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Spring 2013 / Biochemistry > Lecture 8 - Enzymes > Flashcards

Lecture 8 - Enzymes Flashcards

1
Q

what are the 3 basic ways that ENZYMES work on biological molecules?

A
  1. building larger molecules (anabolism)
  2. breaking down larger molecules (catabolism)
  3. rearranging atoms and molecules within the molecule being acted upon - enantiomers and chiral formations
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2
Q

what are the 2 ways that enzymes CATALYZE biological reactions?

A

specificity

reaction rate

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3
Q

catalysts work to?

A

lower the activation energy of chemical reactions

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4
Q

by reducing the activation energy of biological reactions, what is greatly accelerated?

A

reaction rate

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5
Q

T/F

without enzymes, most reaction rates would be at or near zero (reactions per sec), and life systems would not function.

A

True

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6
Q

how fast is the enzymatic reaction rate?

A

between 1x 10 (to 6th power) and 1x10 (9th power)

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7
Q

what is specificity?

A

the ability of enzymes to work on or select the exact molecules or atoms they are designed for

[there are thousands of compounds within a cell, and each type of enzyme will only act upon its designated substrate)

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8
Q

what is a substrate?

A

the generic name for molecule that will be worked on by an enzyme
[ex. starch is the substrate of amylase enzymes - amylases break down starches]

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9
Q

when drugs and herbs “fool” the specificity of enzymes, what happens?

A

causes competitive inhibition of active site

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10
Q

is there a POS or NEG consequences in artificially interfering with the active site and specificity of an enzyme?

A

both pos and neg consequences

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11
Q

enzymes are made of proteins, but also incorporates what? to do what?

A 
cofactors of many sorts, such as coenzymes, vitamins, porphyrins and mineral ions to facilitate their functioning
and rRNA (ribosomes) is also another factor which cooperates with enzymes
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12
Q

mostly enzymes are shaped?

A

globular shape
their tertiary structure includes at least one active site, where molecules fit and are transformed through biochemical reactions
also found are huge quaternary structures, with concatenated tertiary subunit proteins

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13
Q

enzymes and use of ATP?

A
  • some enzymes use ATP to facilitate the breaking and fusing of bonds in affected substrates
  • other enzymes, because they rearrange molecules in orientation, will catalyze a change without using ATP
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14
Q

what are the external factors that affect enzyme activity?

A
  • presence or absence of substrates
  • pH changes or other ionic factors
  • temp range
  • availability of nutrients: ATP, cofactors, coenzymes, and ions
  • the functionality of enzyme - is it damaged and not yet replaced?
  • molecules may be present causing competitive inhibition of the active site - drugs, herbs, toxins, organisms
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15
Q

enzymes are typically classified by?

A

the chemical nature of the reactions they catalyze

“-ase” always indicates an enzyme

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16
Q

oxidoreductases

A

remove molecules or atoms from substrates

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17
Q

transferases

A

transfer functional groups from one molecule to another, such as moving phosphate group

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18
Q

hydrolases

A

add water to substrates

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19
Q

lyases

A

work with double bonds

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20
Q

isomerases

A

change the isomeric status of molecule

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21
Q

ligases

A

join or release carbon bonds and requires ATP

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22
Q

enzymes are also named for what?

A

the substrate upon which they work

ex. urease works upon urea molecule

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23
Q

what term is commonly used to signify that a number of enzymes work on substrates in a specific order - an orderly chain of events facilitated by different enzymes?

A

enzyme cascade

ex: glycolysis is a typical enzyme cascade

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24
Q

what is a non-protein molecule that has either a tight or loose affinity to an enzyme and is required for enzymatic action?

A

cofactors

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25
Q

when an enzyme does not have its cofactors present, it is called?

A

apoenzyme and is NOT functional

26
Q

an enzyme with cofactors and fully functioning is a ?

A

holoenzyme

27
Q

what are 2 types of cofactors?

A

prosthetic group

coenzymes

28
Q

what are common prosthetic group?

A

porphyrin group
vitamins
metallic ions

29
Q

which group is often the limiting factor in nutrition and energy? and why?

A

the prosthetic group (includes porphyrin, vitamins, metallic ions)

bc def in vitamins and minerals slows the overal metabolism in the organism bc the cellular enzymes revert back to apoenzyme status

30
Q

magnesium ions and postassium ions belong to which group?

A

vitamin prosthetic group

31
Q

what are called cosubstrates bc they act to donate a part of themselves like a substrate to a reaction happening in an active site?

A

coenzymes

they are rapidly consumed, renewed and reused

32
Q

what are coenzymes used repeatedly in production of ATP in the mitochondrion?

A

NAD/NADH (nicotinamide adenine dinucleotide

ACA (acetyl coenzyme A)

33
Q

what are other important coenzymes?

A

ATP, lipoamine, FAD/FADH, Ubiquinone (coenzyme Q 10) and S-adenyl methionine (Sam-e)

34
Q

what does coenzymes do?

A

ATP splits off a high energy-binded phosphate group in the active sites of enzymes to propel the reaction

35
Q

enzyme production is regulated by?

A

gene expression

36
Q

genes coding for enzymes are either _____ or ____ by gene expression factors?

A

induced or inhibited

37
Q

some enzymes are regulated by inhibitor or activator molecules that tell an enzyme to operate or not.
for instance, if the product produced bu the enzyme reaches a plateau concentration, this turns off the enzyme - this is called?

