Chapter 9: Cellular Respiration and Fermentation

Chapter 9: Cellular Respiration and Fermentation

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1Cellular Respiration 2009

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Voc Terms

• Cellular respiration• Aerobic• Anaerobic• Glycolysis• NAD+• Krebs cycle• Matrix• Fermentation


Chapter 9: Big IdeaCellular Basis of life- How do organisms obtain

Energy

9.1- Why do most organisms undergo the process of cellular respiration?

9.2- How do cell release energy from food in the presence of oxygen?

9.3- How do cells release energy from food without oxygen?


THINK ABOUT IT

– You feel weak when you are hungry because food serves as a source of energy. How does the food you eat get converted into a usable form of energy for your cells?


chapter 7 biology notes 5

Harvesting Chemical Energy• Cellular respiration- complex process in which cells make ATP by

breaking down organic cpds.• What are Autotrophs?

use photosynthesis to convert light energy from the sun into chemical energy, stored organic cpds

Both auto and heterotrophs undergo cellular respiration to break organic cpds into simpler molecules to release energy

(ATP and work)

Chemical Energy and Food

– Where do organisms get energy?

– Organisms get the energy they need from food.


Chemical Energy and Food

– Food provides living things with the chemical building blocks they need to grow and reproduce.

– Food molecules contain chemical energy that is released when its chemical bonds are broken.


Chemical Energy and Food– Energy stored in food is expressed in units of

calories. A Calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. 1000 calories = 1 kilocalorie, or Calorie.

– Cells use all sorts of molecules for food, including fats, proteins, and carbohydrates. The energy stored in each of these molecules varies because their chemical structures, and therefore their energy-storing bonds, differ.

– Cells break down food molecules gradually and use the energy stored in the chemical bonds to produce compounds such as ATP that power the activities of the cell.


Overview of Cellular Respiration

What is cellular respiration?

– Cellular respiration is the process that releases energy from food in the presence of oxygen.



Glycolysis

• Is a biochemical pathway in which one 6C molecule of glucose is oxidized to produce two 3C molecule

Terms:1. Pyruvic acid- 3 carbon molecule2. NADH/FADH2- electron carrier molecule3. Anaerobic- does not require the presence of

oxygen4. Aerobic- requires oxygen

Overview of Cellular Respiration

– If oxygen is available, organisms can obtain energy from food by a process called cellular respiration. The summary of cellular respiration is presented below.

– In symbols:6 O2 + C6H12O6 6 CO2 + 6 H2O + Energy

– In words:– Oxygen + Glucose Carbon dioxide + Water +

Energy

– The cell has to release the chemical energy in food molecules (like glucose) gradually, otherwise most of the energy would be lost in the form of heat and light.


Stages of Cellular Respiration

The three main stages of cellular respiration:

1. Glycolysis

2. Krebs cycle

3. Electron transport chain.



Glycolysis produces only a small amount of energy. Most of glucose’s energy (90%) remains locked in the chemical bonds of pyruvic acid at the end of glycolysis.

(2 net ATP)



– During the Krebs cycle, a little more energy is generated from pyruvic acid.

– (2 Net ATP)



The electron transport chain produces the bulk of the energy in cellular respiration by using oxygen, a powerful electron acceptor.

(34- 36 Net ATP)


Oxygen and Energy

– Pathways of cellular respiration that require oxygen are called aerobic. The Krebs cycle and electron transport chain are both aerobic processes. Both processes take place inside the mitochondria.


Oxygen and Energy

– Gylcolysis is an anaerobic process. It does not directly require oxygen, nor does it rely on an oxygen-requiring process to run. However, it is still considered part of cellular respiration. Glycolysis takes place in the cytoplasm of a cell.


Comparing Photosynthesis and Cellular Respiration

– What is the relationship between photosynthesis and cellular respiration?

– Photosynthesis removes carbon dioxide from the atmosphere, and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere, and cellular respiration uses that oxygen to release energy from food.



– Photosynthesis and cellular respiration are opposite processes.

