cellular respiration topic 3.7 and 3.8. assessment statements: core 3.7.1 define cell respiration....
TRANSCRIPT
Cellular Respiration
Topic 3.7 and 3.8
Assessment Statements: Core
3.7.1 Define cell respiration.3.7.2 State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP.3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP.3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP.
Assessment Statements: Higher Level
Energy metabolism and REDOX reactions
• Metabolism is the sum of all of the chemical reactions in an organism: catabolic (breakdown) and anabolic (synthetic)
• Respiration is a catabolic pathway
• Photosynthesis is an anabolic pathway
• The two processes are closely linked in plants
• REDOX (oxidation-reduction) reactions play a key role in energy flow
through organisms
• This is because the electrons flowing from
one molecule to another are carrying energy with
them
REDOX reactionsOXIDATION REDUCTION
Loss of electrons Gain of electrons
Gain of oxygen Loss of oxygen
Loss of hydrogen Gain of hydrogen
Results in C-O bonds Results in C-H bonds
Results in a compound with lower potential energy
Results in a compound with higher potential energy
OIL RIGLEO says GER
Definition of cellular respiration
Controlled release of energy from
organic compounds to produce ATP
• Cells break down organic compounds by SLOW oxidation
• Chemical energy is stored in covalent bonds
• By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP
REDOX reactions in respirationCells tap energy from electrons transferred from organic fuels to oxygen
Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water
The protons follow the electrons to produce water
Loss of hydrogen atoms
Energy
Gain of hydrogen atoms
Where Does Cellular Respiration Take Place?
glycolysis occurs in the cytoplasm
Krebs Cycle & ETC Take
place in the mitochondria
Cellular Respiration: Standard level
How does the process of cellular respiration yield ATP (chemical energy) from food?
1. What do you already know about cellular respiration?
2. What organelle in the cell is the “powerhouse” that makes energy for the cell?
What is ATP?• Energy ‘currency’ used by all cells• Adenosine triphosphate• Organic molecule containing high-energy
phosphate bonds
Chemical Structure of ATP
3 Phosphates
Ribose Sugar
Adenine Base
How Do We Get Energy From ATP?
By breaking the high- energy bonds between the last two phosphates in ATP
ATP hydrolase (ATP’ase) catalyses the breakdown of ATP into ADP + Pi
Each day, you hydrolyse 1025 ATP molecules
ATP-ase ATP Synthetase
H2O
HYDROLYSIS (Adding H2O)
How is ATP re-made?
• Substrate-level phosphorylation (using enzymes: in the cytoplasm of the cell and the matrix of the mitochondrion)
• Chemiosmosis (in the mitochondria, using ATP synthase)
Substrate level phosphorylation and chemiosmosis
GLYCOLYSIS
Glucose Pyruvicacid
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
Substrate Level Phos. Substrate Level Phos. Oxidative Phos.
REDOX reactions in respirationCells tap energy from electrons transferred from organic fuels to oxygen
Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water
The protons follow the electrons to produce water
Loss of hydrogen atoms
Energy
Gain of hydrogen atoms
Enzymes remove electrons from glucose molecules and transfer them to a coenzyme
Hydrogen carriers such as NAD+ shuttle electrons in redox reactions
OXIDATION
Dehydrogenaseand NAD+
REDUCTION
• NADH delivers electrons to a series of electron carriers in an electron transport chain
• As electrons move from carrier to carrier, their energy is released in small quantities
Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen
Energy released and now
available for making ATP
ELECTRON CARRIERS
of the electron transport chain
Electron flow
Two mechanisms generate ATP
• ATP can be made by transferring phosphate groups from organic molecules to ADP
• This process is called substrate-level phosphorylation
• Occurs in cytoplasm and in matrix of the mitochondrion
1. Cells use the energy released by “falling” electrons to pump H+ ions across a membrane• The energy of the
gradient is harnessed to make ATP by the process of chemiosmosis
• also known as oxidative phosphorylation
Two mechanisms generate ATP
Figure 6.7A
High H+concentration
ATP synthase uses gradient energy to make ATPMembrane
Energy from
Low H+concentration
ATPsynthase
Electron transport
chain
Definition of cellular respiration
Controlled release of energy from
organic compounds to produce ATP
• Cells break down organic compounds by SLOW oxidation
• Chemical energy is stored in covalent bonds
• By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP
Cellular RespirationBreakdown of one
glucose results in 36 to 38 ATP molecules
• Metabolic Pathway that breaks down carbohydrates
• Process is exergonic as high-energy glucose is broken into CO2 and H2O
• Process is also catabolic because glucose breaks into smaller molecules
Equations for aerobic respirationAll of these are fine!....
