3.3 Cellular Energy

Energy

the ability to do work, which is any change in the state or motion of matter

all living systems require an input of energy to survive and function

to sustain life, energy input must exceed energy output

significant loss of order or energy flow can result in death

cells need ways to extract energy and turn it into usable forms(ATP), metabolic pathways(ex. glycolysis and oxidative phosphorylation) to do this are conserved across all domains(supports common ancestry of life)

cells receive energy in many forms(light,organic molecules like glucose, etc.), but can rarely use it as-is, so it must be converted/transformed before it can be used ex. kinetic energy converted to potential(chemical energy) and vice versa

Kinetic energy

energy associated with motion

Potential energy

stored energy

chemical energy is potential energy available for release in a chemical reaction

Laws of thermodynamics

the study of energy transformations in matter is called thermodynamics

the laws apply to the universe as a whole

life requires a highly ordered system that does not violate the first and second law of thermodynamics

1st law: energy cannot be created or destroyed

energy can be transferred or transformed

ex. chemical(potential) energy in a nut will be transformed into kinetic energy for a squirrel to climb a tree

2nd law: energy transformation increases the entropy (measure of disorder) of the universe. The entropy/disorder of organisms can decrease as long as the entropy/disorder of the entire universe is still always increasing

when energy is converted from one form to another, some energy is lost as heat

heat=less usable energy=disorganized

organized/ordered is energy we can use and disorganized/disordered is energy that is less usable

the organization seen in organisms(like living cells, tissues, and organs)represents a local(not universal) decrease in entropy, which requires a constant input of energy. Some of this energy is lost to heat to the organism’s surroundings, which increases the total amount of entropy/disorder in the universe, which makes sure the 2nd law of thermodynamics is not violated

Metabolism

the sum of all chemical reactions in a cell that transform energy and matter

Metabolic pathways

series of linked chemical reactions that either break down complex molecules(catabolic pathways) or build complex molecules(anabolic pathways)

paths are sequential, meaning the product of a reaction is the reactant in the next step

substrate→intermediate→intermediate→product

ex. glycolysis and oxidate phosphorylation

metabolic pathways are conserved across all domains( archea, bacteria, eukarya), which supports the theory of common ancestry

the specific chemical reactions happening within metabolic pathways can be classified as either endergonic or exergonic

reactions that are endergonic are often coupled with those that are exergonic through the use of ATP

Catabolic pathways

pathways that breakdown complex molecules

releases energy

Anabolic pathways

pathways that build complex molecules from simpler compounds

require energy

Endergonic

chemical reaction that needs energy

Exergonic

chemical reaction that releases energy

ATP

adenosine triphosphate

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

ADP can be regenerated to ATP via the ATP cycle

Coupling reactions

cells carry out energy-needing reactions(anabolic) by coupling them to ATP hydrolysis (catabolic)

ATP + H2O→ADP + P(free phosphate)+energy- 1. releases energy(the catabolic reaction,ATP hydrolysis)

the free phosphate that was released moves to another molecule and phosphorylates it(intermediate)- 2. transfers the energy(intermediate)

phosphorylation makes the molecule more reactive, which drives the energy needing reaction- 3. energy needing reaction occurs(anabolic)