ATP Synthase and Glycogen Metabolism Lecture Flashcards

Comprehensive vocabulary flashcards covering the regulatory mechanisms and biochemistry of ATP synthesis and glycogen metabolism.

Glycerol phosphate shuttle

The mechanism used in muscles to transport NADH electrons into the mitochondria.

NADH shuttle (Heart and Liver)

The specific transport mechanism for NADH electrons used in the heart and liver.

ATP–ADP translocase

Enables the exchange of cytoplasmic ADP for mitochondrial ATP; powered by the proton-motive force.

ATP synthasome

A large complex formed by the association of the ATP–ADP translocase, the phosphate carrier, and the ATP synthase.

Oxidative phosphorylation yield

Responsible for the formation of $26$ out of the $30$ molecules of ATP produced by the complete combustion of glucose.

Glycolysis yield

The metabolism of glucose to two molecules of pyruvate which yields $4$ ATP.

Fermentation yield

Process in which only $2$ molecules of ATP are generated per glucose molecule.

Acceptor control

Also called respiratory control; the regulation of oxidative phosphorylation by the availability of ADP.

Energy charge

The metabolic state that governs acceptor control as an example of control of metabolism.

Glycogen

A highly branched homopolymer of glucose present in all tissues, with the largest stores in liver and muscle.

Liver glycogen

Broken down to release glucose into the blood to provide energy for the brain and red blood cells.

Muscle glycogen

Mobilized to provide energy for muscle contraction rather than maintaining blood glucose.

Glucose 6-phosphatase

An enzyme present in the liver that generates free glucose from glucose 6-phosphate; it is absent in most other tissues.

Glucagon

A hormone that stimulates glycogen phosphorylation in the liver during fasting.

Epinephrine (Adrenaline)

A hormone that stimulates phosphorylation in the liver during fasting and in the muscle during exercise.

Phosphorylase b form

The less active form of phosphorylase, which is not phosphorylated.

Phosphorylase a form

The more active form of phosphorylase, characterized by a phosphorylated serine residue 14.

Serine 14

The specific residue on phosphorylase that is phosphorylated to convert the b form into the a form.

Isozymes

Different forms of the same enzyme, such as liver phosphorylase and muscle phosphorylase.

Liver phosphorylase default

The a form in the R state, being phosphorylated and more active to maintain blood glucose.

Muscle phosphorylase default

The b form in the T state, being unphosphorylated and less active.

R state (Relaxed)

The more active conformation of glycogen phosphorylase.

T state (Tense)

The less active conformation of glycogen phosphorylase.

Glucose (Liver phosphorylase regulator)

A negative regulator of liver phosphorylase that stabilizes the T state and reduces activity.

$[AMP]$ (Muscle phosphorylase regulator)

High concentrations of this molecule shift muscle phosphorylase b to the active R state.

$[ATP]$ (Muscle phosphorylase regulator)

High concentrations of this molecule shift muscle phosphorylase b to the inactive T state.

GTPase activity

The inherent activity of G proteins that renders them inactive, helping turn off glycogen degradation.

Phosphodiesterase

An enzyme that converts ext{cAMP} into ext{AMP}, preventing the stimulation of protein kinase A.

Protein phosphatase 1 (PP1)

Removes phosphoryl groups from phosphorylase kinase and glycogen phosphorylase to inactivate degradation; also activates synthesis.

Glycogen synthase

The key regulatory enzyme in glycogen synthesis that forms $\alpha$-1,4-glycosidic bonds.

UDP-glucose

The activated glucose donor used by glycogen synthase to extend glycogen chains.

$\alpha$-1,4-glycosidic bond

The type of chemical bond formed by glycogen synthase between a glucose moiety and the C-4 terminal residue of glycogen.

Glycogenin

A small protein homodimer that synthesizes the primer required by glycogen synthase.

Glycogenin primer length

An oligosaccharide of glucose residues between $10$ and $20$ glucosyl units long.

Glycogen synthase b form

The phosphorylated, usually inactive form of glycogen synthase.

Glycogen synthase a form

The unphosphorylated, more active form of glycogen synthase.

Glucose 6-phosphate (Synthase regulator)

An allosteric regulator that converts the T form of glycogen synthase to the R form, favoring dephosphorylation.

Insulin (Sensation effect)

Promotes the dephosphorylation of glycogen synthase to activate glycogen synthesis.

Glucagon (Synthesis effect)

Inhibits glycogen synthesis by promoting phosphorylation through the same signaling pathways that stimulate breakdown.

Epinephrine (Synthesis effect)

Inhibits glycogen synthesis by promoting the phosphorylation of glycogen synthase.

Glycogen synthase kinase

An enzyme that phosphorylates and inhibits glycogen synthase.

Protein kinase A (PKA)

Phosphorylates glycogen synthase to form the b form, thereby inhibiting glycogen synthesis.

Proton-motive force

The energy source used to power the ATP–ADP translocase.

Degradation mode vs. Synthesis mode

The metabolic shift controlled by Protein Phosphatase 1 (PP1).

Homopolymer

A polymer consisting of identical monomer units; glycogen is a homopolymer of glucose.

C-4 terminal residue

The location on a glycogen chain where glycogen synthase adds a new glucose moiety.

Phosphorylase kinase

An enzyme from which Protein Phosphatase 1 (PP1) removes a phosphoryl group to inhibit glycogen degradation.

Respiratory control

The regulation of the rate of oxidative phosphorylation by the level of ADP.

Active site alteration (Phosphorylase)

Phosphorylation removes $\alpha$ helices that partially block the active site in the b form.

Insulin (Dephosphorylation cascade)

Triggered by very high blood glucose levels to dephosphorylate liver phosphorylase.