Cell Respiration

Question 1

cell respiration

Answer 1

cells extract energy in food and transfer the energy to molecules of ATP

Question 2

equation for aerobic respiration of one molecules of glucose

Answer 2

C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O + ATP
(Glucose + oxygen) → (Carbon dioxide + water + energy)

highly exergonic process (releases energy)

Question 3

two types of cell respiration

Answer 3

anaerobic and aerobic
- if anaerobic, glycolysis is followed by alcoholic/lactic acid fermentation
- if aerobic, glycolysis is the first phase of respiration fllowed by citric acid cycle (Krebs), electron transport chain, oxidative phosphorylation

Question 4

reduction

Answer 4

gain of electrons (e-) or hydrogen (H+)

Question 5

oxidation

Answer 5

loss of electrons or protons

in equation, glucose is oxidized because it loses protons and electrons to oxygen (reduced)

Question 6

redox reaction

Answer 6

one substance is reduced while the other is oxidized

glucose is oxidized and oxygen is reduced

Question 7

ATP

Answer 7

consist of adenosine + 3 phosphates
- unstable molecule because 3 phosphates are negatively charged and repel each other
- when one phosphate group is removed by hydrolysis, a more stable (ADP) is formed
- changing from unstable to stable always relases energy

provides energy fo all cellular activities by transferring phosphates

Question 8

glycolysis

Answer 8

• 10 step process that breaks down 1 molecule of glucose (six carbon molecule) into 2 three carbon molecules of pyruvate or pyruvic acid, releases 4 molecules of ATP
• occurs in the cytoplasm
• releases ATP without oxygen
• each step catalyzed by different enzyme
• releases 1/4 of energy in glucose (most remains in pyruvate)
• end result (pyruvate) is raw material for the Krebs cycle (next step in aerobic respiration)

Equation: 2 ATP + Glucose → 2 Pyruvate + 4 ATP
net gain of 2 ATP

Question 9

How is ATP produced during glycolysis?

Answer 9

by substrate level phosphorylation (direct enzymatic transfer of phosphate to ADP releasing a small amount of ATP)

Question 10

phosphofructokinase (PFK)

Answer 10

• enzyme that catlyzes 3rd step of glycolysis
• allosteric enzyme
• inhibits glycolysis when cell contains enough ATP and acts as inhibitor

Question 11

structure of mirtochondrion

Answer 11

double membrane with outer compartment and matrix
Krebs cycle takes place in matrix, electron transport chain takes place in cristae membrane

Question 12

citric acid cycle

Answer 12

• one part out of the two parts in the aerobic phase of aerobic respiration
• cyclical series of enzyme-catalyzed reactions (aka Krebs cycle)
• takes place in matrix of mitochondria and requires pyruvate (product of glycolysis)
• completes oxidation of glucose to CO2
• turns twice for each glucose molecule that enters glycolysis, generates 1 ATP per turn by (substrate-level phosphorylation, the direct enzymatic transfer of phosphate to ADP)
• remainder of chemical energy trasnferred to NAD+ and FAD (NAD2 + H → NADH; FAD+ + 2H → FADH2)
• reduced coenzymes (NADH + FADH2) shuttle high-energy electrons into electron transport chain in cristae membrane
• 1st step, acetyl-CoA combines with oxaloacetic acid (OAA/oxaloacetate) to produce citric acid
• each molecule of glucose broken down into 2 molecules of pyruvate during glycolysis, meaning that the respiration of each glucose molecule causes cycle to turn 2 times
• before entering cycle, pyruvate must combine with coenzyme A (vitamin) to form acetyl-CoA (conversion produces 2 moelcules of NADH, 1 for each pyruvate)
• each turn in cycle releases 3 NADH, 1 ATP, 1 FADH, and CO2 (waste)
• ATP produced by substrate level phosphorylation (direct enzymatic transfer of phosphate to ADP, very little energy produced compared with amount produced by oxidative phosphorylation)