– The energy flows in opposite directions. Photosynthesis “deposits” energy, and cellular respiration “withdraws” energy.

– The reactants of cellular respiration are the products of photosynthesis and vice versa.



– The release of energy by cellular respiration takes place in plants, animals, fungi, protists, and most bacteria.

– Energy capture by photosynthesis occurs only in plants, algae, and some bacteria.


THINK ABOUT IT

– Food burns! How does a living cell extract the energy stored in food without setting a fire or blowing things up?


Glycolysis

What happens during the process of glycolysis?

– During glycolysis, 1 molecule of glucose, a 6-carbon compound, is transformed into 2 molecules of pyruvic acid, a 3-carbon compound.


Glycolysis

Glycolysis is the first stage of cellular respiration.

– During glycolysis, glucose is broken down into 2 molecules of the 3-carbon molecule pyruvic acid. Pyruvic acid is a reactant in the Krebs cycle.

– ATP and NADH are produced as part of the process.


The Advantages of Glycolysis

– Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase.

– Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.


The Krebs Cycle

What happens during the Krebs cycle?

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



Krebs Cycle• Biochemical pathway that breaks down acetyl Co A,

producing CO2, hydrogen atoms, and ATP• Hans Krebs (1900-1981), German biochemistFive main steps that occur in the mitochondrial matrix,

aerobic process that oxidizes pyruvates to CO2** this process yields 2 ATP same as glycolysis, but it

does give 10NADH molecules and 2 FADH2 molecules which will drive the next stage ETC , where most energy is transferred from glucose to ATP

The Krebs Cycle

– During the Krebs cycle, the second stage of cellular respiration, pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions.

– The Krebs cycle is also known as the citric acid cycle because citric acid is the first compound formed in this series of reactions.



Energy Extraction– Remember! Each

molecule of glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle. So each molecule of glucose results in two complete “turns” of the Krebs cycle.

– Therefore, for each glucose molecule, 6 CO2 molecules, 2 ATP molecules, 8 NADH molecules, and 2 FADH2 molecules are produced.


Electron Transport and ATP Synthesis

How does the electron transport chain use high-energy electrons from glycolysis and the Krebs cycle?

– The electron transport chain uses the high-energy electrons from glycolysis and the Krebs cycle to convert ADP into ATP.



Electron Transport

– NADH and FADH2 pass their high-energy electrons to electron carrier proteins in the electron transport chain.



Importance of oxygen

• ATP can be synthesized by chemiosmosis only if electrons continue to move from molecule to molecule in the ETC.

• The last molecule in the ETC must pass e- on to a final electron acceptor. If not it will stop!!

• The oxygen allows for additional electron to pass along the chain, ATP can continue to be made through chemiosmosis

The Totals

How much energy does cellular respiration generate?

– Together, glycolysis, the Krebs cycle, and the electron transport chain release about 36-38 molecules of ATP per molecule of glucose.


Energy Totals

– In the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules.

– This represents about 36 percent of the total energy of glucose. The remaining 64 percent is released as heat.


Energy Totals

– The cell can generate ATP from just about any source, even though we’ve modeled it using only glucose. Complex carbohydrates are broken down into simple sugars like glucose. Lipids and proteins can be broken down into molecules that enter the Krebs cycle or glycolysis at one of several places.



Efficiency of cellular respiration

• glycolysis and the Krebs cycle give a max yield of 38 ATP molecules per molecule of glucose

• It can vary from cell to cell• As a result most euk cells produce only 36 ATP

(39% efficiency) (38 x7)/ 686**Cellular resp is 20x more efficient than

glycolysis alone


THINK ABOUT IT

– We use oxygen to release chemical energy from the food we eat, but what if oxygen is not around?

– Is there a pathway that allows cells to extract energy from food in the absence of oxygen?


FermentationHow do organisms generate energy when

oxygen is not available?– In the absence of oxygen, fermentation

releases energy from food molecules by producing NAD+ to regenerate glycolysis.

– Takes place in the cytoplasm of the cell


Fermentation– Under anaerobic conditions, fermentation

follows glycolysis. During fermentation, cells convert NADH produced by glycolysis back into the electron carrier NAD+, which allows glycolysis to continue producing ATP.



