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Limiting factors. Factors affecting the rate of reactions. EFFECT OF SUBSTRATE CONC. ON REACTIONS. Substrate concentration. Enzyme limiting. More substrate  more chance of a collision between substrate and enzyme ↑substrate  ↑number of reactions. Product formation.

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limiting factors

Limiting factors

Factors affecting the rate of reactions

substrate concentration

EFFECT OF SUBSTRATE CONC. ON REACTIONS

Substrate concentration

Enzyme limiting

More substrate  more chance of a collision between substrate and enzyme

↑substrate  ↑number of reactions

Product formation

Substrate conc. limiting

enzyme 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

enzyme concentration1

EFFECT OF ENZYME CONC. ON REACTIONS

Enzyme concentration

Reaction rate levels off or stops.

eg substrate runs out

Rate of reaction

Reaction rate increases rapidly.

Enzyme conc. is limiting

enzyme cofactors
Enzyme cofactors
  • May be
    • Organic co-enzymes, usually vitamins egvit B
    • Activating ions eg Na+, K+, Ca2+, Mg2+
  • 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.
cofactor concentration

EFFECT OF COFACTOR CONC. ON REACTIONS

Cofactor concentration

Rate of reaction levels off.

Not enough enzyme for the co-factors to attach to – enzymes are limiting

Rate of reaction

Rate of reaction increases rapidly.

Cofactor conc. is limiting

inhibitors
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

inhibitor concentration

EFFECT OF INHIBITOR CONC. ON REACTIONS

Inhibitor concentration

Rate of reaction decreases rapidly.

Rate of reaction

temperature
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  enzyme can’t function

temperature1

EFFECT OF TEMPERATURE ON REACTIONS

Temperature

Low temp. limits the rate of reaction, up to an optimal temp.

Optimum

↑ temp  ↑ energy  ↑ reaction rate

Denaturation

– irreversible shape change

- can’t function

Rate of reaction

3 dimensional enzyme structure
3-dimensional enzyme structure

Globular proteins with a very specific shape

Change shape  active site changes

  • Cannot bind substrate
  • Enzyme cannot function
slide12

Each enzyme has its own optimal pH

At pHs above or below this optimum, enzyme denatures

pH

Rate of reaction

PEPSIN

AMYLASE

TRYPSIN

pH 2 pH7 pH9

EFFECT OF pH ON ENZYME ACTIVITY

slide13
MENU

Quick Quiz

Key Words

Videos

MCQ

Exercises

key words
Key words

Back to menu

  • Limiting
  • Reaction rate
  • Optimal
  • Substrate conc.
  • Enzyme conc.
  • Co-factor
  • Co-enzyme
  • Activating ion
  • Competitive inhibitor
  • Non-competitive inhibitor
  • Temperature
  • Denaturation
  • pH
quick quiz
Quick quiz

Back to menu

  • ____ factors prevent reaction occurring at optimal rate
  • As substrate conc. increases, the chance of a ____ between substrate and enzyme increases
  • As enzyme increases, reaction rate increases until another factor becomes ____
  • Enzyme ____ include co-enzymes and ions
  • ____, such as poisons, decrease reaction rates
  • 35-37oc is the ____ range of temp.s for most enzymes
  • Enzymes become ____ at high temperatures
  • Different enzymes have different ____ pH ranges
  • Vitamins often act as ____
  • Low temperatures denature enzymes – True / False?

Answers

quick quiz1
Quick quiz

Back to menu

  • Limitingfactors prevent reaction occurring at optimal rate
  • As substrate conc. increases, the chance of a collision between substrate and enzyme increases
  • As enzyme concentration increases, reaction rate increases until another factor becomes limiting
  • Enzyme co-factors include co-enzymes and ions
  • Inhibitors, such as poisons, decrease reaction rates
  • 35-37oc is the optimalrange of temp.s for most enzymes
  • Enzymes become denatured at high temperatures
  • Different enzymes have different optimal pH ranges
  • Vitamins often act as co-enzymes
  • Low temperatures denature enzymes – True / False?
exercise
Exercise

Back to menu

  • Workbook pp50-52, qq18-20 and 22-23
  • Booklet p3
  • READING
  • Pathfinder p48 (or p42) Enzymes & reaction rate
  • Excellence in Biology pp114-6
videos
Videos
  • http://www.youtube.com/watch?v=E90D4BmaVJM&feature=related (10 min, includes biotechnology)

http://www.youtube.com/watch?v=2DRWqBld7XU&feature=related (feedback inhibition, 1 min)

http://www.youtube.com/watch?v=PILzvT3spCQ&feature=related (1 min)

question 1
Question 1

34

Increasing substrate conc. increases rate of reaction because...

(a)the activation energy decreases

(b)the enzymes act as catalysts

(c)there is more chance of a collision with enzymes

(d)the enzymes are proteins

question 2

35

Question 2

Increasing enzyme conc. increases the reaction rate because....

(a)enzymes form an enzyme-substrate complex

(b)reactions are exergonic

(c)there is more chance of a collision with substrate

(d)enzymes are specific

question 3

37

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

question 4

38

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

question 5
Question 5

39

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

question 6

40

Question 6

Inhibitors

(a) combine with different substrates

(b) form different kinds of end-product

(c) function at temperatures above 90oC

(d)may be competitive or non-competitive

question 7

41

Question 7

Inhibitors can include

(a)co-enzymes

(b) poisons

(c) co-factors

(d) activating ions

question 8
Question 8

42

After being exposed to a high temperature an enzyme cannot function because.....

(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
ANSWER

43

Back to menu

Correct

click arrow to return

answer1

44

ANSWER

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IncorrectX

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