Cellular Energy, Enzymes, and Photosynthesis

Vocabulary practice flashcards covering thermodynamics, enzyme kinetics and inhibition, ATP structure and cycling, and the stages of photosynthesis (Light Dependent Reactions and the Calvin Cycle).

Photosystems

Light-collecting units of the chloroplast composed of a reaction center and light-capturing complexes.

Reaction Center

A complex of proteins with chlorophyll and an electron acceptor.

Light-Capturing Complexes

Pigments associated with proteins that absorb light energy in photosystems.

ATP Synthase

An enzyme complex that couples the diffusion of $H^+$ to the formation of ATP.

Calvin Cycle

A cyclic pathway that uses ATP and NADPH to reduce $CO_2$ to glucose. Its inputs are $3\text{ }CO_2$, $9\text{ ATP}$, and $6\text{ NADPH}$; its outputs are $1\text{ Glucose}$, $9\text{ ADP}$, and $6\text{ }NADP^+$.

Competitive Inhibitors

Molecules that reduce enzyme activity by blocking substrates from binding to the active site; this inhibition can be reversed by increasing substrate concentration.

Noncompetitive Inhibitors

Inhibitors that bind to an area other than the active site (allosteric site), changing the shape of the active site and preventing substrates from binding.

Feedback Inhibition

A control mechanism where the end product of a metabolic pathway acts as an inhibitor to early enzymes in the same pathway by binding to an allosteric site (e.g., on enzyme 1).

Catabolic Reaction

A reaction in which energy is released when chemical bonds are broken, which may be released as heat or light, or transferred to another molecule.

Anabolic Reactions

Reactions in which energy is required to form bonds, such as taking amino acids and building them into protein.

1st Law of Thermodynamics

The law stating that energy cannot be created or destroyed, but can be converted, such that the sum of energy before conversion equals the sum of energy after conversion.

2nd Law of Thermodynamics

The law stating that some usable energy dissipates during transformations and is lost as heat, meaning organisms cannot continuously recycle energy and every transformation increases the entropy of the universe.

ATP (Adenosine Triphosphate)

The energy currency of organisms composed of adenine, ribose, and three phosphate groups; it powers cellular work by coupling exergonic to endergonic reactions and releases energy when the bond between the 2nd and 3rd phosphate is broken via hydrolysis.

Phosphorylation

The transfer of a released phosphate group from ATP to another molecule to give it energy.

Chloroplasts

The organelles that serve as the site and location of photosynthesis in plant cells.

Stomata

Pores in leaves that allow $CO_2$ to enter and $O_2$ to exit.

Stroma

The aqueous internal fluid of the chloroplast where the Calvin cycle occurs.

Thylakoids

Membrane-bound compartments inside chloroplasts that form stacks known as grana and serve as the site of light-dependent reactions (LDRs).

Chlorophyll

The green pigment located in thylakoid membranes that absorbs visible light for photosynthesis.

Redox Reaction

A chemical reaction involving the complete or partial transfer of one or more electrons from one reactant to another; in photosynthesis, electrons are transferred with $H^+$ to $CO_2$, reducing it to sugar.

Light Dependent Reaction (LDR)

The stage of photosynthesis that absorbs light and splits $H_2O$ into hydrogen and oxygen; it takes in $H_2O$, ADP, and $NADP^+$ to generate $O_2$, ATP, and NADPH.