Metabolism Flashcards
Describe oxidative phosphorylation.
Electrons are transferred to the electron transport chain, creating a proton gradient used by ATP synthase to form ATP.
What happens to electrons in the electron transport chain?
Electrons move from a higher to a lower energy level, releasing energy that pumps protons to form a gradient.
What is the final electron acceptor in the electron transport chain?
Oxygen, which forms water.
What enzyme synthesizes ATP as protons flow down their gradient?
ATP synthase.
Name two important electron carriers in cellular respiration.
NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide).
What happens when NAD+ or FAD picks up electrons?
They are reduced to NADH and FADH2, respectively.
What happens when NADH or FADH2 donates electrons?
They return to their oxidized forms, NAD+
and FAD.
Why does the cell transfer electrons through the electron transport chain?
To release energy gradually and capture it as ATP.
Why do electrons release energy when moving from glucose to oxygen?
They move from a higher-energy state (less electronegative atoms) to a lower-energy state (more electronegative oxygen).
What is cellular respiration
A metabolic pathway that breaks down glucose into carbon dioxide and water, producing ATP
Name the four major stages of cellular respiration.
Glycolysis, Pyruvate oxidation, Citric acid cycle, and Oxidative phosphorylation.
Where does glycolysis occur, and what does it produce?
In the cytosol; it produces two pyruvates, ATP, and NADH from one glucose.
What happens during pyruvate oxidation?
Pyruvate is converted to acetyl CoA in the mitochondrial matrix, releasing CO₂ and generating NADH.
What is oxidative phosphorylation?
A process where NADH and FADH₂ transfer electrons to the electron transport chain, generating ATP via a proton gradient.
Can glycolysis occur without oxygen?
Yes, glycolysis can occur anaerobically through fermentation.
Why are the last three stages of cellular respiration oxygen-dependent?
Pyruvate oxidation and the citric acid cycle rely on oxidative phosphorylation, which requires oxygen directly.
What is glycolysis?
Glycolysis is a series of reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates.
Where does glycolysis occur in the cell?
Glycolysis takes place in the cytosol of the cell.
What are the two main phases of glycolysis?
The energy-requiring phase (investment phase) and the energy-releasing phase (payoff phase).
What happens during the energy-requiring phase of glycosis?
Glucose is rearranged and phosphorylated to form fructose-1,6-bisphosphate, using two ATP molecules.
What happens during the energy-releasing phase?
Two three-carbon sugars are converted into pyruvate, producing four ATP and two NADH molecules.
Which enzyme regulates glycolysis?
Phosphofructokinase, which catalyzes the formation of fructose-1,6-bisphosphate, regulates glycolysis based on the cell’s energy needs. It is inhibited by high ATP levels and activated by high AMP levels, helping balance the cell’s energy needs.
What is the role of pyruvate oxidation in cellular respiration?
Pyruvate oxidation links glycolysis to the citric acid cycle, converting pyruvate into acetyl CoA, which is used as fuel for the citric acid cycle.
Where does pyruvate oxidation occur in eukaryotes?
In eukaryotes, pyruvate oxidation takes place in the mitochondrial matrix.
What is produced during pyruvate oxidation?
Pyruvate oxidation produces acetyl CoA, NADH, and carbon dioxide.
What are the three steps involved in pyruvate oxidation?
- A carboxyl group is removed from pyruvate, releasing carbon dioxide.
- The two-carbon molecule is oxidized, and NAD+ forms NADH.
3.The oxidized two-carbon molecule attaches to Coenzyme A to form acetyl CoA.
What enzyme complex is responsible for pyruvate oxidation?
The pyruvate dehydrogenase complex,
How many molecules of pyruvate enter pyruvate oxidation from glycolysis of one glucose?
Two molecules of pyruvate enter pyruvate oxidation for each glucose molecule.
What is another name for the citric acid cycle?
the tricarboxylic acid (TCA) cycle or the Krebs cycle.
What molecule does the citric acid cycle begin with?
The citric acid cycle begins with acetyl-CoA, derived from the oxidation of pyruvate.
Where does the citric acid cycle take place in eukaryotes?
In eukaryotes, the citric acid cycle takes place in the mitochondrial matrix.
What is the main purpose of the citric acid cycle?
