Biochemistry Lab Notes: Carbohydrate and Lipid Metabolism

Vocabulary flashcards covering glycolysis, gluconeogenesis, glycolytic regulation, PPP, lipid metabolism, and lipid tests based on the provided notes.

Glycolysis

Metabolic pathway converting one glucose into two pyruvate, producing ATP and NADH; occurs in two stages: energy investment (6-carbon) and energy payoff (3-carbon).

Glucose-6-Phosphate (G6P)

Phosphorylated form of glucose formed in Step 1; product of hexokinase; irreversible; traps glucose inside the cell.

Hexokinase

Enzyme that catalyzes the phosphorylation of glucose to glucose-6-phosphate using ATP; regulated by feedback inhibition.

Fructose-6-Phosphate (F6P)

Isomerized form of glucose-6-phosphate in glycolysis; produced from G6P in Step 2; reversible.

Phosphoglucose isomerase

Enzyme that converts glucose-6-phosphate to fructose-6-phosphate (isomerization).

Fructose-1,6-bisphosphate (F1,6BP)

Highly phosphorylated intermediate in glycolysis; produced from fructose-6-phosphate; irreversible step.

Phosphofructokinase (PFK)

Key allosteric rate-limiting enzyme that converts F6P to F1,6BP; inhibited by high ATP and citrate, activated by AMP.

Dihydroxyacetone phosphate (DHAP)

Triose phosphate formed from fructose-1,6-bisphosphate; isomerized to glyceraldehyde-3-phosphate for glycolysis.

Glyceraldehyde-3-phosphate (GAP)

Phosphorylated triose phosphate that proceeds through glycolysis after DHAP is isomerized to GAP.

Triosephosphate Isomerase

Enzyme that interconverts DHAP and GAP; DHAP is converted to GAP to continue glycolysis.

1,3-Bisphosphoglycerate (1,3-BPG)

High-energy intermediate formed from GAP; NAD+ is reduced to NADH in this step.

Glyceraldehyde-3-phosphate Dehydrogenase

Enzyme that oxidizes GAP to 1,3-BPG and reduces NAD+ to NADH; links glycolysis to energy capture.

3-Phosphoglycerate (3-PG)

Mid-step product produced by phosphoglycerokinase; site of substrate-level phosphorylation forming ATP.

Phosphoglycerokinase

Enzyme that transfers a high-energy phosphate from 1,3-BPG to ADP, yielding ATP and 3-PG.

2-Phosphoglycerate (2-PG)

Isomerized form of 3-PG; produced by phosphoglyceromutase. Hisotopic rearrangement prepares for enolase reaction.

Phosphoglyceromutase

Enzyme that shifts the phosphate group from the 3- to the 2-position in phosphoglycerate.

Phosphoenolpyruvate (PEP)

High-energy enol phosphate formed from 2-PG; substrate for pyruvate kinase; dehydration by enolase.

Enolase

Enzyme that catalyzes the dehydration of 2-phosphoglycerate to phosphoenolpyruvate (PEP).

Pyruvate Kinase

Enzyme that catalyzes the final glycolysis step, converting PEP to pyruvate and producing ATP; irreversible. Regulated by energy status.

Energy investment phase

First part of glycolysis where ATP is consumed to phosphorylate glucose and intermediates (Steps 1–3).

Energy payoff phase

Second part of glycolysis where ATP is produced (Steps 7–10) and pyruvate is formed.

Regulation: Hexokinase

Hexokinase is subject to feedback inhibition by its product G6P, helping regulate the start of glycolysis.

Regulation: Phosphofructokinase

PFK is allosterically regulated; inhibited by high ATP and citrate, activated by AMP; controls the pace of glycolysis. (Step 3 regulation)

Regulation: Pyruvate Kinase

PK is regulated allosterically; activated by fructose-1,6-bisphosphate, inhibited by ATP and alanine; governs Step 10.

Pyruvate

End product of glycolysis; can enter mitochondria for further oxidation or be reduced to lactate under anaerobic conditions.

Lactate

Reduced form of pyruvate produced in anaerobic glycolysis; can be transported to liver for gluconeogenesis via the Cori cycle.

Glycerol

Glycerol is transported to liver/ kidney and converted to DHAP to enter glycolysis after phosphorylation and oxidation steps.

