MCAT BIC Ch 9

GLUT 1 through 4

GLUT 2: low-affinity in hepatocytes and pancreatic  cells (high Km) ; fx only when glucose concentrations are high

GLUT 4: adipose and mscle; rate of glucose transport increased by insulin; Km is lower; responds when glucose just a tad above normal

gycogen

DHAP

triacylglycerols

excess glucose is converted to fatty acids for storage

phosphorylate glucose to trap it in the cell

low Km

inhibited by glucose-6-phosphate

high Km

located in hepatocytes and pancreatic beta-islet cells

induced by insulin

• rate-limiting enzyme
• fructose-6-phosphate is phosphorylated to fructose 1,6-bisphosphate

• inhibited by: ATP and citrate; glucagon
• activated by: cAMP; insulin

• PFK-2
• fructose-6-phosphate
• fructose-2,6-bisphosphate
• PFK-1

• PFK-2
• F2,6-BP
• PFK-1

PFK-1

catalyzes an oxidation and addition of inorganic phosphate to its substrate, glyceraldehyde 3-phosphate, which results in production of a high energy intermediate 1,3-bisphosphoglycerate and reduction of NAD+ to NADH

transfers phosphate from 1,3-bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate

catalyzes the substrate-level phosphorylation of ADP using the high-energy substrate PEP

activated by fructose 1, 6-bisphosphate from PFK-1 reaction

lactate dehydrogenase (oxidizes NADH to NAD+)

used in hepatic and adipose for triacylglycerol synthesis

can be isomerized to glycerol 3-phosphate

high-energy intermediates used to generate ATP by substrate-level phosphorylation

• Glucokinase
• hexokinase
• PFK1
• pyruvate kinase

uses bisphosphoglycerate mutase, which produces 2,3-bisphosphoglycerate (2,3-BPG) from 1,3-BPG

• increased respiration
• increased oxygen affinity for hemoglobin
• increased rate of glycolysis
• increased [2,3-BPG] in RBC (over a 12-24 hour period)
• normalized oxygen affinity for hemoglobin restored by increased level of 2,3-BPG
• increased hemoglobin (over days to weeks)

Phosphorylated to galactokinase, trapping it in cell. 

The resulting galactose 1-phosphate is converted to glucose 1-phosphate by galactose-1-phosphate uridyltransferase and an epimerase

fructose converted to frucose 1-phosphate by fructokinase. Then, glyceraldehyde and DHAP convert it to aldolase B.

irreversible

cannot convert acetyl-CoA to pyruvate or to glucose

activated by insulin (liver)

• 1) conversion to acetyl-CoA by PDH
• 2) coversion to lactate by lactate dehydrogenase
• 3) Conversion to oxaloacetate by pyruvate carboxylase

central protein core with polyglucose chains radiating outward to form a sphere

composed entirely of linear chains and have the highest density of glucose near the core

branched chains are more dense at periphery, allowing more rapid release of glucose on demand

synthesis of glycogen granules

begins with core protein glycogenin and glucose addition begines with glucose 6-phosphate, which is converted to glucose 1-phosphate

uridine diphosphate permits integration into glycogen chain by glycogen synthase

rate limiting enzyme of glycogen synthesis and forms alpha-1,4 glycosidic bond found in linear glucose chains of the granule

stimulated by glucose 6-phosphate and insulin

inhibited by epinephrine and glucagon

introduces alpha-1,6-linked branches into the ranule

• hydrolyzes one alpha-1,4-bonds to release oligoglucose
• form an alpha-1,6-bond to create a branch

breakdown of glycogen granules

glycogen phosphorylase: breaks alpha-1,4-glycosidic bonds, releasing glucose 1-phosphate 

cannot break alpha-1,6 bonds

breaks alpha-1,4 bond adjacent to the branch point and moves the small oligoglucose chain that is released to teh exposed end of the other chain

form a new alpha-1,4-bond

hydrolyzes the alpha-1,6-bond, releasing the single residue at the branch point as free glucose

the production of glucose from other biomolecules; carried out by the liver and kidney

• glycogenolysis
• gluconeogenesis

stimulated by glucagon and epinephrine

inhibited by insulin

glycogen reserves drop dramatically in the first 12 hours, during which time gluconeogenesis increases. After 24 hours, it represents the sole source of glucose

• glycerol 3-phosphate
• lactate
• glucogeneic amino acids

can be converted into intermediates that feed into gluconeogenesis

converted into ketone bodies, which can be converted into alternative fuel, particularly during periods of prolonged starvation

False: it is not

lactate dehydrogenase

alanine aminotransferase

glycerol 3-phosphate dehydrogenase

• pyruvate carboxylase
• PEPCK
• fructose-1,6-bisphophatase
• glucose-6-phosphatase

mitochondrial enzyme activated by acetyl CoA and produces OAA

induced by glucagon and cortisol

• acts to raise blood sugar levels
• converts OAA to PEP in a reaction that requires GTP

key control point of gluconeogenesis and represents rate limiting step of the process

reverse the action of PFK-1, the RLS of glycolysis, by hydrolyzing phosphate from fructose 1,6-bisphosphate to produce fructose 6-phosphate

• activated by ATP
• inhibted by AMP

converts glucose-6-phosphate into glucose

• glucogenic amino acid
• glucogenic

Beta-oxidation of fatty acids

hepatic gluconeogenesis always dependent on Beta-oxidation of fatty acids in the liver

high levels of ketones in the blood

two functions: 

• production of NADPH
• serving as a source of ribose 5-phosphate for nucleotide synthesis

begins with glucose 6-phosphate, ends with ribulose 5-phosphate, and is irreversible

produces NADPH and involves the important rate limiting enzyme glucose-6-phosphate dehydrogenase

G6PD is induced by insulin because the abundance of sugar entering the cell under insulin stimulation will be shunted into both fuel utilization pathways (glycolysis and aerobic respiration) as well as fuel storage pathways

The shunt is also inhibted by its product, NADPH, and is activated by one of its reactants, NADP+

represents series of reversible reactions that produce an equilibrated pool of sugars for biosynthesis, inclduign ribose 5-phosphate for nucleotide synthesis

electron donor in a number of biochemical reactions; ptent reducing agent

• biosnthesis
• assisting in celular bleach production in certain white blood cells
• maintenance of a supply of reduced glutathione to protect against reactive oxygen species