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(HS) Biology 12 > 5.2 Enzymes and Metabolic Pathways > Flashcards

5.2 Enzymes and Metabolic Pathways Flashcards

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1
Q

What is a metabolic pathway?

A

a series of linked reactions that begin with a particular reactant and terminate with an end product

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2
Q

Some metabolic pathways are cyclical. What does cyclical mean?

A

regenerating the starting material

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3
Q

When is energy captured and used more easily?

A

if it is released in small increments rather than all at once

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4
Q

What are enzymes?

A

typically proteins that function as catalysts to speed a chemical reaction

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5
Q

What are ribozymes?

A

a form of RNA molecules that can act as catalysts

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6
Q

What do catalysts do?

A

participate in chemical reactions, but are not used by the reaction

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7
Q

What determines whether a reaction goes forward?

A

NOT THE ENZYME

the free energy of the reaction

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8
Q

What is a substrate?

A

the reactants in an enzymatic reaction for that enzyme

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9
Q

What does the presence or absence of an active enzyme determine?

A

which reaction takes place

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10
Q

How is activation achieved in the absence of an enzyme?

A

by heating a reaction flask to increase the number of effective collisions between molecules

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11
Q

What is energy of activation?

A

energy that must be added to cause molecules to react with one another

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12
Q

What needs to happen in order for a reaction to occur?

A

even though the reaction will proceed (free energy is negative), energy of activation must be overcome

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13
Q

What kind of reaction is the burning of firewood?

A

very exergonic reaction, but firewood in a pile does not spontaneously combust

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14
Q

What is required to overcome the energy of activation?

A

the input of some energy

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15
Q

What do enzymes do to energy?

A

enzymes lower the amount of energy required for activation to occur

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16
Q

What does the addition of an enzyme change?

A

NOTHING, it does not change the end result of the reaction

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17
Q

What results in a negative amount of free energy?

A

energy of the products is less than then energy of the reactants, but the reaction will not go at all unless the energy of activation is overcome

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18
Q

What happens when you lower the energy of activation?

A

enzyme increases the rate of reaction

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19
Q

Why will sugar in your kitchen breakdown into CO2 and H2O?

A

because the energy of the products is much less than the free energy of the reactant, the reaction is really slow

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20
Q

What happens when you eat the sugar?

A

enzymes in your digestive system greatly increase the speed at which the sugar is broken down, the end result is still the same

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21
Q

What is the active site?

A

one small party of the enzyme that, in most instances, complexes with the substrate

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22
Q

What happens at the active site?

A

enzyme and substrate fit together and form an enzyme-substrate complex

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23
Q

What is the induced fit model?

A

the active site undergoes a slight change in shape in order to accommodate substrates

the enzyme is induced to undergo a slight alteration to achieve optimum fit

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24
Q

Describe enzymatic action.

A
  • enzyme has an active site where the substrates and enzyme fit together in such a way that the substrates react
  • following the reaction, products are released, and the enzyme is free to act again
25
Q

What can an enzymatic reaction result in?

A
  • degradation of a substrate into multiple products (catabolism)
  • synthesis of a product from multiple substrates (anabolism)
26
Q

What does the change in shape of the active site do?

A

forms the enzyme-substrate complex, which facilitates the reaction that now occurs

27
Q

What happens after a reaction has been completed?

A
  • product is released
  • active site returns to its original state
  • ready to bind to another substrate molecule
28
Q

Why is only a small amount of enzyme actually needed in a cell?

A

because enzymes are not used by the reaction

29
Q

Give an example of an enzyme that participates in the reaction.

A

trypsin digests protein by breaking peptide bonds

  • active site of trypsin contains 3 amino acids with R groups that actually interact with members of the peptide bond: first to break the bond and then to introduce the components of water
  • this illustrates that the formation of the enzyme-substrate complex is very important in speeding up the reaction
30
Q

How are enzymes named?

A

because enzymes complex only with their substrates, they are name for their substrates with the suffix -ase

31
Q

What is the enzyme for the substrate lipid?

A

lipase

32
Q

What is the enzyme for the substrate starch?

A

amylase

33
Q

What is the enzyme for the substrate maltose?

A

maltase

34
Q

What is the enzyme for the substrate ribonucleic acid?

A

ribonuclease

35
Q

What is the enzyme for the substrate lactose?

A

lactase

36
Q

What factors affect enzymatic speed?

A
  • substrate concentration
  • temperature
  • pH
  • enzyme activation
  • enzyme inhibition
  • enzyme cofactors
37
Q

Describe how substrate concentration affects enzymatic speed.

