Unit 3 Cellular Energetics

Metabolism

all of the chemical reactions in an organism

Metabolic pathways

series of chemical reactions that either build complex molecules or break down complex molecules

Catabolic pathways

processes that break down molecules to release energy

Anabolic pathways

processes that build complex molecules from simpler ones, requiring energy input

Kinetic energy

energy associated with motion

Thermal energy

energy associated with the movement of atoms or molecules

Potential energy

stored energy

Chemical energy

potential energy available for release in a chemical reaction

Thermodynamics

study of energy transformations in matter

1st Law of Thermodynamics

Energy cannot be created or destroyed, only transformed and transferred

2nd Law of Thermodynamics

Energy transformation increases the entropy (disorder) of the universe

Free energy

ΔG = ΔH - TΔS where ΔG is the change in free energy, ΔH is the change in total energy, T is the temperature in Kelvin, and ΔS is the change in entropy

Exergonic reactions

reactions that release energy, ΔG＜0

Endergonic reactions

reactions that absorb energy, ΔG＞0

Mechanical

movement (i.e. beating cilia, movement of chromosomes, contraction of muscle cells)

Transport

pumping substances across membranes against spontaneous movement

Chemical

synthesis of molecules (ie building polymers from monomers)

Adenosine triphosphate

molecule that organisms use as a source of energy to perform work

Phosphorylation

the released phosphate moves to another molecule to give energy

Enzymes

macromolecules that catalyze (speed up) reactions by lowering the activation energy

Substrate

the substance on which an enzyme acts, undergoing a chemical reaction during the process

Active site

the region on an enzyme where substrate molecules bind and undergo a chemical reaction

Induced fit

enzymes will change the shape of their active site to allow the substrate to bind better

Optimal conditions

the conditions (temperature and pH) that allow enzymes to function optimally (at their best)

Cofactors

Non protein molecules that assist enzyme function, inorganic cofactors consist of metals

Coenzymes

Organic cofactors (e.g vitamins)

Holoenzyme

an enzyme with the cofactor attached

Enzyme inhibitors

reduce the activity of specific enzymes

Competitive inhibitors

reduce enzyme activity by blocking substrates from binding to the active site

Noncompetitive inhibitors

bind to an area other than the active site (allosteric site), which changes the shape of the active site preventing substrates from binding

Allosteric regulation

molecules bind (noncovalent interactions) to an allosteric site which changes the shape and function of the active site

Allosteric activator

substrate binds to allosteric site and stabilizes the shape of the enzyme so that the active sites remain open

Allosteric inhibitor

substrate binds to allosteric site and stabilizes the enzyme shape so that the active sites are closed (inactive form)

Cooperativity

substrate binds to one active site (on an enzyme with more than one active site) which stabilizes the active form

Photosynthesis

the conversion of light energy to chemical energy

Autotrophs

organisms that produce their own food using light or chemical energy, such as plants and some bacteria

Heterotrophs

organisms that obtain their food by consuming other organisms, such as animals and fungi

Cyanobacteria

early prokaryotes capable of photosynthesis

Chloroplast

organelle for the location of photosynthesis

Stomata

pores in leaves that allow CO₂ in and O₂ out

Stroma

aqueous internal fluid

Thylakoids

form stacks known as grana

Chlorophyll

green pigment in thylakoid membranes

Photosynthesis formula

6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂

Redox reaction

reaction involving complete or partial transfer of one or more electrons from one reactant to another

Chlorophyll a

Primary pigment

Involved in the light reactions 

Blue/green pigment

Chlorophyll b

Accessory pigment

Yellow/green pigment

Carotenoids

Broaden the spectrum of colors that drive photosynthesis

Yellow/orange pigment

Photoprotection

carotenoids absorb and dissipate excessive light energy that could damage chlorophyll or interact with oxygen

Light reactions

The first stage of photosynthesis where light energy is converted into chemical energy in the form of ATP and NADPH