Rumen Microbes

• The rumen is a special stomach chamber in cows and other large hoofed mammals. It acts as a fermentation vat and has been estimated in some cows to contain as many as 8.2 X 10^15 microbes, including over 200 species of bacteria, protozoa and fungi!! (adaptation for digesting plants)


Fermentation• When O2 is present CR continues as pyruvic

acid enter the pathways of aerobic respiration.

• When no O2 is present- anaerobic environment cells must convert pyruvic acid into other cpds through additional biochemical pathways that occur in the cytoplasm

• The combination of glycolysis and these pathways that regenerate NAD+ is fermentation


Fermentation cont:

• Additional pathways do not produce ATP• If there were not a cellular process that

recycled NAD+ from NADH, glycolysis would quickly use up all the NAD+ in the cell

• Glycolysis would STOP! ATP production would STOP!! fermentation pathways allow for the continued production of ATP


Fermentation cont:• There are many fermentation pathways • They differ in terms of enzymes that are

used• They differ in the cpds that are made from

pyruvic acidTwo common fermentation pathways result in

the production of 1. Lactic acid2. Ethyl alcohol


Alcoholic Fermentation– Yeast and a few other microorganisms

use alcoholic fermentation that produces ethyl alcohol and carbon dioxide.

– This process is used to produce alcoholic beverages and causes bread dough to rise.

Chemical equation:

Pyruvic acid + NADH Alcohol + CO2 + NAD



Alcoholic Fermentation cont• The ethyl alcohol is the alcohol in alcoholic

beverages• To make wines, the CO2 that is generated is allowed

to escape• If you make champagne it is retained for the

carbonation• Bread making also depends on alcoholic

fermentation performed by yeast cells, CO2 produced makes the bread rise because of the bubbles produced the ethyl alcohol evaporates during the baking process

Lactic Acid Fermentation

– Most organisms, including humans, carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid.

Chemical equation:

Pyruvic acid + NADH Lactic acid + NAD+



Lactic Acid Fermentation cont:

• Why is this importantLA fermentation by microorganisms play an

essential role in the manufacture of many dairy products

Ex. Fermentation of milk spoiling, if controlled we can use it to make buttermilk, cheese, yogurt, sour cream


Lactic Acid Fermentation cont• Also occurs in your bodyMuscle cells during strenuous exerciseMuscle cells use up O2 more rapidly than it can be

delivered to themO2 becomes depleted, muscles switch from cellular

respiration to LAFThis LA accumulated in the muscle making the cytosol

more acidic, this increased acidity may reduce the cells ability to contract causing cramping pain, fatigue, later id will diffuse into the blood and is transported to the liver to be converted back to pyruvic acid

Energy and Exercise

How does the body produce ATP during different stages of exercise?

– For short, quick bursts of energy, the body uses ATP already in muscles as well as ATP made by lactic acid fermentation.

– For exercise longer than about 90 seconds, cellular respiration is the only way to continue generating a supply of ATP.


Quick Energy

– Cells normally contain small amounts of ATP produced during cellular respiration, enough for a few seconds of intense activity.

– Lactic acid fermentation can supply enough ATP to last about 90 seconds. However, extra oxygen is required to get rid of the lactic acid produced. Following intense exercise, a person will huff and puff for several minutes in order to pay back the built-up “oxygen debt” and clear the lactic acid from the body.


Long-Term Energy

– For intense exercise lasting longer than 90 seconds, cellular respiration is required to continue production of ATP.

– Cellular respiration releases energy more slowly than fermentation does

– The body stores energy in the form of the carbohydrate glycogen. These glycogen stores are enough to last for 15 to 20 minutes of activity. After that, the body begins to break down other stored molecules, including fats, for energy.


Long-Term Energy

– Hibernating animals like this brown bear depend on stored fat for energy when they sleep through the winter.



Cellular Respiration 2009 57

Cellular Respiration 2009 58

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Chapter 9: Cellular Respiration and Fermentation