2.4 enzymes

Question 1

what is an enzyme

Answer 1

• biological catalysts
• globular proteins with complex tertiary structures
• sometimes may be quaternary structures
• control metabolic pathways

Question 2

role of enzymes

Answer 2

• anabolic reactions - build up molecules together
• catabolic reactions - breaking molecules down
• speed up reactions (catalysts, reduce the activation energy)

Question 3

mechanism of enzymes

Answer 3

• have an active site that is complementary to a specific substrate
• an enzyme is a protein - usually tertiary structure sometimes a protein with a quaternary structure
• enzyme specificity - complementary naturebetween theshapeof theactive siteon the enzyme and itssubstrate
• enzymes can be extracellular or intracellular

Question 4

extrecellular enzymes

Answer 4

• have an active site that is complementary to a specific substrate
• an enzyme is a protein - usually tertiary structure sometimes a protein with a quaternary structure
• enzyme specificity - complementary naturebetween theshapeof theactive siteon the enzyme and itssubstrate
• enzymes can be extracellular or intracellular

Question 5

intercellular enzymes

Answer 5

enzymes that act within cells eg catalase (breaks down hydrogen peroxide), DNA polymerase

Question 6

lock and key hypothesis

Answer 6

• active site is an area within the tertiary structure of the enzyme which is complementary to the shape of a specific substrate molecule
• substarte held in such a way by enzyme that the right atom-groups are close enough to react, R-group within the actiev site of the enzyme also interact with the substrate forming temporary bonds putting strain on bonds within substrate also helping the reaction along

Question 7

induced fit hypothesis

Answer 7

• enzyme changes shape slightly - conformational changes
• initial interactions between the enzymes and substrate is relatively weak but these weak interaction rapidly induces changes in the substrate molecules - weakens particular bonds in substrate therefore lowering activation energy for reaction

Question 8

factors affecting enzymes

Answer 8

• temperature
• pH
• substrate concentration
• enzyme concentration

Question 9

how does temperature affect eznymes

Answer 9

• increase in temp means substrates and enzymes get more kinetic energy so more collisions between enzymes and substrate therefore higher frequency of successful collisions so increase in reaction
• As temp increases vibrations increase until bonds strain and break result in a change in the precise tertiary structure of the protein - denaturing
• denaturing - changed active shape so substrate no long can fit and enzyme can no longer function
• optimum temperature is the temp when enzymes have the highest rate of reactivity
• once enzymes denatured above optimum temperature decrease in rate of reaction is rapid
• when temp below optimum enzymes don’t denature, they are just less active

Question 10

what is the temperature coefficient

Answer 10

Temperature coefficient = (rate of reaction at (x+ 10) °C) ÷ (rate of reaction atx°C)
Temperature coefficient Q10 is a measure of how much the rate of a reaction increase with a 10C rise in temperature, usually take as 2 so rate of reaction doubles with a 10C temp increase

Question 11

how have organisms adapted for extreme tmperatures

Answer 11

living organisms have evolved to cope with extreme temperatures eg in cold temperatures enzymes have more flexible structure making them less stable as smaller temperature changes will denature them, hot temperatures have increased number of bonds - H bonds and sulfur bridges in tertiary structure - more resistant to temperature rises

Question 12

how does pH affect enzymes

Answer 12

• Hydrogen bonds and ionic bonds between amino acid R-groups hold proteins in their precise three-dimensional shape
• change in pH refers to change in H+ ion concentration
• more H+ ions present in low pH(acid), less H+ ions in high pH(alkaline, more3 OH-)
• active site only in right shape at certain H+ concentration - optimum pH
• when pH changes form optimum structure of enzyme and therefore active site is altered
• HOWEVER if pH returns back to normal the enzymes will resume its normal shape and catalyse again - renaturation
• when pH change is more significant shape is irreversible and active site no longer complementary - denatured
• more H+ ions present the less R-groups are able to interact with each other - leads to breaking bonds and shape of enzyme changing, reverse true when less H+ ions
• enzymes only work within a narrow pH ranges