A
  • enzyme activity increases as substrate concentration increases because there are more collisions between substrate molecules and the enzyme
  • as more substrate molecules fill active sites, more product results per unit time
  • but when the enzyme’s active sites are filled almost continuously with substrate, enzyme’s rate of activity cannot increase any more
  • maximum rate has been reached
38
Q

Describe how temperature affects enzymatic speed.

A
  • as temperature rises, enzyme activity increases because higher temperatures cause more effective collisions between enzyme and substrate
  • if temperature rises beyond a certain point, enzyme activity eventually levels out and then declines rapidly because the enzyme is denatured
39
Q

What does denatured mean?

A

describes a protein that has had an irreversible change in its shape; occurs when proteins are exposed to extremes in heat and pH

40
Q

Why does an enzyme’s shape change during denaturation?

A

due to the loss of secondary and tertiary structure, and then it can no longer bind its substrates efficiently

41
Q

Describe how pH affects enzymatic speed.

A
  • each enzyme has a preferred pH at which the rate of reaction is highest; at this pH, enzymes have their normal configurations
  • change in Ph can alter the ionization of R groups and disrupt normal interactions
  • under extreme pH conditions, denaturation eventually occurs
42
Q

What does the globular structure of an enzyme depend on?

A

interactions such as hydrogen bonding between R groups

43
Q

Describe how enzyme activation affects enzymatic speed.

A
  • not all enzymes are needed by the cell all the time
  • genes can be turned on/off to increase/decrease CONCENTRATION OF ENZYME
  • enzymes can be present in a cell in inactive form
44
Q

Describe how enzyme activation affects enzymatic speed.

How does activation occur?

A
  • covalently modified by addition or removal of phosphate group
  • kinase adds phosphates to proteins
  • enzyme called phosphatase removes them
45
Q

Describe how enzyme activation affects enzymatic speed.

How can enzymes be activated?

A
  • in some proteins, adding phosphates activates them

- by removing part of the protein or by associating with another protein or cofactor

46
Q

Describe how enzyme activation affects enzymatic speed.

How does enzyme activity in a cell often change?

A

in response to the action of messengers and hormones of a cell

47
Q

Describe feedback inhibition.

A
  • in an active pathway, first reactant is able to bind to the active site of enzyme
  • feedback inhibition occurs when the end product of the metabolic pathway binds to the first enzyme of the pathway at a site other than the active site
  • this binding causes the active site to change its shape
  • now reactant is unable to bind to the enzyme’s active site and the whole pathway shuts down
48
Q

What is enzyme inhibition?

A

occurs when substrate is unable to bind to the active site of an enzyme

49
Q

What does feedback inhibition regulate?

A

the activity of almost every enzyme in a cell

50
Q

Describe how enzyme inhibition affects enzymatic speed.

A
  • when there is plenty of product, it binds to the enzyme’s active site and then the substrate is unable to bind
  • as product is used, inhibition is reduced, more product can be produced
  • concentration of the product always kept within a certain range
51
Q

What are most metabolic pathways regulated by?

A

a more complicated type of feedback inhibition

  • end product of an active pathway binds to a site other than the active site of the first enzyme
  • binding changes the shape of the active site so that the substrate is unable to bind to the enzyme and the pathway shuts down
  • no more product is produced
52
Q

What is cyanide an inhibitor for?

A

an essential enzyme (cytochrome c oxidase) needed for cellular respiration in all cells, which accounts for its lethal effect on humans

53
Q

What is penicillin?

A

an antimicrobial agent that blocks the active site of an enzyme used to construct a molecule of the cell walls of bacteria

a poison that affects bacteria, not humans

54
Q

What do many enzymes require to function properly?

A

COFACTORS: inorganic ion (metals) or an organic nonprotein

55
Q

What are coenzymes?

A

organic, nonprotein molecules that assist the enzyme and may even accept or contribute atoms to the reactions

ie. minerals from our diet

56
Q

What are vitamins?

A

components of coenzymes

relatively small organic molecules that are required in trace amounts in our diet for synthesis of coenzymes that affect health and physical fitness

57
Q

What does vitamin become a part of?

A

coenzyme’s molecular structure

ie. vitamin niacin is part of the coenzyme NAD, riboflavin is part of the coenzyme FAD

58
Q

What does a deficiency of vitamins do?

A

results in a lack of the coenzyme and therefore a lack of certain enzymatic actions

in humans: leads to vitamin-deficiency symptoms
ie. niacin deficiency results in a skin disease called pellagra, riboflavin deficiency results in cracks at the corners of the mouth

(HS) Biology 12 (46 decks)

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