The Working Cell
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Transcript The Working Cell
Chapter 8
Objectives
○ Distinguish between the following pairs or terms:
catabolic and anabolic pathways; kinetic and
potential energy; open and closed systems;
exergonic and endergonic reactions
○ Explain how the nature of energy transformations is
guided by the two laws of thermodynamics
○ Describe how ATP functions as the universal energy
shuttle in cells
○ Describe the structure of enzyme-substrate
interactions and how enzymes catalyze biological
reactions
Introduction
Characteristics of organisms are all the
end-products of the chemical reactions
that occur in their cells
The cell is a mini factory
Roughly 8.64 x 1026 reactions per day
Chemical reactions carried out for the
purpose of energy transformation or making
necessary substances
Energy-The Capacity to do Work
Energy is described and measured by how it
affects matter
Two types of energy:
kinetic-energy of motion
potential-stored energy because of structure or location
Example: the energy stored in chemical bonds
Why we are open systems
Laws of Energy Conservation
Thermodynamics = study of energy
transformations
Two laws govern energy transformation:
First law (energy conservation)
○ total amount of energy in universe is constant
can be transferred or transformed but cannot
be created or destroyed
Second law (entropy-disorder- increases)
○ every energy transformation increases entropy
energy available for doing useful work
decreases with every transformation
Organization of the Chemistry of
Life into Metabolic Pathways
Metabolism transforms matter and energy
Subject to the laws of thermodynamics
○ Metabolism is the sum of an organism’s
chemical reactions
Metabolic pathway has many steps that
begin with a specific molecule and end
with a product
Each step catalyzed by a specific enzyme
Catabolic vs. Anabolic
Catabolic: break down complex
molecules into simpler compounds
Releases energy
Anabolic: build complicated molecules
from simpler ones
Consumes energy
G = Gibbs Free Energy
(Delta) G = Free energy available to do work in
a cell
A - G means a rxn gives off energy; it provides
power
A + G means a rxn needs energy; it will not run
unless energy is first added
Every rxn has a specific G
Energy Relationships in Living Things
Chemical reactions in cells either store or release
energy
endergonic reactions require input of energy
○ energy input equals difference in potential
energy between reactants and products
exergonic reactions release energy
○ energy released equals difference in potential
energy between reactants and products
cellular metabolism is sum total of all endergonic and
exergonic reactions in cells
Energy Relationships
ATP is cell’s energy shuttle
most cell reactions require small amounts of
energy
food storage molecules contain large
amounts of energy
energy in food molecules converted to
energy in ATP
○ one food molecule=many ATP (e.g. 1 x
glucose=36 ATP)
Energy Relationships
Hydrolysis of ATP releases energy
Most energy is located in the covalent bond between
2nd and 3rd phosphate groups
easily hydrolyzed
forms ADP and phosphate group
ATP ADP + Pi ( means PO4 = phosphate)
ATP synthesis
endergonic reactions of cellular respiration
phosphorylate ADP-reforms ATP
ADP + Pi (PO4 = phosphate) ATP
More about this in Chapter 9
Enzymes
Enzymes are large protein molecules that act
as biological catalysts
Energy of activation (EA) is “energy barrier”,
amount of energy needed to start a reaction
Enzymes can lower energy barriers = EA
Enzymes cannot lower G!
Enzyme Process
Specific enzymes
catalyze each cell
reaction
reactant=substrate
reactant binds to
enzyme active site
substrate converted
to product
enzyme unchanged
and releases product
Enzymes and Denaturation
Factors that affect enzyme activity
temperature
pH
salt concentration ( ions)
presence of co-factors
denaturation
Denaturation = disruption of the
enzyme structure due to adverse
conditions
Example: PH to high or low
These factors may lead to
Question: How do you stop enzyme activity but not
destroy the enzyme? Answer: Inhibition
Inhibitors block enzyme action,
○ competitive inhibitors-bind to active
site
○ noncompetitive inhibitors-bind to
second site on enzyme
○ negative feedback-inhibition by
product of reaction
some pesticides and antibiotics
function by inhibiting enzymes
Inhibitors most often work on a
temporary basis
BUT>>>>>>>
A+BC : G= - 8.6 kcal needs 8.6
kcal to run the reaction
A.
B.
True
False
Checklist
What is energy?
What are the types of energy?
What are the laws of thermodynamics?
Catabolic vs anabolic?
What is ∆G?
+ ∆G means what? - ∆G means what?
What do these look like graphed?
What are enzymes? What do they do?
Do enzymes change the ∆G?