Introduction to metabolism Flashcards
Christine
What is the First law of thermodynamics?
Energy can change forms, but cannot be created of destroyed
What is the Second law of thermodynamics?
The entropy of an isolated system always increases
What is the Third law of thermodynamics?
States that the entropy of a system approaches a constant as temperature approaches absolute zero.
What determines whether metabolic reactions can occur?
Energetics/ Energy considerations
Give some examples of energy
Chemical (energy stored in chemical bonds)
Radiation (heat/light)
Mechanical
Electrical
What is an energetically favourable reaction?
A reaction which has energy considerations that will allow the reaction to occur
What is a chemical system?
A huge number of individual molecules which each have a certain amount of energy thanks to its structure (chemical bonds/ state of matter)
What is Enthalpy?
The heat content of a molecule (the energy) (calories)
What does it mean if /H is negative? and what effect does this have?
Heat is lost from molecules and released (temp of surroundings increases) (favours the rection)
What does it mean if /H is positive? and what effect does this have?
Heat is taken up from the surroundings (prohibitive effect)
What is the degree of randomness/ disorder?
The entropy of a system
What does more molecular movement freedom lead to?
Greater randomness/ entropy
What does increasing entropy do to a system?
Lowers the energy level of the system
What does a greater number of individual numbers lead to?
Greater randomness/ entropy /S.
Negative enthalpy and positive entropy reinforce?
The ‘yes’ decision
Positive enthalpy and negative entropy reinforce?
The ‘no’ decision,
What if both /H and /S are positive/negative?
They both disagree on the decision and whether the reaction will occur within these circumstances depends on which is is quantitatively larger (consider ice cube in bucket of hot water)
What is the Gibbs free energy equation?
/G = /H - T x /S (T in K)
Rule for chemical reactions including /G (kilojoules per mole)
A chemical reaction can only occur if the /G value s negative ( products must have less free energy than the reactants)
What is the G value for an exergonic reaction on a free energy/time graph? (+/-)
The G value is negative
What is the G value for an endergonic reaction on a free energy/time graph? (+/-)
The G value is positive
If /G is small will the reverse reaction be possible?
It may be possible in the cell ( dependent on reactant concentrations)
If /G is large will the reverse reaction be possible?
The reaction will proceed in ONE DIRECTION only!!
Importance of IRREVERSIBLE reactions
- Products of the first reaction are reactants or the next etc.
2.A general characteristic of metabolic pathways is they are irreversible
What is the General biochemical principle?
Whenever the overall chemical process of a metabolic pathway has to be reversed- The reverse pathway is not exactly the same as the forward pathway- some of the reactions are different in the two directions
Why are some reactions in metabolic pathway irreversible?
If all reactions in the pathway were reversible then pathway is subject to mass action, having different forward and reverse reactions allows independent control (one pathway ‘on’ and other ‘off’)
Why do reactions not occur spontaneously (even is the value of /G is negative)?
There is a barrier- an energy barrier.
What causes reactions to occur in cells?
Enzymes!
What does it mean if some enzymes are multifunctional?
Enzymes that partake/start several catalytic activities on the same molecule.
What do enzymes do?
Enzymes lower the energy.
