Exam easy to ud erstand flash cards

What is glycolysis?

The breakdown of one glucose molecule into two pyruvates, generating ATP and NADH; occurs in the cytoplasm and doesn’t require oxygen.

What are the two phases of glycolysis?

1) Investment phase – uses 2 ATP to split glucose into two 3-carbon sugars; 2) Payoff phase – produces 4 ATP and 2 NADH; net +2 ATP, +2 NADH.

Why does the cell invest ATP at the start of glycolysis?

To make glucose unstable and trap it in the cell, allowing later energy release.

What enzyme traps glucose in the cell?

Hexokinase, which phosphorylates glucose to glucose-6-phosphate.

Which enzyme is the key regulatory “gatekeeper” of glycolysis?

Phosphofructokinase-1 (PFK-1); activated by AMP, inhibited by ATP and citrate.

Which enzyme forms ATP at the end of glycolysis?

Pyruvate kinase.

What is substrate-level phosphorylation?

ATP made directly from a high-energy substrate, independent of the electron transport chain; occurs via phosphoglycerate kinase and pyruvate kinase.

What are the products of glycolysis under aerobic conditions?

2 pyruvate, 2 ATP, 2 NADH; pyruvate enters mitochondria for the TCA cycle.

What are the products of glycolysis under anaerobic conditions?

2 lactate and 2 ATP; NAD⁺ is regenerated so glycolysis continues.

Where does glycolysis occur?

In the cytoplasm of all cells.

Why is fermentation important?

It regenerates NAD⁺ when oxygen is low, allowing glycolysis to continue.

What happens in lactic acid fermentation?

Pyruvate is reduced to lactate by lactate dehydrogenase, regenerating NAD⁺.

What happens in alcoholic fermentation?

Pyruvate is converted to acetaldehyde, then to ethanol and CO₂; regenerates NAD⁺ in yeast.

Why do muscles burn during intense exercise?

Lactate and H⁺ build up, lowering pH and causing temporary fatigue.

What is the Cori Cycle?

Lactate from muscles travels to the liver, converted to glucose via gluconeogenesis, and returned to muscles.

What is gluconeogenesis?

The synthesis of glucose from non-carbohydrate precursors such as lactate, amino acids, and glycerol; occurs mainly in the liver.

Why is gluconeogenesis necessary?

Some tissues (brain, red blood cells) rely solely on glucose for energy.

Which glycolysis steps are bypassed in gluconeogenesis?

1) Pyruvate → PEP via pyruvate carboxylase and PEP carboxykinase; 2) Fructose-1,6-bisphosphate → fructose-6-phosphate via fructose-1,6-bisphosphatase; 3) Glucose-6-phosphate → glucose via glucose-6-phosphatase.

What cofactor does pyruvate carboxylase use?

Biotin, which carries CO₂ groups.

Where does gluconeogenesis occur?

In the liver and kidney cortex.

What are the three main classes of carbohydrates?

Monosaccharides (single sugars), disaccharides (two sugars), polysaccharides (many sugars).

What bond links sugars together?

A glycosidic bond.

How do starch and cellulose differ?

Starch has α(1→4) linkages and is digestible; cellulose has β(1→4) linkages and is structural and indigestible to humans.

Why do complex carbs give longer energy than simple sugars?

They digest slowly, releasing glucose steadily.

What is lactose intolerance?

Lack of lactase enzyme; undigested lactose increases intestinal osmolarity and causes bloating and diarrhea.

What are glycoconjugates?

Proteins or lipids covalently linked to polysaccharides (glycoproteins, glycolipids, proteoglycans).

What is the role of glycosaminoglycans like heparin and hyaluronan?

Provide structural support and lubrication; heparin prevents blood clotting.

What enzyme breaks down glycogen?

Glycogen phosphorylase.

Why is phosphorolysis more efficient than hydrolysis in glycogen breakdown?

It produces glucose-1-phosphate, which is converted to glucose-6-phosphate without using ATP.

How does fructose enter glycolysis?

Fructose → fructose-1-phosphate → DHAP + glyceraldehyde → glycolysis.

How does galactose enter glycolysis?

Galactose → galactose-1-phosphate → UDP-glucose → glucose-1-phosphate → glycolysis.

What does amylase do?

Breaks α(1→4) linkages in starch to yield maltose and limit dextrins.

Why can’t amylase fully digest starch?

It cannot break α(1→6) branch points.

How many ATP are invested and produced in glycolysis?

2 ATP invested, 4 ATP produced, net gain of 2 ATP.

How many NADH are made per glucose in glycolysis?

2 NADH.

How many pyruvates are made per glucose?

2 pyruvates.

What is the main regulator of glycolysis?

Phosphofructokinase-1 (PFK-1), controlled by ATP, AMP, and citrate.

What does fermentation not do?.

It does not make ATP directly; it only regenerates NAD⁺

Where does gluconeogenesis mainly occur?

Liver.

Why can’t humans digest cellulose?

We lack the enzyme cellulase that breaks β(1→4) bonds.

Why do endurance athletes “carb-load”?

To increase glycogen stores in muscles and delay fatigue.