Lecture 6 - Carbohydrates Continued Flashcards
What are the three fates of glucose in the cell
enters glycogenesis for energy storage
enters glycolysis for energy production
enters hexose monophosphate shunt to generate precursors for biogenesis
What are the 6 steps in carbohydrate metabolism
glycogenesis, glycogenolysis, glycolysis, hexose mono sulphate shunt, Krebs cycle, gluconeogenesis
Where does glycogenesis occur
liver and muscle
What turns glucose from the blood into glucose-6-phosphate
phosphorylation of glucose
What turns glucose-6-phosphate into glucose-1-phosphate
hexokinase
What turns glucose-1-phosphate into glycogen
glycogen synthase
What is glycogenin
an enzyme that serves as a scaffold on which to attach glucose molecules to build glycogen
What occurs in glycogenolysis
glycogen is broken down back to glucose-1-phosphate, which is further broken back down to glucose-6-phosphate, broken down to fructose-6-phosphate, and sent to glycolysis
What breaks glycogen down into glucose-1-phosohate
glycogen phosphorylase
Where is glucose-6-phosphate broken back down to glucose (there is only one place it does this)
the liver
What does insulin stimulate
glucose uptake from food to cells (lowers blood sugar)
What does glucagon stimulate
glycogen breakdown back to glucose (increases blood sugar)
What is the first conversion in glycolysis and what enzyme carries it out
fructose-6-phosphate into fructose-1,6-phosphate
- done via phosphofructokinase
*this is irreversible
What is the net yield from glycolysis
2 NADH and 2 ATP
What are the two anaerobic pathways of glucose breakdown
lactic acid production and ethanol
What is lactic acid production
occurs in muscle during prolonged exercise and in RBCs
pyruvate is converted into lactate
regenerates NAD+, allowing cycling of glycolysis
What is the net of ATP when converting glucose to lactic acid
2 ATP
What is the ethanol production pathway
doesn’t happen in the body
basis of fermentation for making beer and wine
yeast breaks down pyruvate into CO2 and ethanol
regenerates NAD+, allowing cycling of glycolysis
What is the Cori cycle
no oxygen is available during exercise, so lactate is produced, which is then transports back to the liver where gluconeogenesis allows for conversion of pyruvate back to glucose
What is the net ATP in the Cori cycle
for every 2 glucose, 6 ATP are formed
What is the function of the hexose monophosphate shunt
important for NADPH production and ribose synthesis
Where does the hexose monophosphate shunt function
in the cytoplasm of the cell
What is the role of glucose-6-phosphate dehydrogenase in the hexose monophosphate shunt
convert G6P into 6-PG
What is the importance of the oxidative phase of hexose monophosphate shunt
biosynthesis of fatty acids and role in antioxidant production
What is the importance of the non-oxidative phase of hexose monophosphate shunt
biosynthesis of RNA/DNA
What vitamins make up the pyruvate dehydrogenase complex
thiamine, niacin, riboflavin, and pantothenic acid
What is the net production in pyruvate dehydrogenase
~6 ATP (3 per 1 NADH)
2 x [1 NADH/pyruvate]
What is the net production in the Krebs cycle per 1 acetyl CoA
3 NADH, 1 FADH2, 1 GTP (~12 ATP)
What is the total net energy from the breakdown of glucose
38 ATP
(~10 from glycolysis)
(~6 from pyruvate dehydrogenation because 2 pyruvate)
(~24 from Krebs cycle because 2 acetyl CoA)
What is gluconeogenesis
pathway that is active when glucose is needed by the body
very active in liver, but can also happen in kidneys
Where can gluconeogenesis NOT occur
in the muscle and adipose tissue
What is meant by the term integrated metabolism
thinking beyond just carbs, the collective metabolism of all nutrients
