Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions Flashcards
A cell does three main kinds of work
Chemical work, Transport work, Mechanical work
the pushing of endergonic reactions that would not occur spontaneously, such as the synthesis of polymers from monomers
Chemical work
the pumping of substances across membranes against the direction of spontaneous movement
Transport work
such as the beating of cilia (see Concept 6.6), the contraction of muscle cells, and the movement of chromosomes during cellular reproduction
Mechanical work
A key feature in the way cells manage their energy resources to do this work is
energy coupling, the use of an exergonic process to drive an endergonic one.
ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of
energy that powers cellular work.
watch animation energy coupling and learn it
an adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.
ATP (adenosine triphosphate)
ATP contains the sugar ribose, with the nitrogenous base adenine and a chain of
three phosphate groups (the triphosphate group) bonded to it
ATP is also one of the nucleoside triphosphates used to make
RNA
the structure of ATP. ATP powers nearly all forms of
cellular work by providing energy stored in its chemical bonds
ATP is composed of three main components
a 5 carbon ribose sugar molecule, adenine- a nitrogenous base, and a string of phosphate groups
to construct ATP the sugar ribose attaches to a nitrogenous base adenine which is also bonded to a chain of
three phosphate groups (the triphosphates group)
during cellular respiration, glucose release
energy
this energy is stored when a phosphate group is added to __________________ forming ATP or adenosine triphosphate.
ADP ( adenosine diphosphate)
ATP releases energy when the covalent bond between phosphate groups break during
hydrolysis
this energy is used to
drive other biochemical reactions
watch animation space-filling model of ATP and learn it
space-filling model of an ATP molecule shows its three components; in one end, the 3 phosphate groups with their
purple phosphorus atoms and red oxygen atoms
on the other end is the nitrogenous base adenine with its
blue nitrogen atoms, green carbons, and gray hydrogens
both attached in the middle to a
ribose sugar with its green carbon atoms, gray hydrogens, and red oxygens
watch animation stick model of ATP and learn it
The bonds between the phosphate groups of ATP can be broken by
hydrolysis
When the terminal phosphate bond is broken by addition of a water molecule, a molecule of inorganic phosphate, leaves the ATP, which becomes
adenosine diphosphate, or ADP
learn the math of ATP+ H20. I can not make some of the symbols
Because their hydrolysis releases energy, the phosphate bonds of ATP are sometimes referred to as
high-energy phosphate bonds
The phosphate bonds of ATP are not unusually strong bonds, as “high-energy” may imply; rather, the reactants (ATP and water) themselves have
high energy relative to the energy of the products (ADP and ℗ᵢ ).
The release of energy during the hydrolysis of ATP comes from the chemical change of the system to a state of lower free energy, not from the.
phosphate bonds themselves
the cell’s proteins harness the energy released during ATP hydrolysis in several ways to perform the three types of cellular work—
chemical, transport, and mechanical.
with the help of specific enzymes, the cell is able to use the energy released by ATP hydrolysis directly to drive chemical reactions that, by themselves, are
endergonic
If the ∆G of an endergonic reaction is less than the amount of energy released by ATP hydrolysis, then the two reactions can be coupled so that, overall, the coupled reactions are
exergonic.
This usually involves phosphorylation, the transfer of a phosphate group from ATP to some other molecule, such as the
reactant
The recipient molecule with the phosphate group covalently bonded to it is then called a
phosphorylated intermediate
Transport and mechanical work in the cell are also nearly always powered by the
hydrolysis of ATP
ATP hydrolysis leads to a change in a protein’s
shape and often its ability to bind another molecule
In most instances of mechanical work involving motor proteins “walking” along cytoskeletal elements (Figure 8.11b), a cycle occurs in which ATP is first bound noncovalently to the
motor protein.
Next, ATP is hydrolyzed, releasing
ADP and ℗ᵢ
At each stage, the motor protein changes its shape and ability to bind the cytoskeleton, resulting in movement of the protein along the
cytoskeletal track.
ATP is a renewable resource that can be regenerated by the addition of
phosphate to ADP
The free energy required to phosphorylate ADP comes from exergonic breakdown reactions (catabolism) in the
cell
This shuttling of inorganic phosphate and energy is called the
ATP cycle
it couples the cell’s energy-yielding (exergonic) processes to the
energy-consuming (endergonic) ones.
As organisms live and grow, they are constantly in the process of making and breaking bonds in
molecules
metabolism is the sum of all the
chemical reactions that take place in an organism
metabolism includes
catabolism and anabolism
catabolism includes the processes that
break down complex molecules into simpler molecules while harvesting their energy and storing it, usually in the form of ATP
anabolism includes the process that build more complex
molecules from simpler molecules
the energy acquired through catabolic processes is used to
drive anabolic processes
neither catabolism nor anabolism is completely efficient, so, at each step some of the available energy is lost into the
environment as heat
Because both directions of a reversible process cannot be downhill, the regeneration of ATP is necessarily
endergonic
