Chapter 6: Metabolism Flashcards
bioenergetics
study of energy flowing through living systems
metabolism
all the chemical reactions that happen inside of cells
metabolic pathway
series of biochemical reactions that convert a substrate into its final product
What are the two main metabolic pathways?
Anabolic and catabolic
anabolic pathway
synthesises complex molecules from simple ones
catabolic pathway
breaks down complex molecules into simple ones
kinetic energy
energy an object has when in motion
potential energy
energy an object has when it has a potential to do work
chemical energy
potential energy that exists between molecular bonds
Gibbs free energy
refers to the usable energy in a chemical reaction after entropy is taken into account
delta G
change in free energy
delta S
energy lost to entropy
delta H
total energy change in a system
enthalpy
total energy change in a system
What is the formula for calculating the change in free energy?
ΔG = ΔH − TΔS
What does ‘T’ represent in ΔG = ΔH − TΔS?
absolute temperature in Kelvin
What units express change in free energy?
Amount of energy (in kilojoules or kilocalories) per mole of reaction product under standard conditons
What is the conversion rate for kilocalories to kilojoules?
1 kcal = 4.184 kJ
What are the factors for standard conditions for calculating free energy?
Standard pH, temperature and pressure
What is the standard pH value?
pH 7
What is the standard temperature value?
25 degrees Celsius
What is the standard pressure value?
100 kilopascals
How much pressure is 1 atmosphere?
100 kilopascals
What will the value delta G be if energy is released in a reaction?
It will be negative
exergonic reaction
reaction that releases free energy
Are exergonic reactions spontaneous?
Yes, they require no energy input
endergonic reaction
reaction that results in a gain of free energy
Are endergonic reactions spontaneous?
No, they require an energy input to happen
chemical equilibrium
when there is no net change in amount of reactants and products in a chemical reaction
In what condition is there the lowest amount of free energy and maximal entropy?
In equilibrium
What would happen if a cell was in a closed environment?
Its chemical reactions would reach equilibrium and it would run out of energy and die
Do chemical reactions in a cell ever reach equilibrium?
No, they move towards equilibrium but never reach it
Why do cells never reach equilibrium?
They are in an open environment and materials are constantly being moved in and out
activation energy
energy necessary to start a reaction
What is activation energy abbreviated to?
EvA
transition state
high-energy, unstable form between the substrate and product
Why do exergonic reactions need energy to start?
Reactants must be slightly contorted first for bonds to break and need energy to reach this state of contortment
Where does the activation energy for a reaction come from?
From the heat in the surrounding area
How does heat energy provide the activation energy for a reaction?
When the reactants absorb enough heat, they will reach the transition state and the reaction will occur
How does amount of activation energy needed affect the rate of reaction?
The greater the activation energy, the slower the reaction
Why are catalysts important in chemical reactions?
They lower the activation energy required and prevent the body from producing too much heat to overcome the original activation energy
What does the first law of thermodynamics state?
Energy cannot be created or destroyed
What does the second law of thermodynamics state?
The total entropy of the universe is always increasing
entropy
the measure of disorder in a system
What is the relationship between entropy and energy
High entropy means low energy
nucleoside
a nitrogenous base attached to a sugar
adenosine
nucleoside made of adenine and ribose
How are the phosphate groups in ATP named?
In order of closest to furthest from the ribose sugar, they are named alpha, beta and gamma
Where are the high-energy bonds in ATP located?
Between the gamma and beta phosphate, and the beta and alpha phospahte
phosphoanhydride bond
high-energy bonds that hold together the phosphate groups in ATP
How is ATP converted to ADP?
Through hydrolysis
How is an inorganic phosphate group as a chemical formula?
Pi
What is the chemical equation for ATP being converted into ADP?
ATP + H20 -> ADP + Pi + free energy
Is the conversion of ATP into ADP reversible?
Yes
What is the chemical equation for ADP being converted into ATP?
ADP + Pi + free energy -> ATP + H2O
What is the change in Gibbs free energy for hydrolysis of one ATP under standard conditions?
-7.3 kcal/mole or -30.5 kJ/mole
What is the change in Gibbs free energy for hydrolysis of one ATP under cellular conditions?
-14 kcal/mole or -57 kJ/mole
How stable is ATP?
It is highly unstable and will spontaneously dissociate into ADP and Pi if not used
In what form is energy released when ATP dissociates spontaneously?
It is released as heat energy
energy coupling
when the energy from an exergonic reaction is used to drive another reaction
phosphorylation
when a phosphate group binds to another molecule
Do enzymes alter the free energy of a reaction?
No, they only change the activation energy required to start the reaction
substrate
the reactants that bind to an enzyme
active site
the location where the substrate binds with the enzyme
How specific are enzymes for each substrate?
They is generally a unique enzyme for each substrate
Why are enzymes so specialised?
Due to the complexity of enzymes as most of them are intricately composed and folded proteins
What can happen to an enzyme if conditions are too extreme?
The enzymes can denature and lose its properties as an enzyme
Which model previously describes how an enzyme binds to its substrate?
The “lock-and-key” model
induced fit
model that describes how an enzyme binds to its substrate
What does the induced fit model describe?
As the enzyme and substrate come together, the enzyme conforms to fit the substrates shape
enzyme-substrate complex
when an enzyme binds to its substrate
How does an enzyme promote chemical reactions through orientation?
Enzymes bring reactant substrates together in an optimal orientation for reacting
How does an enzyme promote chemical reactions through environment?
The particular arrangement of certain amino acids can create an ideal environment for a reaction to occur
How does an enzyme promote chemical reactions by altering the substrate directly?
It can contort the substrate to reach its transition state
How does an enzyme promote chemical reactions by getting directly involved in the reaction?
It can provide the necessary substances for the chemical reaction to occur
What ways can an enzyme promote chemical reactions?
- Orient substrates in an ideal position for reacting
- Create an ideal reacting environment
- By contorting the substrates into their transition state
- By taking part in the reaction itself
Does an enzyme change after a chemical reaction?
No, it always reverts to its original form
competitive inhibition
inhibitor molecules bind to the active sites of enzymes to prevent substrates from binding instead
noncompetitive inhibition
inhibitor molecules bind to the enzyme in places other than the active and allosteric site and still prevents the substrate from binding to the active site
How does competitive inhibition affect rate of reaction?
It slows the initial rate but does not affect the maximal rate
How does noncompetitive inhibition affect rate of reaction?
It slows the initial rate and lowers the maximal rate
allosteric site
site at which the inhibitor molecule binds to during allosteric inhibition
allosteric inhibition
inhibitor molecule binds to a site other than the active site which conforms the active site to decrease affinity for the substrate
allosteric activation
activator binds to allosteric site which conforms the active to increase affinity for the substrate
How many polypeptide chains comprise most allosterically regulated enzymes?
More than one polypeptide
What are the two types of enzyme helper molecules?
Cofactors and coenzymes
cofactor
inorganic ions that act as enzyme helper molecules
What cofactor does DNA polymerase need to function?
Zn++
coenzyme
organic molecules that act as enzyme helpers
What is the most common source of coenzymes?
Dietary vitamins
How can enzymes be further regulated in cells?
They can be compartmentalised into cell organelles
feedback inhibition
using an enzyme’s reaction products to regulate its own production
