week 8 Flashcards
The Energy of Life.
name all components (5)
• All living organisms require energy in order to survive
• The sunlight is the source of energy on Earth
• The sunlight is used for synthesis of sugars through
photosynthesis (by plants)
• Energy is transferred through metabolism
• The living cell is a miniature factory where thousands of
reactions occur => Converts energy in many ways
• Example: some organisms convert energy to light
(bioluminescence)
Energy flow on Earth.
Steps
• Sun → Producers → Consumers, decomposers
What is Metabolism
is the totality of an organism’s
chemical reactions through which:
- Energy is stored (anabolic processes)
- Energy is released (catabolic processes)
Metabolic Pathways
• A metabolic pathway has many steps that begin with a
specific molecule and end with a product
• Each step is catalyzed by a specific enzyme
• Metabolic pathways are controlled according to cellular
demands
pic page 6
week 8
Catabolic pathways
• Release energy**
• Break down complex molecules into simpler
compounds
• Example: cellular respiration
Anabolic pathways
• Consume energy**
• Synthesize complicated molecules from
simpler ones
• Example: photosynthesis, protein synthesis
from aminoacids
Potential energy includes what?
Includes chemical energy stored in molecular structure
Free energy
Function?
equation?
• Organisms live by spending (consuming) free energy
–Free energy: a living system’s energy that can do work
under cellular conditions
• The free-energy change (ΔG) of a reaction indicates
whether the reaction occurs spontaneously or not
ΔG = Gfinal - Ginitial
Εxergonic reactions:
– Spontaneous reactions
– Free energy released→ ΔG < 0 (negative)
– ΔG = Gfinal - Ginitial => Gfinal < Ginitial
diagram14
Εndergonic reactions:
- Absorb free energy from their surroundings (require energy)
- Non-spontaneous reactions → ΔG > 0
- ΔG = Gfinal - Ginitial => Gfinal > Ginitial
diagram15
do metabolic pathways reach equilibrum?
no
The Structure of ATP?
Function?
• ATP (adenosine triphosphate):
- the cell’s energy shuttle (energy storage and transfer)
- Nucleotide that stores energy in phosphate bonds
- Function: Provides energy for cellular functions
– energy rich => unstable → tends to break down
diagram17
ATP hydrolysis ?
regeneration (synthesis)?
• ATP hydrolysis:
ATP → ADP + Pi => energy release
• ATP synthesis:
ADP + Pi → ATP => energy stored (in
phosphate bonds)
diagram18
Energy coupling by ATP
what is Energy coupling?
Three main kinds of endergonic cellular work (require energy
input)?
-ATP powers cellular work by energy coupling
energy coupling: the use of an exergonic process to drive an
endergonic one
(types):
– Mechanical
– Transport
– Chemical
• ATP – mediated energy coupling:
- an endergonic process can by driven by the ATP hydrolysis (exergonic
process)
=> ATP hydrolysis provides the energy required for the endergonic
reaction to occur
Exergonic reaction:
How is energy released
Energy is released from ATP when
any of the 2 terminal phosphate bonds are broken
diagram20
∆G in
Endergonic reaction:
Exergonic reaction:
Coupled reactions:
- Endergonic reaction: ∆G is positive, reaction is not spontaneous
- Exergonic reaction: ∆G is negative, reaction is spontaneous
-Coupled reactions: Overall ∆G is negative;
together, reactions are spontaneous
phosphorylation and ATP
How does ATP affect endrogenic reactions?
• ATP drives endergonic reactions by phosphorylation (transfer of a phosphate to other molecules)
diagram22
diagram23***
look!
formula
Photosynthesis:
Cellular respiration (aerobic):
CO2 + H20—–) C6H1206 + O2
Carbon dioxide water —–glucose oxygen
Cellular respiration (aerobic):
C6H1206 + Ο2——-) CO2 + H20 + ΑΤP
Glucose oxygen ——-)carbondioxide water
energy
diagram25week8*
look
Enzymes:
Catalyst:
examples
• Enzymes: catalytic proteins that speed up metabolic
reactions by lowering energy barriers
• Catalyst: a chemical agent that speeds up a reaction
without being consumed by the reaction
- Example: sucrose hydrolysis by sucrase
- Sucrase: the enzyme that catalyzes sucrose hydrolysis
The activation energy, EA (4 components)
– The initial amount of energy needed to start a
chemical reaction
Enzymes lower the Ea barrier
Enyme affect on reaction?
-By lowering the activation energy (EA) barrier
=> This speeds up the reaction
– The enzyme does not affect whether the reaction will
happen spontaneously or not (without the input of
energy)
– An enzyme will only speed up a reaction that would
occur anyway
What is a Substrate
example?
