Lecture 8 - Enzymes Flashcards
what are the 3 basic ways that ENZYMES work on biological molecules?
- building larger molecules (anabolism)
- breaking down larger molecules (catabolism)
- rearranging atoms and molecules within the molecule being acted upon - enantiomers and chiral formations
what are the 2 ways that enzymes CATALYZE biological reactions?
specificity
reaction rate
catalysts work to?
lower the activation energy of chemical reactions
by reducing the activation energy of biological reactions, what is greatly accelerated?
reaction rate
T/F
without enzymes, most reaction rates would be at or near zero (reactions per sec), and life systems would not function.
True
how fast is the enzymatic reaction rate?
between 1x 10 (to 6th power) and 1x10 (9th power)
what is specificity?
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)
what is a substrate?
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]
when drugs and herbs “fool” the specificity of enzymes, what happens?
causes competitive inhibition of active site
is there a POS or NEG consequences in artificially interfering with the active site and specificity of an enzyme?
both pos and neg consequences
enzymes are made of proteins, but also incorporates what? to do what?
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
mostly enzymes are shaped?
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
enzymes and use of ATP?
- 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
what are the external factors that affect enzyme activity?
- 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
enzymes are typically classified by?
the chemical nature of the reactions they catalyze
“-ase” always indicates an enzyme
oxidoreductases
remove molecules or atoms from substrates
transferases
transfer functional groups from one molecule to another, such as moving phosphate group
hydrolases
add water to substrates
lyases
work with double bonds
isomerases
change the isomeric status of molecule
ligases
join or release carbon bonds and requires ATP
enzymes are also named for what?
the substrate upon which they work
ex. urease works upon urea molecule
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?
enzyme cascade
ex: glycolysis is a typical enzyme cascade
what is a non-protein molecule that has either a tight or loose affinity to an enzyme and is required for enzymatic action?
cofactors
when an enzyme does not have its cofactors present, it is called?
apoenzyme and is NOT functional
an enzyme with cofactors and fully functioning is a ?
holoenzyme
what are 2 types of cofactors?
prosthetic group
coenzymes
what are common prosthetic group?
porphyrin group
vitamins
metallic ions
which group is often the limiting factor in nutrition and energy? and why?
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
magnesium ions and postassium ions belong to which group?
vitamin prosthetic group
what are called cosubstrates bc they act to donate a part of themselves like a substrate to a reaction happening in an active site?
coenzymes
they are rapidly consumed, renewed and reused
what are coenzymes used repeatedly in production of ATP in the mitochondrion?
NAD/NADH (nicotinamide adenine dinucleotide
ACA (acetyl coenzyme A)
what are other important coenzymes?
ATP, lipoamine, FAD/FADH, Ubiquinone (coenzyme Q 10) and S-adenyl methionine (Sam-e)
what does coenzymes do?
ATP splits off a high energy-binded phosphate group in the active sites of enzymes to propel the reaction
enzyme production is regulated by?
gene expression
genes coding for enzymes are either _____ or ____ by gene expression factors?
induced or inhibited
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?
negative feedback loop
or
allosteric inhibition
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
phosphorylation
what can activate or deactivate an enzyme?
placing the enzyme in a changed environment, as in pH change
a pre-active enzyme is called?
zymogen or proenzyme
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?
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
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?
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.
to combat the potential dangers of electrons creating superoxide instead of normal oxygen, what does most cell make?
superoxide dismutases - SOD - an enzyme that detoxifies superoxide
SOD dismutes superoxide, what is dismutation?
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.]
what is the fastest enzyme discovered? and what can it do?
catalase
a single catalase enzyme can convert hydrogen peroxide to water and O2 by the millions per secon
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?
cytochrone P450
what are the 2 common functions of cytochrome P450?
to oxygenate substrates and to pass electrons in aerobic respiration
why are cytochrome P450 unusual as enzymes?
bc they can catalyze a plethora of substrates, and so are nonspecific
where can you find Cytochrone P450?
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
cytochrome c
one of 57 human cytochromes
part of Electron Transport Chain in Oxidative Phosphorylation
cytochromes are membrane-associated proteins, located where?
either in the inner membrane (cristae) of mitochondria or in the endoplasmic reticulum of cells
what do cytochromes do?
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
cytochrome P450 enzymes are present all tissues of the body, and play important roles in?
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]
Liver does what?
detoxifies or metabolizes drugs and toxic compounds, all food, as well as metabolic products such as bilirubin (a breakdown product of hemoglobin)
many drug side effects have to do with what?
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]
why is taking 2 or more medication potentially problematic?
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
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
C. Glutathione does not remove sulfur from glutathione.
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
(c) removes sulfur from glutathione
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
(b) these easily change the chirality or enantiomeric state of a molecule
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
(c) it donates part of its structure to the molecule in the active site
