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AP Biology
AP Biology
AP Biology
Enzymes
Chapter 8.4, 8.5
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
AP Biology
Reducing Activation EnergyCatalysts
Pheeew…that takes a lot
less energy!
reactant
product
uncatalyzed reaction
catalyzed reaction
NEW activation energy
AP Biology
Catalysts§ Reduce the amount of energy to start a
reaction§ Cells use ENZYMES to reduce
activation energy
DG
Call in the ENZYMES!
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AP Biology
QUESTION 1:How do enzymes speed up chemical reactions?
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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AP Biology
Enzyme 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
“transition state”
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AP Biology
Properties of Enzymes§ Reaction specific
u each enzyme works with a specific substrate § chemical fit between active site & substrate
forming H bonds, ionic bonds§ Not consumed in reaction
u single enzyme molecule can catalyze thousands or more reactions per second§ enzymes unaffected by the reaction (reusable)
§ Affected by cellular conditionsu any condition that affects protein structure
§ temperature, pH, salinity
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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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AP Biology
QUESTION 2:Use slides 3 – 6 to give FOUR WORDS that describe enzymes.
AP Biology
Lock and Key model§ Simplistic model of enzyme action
u substrate fits into 3-D structure of enzyme’ active site§ H bonds between substrate & enzyme
u like “key fits into lock”
In biology…Size
doesn’t matter…Shape matters!
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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
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AP Biology
QUESTION 3:What is the difference between the lock and key model and the induced fit model? Which model is more accurate?
AP Biology
How do enzymes lower Ea?§ Variety of mechanisms to lower activation
energy & speed up reaction1) In synthesis, active site orients substrates
in correct position for reactionw enzyme brings substrate closer together
2) In digestion, active site puts stress on bonds that must be broken, making it easier to separate molecules
3) Providing a favorable microenvironment(ex: pH)
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AP Biology
Got any Questions?!
AP Biology 2007-008
Factors that Affect Enzymes
AP Biology
Factors Affecting Enzyme Function§ Enzyme concentration§ Substrate concentration§ Temperature § pH§ Salinity§ Activators§ Inhibitors
catalase
AP Biology
Enzyme concentration
enzyme concentration
reac
tion
rate
What’shappening here?!
QUESTION 4:IN YOUR OWN WORDS,describe what this graph is showingin a complete sentence.
AP Biology
Factors affecting enzyme function § Enzyme concentration
u as enzyme = reaction rate§ more enzymes = more frequently collide with
substrate u reaction rate levels off
§ substrate becomes limiting factor§ not all enzyme molecules can find substrate
enzyme concentration
reac
tion
rate
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AP Biology
Substrate concentration
substrate concentration
reac
tion
rate
What’shappening here?!
QUESTION 5:IN YOUR OWN WORDS,describe what this graph is showingin a complete sentence.
AP Biology
Factors affecting enzyme function
substrate concentration
reac
tion
rate
§ Substrate concentration u as substrate = reaction rate
§ more substrate = more frequently collide with enzyme
u reaction rate levels off§ all enzymes have active site engaged§ enzyme is saturated§ maximum rate of reaction
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AP Biology
37°
Temperature
temperature
reac
tion
rate
What’shappening here?!
QUESTION 6:IN YOUR OWN WORDS,describe what this graph is showingin a complete sentence.
AP Biology
Factors affecting enzyme function§ Temperature
u Optimum T°§ greatest number of molecular collisions§ human enzymes = 35°- 40°C (body temp = 37°C)
u Heat: increase beyond optimum T°§ increased energy level of molecules disrupts
bonds in enzyme & between enzyme & substratew H, ionic = weak bonds
§ denaturation = protein loses 3D shape (3° structure)u Cold: decrease below optimum T°
§ molecules move slower§ decreased collisions between enzyme & substrate
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AP Biology
Enzymes and temperature§ Different enzymes function in different
organisms in different environments
37°Ctemperature
reac
tion
rate
70°C
human enzymehot spring
bacteria enzyme
(158°F)
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AP Biology
How do ectotherms do it?
AP Biology
7
pH
pH
reac
tion
rate
20 1 3 4 5 6 8 9 10
pepsin trypsin
What’shappening here?!
11 12 13 14
pepsin
trypsin
QUESTION 7:IN YOUR OWN WORDS,describe what this graph is showingin a complete sentence.
AP Biology
Factors affecting enzyme function§ pH
u changes in pH§ adds or remove H+
§ disrupts bonds, disrupts 3D shape w disrupts attractions between charged amino acidsw affects 2° & 3° structurew denatures protein
u optimal pH?§ most human enzymes = pH 6-8
w depends on localized conditionsw pepsin (stomach) = pH 2-3w trypsin (small intestines) = pH 8
720 1 3 4 5 6 8 9 10 11
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AP Biology
Salinity
salt concentration
reac
tion
rate
What’shappening here?!
QUESTION 8:IN YOUR OWN WORDS,describe what this graph is showingin a complete sentence.
