How Cell Obtain Energy from Food

Question 1

Why would cell need to carry out the oxidation of sugar in a stepwise manner?

Answer 1

To prevent a large amount of energy from being released all at once

Question 2

What are the three stages of catabolism?

Answer 2

1. Digestion
2. Glycolysis
3. Citric Acid Cycle and Oxidative Phosphorylation

Question 3

What happens in digestion?

Answer 3

Enzymes convert the large polymeric molecules in food into simpler monomeric subunits, outside of the cell, inside the intestine

Question 4

What happens in glycolysis?

Answer 4

Each molecule of glucose is split into two molecules of pyruvate.

Question 5

Where does glycolysis occur?

Answer 5

Cytosol

Question 6

What does glycolysis yield?

Answer 6

• 2 NADH per glucose
• 2 ATP
  -2 Pyruvate per glucose

Question 7

How does glycolysis work?

Answer 7

1. Glucose is phosphorylated with ATP by hexokinase to form a new sugar (glucose 6-phosphate).
2. Glucose will rearrange itself into fructose and is phosphorylated with ATP again with phosphofructokinase. At this point, glucose has two phosphate group
3. The sugar is cleaved into two 3-carbon molecule (only the glycerldehyde 3-phosphate will proceed)

4.The aldehyde will oxidize to a carboxylic acid, releasing energy which some is stored in NADH and some is used to convert ADP to ATP. At this point, the sugar only has one phosphate group.

5.The remaining sugar is catalyzed by pyruvate kinase by extracting a phosphate group, forming ATP and pyruvate

Question 8

What happens to pyruvate under anaerobic condition?

Answer 8

Under anaerobic condition, the pyruvate is converted into products through fermentation that are excreted into the cell:

• lactase in muscle cell or
• ethanol and CO2 in yeast cell

Question 9

What is fermentation?

Answer 9

Energy-yielding pathways that break down sugar in the absence of oxygen

• Pyruvate breaks down to lactase in muscle cell
• Pyruvate breaks down to CO2 and ethanol in yeast cell

Question 10

What happens to pyruvate under aerobic condition?

Answer 10

The pyruvate is pumped into the mitochondrial matrix where it is oxidized by the pyruvate dehydrogenase complex into acetyl CoA, CO2, and NADH.

Question 11

What oxidizes pyruvate in aerobic condition?

Answer 11

pyruvate dehydrogenase complex

Question 12

Where does pyruvate dehydrogenase complex oxidizes pyruvate?

Answer 12

Mitochondria

Question 13

What does pyruvate dehydrogenase complex produce from oxidizing pyruvate?

Answer 13

acetyl CoA and CO2

Question 14

What is a pyruvate dehydrogenase complex

Answer 14

a large 3-enzyme complex that oxidize pyruvate into CO2 and acetyl CoA

Question 15

Besides the pyruvate dehydrogenase complex, how else are acetyl CoA formed?

Answer 15

Fatty acids and amino acids in the mitochondria

Question 16

What does fatty acid breakdown yield?

Answer 16

1 Acetyl CoA
2 NADH
1 FADH2

Question 17

If oxygen is not used in the kreb cycle, why is oxygen still needed?

Answer 17

Oxygen is the final electron acceptor, which allow for oxidative phosphorylation. Oxygen accepts electron which allows electron to be passed on, maintaining the hydrogen pumping that produces ATP.

Question 18

What is an activated carrier?

Answer 18

Small organic molecules that contain one or more energy-rich covalent bonds. In a cell setting, cells used activated carrier to carry out unfavorable reaction.

Question 19

How does GTP convert to ATP?

Answer 19

Nucleoside diphosphokinase

Question 20

What is the citric acid cycle?

Answer 20

a chain of reactions occurring in the mitochondria, through which almost all living cells produce energy in aerobic respiration.

Question 21

What happens in the citric acid cycle?

Answer 21

1. Citrate Synthase
   - Two carbons from acetyl CoA to oxaloacetate to form citrate.
2. Release of Carbon Dioxide
   - Two molecules of CO2 are released; acetyl CoA oxidized into CO2
3. Malate Dehydrogenase; Oxaloacetate is regenerated
   - Malate molecule is oxidized into oxaloacetate and the produced oxaloacete will enter into the next cycle with the next acetyl coA

Question 22

What does the citric acid cycle yield?

Answer 22

-1 GTP
-1 FADH2
-3 NADH

Question 23

What is oxidative phosphorylation?

Answer 23

chemical energy captured by the activated carriers produced during glycolysis and the citric acid cycle is used to generate ATP

Question 24

What is oxidative phosphorylation?

Answer 24

chemical energy captured by the activated carriers produced during glycolysis and the citric acid cycle is used to generate ATP

Question 25

What happens in oxidative phosphorylation?

Answer 25

NADH and FADH2 transfer their high-energy electrons to the electron transport chain, creating a proton gradients that used to generate ATP by ATP synthase

Question 26

What is the electron transport chain in the mitochondria?

Answer 26

A series of electron carrier embedded in the inner mitochondria membrane in eukaryotic cells

Question 27

What happens after NADH and FADH2 transfer their high-energy electron to the ETC?

Answer 27

The electrons pass through a series of electron acceptor and donors that form the chain. With each pass, the electrons’s energy lowers and the energy released is used to drive protons (H+) across the inner membrane from the mitochondria matrix to the intermembrane space. At the end of the ETC, the electrons are added to a molecule of O2, with hydrogen to produce water. This completes the kreb cycle and all the energy are extracted from the oxidized food molecule.

Question 28

What drives oxidative phosphorylation

Answer 28

The electron transport chain