Glucogenic amino acids

Amino acids that can be converted to substrates for gluconeogenesis, contributing to glucose production.

Gluconeogenesis

Synthesis of glucose from non-carbohydrate sources; mainly in liver; not a simple reverse of glycolysis; uses 4 ATP and 2 GTP to convert pyruvate to glucose.

Liver (site of gluconeogenesis)

Approximately 90% of gluconeogenesis occurs in the liver.

Cori cycle

Gluconeogenesis uses lactate as a substrate; lactate is converted to pyruvate by lactate dehydrogenase, then to glucose.

Lactate Dehydrogenase

Enzyme that converts lactate to pyruvate and back, linking anaerobic glycolysis to gluconeogenesis.

Glycogenesis

Formation of glycogen from glucose for storage; important in liver and muscle.

Glucose-1-phosphate

First intermediate in glycogen synthesis; formed from glucose-1-phosphate.

Phosphoglucomutase

Enzyme that interconverts glucose-1-phosphate and glucose-6-phosphate, enabling UDP-glucose formation.

UDP-glucose

Activated glucose used for glycogen synthesis; formed from glucose-1-phosphate with UDP.

Pentose Phosphate Pathway

Pathway using glucose-6-phosphate to generate NADPH and ribose-5-phosphate; has oxidative and nonoxidative stages.

NADPH

Reducing equivalent produced in the oxidative stage of the pentose phosphate pathway; used in biosynthetic reactions and antioxidant defense.

Ribose-5-phosphate

Sugar for nucleotide and coenzyme biosynthesis; produced in PPP.

Ribulose-5-phosphate

Ketose produced in the oxidative stage of PPP; isomerized to ribose-5-phosphate in the nonoxidative stage.

Oxidative stage (PPP)

Initial steps of PPP converting G6P to ribulose-5-phosphate with CO2 release and NADPH production.

Nonoxidative stage (PPP)

Interconversion of sugar phosphates (e.g., ribulose-5-phosphate to ribose-5-phosphate) to balance nucleotide synthesis needs.

Chylomicrons

Lipoproteins that transport dietary triglycerides from intestinal cells through the lymphatic system to the bloodstream.

Low Density Lipoproteins (LDLs)

Lipoproteins that carry cholesterol from the liver to tissues.

High Density Lipoproteins (HDLs)

Lipoproteins that carry excess cholesterol from tissues back to the liver for disposal.

Very Low-Density Lipoproteins (VLDLs)

Lipoproteins that carry triglycerides from the liver to tissues; transitional form to LDLs.

Intermediate Density Lipoproteins (IDLs)

Transitional lipoproteins between VLDL and LDL in cholesterol transport.

Triacylglycerols (TAGs)

Storage form of fats; hydrolyzed to glycerol and fatty acids for energy.

Beta-oxidation

Catabolic pathway that breaks down fatty acids to acetyl-CoA, NADH, and FADH2 for energy production.

Carnitine-Palmitoyl Transferase (CPT)

Rate-limiting enzyme for mitochondrial transport of fatty acyl-CoA into the matrix for beta-oxidation.

Acetyl-CoA

Two-carbon molecule produced from fatty acids and pyruvate; enters the citric acid cycle and is a precursor for cholesterol synthesis.

Endoplasmic Reticulum (ER)

Main site of cholesterol synthesis in cells.

Palmitate ATP yield

Oxidation of palmitate yields net about 129 ATP after beta-oxidation and TCA/ETC; activation costs 2 ATP.

Saturated fatty acids

Fatty acids with no double bonds between carbon atoms.

Unsaturated fatty acids

Fatty acids containing one or more double bonds; cis or trans geometric isomers.

Cis double bond

Double bond with same-side hydrogen configuration causing a kink in the chain.

Trans double bond

Double bond with opposite-side hydrogen configuration; linear and generally less digestible.

Saponification test

Alkaline hydrolysis of esters in fats; froth formation indicates lipid presence.

Acrolein test

Test to detect glycerol in fats; produces a pungent smell if glycerol is present.

Hublé’s test (Unsaturation test)

Test to detect unsaturation in lipids; pink color disappears when unsaturation is present.

Translucent Spot Test

Qualitative test where a translucent spot appears on filter paper, indicating lipids.