Overview: Life Is Work
- Living cells require energy from outside sources
- Some animals, such as the giant panda, obtain energy by eating plants, and some animals feed on other organisms that eat plants
- Energy flows into an ecosystem as sunlight and leaves as heat
- Photosynthesis generates O2 and organic molecules, which are used in cellular respiration
- Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work
Adenosine Tri-Phosphate (ATP)
- ATP is the energy unit of the cell.
- ATP is composed of an Adeno. Group, a sugar group and three phosphates.
- ATP is easily recycled.
- The cell converts Adenosine Di-Phosphate (ADP) into ATP by the addition of a phosphate.
An Overview of how ATP is Produced
- Cellular respiration
- in mitochondria
Redox Reactions: Oxidation and Reduction
- The transfer of electrons during chemical reactions releases energy stored in organic molecules
- This released energy is ultimately used to synthesize ATP
The Principle of Redox
- Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions
- In oxidation, a substance loses electrons, or is oxidized
- In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
ATP powers cellular work by coupling exergonic reactions to endergonic reactions
- A cell does three main kinds of work:
- To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one
- Most energy coupling in cells is mediated by ATP
- ATP (adenosine triphosphate) is the cell’s energy shuttle
- ATP is composed of:
- ribose (a sugar)
- adenine (a nitrogenous base)
- Three phosphate groups
- The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis
- Energy is released from ATP when the terminal phosphate bond is broken
- This Third Phosphate bond contains LOTS of Energy
- This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves
- Adenosine triphosphate (ATP)
- Adenosine diphosphate (ADP)
- The three types of cellular work are:
- Each is powered by the hydrolysis of ATP
- In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction
- (b) Mechanical work: ATP binds noncovalently
- to motor proteins, then is hydrolyzed
- (a) Transport work: ATP phosphorylates
- transport proteins
- The process of Phosphorylation converts a relatively low energy compound (ADP) into a higher energy compound (ATP)
- ADP (Adenosine Di-Phosphate)- Contains an Adenosine, a ribose group, and two Phosphate groups.
- Energy from
- catabolism (exergonic,
- Energy for cellular
- work (endergonic,
The ATP Cycle
- ATP can be produced from existing ADP molecules
- A phosphate is added to ADP at the mitochondria.
- Requires ATP synthase - A protein complex in the mitochondria that acts a molecular mill and converts ADP into ATP.
The Regeneration of ATP
- ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP).
- Requires ATP synthase and H ions (from water.)
- The energy to phosphorylate ADP comes from catabolic reactions in the cell.
- The chemical potential energy temporarily stored in ATP can then be used to drive most cellular work.
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