An Introduction to Metabolism

An Introduction to
Metabolism

Flow of energy through life


Life is built on chemical reactions

Chemical Reactions of Life

•
Metabolism

–
Is the

of an organism’s chemical
rxns

–
Forming bonds

between molecules

•
Dehydration synthesis

•


reactions

–
Breaking bonds

between molecules

•
Hydrolysis

•


reactions

Examples

•
Dehydration synthesis






•
Hydrolysis


Examples

The Law of Energy Transformation

•

is the study of energy
transformations

•
A closed system, such as that approximated by
liquid in a thermos, is isolated from its
surroundings

•
In an open system, energy and matter can be
transferred between the system and its
surroundings

•
Organisms are



FIRST LAW OF THERMODYNAMICS

•
According to the

,
the energy of the universe is constant:

–

Energy can be transferred and transformed, but it
cannot be created or destroyed

•
The first law is also called the



SECOND LAW OF THERMODYNAMICS

•
During every energy transfer or
transformation, some energy is unusable, and
is often lost as heat

•
According to the




:


–


Every energy transfer or transformation increases
the

(disorder) of the universe


(a) First law of thermodynamics


(b) Second law of thermodynamics


Chemical

energy


Heat


CO
2


H
2
O


+


Chemical reactions & energy

•
Some chemical reactions


–
Exergonic

–
spontaneous

–
Digesting polymers

–
Hydrolysis = catabolism

–


•
Some chemical reactions
require energy

–
Endergonic


–
Non spontaneous

–
Building

–
Dehydration synthesis = anabolism

–
Products


Endergonic vs. exergonic reactions

Energy & life

•
Organisms require energy to live

•
Energy comes from

–
Coupling


with



–
Example: photosynthesis

–
Usually halves of coupled
rxns

occur in different places
so energy


•
Accomplished with carrier molecule such as ATP

Spontaneous Reactions?

•
If reactions are “downhill”, why don’t they just
happen spontaneously?

–
Because


Activation energy

•
Breaking down large molecules



–
Activation energy

–
Large biomolecules are stable

–
Must


Activation energy

•



•
Usually is


•
Most
reactions occur readily at higher temp.

–
Moves the reaction


High

Low

Energy
content of
molecules

Reducing Activation Energy

•
Catalysts

–
Reduce


Catalysts

•
A cell reduces activation energy by using enzymes

Enzymes

•
Biological catalysts

–
Proteins (very specific shape)

–
Facilitate


•
Increase


•
Reduce


•
Don’t change free energy (
Δ
G
) released or required

–



–
Highly specific

•



–
Control reactions

–
Enzyme activity




Enzymes & substrates

•
Substrate

–
Reactant which



–
Enzyme
-
substrate
complex:



•
Product

–
End
result of
reaction

Enzymes and substrates

•
Enzyme + substrate


Product

–
Sucrase

•
Enzyme breaks


down


•
Binds to sucrose &


breaks disaccharide



into




–
DNA polymerase

•
Enzyme builds


•
Adds nucleotides to



a growing






Lock and Key Model

•
Specific shape of the






and catalyze specific reactions

•
Active Site

–
Enzyme


–
Pocket or groove



–
Substrate (= reactant molecule)


Induced Fit

•
When substrate

,
both substrate
and active site change shape

–
Amino acids


–
Electrical charges distort



•
New product is


expelled and enzyme


can go on and accept




Properties of enzymes
-

Specificity

•
Reaction
Specific

–
Each enzyme is

•
Due to fit between


–
Substrates held in


»
H bonds

»
Ionic bonds

–
Enzymes named for reaction they catalyze

•
Sucrase

breaks down sucrose

•
Proteases

break down proteins

•
Lipases

break down lipids

•
DNA

polymerase builds DNA

•
Pepsin

breaks down polypeptides

Properties of enzymes
-

Reusable

•
Not consumed in reaction

–
Single enzyme molecule can



–
Enzymes


Factors affecting enzymes
–

enzyme
concentration

•
Effect on rates of enzyme
activity

–
As
conc

of enzyme increases,



•
More enzyme = more



–
Reaction rate


•
Substrate becomes



•
Not all enzyme


Factors affecting enzymes
–

substrate
concentration

•
Effect on rates of enzyme
activity

–
As conc. of substrate increases,



•
More substrate =



•
Reaction rate levels off

–
all enzymes have



–
Enzyme


–
Maximum rate of reaction

Factors affecting enzymes
–

temperature

•
Effect on rates of enzyme
activity

–
Optimum Temp

•
Greatest



•
Human enzymes = 35
-
40
º C (body
temp = 37º C)

–
Increase beyond optimum Temp

•
Increased



–
H and ionic bonds = weak bonds

–
Denaturation

=


–
Decrease Temp

•
Molecules


•
Decrease


Factors affecting enzymes
–

temperature

•
Different enzymes function at different
temperatures in different organisms

How do ectotherms do it?

