cell and molec chapter 13

Where does the energy that fuels cells come from?

chemical bond energy stored in food molecules

What does the breakdown (catabolism) of sugars produce?

ATP, NADPH, and other activated carrier molecules in cells

Where does the first stage of cellular metabolism occur?

mostly occurs outside cells, although lysosomes can digest large molecules in the cell interior

Where does the second stage of cellular metabolism occur?

occurs mainly in cytosol with one exception

Where does the final step of conversion of pyruvate to acetyl groups on
acetyl CoA occur?

in the mitochondria

Where does the third stage of cellular metabolism occur?

in the mitochondria

How does the controlled (stepwise) oxidation of sugar preserve energy?

it transfers free energy to carrier molecules.

What are the main energy carriers in cellular oxidation?

ATP and NADH

What do enzymes lower during cellular oxidation?

Activation energy barriers

Why doesn't cellular sugar oxidation require extreme heat?

Enzymes lower the required activation energy at every step

How does the total free energy released by cellular glucose oxidation compare to direct sugar burning?

It is exactly the same

What does the oxidation of sugars begin with?

glycolysis

What are the net products of glycolysis?

– 2 Pyruvate
– 2 ATP
– 2 NADH

What molecule is glucose converted into?

fructose 1,6-bisphosphate

What is fructose 1,6-bisphosphate broken down into?

2 molecules of pyruvate

Which enzyme produces NADH?

Glyceraldehyde 3-phosphate dehydrogenase

Which enzyme produces ATP?

Phosphoglycerate kinase

Which enzyme catalyzes the irreversible 10th step of glycolysis?

Pyruvate kinase

What is ATP synthesis in glycolysis called?

Substrate-level phosphorylation

What is substrate-level phosphorylation?

Direct transfer of a phosphate group from a substrate to ADP to form ATP

What is converted into lactate in the absence of oxygen

pyruvate

What is the purpose of converting pyruvate to lactate?

Regenerates NAD⁺

Why is NAD⁺ regeneration necessary during glycolysis?

To allow glycolysis to continue

How does fermentation's energy yield compare with complete glucose oxidation?

Fermentation yields much less energy

What are the products of alcoholic fermentation?

Ethanol and CO₂

What molecule is converted into ethanol during alcoholic fermentation?

Pyruvate

What intermediate forms between pyruvate and ethanol?

Acetaldehyde

What does alcoholic fermentation regenerate?

NAD⁺ from NADH

Why must alcoholic fermentation regenerate NAD⁺?

To allow glycolysis to continue

Under what condition does alcoholic fermentation occur?

In the absence of oxygen

Which enzyme converts pyruvate to acetyl-CoA?

Pyruvate dehydrogenase

Where does pyruvate convert to acetyl-CoA in eukaryotic cells?

Mitochondrial matrix

What are the products of pyruvate oxidation?

Acetyl-CoA, CO₂, and NADH

Where are fatty acids converted to acetyl CoA?

in the mitochondria

What does each turn of the citric acid cycle generate?

1 Acetyl CoA

1 NADH

1 FADH2

How many carbons are removed per cycle of fatty acid breakdown

2 carbons

From which end of a fatty acid are carbons removed?

The carboxyl end

What two nutrient sources provide molecules for acetyl-CoA production?

Sugars and fats

Where do most of the cell’s oxidation reactions occur?

the mitochondria

What happens to the acetyl group during the citric acid cycle?

It is oxidized to CO₂

What process uses high-energy electrons to produce ATP?

Oxidative phosphorylation

Where does oxidative phosphorylation occur?

The electron transport chain (ETC) in the inner mitochondrial membrane

What are the net products of the citric acid cycle?

• 3 NADH
• 1 FADH2
• 1 GTP
• 2 CO2

What is FADH2 a carrier of?

hydrogens and high-energy electrons

What process uses energy from NADH and FADH₂ to produce ATP?

Oxidative phosphorylation

What pathways provide precursors for biosynthesis?

Glycolysis and the citric acid cycle

What type of pathways use glycolysis and citric acid cycle intermediates to build molecules?

Anabolic pathways

Which specific biosynthetic products can glycolysis and citric acid cycle intermediates help produce?

Amino acids, nucleotides, lipids, and other small organic molecules

What must cells strictly regulate in metabolism?

Whether key metabolites enter anabolic or catabolic pathways

Which amino acid can be formed from pyruvate?

Alanine

What determines which pathway pyruvate enters?

the regulation of competing metabolic pathways

How do cells coordinate metabolic reaction rates?

Control mechanisms that regulate enzyme activity

What is gluconeogenesis?

Synthesis of blood glucose from non-carbohydrate precursors

Which glycolysis steps require bypass reactions in gluconeogenesis?

Steps 1, 3, and 10

How many bypass reactions are required in gluconeogenesis?

Four

Which precursors can be used for gluconeogenesis?

Lactate, pyruvate, and amino acids

Where does gluconeogenesis occur mainly?

liver cells

Why does gluconeogenesis require energy input?

Synthesizing glucose is energetically unfavorable and must bypass the irreversible steps of glycolysis

What is the primary function of gluconeogenesis?

Maintaining blood glucose levels

What do animal cells store in times of fasting?

glycogen

What is glycogen?

A branched glucose polymer in animals

How does glycogen branching compare with starch branching?

Glycogen has more branch points than starch

Which enzyme breaks down glycogen into glucose 1-phosphate?

Glycogen phosphorylase

What is glucose 1-phosphate converted into before entering glycolysis?

Glucose 6-phosphate

What two molecules inhibit glycogen phosphorylase?

Glucose 6-phosphate and ATP

How does fat oxidation compare with glycogen oxidation in energy released per gram?

Fat releases about twice as much energy

Why does glycogen require more storage mass than fat for the same energy?

Glycogen binds large amounts of water

How much more mass is required to store the same energy as glycogen versus fat?

About 6 times more

About how long can stored glycogen fuel normal activity in an adult?

About one day