CHAPTER 3: ENZYMES

Question 1

what are biochemical pathways

Answer 1

• biochemical reactions: chemical reactions that occur in living things
• a biochemical pathway is a series of interconnected biochemical reactions
  
  • eg. cellular respiration and photosynthesis
  • each step requires a specific enzyme
  • the product formed by one step of the pathway becomes the reactant for the next step of the pathway and so on

Question 2

why are enzymes needed in living things

Answer 2

• catalyze reactions like growth, repair, cellular respiration, photosynthesis, reproduction, digestion, breathing
• enzymes increasing the rate of chemical reactions (which would otherwise occur too slowly to sustain life)

Question 3

what are enzymes

Answer 3

• are proteins made of 1 or more polypeptides
• speed up chemical reactions - are catalysts
• substrate specific
• have an active site
• works best in certain conditions
• are not used up in the reaction
• the shape (3d structure) is crucial

Question 4

types of reactions

Answer 4

• catabolic reactions: occurs when a large substrate is broken down into smaller products
  
  • energy is released → cellular respiration
• anabolic reactions: occurs when smaller substrates are joined to form a larger product
  
  • energy is used → photosynthesis

Question 5

how do enzymes speed up chemical reactions

Answer 5

• enzymes allow chemical reactions to occur at a greater rate by lowering the activation energy of the reactions
• enzymes bring molecules close together in the correct orientation and bend the substrate to allow bonds to break or form easily
• as activation energy is lower when the enzyme is used, more substrate molecules and enzymes will have sufficient energy to react when they collide
• They DO NOT change the direction of the reaction nor do thy change the amount of product produced

Question 6

what is activation energy

Answer 6

the minimum amount of energy required to initiate a chemical reaction

Question 7

induced fit model vs lock and key model
draw a diagram too

Answer 7

• induced fit model:
  
  • the shape of the active site is not rigid and can adjust to the shape of its substrate
• lock and key model
  
  • substrate and enzyme fit together rigidly and tightly
  • the substrate exactly fits into the enzyme

Question 8

what is a coenzyme

Answer 8

• they are organic, non-protein molecules that bind loosely with an enzyme at its active site, assisting the catalytic function of the enzyme
• bound to their enzyme only when the enzyme is acting on a substrate to alter the rate of reaction
• they act with an enzyme to alter the rate of a reaction and can
  
  • bind to the active site to help the substrate fit
  • cycle energy protons, hydrogen, and electrons around the cell
  • act as shuttles → transfers atoms and energy
• exists in two inter-convertible forms
  
  • high energy form that is loaded w/ a group that can be transferred
  • a lower energy form that is unloaded

Question 9

role of ATP

Answer 9

• energy-rich and its major role is to transfer energy within cells
• this energy is made available when the last phosphate group of ATP is removed to form ADP
• transfers both energy and donates a phosphate group to substrates

Question 10

role of NADP+

Answer 10

acts as hydrogen donors and in the transfer of energy in photosynthesis

Question 11

role of FAD

Answer 11

• the unloaded form acts as a hydrogen and electron acceptor (FAD)
• the loaded form acts as a hydrogen and electron donor (FADH2)

Question 12

role of NAD+

Answer 12

• unloaded NAD+ is a receiver/acceptor of electrons and hydrogen ions from substrates
• loaded NADH transfer their hydrogens and electrons in the last stages of cellular respiration
  
  • catalyses reactions in which substrate is reduced and needs to gain hydrogen ions and electrons
  • when NADH unloads its electrons the energy released is transferred via a number of steps and is used to produce ATP

Question 13

factors affecting enzyme activity

Answer 13

• temperature
• pH
• concentration of enzyme
• concentration of substrate
• competitive and non-competitive enzyme inhibitors

Question 14

factor: temperature

Answer 14

• at low temps, there is less movement of substrate and enzyme
  
  • less chance of molecules colliding
  • lower reaction rate
• as temperature increases, the kinetic energy of the enzymes and substrate increase
  
  • more likely to collide and reactions are more likely to occur (as there is more movement)
• above the optimum temp, the kinetic energy becomes too high
  
  • bonds that hold the shape of the enzyme begin to break
  • the enzyme starts to change shape, causing the active site to be disrupted and enzyme activity quickly starts to drop
  • the change in the shape of the active site of the enzyme is called denaturation
  • it is irreversible

Question 15

factor: pH

Answer 15

• if surrounding pH is too high or low from the optimal ph level, it can alter intra- and inter-molecular bonds of the active site and substrate complex
  
  • changes the shape of the active site
  • reduces or stops the function
• when the ph is above or below the optimum range for enzyme, groups between the active site of enzyme and the substrate are no longer able to form a bond, causing enzyme activity to decline and eventually stop

Question 16

factor: enzyme concentration

Answer 16

a higher concentration of enzyme will result in a higher rate of reaction, provided there is unlimited substrate

Question 17

factor: substrate concentration

Answer 17

• a higher substrate concentration will result in a higher reaction rate, provided there is unlimited enzyme - to a point
• after, adding substrate causes no significant change
• with a finite amount of enzyme, the rate will increase until all the enzymes are working at their maximum rate
  
  • then the rate of reaction will plateau

Question 18

inhibitors

Answer 18

• chemicals can also inhibit enzyme activity (called inhibitors)
• they can be irreversible or reversible
• of the reversible inhibitors, they can be competitive or non-competitive
  
  • reversible inhibitors bind noncovalently (weakly)
  • irreversible inhibitors bind covalently (strongly)

Question 19

competitive inhibition

Answer 19

• the inhibitor has a similar shape to the substrate
  
  • blocks the formation of the enzyme-substrate complex
  • fewer substrates can bind to the enzyme
  • rate of reaction decreases
• effects of competitive inhibitors reduces as substrate concentration increases

Question 20

non-competitive inhibition

Answer 20

• the inhibitor binds to a region other than the active site → allosteric site
• this changes the shape of the active site so the substrate has difficulties binding

Question 21

irreversible inhibitors

Answer 21

• specific molecules can form a strong covalent bond with an enzyme at its active site
  
  • the normal substrate is permanently blocked from accessing the active site
  • are often poisons
• eg. cyanide acts as an enzyme inhibitor for cellular respiration
• penicillin acts as an enzyme inhibitor in bacteria

Question 22

limiting factor

Answer 22

A factor is referred to as limiting, if, in short supply, it restricts the rate of reaction

Question 23

what are cofactors

Answer 23

inorganic substances that are required for, or increase the rate of, catalysis