Substrate: the reactant an enzyme acts on
Example: sucrose is the substrate for sucrase
What is Substrate specificity:
the enzyme will only recognize its specific substrates (and no other related compounds)
What is the The active site:
the region on the enzyme where the substrate binds
Induced fit of a substrate:
enzyme changes shape upon substrate
binding
=>brings chemical groups of the active site into positions that enhance
their ability to catalyze the chemical reaction
Denaturation:
the loss of a protein’s native conformation
due to unravelling => loss of function
Environmental factors that may affect enzyme activity:
- pH
- Temperature
Cofactors:
and what are Inorganic cofactors
Coenzymes:
Cofactors: non-protein enzyme helpers
Inorganic cofactors: e.g. metal ions
Coenzymes: organic cofactors (e.g. vitamins)
Each enzyme has an……….. in which it can function
optimal temperature
Each enzyme as an …….. in which it can
function
optimal pH
Irreversible inhibitors:
examples?
Irreversible inhibitors: bind to an enzyme by covalent
bonding => inhibition is irreversible
-Examples: several toxins, antibiotics and poisons
– Sarin, DDT, parathion: inhibit nervous system enzymes
– Penicillin derivatives: inhibit the enzyme transpeptidase
that synthesize the bacterial cell wall peptidoglycan
Reversible inhibitors:
Types(2)
Reversible inhibitors: bind to enzymes by weak bonds
(non-covalent interactions: H-bonds, hydrophobic
interactions and ionic bonds) => inhibition is reversible
- 2 types of reversible inhibitors:
1. Competitive inhibitors
2. Non-competitive inhibitors
Competitive inhibitors:
bind to what?
function?
How can inhibation be overcome?
Competitive inhibitors: bind to the active site of an enzyme
(weak binding)
• Compete with the substrate => inhibit substrate binding to the
active site
-Inhibition can be overcome by adding excess substrate
Non-competitive inhibitors:
bind to what?
Function?
Can inhibition be overcome?
Non-competitive inhibitors: bind to another part of an
enzyme not to the active site.
Change the shape of the enzyme
Inhibit the function of the enzyme
-Inhibition cannot
be overcome by
adding excess
substrate
Two basic methods of enzyme regulation:
- Regulation of enzyme production by
regulation of gene expression - Regulation of enzyme activity by feedback
inhibition (by allosteric regulation)
diagram44
look
In feedback inhibition:
whats the end product?
Role?
Examples (2)
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**Feedback inhibition prevents waste that occurs when more of a product is made than the cell needs.
– The end product of a metabolic pathway inhibits the pathway
– Role: prevents a cell from wasting chemical resources
by synthesizing more product than is needed
– Examples:
➢ Inhibition of catabolic pathways by ATP (ATP is the
end product)
➢ Inhibition of anabolic pathways by their end product
(e.g tryptophan synthesis pathway inhibition by
tryptophan)
Allosteric Regulation of Enzymes:
– A form of reversible modulation common in enzymes (and proteins)
made from polypeptide subunits
– can be positive (activation) or negative (inhibition)
– a protein’s function (activity) at one site (active site) is affected by
binding of a regulatory molecule usually (not always) at another site
(regulatory site)
– Regulatory molecules bind to regulatory sites via non-covalent binding interactions (similar to reversible non-competitive inhibitors)
– Enzyme changes shape when regulatory molecules bind to specific
sites, affecting their function
– can be heterotropic
(regulatory molecules bind to sites other than the
active sites) or homotropic (regulatory molecule is the substrate and
binds to active sites)
*basically non-competitive inhibtors i think
Allosteric activators
Allosteric activators
stabilize the active
form of the enzyme
Allosteric inhibitors
Allosteric inhibitors
stabilize the inactive
form of the enzyme
Homotropic allosteric regulation:
Binding of substrate to active site
of one subunit locks all subunits into active conformation
Cooperativity:
example
• Cooperativity: special form of positive allosteric regulation
(activation) that can amplify enzyme activity
– Example: O2 binding to haemoglobin
– The binding of substrate (oxygen) at one subunit increases the
binding affinity of the other subunits (oxygen= allosteric
activator)
Allosteric activator
Allosteric activator is
the substrate; locks all
subunits into active
conformation
Allosteric regulation summary
• Allosteric inhibitors can be competitive or noncompetitive inhibitors
• Heterotropic allosteric modulator (non-competitive
inhibitors + activators):
- a regulatory molecule that is NOT the enzyme’s substrate
- Example:
- AMP is a heterotropic allosteric activator of PFK
(phosphofructokinase) - CO2
is a heterotropic allosteric inhibitor (noncompetitive inhibitor) of haemoglobin
=> reduces haemoglobin’s affinity for oxygen
=> Oxygen is released in the tissues
Homotropic allosteric modulator (competitive
inhibitors + activators):
- both a substrate for its target enzyme and a regulatory molecule of the enzyme’s activity.
- It is typically an activator of the enzyme (exception: CO for Hb).
- Example: O2 and CO are homotropic allosteric
modulators of haemoglobin. - O2 is an homotropic allosteric activator of haemoglobin
- CO is a competitive inhibitor: binds to haemoglobin at
the same site as the oxygen => has higher affinity for Hb
than oxygen => does not allow oxygen to be released in
tissues.
diagram53
look has summary
