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Enzymes and Metabolism

from Kim Foglia

Joselyn Ponce

on 17 September 2012

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Transcript of Enzymes and Metabolism

changes in pH
adds or remove H+
disrupts bonds, disrupts 3D shape
disrupts attractions between charged amino acids
affect 2° & 3° structure
denatures protein
optimal pH?
most human enzymes = pH 6-8
depends on localized conditions
pepsin (stomach) = pH 2-3
trypsin (small intestines) = pH 8 Inhibitor permanently binds to enzyme
permanently binds to active site
permanently binds to allosteric site
permanently changes shape of enzyme
nerve gas, sarin, many insecticides (malathion, parathion…)
cholinesterase inhibitors
doesn’t breakdown the neurotransmitter, acetylcholine Irreversible inhibition How do ectotherms do it? Variety of mechanisms to lower activation energy & speed up reaction
active site orients substrates in correct position for reaction
enzyme brings substrate closer together
active site binds substrate & puts stress on bonds that must be broken, making it easier to separate molecules How does it work? Naming conventions Enzymes named for reaction they catalyze
sucrase breaks down sucrose
proteases break down proteins
lipases break down lipids
DNA polymerase builds DNA
adds nucleotides to DNA strand
pepsin breaks down proteins (polypeptides) Reaction specific
each enzyme works with a specific substrate
chemical fit between active site & substrate
H bonds & ionic bonds
Not consumed in reaction
single enzyme molecule can catalyze thousands or more reactions per second
enzymes unaffected by the reaction
Affected by cellular conditions
any condition that affects protein structure
temperature, pH, salinity Properties of enzymes Ghosts of Lectures Past
(storage) 2007-2008 Non-Competitive Inhibitor Inhibitor binds to site other than active site
allosteric inhibitor binds to allosteric site
causes enzyme to change shape
conformational change
active site is no longer functional binding site
keeps enzyme inactive
some anti-cancer drugs
inhibit enzymes involved in DNA synthesis
stop DNA production
stop division of more cancer cells
cyanide poisoning
irreversible inhibitor of Cytochrome C, an enzyme in cellular respiration
stops production of ATP Inhibitor & substrate “compete” for active site
blocks enzyme bacteria use to build cell walls
disulfiram (Antabuse)
treats chronic alcoholism
blocks enzyme that breaks down alcohol
severe hangover & vomiting 5-10 minutes after drinking
Overcome by increasing substrate concentration
saturate solution with substrate so it out-competes inhibitor for active site on enzyme Competitive Inhibitor Inhibitors
molecules that reduce enzyme activity
competitive inhibition
noncompetitive inhibition
irreversible inhibition
feedback inhibition Compounds which regulate enzymes Salt concentration
changes in salinity
adds or removes cations (+) & anions (–)
disrupts bonds, disrupts 3D shape
disrupts attractions between charged amino acids
affect 2° & 3° structure
denatures protein
enzymes intolerant of extreme salinity
Dead Sea is called dead for a reason! Factors affecting enzyme function More accurate model of enzyme action
3-D structure of enzyme fits substrate
substrate binding cause enzyme to change shape leading to a tighter fit
“conformational change”
bring chemical groups in position to catalyze reaction Induced fit model Don’t be inhibited! Ask Questions! Temperature
Optimum T°
greatest number of molecular collisions
human enzymes = 35°- 40°C
body temp = 37°C
Heat: increase beyond optimum T°
increased energy level of molecules disrupts bonds in enzyme & between enzyme & substrate
H, ionic = weak bonds
denaturation = lose 3D shape (3° structure)
Cold: decrease T°
molecules move slower
decrease collisions between enzyme & substrate Factors affecting enzyme function 2007-2008 Enzymes Biological catalysts
proteins (& RNA)
facilitate chemical reactions
increase rate of reaction without being consumed
reduce activation energy
don’t change free energy (G) released or required
required for most biological reactions
highly specific
thousands of different enzymes in cells
control reactions of life isoleucine threonine Example
synthesis of amino acid, isoleucine from amino acid, threonine
isoleucine becomes the allosteric inhibitor of the first step in the pathway
as product accumulates it collides with enzyme more often than substrate does Feedback inhibition Allosteric regulation Conformational changes Conformational changes by regulatory molecules
keeps enzyme in inactive form
keeps enzyme in active form Allosteric regulation catalase Enzyme concentration
Substrate concentration
Inhibitors Factors Affecting Enzyme Function Metabolism & Enzymes 2007-2008 Hemoglobin
4 polypeptide chains
can bind 4 O2;
1st O2 binds
now easier for other 3 O2 to bind Substrate acts as an activator
substrate causes conformational change in enzyme
induced fit
favors binding of substrate at 2nd site
makes enzyme more active & effective
