Wiley Plus Assignment 9
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When GTP is bound to G proteins (alpha subunit) the complex is active .
 Heterotrimeric G-proteins work through ligand binding to a receptor activates the G-protein, by allowing
GTP to exchange for GDP at the α subunit, while the β and γ subunits dissociate.
 cAMP functions as a second messenger because cAMP is produced by adenylate cyclase in response to
G-protein activation, it activates many enzymes through cAMP-dependent protein kinase, and it is
eliminated through cAMP phosphodiesterase.

Receptors have a ligand binding site on the extracellular side of the membrane.
 Addition of a substance which inhibits adenylate cyclase would diminish a hormone signal mediated via
a G protein signal transduction system.

A Protein is never a second messenger!
The following statements are true of receptors:
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Receptors are integral membrane proteins with a portion of their structure exposed outside the
lipid bilayer on both sides of the membrane.
Upon binding the first messenger, receptors undergo a conformational change
Receptors bind the first messenger at a specific binding site on the extracellular side of the cell
membrane.

In a G protein signal-transduction system, the G protein transmits the signal from the receptor to other
components of the signaling system.

In G protein signal transduction systems cAMP is a second messenger.

Proteins that bind molecules and elicit a response are called receptors.
The advantages of protein phosphorylation as a signaling event are:
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Phosphorylation is rapid and specific.
Phosphorylation is enzymatically reversible.
Phosphorylation can be amplified by cascade systems.

Phospholipase C cleaves PIP2, generating IP3 and DAG (inositol-1,4,5-trisphosphate and 1,2diacylglycerol).

The interaction of various signaling pathways is called crosstalk.

Insulin binds a receptor that possesses tyrosine kinase activity.

Protein kinases are involved in the phosphorylation of a wide variety of proteins.
Wiley Plus Assignment #10

Two molecules of glyceraldehyde-3-phosphate are converted to pyruvate for every molecule of glucose
that enters Stage I of glycolysis.

The glycolytic pathway must be supplied with its primary oxidizing agent, NAD.

Energy investment in the first stage of glycolysis requires glucose to be phosphorylated and cleaved to
yield two molecules.

In anaerobic glycolysis, alcoholic fermentation in yeast and homolactic fermentation in muscle serve to
regenerate NAD .

It is under anaerobic conditions that pyruvate must be converted to a reduced end product in order to
reoxidize the NADH produced by the glyceraldehyde-3-phosphate dehydrogenase reaction.

Enzymes that operate far from equilibrium are potential control points.

Red blood cells convert pyruvate to lactate even under aerobic conditions.

Oxidation of NADH is not involved in the reactions of glycolysis between glyceraldehyde-3-phosphate
and 3-phosphoglycerate.
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1,3-Bisphosphoglycerate is a high-energy intermediate produced in glycolysis: 1,3 BPG contains an acyl
phosphate bond, which has a free energy of hydrolysis greater than that of a phosphoanhydride bond.

Phosphofructokinase-1 catalyzes a regulated step in glycolysis and is affected by insulin. Insulin exerts its
effect indirectly, via PFK-2 and the production of fructose-2,6-bisphosphate.

Pyruvate has several metabolic fates depending on the cell, under aerobic or anaerobic conditions.
Reduction to lactate is a metabolic fate for pyruvate. Under anaerobic conditions in muscle cells, the
reduction of pyruvate to lactate regenerates NAD+, which is necessary for glycolysis to continue.

If pyruvate could not be converted to lactate in muscle cells during strenuous exercise glycolysis would
stop.

Gluconeogenesis is likely to occur when cellular ATP levels are high.
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Leucine is degraded to acetyl-CoA which cannot be used to produce glucose. It is NOT a substrate for the
synthesis of glucose via gluconeogenesis.
NADH must be re-oxidized to NAD+ if glycolysis is to continue. Under "normal" aerobic conditions, when
oxygen is available, re-oxidation of NADH occurs via the electron transport chain. Under anaerobic
conditions, however, the NAD+ is regenerated by reactions in which pyruvate is a substrate.
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Fructose-2,6-bisphosphate is an allosteric inhibitor of fructose-1,6-bisphosphatase.
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Glyceraldehyde-3-phosphate dehydrogenase also plays a role in gluconeogenesis.
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Phosphofructokinase-1 catalyzes a regulated step in glycolysis and is affected by insulin.

The biochemical purpose for the production of lactate in muscle cells is that it is produced to reoxidize
cytoplasmic NADH under anaerobic conditions.
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The primary purpose of gluconeogenesis in the liver is o produce glucose for its release into the
circulation to help maintain constant blood glucose levels.
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One product of glycolysis under aerobic or anaerobic conditions is ATP.

Glucose is converted to lactate in skeletal muscle under anaerobic conditions.

The enzymes that catalyze glycolysis are located in the cytosol.

Glucose can be synthesized from noncarbohydrate precursors by gluconeogenesis.

The citric acid cycle considered to be part of aerobic metabolism even though oxygen does not explicitly
appear in any reaction because it produces reduced electron carriers, which are re-oxidized by
transferring their electrons ultimately to oxygen.

NADH and FADH2 produced by the citric acid cycle can only be re-oxidized via the electron transport
chain, and this ultimately passes the electrons to O2

The consumption of acetyl-CoA by the citric acid cycle is DECREASED when the mitochondrial ATP
synthase is inactive.

The ubiquitous chemistry of acetyl-CoA is centered on its high-energy Thioester bond.

In the mitochondrial matrix, eukaryotes house the enzymes of the citric acid cycle.

It is important for recovery of energy from several metabolic fuels that are broken down to acetyl-CoA.
This best describes the citric acid cycle as a central pathway of metabolism.
The major pathways for fuel metabolism in mammals converge on the molecules pyruvate and acetylCoA.
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The following are true of glycogen:
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The first step in glycogen synthesis is catalyzed by hexokinase.
Glucose is stored as a polymer to reduce its chemical reactivity.
Branching enables more rapid breakdown of glycogen.
The part labeled D will not
proceed in the absence of
NAD+. NAD+ is required by
glyceraldehyde-3-phosphate
dehydrogenase for the
oxidation of glyceraldehyde3-phosphate.
The parts labeled D, E, and H
are “energy capture” steps.
The curves that best represent the
behaviour of pyruvate kinase in i) the
absence, and ii) the presence of ADP
are Absence = 4, and presence = 3