3 Cellular Respiration Flashcards
A step-by-step breakdown of high-energy glucose molecules to release energy, occurring day and night in all living cells.
Cellular respiration
What are the four metabolic stages of cellular respiration?
Anaerobic Respiration
1. Glycolysis
Aerobic Respiration
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain
- Respiration without O₂, occurs in the cytosol.
- only involving glycolysis and producing less energy.
Anaerobic respiration
- Respiration using O₂, occurs in the mitochondria.
- Breaking down glucose completely and releasing large amounts of energy.
Aerobic respiration
Where does glycolysis occur and does it require oxygen?
- cytosol
- does not require oxygen.
What is the process that follows glycolysis in aerobic respiration?
Pyruvate oxidation
What is the main function of the Krebs cycle?
To produce electron carriers (NADH, FADH₂) for the electron transport chain
Flavin adenine dinucleotide
Nicotinamide adenine dinucleotide
Electrons are transferred through protein complexes to produce ATP.
Electron transport chain
What is the overall equation for cellular respiration?
C₆H₁₂O₆ + 6O₂ → ATP + 6H₂O + 6CO₂ (+ heat)
What controls cellular respiration?
Enzymes
The phase where pyruvate migrates from the cytosol to the mitochondrial matrix.
Grooming phase
A stage of cellular respiration that occurs in the mitochondrial matrix, producing electron carriers.
Krebs Cycle (Citric Acid Cycle)
Where does the Electron Transport Chain (ETC) occur?
inner mitochondrial membrane (cristae)
What is oxidative phosphorylation also called? (3)
- electron transport chain
- electron transport-linked phosphorylation
- terminal oxidation
What is ATP often referred to as?
energy currency of cells
How does an ATP molecule release energy?
- When a phosphate group is pulled away during a chemical reaction, releasing energy like a compressed spring.
- ATP releases energy when its high-energy bond between the second and third phosphate groups is broken, converting ATP to ADP and an inorganic phosphate.
The fundamental mode of energy exchange in biological systems, where ATP is converted to ADP and back.
ATP-ADP Cycle
Name some processes in the body that rely on ATP-ADP (4)
- Motion
- Active transport
- Biosyntheses
- Signal amplification
How is ADP converted back to ATP?
general process and chemical explanation
- oxidation of fuel molecules or photosynthesis.
- by the enzyme ATP synthase by adding inorganic phosphate to ADP
How often is ATP recycled in a working muscle cell?
All ATP molecules are recycled about once per minute.
How many ATP molecules are spent and regenerated per second in a working muscle cell?
10 million ATP molecules.
What are two types of anaerobic respiration? What do they produce? (2)
- Homolactic fermentation (produces lactic acid)
- yeast fermentation (produces alcohol + CO2)
Why is glycolysis considered an ancient pathway?
It is where energy transfer first evolved, transferring energy from organic molecules to ATP.
How many ATP molecules are generated from 1 glucose molecule in glycolysis?
2 ATP molecules.
Why is glycolysis considered inefficient?
It generates only 2 ATP for each glucose molecule.
How did early life capture energy without oxygen?
By capturing energy from organic molecules
All modern cells that use glycolysis evolved from __, making it a fundamental metabolic process for all life.
early prokaryotes
How many reactions occur during glycolysis?
10
What does glycolysis convert glucose (6C) into?
2 pyruvate (3C) molecules
- How many ATP and NADH molecules are produced during glycolysis?
- How many ATP molecules are consumed during glycolysis?
- What is the net gain of ATP and NADH from glycolysis?
- 4 ATP molecules; 2 NADH molecules
- 2 ATP molecules
- 2 ATP molecules and 2 NADH molecules
What does DHAP stand for in glycolysis?
Dihydroxyacetone phosphate.
What does G3P stand for in glycolysis?
Glyceraldehyde-3-phosphate
What does NAD+ and NADH stand for? What is there difference?
- Nicotinamide adenine dinucleotide
- nicotinamide adenine dinucleotide (NAD) + hydrogen (H)
- NAD+ Is the oxidized form, that is, a state in which it loses an electron. NADH is a reduced form of the molecule, which means that it gains the electron lost by NAD+.
What occurs during the first half of glycolysis?
General term
Glucose “priming,” preparing glucose to split through phosphorylation and molecular rearrangement.
What is the purpose of phosphorylating glucose in glycolysis?
To destabilize the glucose molecule, making it easier to split.
How many reactions are in the first half of glycolysis?
5 reactions
What key process occurs in the second half of glycolysis?
