L13. Obtaining Energy from Food

Question 1

direct burning in a nonliving system vs stepwise oxidation - direct burning

Answer 1

• large activation energy is overcome by the heat from a fire
• all the free energy is released as heat (none is stored)

Question 2

direct burning in a nonliving system vs stepwise oxidation - stepwise oxidation

Answer 2

• also cellular respiration
• small activation energies are overcome by enzymes that work at body temperature
• some of the free energy is stored in activated carrier molecules

Question 3

how are the activated carriers ATP and NADH are used

Answer 3

• the energy from food breakdown (oxidation and favorable) is transferred to ATP and NADH
• the energy from ATP is then coupled with ATP synthesis
• energy from other carriers drive oxidative phosphorylation

Question 4

what is oxidative phophorylation

Answer 4

• takes place in inner mitochondrial membrane
• it is when the cell uses energy from activated carriers to drive ATP production

Question 5

what are the three stages to breaking down food molecules

Answer 5

1. mouth, gut, and lysozymes
2. cytosol
3. mitochondria

Question 6

three stages to breaking down food molecules - mouth, gut, and lysozymes

Answer 6

large macromolecules are digested and converted into simple monomers via enzymes

Question 7

three stages to breaking down food molecules - cytosol

Answer 7

• glucose enters via glucose/Na+ symporter
• gradual oxidation breakdown of simple monomers via glycolysis
• glycolysis takes 1 glucose and converts it into 2 pyruvates
• also produces ATP and NADH

Question 8

three stages to breaking down food molecules - mitochondria

Answer 8

• pyruvate enters the mitochondria matrix and is converted into Acetyl CoA
• acetyl CoA then goes into the citric acid cycle and this makes a large amount of NADH
• electrons from NADH is passed to the electron transport chain
• this causes oxidative phosphorylation to begin, producing a large amount of ATP

Question 9

explain the location of the reactions for aerobic respiration

Answer 9

• glycolysis: cytosol
• citric acid cycle and oxidative phosphorylation: mitochondria

Question 10

three stages to breaking down food molecules: cytosol - explain ATP and NADH in glycolysis

Answer 10

• 2 ATP is required and produces 4 ATP with a net ATP of 2
• also produces 2 NADH

Question 11

three stages to breaking down food molecules: cytosol - glycolysis in absence of O2

Answer 11

products are ethanol or lactic acid fermentation

Question 12

three stages to breaking down food molecules: cytosol - glycolysis in presence of O2

Answer 12

pyruvate goes to mitochondria

Question 13

three stages to breaking down food molecules: cytosol - how does glycolysis initiate the breakdown of sugars

Answer 13

• the breakdown of glucose provides energy for ATP synthesis from ADP and Pi
• during ATP synthesis, substrate-level phosphorylation occurs
• NADH electron is then donated to the electron transport chain (for aerobic organisms)

Question 14

three stages to breaking down food molecules: cytosol - substrate level phosphorylation

Answer 14

Pi is transferred from substrate molecules (sugar intermediates) to ADP

Question 15

three stages to breaking down food molecules: cytosol - explain NAD+

Answer 15

• an intermediate in catabolic reactions that generate ATP through the oxidation of food molecules
• it is an oxidizing agent (takes e-)
• kept high in the cell

Question 16

three stages to breaking down food molecules: cytosol - NADPH

Answer 16

• operates with enzymes that catalyze anabolic pathways
• it is a reducing agent (gives e-)
• kept low in the cell

Question 17

three stages to breaking down food molecules: cytosol - anaerobic metabolism

Answer 17

• anaerobic organisms use glycolysis
• pyruvate and NADH remain in the cytosol
• after glycolysis, fermentation begins
• NADH will give up an electron to be turned into NAD+

Question 18

three stages to breaking down food molecules: cytosol - define fermentation

Answer 18

energy-yielding pathways that break down sugar in absence of O2

Question 19

three stages to breaking down food molecules: anaerobic metabolism - what does pyruvate convert to after fermentation

Answer 19

• muscle cells: lactate
• yeast: ethanol and CO2

Question 20

three stages to breaking down food molecules: cytosol - explain how reactions are coupled for glycolysis

Answer 20

• during step 6: an energetically favorable C-H bond is oxidized and it drives the unfavorable NADH synthesis and the formation of a high-energy phosphate bond
• during step 7: an energetically favorable hydrolysis of the phosphate bond drives ATP synthesis

Question 21

three stages to breaking down food molecules: cytosol - explain the ΔG° for ATP formation to be coupled

Answer 21

since the transfer of Pi is favorable, the ΔG° for hydrolysis of the phosphate bond must be more negative for the donor than the acceptor

Question 22

three stages to breaking down food molecules: cytosol - what is gluconeogenesis

Answer 22

• it makes glucose from pyruvate (opposite of glycolysis)
• it is costly and anabolic
• uses many of the same enzymes as glycolysis but uses specific enzymes to bypass the three irreversible steps in glycolysis

Question 23

three stages to breaking down food molecules: cytosol - example of an enzyme in gluconeogenesis

Answer 23

• phosphofructokinase
• it is allosterically regulated
• activated by ADP, AMP, and Pi
• and inhibited by ATP

Question 24

three stages to breaking down food molecules: mitochondria - explain the pyruvate dehydrogenase complex

Answer 24

converts pyruvate to acetyl CoA and CO2

Question 25

three stages to breaking down food molecules: mitochondria - explain how fatty acids are converted to acetyl CoA

Answer 25

• lipases cleave the bonds that link fatty acids to glycerol
• the fatty acids are then coupled to coenzyme A
• fatty acyl CoA is then oxidized in a four-enzyme cycle, generating one molecule of acetyl CoA and one each of NADH and FADH2

Question 26

three stages to breaking down food molecules: mitochondria - explain the citric acid cycle

Answer 26

• it does not use O2 but it requires it for the turnover of NADH to NAD+ (keeps electron transport chain running)
• it completely oxidizes carbon atoms from acetyl CoA to CO2

Question 27

three stages to breaking down food molecules: mitochondria - explain GTP and FADH

Answer 27

• produced from the citric acid cycle
• they are both activated carriers (donates electrons)
• they have high-energy electrons stored and it can be used to produce ATP via oxidative phosphorylation (the only step that directly requires O2)

Question 28

three stages to breaking down food molecules: mitochondria - explain the process of oxidative phosphorylation

Answer 28

• NADH and FADH2 transfers electrons to the electron transport chain via electron carriers embedded in the inner mitochondrial matrix
• in the chain, the energy released will be used to drive H+ efflux across the inner membrane
• this creates a gradient and will be used to ATP synthesis (ADP phosphorylation)
• electrons are added to O2 and it will be combined with H+ to generate H2O
• creates more ATP than glycolysis