Bioenergetics
63 flashcards covering Bioenergetics for the MCAT Biology & Biochemistry section.
Bioenergetics is the study of how living organisms manage and transform energy to sustain life. At its core, it involves processes like cellular respiration, photosynthesis, and metabolism, where energy from sources such as food or sunlight is converted into usable forms like ATP. This field helps us understand how cells efficiently capture, store, and use energy, making it essential for grasping the fundamentals of biology and biochemistry.
On the MCAT, bioenergetics frequently appears in Biology & Biochemistry questions, often as multiple-choice items testing energy pathways, enzyme roles, or free energy changes. Common traps include confusing anabolic and catabolic processes or miscalculating energy yields, so watch for questions that integrate concepts like Gibbs free energy with real-world scenarios. Focus on key topics such as ATP production, electron transport chains, and metabolic regulation to handle passage-based and standalone questions effectively.
A concrete tip: Practice sketching energy diagrams to visualize transformations quickly.
Terms (63)
- 01
ATP
Adenosine triphosphate is the main energy carrier in cells, releasing energy when its phosphate bonds are hydrolyzed to ADP and inorganic phosphate.
- 02
ADP
Adenosine diphosphate is the molecule formed when ATP loses a phosphate group, and it can be phosphorylated back to ATP using energy from cellular processes.
- 03
Cellular respiration
The process by which cells convert biochemical energy from nutrients into ATP, primarily through glycolysis, the Krebs cycle, and oxidative phosphorylation.
- 04
Glycolysis
The metabolic pathway that breaks down one glucose molecule into two pyruvate molecules in the cytoplasm, yielding a net gain of two ATP and two NADH.
- 05
Pyruvate
The three-carbon compound produced at the end of glycolysis, which can enter the mitochondria for further oxidation or be converted to lactate in anaerobic conditions.
- 06
Krebs cycle
A series of reactions in the mitochondrial matrix that oxidize acetyl-CoA to CO2, producing NADH, FADH2, and ATP or GTP while transferring electrons to the electron transport chain.
- 07
Electron transport chain
A series of protein complexes in the inner mitochondrial membrane that pass electrons from donors like NADH to acceptors, ultimately reducing oxygen to water and creating a proton gradient.
- 08
Oxidative phosphorylation
The process where the energy from the electron transport chain's proton gradient is used to synthesize ATP from ADP and inorganic phosphate via ATP synthase.
- 09
Chemiosmosis
The movement of protons across a membrane down their concentration gradient, driving ATP synthesis in mitochondria and chloroplasts.
- 10
Proton gradient
The difference in hydrogen ion concentration across the inner mitochondrial membrane, generated by the electron transport chain and used to power ATP production.
- 11
NADH
Nicotinamide adenine dinucleotide in its reduced form, a key electron carrier that donates electrons to the electron transport chain during cellular respiration.
- 12
FADH2
Flavin adenine dinucleotide in its reduced form, another electron carrier that donates electrons to the electron transport chain, typically producing less ATP than NADH.
- 13
Photosynthesis
The process by which plants, algae, and some bacteria convert light energy into chemical energy, storing it as glucose through the light-dependent and light-independent reactions.
- 14
Light-dependent reactions
The phase of photosynthesis where light energy is absorbed by chlorophyll and used to split water, producing ATP, NADPH, and oxygen in the thylakoid membranes.
- 15
Light-independent reactions
Also known as the Calvin cycle, this phase uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide into glucose in the stroma of chloroplasts.
- 16
Chlorophyll
The green pigment in chloroplasts that absorbs light energy, primarily in the blue and red wavelengths, to drive the electron transfers in photosynthesis.
- 17
Free energy
The Gibbs free energy, denoted as ΔG, measures the amount of energy available to do work in a system at constant temperature and pressure, determining if a reaction is spontaneous.
- 18
Enthalpy
A measure of the total heat content of a system, represented as ΔH, which includes the internal energy and the energy required to displace the environment.
- 19
Entropy
A measure of disorder or randomness in a system, denoted as ΔS, where an increase in entropy favors spontaneous reactions in isolated systems.
- 20
Exergonic reaction
A chemical reaction with a negative ΔG, meaning it releases free energy and proceeds spontaneously without external energy input.
- 21
Endergonic reaction
A chemical reaction with a positive ΔG, requiring an input of energy to proceed and often coupled with exergonic reactions in cells.
- 22
Activation energy
The minimum energy required to start a chemical reaction by overcoming the energy barrier, which enzymes help lower in biological systems.
- 23
Enzymes
Proteins that act as biological catalysts, speeding up chemical reactions by lowering activation energy without being consumed in the process.
- 24
Substrate
The specific molecule that an enzyme acts upon, binding to the enzyme's active site to form an enzyme-substrate complex and undergo reaction.
- 25
Active site
The specific region on an enzyme where the substrate binds and the chemical reaction occurs, shaped to fit the substrate like a lock and key.
- 26
Michaelis-Menten kinetics
A model describing the rate of enzymatic reactions, where the reaction velocity depends on substrate concentration and reaches a maximum at enzyme saturation.
- 27
Km
The Michaelis constant, representing the substrate concentration at which an enzyme operates at half its maximum velocity, indicating enzyme affinity for the substrate.
- 28
Vmax
The maximum reaction velocity of an enzyme when it is fully saturated with substrate, reflecting the enzyme's catalytic efficiency.
- 29
Competitive inhibition
A type of enzyme inhibition where an inhibitor molecule competes with the substrate for the active site, reducing the enzyme's effectiveness by increasing Km.
