cellular respiration - biology courses...

Lecture 12-13

Chapter 6

CellularRespiration

Lecture 12-13

Chapter 6

CellularRespiration

• Long-distance runners have manySLOW FIBERS in their muscles– Slow fibers break down glucose for ATP

production aerobically (using oxygen)– These muscle cells can sustain repeated, long

contractions

How do marathon runners and sprinters differ?

• Sprinter’s muscles have more FAST FIBERS

- Fast fibers make ATP without oxygen—anaerobically- They can contract quickly and supply energy for short bursts of intense activity

The dark meat of a cooked turkey is an example of slow fiber muscleLeg muscles support sustained activity

The white meat consists of fast fibers- Wing muscles allow for quick bursts of flight

• Nearly all the cells in our body break down sugars for ATP production

• Most cells of most organisms harvest energy aerobically, like slow muscle fibers– The aerobic (+O2) harvesting of energy from

sugar is called cellular respiration– Cellular respiration yields CO2, H2O, and a large

amount of ATP

INTRODUCTION TOCELLULAR RESPIRATION

• Cellular respiration breaks down glucose molecules and banks their energy in ATP– The process uses O2 and releases CO2 and H2O

Glucose Oxygen gas Carbon dioxide

Water Energy

O2 CO2BREATHING

Lungs

CO2 O2Bloodstream

Muscle cells carrying out

CELLULAR RESPIRATION

• Breathing supplies oxygen to our cells and removes carbon dioxide

MITOCHONDRION

Mitochondria use the energy in sugars, fats and proteinsto make ATP

High-energy electrons carried by NADH

GLYCOLYSISGlucose Pyruvic

acid

KREBSCYCLE

ELECTRONTRANSPORT CHAIN

AND CHEMIOSMOSIS

MitochondrionCytoplasmic

fluid

Fig. 6.16

•Cellular respiration oxidizes sugar and produces ATP in three main stages:–GLYCOLYSIS occurs in the cytoplasm –The KREBS CYCLE (TCA) and

the ELECTRON TRANSPORT CHAINoccur in the mitochondria

Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid

Glucose Pyruvicacid

• Details of glycolysis

• Read and think about each step so that you can ‘see’the big picture

• Memorize and understand the NET REACTIONS

See Figure 6.18

PREPARATORYPHASE

(energy investment)

ENERGY PAYOFF PHASE

Steps – A fuelmolecule is energized,using ATP.

1 3

1

GlucoseStep

2

3

4

Glucose-6-phosphate

Fructose-6-phosphate

Glyceraldehyde-3-phosphate (G3P)

Step A six-carbonintermediate splits into two three-carbon intermediates.

4

Step A redoxreaction generatesNADH.

55

1,3-Diphosphoglyceric acid(2 molecules)

6

Steps – ATPand pyruvic acidare produced.

6 9 3-Phosphoglyceric acid(2 molecules)7

2-Phosphoglyceric acid(2 molecules)8

2-Phosphoglyceric acid(2 molecules)

9

(2 moleculesper glucose molecule)

Pyruvic acid

Fructose-1,6-diphosphate

6.7 Using Coupled Reactions to Make ATP• Glycolysis is the first stage in cellular respiration

– Takes place in the cytoplasm – Occurs in the presence or absence of oxygen– Involves ten enzyme-catalyzed reactions

• These convert the 6-carbon glucose into two 3-carbon molecules of pyruvate

1 6-carbon glucose(Starting material)

6-carbon sugar diphosphate

P P

2 ATP

Priming reactions

2

6-carbon sugar diphosphate

P P

3-carbon sugarphosphate

P

3-carbon sugarphosphate

P

Cleavage reactions

3

3-carbonpyruvate

3-carbonpyruvate

NADH

ATP2

3-carbon sugarphosphate

P

3-carbon sugarphosphate

P

NADH

ATP2

Energy-harvesting reactions

Fig. 6.17

6.8 Harvesting Electrons from Chemical Bonds

• The oxidative stage of aerobic respiration occurs in the mitochondria

• It begins with the conversion of pyruvate into acetyl coA

Depending on needs

Fig. 6.20

• Takes place in the mitochondria• It consists of nine enzyme-catalyzed reactions that can be divided into three stages