Equation for Cellular Respiration
6CO2 + 6H20 + e- + 36-38ATP
+ heat
C6H12O6 + 6O2
YIELDS
Stages of Cellular Respiration1. Glycolysis ALWAYS
OCCURS
2. Anaerobic pathways if no oxygen available (Lactic acid and Ethanol fermentation)
3. Aerobic pathways if oxygen available (Link reaction, Krebs cycle, electron transport chain)
Where Does Cellular Respiration Take Place?
glycolysis occurs in the cytoplasm
Krebs Cycle & ETC Take
place in the mitochondria
Glycolysis: Always the initial stage of respiration
• Location: cytoplasm• Substrate: glucose• Requires input of 2 ATP• Products: pyruvate,
(NADH), 4 ATP Glycolysis is an anaerobic process: no oxygen required
the movie...
Glycolysis
Summary of glycolysis
1. Occurs in the cytoplasm of the cell2. Two ATP molecules are used to start the process
(‘energy investment phase’)3. A total of 4 ATP’s are produced (net gain of 2 ATP)4. 2 molecules of NADH are produced5. Involves substrate level phosphorylation, lysis, oxidation
and ATP formation6. Controlled by enzymes: when ATP levels in the cell are
high, feedback inhibition will block the first enzyme in the pathway
7. Produces 2 pyruvate molecules at the end
If no oxygen is available, glycolysis
(anaerobic) is followed by
fermentation (anaerobic)
Why fermentation?
In the absence of oxygen, glycolysis soon stops unless there is an alternative
acceptor for the electrons produced from the glycolytic pathway
Fermentation1. Alcoholic fermentation Pyruvate is converted into ethanol plus carbon dioxide and NAD+
2. Lactate fermentation
Pyruvate is converted into lactate and NAD+
Alcoholic fermentation in yeast
Alcoholic fermentation in yeast
• Pyruvate is produced from glycolysis• 3-carbon pyruvate is converted to 2-carbon ethanol and
carbon dioxide• Generation of carbon dioxide helps bread products to rise• Yeast is used to produce ethanol
Lactate fermentation in mammals
• Lactate is a 3-carbon molecule
• NAD+ is regenerated to allow glycolysis to continue
Aerobic respiration: Higher level
8.1.4: Explain aerobic respiration: the Link reaction, the Krebs cycle, the role of NADH and H+, the electron transport chain and the role of oxygen8.1.5: Explain oxidative phosphorylation in terms of chemiosmosis
Aerobic respiration
• Takes place in the mitochondria of eukaryotic cells
• Substrate: pyruvate• Produces LOTS of ATP (28 –
38 ATP): 90% of total ATP from respiration
• Also produces carbon dioxide, water and heat
• Oxygen is the final electron acceptor
Aerobic respiration
• 2 pyruvate molecules enter the mitochondrion
• Pyruvate loses a CO2 molecule and becomes acetyl CoA
• Krebs cycle produces 2 ATP, 4 CO2, 6 NADH and 3 FADH2
• Electron transport chain produces 34 ATP and water
• Aerobic respiration completely oxidises glucose
• Anaerobic respiration does not completely oxidise glucose – ethanol, lactate and carbon dioxide are by-products
Get to know your mitochondrial structure!
Stages of aerobic respiration
1. The ‘link’ reaction2. The Krebs cycle
3. The electron transport chain4. Chemiosmosis and oxidative phosphorylation
The Link Reaction
Steps 2 in aerobic respiration (step 1 is glycolysis in the cytoplasm)
After glycolysis, when there is ample oxygen…2 pyruvate molecules from glycolysis move into the matrix of the mitochondrion for the Link reaction and the Krebs cycle
Matrix – Link Reaction
Krebs Cycle
2
2
The Link reaction
The link reaction converts pyruvate (3C) into acetyl Coenzyme A (2C), producing carbon dioxide and NADH in the process
• Krebs: The walk-through...• Krebs: the movie…• The 2C acetyl Coenzyme A enters the Krebs cycle • It joins oxaloacetate (4C) to form citrate (6C). • Two carbon atoms are then lost as carbon dioxide
and the cycle repeats.• Hydrogen is released during this cycle to reduce
the coenzymes NAD+ and FAD to 3 NADH and 1 FADH2 for each cycle
• ATP is also released
The Krebs Cycle (Citric Acid/TCA cycle)
Each molecule of glucose produces• 2 pyruvates in
glycolysis• Leading to 2 acetyl CoA
molecules in the link reaction
Krebs cycle turns TWICE for each molecule of glucose
Fill in your table!
