Transcript Limiting factors Factors affecting the rate of reactions EFFECT OF SUBSTRATE CONC.
Limiting factors
Factors affecting the rate of reactions
EFFECT OF SUBSTRATE CONC. ON REACTIONS Enzyme limiting More substrate a collision between substrate and enzyme more chance of ↑ substrate ↑ number of reactions Substrate conc. limiting Substrate concentration
Enzyme concentration
More enzyme more chance of a collision ↑ Reaction rate Enzyme activity will not increase If enzymes are limiting, reaction rate will drop off, but enzymes are re-usable, so the reaction will continue
EFFECT OF ENZYME CONC. ON REACTIONS Reaction rate levels off or stops.
eg substrate runs out Reaction rate increases rapidly.
Enzyme conc. is limiting Enzyme concentration
Enzyme cofactors
• May be – Organic co-enzymes, usually vitamins eg vit B – Activating ions eg Na
+ , K + , Ca 2+ , Mg 2+
• complete or alter the enzyme active site • increase enzyme activity (enzyme molecules work
more effectively)
• Without the cofactors the enzyme will not work,
or will work too slowly.
EFFECT OF COFACTOR CONC. ON REACTIONS Rate of reaction levels off.
Not enough enzyme for the co factors to attach to – enzymes are limiting Rate of reaction increases rapidly.
Cofactor conc. is limiting Cofactor concentration
Inhibitors
Competitive inhibitors
bind to the enzyme active site, so substrate cannot bind (eg the product of a reaction may bind, preventing too much product being formed)
Non-competitive inhibitors
(allosteric) usually bind somewhere other than the active site, denaturing the enzyme permanently (eg many poisons, such as heavy metal ions, act this way) Reactions stops or occurs at a very low rate
EFFECT OF INHIBITOR CONC. ON REACTIONS Rate of reaction decreases rapidly.
Inhibitor concentration
Temperature
At low temperatures enzymes and substrates have less energy, so they move less and collide less often. However, at temperatures a little over the optimal temperature the enzymes become denatured and reaction comes to a stop.
Denaturation = change in protein shape function enzyme can’t
EFFECT OF TEMPERATURE ON REACTIONS Low temp. limits the rate of reaction, up to an optimal temp.
Optimum
↑ temp ↑ energy ↑ reaction rate Denaturation – irreversible shape change can’t function Temperature
3-dimensional enzyme structure
Globular proteins with a very specific shape Change shape active site changes Cannot bind substrate Enzyme cannot function
Each enzyme has its own optimal pH At pHs above or below this optimum, enzyme denatures PEPSIN AMYLASE TRYPSIN pH 2 pH7 pH9 pH EFFECT OF pH ON ENZYME ACTIVITY
MENU
Key words
• Limiting • Reaction rate • Optimal • Substrate conc.
• Enzyme conc.
• Co-factor • Co-enzyme • Activating ion • Competitive inhibitor • Non-competitive inhibitor • Temperature • Denaturation • pH
Quick quiz
1. ____ factors prevent reaction occurring at optimal rate 2. As substrate conc. increases, the chance of a ____ between substrate and enzyme increases 3. As enzyme increases, reaction rate increases until another factor becomes ____ 4. Enzyme ____ include co-enzymes and ions 5. ____, such as poisons, decrease reaction rates 6. 35-37 o c is the ____ range of temp.s for most enzymes 7. Enzymes become ____ at high temperatures Answers 8. Different enzymes have different ____ pH ranges 9. Vitamins often act as ____ 10. Low temperatures denature enzymes – True / False?
Quick quiz
1. Limiting
factors prevent reaction occurring at optimal rate 2. As substrate conc. increases, the chance of a
collision
between substrate and enzyme increases 3. As enzyme concentration increases, reaction rate increases until another factor becomes
limiting
4. Enzyme
co-factors
include co-enzymes and ions
5. Inhibitors
, such as poisons, decrease reaction rates 6. 35-37 o c is the
optimal
range of temp.s for most enzymes 7. Enzymes become
denatured
at high temperatures 8. Different enzymes have different
optimal
pH ranges 9. Vitamins often act as
co-enzymes
10. Low temperatures denature enzymes – True /
False
?
Exercise
• Workbook pp50-52, qq18-20 and 22-23 • Booklet p3
READING
• Pathfinder p48 (or p42) Enzymes & reaction rate • Excellence in Biology pp114-6
Competitive and non competitive inhibitors
Videos
• http://www.youtube.com/watch?v=E90D4BmaVJ M&feature=related (10 min, includes biotechnology) http://www.youtube.com/watch?v=2DRWqBld7XU&fe ature=related (feedback inhibition, 1 min) http://www.youtube.com/watch?v=PILzvT3spCQ&fea ture=related (1 min)
Question 1
Increasing substrate conc. increases rate of reaction because...
(a)
the activation energy decreases
(b) (c) (d)
the enzymes act as catalysts there is more chance of a collision with enzymes √ the enzymes are proteins 34
35
Question 2
Increasing enzyme conc. increases the reaction rate because.... (a) enzymes form an enzyme-substrate complex (b) reactions are exergonic
(c)
(d) enzymes are specific
Question 3
At very high substrate concentrations, the increase in reaction rate levels off because... (a) enzymes become limiting √ (b) the substrate precipitates out (c) the enzymes become denatured (d) a combination of these 37
Question 4
Co-factors (a) lower reaction rates (b) inhibit the action of enymes (c) slow down a reaction (d) include co-enzymes and activating ions √ 38
Question 5
Co-factors
(a)
complete or alter the active site of the enzyme √ (b) are always organic molecules (c) are a type of enzyme (d) can be any chemical substance in a cell 39
Question 6
Inhibitors (a) combine with different substrates (b) form different kinds of end-product (c) function at temperatures above 90 o C (d) may be competitive or non-competitive √ 40
Question 7
Inhibitors can include (a) co-enzymes (b) poisons (c) co-factors (d) activating ions √ 41
Question 8
After being exposed to a high temperature an enzyme cannot function because.....
42 (a) it has been broken down (b) its shape has been changed √ (c) its composition has been changed (d) it cannot separate from its substrate
ANSWER
Correct √
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ANSWER
44
Incorrect
X
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