hemoglobin Cooperativity Fe in hemoglobin Mg in chlorophyll Compounds which help enzymes Activators
non-protein, small inorganic compounds & ions
Mg, K, Ca, Zn, Fe, Cu
bound within enzyme molecule
non-protein, organic molecules
bind temporarily or permanently to enzyme near active site
many vitamins
NAD (niacin; B3)
FAD (riboflavin; B2)
Coenzyme A That’s why they’re called anabolic steroids! Chemical reactions of life
forming bonds between molecules
dehydration synthesis
anabolic reactions
breaking bonds between molecules
catabolic reactions Metabolism Whoa! All that going on in those little mitochondria! Organized groups of enzymes
enzymes are embedded in membrane and arranged sequentially
Link endergonic & exergonic reactions Efficiency Factors that Affect Enzymes 2007-2008 In biology… Size doesn’t matter… Shape matters! Simplistic model of enzyme action
substrate fits into 3-D structure of enzyme’ active site
H bonds between substrate & enzyme
like “key fits into lock” Lock and Key model What’s happening here?! Salinity reaction rate salt concentration What’s happening here?! Temperature temperature reaction rate 37° What’s happening here?! reaction rate substrate concentration Substrate concentration What’s happening here?! reaction rate enzyme concentration Enzyme concentration CO2 + H2O + heat cellulose energy Breaking down large molecules requires an initial input of energy
This is known as activation energy
large biomolecules are stable
must absorb energy to break bonds Activation energy Some chemical reactions release energy
digesting polymers
hydrolysis = catabolism
Some chemical reactions require input of energy
building polymers
dehydration synthesis = anabolism Chemical reactions & energy active site products enzyme substrate substrate
reactant which binds to enzyme
enzyme-substrate complex: temporary association
end result of reaction
active site
enzyme’s catalytic site; substrate fits into active site Enzymes vocabulary Call in the ENZYMES! G ENZYMES So what’s a cell got to do to reduce activation energy?
get help! … chemical help… Catalysts starch Why don’t stable polymers spontaneously digest into their monomers? If reactions are “downhill”, why don’t they just happen spontaneously?
because covalent bonds are stable bonds What drives reactions? glucose Not a match! That’s too much energy to expose living cells to! Activation energy
amount of energy needed to destabilize the bonds of a molecule
moves the reaction over an “energy hill” Too much activation energy for life +G G = change in free energy = ability to do work -G energy invested
synthesis - energy released
- digestion endergonic exergonic Endergonic vs. Exergonic reactions enzyme enzyme hydrolysis (digestion) dehydration synthesis (synthesis) Examples Factors affecting enzyme function (158°F) hot spring bacteria enzyme human enzyme 70°C reaction rate temperature 37°C Different enzymes function in different organisms in different environments Enzymes and temperature Substrate concentration
as ^ substrate =  ^ reaction rate
more substrate = more frequently collide with enzyme
reaction rate levels off
all enzymes have active site engaged
enzyme is saturated
maximum rate of reaction reaction rate substrate concentration Factors affecting enzyme function catalyzed reaction uncatalyzed reaction product reactant NEW activation energy Pheeew… that takes a
lot less energy! Catalysts
reducing the amount of energy to start a reaction Reducing Activation energy sun organic molecules  ATP & organic molecules organic molecules  ATP & organic molecules solar energy 
ATP & organic molecules Life is built on chemical reactions
transforming energy from one form to another Flow of energy through life Enzyme concentration
as ^ enzyme =  ^ reaction rate
more enzymes = more frequently collide with substrate
reaction rate levels off
substrate becomes limiting factor
not all enzyme molecules can find substrate Factors affecting enzyme function synthesis digestion + energy + energy + + Organisms require energy to live
where does that energy come from?
coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) Energy & life  A  B  C  D  E  F  G       enzyme 1
Metabolic pathways Chemical reactions of life are organized in pathways
divide chemical reaction into many small steps
artifact of evolution
^ efficiency
intermediate branching points
 ^ control = regulation trypsin pepsin 14 13 12 11 What’s happening here?! trypsin pepsin 9 8 6 5 4 3 1 0 2 reaction rate pH pH and Enzymes 7 10       enzyme 1 X A  B  C  D  E  F  G Regulation & coordination of production
product is used by next step in pathway
final product is inhibitor of earlier step
allosteric inhibitor of earlier enzyme
feedback inhibition
no unnecessary accumulation of product Feedback Inhibition allosteric inhibitor of enzyme 1 enzyme enzyme H2O + H2O + hydrolysis (digestion) dehydration synthesis (synthesis) Examples water water enzyme concentration reaction rate enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 6 enzyme 7 enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 6
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