1 Division Ave. High School Ms. Foglia AP Biology AP Biology 2007-2008 Metabolism & Enzymes AP Biology From food webs to the life of a cell energy energy energy AP Biology Flow of energy through life § Life is built on chemical reactions u transforming energy from one form to another organic molecules ® ATP & organic molecules organic molecules ® ATP & organic molecules sun solar energy ® ATP & organic molecules
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Metabolism & Enzymes - Springfield Public Schools · AP Biology AP Biology 2007-2008 Metabolism & Enzymes AP Biology From food webs to the life of a cell energy energy energy AP Biology
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Division Ave. High School Ms. FogliaAP Biology
AP Biology 2007-2008
Metabolism & Enzymes
AP Biology
From food webs to the life of a cell
energy
energy
energy
AP Biology
Flow of energy through life§ Life is built on chemical reactions
u transforming energy from one form to another
organic molecules ®ATP & organic molecules
organic molecules ® ATP & organic molecules
sun
solar energy ®ATP & organic molecules
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Division Ave. High School Ms. FogliaAP Biology
AP Biology
Metabolism§ Chemical reactions of life
u forming bonds between molecules§ dehydration synthesis§ synthesis§ anabolic reactions
u breaking bonds between molecules§ hydrolysis§ digestion§ catabolic reactions
That’s why they’re called
anabolic steroids!
AP Biology
Examples § dehydration synthesis (synthesis)
§ hydrolysis (digestion)
+
H2O
+
H2O
enzyme
enzyme
AP Biology
Examples § dehydration synthesis (synthesis)
§ hydrolysis (digestion)
enzyme
enzyme
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Division Ave. High School Ms. FogliaAP Biology
AP Biology
Chemical reactions & energy§ Some chemical reactions release energy
u exergonicu digesting polymersu hydrolysis = catabolism
§ Some chemical reactions require input of energyu endergonicu building polymers u dehydration synthesis = anabolism
digesting molecules= LESS organization=lower energy state
building molecules= MORE organization=higher energy state
AP Biology
Endergonic vs. exergonic reactionsexergonic endergonic- energy released- digestion
- energy invested- synthesis
-DG
DG = change in free energy = ability to do work
+DG
AP Biology
Energy & life§ Organisms require energy to live
u where does that energy come from?§ coupling exergonic reactions (releasing energy)
with endergonic reactions (needing energy)
+ + energy
+ energy+
digestion
synthesis
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Division Ave. High School Ms. FogliaAP Biology
AP Biology
What drives reactions?§ If reactions are “downhill”, why don’t they
just happen spontaneously?u because covalent bonds are stable bonds
Why don’tstable polymersspontaneously
digest into theirmonomers?
starch
AP Biology
Activation energy§ Breaking down large molecules
requires an initial input of energyu activation energyu large biomolecules are stableu must absorb energy to break bonds
energycellulose CO2 + H2O + heat
AP Biology
Too much activation energy for life§ Activation energy
u amount of energy needed to destabilize the bonds of a molecule
u moves the reaction over an “energy hill”
Not a match!That’s too much energy to expose
living cells to!
glucose
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Division Ave. High School Ms. FogliaAP Biology
AP Biology
Reducing Activation energy§ Catalysts
u reducing the amount of energy to start a reaction
Pheeew…that takes a lot
less energy!
reactant
product
uncatalyzed reaction
catalyzed reaction
NEW activation energy
AP Biology
Catalysts§ So what’s a cell got to do to reduce
activation energy?u get help! … chemical help…ENZYMES
DG
Call in the ENZYMES!
AP Biology
Enzymes § Biological catalysts
u proteins (& RNA)u facilitate chemical reactions
§ increase rate of reaction without being consumed§ reduce activation energy§ don’t change free energy (DG) released or required
u required for most biological reactionsu highly specific
§ thousands of different enzymes in cellsu control reactions
of life
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Division Ave. High School Ms. FogliaAP Biology
AP Biology
Enzymes vocabularysubstrate
§ reactant which binds to enzyme§ enzyme-substrate complex: temporary association
product§ end result of reaction
active site§ enzyme’s catalytic site; substrate fits into active site
substrate
enzyme
productsactive site
AP Biology
Properties of enzymes§ Reaction specific
u each enzyme works with a specific substrate § chemical fit between active site & substrate
w H bonds & ionic bonds
§ Not consumed in reactionu single enzyme molecule can catalyze
thousands or more reactions per second§ enzymes unaffected by the reaction
§ Affected by cellular conditionsu any condition that affects protein structure
§ temperature, pH, salinity
AP Biology
Naming conventions§ Enzymes named for reaction they catalyze
u sucrase breaks down sucroseu proteases break down proteinsu lipases break
down lipidsu DNA polymerase builds DNA
§ adds nucleotides to DNA strand
u pepsin breaks down proteins (polypeptides)
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Division Ave. High School Ms. FogliaAP Biology
AP Biology
Lock and Key model§ Simplistic model of
enzyme actionu substrate fits into 3-D
structure of enzyme’ active site§ H bonds between
substrate & enzymeu like “key fits into lock”
In biology…Size
doesn’t matter…Shape matters!
AP Biology
Induced fit model§ More accurate model of enzyme action
u 3-D structure of enzyme fits substrateu substrate binding cause enzyme to
change shape leading to a tighter fit § “conformational change”§ bring chemical groups in position to catalyze
reaction
AP Biology
How does it work?§ Variety of mechanisms to lower
activation energy & speed up reactionu synthesis
§ active site orients substrates in correct position for reactionw enzyme brings substrate closer together
u digestion§ active site binds substrate & puts stress on
bonds that must be broken, making it easier to separate molecules