An Introduction to Metabolism

forestercuckooMechanics

Oct 27, 2013 (4 years and 13 days ago)

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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