Enzymes Part 1 Flashcards
Are proteins that are catalysts of biochemical reactions.
Enzymes
Typically has a globular shape
Enzymes
Complex 3-D structure
Enzymes
Are biological catalysts
Enzymes
Increase the rate of reaction by lowering the energy of activation.
Enzymes
Catalyze nearly all the chemical reactions taking place in the cells of the body.
Enzymes
Have a unique three-dimensional shape that fit the shapes of reactants
Enzymes
First clear recognition was made by
Payen and Pesos (around 1833)
An alcohol precipitate of malt extract contained in a thermolabile substance that converted starch into sugar.
Diastase
First to catalyze (urease)
J.B Sumner (1924-1930)
use of -ase
Duclaux (1898)
More than 2500 biochemically important enzyme catalyzed reactions.
Enzymes
Are characterized by specificity for substrates.
Enzymes
An enzyme activity (Activators, inhibitors, both, or depending on conditions).
Effectors modulates
Can have small single unit to large multiple units
Enzymes
Found in animal and plant cells
Catalase
Needed to speed up the breakdown of HYDROGEN PEROXIDE
Catalase
Breaks it down to OXYGEN and WATER
Catalase
HPCOW
HYDROGEN PEROXIDE β(Catalase) β OXYGEN + WATER
Found in saliva and in the pancreas
Amylase
Break down enzyme
Amylase
Breaks STARCH down to MALTOSE
Amylase
SAM
STARCH β(AMYLASE)β MALTOSE
Builds up Glucose-1- Phosphate molecules into Starch
Potato Phosphorylase
Synthesis enzyme (build up)
Potato Phosphorylase
G1PPS
Glucose-1- Phosphate β(PHOSPORYLASE)β Starch
High efficiency. 10^3 to 10^17 faster than the corresponding uncatalyzed reactions
Catalytic Efficiency
High specificity interacting with one or a few specific substrates and catalyzing only one type of chemical reaction
Specificity
37Β°C, physiological pH, ambient atmospheric pressure.
Mild reaction conditions
Is a part of the enzyme where the reactants bind, where the biochemical reaction occurs.
Active site
Is usually composed of amino acid side chains interact, metal ions, various types of polar, non-polar, ionic interactions
The enzyme active site
Is a region within an enzyme that fits the shape of molecules called substrates or reactants.
The active site
Contains amino acid R groups that align and bind the substrate.
The active site
releases products when the reaction is complete
The active site
In active sites: The substrates fit like a key in a lock and the active site is the lock itself. If the conditions are
Lock and Key Model
(cofactors (metal ions, ionically bonded to the enzyme)
Small nonprotein molecules or subunits
(anything that is covalently bonded to an enzyme))
prosthetic group
(apoenzyme and the nonprotein part).
holoenzyme
(apoenzyme and a cofactor).
Simple protein and the conjugated protein or the holoenzyme
Are additional non-protein molecule that is needed by some enzymes to help the reaction. Tightly bound cofactors are called prosthetic groups.
Cofactors
That are bound and released easily are called coenzymes. Many vitamins are coenzymes.
Cofactors
Are present in trace amounts within the enzyme
Metal ions
Many active enzymes require a ________. ______a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of the peptide bond.
metal ion, ππ^2+
Are non-protein or organic, maybe a vitamin.
Coenzyme
First created the classifications in enzyme system.
IUPAC (International Union for Pure and Applied Chemistry)
Catalyze the same reaction in different tissues in the body
Isoenzyme
Which converts lactate to pyruvate consists of five isoenzymes.
Lactate dehydrogenase
Have slight variations in the amino acid sequences of the subunits of their quaternary structure
Isoenzyme
Under the IUPAC, there is_________which developed the four-integer number system and a name.
EC or the Enzyme Commission
IUPAC
(International Union for Pure and Applied Chemistry)
Aside from the IUPAC name, there are enzymes that uses the common name. Usually, the principal specific reactant plus the _____ at the end of the name.
-ase
The name also describes the function of the enzyme.
Oxidases as example.
Some enzymes do not follow any rule (specific name).
pepsin and rhodanese.
The name of an enzyme identifies the reacting substance and usually ends in _______.
-ase.
Sometimes common names are used, particularly for the ____________ such as _______ and ________.
digestion enzymes, pepsin and trypsin.
Some names describe both the substrate and the function.
Alcohol Dehydrogenase as example.
For oxidation-reduction reactions.
Oxidoreductases
For transport/transfer of group of atoms or single atoms.
Transferases
For hydrolysis.
Hydrolases
For adding or removing atoms to form a double bond.
Lyases
For rearranging atoms.
Isomerases
For using ATP to combine molecules (substrates).
Ligases
Six major classes of enzyme catalyzed reactions.
