How Cells Harvest Chemical Energy

1
How Cells Harvest Chemical Energy
2
ATP Is Universal Energy Source

• Photosynthesizers get energy from the sun
• Consumers get energy from plants or other
  organisms
• ENERGY is ALWAYS converted to the chemical bond
  energy of ATP
• Photosynthesis and Respiration are LINKED

3
Photosynthesis

• Overall reaction
• 6 CO2 12 H2O ? C6 H12O6 6 O2 6 H2O
• Often shown as
• 6 CO2 6 H2O ? C6 H12O6 6 O2

4
Photosynthesis Overview
Sunlight 12 H2O
6 CO2
ATP
ADP P
Light Dependent Reactions
Light-Independent Reactions
NADPH
NADP
6 O2
Glucose-P 6 H2O
Reactions occur in grana of the thylakoid
membrane system
Reactions occur in stroma
5
Overview of Cellular Respiration

• Glucose 6 O2 ? 6 CO2 6 H2O
• The overall reaction is exergonic.
• The energy given off is used to make ATP.

36-38 ATP
6
Breathing
O2
CO2
Lungs
Bloodstream
O2
CO2
Muscle cells carrying out
Cellular Respiration
Glucose ? 6 O2
6 CO2 ? 6 H2O ? 36-38 ATP

• Breathing and cellular respiration are closely
  related

7
Cellular Respiration and ATP

• Cellular respiration releases the energy stored
  in glucose in a series of steps
• The energy released is stored as ATP and released
  as heat
• Aerobic respiration is 40 efficient
• Meaning40 of the energy stored in the glucose
  is stored as ATP

8
How Cells Make ATP

• ATP is made in two ways during cellular
  respiration
• Substrate level phosphorylation
• Glycolysis
• Citric acid cycle (Krebs cycle)
• Oxidative phosphorylation
• Electrons transport system and chemiosmosis

9
Substrate-level phosphorylation
ENZYME
ATP is made in an enzyme in a coupled reaction.
Substrate gives energy and phosphate group
(Pi) to ADP and makes ATP.
Substrate
Product
Fig. 9.7
10

• Oxidative phosphorylation
• Electron carriers (NADH and FADH2) deliver
  electrons to the Electron Transport Chain (ETC)
  on the inner membrane of the mitochondria
• Electrons are passed from membrane protein to
  protein.
• Each transfer releases energy and pumps H out
  of the matrix
• Energy is used to create a chemical gradient
• Gradient is used to drive ATP synthesis by the
  enzyme ATP synthase

11

Overview of Cellular Respiration
12
Carbohydrate Metabolism

• The first pathway of carbohydrate metabolism is
  called glycolysis.
• Glucose is the starting material for glycolysis.
• Glycolysis reactions occur in the cytoplasm.

13
Glycolysis

• Step 1 Glucose is converted to
  glucose-6-phosphate in a phosphorylation reaction
• Reaction is endergonic
• Reaction requires an input of ATP
• Step 2 A rearrangement reaction occurs to make
  fructose-6-phosphate

14
Glycolysis

• Step 3 Another phosphorylation reaction occurs
  to made fructose-1,6-diphosphate
• Reaction is endergonic
• Reaction requires an input of ATP
• Step 4 Fructose-1,6-diphosphate is broken in to
  2 three carbon compounds

15
Glycolysis

• 5 more steps occur and 2 pyruvate are made
• These steps release energy and electrons.
• Energy released is used to make ATP by substrate
  level phosphorylation
• Electrons are attached to the electron carrier
  NAD to form 2 NADH
• The NADH deliver electrons and H to the electron
  transport system

16
More on NADH

• Synthesis of NADH
• NAD 2 e 2 H ? NADH
• Is NAD oxidized or reduced in this reaction?

17
Glycolysis

• Energy requiring steps
• 2 ATP invested
• Energy releasing steps
• 2 NADH formed
• 4 ATP formed
• Net yield is 2 ATP and 2 NADH
• Does NOT require O2
• Occurs in the cytoplasm

18
Glycolysis Summary

• Where it occurs
• First substrate (starting material)
• End product
• Also made
• net gain of ____ ATP (why net?, how made?)
• _____ NADH (made from?)

