Enzymes Flashcards
a prosthetic group can never be composed of
amino acids
what are co-enzymes often derived from
vitamins
what is the difference between coenzymes and prosthetic groups
coenzymes are helper/partner molecules that bind loosely to the enzyme while prosthetic groups bind tightly to an enzyme
what enzyme was first isolated and what is it now known as
diastase now known as amylase
what name was first given to enzymes
ferments
how are proteolytic enzymes named and give an example
end with “in” for example trypsin
give an example of an enzyme that indicate the nature of the reaction without specifying the substrates
trans-carboxylase
what are the six primary classes of enzymes
oxidoreductases (EC1), transferases (EC2), hydrolases (EC3), lyases (EC4), isomerases (EC5), and ligases (EC6)
what new class of enzymes was added in 2018
translocases (EC7)
what is are the second digits of oxidoreductases
Second digit Hydrogen or electron donor
1 Alcohol ( >CHOH )
2 Aldehyde or ketone ( >C=O )
3 -CH = CH-
4 Primary amine ( -CHNH2 or -CHNH3 )
5 Secondary amine ( >CHNH- )
6 NADH or NADPH
what are the third digits of oxidoreductases
Third digit Hydrogen or electron acceptor
1 NAD+ or NADP+
2 Fe+³ ( e.g. cytochromes )
3 O2
99 An otherwise unclassified
acceptor
what are the second digits of transferases
Second digit Group transferred
1 1-carbon group
2 aldehyde or ketone group ( >C=O )
3 acyl group ( –C–R )
||
O
4 glycosyl ( carbohydrate ) group
7 phosphate group
what are the third didgits of transferases
E.C. 2.1.1 : Enyzmes are methyltransferases (transfer –CH 3 )
E.C. 2.1.2 : Enyzmes are hydroxymethyltransferases
(transfer –CH 2OH )
E.C. 2.1.3 : Enyzmes are carboxyl- or carbamoyl-transferases
E.C. 2.4.1 : Enyzmes are hexosyltransferases (transfer hexose units)
E.C. 2.4.2 : Enyzmes are pentosyltransferases (transfer pentose units)
what is the exception of the third digit of tranferases
where there is transfer of phosphate groups: these cannot be described further, so there is opportunity to indicate the acceptor
give the digits of phosphate group transferases
E.C. 2.7.1 : Enzymes are phosphotransferases with an
alcohol group as acceptor
E.C. 2.7.2 : Enzymes are phosphotransferases with a
carboxyl group as acceptor
E.C. 2.7.3 : Enzymes are phosphotransferases with a
nitrogenous group as acceptor
what is the second digits of hydrolases
Second digit Bond hydrolysed
1 ester
2 glycosidic ( linking carbohydrate
units )
4 peptide
5 C – N bonds other than peptides
describe the third digits of hydrolases
E.C. 3.1.1 enzymes are carboxylic ester hydrolases
E.C. 3.1.2 enzymes are thiol ester hydrolases
E.C. 3.1.3 enzymes are phosphoric monoester
hydrolases
E.C. 3.1.4 enzymes are phosphoric diester hydrolases
what are the second digits of lyases
Second digit Bond broken
1 C – C 2 C – O 3 C – N 4 C – S
what are the third digits of lyases
Third digit Group removed
1 Carboxyl group ( CO2 )
2 Aldehyde group ( –CH=O )
3 Ketoacid group ( –C.CO2 )
| |
O
what is the second digit of isomerases
Second digit Type of reaction
1 Racemization or epimerization 2 Cis-trans izomerization 3 Intramolecular oxidoreductases 4 Intramolecular transfer reactions
what are the third digits of isomerases
Third digit Substrate
1 Amino acids 2 Hydroxy acids 3 Carbohydrates
what are the second digits of ligases
Second digit Bond synthesized
1 C — O 2 C — S 3 C — N 4 C — C
what are the third digits of ligases
The third digit further describes the bond being formed. Thus,
O
||
E.C. 6.3.1 enzymes are acid-ammonia ligases ( amide, —C —NH2 synthetases)
O
||
E.C. 6.3.2 enzymes are acid-amino ligases ( peptide, —C —N —, synthetases )
what are the main classes of specificity of an enzyme
- absolute specificity
- group specificity (common functional group)
- Linkage specificity (particular type of chemical bond)
- stereospecificity (between D and L stereoisomers)
true or false, catalysts effect equilibria
false
what is the rate-limiting step
step in the overall reaction with the highest activation energy (highest-energy point in the diagram for interconversion of S and P)
what equation is used to relate Keq and G
ΔG’° = -RT ln K’eq
What is one I.U. defined as
as the amount of enzyme that can convert 1 micromole (μmol) of substrate into product per min at 25 ̊C
what is specific activity
number of International Units of enzyme per milligram (mg) of protein. This term indicates the purity of the enzyme preparation
what is the turnover number
amount of enzyme activity (in International Units) per mole of enzyme. tells how many substrate molecules are converted into products by each enzyme molecule
at what temperature does enzymatic rates rise significantly
10 ̊C
what is the pH rate for
a) pepsin
c) trypsin
a) 1-2
b) 7-8
how does pH affect enzyme activity
Substrates can possess acidic or basic functional groups that also are affected by the pH solution. significantly influences the tertiary structure of the enzyme molecule and, thus, the activity of the enzyme
where is glucose-6-phosphate found, and what is its optimum pH
in hepatocytes with optimum of 7.8
what is Km
The substrate concentration that produces a velocity of 1/2 Vmax i.e. the Michaelis-Menten constant
what happens to the Michaelis-Menten equation when the substrate concentration is very high
Michaelis-Menten equation reduces v ~ Vmax
what cant increase the velocity of the reaction
increasing the substrate concentration
what dies Km indicate
indicates the affinity of the substrate for the enzyme active site
small Km= strong affinity
what happens when a phosphoryl group is added to Ser, Thr or Tyr residue
introduces a bulky, charged group into a region that was only moderately polar