– 1 Acetyl CoA binds a 4-carbon molecule producing a 6-carbon molecule– 2 Two carbons are removed as CO2– 3 The four-carbon starting material is regenerated

• Krebs cycle enzymes strip away electrons and H+ from each acetyl group generatingmany NADH and FADH2 molecules

The Krebs Cycle

1CoA–

(Acetyl-CoA)

4-carbon molecule(Starting material) 6-carbon

molecule

2

6-carbon molecule

4-carbonmolecule

5-carbonmolecule

NADH

NADH

CO2

ATP

CO2

3

NADH

FADH2

4-carbon molecule(Starting material)

4-carbon molecule

Fig. 6.22

6.9 Using the Electrons to Make ATP

Energy Transferin the Mitochondria

• Glucose is entirely consumed in the process of cellular respiration

• Glucose is converted to six molecules of CO2– used to buffer the pH of blood– breathe out as waste

• The glucose energy is transformed to– 4 ATP molecules– 10 NADH electron carriers– 2 FADH2 electron carriers

• THE REDUCING POWER INTHESE ELECTRON CARRIERSIS USED TO MAKE 32 ATPMOLECULES IN THEELECTRON TRANSPORT CHAIN

6.9 Using the Electrons to Make ATP

Mitochondrial matrix

Intermembrane spacePyruvate from

cytoplasm

NADH

Acetyl-CoA

FADH2

NADH

Krebscycle

ATP2

CO2

e–

e–

1. Electrons are harvestedand carried to the transportsystem.

e–

2. Electrons provideenergy to pumpprotons across themembrane.

H+ H+

H+

O2O2

1

2

H2O

3. Oxygen joins withprotons to form water.

+ 2H+

H+ATP32

4. Protons diffuse backin, driving the synthesisof ATP.

ATPsynthase

Fig. 6.26 An overview of the electron transport chain and chemiosmosis

6.9 Using the Electrons to Make ATP

Fig. 6.25

• In chemiosmosis,the H+ ions diffuse throughATP synthase complexes,which capture the energyto make ATP

• The electrons carried by NADH and FADH2are donated to the electron transport chain

• Energy released by the electrons is used topump H+ into the space between themitochondrial membranes

• Chemiosmosis in the mitochondrion

Figure 6.12

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Proteincomplex

Electroncarrier

Electronflow

ELECTRON TRANSPORT CHAIN ATP SYNTHASE

• Food sources, other than sugars, can be used in cellular respiration

• These complex molecules are first digested into simpler subunits– Polysaccharides can be hydrolyzed to

monosaccharides and then converted to glucose for glycolysis

– Proteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycle

– Fats are broken up and fed into glycolysis and the Krebs cycle

Other Sources of Energy

Fig. 6.27 How cells obtain energy from foods

• The use of inorganic terminal electron acceptors other than oxygen

Anaerobic Respiration

Sulfur bacteria

Methanogens

Reduced Product

Terminalelectron

acceptor

Organism

CO2ArchaeaCH4

Methane

SO4Sulfate

H2SHydrogen

sulfide

• The use of organic terminal electron acceptors• The electrons carried by NADH are donated to a derivative of pyruvate

– This allows the regeneration of NAD+ that keeps glycolysis running• Two types of fermentation are common among eukaryotes

– Lactic fermentation and Ethanolic fermentation

Fermentation

Fig. 6.19

Occurs in animal

muscle cells

Occurs in yeast

cells

BIG PICTURELife from the Sun

• Nearly all the chemical energy that organisms use comes ultimately from sunlight

Sunlight energy

Chloroplasts,site of photosynthesis

CO2+

H2O

Glucose+O2Mitochondria

sites of cellularrespiration

(for cellular work)

Heat energy

This is aVERY IMPORTANT

cycle