19
Glycolysis Summary

• Where it occurs Cytoplasm
• First Substrate Glucose (6C)
• End product 2 Pyruvate (3C)

20
Glycolysis Summary

• Also made
• net gain of 2 ATP made by substrate-level
  phosphorylation
• Pathway requires an input of 2 ATP to start and
  makes a total of 4 ATP
• 2 NADH each made from NAD ,2e and H

21
Energy Releasing Pathways

• What happens to the products of glycolysis
  depends upon cell conditions.
• ? Aerobic conditions
• Preparatory step and Citric Acid/Krebs cycle
• Electron transport chain
• ? Anaerobic conditions
• Fermentation

22

• GLYCOLYSIS

OR
ANAEROBIC Conditions No oxygen present Net gain
of 2 ATP
AEROBIC RESPIRATION Oxygen present Net gain of
36-38 ATP
23

• GLYCOLYSIS

OR

• AEROBIC
• RESPIRATION
• Preparatory step
• Krebs Cycle
• Electron Transport Chain
• Reactions occur in mitochondria

• ANAEROBIC
• Fermentation occurs
• Type depends upon cell type
• Reactions occur in cytoplasm

24
Pathways of Aerobic Respiration

• Glycolysis
• followed by Pyruvate oxidation
• Citric Acid cycle
• Also called Krebs Cycle
• Electron Transport Chain (ETC) and Chemiosmosis

25
Aerobic Conditions

• The first reaction that occurs after glycolysis
  is pyruvate oxidation
• Also called the Preparatory Step
• This reaction occurs as the pyruvate enter the
  matrix of the mitochondria

26
Pyruvate Oxidation

• As the pyruvate enter the mitochondria each has a
  carbon removed and co-enzyme A added
• Produced in the Prep. Step
• 2 NADH (go to ETC)
• 2 CO2 (diffuse out of mitochondria and cell)

27

• Pyruvate Oxidation

Cytoplasm
------------------------------
------------------------------
Matrix of the mitochondria
28
Aerobic Respiration

• For each glucose metabolized the Preparatory Step
  makes
• 2 NADH - go to ETC
• 2 CO2 - diffuse out of mitochondria and cell
• 2 Acetyl Co-A - enter into Citric acid cycle
• aka Krebs cycle

29
Pyruvate Oxidation Summary

• Where and when it occurs
• Substrate
• End Product
• Also made
• ___________
• ___________

30
Pyruvate Oxidation Summary

• Where and when it occurs Occurs as pyruvate
  enter mitochondria, occurs under aerobic
  conditions
• Substrate 2 Pyruvate (3C)
• End Product 2 Acetyl-CoA (2C)
• Also made
• 2 CO2
• 2 NADH

31
Citric Acid Cycle Krebs Cycle

• Step 1 Each Acetyl-CoA (2C) joins with an
  oxaloacetate (4C) to form a citrate (6C)
• Rest of the citric acid cycle reactions occur
• Last reaction produces another oxaloacetate (4C)
  which joins with the next available acetyl-co
  A.
• ATP, NADH, FADH2, and CO2 are made in these
  reactions.see board

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CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
Citrate
?H
NADH
leaves cycle
CO2
NAD
CITRIC ACID CYCLE
NAD
Malate
H
NADH

ADP
P
FADH2
ATP
Alpha-ketoglutarate
FAD
leaves cycle
CO2
Succinate
NAD
?H
NADH
33
(No Transcript)
34

• In the Krebs cycle, the metabolism of 2 pyruvates
  made from a single glucose produces
• 2 ATP - by substrate-level phosphorylation
• 6 NADH - go to ETC
• 2 FADH2 - go to ETC
• 4 CO2 - diffuse out of mitochondria and cell

35
Citric Acid Cycle Summary

• Where it occurs
• Starting substrates
• Last product of pathway
• Also made (in total for 2 acetyl-CoA entering)
• ____ CO2
• ____ ATP (method made by?)
• ____ NADH
• ____ FADH2

