Transcript Chapter 1 Notes

Chapter 8 notes
An Introduction to
Metabolism
Concept 8.1
Metabolism: the totality of an
organism’s chemical reactions
A metabolic pathway begins with a
specific molecule and is altered into a
product
- each step is catalyzed by an enzyme
Concept 8.1
Catabolic pathway: release energy in
the breaking down of complex
molecules into simpler compounds
- ex. glucose  CO2 + H2O
Anabolic pathway: consume energy to
build complicated molecules from
simpler ones
- ex. amino acids  proteins
Concept 8.1
Energy: the capacity to do work
Reactions (Rxns.) are either exergonic
(energy outward) or endergonic
(energy inward)
Concept 8.2
Exergonic rxns. proceed with a net
release of energy
- occur spontaneously
Endergonic rxns. absorb free energy from
their surroundings
- nonspontaneous
Concept 8.2
Concept 8.2
Cells do three kinds of work:
- mechanical work (ex. contraction of a
muscle cell)
- transport work (ex. pumping of
substances across a memebrance)
- chemical work (ex. synthesis of
polymers from monomers)
Concept 8.3
Energy coupling: the use of an
exergonic process to drive an
endergonic one
ATP is the energy source used in most
rxns.
- contains a ribose (sugar), adenine
(base), and 3 phosphate molecules
Concept 8.3
Concept 8.3
Energy is released from ATP when the
terminal phosphate bond is broken
ATP  ADP + Pi + Energy
- work is accomplished by
phosphorylation
- the transferring of the Pi to another
molecule (ex. channel protein)
Concept 8.3
Concept 8.3
ATP is regenerated in the cell by
phosphorylating ADP through an
exergonic rxn. in the cell
- in a muscle cell 10 million ATP are
consumed and regenerated per second
per cell
Concept 8.3
Concept 8.4
Spontaneous rxns. May occur at very slow
rates
- sucrose  glucose + fructose
- if an enzyme is added, the same rxn.
can completed in seconds
Catalyst: a chemical agent that speeds
up reaction w/out being consumed
Concept 8.4
Enzyme: a biological catalyst
Activation energy, the energy needed
to begin a rxn, prevents many rxns
from occurring quickly
Heat is used to speed up rxns b/c it
increases the speed of reactant
molecules (to collide more often)
Concept 8.4
Concept 8.4
In biological systems heat alone would
not work
- too much heat denatures proteins and
kills cells
An enzyme (catalyst) lowers the amt. of
activation energy needed
- enzymes are very selective
Concept 8.4
Concept 8.4
Concept 8.4
The reactant an enzyme binds to is called
the substrate
- binds to the active site of the enzyme
- the enzyme converts the substrate to
product
- the product is released
Enzyme animation
Concept 8.4
Up to a point, the rate of an enzymatic
reaction will increase with temperature
- eventually it will drop because of
thermal agitation and protein
denaturing
Concept 8.4
Most human enzymes function best at 3540 oC.
- some bacteria that live in hot springs
have proteins that work best at 70 oC.
Most human enzymes also work best at 68 pH.
- pepsin in the stomach work best at PH
2
Concept 8.4
Concept 8.4
Certain chemicals can selectively inhibit
the activity of specific enzymes
Competitive inhibitors: reduce enzyme
activity by blocking the substrate from
binding to the active site
- can be overcome by increasing
[substrate]
Concept 8.4
Noncompetitive inhibitors: impede
the reaction by attaching to another
part of the enzyme, thus changing its
shape
- ex. toxins and poisons