Becker's World of the Cell - Bioenergetics (Chapter 5) Flashcards

Flashcards covering energy needs of cells, forms of work, energy flow, thermodynamics, and key concepts in bioenergetics from Chapter 5.

What are the four essential needs of every cell?

Molecular building blocks; chemical catalysts (enzymes); information to guide activities; energy to drive reactions and processes.

Name the six categories of work that require energy in cells.

Synthetic work; Mechanical work; Concentration work; Electrical work; Generation of heat; Generation of light.

What is synthetic work in bioenergetics?

Biosynthesis that forms new chemical bonds and molecules; required for growth and maintenance; energy is used to make energy-rich organic molecules incorporated into macromolecules.

What is mechanical work in the cell?

Changes in the location or orientation of a cell or subcellular structure; requires energy.

Provide examples of mechanical work in cells.

Movement of a cell or organelles via cilia/flagella; muscle contraction; chromosome movement along spindle fibers during mitosis; cytoplasmic streaming; movement of ribosomes along mRNA; movement of organelles along microtubules.

What is concentration work?

Moving molecules across a membrane against a concentration gradient; accumulates substances or removes toxic by-products.

Give examples of concentration work.

Import of sugars and amino acids into cells; concentration of specific molecules and enzymes in organelles; digestive enzymes in secretory vesicles.

What is electrical work in bioenergetics?

Moving ions across a membrane against an electrochemical gradient, creating membrane potential.

Why is electrical work important in biology?

Generation of membrane potential; ATP production in mitochondria/chloroplasts; transmission of nerve impulses; Na+ and K+ transport across membranes.

What is heat as a form of energy in living systems?

Heat is a by-product of many reactions and is used by homeotherms to regulate body temperature; not typically a primary energy source for cellular work.

Define homeotherms.

Animals that regulate their body temperature independently of the environment.

What is bioluminescence?

Production of light using an energy source (ATP or chemical oxidation) and fluorescence; seen in organisms like fireflies and some jellyfish.

What is fluorescence in bioluminescent systems?

Emission of light following absorption of light of a shorter wavelength.

What is Green Fluorescent Protein (GFP) and where does it come from?

A protein from the jellyfish Aequorea victoria; GFP absorbs blue light and emits pale green fluorescence; used to study protein locations by fusing GFP to proteins.

How do organisms obtain their energy and carbon sources?

Energy from sunlight (phototrophs) or oxidation of organic compounds (chemotrophs); carbon from CO2 (autotrophs) or organic molecules (heterotrophs).

Differentiate phototrophs and chemotrophs.

Phototrophs obtain energy from light; chemotrophs obtain energy from chemical bonds in molecules.

Differentiate autotrophs and heterotrophs.

Autotrophs use CO2 as a carbon source; heterotrophs rely on preformed organic molecules for carbon.

What is a photoautotroph?

Photoautotrophs use solar energy to produce all carbon compounds from CO2 (photosynthesis).

What are chemoautotrophs?

Organisms that oxidize inorganic compounds (like H2S, H2, or inorganic ions) for energy and use CO2 as a carbon source.

What are chemoheterotrophs?

Organisms that ingest and use organic compounds for both energy and carbon (e.g., animals, fungi, many bacteria).

Define oxidation in the context of bioenergetics.

Removal of electrons from a substance, usually accompanied by hydrogen loss; oxidation reactions release energy.

Define reduction in bioenergetics.

Addition of electrons to a substance (often with hydrogen); reduction requires energy input.

How is energy flow characterized in the biosphere?

Energy from the sun drives the formation of reduced compounds via photosynthesis; energy is released by oxidation; energy flow is unidirectional while matter cycles.

Who are producers and consumers in bioenergetics?

Producers (phototrophs) create reduced compounds via photosynthesis; consumers (chemotrophs) oxidize those compounds to release stored energy.

Is biological energy conversion 100% efficient?

No; some energy is lost as heat, which can be used to maintain body temperature in warm-blooded animals or for other functions in plants.