Substance Oxidised/Reduced/Neither Reason
NAD+
NADH
FADH2
FAD
How did you do?Substance Oxidised/
Reduced/NeitherReason
NAD+
NADH
FADH2
FAD
oxidised
reduced
reduced
neither
+ve due to lost electrongained H from organic moleculegained H from organic moleculeno loss/gain of H/electrons
Glycolysis: 2 ATP, 2 NADH, 2 pyruvate
Link: 2 NADH, CO2
Krebs : 2 ATP, 6 NADH, 2 FADH2, 2 CO2
Overall: 4 ATP, 10 NADH, 2 FADH2
Production PER glucose molecule
and finally….
The electron transport chain, chemiosmosis and oxidative
phosphorylation
• The movie…
Chemiosmosis in the mitochondrion
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Proteincomplex
Electroncarrier
Electronflow
ELECTRON TRANSPORT CHAIN ATP SYNTHASE
Rotenone Cyanide,carbon monoxide
Oligomycin
ELECTRON TRANSPORT CHAIN ATP SYNTHASE
Poisons interrupt critical events in cellular respiration
• The electrons from NADH and FADH2 travel down the electron transport chain to oxygen
• Energy released by the electrons is used to pump H+ (protons) into the space between the mitochondrial membranes
• In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase, which capture the energy to make ATP
Chemiosmosis powers most ATP production
Questions…
• What is the role and the position of oxygen in the electron transport chain?
• What is the benefit of having cristae in the mitochondria?
Chemiosmosis/ ETC occurs on the inner membrane of the mitochondria
Figure 6.12
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Proteincomplex
Electroncarrier
Electronflow
ELECTRON TRANSPORT CHAIN ATP SYNTHASE
Final checks and balancesProcess ATP used ATP produced Net ATP gain
Glycolysis
Krebs cycle
Electron Transport Chain/
ChemiosmosisTotal
Final checks and balances
Process ATP used ATP produced Net ATP gain
Glycolysis 2 4 2
Krebs cycle 0 2 2
Electron Transport Chain/
Chemiosmosis
0 32 32
Total 2 38 36
Review of mitochondrial structure and function
Outer mitochondrial membrane
Matrix
Cristae
Inner mitochondrial membrane
Space between inner and outer membranes
Review of mitochondrial structure and function
Outer mitochondrial membrane Separates contents of mitochondrion from rest of cell
Matrix Like cytoplasm: enzymes for the Link reaction and the Krebs cycle
Cristae Increases surface area for oxidative photophosphorylation
Inner mitochondrial membrane Carriers for electron transport chain and ATP synthase and
Space between inner and outer membranes
Reservoir for protons (H+ ions) to create concentration gradient
For each glucose molecule that enters cellular respiration, respiration produces up to 38 ATP molecules
KREBSCYCLE
Electron shuttleacrossmembranes
Cytoplasmic fluid
GLYCOLYSIS
Glucose2
Pyruvicacid
2AcetylCoA
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
by substrate-levelphosphorylation
used for shuttling electronsfrom NADH made in glycolysis
by substrate-levelphosphorylation
by chemiosmoticphosphorylation
Maximum per glucose:
Some practice questions on respiration…
1. How do cells capture the energy released by cell respiration?
A. They store it in molecules of carbon dioxide.
B. They produce glucose.
C. The energy is released as pyruvate.
D. They produce ATP.
(Total 1 mark)
Some practice questions on respiration…
2. Which process produces the most ATP per molecule of glucose?
A. Anaerobic respiration in a yeast cell
B. Aerobic respiration in a bacterial cell
C. Glycolysis in a human liver cell
D. The formation of lactic acid in a human muscle cell
(Total 1 mark)
Some practice questions on respiration…
3. Which of the following is the best definition of cell respiration?
A. A process needed to use energy, in the form of ATP, to produce organic compounds
B. A process used to provide oxygen to the atmosphere
C. A controlled release of energy, in the form of ATP, from organic compounds in cells
D. A controlled release of energy in the production of food from organic compounds
(Total 1 mark)
Some practice questions on respiration…
4. Which of the following processes produces CO2?
I. Glycolysis
II. Alcohol (ethanol) fermentation
III. Lactic acid production
A. I only
B. II only
C. I and II only
D. I, II and III
(Total 1 mark)
Some practice questions on respiration…
4. Which of the following processes produces CO2?
I. Glycolysis
II. Alcohol (ethanol) fermentation
III. Lactic acid production
A. I only
B. II only
C. I and II only
D. I, II and III
(Total 1 mark)
Some practice questions on respiration…
4. State a word equation for anaerobic cell respiration in humans.
(1 mark)