life at the cellular level (4) - energy (thermodynamics) Flashcards
Give examples of types of energy
Heat
Light
Mechanical
Electrical
What is the first law of thermodynamics
Energy can be converted from one form to another but the total energy of the universe remains constant
What is the second law of thermodynamics
All energy transformations ultimately lead to more disorder in the universe, i.e. increase the entropy
What is entropy
The degree of disorder As usable energy decreases unusable energy increases, entropy increases Entropy is also a gauge of randomness or chaos within a closed system. As usable energy is irretrievably lost, disorganization, randomness and chaos increase.
How do cells maintain order
By performing lots of chemical reactions which require energy
What do cells use energy for
To grow and form complex molecules and systems
Do cells live in isolation
No, they are open systems, taking energy from the sun and food molecules to generate the order required for life
How do cells apply the 2nd law of thermodynamics
The chemical reactions that generate the cell’s order produce heat, which is discharged into the surrounding environment and disorders it, so the total entropy increases
What is Gibbs free energy
“useful”, or Free energy in a closed system can be defined by 3 quantities:
– Enthalpy, H – heat released to surroundings (reflects number/kind of bonds formed/broken)
– Entropy, S – randomness/disorder – Absolute temperature, T
G = H - TS
What can free energy change be used to define
The spontaneity of a reaction
When can spontaneous reactions occur
If a system:
– Gives up energy (water runs downhill spontaneously, giving up potential energy as it goes)
And/or
– Becomes more random and increases in entropy (complex structures decay spontaneously giving up potential energy)
What must a spontaneous process do to enthalpy and entropy
Decrease enthalpy (H) and/or increase entropy (S)
spontaneous reactions only occur if ΔG is
negative
what is the free energy change equation
ΔG = ΔH - TΔS
what does it mean if ΔG is -ve
the reaction releases energy
how much order do biological processes require
more rather than less, so reactions to generate proteins, DNA, cells, organs, etc, etc require reactions that have +ve ΔG
why do cells use a process called “energy coupling”
to carry out thermodynamically unfavourable reactions
what does ΔG = 0 mean
it is incompatible with life
do reactions reach equilibreium
no, as energy passes from the environment to the organism and back to the environment
This works because organisms use pathways of reactions: e.g. food molecules to excretory products
spontaneous reactions move towards equilibrium but do not reach equilibrium
what does life do to maintain a steady state
utilises series of reactions
what does free energy flow between
catabolic processes and anabolic processes allowing them to occur
what is each step in metabolic pathways catalysed by
enzymes
what do enzymes do
function to selectively alter the rate of particular parts of metabolic pathways
what are intermediate metabolites
tend to be compartments of several pathways
there aren’t many of them compared to the number of reactions that exist in the cells of our bodies
how much potential energy does glucose have and what does that mean
has a high potential energy and is used as a food molecule by many organisms
how can glucose be degraded
by heating in air, releasing its potential energy as heat
starts off with high potential energy and ends with low potential energy
glucose+6O2 -> 6CO2+H2O
and releases heat
The same reaction occurs in cells but in a series of small chemical reactions facilitated by enzymes
what do small reactions allow
the potential energy to be used or stored at a particular point along the pathway
what happens when ATP is converted into ADP
Free Energy is released, which is harnessed from this catabolic process to drive thermodynamically unfavourable reactions (+ΔG)
what is an exergonic reaction
a reaction that have a negative ∆G and release free energy
what is an endergonic reaction
Reactions that have a positive ∆G and require input of free energy
give an example of an exergonic reation
catabolic pathways
give an example of an endergonic reaction
anabolic pathways
why is a catabolic reaction exergonic
as it “saves” Free Energy within a system by forming ATP
catabolic reactions are thermodynamically favourable reactions
why is an anabolic pathway endergonic
as it is “supplies” with Free Energy within a system by forming ADP through the conversion of ATP to ADP
anabolic reactions are thermodynamically unfavourable reactions
what type of reaction is
ATP+H2O -> ADP+Pi
hydrolysis
what type of reaction is
ADP+Pi -> ATP+H2O
condensation
what has a higher potential energy ATP or ADP+Pi
ATP, so hydrolysis occurs with a decrease in Free Energy (exergonic)
ADP to ATP condensation reaction requires Free Energy input (endergonic)
is a hydrolysis reaction endergonic or exergonic
exergonic
is a condensation reaction endergonic or exergonic
endergonic
ATP allows anabolic, thermodynamically unfavourable reactions, to
proceed through coupling of catabolic thermodynamically favourable reactions
what is phosphoenolypyruvate (PEP)
produced in an intermediate step during the process of glucose releasing its potential energy when degraded
acts as an intermediate for a reaction that goes on to produce ATP during PEP to pyruvate conversion
potential energy released from PEP to pyruvate conversion is “stored” in the form of ATP
what is the ΔG for the reaction PEP→pyruvate
-31.4kJ/mol
when is the potential energy of PEP “released”
it is converted into pyruvate
when is the potential energy of PEP “saved”
it is “saved” as potential energy in an ATP molecule
why is ATP called the “universal currency” of Free Energy
because energy flows through many biological pathways by utilising phosphoryl group transfer between molecules
why does potential energy in food molecules arise
because they contain large numbers of H atoms
give examples of molecules containing large numbers of H atoms
carbohydrates, glucose
fatty acids, palmitate (palmitate has lots of H atoms making it similar to petroleum – another molecule that is rich in energy)
what will the oxidation of glucose release
electrons that spontaneously flow through a series of intermediate steps to another chemical species, such as O2
this can be described as an electron motive force (emf)
what is enf
describes that electrons can accomplish work as they pass through chemical intermediates
from the thousands of metabolic reactions that occur within the cell, how many activated carriers of energy are used
a small number
this hints as the evolutionary background of metabolic processes
these activated carriers act as coenzymes in biochemical pathways to facilitate fuel oxidation and biosynthesis reactions
