2. Living cells require energy from outside sources
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
3. 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.
5. 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)
6. 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
7. ATP powers cellular work by coupling
exergonic reactions to endergonic reactions
A cell does three main kinds of work:
Chemical
Transport
Mechanical
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
8.
9. ATP
• ATP (adenosine triphosphate) is the cell’s energy shuttle
• ATP is composed of:
– ribose (a sugar)
– adenine (a nitrogenous base)
– Three phosphate groups
11. • 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
13. The three types of cellular work are:
mechanical
transport
chemical
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
14. Fig. 8-11
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed
Membrane protein
P i
ADP
+
P
Solute Solute transported
P i
Vesicle Cytoskeletal track
Motor protein Protein moved
(a) Transport work: ATP phosphorylates
transport proteins
ATP
ATP
15. Phosphorylation
ATP drives endergonic reactions by phosphorylation,
transferring a phosphate group to some other molecule, such
as a reactant
The recipient molecule is now phosphorylated
16. Phosphorylation
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.
17. Fig. 8-12
P iADP +
Energy from
catabolism (exergonic,
energy-releasing
processes)
Energy for cellular
work (endergonic,
energy-consuming
processes)
ATP + H2O
18. 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.
20. 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.
Editor's Notes
For the Discovery Video Space Plants, go to Animation and Video Files.
Figure 9.2 Energy flow and chemical recycling in ecosystems
For the Cell Biology Video Space Filling Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
Figure 8.8 The structure of adenosine triphosphate (ATP)
For the Cell Biology Video Stick Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
Figure 8.9 The hydrolysis of ATP
Figure 8.11 How ATP drives transport and mechanical work