- 30
Noncompetitive inhibition
A form of enzyme inhibition where the inhibitor binds to a site other than the active site, altering the enzyme's shape and decreasing Vmax without affecting Km.
- 31
Allosteric regulation
The modulation of an enzyme's activity by the binding of a molecule at a site other than the active site, which can either activate or inhibit the enzyme.
- 32
Feedback inhibition
A regulatory mechanism where the end product of a metabolic pathway inhibits an earlier enzyme, preventing overproduction of the product.
- 33
ATP synthase
An enzyme complex that uses the energy from a proton gradient to catalyze the formation of ATP from ADP and inorganic phosphate.
- 34
Fermentation
An anaerobic process that converts pyruvate into products like lactate or ethanol, regenerating NAD+ to allow glycolysis to continue without oxygen.
- 35
Anaerobic respiration
A metabolic process similar to aerobic respiration but using an electron acceptor other than oxygen, yielding less ATP than aerobic processes.
- 36
Aerobic respiration
The oxygen-dependent process of producing ATP through glycolysis, the Krebs cycle, and oxidative phosphorylation, maximizing energy yield from glucose.
- 37
Energy coupling
The linking of an exergonic reaction, like ATP hydrolysis, to an endergonic reaction to drive it forward in cellular processes.
- 38
Substrate-level phosphorylation
The direct transfer of a phosphate group to ADP from a substrate in a reaction, producing ATP without involving the electron transport chain.
- 39
Redox reaction
A chemical reaction involving the transfer of electrons between molecules, where one is oxidized and the other is reduced.
- 40
Oxidation
The loss of electrons from a molecule, often involving the addition of oxygen or removal of hydrogen, as seen in metabolic pathways.
- 41
Reduction
The gain of electrons by a molecule, typically involving the addition of hydrogen or removal of oxygen, common in energy production.
- 42
Standard reduction potential
A measure of the tendency of a chemical species to gain electrons and be reduced, compared to the hydrogen ion, guiding electron flow in redox reactions.
- 43
Electron carriers
Molecules like NADH and FADH2 that transport electrons between reactions in metabolic pathways, facilitating energy transfer.
- 44
Catabolism
The set of metabolic pathways that break down molecules into smaller units, releasing energy for ATP production.
- 45
Anabolism
The metabolic processes that build complex molecules from simpler ones, requiring energy input and often using ATP.
- 46
Amphibolic pathway
A metabolic pathway that serves both catabolic and anabolic functions, such as the Krebs cycle, which provides intermediates for biosynthesis.
- 47
Net ATP from glycolysis
Glycolysis produces a net gain of two ATP molecules per glucose molecule, after accounting for the two ATP used in the early steps.
- 48
Difference between NADH and NADPH
NADH is primarily involved in catabolic reactions for energy production, while NADPH is used in anabolic reactions for biosynthesis and reduction.
- 49
Photosystems I and II
Protein complexes in the thylakoid membrane that absorb light and transfer electrons; Photosystem II splits water, and Photosystem I produces NADPH.
- 50
Calvin cycle
The light-independent phase of photosynthesis that fixes CO2 into organic molecules using ATP and NADPH to produce glyceraldehyde-3-phosphate.
- 51
Common trap in enzyme inhibition
Students often confuse competitive and noncompetitive inhibition; the former increases Km while the latter decreases Vmax without changing Km.
- 52
ΔG equation
The Gibbs free energy change is given by ΔG = ΔH - TΔS, where T is temperature in Kelvin, used to predict reaction spontaneity.
For a reaction with ΔH of -10 kJ/mol and ΔS of 0.05 kJ/mol·K at 298 K, ΔG = -10 - 2980.05 = -10 - 14.9 = -24.9 kJ/mol, indicating it's spontaneous.
- 53
Energy yield from glucose
Complete oxidation of one glucose molecule through aerobic respiration yields about 30-32 ATP, depending on the shuttle system used for NADH.
- 54
Role of oxygen in respiration
Oxygen serves as the final electron acceptor in the electron transport chain, allowing the chain to continue and produce a proton gradient.
- 55
C4 photosynthesis
A variation of photosynthesis in certain plants that minimizes photorespiration by initially fixing CO2 into a four-carbon compound in mesophyll cells.
- 56
Strategy for calculating ATP yield
To calculate net ATP from a metabolic pathway, add ATP produced directly and from oxidative phosphorylation, subtracting any used in the process.
- 57
Allosteric site
A specific location on an enzyme, distinct from the active site, where regulatory molecules bind to alter the enzyme's activity.
- 58
Proton motive force
The energy stored in the form of a proton gradient across a membrane, which drives ATP synthesis and other transport processes.
- 59
Irreversible inhibitors
Compounds that permanently bind to and inactivate enzymes, unlike reversible inhibitors, leading to long-term effects on metabolic pathways.
- 60
Bioenergetic efficiency
The ratio of useful energy output, like ATP produced, to the total energy input in metabolic processes, often less than 50% due to heat loss.
- 61
Common trap in thermodynamics
A negative ΔG means a reaction is spontaneous, but it does not indicate the reaction rate; enzymes are needed to speed it up.
- 62
Rubisco
The enzyme in the Calvin cycle that catalyzes the fixation of CO2 to ribulose bisphosphate, though it can also react with oxygen, leading to photorespiration.
- 63
Uncoupling proteins
Proteins in the inner mitochondrial membrane that dissipate the proton gradient as heat instead of ATP, as seen in brown fat for thermogenesis.