BIO 403 – Bioenergetics, ATP Chemistry & Glucose Transport

31 question-and-answer flashcards covering ATP group-transfer chemistry, phosphate bond energetics, key metabolic group-transfer reactions, families and mechanisms of glucose transporters (GLUT, SGLT, SWEET), AKT signaling effects on metabolism, and bacterial glucose uptake systems.

How does ATP primarily provide energy to biological reactions?

By transferring a phosphoryl group to another molecule (group transfer), not by simple hydrolysis.

What are the names of the three phosphate groups attached to ATP?

Alpha (α), Beta (β), and Gamma (γ) phosphates.

Which bond connects the α-phosphate of ATP to ribose?

A phosphoric acid ester bond.

What type of bonds link the α-β and β-γ phosphates of ATP?

High-energy phosphoric acid anhydride bonds.

Approximate standard free-energy change (ΔG°′) for ATP → ADP + Pi hydrolysis

−30.5 kJ mol⁻¹ (≈ −7.4 kcal mol⁻¹).

Why is phosphorylation of glucose by hexokinase thermodynamically favorable in cells?

Because the endergonic phosphorylation of glucose is coupled to exergonic ATP hydrolysis, making the overall reaction highly exergonic and essentially irreversible.

During fatty-acid activation, ATP is converted into which products?

AMP and pyrophosphate (PPi), followed by PPi hydrolysis to 2 Pi.

What kind of group transfer occurs in the activation of methionine to S-adenosyl-methionine (SAM)?

Adenylyl (adenosine moiety) transfer.

Define ‘Ping-Pong’ (double-displacement) enzyme mechanism.

An enzymatic mechanism in which one or more products are released before all substrates bind, involving a substituted enzyme intermediate.

Name the three mammalian families of glucose carriers across the plasma membrane.

GLUTs (SLC2), SGLTs (SLC5), and SWEETs (SLC50).

Transport direction and energy source for GLUT proteins

Facilitated diffusion of glucose down its concentration gradient; no direct energy input.

Key feature distinguishing SGLT transport from GLUT transport

SGLTs use secondary active transport, coupling glucose uptake to the inward Na⁺ gradient; GLUTs use passive facilitated diffusion.

Which pump creates the Na⁺ gradient that drives SGLT1?

The Na⁺/K⁺-ATPase (primary active transporter).

Does SGLT1 directly hydrolyze ATP at the transport site?

No; it relies on the Na⁺ gradient generated elsewhere.

Major tissues expressing GLUT1 and its functional role

Brain (blood–brain barrier), red blood cells, fetal tissues; provides high-affinity basal glucose uptake independent of insulin.

Primary locations and role of GLUT2

Liver, kidney, pancreatic β-cells, intestinal basolateral membrane; low-affinity, high-capacity transporter acting as a glucose sensor.

Where is GLUT3 abundant and why is its affinity important?

Neurons/brain; very high affinity ensures adequate glucose supply even at low blood glucose levels.

Which GLUT isoform is insulin-responsive and found in muscle and adipose tissue?

GLUT4.

What fructose-specific transporter is located on the apical membrane of intestinal cells?

GLUT5.

Describe AKT’s role in GLUT4 translocation.

AKT phosphorylates AS160 (TBC1D4), releasing its inhibition so GLUT4 vesicles fuse with the plasma membrane, increasing glucose uptake.

How does AKT promote glycogen synthesis?

By inhibiting GSK-3, which activates glycogen synthase.

AKT’s effect on hepatic gluconeogenesis

Phosphorylates and inactivates FOXO1, reducing transcription of gluconeogenic enzymes (e.g., PEPCK, G6Pase).

Which GLUT isoforms are commonly up-regulated in tumors?

GLUT1 and GLUT3.

Bacterial system that simultaneously transports and phosphorylates glucose

The phosphotransferase system (PTS).

Energy source for bacterial ABC glucose transporters

Direct ATP hydrolysis by the transporter complex.

Role of Major Facilitator Superfamily (MFS) glucose transporters in bacteria

Act as passive facilitators or proton symporters for glucose movement across the membrane.

Secondary active transport: definition and example

Transport that uses the potential energy of an ion gradient (not direct ATP) to move another molecule; e.g., Na⁺-glucose symport by SGLT1.

Facilitated diffusion vs. simple diffusion

Facilitated diffusion uses specific carrier proteins (e.g., GLUTs) but still moves solute down its gradient; simple diffusion requires no carrier and is limited to small non-polar molecules.

Why does phosphorylation ‘trap’ glucose inside cells?

Glucose-6-phosphate carries a negative charge, preventing it from freely crossing the plasma membrane via GLUTs.

What is the free-energy rationale behind ATP’s ‘high-energy’ designation?

Relief of electrostatic repulsion, resonance stabilization of products, and solvation energy make its anhydride bonds highly exergonic upon hydrolysis.