The citric acid cycle harvests energy in the form of NADH, FADH2, and ATP, which are used in oxidative phosphorylation to generate ATP.
What happens in the first step of the citric acid cycle?
Acetyl-CoA combines with oxaloacetate to form citrate, a six-carbon molecule.
What happens in step 3 of the citric acid cycle?
Isocitrate is oxidized, releasing a molecule of carbon dioxide and producing NADH, leaving a five-carbon molecule (α-ketoglutarate)
What is produced in step 5 of the citric acid cycle?
Succinyl-CoA is converted to succinate, producing ATP (or GTP) and releasing CoA.
What is the role of FAD in step 6?
In step 6, succinate is oxidized to fumarate, and FAD is reduced to FADH2.
What is regenerated at the end of the citric acid cycle?
The starting molecule, oxaloacetate, is regenerated, allowing the cycle to begin again.
Why do we need oxygen?
Oxygen is needed for oxidative phosphorylation, the final stage of cellular respiration. It acts as the final electron acceptor in the electron transport chain, allowing ATP to be produced.
What happens if oxygen is not available for cellular respiration?
Without oxygen, the electron transport chain stops, ATP is not produced, and cells can’t carry out necessary functions, which can lead to cell death.
What is oxidative phosphorylation?
Oxidative phosphorylation is the process in cellular respiration where the electron transport chain and chemiosmosis work together to generate ATP.
What happens during chemiosmosis?
Protons flow back into the mitochondrial matrix through ATP synthase, using the energy from this flow to synthesize ATP.
What is the proton gradient, and why is it important?
The proton gradient is created by proton pumping in the electron transport chain. It stores energy that is used by ATP synthase to produce ATP.
What happens if the electron transport chain is inhibited by cyanide?
Cyanide inhibits complex IV, stopping the electron transport chain and reducing the proton gradient.
What happens in fermentation when oxygen is absent?
When oxygen is absent, organisms use fermentation, a process where glycolysis is followed by additional reactions to regenerate NAD+ and continue ATP production.
What are the main types of fermentation?
Lactic acid fermentation and alcohol fermentation
What is the difference between anaerobic cellular respiration and fermentation?
Anaerobic cellular respiration uses an electron transport chain and a different electron acceptor like sulfate, while fermentation only involves glycolysis and additional reactions to regenerate NAD+.
What is the byproduct of lactic acid fermentation?
Lactic acid fermentation produces lactate (lactic acid), which regenerates NAD+ from NADH.
Which cells use lactic acid fermentation?
Muscle cells (during low oxygen conditions) and certain bacteria (such as those used in yogurt production) perform lactic acid fermentation.
How does alcohol fermentation work?
Alcohol fermentation involves converting pyruvate to acetaldehyde (releasing CO2), and then acetaldehyde is reduced to ethanol, regenerating NAD+.
What limits the alcohol content in fermented beverages like beer and wine?
Alcohol is toxic to yeast in high concentrations, and the ethanol tolerance of yeast limits the alcohol content, typically between 5% and 21%.
What is the difference between facultative anaerobes and obligate anaerobes?
Facultative anaerobes can switch between aerobic and anaerobic metabolism, while obligate anaerobes can only survive in the absence of oxygen.
What happens when a cell’s ATP supply is high?
The cell may slow down glucose breakdown to prevent wasting ATP, which could hydrolyze back to ADP.
How is the activity of metabolic pathways controlled?
Through the regulation of enzymes that catalyze individual steps in the pathway.
What is the “committed step” in a metabolic pathway?
It is the first irreversible step in a pathway, often targeted for regulation.
What is an allosteric site?
A regulatory site on an enzyme, other than the active site, where molecules can bind to control enzyme activity.
What is feedback inhibition?
When a product (e.g., ATP) inhibits the pathway that produces it, preventing excess production.
What molecule regulates the enzyme phosphofructokinase (PFK) in glycolysis?
ATP (inhibits), AMP (activates), and citrate (inhibits).
What is the role of AMP in glycolysis regulation?
AMP activates PFK, signaling the cell is low on energy and needs more ATP from glycolysis.
How does citrate affect glycolysis?
Citrate inhibits PFK, signaling that the citric acid cycle is backed up and glycolysis can slow down.
What regulates pyruvate dehydrogenase during pyruvate oxidation?
ATP and NADH inhibit it, while ADP and pyruvate activate it.
