biochemistry chapter 9: glycolysis, glycogenolysis, gluconeogenesis, and the ppp

What is the function of GLUT 2?

Found in the liver for storage and pancreatic B-islet cells as a glucose sensor. It has a high Km.

What role does GLUT 4 play in glucose metabolism?

Found in adipose tissue and muscle; stimulated by insulin, it has a low Km.

Where does glycolysis occur?

In the cytoplasm of all cells, it does not require oxygen.

How many ATP are produced in glycolysis?

2 ATP per molecule of glucose.

What does glucokinase do?

Converts glucose to glucose 6-phosphate and is present in pancreatic B-islet cells.

Where is hexokinase found and what is its function?

Converts glucose to glucose 6-phosphate in peripheral tissues.

What is the rate-limiting step of glycolysis?

Phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate by PFK-1.

What activates PFK-1?

AMP and Fructose 2,6-bisphosphate (F2,6-BP)

What inhibits PFK-1?

ATP and Citrate

What does PFK-2 produce?

Fructose 2,6-bisphosphate (F2,6-BP), activating PFK-1.

What regulates PFK-2?

Activated by insulin and Inhibited by glucagon

What does glyceraldehyde-3-phosphate dehydrogenase produce?

NADH, which can feed into the electron transport chain.

What is substrate-level phosphorylation?

Performed by 3-phosphoglycerate kinase and pyruvate kinase.

Which enzymes catalyze irreversible reactions in glycolysis?

Glucokinase/Hexokinase, PFK-1, Pyruvate kinase

What happens to NADH produced in glycolysis when oxygen is present?

Oxidized by the mitochondrial electron transport chain.

What occurs to NADH if oxygen or mitochondria are absent?

Oxidized by cytoplasmic lactate dehydrogenase.

What is the Pentose phosphate pathway?

A metabolic pathway parallel to glycolysis, producing NADPH and ribose-5-phosphate.

What is the importance of glycogenesis?

The process of synthesizing glycogen from glucose for energy storage.

What is glycogenolysis?

The breakdown of glycogen into glucose-1-phosphate and glucose.

What is the function of NAD+ in glycolysis?

Acts as an electron carrier in the conversion of glyceraldehyde-3-phosphate.

How is pyruvate utilized in aerobic metabolism?

Converted to acetyl-CoA for entry into the citric acid cycle.

What does ATP stand for?

Adenosine triphosphate, the energy currency of the cell.

What is a key role of NADH in metabolism?

It provides reducing power for anabolic reactions and contributes to ATP production.

Review the main concept of carbohydrate metabolism.

Includes glycolysis, gluconeogenesis, and related pathways like the pentose phosphate pathway.

Which cellular processes involve galactose and fructose?

Conversion to glucose or entry into glycolysis.

What do insulin and glucagon regulate in metabolism?

Glycolysis, gluconeogenesis, glycogen synthesis, and breakdown.

What is the overall goal of gluconeogenesis?

To synthesize glucose from non-carbohydrate precursors.

Describe a key feature of glycolysis.

It is an anaerobic process, producing ATP and NADH from glucose.

Show the importance of pentose phosphate pathway.

Produces NADPH for biosynthetic reactions and ribose-5-phosphate for nucleotide synthesis.

How does glycolysis link to the citric acid cycle?

Provides pyruvate and NADH, which feed into the cycle for further oxidation.

What is produced during glycolysis

Enzymes like fructose 1,6-bisphosphate facilitate key steps.

What monosaccharide comes from lactose in milk?

Galactose

What enzyme converts galactose to glucose 1-phosphate?

Galactose-1-phosphate uridyltransferase

What enzyme traps fructose in the cell?

Fructokinase

What products does aldolase B produce from fructose?

Glyceraldehyde and DHAP

What does pyruvate dehydrogenase convert?

Pyruvate to acetyl-CoA

What stimulates pyruvate dehydrogenase?