Photosystems

reaction center and light capturing complexes

Reaction center

a complex of proteins associated with chlorophyll a and an electron acceptor

Light capturing complexes

pigments associated with proteins

Photosystem 2

reaction center P680, absorbs light at 680 nm

Photosystem 1

reaction center P700, absorbs light at 700 nm

ATP synthase

couples the diffusion of H⁺ to the formation of ATP

Light reaction inputs

• H₂O

• ADP

• NADP+

Light reaction outputs

• O₂

• ATP

• NADPH

Calvin Cycle

a series of reactions that convert CO2 into glucose using ATP and NADPH produced in the light reactions

Carbon fixation

the initial step in the Calvin Cycle where CO2 is attached to a five-carbon sugar, ribulose bisphosphate (RuBP), forming a stable six-carbon intermediate

Reduction

the stage in the Calvin Cycle where the six-carbon intermediate is converted into glyceraldehyde-3-phosphate (G3P) using ATP and NADPH

Regeneration of RuBP

the final phase of the Calvin Cycle that involves the conversion of G3P back into ribulose bisphosphate (RuBP) using ATP, allowing the cycle to continue

Calvin Cycle Inputs

• 3 CO₂

• 9 ATP

• 6 NADPH

Calvin Cycle Outputs

• 1 G3P

• 9 ADP

• 6 NADP+

Photorespiration

a process in plants where oxygen is taken up and carbon dioxide is released, often occurring when carbon dioxide levels are low and oxygen levels are high. It decreases the efficiency of photosynthesis by using energy and reducing the production of glucose

C4 Plants

a type of plant that efficiently fixes carbon dioxide using a four-carbon compound as the first product of photosynthesis, adapting to hot and dry environments to minimize photorespiration

CAM Plants

a type of plant that conserves water by using a unique carbon fixation pathway, allowing them to open their stomata at night and fix carbon dioxide into a four-carbon compound, which is then used during the day for photosynthesis

Cellular respiration formula

C₆H₁₂O₆ + 6O_{2 →} 6CO₂ + 6H₂O + energy (ATP and heat)

Oxidation of glucose

transfers e- to a lower energy state, releasing energy to be used in ATP synthesis

Electron transport chain (ETC)

a sequence of membrane proteins that shuttle electrons down a series of redox reactions

Glycolysis

the metabolic pathway that breaks down glucose into pyruvate, producing ATP and NADH in the process

Energy investment stage

the cell uses ATP to phosphorylate compounds of glucose

Energy payoff stage

energy is produced by substrate level phosphorylation

Pyruvate oxidation

the process where pyruvate is converted into acetyl-CoA, producing NADH and releasing CO2, occurring in the mitochondria

Citric Acid Cycle (Krebs Cycle)

the series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins. It produces NADH, FADH2, and ATP

Oxidative Phosphorylation

the process that produces ATP using the electron transport chain and chemiosmosis, occurring in the inner mitochondrial membrane. It relies on oxygen as the final electron acceptor

Electron Transport Chain

a series of protein complexes located in the inner mitochondrial membrane that transfer electrons through redox reactions, ultimately driving the production of ATP

Chemiosmosis

the movement of ions across a selectively permeable membrane, particularly in the generation of ATP in cellular respiration by allowing protons to flow back into the mitochondrial matrix

Cristae

the folded inner membrane of mitochondria that increases surface area for ATP production during oxidative phosphorylation

ATP synthase

the enzyme that makes ATP from ADP + P

Anaerobic respiration

generates ATP using an ETC in the absence of oxygen

Fermentation

generates ATP without an ETC

Alcohol fermentation

pyruvate is converted into ethanol (bacteria, yeast)

Lactic acid fermentation

pyruvate is reduced directly by NADH to form lactate

Lactic acidosis

a medical condition characterized by the buildup of lactic acid in the body, often due to insufficient oxygen or metabolic issues