8 An Introduction to Metabolism Flashcards
What is a metabolic pathway?
A sequence of reactions, catalysed by enzymes, which converts one substance to another through various intermediaries.
What are the types of metabolic pathway and what do they refer to?
Catabolic pathways: breakdown
Anabolic pathways: build up
Generally speaking, which type of metabolic pathway release energy?
Catabolic i.e. respiration.
What is bioenergetics?
The study of how energy is used within a cell, within an organism and within an ecosystem.
Which disciple deals with the study of the flow of energy through living entities?
Bioenergetics.
What is the first law of thermodynamics?
Energy is neither created nor destroyed, only transferred between states.
What is the implication of the first law of thermodynamics?
No new energy can ‘appear’ so it must be taken from sources i.e. food
What is the second law of thermodynamics?
No energy transfer or transformation is completely efficient and thus the entropy of a system must increase.
Define entropy.
The randomness of energy in the universe i.e higher entropy = more spread out.
What is the implication of the second law of thermodynamics?
An organism can’t just reuse its energy-it must replace the energy it has lost.
What is an isolated system? What is its opposite?
A system in which no energy enters or leaves. The opposite is an open system in which energy enters and/or leaves/
What is an example of an open and an isolated system?
Open: organism
Isolated: earth (pretty much)
For a reaction to occur without outside help what must it do?
Increase the entropy of the universe i.e. release energy.
What is the name for a process i.e. reaction that can occur without the input of energy?
Spontaneous.
True or False, spontaneous reactions are fast?
Not necessarily some are (explosions), other aren’t (rusting)
Why does catabolism generally release energy?
Anabolism decreases the entropy of the universe so must take energy. Therefore the opposite, catabolism, must release energy.
At what temperature is absolute zero?
-273.15ºC
How can the energy change of a reaction be quantified?
By calculating the change in ‘Gibbs free energy’ (ΔG)
How is the change in free energy calculated?
ΔG = ΔH - TΔS
where: ΔG is change in free energy ΔH is change in enthalpy (total energy) ΔS is change in the system's entropy and T is temperature as measured in Kelvin
What does a change in free energy mean?
If the number is negative this means the system has less free energy. Therefore this free energy must have been emitted.
Therefore a negative ΔG means energy has been released.
What is a reaction which the system loses free energy termed?
Exergonic
What is a reaction which the system absorbs free energy termed?
Endergonic
What type of reaction is spontaneous?
Exergonic
If a system reached equilibrium, what can it no longer do?
Work
What is ATP composed of?
3 phosphate groups, a ribose sugar and an adenine
How does broadly ATP power cellular work?
By energy coupling: the use of an exergonic reaction to drive an endergonic reaction.
What is energy coupling?
The use of an exergonic reaction (hydrolysis of ATP) to drive an endergonic reaction.
Specifically, how does ATP drive cellular work?
It transfers one of its phosphate groups (phosphorylation) This forms a high energy phosphorylated intermediate which can then undergo a exergonic reaction to the final product
What is the symbol for activation energy?
Ea (big E, subscript a)
What is activation energy?
Energy that must be added before an exergonic reaction can take place. i.e. heat to ignite a fire.
How can activation energy be lowered?
With enzymes.
How do enzymes increase the rate of a reaction?
By lowering the activation energy by guiding the reactants into their correct orientation.
What is an enzyme-substrate complex?
The enzyme and its bound substrate.
What is an enzyme bound to its substrate called?
An enzyme substrate complex.
How does the enzyme bond with its substrate?
As the substrate enters the active site it forms weak bonds with the enzyme which change its shape and ‘clamp’ it shut.
This is known as ‘induced fit’
How does an enzyme speed up a reaction?
1) If 2 or more reactants guides them together
2) As the enzyme clamps during ‘induced fit’ it may pull apart
3) The active site might provide a beneficial environment - for example if it is made of acidic amino acids it could provide low pH
Why do spontaneous reactions take time?
It is random which reactants actually have the activation energy (and orientation) to react.
What conditions affect the rate of enzymatic catalysis?
Concentration of enzyme and substrate, temperate, and pH.
What is the name for helpers needed for an enzyme to function?
Cofactors or more specifically coenzymes if they are organic (not proteins ie. vitamins)
What role do vitamins often play?
Coenzymes (organic cofactors) of enzymatic reactions.
How can enzymes be inhibited?
Competitive inhibition and Noncompetitive inhibition.
What is competitive inhibition?
When a substance, but not the normal substrate, binds to the active site of the enzyme and thus blocks it.
What is non-competitive inhibition?
When a substance binds to the enzyme outside the active site but in a way that changes the shape of the enzyme so that the active site is inaccessible.
Is non-competitive/competitive inhibition permanent?
Sometimes, depending whether the bonds to the active site/enzyme are strong and permanent or not.
In what ways can enzyme activity be regulated?
(Non)competitive inhibition, allosteric regulation and feedback inhibition.
What is allosteric regulation.
Reversible regulation of enzyme activity based on molecules that bind outside the active site of an enzyme.
How does allosteric regulation occur?
When the protein etc. binds it changes the shape of the enzyme and thus blocks its active site or makes it accessible.
What forms does allosteric regulation divide into?
Allosteric activation and allosteric inhibition.
A special form of allosteric activation is cooperativity.
What is cooperativity?
A form of allosteric activation that occurs in proteins that can bind to more than one molecule of the same substrate at the same time.
When one substrate binds to one of the enzymes active sites it changes an protein’s shape so that the other active sites are more accessible, causing the protein to become saturated.
As one substrate molecule leaves the reverse happens so they all might be dumped at the same time.
Note: this often occurs in transport proteins
Where is cooperativity seen and why?
The binding of an oxygen molecule to one binding site increases the affinity for oxygen of the remaining binding sites. Thus, where oxygen is at high levels, such as in the lungs or gills, hemoglobin’s affinity for oxygen increases as more binding sites are filled.
In oxygen-deprived tissues, the re- lease of each oxygen molecule decreases the oxygen affinity of the other binding sites, resulting in the release of oxygen where it is needed.
What is feedback inhibition?
A feature seen in many metabolic pathways where the end product of the pathways acts as an allosteric inhibitor to the enzyme that starts the pathway.
This means that when the end product is plentiful no resources are wasted to continue making it. When the end product is used production starts again.
