Cellular Respiration Process whereby cells breakdown glucose and other food molecules to release energy

Cellular Respiration

Process whereby cells breakdown glucose and other food molecules to release energy.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The efficiency of cellular respiration

– Provides a high % of energy in a controlled manner

Figure 6.2B

Burning glucose in an experiment

Energy released from glucose

(as heat and light)

100%

Energy released from glucose

banked in ATP

“Burning” glucosein cellular respiration

About 40%

Gasoline energy converted to movement

Burning gasolinein an auto engine

25%


• When you exercise

BIOLOGY AND SOCIETY: FEELING THE “BURN”

– Muscles need energy in order to perform work• Enzymes in muscle cells help a cell use glucose and

oxygen to produce ATP


• Aerobic metabolism

– When enough oxygen reaches cells to support energy needs

• Anaerobic metabolism

– When the demand for oxygen outstrips the body’s ability to deliver it


• Anaerobic metabolism

– Without enough oxygen, muscle cells break down glucose to produce lactic acid

– Lactic acid is associated with the “burn” associated with heavy exercise

– If too much lactic acid builds up, your muscles give out


• Physical conditioning allows your body to adapt to increased activity

– The body can increase its ability to deliver oxygen to muscles

• Long-distance runners wait until the final sprint to exceed their aerobic capacity

Figure 6.1


ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHERE

• Fuel molecules in food represent solar energy

– Energy stored in food can be traced back to the sun

• Animals depend on plants to convert solar energy to chemical energy

– This chemical energy is in the form of sugars and other organic molecules


Figure 6.3

Sunlightenergy

Ecosystem

Photosynthesis(in chloroplasts)

Glucose

Oxygen

Carbon dioxide

Cellular respiration(in mitochondria)

Water

for cellular work

Heat energy

Energy and Food• A large amount of

energy is stored within the chemical bonds of food.

• Burning 1g glucose (C6H12O6) releases 3811 C of heat.

• Calorie - amount of energy needed to raise the temperature of 1g of H2O 1ºC.

• Cells do not burn glucose , but gradually break it down to release the energy.

• Cellular respiration

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY

– The main way that chemical energy is harvested from food and converted to ATP

– This is an aerobic process—it requires oxygen

• Cellular respiration and breathing are closely related

– Cellular respiration requires a cell to exchange gases with its surroundings

– Breathing exchanges these gases between the blood and outside air

The Relationship Between Cellular Respiration and Breathing

Figure 6.4

Breathing

Lungs

Musclecells

Cellularrespiration

Cellular Respiration

Three Steps

I. GlycolysisII. Krebs CycleIII. Electron Transport

Chain

• A common fuel molecule for cellular respiration is glucose

– This is the overall equation for what happens to glucose during cellular respiration

The Overall Equation for Cellular Respiration

Unnumbered Figure 6.1

Glucose Oxygen Carbondioxide

Water Energy

Cellular respiration can produce up to 38 ATP molecules for each glucose molecule consumed

• ATP molecules are the key to energy coupling

• ATP molecules store energy during the process of cellular respiration

• ATP power nearly all forms of cellular work

ATP the cell’s chemical energy

The Role of ATP

• Cellular money

• Cells “earn” ATP in exergonic reactions

• Cells “spend” ATP in endergonic reactions

P P P

ribose

adenine

• Hydrolysis breaks a phosphate group bond from the ATP molecules releasing energy

• The exergonic reaction supplies energy for cellular work

Figure 5.4A

Phosphategroups

Adenine

Ribose

Adenosine triphosphate

Hydrolysis

Adenosine diphosphate(ADP)

Energy

Energy Coupling

• Phosphorylation – How ATP powers cellular work

Figure 5.4B

Reactants

Po

ten

tia

l en

erg

y o

f m

ole

cule

s

Products

Protein Work

• The ATP cycle

Figure 5.4C

Energy from exergonic reactions

Deh

yd

rati

on

syn

thes

is

Hyd

roly

sis

Energy for endergonic reactions

• During cellular respiration, hydrogen and its bonding electrons change partners

– Hydrogen and its electrons go from sugar to oxygen, forming water

The Role of Oxygen in Cellular Respiration

• Why does electron transfer to oxygen release energy?

