Ch. 9: Carbohydrate Metabolism I Flashcards
what drives glucose entry into the cells
concentration
where is GLUT 2 located
hepatocytes and pancreatic cells
what does GLUT 2 do
captures excess glucose from the digestive tract primarily for storage
when does GLUT 2 function
when blood glucose levels are high until the concentration drops below the Km T (which is high) for the transporter
where is GLUT 4 located
adipose tissue and muscle
how does GLUT 4 function with insulin
when insulin is high, transporters move from inside cell to membrane
how high is the Km of GLUT 4 in relationship to nl blood glucose levels
Km is slightly higher than normal blood glucose
what does GLUT 4 do
captures excess blood glucose for for storage in muscles (as glycogen) and adipose tissue (DHAP)
what occurs (big picture) during glycolysis
- glucose is converted into two pyruvate molecules
- which release energy that
- is captured in two substrate level phosphorylations and
- one oxidation reaction
how are the products of glycolysis used by the body (big picture)
if oxygen + mitochondria, NADH feeds into aerobic respiratory pathway
if no oxygen or mitochondria, anaerobic energy
sometimes, intermediates for other pathways
what do hexokinase and glucokinase do
phosphorylate glucose inside the cell to prevent it from leaving the cell via the transporter
where is hexokinase located
most tissues (GLUT 4)
where is glucokinase located
hepatocytes and pancreas cells (GLUT 2)
what does phosphofructokinase-1 do
rate-limiting enzyme and main control point in glycolysis
phosphorylates fructose
activated (turns on glycolysis) by AMP and citrate and inhibited (turns off glycolysis) by ATP
what does phosphofructokinase-2 do
phosphorylates F6P to F26P, which activated PFK-1
what does glyceraldehyde-3-phosphate dehydrogenase do
catalyzes an oxidation and addition of inorganic phosphate to its substrate –> high energy intermediate: 1,3 - biphosphoglycerate
reduces NAD+ to NADH
what does 3-phosphoglycerate kinase do
transfers the high-energy phosphate from 1,3 - biphosphoglycerate to ADP –> ATP
substrate-level phosphorylation
what occurs during substrate-level phosphorylation
ADP is directly phosphorylated to ATP using high energy intermediate
not oxygen dependent, like oxidative phosphorylation
what does pyruvate kinase do
catalyzes substrate-level phosphorylation of ADP –> ATP and pyruvate
what occurs during fermentation
anaerobic ATP production
lactate dehydrogenase reduces pyruvate to lactate and oxidizes NADH to NAD+
what is dihydroxyacetone phosphate (DHAP)
intermediate of glycolysis
used in hepatic and adipose tissue for tracylglycerol synthesis
what are the irreversible enzymes of glycolysis
hexokinase, glucokinase, PFK-1, pyruvate kinase
how is ATP produced in erythrocytes
anaerobic glycolysis
what is the disaccharide precursor to galactose
lactose (glucose + galactose)
what is the disaccharide precursor to fructose
sucrose
what enzyme phosphorylates fructose
fructokinase
what enzyme phosphorylates galactose
galactokinase
what can pyruvate be converted to in the mitochondria
acetyl coA –>citric acid cycle (makes ATP)
OR –> fatty acid synthesis (when enough ATP)
what enzyme converts pyruvate to acetyl coA
pyruvate dehydrogenase enzyme (PDH)
what is glycogen
a branched polymer of glucose, glucose in its storage form
where is glycogen stored
the cytoplasm as a granule
where is glycogen synthesized
the liver and skeletal muscle
what occurs during glycogenesis (big picture)
glycogen granules are synthesized
what is glycogenin
the core protein of a glycogen granule
what is glycogen synthase
- rate-limiting enzyme of glycogenesis
- forms alpha 1,4 glycosidic bond
- stimulated by insulin, inhibited by epinephrine
what does branching enzyme do
introduces alpha 1,6 linkages to glycogen, creating branches
1,4 goes 4ward…1,6 puts a branch in the mix
what occurs during glycogenolysis (big picture)
glycogen is broken down
what is the rate limiting enzyme of glycogenolysis
glycogen phosphorylase –> breaks alpha 1,4 bonds, stops when reaching branches
what does debranching enzyme do
deconstructs branches in glycogen by
- breaking adjacent 1,4 bonds,
- moving the oligoglucose chain to the exposed end of the other chain,
- hydrolyzing the 1,6 bond
glycogen storage diseases
genetic deficiencies that result in the accumulation/lack of glycogen in the tissues
what occurs during glyconeogenesis (big picture)
the liver produces glucose during times of fasting to maintain blood glucose levels by essentially reversing glycolysis
what can glycogenic amino acids (except leucine and lysine) be converted into
intermediates that feed into gluconeogenesis
what can ketogenic amino acids be converted into
ketone bodies which are used for alternative fuels during prolonged starvation
what does pyruvate carboxylase do
mitochondrial enzyme
activated by acetyl co-A (from fatty acids) to produce oxaloacetate
what does phosphoenolpyruvate carboxykinase (PEPCK)
converts OAA to PEP in the cytoplasm with GTP
what does fructose 1,6 bisphosphatase do
key control enzyme of gluconeogenesis
reverses action of PFK-1, removing phosphate from biphosphorylated fructose, in the cytoplasm
what does glucose-6-phosphatase do
circumvents gucokinase and hexokinase, allowing free glucose to be transported out of the cell
what are the major functions of the pentose phosphate pathway/hexose monophosphate shunt
- produce NADPH
- source of ribose phosphate for nucleotide synthesis
what is the rate limiting enzyme of PPP
glucose-6-phosphate dehydrogenase (G6PD)
produces NADPH