NADH and ATP production.
How does G3P contribute to NADH production?
- In the sixth step of glycolysis, G3P undergoes an oxidation reaction. The enzyme responsible for this step is glyceraldehyde-3-phosphate dehydrogenase.
- As G3P is oxidized, electrons are transferred from G3P to the electron carrier NAD⁺.
- The transfer of electrons to NAD⁺ reduces it to NADH. For each molecule of G3P oxidized, one molecule of NADH is produced.
What happens to G3P in the second half of glycolysis?
- G3P is oxidized and phosphorylated by glyceraldehyde-3-phosphate dehydrogenase, forming 1,3-bisphosphoglycerate (1,3-BPG). During this step, NAD⁺ is reduced to NADH.
- 1,3-BPG transfers a phosphate group to ADP via phosphoglycerate kinase, producing 1 ATP and forming 3-phosphoglycerate (substrate-level phosphorylation).
- 3-phosphoglycerate is rearranged by phosphoglycerate mutase to form 2-phosphoglycerate.
- 2-phosphoglycerate undergoes dehydration catalyzed by enolase, forming phosphoenolpyruvate (PEP).
- PEP donates its phosphate group to ADP, forming another 1 ATP through substrate-level phosphorylation. The enzyme pyruvate kinase catalyzes this reaction, producing pyruvate as the final product of glycolysis.
What role does phosphoenolpyruvate (PEP) play in ATP production?
PEP donates a phosphate group (P) to ADP, producing ATP.
A process in glycolysis where a phosphate group (P) is transferred from a substrate (PEP) to ADP to form ATP.
Substrate-level phosphorylation?
What enzyme facilitates the transfer of the phosphate group from PEP to ADP?
Pyruvate kinase
What is the reaction (equation) that summarizes glycolysis?
Glucose + 2ADP + 2Pi + 2NAD⁺ → 2 pyruvate + 2ATP + 2NADH.
Why is the energy yield from glycolysis considered low?
Only about 3.5% of the energy stored in glucose is harvested, as many carbons remain to be stripped for more energy.
How is NADH recycled to NAD⁺?
Another molecule must accept the hydrogen (H) from NADH, allowing NAD⁺ to be regenerated.
Aerobically, NADH donates its electrons to the electron transport chain (ETC). __acts as the final electron acceptor, allowing NADH to be oxidized back to __.
- Oxygen
- NAD⁺
In the absence of oxygen, NADH cannot enter the electron transport chain. Instead, it donates its electrons to other organic molecules through __ processes.
fermentation
What do bacteria and yeast produce during alcoholic fermentation?
Ethanol and carbon dioxide
What are some products of alcoholic fermentation? (3)
- Beer
- wine
- bread
What do animals and some fungi produce during fermentation?
Lactic acid
Why is alcoholic fermentation considered a dead-end process?
At approximately 12% ethanol concentration, it kills yeast and the reaction cannot be reversed.
What makes lactic acid fermentation a reversible process?
Once oxygen becomes available, lactate can be converted back to pyruvate by the liver.
What are the three (3) fates of pyruvate produced by glycolysis?
- Anaerobic - Lactic acid fermentation
- Aerobic oxidation (Citric acid cycle and oxidative phosphorylation)
- Anaerobic - Alcoholic fermentation
What enzyme is responsible for making ATP?
ATP synthase
- a large enzyme complex found in the membranes of mitochondria (in eukaryotic cells) and chloroplasts (in plants), as well as in bacterial plasma membranes.
- Its primary function is to synthesize ATP (adenosine triphosphate), the main energy currency of the cell, using energy derived from a proton gradient (H⁺ gradient).
ATP synthase
an electrochemical difference across a membrane that drives ATP synthesis by ATP synthase during chemiosmosis.
H⁺ (proton) gradient
an electrochemical difference across a membrane that drives ATP synthesis by ATP synthase during chemiosmosis.
H⁺ gradient
How is the H⁺ gradient created in mitochondria?
During the electron transport chain (ETC), energy from electrons is used to pump H⁺ ions from the mitochondrial matrix into the intermembrane space.
How is the H⁺ gradient created in chloroplasts?
During the light-dependent reactions of photosynthesis, energy from light pumps H⁺ ions into the thylakoid lumen.
It is the combination of the concentration gradient and charge gradient created by the accumulation of H⁺ ions, driving protons back through ATP synthase.
Proton-motive force
What happens when H⁺ ions flow back through ATP synthase?
The flow of H⁺ ions provides energy to rotate part of ATP synthase, enabling the enzyme to catalyze the conversion of ADP and Pi into ATP.