Factors affecting enzymes
–

pH

•
Effect on rates of enzyme
activity

–
Protein shape (conformation)

•
Attraction


–
pH changes

•
Changes charges



•
Disrupt bonds,


–
Most human enzymes are active
at pH 6
-
8

•
Depends


•
Pepsin (stomach)


•
Trypsin
(

Factors affecting enzymes
–

salt
concentration

•
Effect on rates of enzyme
activity

–
Protein shape
(conformation)

•
Depends



–
Salinity changes

•
Change



•
Disrupt bonds,



–
Enzymes intolerant of
extreme salinity

•
Dead Sea is called dead for a
reason!

Factors affecting enzymes
–

Activators

•
Compounds


•
Cofactors

–
Non
-
protein,



•
Mg, K,
Ca
, Zn, Fe, Cu

•
Coenzymes

–
Non
-
protein,


•
Bind temporarily



–
Many vitamins

•
NAD


•
FAD


•
Coenzyme A

Factors affecting enzymes
–

Inhibitors

•
Regulation of enzyme activity

–
Certain chemicals


•
Selective inhibition and
activation

–
Competitive inhibition

–
Noncompetitive inhibition

–
Irreversible inhibition

–
Feedback inhibition

Factors affecting enzymes
–

Competitive
Inhibitors

•
Effect

–
Inhibitor resembles the shape of the
normal


•
Ex
. Penicillin blocks



–
Overcome
by



•
Saturate solution with substrate so it
out
-
competes


Factors affecting enzymes
–

Noncompetitive Inhibitors

•
Effect

–
Inhibitor binds to



•
Allosteric site

•
Called allosteric inhibitor

–
Ex. Some anti
-
cancer drugs inhibit




& therefore in building of
DNA= stop DNA production,



•
Causes
enzyme to


•
Renders


Factors affecting enzymes
–

Irreversible
Inhibitors

•
Inhibitor permanently binds to enzyme

–
Competitor

•
Permanently


–
Allosteric

•
Permanently


•
Ex. Nerve gas,
sarin
, many insecticides (
malathion
,
parathion…)

–
Cholinesterase inhibitors


Factors affecting enzymes
–

feedback
inhibition

•
Regulation & coordination of
production: the end
product of a metabolic pathway shuts down the
pathway

–
Product is


–
Final product is


•
Allosteric inhibitor of earlier enzyme

•
Feedback inhibition

–
No unnecessary accumulation of product

Factors affecting enzymes
–

feedback

inhibition

•
Example

–
Synthesis of amino
acid isoleucine
from amino acid
threonine

Action of Allosteric Control

•
Inhibitors and activators

–
Regulatory molecules



–
Inhibitor keeps enzyme


–
Activator keeps enzyme


Cooperativity


is a form of allosteric regulation that can
amplify enzyme activity

•
Substrate acts as an activator

–
Substrate causes



•
Induced fit

–
Favors binding


–
Makes enzyme


•
Ex. hemoglobin

Metabolic pathways

•
Chemical reactions of
life are organized in
pathways

–
Divide chemical



•
Efficiency

•
Control = regulation

Efficiency

•
Groups of enzymes organized

–
If enzymes are embedded in
membrane



•
Link endergonic


& exergonic


reactions

Industrial Uses of Enzymes

•
Enzymes have long been used for industrial purposes

–


•
Proteases are used to soften hides and remove hair

–


•
Enzymes in barley grains at germinations are used to convert
stored starch to sugars that can be fermented by yeast

–


•
Enzymes are frequently used in genetic engineering

–


•
Some people are “lactose
-
intolerant” (do not produce lactase
in pancreatic juices)
–

cannot digest milk and milk products

–
Lactase is obtained from bacteria

–
Milk and milk products are treated with lactase before
consumption to remove lactose