Carbohydrate and Lipid Metabolism Flashcards

Flashcards based on lecture notes covering carbohydrate pathways (glycogen metabolism, gluconeogenesis, pentose phosphate shunt, galactose catabolism) and an introduction to lipid metabolism.

What are the two main functions of glycogen in the body?

Readily available energy store and glucose buffer

What type of linkages are found in the straight chains of glycogen?

α1→4 linkages

What type of linkages are found at the branch points of glycogen?

α-1,6-linkages

What protein is at the core of a glycogen molecule?

Glycogenin

What two locations are glycogen stored in the body?

Liver and Muscle

What enzyme catalyzes the rate-limiting step of glycogen synthesis?

Glycogen Synthase

What molecule inhibits glycogen synthase?

Glucolactone

How many glucosyl units are added before branching occurs in glycogen synthesis?

10

What enzyme creates the α-1,6-bond branch point in glycogen synthesis?

Glycogen branching enzyme

What is the dual role of glycogenin in glycogen synthesis?

Enzyme and scaffold

What enzyme breaks down glycogen?

Glycogen phosphorylase

What cofactor is bound to glycogen phosphorylase?

Pyridoxal phosphate

What molecule also inhibits glycogen phosphorylase?

Glucolactone

What enzyme removes branch points in glycogenolysis?

Debranching enzyme

What triggers glycogenolysis in muscle?

Increase in Ca2+

What hormone controls glycogen syntheis?

Insulin

What hormone triggers glycogenolysis in the liver?

Glucagon

What type of receptor does glucagon target?

Glucagon receptors

What molecule is created by adenylate cyclase?

Cyclic AMP (cAMP)

What is the role of cAMP in glycogen metabolism by glucagon?

Activates protein kinase A (PKA)

What enzyme removes cAMP?

Phosphodiesterases

What are the two proteins that PKA phosphorylates?

Glycogen synthase and glycogen phosphorylase kinase

In muscle, what receptor does epinephrine bind to?

β-adrenergic receptor

In liver, what receptor does epinephrine bind to?

α-adrenergic receptor

What does phospholipase C catalyze the hydrolysis of, and what does it produce?

Hydrolysis of phosphatidylinositol-4,5-P2; produces inositol triphosphate (IP3) and diacylglycerol (DAG)

What does insulin lead to?

Increased glycogen synthesis

What enzyme is a key regulator of glycogen synthase?

Glycogen synthase kinase (GSK3)

What does insulin binding to its receptor lead to which leads to inactivation of GSK3?

Phosphorylation

What becomes activated when IRS-1 is phosphorylated?

PI3K (phosphatidylinositol phosphate 3-kinase)

What kinase does PIP3 anchor?

Phospholipid dependent kinase (PDK)

What does protein kinase B (PKB) phosphorylate?

GSK3 (inactivated)

What is AMP-dependent protein kinase (AMPK) involved in?

Cell-cell signaling

What is required for AMPKs activation?

Phosporylation

What non-carbohydrate precursors can form glucose?

Lactate, glycerol, and amino acids

In what organ does gluconeogenesis almost exclusively occur?

Liver

What is the role of gluconeogenesis?

Maintaining blood glucose levels

What two enzymes are required to convert pyruvate to phosphoenolpyruvate (PEP)?

Pyruvate carboxylase and phosphoenolpyruvate carboxykinase

What vitamin is required for the incorporation of CO2?

Biotin

What two conversions occur if PEPCK catalyzes the conversion of oxaloacetate to PEP in the cytosol?

1. Reduction to malate 2. Transamination to aspartate

What activates fructose-1,6-P2 phosphatase allosterically?

Citrate

What inhibits fructose-1,6-P2 phosphatase allosterically?

Fructose-2,6-P2

What regulates Glucose-6-phosphatase?

Genetic means

What activates glycogen synthesis in the liver and muscle during a meal?

Insulin release

What is a major consumer of glucose in resting state?

Skeletal Muscle

During exercise, what activates AMPK?

Increased AMP

What are epinephrine and elevated [Ca2+] used?

Stimulating liver glycogen breakdown

What are the two distinct contributions of the pentose phosphate shunt?

1. Partially oxidize glucose-6-P and generate NADPH 2. Produce sugar phosphates including ribose phosphates

What inhibits glucose-6-P DH allosterically?

NADPH

What organ metabolizes galactose?

Liver

What are the two routes of lipid assimilation in mammals?

1. Endogenus 2. Exogenous