Uses the energy from the flow of H⁺ ions to synthesize ATP from ADP and inorganic phosphate (Pi).
ATP synthase
What processes use the H⁺ gradient for ATP synthesis? (in animals and plants) (2)
- Oxidative phosphorylation in mitochondria
- photophosphorylation in chloroplasts.
The process by which the energy from a H⁺ gradient is used to drive ATP synthesis through ATP synthase.
Chemiosmosis
What happens to pyruvate during oxidation?
Pyruvate enters the mitochondria and undergoes a 3-step oxidation process.
1. Decarboxylation - pyruvate (a 3-carbon molecule) loses one carbon atom in the form of carbon dioxide (CO₂). enzyme: pyruvate dehydrogenase
2. Oxidation - 2-carbon fragment is oxidized, transferring electrons to NAD⁺, reducing it to NADH. This step helps capture some of the energy released from pyruvate.
3. Formation of Acetyl-CoA - oxidized 2-carbon fragment, now an acetyl group, is attached to coenzyme A (CoA), forming acetyl-CoA, which then enters the Krebs cycle for further energy production.
What are the three steps in the oxidation of pyruvate?
- Release of 1 CO₂ (carbon counting: 3C → 2C).
- Reduction of NAD⁺ to NADH by transferring electrons.
- Formation of acetyl CoA.
What happens to the acetyl CoA produced?
enters the Krebs cycle
What is the yield from oxidizing 2 pyruvate molecules? (3)
- 2 acetyl CoA (2C sugar)
- 2 NADH
- 2 CO₂.
Why is the oxidation of pyruvate important?
It links glycolysis to the Krebs cycle (citric acid cycle), enabling continued ATP production through aerobic respiration.
Where does the Krebs cycle occur?
mitochondrial matrix.
How many steps are in the Krebs cycle?
8 steps
What is broken down during the Krebs cycle?
A 6-carbon citrate (citric acid) molecule is catabolized step-by-step.
- acetyl-CoA (2 carbons) combined with oxaloacetate (4 carbons) to form citrate (aka citric acid, 6 carbons)
The Krebs cycle evolved later because free oxygen became available around __ years ago with the advent of photosynthesis, allowing for aerobic respiration in eukaryotes.
- 2.7 billion
When did glycolysis and aerobic respiration evolve in relation to Earth’s history?
- Glycolysis in bacteria 3.5 billion years ago
- aerobic respiration evolved around 1.5 billion years ago
- development of organelles like mitochondria in eukaryotes.
What does the Krebs cycle produce in large quantities?
Electron carriers (NADH and FADH₂).
What are the two main electron carriers produced in the Krebs cycle?
NADH and FADH₂.
Where do NADH and FADH₂ go after being produced in the Krebs cycle?
Electron Transport Chain to donate their electrons
What is produced from each pyruvate molecule during the Krebs cycle?
1 ATP, 4 NADH, 1 FADH₂, and CO₂.
What is the net gain from two turns of the Krebs cycle (for 2 pyruvate)? (3)
- 6 NADH
- 2 FADH₂
- 2 ATP.
What happens to the pyruvate during the Krebs cycle?
It is fully oxidized to CO₂.
Why is the Krebs cycle considered an important adaptation despite the low ATP yield?
Its main value lies in the production of NADH and FADH₂, which are essential electron carriers.
What role do NADH and FADH₂ play in cellular respiration?
They carry electrons and H⁺ ions to the Electron Transport Chain for further ATP production.
How do reduced molecules from the Krebs cycle contribute to energy production?
They facilitate the movement of electrons and H⁺ ions, enhancing the efficiency of ATP synthesis in the Electron Transport Chain.
What is the total ATP yield from glycolysis and the Krebs cycle combined?
4 ATP (2 ATP from glycolysis and 2 ATP from the Krebs cycle).
- How much ATP does a working muscle cell recycle per second?
- Why is the recycling of ATP so rapid in muscle cells?
- over 10 million ATP molecules per second.
- Muscle cells require a constant supply of ATP for activities like contraction and relaxation, which are essential for movement and maintaining homeostasis.
What happens to muscles during intense exercise when oxygen is limited? What is/are the byproducts?
anaerobic respiration (fermentation) to produce ATP.
Lactic acid is produced, which can contribute to muscle fatigue and cramps.
A series of molecules embedded in the inner mitochondrial membrane that facilitates electron transport.
Electron Transport Chain (ETC)
Where is the ETC located in the mitochondria?