EC first integer
A subclass
Second integer
Subclassification depending on 1st and 2nd integer.
Third integer
Serial number
Fourth integer
Modes of enhancement of rates of bond cleavage (for organic reactions):
1.Facilitation of Proximity
2. Covalent Catalyst
3. General Acid-Base Catalyst
4. Binding Energy
5. Metal Ion Catalyst
6. Strain Molecular Distortion and Shape Change
Rate of reaction between two molecules is enhanced if they are abstracted from dilute solution and held in close proximity to each other (in the enzymeβs active site)
Facilitation of Proximity
Accounts for the overall lowering of activation energy for a reaction, and it can also be considered as a catalytic mechanism for a reaction. Several catalytic factors in the binding of a substrate and enzyme can be considered:
Binding Energy
Amino acid side chains: nucleophilic groups (more prone to undergoing covalent catalysis reactions). This mechanism involves the transient covalent bonding of the substrate to an amino acid residue in the active site. Generally, this is to the hydroxyl group of a serine, although the side chains of threonine, cysteine, histidine, arginine, and lysine can also be involved.
Covalent Catalysis
Many reactions involve the formation of normally unstable, charge intermediates. These intermediates can be transiently stabilized in an enzyme active site by interaction of amino acid residues acting as weak acids (proton donors) or weak bases (proton acceptors).
General Acid-Base Catalysis
Several catalytic factors in the binding of a substrate and enzyme can be considered:
- Transient limiting of substrate and enzyme movement by reducing the relative motion (or entropy) of the two molecules.
- Solvation disruption of the water shell is thermodynamically favorable.
- Substrate and enzyme conformational changes.
Various metals, all positively charged including zinc, iron, magnesium, manganese, and copper are known to form complexes with different enzymes or substrates. This metal-substrate-enzyme complex can aid in the orientation of the substrate in the active site, and metals are known to mediate oxidation-reduction reactions by reversible changes in their oxidation states.
Metal Ion Catalysis
The binding of the substrate results in the distortion of the substrate in a way that makes the chemical reaction easier
Strain, Molecular Distortion, and Shape Change
In body fluids reflects organ status
Enzyme activity
Increased serum activity of an enzyme can be correlated with quantity or severity of damaged tissues. Example is creatine kinase levels following heart attack.
Cells die and release intracellular contents
Can be induced and release in serum correlates with degree of stimulation. Example is alkaline phosphatase activity as a liver status marker.
Increased enzyme synthesis
Reflects the presence of inhibitors and activators.
Enzyme activity
Can be altered genetically.
Enzyme activity
A mutation in an enzyme can alter its ______ which can be used as a diagnostic in comparison with normal enzyme.
substrate affinity, co-factor binding stability, etc.
(like an essential vitamin) by enzyme activity. Example is adding back vitamin to assay, if activity increases, suggests deficiency in that vitamin.
Determine co-factor deficiencies
Decreases in presence of an inhibitor. Example is some insecticides inhibit serum cholinesterase.
Activity of serum enzymes
As detected by increased enzyme substrate and/or lack of product leading to a dysfunction.
Loss of enzyme presence due to genetic mutation
That identify specific messenger RNA or DNA sequences are replacing many traditional enzymatic based markers of genetic disease.
PCR techniques
An _________is a blood test or a urine test that measures levels of certain enzymes to assess how well the bodyβs systems are functioning and whether there has been any tissue damage.
Enzyme Test
Chemical reactions need an ____________________.
initial input of energy (the activation energy)
Include alanine aminotransferase (ALT, also called glutamate pyruvate transaminase GPT), alkaline phosphatase, amylase, aspartate aminotransferase, creatine kinase, and lactate dehydrogenase.
Common enzymes used for clinical diagnosis
During this part of the reaction, the molecules are said to be in a transition state. ____________ is where the reaction is in between the reactant consumption and product formation (peak).
Transition state
_______________ make molecules move faster.
Increasing the temperature
Are very sensitive to temperature changes.
Biological systems
Controlled reactions proceed 108 to 1011 times faster than corresponding non-enzymic reactions.
Enzyme
May recognize and catalyze a single substrate, a group of similar substrates, and a particular type of bond
Enzymes
Enzymes can increase the rate of reactions without increasing/requiring an increase in the temperature.
- They do this by lowering the activation energy.
- They create a new reaction pathway (shortcut).
Have varying degrees of specificity for substrates.
Enzymes
They catalyze one type of reaction for a single substrate. Example of this is urease catalyzes only the hydrolysis of urea.
absolute enzymes
The catalyze one type of reaction for similar substrates. Example of this is hexokinase adds a phosphate group to hexoses.
group enzymes
They catalyze one type of reaction for a specific type of bond. Example of this is chymotrypsin catalyzes the hydrolysis of peptide bonds.