Insulin

What inhibits pyruvate dehydrogenase?

Acetyl-CoA

What is glycogenesis?

Production of glycogen

What enzyme creates α-1,4 glycosidic links in glycogenesis?

Glycogen synthase

How is glycogen synthase activated?

By insulin in liver and muscle

What does the branching enzyme do?

Adds branches to glycogen using α-1,6 links

What enzyme removes glucose 1-phosphate from glycogen?

Glycogen phosphorylase

What activates glycogen phosphorylase in the liver?

Glucagon

What activates glycogen phosphorylase in exercising muscle?

Epinephrine and AMP

What does the debranching enzyme do?

Connects glycogen branches using α-1,4 links and Releases free glucose

What occurs during gluconeogenesis?

Synthesis of glucose from non-carbohydrate sources

What are the three irreversible steps of gluconeogenesis?

Pyruvate carboxylase, PEPCK, Fructose-1,6-bisphosphatase

What does pyruvate carboxylase convert?

Pyruvate to oxaloacetate

What activates pyruvate carboxylase?

Acetyl-CoA

What bypasses phosphofructokinase during gluconeogenesis?

Fructose-1,6-bisphosphate

What is the role of glucose-6-phosphatase?

Converts glucose-6-phosphate to glucose

What is the pentose phosphate pathway (PPP)?

A metabolic process for producing NADPH and sugars

What is the rate-limiting enzyme of the pentose phosphate pathway?

Glucose-6-phosphate dehydrogenase

What activates the pentose phosphate pathway?

NADP+ and Insulin

What are the products of the pentose phosphate pathway?

NADPH and ribose-5-phosphate

Where does gluconeogenesis primarily occur?

In the liver

What does insulin do to carbohydrate metabolism?

Stimulates glycogenesis and inhibits gluconeogenesis

What is the function of fructose-2,6-bisphosphate?

Regulates gluconeogenesis and glycolysis

What acute physiological state activates gluconeogenesis?

Fasting or low blood sugar

What is gluconeogenesis?

A metabolic process that generates glucose from non-carbohydrate precursors, primarily occurring in the liver and kidneys.

Where does gluconeogenesis mainly occur?

In the liver and to a lesser extent in the kidneys.

What is the main role of pyruvate carboxylase?

Converts pyruvate into oxaloacetate in gluconeogenesis.

How is pyruvate carboxylase activated?

Activated by acetyl-CoA from fatty acid oxidation.

What enzyme converts oxaloacetate to phosphoenolpyruvate?

Phosphoenolpyruvate carboxykinase (PEPCK).

What does fructose-1,6-bisphosphatase do?

Converts fructose 1,6-bisphosphate to fructose 6-phosphate, bypassing phosphofructokinase-1.

What activates fructose-1,6-bisphosphatase?

Activated by ATP and glucagon.

What inhibits fructose-1,6-bisphosphatase?

Inhibited by AMP and insulin.

What enzyme converts glucose 6-phosphate to free glucose?

Glucose-6-phosphatase.

Where is glucose-6-phosphatase found?

In the endoplasmic reticulum of the liver.

What activates glucose-6-phosphate dehydrogenase?

Activated by NADP+ and insulin.

What inhibits glucose-6-phosphate dehydrogenase?

Inhibited by NADPH.

Which sugars are derived from ribulose 5-phosphate in PPP?

Generates various sugars for biosynthesis.

What is the physiological importance of gluconeogenesis?

Maintains blood glucose levels during fasting or intensive exercise.

What is the role of glucagon in gluconeogenesis?

Stimulates gluconeogenesis by activating specific enzymes.

Describe the overall function of the pentose phosphate pathway.

To produce NADPH and ribose sugars for anabolic reactions.

What pathways are interconnected with gluconeogenesis?

Linked with glycolysis, glycogenesis, and the pentose phosphate pathway.

What role does insulin play in gluconeogenesis?

Inhibits gluconeogenesis by affecting enzyme levels.