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the three main catalytic strategies used by enzymes
covalent catalysis, general acid-base catalysis, and metal ion catalysis
covalent catalysis
the active site contains a nucleophile that is briefly covalently modified
refers to enzymes where an intermediate forms a temporary covalent bond to the enzyme during the reaction
general acid-base catalysis
a molecule other than water donates or accepts a proton
metal ion catalysis
metal ions like Zn²⁺, Mg²⁺, and Fe³⁺ function in a number of ways, including serving as an electrophilic catalyst
catalysis by approximation and orientation
they enzyme brings two substrates together in an orientation that facilitates catalysis.
(water) —> H+ acts as both an acid and base. this is called
Amphiprotic
why enzyme activity is affected by temperature and pH.
Temperature enhances the rate of enzyme-catalyzed reactions. Too low temperatures slow reaction rates, while too high temperatures can denature the enzyme, disrupting its structure and function.
most enzymes have an optimal pH
many important drugs act as enzyme inhibitors.
Aspirin: Irreversible inhibitor, reducing inflammation
Statins: Competitive inhibitors, lowering cholesterol levels
Penicillin: Irreversible inhibitor, disrupting bacterial cell wall synthesis
how competitive inhibitors work.
resembles the substrate
bind to the enzyme’s active site,
blocking the actual substrate from binding.
do not change the maximum reaction velocity (Vmax)
increase the Michaelis constant (Km)
Irreversible Inhibitors
bind very tightly to enzymes (permanently)
can form covalent bonds or stable non-covalent interactions
preventing enzyme function
suicide inhibitors
mimic the substrate and bind to active site
enzyme begins reaction
groups at active site are irreversibly modified
active site can no longer catalyze a reaction
example: penicillin
Transition-state Analog
designed to bind strongly to active site but not react
Example: HIV protease inhibitors(like Ritonavir) that block viral replication.
statins, drugs used to treat high cholesterol, and Mevalonate, the substrate for the first enzyme in the cholesterol synthesis pathway. statins inhibit this first reaction. from a comparison of the structures, it is likely that statins work by….
binding to the the active site as a competitive inhibitor, blocking mevalonate from entering
competitive inhibitors can bee reversed by….
increasing the concentration of the substrate
What is the significance of cooperative behavior in hemoglobin?
The binding of oxygen to one subunit increases the affinity of the remaining subunits for oxygen, allowing for efficient oxygen uptake in the lungs and release in tissues.
What is the difference between myoglobin and hemoglobin in terms of oxygen binding?
Both bind oxygen in heme groups. Myoglobin is a monomer that stores oxygen in muscles and has a higher affinity for oxygen than hemoglobin, which is a tetramer that transports oxygen in the blood.
Hemoglobin is…
a red blood cell protein that carries oxygen from the lungs to tissue
an allosteric protein that displays cooperatively in oxygen binding and release
when one oxygen molecule binds, the remaining subunits increase their affinity for oxygen, enhancing oxygen uptake and release.
the binding of oxygen by myoglobin is
Not cooperative
What happens to hemoglobin when oxygen binds?
Hemoglobin undergoes a structural shift from the T form (low affinity, deoxygenated) to the R form (high affinity, oxygenated), as the iron atom moves into the plane of the heme group.
What are the T and R forms of hemoglobin?
The T form has low oxygen affinity and is predominant in tissues (for oxygen release). The R form has high oxygen affinity and is predominant in the lungs (for oxygen uptake).
How does BPG affect hemoglobin?
BPG binds to the T form of hemoglobin, stabilizing it and reducing its affinity for oxygen, promoting oxygen release in tissues, especially at high altitudes.
Why does fetal hemoglobin have a higher affinity for oxygen?
Fetal hemoglobin has gamma (y) subunits instead of beta (b) subunits, which reduces its affinity for BPG, allowing it to stay in the R form longer and have a higher oxygen affinity.
What factors influence hemoglobin’s oxygen affinity?
Allosteric regulators like BPG, CO₂, and protons (H⁺) influence oxygen affinity by stabilizing the T form, promoting oxygen release in metabolically active tissues.
What is the Bohr effect?
The Bohr effect describes how increased CO₂ and H⁺ (low pH) reduce hemoglobin’s oxygen affinity, enhancing oxygen release in tissues.
How do hydrogen ions (H⁺) and CO₂ promote the release of oxygen from hemoglobin?
H⁺ and CO₂ bind to hemoglobin, stabilizing the Tensed form and promoting oxygen release. CO₂ is transported in three forms: dissolved CO₂, bicarbonate (HCO₃⁻), and carbaminohemoglobin.
How does pH affect hemoglobin's oxygen binding?
Lower pH (high H⁺) decreases oxygen affinity, promoting oxygen release, while higher pH (low H⁺) increases oxygen affinity, promoting oxygen uptake.
How do mutations in hemoglobin genes cause disease?
In sickle cell disease, a mutation in the β-globin gene causes hemoglobin to polymerize under low oxygen, deforming red blood cells. Thalassemia mutations lead to reduced or defective hemoglobin production, causing anemia.
Triose
3-carbon sugar
Tetrose:
4-carbon sugar
Pentose
5-carbon sugar
Hexose:
6-carbon sugar
Aldose:
A sugar with an aldehyde group
Ketose:
A sugar with a ketone group
What are the four monosaccharides that need to be drawn as Fischer projections?
D-glyceraldehyde
Dihydroxyacetone
D-glucose
D-fructose
What is the system for numbering the carbon atoms of monosaccharides?
The numbering starts at the aldehyde or ketone group and proceeds to the furthest carbon from it. For aldoses, the numbering starts at the carbonyl carbon (C1), and for ketoses, it starts at the second carbon (C2).
What happens to 5-C and 6-C sugars in solution?
For 5-carbon and 6-carbon sugars, the open-chain forms are in equilibrium with two cyclic forms called anomers.
What is the difference between α-D-glucose and β-D-glucose?
The difference is in the position of the hydroxyl group on the anomeric carbon (C1):
α-D-glucose: The OH group on C1 is on the opposite side of the CH2OH group.
β-D-glucose: The OH group on C1 is on the same side as the CH2OH group.
How do monosaccharides link together?
Monosaccharides are linked together by the formation of glycosidic bonds, where the hydroxyl group of one sugar reacts with the anomeric carbon of another sugar.
What are the types of glycosidic bonds found in starch, glycogen, and cellulose?
Starch: Mainly α-1,4 and α-1,6 glycosidic bonds
Glycogen: Mainly α-1,4 and α-1,6 glycosidic bonds
Cellulose: β-1,4 glycosidic bonds
What are the differences in structure and function of starch, glycogen, and cellulose?
Starch: A polysaccharide made of glucose, stored in plants as energy. It has both α-1,4 and α-1,6 glycosidic bonds, forming helical structures.
Glycogen: Similar to starch but more branched (α-1,6 bonds), stored in animals for energy.
Cellulose: A polysaccharide of glucose with β-1,4 glycosidic bonds, forms straight chains, and is used for structural support in plant cell walls.
What do glycoproteins contain, and how are they formed?
contains complex sugar structures attached to specific amino acid residues (often serine, threonine, or asparagine) through covalent bonds.
What are the important functions of glycoproteins?
Cell recognition and signaling
Immune response (e.g., antibodies)
Structural roles (e.g., extracellular matrix proteins)
Enzyme regulation and catalysis