36
Citric Acid Cycle Summary

• Where it occurs matrix of mitochondria
• Starting substrates acetyl-CoA, oxaloacetate
• Last product of pathway oxaloacetate
• Also made (in total for 2 acetyl-CoA)
• 4 CO2
• 2 ATP (by substrate level phophorylation)
• 6 NADH
• 2 FADH2

37
Electron Transport Chain (ETC)

• ETC occurs at electron carriers (proteins)
  located on the inner membrane of the mitochondria
• Electrons from NADH and FADH2 are passed from one
  electron carrier to the next.
• Transfers are called red-ox reactions
• Each transfer releases energy

38
ETC

• Some of the electron carriers are also proton
  (H) pumps
• Use the energy released by the red-ox reactions
  (e transfer reactions) to pump H out of the
  matrix.

39
H
H
H
H
H
Protein complex
H
H
Electron carrier
H
ATP synthase
H
Intermembrane space
Inner mitochondrial membrane
FAD
FADH2
Electron flow
1 2

O2
H
2
NADH
NAD
H
Mitochondrial matrix
H
P

ADP
ATP
H
H2O
H
Chemiosmosis
Electron Transport Chain
40
ETC

• NADH and FADH2 each transfer 2e and H to a
  specific ETS protein
• Notice -- they do NOT start with the same ETC
  protein
• In the process are the NADH and FADH2 oxidized or
  reduced?

41
H
H
H
H
H
Protein complex
H
H
Electron carrier
H
ATP synthase
H
Intermembrane space
Inner mitochondrial membrane
FAD
FADH2
Electron flow
1 2

O2
H
2
NADH
NAD
H
H
P

ADP
ATP
H
H2O
Mitochondrial matrix
H
Chemiosmosis
Electron Transport Chain
42
ETC

• H from the matrix follow the electrons into
  proton pumps
• At each proton pump the H are pumped out of the
  matrix into the intermembrane space
• This creates an electrical chemical gradient
• Form of _________ energy

43
ETC

• Electron transfers stop when the last ETC protein
  transfers the 2e to oxygen which
• Joins with H to form water
• The last electron acceptor is oxygen and water
  forms. (know this)

44
Chemiosmosis and ATP Synthesis

• .back to the H ions pumped into the
  intermembrane space
• The potential energy of H gradient is drive ATP
  synthesis at the enzyme ATP synthase

45
ETC and ATP Synthesis

• The enzyme ATP synthase is embedded in the inner
  membrane of the mitochondria
• The flow of H through this enzyme releases
  energy and this energy is used to make ATP .

46
Chemiosmosis and ATP Synthesis

• This method of making ATP is called
• Oxidative phosphorylation
• Also referred to as chemiosmosis

47
Chemiosmosis and ATP Synthesis

• The more H pumped out of the matrix
• The steeper the gradient
• the more potential energy
• the more ATP that can be made by ATP synthase

48
ETC and ATP Synthesis

• Each NADH made in the mito. results in enough H
  being pumped out of the matrix to make 3 ATP.
• Each FADH2 results in enough H being pumped out
  of the matrix to make 2 ATP.

49
NADH from Glycolysis

• The NADH made in glycolysis must enter the matrix
  in order to deliver their electrons to the ETC
• How they enter the mitochondria depends upon
  the cell type.

50
NADH from Glycolysis

• In most cells the 2 NADH made in glycolysis pass
  their electrons and H to FAD in the matrix
  making
• 2 FADH2 -- take the electrons and H to the ETC
  where a total of ____ ATP are made

51
NADH from Glycolysis

• In liver, heart, and kidney cells the 2 NADH made
  in the cytoplasm pass their electrons and H to
  NAD in the matrix making
• 2 NADH -- which take the electrons and H to the
  ETC where a total of ____ ATP are made

52
or 2 NADH
53
ATP Synthesis Summary

• Glycolysis
• ____ ATP (net) (method?)
• ____ NADH ? ____ ATP (most cells)
• Preparatory step
• ____ ATP
• _____ NADH ? ____ ATP (method?)

54
ATP Synthesis Summary

• Krebs Cycle
• ____ ATP (method?)
• ____ NADH ? ____ ATP (method?)
• ____ FADH2 ? ____ ATP (method?)