AP Biology
Factors affecting enzyme function§ Salt concentration
u changes in salinity§ adds or removes cations (+) & anions (–)§ disrupts bonds, disrupts 3D shape
w disrupts attractions between charged amino acidsw affect 2° & 3° structurew denatures protein
u enzymes intolerant of extreme salinity§ Dead Sea is called dead for a reason!
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AP Biology
QUESTION 9:What does the following words mean in everyday language?- “regulate”/”regulation”- “activate”- “inhibit”- “competitive”- “irreversible”- “feedback”
AP Biology
Compounds which help enzymes§ Activators
u cofactors§ non-protein, small inorganic
compounds & ionsw Mg, K, Ca, Zn, Fe, Cuw bound within enzyme molecule
u coenzymes§ non-protein, organic molecules
w bind temporarily or permanently toenzyme near active site
§ many vitaminsw NAD (niacin; B3)w FAD (riboflavin; B2)w Coenzyme A
Mg inchlorophyll
Fe inhemoglobin
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AP Biology
QUESTION 10:Compare and contrast cofactorsand coenzymes.
AP Biology
Compounds which regulate enzymes§ Inhibitors
u molecules that reduce enzyme activity
u competitive inhibitionu noncompetitive inhibition
(both could be irreversible)
u feedback inhibition
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AP Biology
Competitive Inhibitor § Inhibitor & substrate “compete” for active site
u penicillinblocks enzyme bacteria use to build cell walls
u disulfiram (Antabuse)treats chronic alcoholism§ blocks enzyme that
breaks down alcohol § severe hangover & vomiting
5-10 minutes after drinking§ Overcome by increasing substrate
concentrationu saturate solution with substrate
so it out-competes inhibitor for active site on enzyme
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AP Biology
Non-Competitive Inhibitor § Inhibitor binds to site other than active site
u allosteric inhibitor binds to allosteric siteu causes enzyme to change shape
§ conformational change§ active site is no longer functional binding site
w keeps enzyme inactiveu some anti-cancer drugs
inhibit enzymes involved in DNA synthesis § stop DNA production§ stop division of more cancer cells
u cyanide poisoningirreversible inhibitor of Cytochrome C, an enzyme in cellular respiration§ stops production of ATP
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AP Biology
QUESTION 11:What is the difference between a competitive inhibitor and a non-competitive (allosteric) inhibitor?
AP Biology
Irreversible Inhibition§ Inhibitor (either competitive or
noncompetitive) permanently binds to enzymeu competitor
§ permanently binds to active siteu allosteric (non-competitor)
§ permanently binds to allosteric site§ permanently changes shape of enzyme§ nerve gas, sarin, many insecticides
(malathion, parathion…)w cholinesterase inhibitors - doesn’t breakdown
the neurotransmitter, acetylcholine
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AP Biology
Allosteric regulation§ Conformational changes by regulatory
molecules u inhibitors
§ keeps enzyme in inactive formu activators
§ keeps enzyme in active form
Conformational changes Allosteric regulation
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AP Biology
Metabolic pathways
A ® B ® C ® D ® E ® F ® Genzyme
1
®enzyme
2® enzyme
3
®
enzyme4
® enzyme5
® enzyme6
®
§ Chemical reactions of life are organized in pathwaysu divide chemical reaction
into many small steps§ artifact of evolution§ efficiency
w intermediate branching points § control = regulation
A ® B ® C ® D ® E ® F ® Genzyme
®
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AP Biology
Efficiency§ Organized groups of enzymes
u enzymes are embedded in membrane and arranged sequentially
§ Link endergonic & exergonic reactionsWhoa!
All that going onin those littlemitochondria!
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AP Biology allosteric inhibitor of enzyme 1
Feedback Inhibition§ Regulation & coordination of production
u product is used by next step in pathwayu final product is inhibitor of earlier step
§ allosteric inhibitor of earlier enzyme§ feedback inhibition
u no unnecessary accumulation of product
A ® B ® C ® D ® E ® F ® Genzyme
1
® enzyme2
® enzyme3
® enzyme4
® enzyme5
® enzyme6
®X
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AP Biology
Feedback inhibition§ Example
u synthesis of amino acid, isoleucine from amino acid, threonine
u isoleucine becomes the allosteric inhibitor of the first step in the pathway§ as product
accumulates it collides with enzyme more often than substrate does
threonine
isoleucine
AP Biology
Don’t be inhibited!Ask Questions!
QUESTION 12:Write down questions, vocabulary,or concepts that you are unclear about. Be prepared to share with me (Ms. Lin)so that we can go over it as a class!
Ask now or forever hold your peace!!!!!!!!!
AP Biology
Cooperativity § Substrate acts as an activator
u substrate causes conformational change in enzyme§ induced fit
u favors binding of substrate at 2nd siteu makes enzyme more active & effective
§ hemoglobin
Hemoglobin§ 4 polypeptide chains§ can bind 4 O2;§ 1st O2 binds § now easier for other
3 O2 to bind