– When electrons move from glucose to oxygen, it is as though they were falling

– This “fall” of electrons releases energy during cellular respiration

Figure 6.5

Releaseof heatenergy

Cell with Mitochondria (red spots)

Mitochondria

Site of Krebs cycle and Electron Transport Chain


• An overview of cellular respiration

Figure 6.8

High-energy electrons carried by NADH

GLYCOLYSIS

Glucose Pyruvicacid

KREBSCYCLE

ELECTRONTRANSPORT CHAIN

AND CHEMIOSMOSIS

MitochondrionCytoplasmic

fluid


Stage 1: Glycolysis

• A molecule of glucose is split into two molecules of pyruvic acid


• Glycolysis breaks a six-carbon glucose into two three-carbon molecules

– These molecules then donate high energy electrons to NAD+, forming NADH


• Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP

Figure 6.9

Enzyme

Cell with Mitochondria (red spots)

Mitochondria

Site of Krebs cycle and Electron Transport Chain


Figure 6.8


GLYCOLYSIS

Glucose Pyruvicacid

KREBSCYCLE


AND CHEMIOSMOSIS


fluid

Stage 2: The Krebs Cycle• The Krebs cycle completes the breakdown

of sugar

• The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2

– The cycle uses some of this energy to make ATP

– The cycle also forms NADH and FADH2

II. Krebs CycleProcess whereby pyruvate is broken down into CO2 in a

series of energy releasing reactions.

• Only occurs if O2 is present (aerobic respiration).

• Takes place within the mitochondria of the cell.

• Each pyruvate that goes through the cycle produces 1 ATP, 4 NADH, 1 FADH2 and 3 CO2 (2 X that amount for each glucose molecule).


Figure 6.8


GLYCOLYSIS

Glucose Pyruvicacid

KREBSCYCLE


AND CHEMIOSMOSIS


fluid

Stage 3: Electron Transport• Electron transport releases the energy your

cells need to make the most of their ATP

• The molecules of electron transport chains are built into the inner membranes of mitochondria

– The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane

– These ions store potential energy

• When the hydrogen ions flow back through the membrane, they release energy

– The ions flow through ATP synthase– ATP synthase takes the energy from this flow

and synthesizes ATP

The Versatility of Cellular Respiration• Cellular respiration can “burn” other kinds of

molecules besides glucose

– Diverse types of carbohydrates– Fats– Proteins

• Pathways of molecular breakdown

Figure 6.16

Food, such as peanuts

Polysaccharides Fats Proteins

Sugars Glycerol Fatty acids Amino acids

Amino groups

Glucose G3PPyruvic

acid

GLYCOLYSIS

AcetylCoA

KREBSCYCLE


AND CHEMIOSMOSIS

• The path that electrons take on their way down from glucose to oxygen involves many stops

NADH and Electron Transport Chains

Figure 6.6

1/2

(from food via NADH)

2 H 2 e

Energy forsynthesis

of

Electro

n tran

spo

rt chain 2 e

2 H1/2

• Cellular respiration is an example of a metabolic pathway

– A series of chemical reactions in cells• All of the reactions involved in cellular respiration can be grouped into three

main stages

– Glycolysis– The Krebs cycle– Electron transport

The Metabolic Pathway of Cellular Respiration

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY

• Some of your cells can actually work for short periods without oxygen

– For example, muscle cells can produce ATP under anaerobic conditions

• Fermentation

– The anaerobic harvest of food energy

• Human muscle cells can make ATP with and without oxygen

– They have enough ATP to support activities such as quick sprinting for about 5 seconds

– A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds

– To keep running, your muscles must generate ATP by the anaerobic process of fermentation

Fermentation in Human Muscle Cells

• Various types of microorganisms perform fermentation

– Yeast cells carry out a slightly different type of fermentation pathway

– This pathway produces CO2 and ethyl alcohol

Fermentation in Microorganisms

• The food industry uses yeast to produce various food products

Figure 6.16

SUMMARY OF KEY CONCEPTS• Chemical Cycling Between Photosynthesis and Cellular Respiration

Visual Summary 6.1

Sunlight

Heat

PhotosynthesisCellular

respiration

• The Overall Equation for Cellular Respiration

Visual Summary 6.2

Oxidation:Glucose loses electrons(and hydrogens)

Glucose Carbon dioxide

Electrons(and hydrogens) Energy

Oxygen

Reduction:Oxygen gainselectrons (andhydrogens)

• The Metabolic Pathway of Cellular Respiration

Visual Summary 6.3

Glucose Oxygen Water Energy


• Long-distance runners have many slow fibers in their muscles

– Slow fibers break down glucose for ATP production aerobically (using oxygen)

– These muscle cells can sustain repeated, long contractions

How is a Marathoner Different from a Sprinter?


• Sprinters have more fast muscle fibers

– Fast fibers make ATP without oxygen - -anaerobically

– They can contract quickly and supply energy for short bursts of intense activity


• The dark meat is an example of slow fiber muscle

– Leg muscles support sustained activity

• The white meat consists of fast fibers

– Wing muscles allow for quick bursts of flight

• Biosynthesis of macromolecules from intermediates in cellular respiration

Figure 6.17

ATP needed todrive biosynthesis

PolyscaccharidesFatsProteins

KREBSCYCLE

AcetylCoA

Pyruvicacid G3P Glucose

GLUCOSE SYNTHESIS

Aminogroups

Amino acids Fatty acids Glycerol Sugars

Cells, tissues, organisms

Documents

Cellular Respiration Process whereby cells breakdown glucose and other food molecules to release energy