Linkage Enzymes
The active site has rigid shape, only substrates with the matching shape can fit, and the substrate is a key that fits the lock of the active site forming the enzyme-substrate complex.
lock and key model
- The lock and key hypothesis:
- Temporary structure called the enzyme-substrate complex formed.
- Products have a different shape from the substrate.
- Once formed, they are released from the active site.
- Leaving it free to become attached to another substrate.
Explain the enzyme specificity and the loss of activity when enzymes denature.
The lock and key hypothesis
Induced fit theory:
- Enzyme changes shape with substrate.
- The active site is not rigid.
- The active site is capable of changing its shape depending upon the substrate
The active site is flexible, not rigid, the shapes of the enzyme, active site, and substrate adjust to maximum the fit which improves the catalysis, and there is a greater range of substrate specificity.
In the induced fit model of enzyme action
The induced fit hypothesis:
- Some proteins can change their shape (conformation).
- When a substrate combines with an enzyme, it induces a change in the enzymeβs conformation.
- The active site is then molded into a precise conformation.
- Making the chemical environment suitable for the reaction.
- The bonds of the substrate are stretched to make the reaction easier (lowers activation energy).
Explains the enzymes that can react with a range of substrates of similar types.
The induced fit model
When a substrate (S) fits properly in an active site, an enzyme-substrate complex (ES) is formed:
πΈ + π β πΈπ (πππ£πππ ππππ)
Within the active site of the ES complex, the reaction occurs to convert substrate to product (P):
πΈπ β πΈ + π (πππππ£πππ ππππ)
The overall reaction for the conversion of substrate can be written as follows:
πΈ + π β πΈπ(πππ£πππ ππππ) β πΈ + π (πππππ£πππ ππππ)
The products are then released, allowing another substrate molecule to bind the enzyme
(this cycle can be repeated million times per minute).
Enzymatic reaction steps:
- Substrate approaches the active site.
- Enzyme-substrate complex forms.
- Substrate transformed into products
- Products released
- Enzyme recycled (depends on the enzyme, not always)
The reaction for the sucrase catalyzed hydrolysis of sucrose to glucose and fructose.
ππ’ππππ π + ππ’ππππ π β πΈπ πππππππ₯ (πππ£πππ ππππ)
β ππ’ππππ π + πΊππ’πππ π + πΉππ’ππ‘ππ π (πππππ£πππ ππππ)
Are never expressed in terms of their concentration, but are expressed only as activities.
- Enzymes
Test the absorbance:
spectrophotometer
Enzyme activity is moles of substrate converted to product per unit time.
The rate of appearance of product or the rate of disappearance of substrate.
Factors affecting enzyme activity:
- Concentration of substrate
- Concentration of enzyme
- Temperature
- pH
- Activators
- Inhibitors
The increase in velocity is ____________ to the substrate concentration.
proportional
But it reaches a saturation point when all the enzyme molecules are occupied.
Faster reaction
As substrate concentration increases (at constant enzyme concentration).
The rate of reaction increases
The relationship between reaction rate and substrate concentration is exponential and asymptotes when the _________________.
enzyme is saturated
Maximum activity occurs when the enzyme is ___________.
saturated
The initial rate of an enzyme catalyzed reaction is ____________ to the concentration of enzyme.
always proportionate
This property of enzyme is made use in determining the serum enzyme for the diagnosis of diseases
Their Activity
The rate of reaction _____ as enzyme concentration increases (at constant substrate concentration).
Increases
More enzymes are available to catalyze the reaction (more reactions at once).
At higher enzyme concentrations
There is a _________between reaction rate and enzyme concentration (at constant substrate concentration)
linear relationship
Enzymes are most active at an ____________ shows little activity at low temperatures, lose activity at high temperatures as denaturation occurs.
optimum temperature (usually 37 degrees Celsius in humans)
Effect of temperature in enzymic activity:
- Speed of reaction increases until an optimum temperature is reached.
- Optimum temperature is the temperature at which the enzyme works best.
- After this point, the rate of reaction decreases until there is no reaction.
- At this point, enzyme is said to be denatured (active site is destroyed).
A reaction rate will generally _____________ with _____________ temperature due to increased kinetic energy in the system until a maximal velocity is reached. Above this maximum, the kinetic energy of the system exceeds the energy barrier for breaking H-bonds and hydrophobic interactions, thus leading to unfolding and denaturation of the enzyme and a decrease in reaction rate.
increase with increasing
Greatest number of collisions between enzyme and substrate.
At optimum temperature
Denatures the protein (unfold and lose shape).
Raise temperature (boiling)
Molecules move slower and fewer collisions between enzyme and substrate.
At lower temperatures