It is located along the cristae of the inner mitochondrial membrane.
How does the transport of electrons in the ETC contribute to ATP production?
The transport of electrons is linked to the pumping of H⁺ ions, creating a proton gradient that drives ATP synthesis.
How many ATP molecules can be produced from one glucose molecule via the ETC?
approximately 34 ATP
Under what condition does the Electron Transport Chain operate?
It operates only in the presence of oxygen (aerobic respiration).
What happens to NADH in the Electron Transport Chain (ETC)?
NADH passes electrons to the ETC, where hydrogen is cleaved off.
What occurs when hydrogen is cleaved off NADH and FADH₂?
Electrons are stripped from hydrogen atoms, resulting in H⁺ (protons) and free electrons.
What is the role of transport proteins in the ETC?
pump H⁺ (protons) across the inner membrane into the intermembrane space.
What is the result of pumping protons into the intermembrane space?
It creates a proton gradient that is essential for ATP synthesis.
How do electrons move in the Electron Transport Chain (ETC)?
- from one carrier to another
- flowing downhill to oxygen, with each carrier being more electronegative.
What is meant by “controlled oxidation” in the ETC?
gradual release of energy as electrons are passed from one carrier to the next, preventing rapid energy loss.
How do protons contribute to ATP synthesis?
Protons flow through ATP synthase, which uses the energy from this flow to synthesize ATP from ADP and inorganic phosphate (Pi).
- The diffusion of ions, specifically protons (H⁺), across a membrane, contributing to ATP synthesis.
- the process by which the H⁺ gradient established by the ETC drives the synthesis of ATP through ATP synthase.
chemiosmosis
Who proposed the chemiosmotic hypothesis?
Peter Mitchell
It is the idea that the energy generated from the movement of electrons through the Electron Transport Chain is used to pump protons across a membrane, creating a gradient that drives ATP synthesis.
chemiosmotic hypothesis
What are the four (4) steps of the chemiosmotic hypothesis proposed by Peter Mitchell?
- Electrons are harvested and carried to the transport system.
- Electrons provide energy to pump protons across the membrane.
- Oxygen joins with protons to form water.
- Protons diffuse back in down their concentration gradient, driving the synthesis of ATP.
Where did the glucose come from?
photosynthesis in plants, where carbon dioxide (CO₂) and water (H₂O) are converted into glucose using sunlight.
Where did the O₂ come from?
photosynthesis by plants, algae, and cyanobacteria as a byproduct of splitting water molecules.
Where did the CO₂ come from?
- produced during cellular respiration when glucose is broken down for energy, as well as from the combustion of fossil fuels and respiration of animals.
Where did the CO₂ go?
atmosphere, where it can be used by plants for photosynthesis or contribute to the greenhouse effect.
Where did the H₂O come from?
during cellular respiration as a byproduct when electrons combine with oxygen and protons, and it is also a reactant in photosynthesis.
Where did the ATP come from?
During cellular respiration through
- glycolysis
- Krebs cycle, and
- oxidative phosphorylation via the electron transport chain.
What else is produced that is not listed in the cellular respiration equation?
Heat is also produced as a byproduct of cellular respiration, which helps maintain body temperature in living organisms.
Why do we breathe?
We breathe to obtain oxygen (O₂) for cellular respiration, which is necessary for producing ATP and to expel carbon dioxide (CO₂), a waste product of metabolism.
What is the final electron acceptor in the Electron Transport Chain (ETC)?
oxygen (O₂)
So what happens if O₂ is unavailable? (4)
If oxygen is unavailable:
- The ETC backs up because there is nothing to pull electrons down the chain.
- NADH and FADH₂ cannot unload hydrogen (H) ions.
- ATP production ceases.
- Cells run out of energy, leading to cell death and potentially death of the organism.
What happens to proteins during metabolism? (2)
- broken down into amino acids (AAs)
- undergo deamination.
How does alanine enter the Krebs cycle?
pyruvate.
glutamate -> a-ketoglutamate
How does glutamate enter the Krebs cycle?
Glutamate is converted to α-ketoglutarate.
What happens to fats during metabolism?
degraded into individual fatty acids and glycerol.
What is the process of fatty acid oxidation called?
Beta oxidation, where long fatty acid chains are attacked by enzymes to remove 2C chunks.
What do fatty acids convert into?
acetyl-CoA.
How does aspartate enter the Krebs cycle?
oxaloacetate.
How do amino acids join the Krebs cycle?
Amino acids can join the Krebs cycle at different points, depending on their conversion products.
