--- title: "1,3-Bisphosphoglycerate — General Biology I Definition" description: "1,3-bisphosphoglycerate (1,3-BPG) is a high-energy glycolysis intermediate that powers ATP production in the energy payoff phase of cellular respiration." canonical: "https://fiveable.me/college-bio/key-terms/13-bisphosphoglycerate" type: "key-term" subject: "General Biology I" unit: "Unit 7" --- # 1,3-Bisphosphoglycerate — General Biology I Definition ## Definition 1,3-bisphosphoglycerate (1,3-BPG) is a high-energy, two-phosphate intermediate of glycolysis formed from glyceraldehyde-3-phosphate. Because its phosphate has a higher transfer potential than ATP, it can directly donate a phosphate to ADP, making ATP through substrate-level phosphorylation. ## What It Is 1,3-bisphosphoglycerate (often written 1,3-BPG) is a three-carbon molecule that shows up in the middle of **glycolysis**, the pathway that breaks glucose down in the cytoplasm. It forms when the enzyme glyceraldehyde-3-phosphate dehydrogenase takes **glyceraldehyde-3-phosphate** and does two things at once: it oxidizes the molecule (passing electrons to NAD+ to make NADH) and attaches a second phosphate group. The result is a molecule carrying two phosphates, which is where the "bis" in the name comes from. What makes 1,3-BPG special is that it's a "high-energy" intermediate. The bond holding its top phosphate is unstable and packed with transfer potential, even higher than the phosphate bonds in ATP. That instability is exactly the point: in the next step, 1,3-BPG hands that phosphate straight to ADP, creating ATP and leaving behind **3-phosphoglycerate**. So 1,3-BPG is basically a loaded spring that the cell uses to pay back energy. ## Why It Matters 1,3-BPG lives in topic 7.2 Glycolysis, the first stage of cellular respiration. Glycolysis is split into an **energy investment phase** (where the cell spends ATP) and an **energy payoff phase** (where it gets ATP back), and 1,3-BPG is the molecule that kicks off the payoff. Its conversion to 3-phosphoglycerate is one of the two ATP-generating steps in glycolysis, so without 1,3-BPG, the whole pathway wouldn't turn a profit. It also ties together two big themes in General Biology I: energy capture and redox balance. The same reaction that builds 1,3-BPG also reduces NAD+ to NADH, so this single step shows how cells link making energy carriers to managing electron flow. Understanding it helps you see why glycolysis produces both ATP and NADH. ## Connections ### Glyceraldehyde-3-phosphate (Unit 7) G3P is the molecule that becomes 1,3-BPG. The enzyme oxidizes G3P and slaps on a phosphate, capturing energy from that oxidation in the new high-energy bond. ### 3-Phosphoglycerate (Unit 7) This is what's left after 1,3-BPG donates its phosphate to ADP. That phosphate transfer is the substrate-level phosphorylation step that produces the first ATP of the payoff phase. ### ATP (Unit 7) 1,3-BPG has higher phosphate transfer potential than ATP, which is why it can directly phosphorylate ADP and make ATP without needing oxygen or the electron transport chain. ### [Energy Payoff Phase (Unit 7)](/college-bio/key-terms/energy-payoff-phase) 1,3-BPG is the first molecule of the payoff phase, marking the switch from spending ATP to earning it back during glycolysis. ## On the AP Exam On General Biology I quizzes and exams, 1,3-BPG usually appears in questions about the steps and energetics of glycolysis. You might be asked to identify where in the pathway it forms, name the enzyme involved (glyceraldehyde-3-phosphate dehydrogenase), or explain why this step both makes NADH and sets up ATP production. Short-answer questions often ask you to describe substrate-level phosphorylation, and 1,3-BPG is the textbook example: it donates a phosphate directly to ADP. On diagram-based problems, expect to trace the carbon flow from G3P to 1,3-BPG to 3-phosphoglycerate and explain what's gained at each step. ## 1,3-bisphosphoglycerate vs 3-phosphoglycerate 1,3-BPG has two phosphate groups and is the high-energy molecule before ATP is made; 3-phosphoglycerate is the lower-energy product left over after 1,3-BPG gives one phosphate to ADP. The transition between them is what generates ATP. ## Key Takeaways - 1,3-bisphosphoglycerate forms when glyceraldehyde-3-phosphate dehydrogenase oxidizes G3P and adds a second phosphate. - The same reaction that makes 1,3-BPG also reduces NAD+ to NADH, linking energy capture to redox balance. - 1,3-BPG has higher phosphate transfer potential than ATP, so it can directly phosphorylate ADP to make ATP. - Converting 1,3-BPG to 3-phosphoglycerate is a substrate-level phosphorylation step and produces the first ATP of the energy payoff phase. - 1,3-BPG carries two phosphate groups, which is why the name uses 'bis' (bisphosphate). ## FAQs ### What is 1,3-bisphosphoglycerate in glycolysis? It's a high-energy, three-carbon intermediate with two phosphate groups, formed from glyceraldehyde-3-phosphate during glycolysis. It donates a phosphate to ADP to make ATP, kicking off the energy payoff phase. ### Does the formation of 1,3-BPG produce ATP directly? No. Forming 1,3-BPG produces NADH, not ATP. The ATP comes one step later, when 1,3-BPG transfers a phosphate to ADP and becomes 3-phosphoglycerate. ### How is 1,3-bisphosphoglycerate different from 3-phosphoglycerate? 1,3-BPG carries two phosphates and high energy; 3-phosphoglycerate is the lower-energy product made after 1,3-BPG gives up one phosphate to make ATP. They're consecutive steps in glycolysis. ### What enzyme makes 1,3-bisphosphoglycerate? Glyceraldehyde-3-phosphate dehydrogenase converts glyceraldehyde-3-phosphate into 1,3-BPG, oxidizing it and reducing NAD+ to NADH in the process. ### Why is 1,3-BPG called a high-energy molecule? Its top phosphate bond has a higher transfer potential than the phosphate bonds in ATP, so the molecule readily donates that phosphate to ADP, which is why it can drive ATP synthesis. ## Related Study Guides - [7.2 Glycolysis](/college-bio/unit-7/2-glycolysis/study-guide/XvpWhCdJCs2gWC9n) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/college-bio/key-terms/13-bisphosphoglycerate#resource","name":"1,3-Bisphosphoglycerate — General Biology I Definition","url":"https://fiveable.me/college-bio/key-terms/13-bisphosphoglycerate","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/college-bio/key-terms/13-bisphosphoglycerate#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-06-29T17:36:58.157Z","isPartOf":{"@type":"Collection","name":"General Biology I Key Terms","url":"https://fiveable.me/college-bio/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/college-bio/key-terms/13-bisphosphoglycerate#term","name":"1,3-bisphosphoglycerate","description":"1,3-bisphosphoglycerate (1,3-BPG) is a high-energy, two-phosphate intermediate of glycolysis formed from glyceraldehyde-3-phosphate. 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