain is an enzyme that combines these electrons with hydrogen ions (H+) and oxygen to form water.

B. For every 2 high-energy electrons, their energy is used to transport H+ across the membrane. H+ build up in the intermembrane space making it positively charged.

C. As H+ escape the ATP synthase spins. Each time it rotates, it grabs an ADP and attached a phosphate to create ATP.

Cellular Respiration - Overview

= 38 ATP

Objectives





6CO2 + 6H2O C6H12O6 + 6O2

LIGHT

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Cellular Respiration How do living things release energy from the foods they consume or produce?