Question 13

NAD+ and FAD

Answer 13

required for normal cell respiration
- coenzymes that carry protons or electrons from glycolysis and citric acid cycle to electron trasnport chain
- enzyme NAD/FAD dehydrogenase faciliatates trasnfer of hydrogen atoms from substrate (eg. glucose) to coenzyme NAD+
- without NAD+ to accept protons/electrons from glycolysis/Krebs cycle, both processes would die
- vitamin derivatives

• NAD+ is oxidized form, NADre or NADH is reduced form, NADH carries 1 proton and 2 electrons
• FAD is oxidized form, FADre or FADH2 is reduced form

Question 14

electron transport chain (ETC)

Answer 14

-proton pump in mitochondria that couples an exergonic and endergonic reaction
- uses energy released from exergonic flow of electrons to pump protons against gradient from matrix to outer compartment
- proton gradient inside the mitochonrdrion
- ETC makes no ATP, but sets stage for ATP production during chemiososis

Question 15

important things about the ETC

Answer 15

• collection of molecules embedded in cristae membrane
• 1000s of copies of ETC in every mitochondrion because of extensive folding of cristae membrane
• ETC carries electrons delivered by NADH and FADH2 from glycolysis and Krebs cycle to oxygen, the final electron acceptor, through series of redox reactions
• highly electronegative oxygen pulls electrons through ETC
• NADH delivers electrons to higher energy levle in chain than FADH2, NADH provides more energy for ATP synthesis than FAD (NADH produces 3 ATP, FADH2 produces 2)
• mostly consists of cytochromes, proteins structurally similar to hemoglobin

Question 16

most of the energy relased during cell respiration occurs in the mitochondria by a process known as…

Answer 16

oxidative phosphorylation

Question 17

oxidative phosphorylation

Answer 17

• phosphorylation of ADP → ATP by oxidation of NADH and FADH2
• is an energy-coupling mechanism called chemiosmosis
• powered by redox reactions of ETC
• protons pumped from matrix to outer compartment against gradient by ETC
• proton gradient between outer compartment + matrix
• protons cannot diffuse through cristae membrane, and can only flow down into matrix through ATP synthase channels
• as protons flow through synthase channels, energy generated to phosphorylate ADP
• oxygen = final hydrogen acceptor, half an oxygen molecule + 2 electrons + 2 protons = water (waste product)

Question 18

chemiosmosis

Answer 18

uses potential energy stored in proton (H+) gradient to phosphorylate ADP

Question 19

ATP produced in two ways:

Answer 19

1. substrate level phosphorylation - when a kinase transfers phosphate from substrate directly to ADP (little ATP produced this way, the way energy produced during glycolysis + Krebs cycle)
2. oxidative phosphorylation - depends on chemiosmosis, producing 90% of the ATP in cell respiration

Question 20

Energy flow in respiration:

Answer 20

Glucose → NADre + FADre → ETC → chemiosmosis → ATP

Question 21

1 glucose can theoretically produce

Answer 21

36-38 ATP

(hypothetical besome cells are more efficient and cells vary in efficiency at different times)

Question 22

anaerobic respiration/fermentation

Answer 22

• from billions of years ago when there was no oxygen in atmosphere
• can generate ATP if there is enough NAD+ to accept electrons during glycolysis
• glycolysis would shut down if NADH can’t be converted back to NAD+

Question 23

2 types of anaerobes:

Answer 23

facultative (can tolerate oxygen but doesn’t use) and obligate (can’t live with oxygen)

Question 24

alcohol fermentation

Answer 24

• pyruvate from glycolysis converted into ethyl alcohol + carbon dioxide in absense of oxygen (oxidizing NADH back to NAD+)

Question 25

lactic acid fermentation

Answer 25

pyruvate from glycolysis reduced to form lactic acid/lactate (oxidizing NADH back to NAD+)