A

negative feedback loop
or
allosteric inhibition

38
Q

enzymes can be modified by addition or subtraction of functional groups to make the enzyme active or not - for example ______ of enzyme will turn turn on the breakdown of glycogen

A

phosphorylation

39
Q

what can activate or deactivate an enzyme?

A

placing the enzyme in a changed environment, as in pH change

40
Q

a pre-active enzyme is called?

A

zymogen or proenzyme

41
Q

which enzyme reduces glutathione disulfide (GSSG) to sulfhydryl form - reduced glutathione (GSH), which is the most IMPORTANT CELLULAR ANTIOXIDANT?

this process is especially important in?

A

glutathione reductase (GSR)

esp. important in red blood cells, where lack of NADPH and GSH will allow oxidants to damage and lyse the cells, leading to anemia if widespread enoguh

42
Q

our cells rely on oxygen as the final acceptor of electrons in cellular respiration, allowing us to extract far more energy from food than would be possible without it.
But when is oxygen dangerous? why?

A

in reactive forms such as SUPEROXIDE (oxygen with extra electron)

it leaks from mitochondrial respiration enzymes and wreak havoc on a cell. it can cause mutations in DNA or attack enzymes that make essential molecules.

43
Q

to combat the potential dangers of electrons creating superoxide instead of normal oxygen, what does most cell make?

A

superoxide dismutases - SOD - an enzyme that detoxifies superoxide

44
Q

SOD dismutes superoxide, what is dismutation?

A

a special type of reaction, where 2 equal but opposite reactions occur on 2 separate molecules.

[SOD takes 2 molecules of superoxide, stripes the extra electron off of one, and places it on the other.
the 1st oxygen ends up forming normal oxygen, the other has an extra electron.
the one with extra electron rapidly picks up dihydrogen oxide (H2O) to from hydrogen peroxide.
Hydrogen peroxide is toxic, so cell must use enzyme CATALASE to destroy it.]

45
Q

what is the fastest enzyme discovered? and what can it do?

A

catalase

a single catalase enzyme can convert hydrogen peroxide to water and O2 by the millions per secon

46
Q

what is a common, large and diverse group of hemoprotein enzymes (proteins containing an iron porphyrin ring) found in many types of life forms, mostly in eukaryotes?

A

cytochrone P450

47
Q

what are the 2 common functions of cytochrome P450?

A

to oxygenate substrates and to pass electrons in aerobic respiration

48
Q

why are cytochrome P450 unusual as enzymes?

A

bc they can catalyze a plethora of substrates, and so are nonspecific

49
Q

where can you find Cytochrone P450?

A

in all mitochondria, as part of the electron transport chain of oxidative phosphorylation
And in lumen of endoplasmic reticulum in cells, performing many detoxification functions

50
Q

cytochrome c

A

one of 57 human cytochromes

part of Electron Transport Chain in Oxidative Phosphorylation

51
Q

cytochromes are membrane-associated proteins, located where?

A

either in the inner membrane (cristae) of mitochondria or in the endoplasmic reticulum of cells

52
Q

what do cytochromes do?

A

metabolize thousands of endogenous and exogenous compounds.
many can catalyze multiple reactions, which accounts for their central importance in metabolizing an extremely large # of molecules

53
Q

cytochrome P450 enzymes are present all tissues of the body, and play important roles in?

A

hormone synthesis and breakdown (including estrogen and testosterone synthesis and metabolism)
cholesterol synthesis, and vitamin D metabolism
[detox fx of LIVER is due to P450’s]

54
Q

Liver does what?

A

detoxifies or metabolizes drugs and toxic compounds, all food, as well as metabolic products such as bilirubin (a breakdown product of hemoglobin)

55
Q

many drug side effects have to do with what?

A

the overuse or inhibition of the cytochrome detoxification potential in liver hepatocytes

[all substances, including drugs are processed and eventually excreted from the body if not used for fuel or structure, and cytochromes are the major enzymes involved in drug metabolism and drug bioactivation, accounting for 75% of total drug metabolism]

56
Q

why is taking 2 or more medication potentially problematic?

A

the flood of drugs that affect cytochromes can either cause reduced dosage of medications from too rapid metabolism - Induction, or slow the breakdown of drugs, possibly causing an overdose - inhibition

57
Q

Glutathione reductase is an enzyme that does all but;
A. Recycles oxidized glutathione
B. converts GSSG to GSH
C. Removes sulfur from glutathione
D. Helps maintain proper levels of cellular antioxidant potential

A

C. Glutathione does not remove sulfur from glutathione.

58
Q

Glutathione reductase is an enzyme that does all but:

(a) recycles oxidized glutathione
(b) converts GSSG to GSH
(c) removes sulfur from glutathione
(d) helps maintain proper levels of cellular antioxidant potential

A

(c) removes sulfur from glutathione

59
Q

Some enzyomes do not use ATP to perform their functions:

(a) they use AMP instead
(b) these easily change the chirality or enantiomeric state of a molecule
(c) the cytoskeleton moves the enzyme into action
(d) these enzymes are called ribozymes

A

(b) these easily change the chirality or enantiomeric state of a molecule

60
Q

Which role does a coenzyme play in catalysis?

(a) it rearranges the active site so new substrates can enter
(b) it is a secondary enzyme that adds functionality to the primary enzyme
(c) it donates part of its structure to the molecule in the active site
(d) it recycles substrate

A

(c) it donates part of its structure to the molecule in the active site

Spring 2013 / Biochemistry (13 decks)

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