EXAM #3 Flashcards
what is the first law of thermodynamics?
the universe contains a constant amount of energy, therefore energy is never created nor destroyed. energy simply changes from one form to another.
what is the second law of thermodynamics?
energy transformations always result in an increase in disorder in the universe. when going from one form of energy to another, the energy available to do work decreases.
why are energy transformations never 100% efficient?
because the amount of energy available to do work decreases every time energy changes forms
the degree of disorder is called ______
entropy, however, disorder is just one way to describe entropy.
another way to think about entropy is to consider the number of possible ______ and _____ a molecule can adopt.
positions and motions (collectively called microstates)
as entropy _____, the number of positions and motions available to the molecule increases
increases
in chemical reactions, what causes the entropy to increase?
most of the entropy increase occurs through the release of thermal energy, which we experience as heat.
the higher the temperature, the more rapidly molecules move, and the _____ the disorder.
higher
all cells and organisms require a constant input of energy to maintain their high degree of organization and function. what are energy inputs for cells?
energy comes either from the sun or from the energy stored in chemical compounds.
when does a chemical reaction occur?
when molecules interact. molecules called reactants are transformed into other molecules called products.
during a chemical reaction, atoms ____ their identity, but the atoms that share bonds _____.
keep
change
can chemical reactions be reversed?
yes, chemical reactions in cells are readily reversable: products can react to form their original reactants
_____ ______ is when the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of the products and reactants do not change.
chemical equilibrium
the amount of energy available to do work is called _____ ____ ______ (G).
Gibbs free energy
delta G is the free energy of the _____ minus the free energy of the ______
products
reactants
reactions with a negative delta G value that release energy and proceed spontaneously are called ______
exergonic
reactions with a positive delta G value that require an input of energy and are not spontaneous are called ______
endergonic
H = G + TS
G = H - TS
what do the variables stand for?
G = Gibbs free energy// the amount of energy available to do work
H = the total amount of energy is enthalpy
T = absolute temperature (Kelvin)
S = entropy
T*S = the total energy lost to entropy
the hydrolysis of ATP is an ______ reaction
exergonic (releases energy available to do work)
hydrolysis reactions often break down _____ into their _____, and in the process one product gains a ______ (H+) and the other gains a ______ (OH-) group.
polymers into their subunits
proton
hydroxyl
where/what does the release of energy during ATP hydrolysis come from?
breaking weaker bonds (with more chemical energy) in the reactants and forming more stable bonds (with less chemical energy) in the products
true or false: nonspontaneous reactions are infrequently coupled to spontaneous reactions
false. nonspontaneous reactions are often coupled to spontaneous reactions
catalysts are substances that ____ the rate of chemical reactions without themselves being consumed.
increase
catalysts are usually proteins called _______ which are highly ______, acting only on certain reactants and catalyzing only some reactions.
enzymes
specific
true or false: only some chemical reactions require an initial input of energy to proceed
false, all chemical reactions require an input of energy
an intermediate compound between reactants and products is formed, called the _____ _____ in which the old bonds are breaking, and the new bonds are forming simultaneously.
transition state. it is highly unstable and has a large amount of free energy
the energy input necessary to reach the transition state is called the ______ _____
activation energy (Ea)
enzymes accelerate chemical reactions by reducing the activation energy by stabilizing the _____ ____ and decreasing its free energy
transition state
enzymes form a _____ with reactants and products that allows them to emerge from the chemical reaction unchanged.
complex
describe a chemical reaction catalyzed by an enzyme (reactant is called a substrate)
1) substrate (S) combines with an enzyme (E) to form first complex (E-S)
2) the substrate (while with the enzyme E-S) is converted to a product (E-P)
3) finally the complex disassociates, releasing the enzyme and the product (P + E)
substrates bind to enzymes at a specific region of the enzyme called the ____ ___ where the substrate and the enzyme form transient ____ bonds, weak noncovalent interactions or both.
active site
covalent
enzymes are folded into 3-dimensional shapes that bring particular _____ _____ into close proximity to form the active site.
amino acids
catalytic amino acids are typically spaced ___ apart in the linear sequence of amino acids (_____ structure) of the enzyme, but brought close together by protein ______.
far
linear
folding
enzymes are specific for certain substrates (reactants) as keys…..
are specific for certain locks
true or false: enzymes only interact with substrates that have a complimentary structure
true
some enzymes rely on ______ for their activity.
cofactors. cofactors can be organic or inorganic
breaking a chemical bond requires the ____ of energy. forming a chemical bond is associated with the ______ of energy.
input
release
the hydrolysis of ATP is spontaneous and ______ ____ ____ that can be used to drive other reactions
produces free energy
when the activation energy is low, chemical reactions occur _____
faster
there is a number of inhibitors that ____ ____ _____ when their products are not needed.
“turn off” enzymes
reversible inhibitors form ____ bonds with the enzyme
weak
irreversible inhibitors form ______ bonds with the enzyme
covalent
enzymes that are regulated by allosteric regulators are called _______ _______
allosteric enzymes
DNA replication is the molecular basis for ______
inheritance
describe how DNA replicates (simple)
DNA double helix unwinds and separates into two single strands at the replication fork. then each individual strand of DNA acts as a template for the synthesis of a daughter strand.
DNA replicates _________, which means that each new DNA molecule consists of one strand that was part of the parental molecule and one newly synthesized strand.
semi conservatively
what enzyme separates the two strands of the parental double helix by breaking hydrogen bonds holding the base pairs together?
helicase
what enzyme binds to these single stranded regions to prevent them from coming back together?
single-strand binding protein
true or false: topoisomerases are a family of enzymes that wind or unwind DNA to help relieve stress that occurs during both replication and replication and transcription
true
how many types of topoisomerases are there?
2; type I- cut one strand of DNA
type 2- cut both strands of DNA
what is the enzyme that is a critical component in DNA replication that synthesizes a new DNA strand from an existing template.
DNA polymerase
what are DNA polymerase’s two main properties?
-it can only attach a nucleotide to another nucleotide
-it can only add nucleotides to the 3’ (hydroxyl) end of another nucleotide
true or false: each new DNA strand must begin with a short stretch of RNA on their 5’ end that serves as a primer or starter for DNA synthesis
true
what is the enzyme called that forms a primer which synthesizes a short piece of RNA complementary to the DNA parental strand?
RNA primase.
in DNA replication, one daughter strand is synthesized _________ and the other strand in a series of ____ ______
continuously
short pieces
the ______ strand is synthesized continuously into one long polymer (daughter strand grows towards the replication fork)
leading
the _______ strand is synthesized in small discontinuous pieces that’re later joined together (daughter strand grows away from the replication fork)
lagging
what are the short pieces in the lagging daughter strand of DNA called?
Okazaki fragments
what is the enzyme that will join or ligate adjacent Okazaki fragments together?
DNA ligase
true or false: the DNA polymerase complexes in each daughter strand don’t communicate with each other
false; the DNA polymerase complexes in each daughter strand stay in contact with each other so that the synthesis of the leading and lagging strands is coordinated to occur at the same time/rate