55
NADH and FADH2 Summary

• Glycolysis ? 2 NADH
• Made in the cytoplasm
• How they enter the mitochondria depends upon the
  type of cell
• Preparatory Step ? 2 NADH
• Krebs Cycle ? 6 NADH and 2 FADH2

56
Fermentation

• Under anaerobic conditions the products of
  glycolysis enter fermentation reactions.
• All fermentation reactions occur in the
  cytoplasm.

57
Fermentation

• The purpose of all types of fermentation is to
  regenerate NAD so that glycolysis can continue.

58
Fermentation

• Cells have a limited supply of NAD
• Under aerobic conditions the cells major source
  of NAD is the first step of the ETC
• Under anaerobic conditions the Krebs cycle and
  ETC stop
• As a result NAD are no longer made in the
  mitochondria.

59
Fermentation

• The two most common forms of fermentation are
• Lacate fermentation
• Alcoholic fermentation
• Which type of fermentation occurs depends upon
  the organism.

60
Lactate Fermentation

• Lactate fermentation occurs in
• Humans and all other animals
• Many bacteria

61
Lactate Fermentation

• 2 Pyruvate (3C)
• 2 Lactate (3C)
• Also called pyruvic acid and lactic acid

2 NADH
2 NAD ? reused in glycolysis
62
Lactate build up in the cell results in

• Increased blood supply to the area, which
• Blood brings oxygen
• Blood washes out the lactate
• Lactate is taken to the liver where it is
  converted back to pyruvate (called the Cori
  cycle)
• Too much lactate in the blood can cause acidosis
• Muscle cramps if the lactate levels get too high
  occurs - painful

63
Alcoholic Fermentation

• Alcoholic fermentation occurs in
• Yeast (a fungus)
• used in making alcoholic beverages and yeast
  breads
• Many bacteria
• Including those used to make Swiss cheese

64
Alcoholic Fermentation

• 2 Pyruvate (3C)
• 2 Acetaldehyde (2C)
• 2 Ethanol (2C)

__________
2 NADH
2 NAD - reused in glycolysis
65
Alcoholic Fermentation

• Ethanol (alcohol) builds up in the cell
• When it reaches too high a level it denatures
  the cells proteins.
• This results in cell death!
• Wild yeasts die at 4 alcohol, wine making yeasts
  die at 14 alcohol.

66
Alcoholic Fermentation

• Reactions cannot be reversed.
• Remember, the lactate fermentation reaction is
  reversible
• Lactate can be converted back to pyruvate in the
  liver, not in the cell its made in

67

• This is the end of the slides needed.
• The slides that follow are slides that give an
  overview of concepts related to the ETC.

68
Electron Transfers and Energy

• Electron transfer reactions are called oxidation
  reduction reactions
• Oxidation loss of electron(s)
• Reduction gain of electron(s)
• H often follow the electrons

69
Electron Transfers and Energy

• ALL cells use the transfer of electrons and H to
  capture some of the energy stored in chemical
  bonds
• Energy is temporarily stored in NADH and FADH2
• The stored energy is then used to make ATP

70
Electron Transfers and Energy

• NAD H 2 e ? NADH
• FAD 2 H 2 e ? FADH2
• Is the NAD oxidized or reduced in this
  reaction?
• In general the reduced molecule is of greater
  energy due to the added energy of the electrons

71
Electron Transfer Chains

• In mitochondria and chloroplasts there are
  electron transfer chains embedded in the inner
  membranes
• The passage of the electrons from electron
  transfer protein to protein results in creation
  of an electrochemical gradient
• This gradient is a form of stored energy and can
  be used to make ATP

72
Electron Transfer Chains

• In mitochondria
• NADH and FADH2 give electrons and H to specific
  proteins on the inner membrane of the
  mitochondria
• this releases their stored energy
• H follow the electrons into the proteins

73
Electron Transfer Chains

• Energy given off by the electron transfers is
  used to pump H across the inner membrane into
  the outer compartment
• This creates a chemical/electrical gradient
• A form of potential energy
• An ATP-synthesizing enzyme uses this energy to
  make ATP