UNIT 4 - Catalysis Flashcards
Distinguish between a coenzyme, a prosthetic group, and a cosubstrate.
A coenzyme is molecule that makes the active site of an enzyme more chemically reactive. A coenzyme may be a metal ion or a metal ion complex or a small organic group.
A prosthetic groups is a covalently bound coenzyme.
A cosubstrate is a noncovalently bound coenzyme.
List the six mechanisms of enzyme catalysis.
acid-base catalysis,
electrostatic or ionic catalysis,
metal ion catalysis,
proximity and substrate orientation catalysis,
covalent catalysis, and
transition state binding.
List and define the four general mechanisms of enzymatic control. Are some enzymes controlled by more than one mechanism?
Allosterism, substrate control, gene production (enzyme synthesis and break down), covalent modification (active/inactive enszymes)
Allosteric control (allosterism): The small molecules that bind the enzyme and affect its activity are not substrates, and they bind in a location separate from the active site. These molecules may activate or inhibit an enzyme.
Covalent modification: when enzymes are synthesized in an inactive form and activation of the enzyme requires that covalent bonds in them be cleaved
Access to the substrate: also called substrate-level control. This involves inhibition of the enzyme by its product.
Control of enzyme synthesis/breakdown: This type of control occurs at the level of gene expression (transcription). This can be through signal transduction resulting in a transcriptional activator binding to the promoter region of the gene encoding the enzyme, or through the binding of other activators that induce transcription of the gene encoding a particular enzyme.
Outline the allosteric control of the enzyme HMG‑CoA reductase, which is involved in the synthesis of cholesterol.
HMG‑reductase is allosterically controlled by cholesterol
What is a ribozyme?
rna that can cut rna.
Ribozymes are a special form of enzymes. Unlike most enzymes, ribozymes are not proteins. They are RNAs. A ribozyme is a catalytic RNA capable of cutting RNA (self-splicing). Ribosomes can also be considered to be ribozymes because they catalyse the formation of peptide bonds.
