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Reactions in a closed system eventually reach equilibrium and then ___________
do no work
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Do cells reach equilibrium? why?
cells are not in equilibrium because they are open systems experiencing a constant flow of materials
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What is a defining feature of metabolism in life?
Metabolism is never at equilibrium
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How does a catabolic pathway in a cell release free energy?
in a series of reactions
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What are the three main kinds of work a cell does? give an example for each?
- Chemical: breaking down of food
- Transport: diffusion
- Mechanical: movement in cytoskeleton
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How do cells manage energy resources to do work?
by energy coupling, which is the use of an exergonic process to drive an endergonic one
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How are most energy coupling in cells mediated?
by ATP
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What class of large biological molecule is ATP?
nucleic acid
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What type of molecule is adenosine?
nucleotide
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How can the bonds between the phosphate groups of ATP be broken?
by hydrolysis, adding water to break the bonds
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How is energy released from ATP?
When the terminal phosphate bond is broken
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Where does the release of free energy come from?
comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves.
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What is the free energy if the hydrolysis of ATP?
-7.3 kcal/mol
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What are the 3 types of cellular work powered by?
hydrolysis of ATP
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Overall, what are coupled reactions, endergonic or exergonic?
exergonic
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ATP drives endergonic reactions by ___________.
Phosphorylation
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Define phosphorylation. What is the recipient molecule called?
- involves the transfer of a phosphate group to some other molecule
- It's now called a phosphorylated intermediate
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ATP is a renewable resource that is regenerated by _______________________________.
addition of phosphate group to adenosine diphosphate (ADP)
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Where does the energy to phosphorylate ADP come from?
catabolic reactions in the cell
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What are the three processes that ATP is regenerated by?
- substrate-level phosphorylation
- oxidative phosphorylation
- photophosphorylation
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How do enzymes speed up metabolic reactions?
by lowering energy barriers (activation energy)
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What is a catalyst?
a chemical agent that speeds up a reaction without being consumed by the reaction
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What is an enzyme?
a catalytic protein
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What is the initial energy needed to start a chemical reaction called?
- free energy of activation or activation energy (EA)
- barrier that reaction must overcome
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How do enzymes catalyze reactions?
by lowering the activation energy barrier
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What is the enzyme's substrate?
the reactant that an enzyme acts on
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What is the active site on an enzyme?
the region on the enzyme where the substrate binds
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The active site can lower an activation energy barrier by:(4)
- orienting substrates correctly
- straining substrate bonds
- provide a favourable microenvironment
- covalently bonding to the substrate
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How can an enzyme's activity be affected? (2)
- general environmental factors such as pH and temperature
- chemicals that specifically influence an enzyme
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Each enzyme has an optimal _________ and _________ in which it can function
temperature and pH
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What are cofactors? (2)
- non-protein enzyme helpers
- may be inorganic (such as metal in ionic form) or organic
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What is a coenzyme, give an example?
- organic cofactor
- example is vitamins
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What are competitive inhibitors?
they bind to the active site of an enzyme, competing with the substrate
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What are non-competitive inhibitors?
They bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective
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How is a cell's metabolic pathways regulated?
A cell does this by switching on or off the genes that encode specific enzymes or by regulating the activity of enzymes
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What is allosteric regulation?
occurs when a regulatory molecule bonds to a protein at one site and affects the protein's function at another site
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What are the two things that allosteric regulation can do?
may either inhibit or stimulate an enzyme's activity
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What does the activator in allosteric regulation stabilize?
stabilizes the active form of the enzyme
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What does the inhibitor in allosteric regulation stabilize?
stabilizes the inactive form of the enzyme
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Define cooperativity.
It's a form of allosteric regulation than can amplify enzyme activity.
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What happens in feedback inhibition?
The end product of a metabolic pathway shuts down the pathway
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What does feedback inhibition prevent?
It prevents a cell from wasting chemical resources by making product than needed.
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