Substrate-level phosphorylation
MCAT glossary · MCAT
Definition
ATP/GTP synthesis by direct enzyme-mediated phosphate transfer from a substrate (as in glycolysis and the TCA cycle).
Substrate-level phosphorylation in plain English
This is one of the two ways your cells make ATP, the tiny rechargeable battery that powers everything you do. Here, an enzyme (a cellular machine) grabs a phosphate group that's already sitting on some molecule and hands it directly onto ADP to build ATP — a direct handoff, no middleman. Think of it like transferring cash straight from one person's hand to another, versus routing it through a bank. It shows up in glycolysis (breaking down sugar) and the TCA cycle, and it's the fast, simple way to make a little energy without needing oxygen or a fancy membrane setup.
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