Unit 3: Cellular Energetics

Energy

the capacity to cause change

Metabolism

the chemical reactions occurring within a living organism

Catabolic pathways (Catabolism)

release energy by breaking down complex molecules into simpler compounds

Anabolic pathways (Anabolism)

consume energy to build complex molecules from simpler ones

Free energy (ΔG)

energy that can do work when temperature and pressure are uniform, as in a living cell

Exergonic reaction

a reaction with a net release of free energy and is spontaneous

Endergonic reaction

absorbs free energy from its surroundings and is nonspontaneous

Catalyst

a chemical agent that speeds up a reaction without being consumed by the reaction

Enzyme

a catalytic protein that speeds up a reaction without being consumed by the reaction

Activation energy

the initial energy needed to start a chemical reaction

Substrate

the reactant that an enzyme acts on

Active site

the region on the enzyme where the substrate binds

Enzyme-substrate complex

the complex formed when the enzyme binds to its substrate

Induced fit

enzymes change shape due to chemical interactions with the substrate and the active site

Competitive inhibitors

bind to the active site of an enzyme, competing with the substrate

Noncompetitive inhibitors

bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective

Allosteric regulation

may either inhibit or stimulate an enzyme's activity by binding to a different site on the enzyme

Cofactors

non-protein enzyme helpers

Coenzyme

an organic cofactor

Cooperativity

a form of allosteric regulation that can amplify enzyme activity

Feedback inhibition

the end product of a metabolic pathway shuts down the pathway

Adenosine Triphosphate (ATP)

a modified nucleotide that serves as the primary energy currency of cells

Fermentation

a partial degradation of sugars that occurs without oxygen

Aerobic respiration

consumes organic molecules and oxygen and yields ATP

Glycolysis

breaks down glucose into two molecules of pyruvate

Citric acid cycle

completes the breakdown of glucose in the mitochondrial matrix

Oxidative phosphorylation

accounts for most of the ATP synthesis and occurs in the inner membrane of the mitochondria

NADH and FADH2

electron carriers that donate electrons to the electron transport chain

Photosynthesis

the process that converts solar energy into chemical energy

Chloroplasts

the site of photosynthesis in plants

Stomata

microscopic pores on leaves through which CO2 enters and O2 exits

Thylakoids

connected sacs in the chloroplasts where chlorophyll is located

Stroma

a dense interior fluid in the chloroplast where the Calvin cycle occurs

Pigments

substances that absorb visible light

Photosystem

a reaction-center complex surrounded by light-harvesting complexes

Primary electron acceptor

accepts excited electrons from the reaction center

Linear electron flow

involves the flow of electrons through the photosystems and ETC to produce ATP and NADPH

Calvin cycle

uses the chemical energy of ATP and NADPH to reduce CO2 to sugar

Carbon fixation

the incorporation of CO2 into organic molecules using the enzyme rubisco

Glyceraldehyde 3-phosphate (G3P)

a sugar produced in the Calvin cycle that can be used by the cell

RuBP

RuBP stands for ribulose-1,5-bisphosphate, which is a CO2 receptor molecule involved in the Calvin Cycle of photosynthesis.

ATP

ATP stands for adenosine triphosphate, which is a molecule that provides energy for cellular processes, including the regeneration of RuBP in photosynthesis.

Photorespiration

Photorespiration is a metabolic process in plants that occurs when CO2 levels are low and O2 levels are high, leading to the release of CO2 and the consumption of O2 without the production of sugar.

C4 plants

C4 plants are a type of plants that have evolved a mechanism to minimize photorespiration by incorporating CO2 into a four-carbon compound before entering the Calvin Cycle.

CAM plants

CAM plants, or crassulacean acid metabolism plants, are plants that open their stomata at night to incorporate CO2 into organic acids, which are then used during the day in the Calvin Cycle when stomata are closed.