What is meant by an open vs a closed system in bioenergetics?

Open systems can exchange energy with their surroundings; organisms are open systems; closed systems do not exchange energy.

What is internal energy (E)?

The total energy stored within a system.

What defines the state of a system in thermodynamics?

A set of variable properties held at specific values; when the state changes, the energy change depends only on initial and final states.

Which biological variables are effectively constant during most reactions?

Temperature, pressure, and volume.

Differentiate heat and work.

Heat is energy transfer due to temperature differences; work is energy used to drive a process other than heat flow.

What units quantify energy changes in chemistry?

Calories (cal) and kilocalories (kcal); 1 cal raises 1 g of water by 1°C; 1 kcal = 1000 cal; Joule (J) = 0.239 cal.

State the First Law of Thermodynamics.

Energy is conserved; it can be transformed from one form to another but cannot be created or destroyed.

How is energy conserved in biological systems?

Energy entering a system plus stored energy equals energy leaving the system plus stored energy, maintaining overall balance.

Define ΔE.

The difference in internal energy: ΔE = E2 − E1 for a process.

What is enthalpy (H) and how is ΔH interpreted in biology?

H = E + PV; ΔH is the heat content change; in biology, pressure and volume changes are small, so ΔH indicates heat exchange and can be positive or negative.

What does a negative ΔH indicate?

An exothermic reaction that releases energy.

What does a positive ΔH indicate?

An endothermic reaction that absorbs energy.

State the Second Law of Thermodynamics.

In every physical or chemical change, the universe tends toward greater disorder (entropy); reactions have directionality and spontaneity.

What is entropy (S)?

A measure of randomness or disorder; spontaneous processes tend to increase entropy.

Define ΔG and its relation to spontaneity.

ΔG is the change in free energy; ΔG = ΔH − TΔS; a negative ΔG indicates a thermodynamically spontaneous process.

Differentiate exergonic and endergonic reactions.

Exergonic: ΔG < 0, energy-yielding and spontaneous; Endergonic: ΔG > 0, energy-requiring and not spontaneous under stated conditions.

How are ΔGº′ and Keq related?

ΔGº′ = −RT ln K′eq; under standard conditions, a larger K′eq (more products) gives a more negative ΔGº′.

What is the standard state for ΔGº′ calculations?

25°C (298 K), 1 atm, and all reactants/products at 1.0 M; standard pH 7.0 ( [H+] = 10−7 M ); water not included in calculations.

What is ΔG′ and how does it differ from ΔGº′?

ΔG′ is the free energy change under cellular (non-standard) conditions; it reflects how far a reaction is from equilibrium in a cell; ΔGº′ is under standard conditions and is often used for comparisons.

What is the relationship between ΔG′ and being at equilibrium?

When ΔG′ = 0, the reaction is at equilibrium; in living cells, reactions are rarely at equilibrium and ΔG′ is typically negative or positive depending on conditions.

What is the significance of activation energy and enzymes in bioenergetics?

Activation energy is the energy barrier to reaction; enzymes lower this barrier, increasing reaction rates without changing ΔG.

What is a practical example of ΔG°′ for glucose oxidation given in the notes?

Under standard conditions, ΔG°′ for glucose oxidation is −686 kcal/mol (with ΔH = −673 kcal/mol and −TΔS = −13 kcal/mol).

How is the reverse reaction of glucose oxidation described in terms of ΔG?

The reverse reaction is endergonic with ΔG = +686 kcal/mol under standard conditions.

What analogy is used to illustrate bioenergetics in the notes?

Jumping beans and the jumping reaction, used to explain enthalpy, entropy, and free energy.

What does the jumping beans analogy illustrate about enthalpy and entropy?

Enthalpy relates to heat content (ΔH) and can drive movement between chambers; entropy relates to disorder (ΔS) and can drive the distribution; together they determine ΔG.

Why do cells maintain steady-state conditions rather than equilibrium?

Because life requires continuous energy input in open systems to keep reactions from reaching equilibrium, allowing ongoing work and metabolism.