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Questions and Answers
What is a characteristic of kinases?
What is a characteristic of kinases?
What is the role of phosphatases in cellular signaling?
What is the role of phosphatases in cellular signaling?
What is the mechanism by which GTPases switch proteins on and off?
What is the mechanism by which GTPases switch proteins on and off?
What is the function of motor proteins?
What is the function of motor proteins?
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What is a common feature of kinases and phosphatases?
What is a common feature of kinases and phosphatases?
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What is the result of hydrolyzing GTP to GDP in GTPases?
What is the result of hydrolyzing GTP to GDP in GTPases?
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What is the characteristic of protein machines?
What is the characteristic of protein machines?
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What is the role of ATP hydrolysis in motor proteins?
What is the role of ATP hydrolysis in motor proteins?
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What is the characteristic of motor proteins that move along actin filaments?
What is the characteristic of motor proteins that move along actin filaments?
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What is the purpose of adding ligands to change conformation in proteins?
What is the purpose of adding ligands to change conformation in proteins?
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Study Notes
Enzymes as Catalysts
- Most enzymes are proteins that bind to their ligand as the first step in a process, with the output of the reaction being called the product.
- Enzymes can repeat these steps many times and rapidly, making them catalysts.
- An enzyme's ligand is called a substrate, which may be one or more molecules.
Enzymes at Work
- Lysozyme is an important enzyme that protects against bacteria by making holes in the bacterial cell wall, causing it to break.
- Lysozyme adds H2O to the glycosidic bond in the cell wall, holding the polysaccharide in a position that allows the H2O to break the bond.
- This is called the transition state, the state between substrate and product.
Features of Enzyme Catalysis
- Enzyme performance involves binding of the substrate (E + S → ES), followed by stabilization of the transition state (ES → EP), and finally the release of the product (EP → E + P).
- Vmax is the maximum rate of the reaction, and the turnover number determines how fast the substrate can be processed.
- KM is the [S] that allows the reaction to proceed at half its maximum rate.
Prosthetic Groups
- Occasionally, the sequence of the protein is not enough for its function, and a non-protein molecule is required to enhance the performance of the protein.
- Hemoglobin requires heme (an iron-containing compound) to carry oxygen.
- When a prosthetic group is required by an enzyme, it is called a co-enzyme, which is usually a metal or vitamin.
Regulation of Enzymes
- Regulation of enzymatic pathways prevents the depletion of substrate, and happens at the level of the enzyme in a pathway.
- Feedback inhibition occurs when the end product regulates the enzyme early in the pathway.
Feedback Regulation
- Negative feedback occurs when the pathway is inhibited by the accumulation of the final product.
- Positive feedback occurs when a regulatory molecule stimulates the activity of the enzyme, usually between two pathways.
Allostery
- Conformational coupling of two widely separated binding sites is responsible for regulation, with the active site recognizing the substrate and the second site recognizing the regulatory molecule.
- Proteins regulated this way undergo allosteric transition or a conformational change.
Allosteric Regulation
- Method of regulation is also used in other proteins besides enzymes, such as receptors, structural, and motor proteins.
Phosphorylation
- Some proteins are regulated by the addition of a PO4 group, which allows for the attraction of + charged side chains, causing a conformation change.
- Reversible protein phosphorylations regulate many eukaryotic cell functions, turning things on and off.
- Protein kinases add the PO4, and protein phosphatases remove them.
Phosphorylation/Dephosphorylation
- Kinases can put the PO4 on three different amino acid residues: serine, threonine, and tyrosine.
- Phosphatases remove the PO4 and may be specific for one or two reactions or non-specific.
GTP-Binding Proteins (GTPases)
- GTP does not release its PO4 group, but rather the guanine part binds tightly to the protein, making it active.
- Hydrolysis of GTP to GDP (by the protein itself) makes the protein inactive.
Molecular Switches
- Proteins can move in the cell, but with very little uniformity.
- The hydrolysis of ATP can direct the movement as well as make it unidirectional.
Motor Proteins
- Motor proteins move along actin filaments or myosin, using the hydrolysis of ATP to direct the movement.
Protein Machines
- Complexes of 10 or more proteins that work together, such as in DNA replication, RNA or protein synthesis, trans-membrane signaling, etc.
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Description
Learn about the function of enzymes in protein chemistry, including their role as catalysts, binding to ligands, and producing products. Explore different types of enzymes and their importance, such as Lysozyme.
