Chapter 6: Cellular Respiration

Question 1

ATP

Answer 1

Adesonine Triphosphate - an energy-toting molecule, essential for nearly every activity that requires energy input in the cell. Creation of ATP falls into three categories - aerobic respiration, fermentation, and anaerobic respiration

Question 2

Photosynthesis

Answer 2

Carbon Dioxide + water = glucose (energy for reaction supplied by light)

Question 3

Aerobic respiration

Answer 3

A cell uses Oxygen gas and glucose to generate ATP. The equation for this is essentially the reverse of photosynthesis : Glucose + oxygen –> carbon dioxide + water + 36 ATP. *acquires O2 (oxygen) and gets rid of CO2 (carbon dioxide)

Question 4

formation of ATP

Answer 4

an enzyme tacks a phosphate group onto ADP, yielding ATP

Question 5

Respiration 1

Answer 5

• an redox (oxidation - reduction reaction)
• pathways of aerobic respiration OXIDIZE (remove electrons from) GLUCOSE and REDUCE (add electrons to) OXYGEN. This reaction RELEASES ENERGY, and is the energy needed to form ATP

Question 6

Why does respiration happen in a series of small steps, as opposed to all at once?

Answer 6

If a cell released all the potential energy in glucose’s chemical bonds in one uncontrolled step, the sudden release of heat would destroy the cell! Instead, the chemical bonds and atoms in glucose are rearranged one step at a time, releasing a tiny bit of energy with each transformation. *some energy is released as heat, but most of it is stored in ATP

Question 7

Respiration 2

Answer 7

broken down into 3 steps: 1) glycolysis 2) Krebs cycle 3) electron transport

Question 8

Step # 1) Glycolysis basics

Answer 8

• (literally means “breaking sugar”)
• a 6 carbon glucose molecule splits into two 3-carbon molecules of pyruvate.
• Harvests energy in 2 forms:
  1) some electrons from glucose are transferred to electron carrier molecule NADH
  2) glycolysis generates 2 molecules at ATP
• always occurs in CYTOSOL, both procaryotes and eucaryotes

Question 9

NADH

Answer 9

electron carrier molecule - Nicotinamide adenine dinucleotide

Question 10

Step # 2) Krebs Cycle basics

Answer 10

• pyruvate is OXIDIZED
• oxygen is RELEASED
• Enzymes rearranged atoms and molecules, transferring pyruvate’s potential energy and electrons to ATP, NADH, and FADH2
• at the end of the Krebs cycle, carbon atoms that made up glucose are gone, liberated at CO2
• a few ATP molecules are formed, but most still lie in the high energy electron carriers NADH and FADH2
• happens in cell membrane in procaryotes and mitochondria in eucaryotes

Question 11

FADH2

Answer 11

Calvin adenine dinucleotide

Question 12

H+

Answer 12

H+ is a hydrogen atom stripped of its electrons, leaving just a proton

Question 13

Step # 3) Electron Transport Chain (Phase)

ETP basics

Answer 13

• transfers electrons from NADH and FADH2 through membrane proteins
• as electrons pass through the electron transport chain, energy is used to CREATE A GRADIENT OF HYDROGEN IONS (therefore a PROTON GRADIENT)
• mitochondrian uses potential energy in the proton gradient to generate ATP

Question 14

ATP synthase

Answer 14

• enzyme that forms a channel in the membrane during electron transport phase, releasing protons and using energy to add phosphate to ADP, creating ATP.
• “spent” electrons are transferred to O2, generating WATER AS A WASTE PRODUCT

Question 15

Respiration 3

Answer 15

All forms of respiration, anaerobic and aerobic, use an electron transport chain

Question 16

Respiration in Eucaryotes

Answer 16

• begins in cytosol

- ends in mitochondria

Question 17

Respiration in Procaryotes

Answer 17

• begins in cytosol

- ends in cell membrane

Question 18

Mitochondria

Answer 18

• bound by 2 membranes, OUTER MEMBRANE and INNER MEMBRANE
• inner membrane that is tightly folded is the CRISTAE
• area between the inner and outer membranes is the INTERMEMBRANE COMPARTMENT
• The fluid enclosed within the inner membrane is the MATRIX
• mitochondria creates most of the ATP in Krebs and ETP

Question 19

Krebs cycle in the mitochondria

Answer 19

• the two pyruvate molecules (produced in glycolysis) cross the two mitochondrial membranes and move INTO the MATRIX
• enzymes cleave pyruvate and carry out Krebs cycle

Question 20

ETP in mitochondria

Answer 20

• FADH and NAHD2 from glycolysis and the Krebs cycle move into the inner membrane

Question 21

Glycolysis 1

Answer 21

• requires 10 steps, broken down into 2 stages: “energy investment” and “energy harvest”.
• overall, breaks down glucose into two 3-carbon pyruvate molecules.
• all occurs in the cytosol of the cell
• this step does NOT REQUIRE OXYGEN, so can occur in aerobic and anaerobic environments.
• Energy investment step: cell “spends” TWO ATP molecules to ACTIVATE glucose, splitting it in half
• energy harvest step: cell generates a return on its “investment”, producing 2 molecules of NADH and 4 molecules of ATP.
• **NET GAIN OF GLYCOLYSIS IS 2 NADHs AND 2 ATP PER MOLECULE OF GLUCOSE

Question 22

Substrate-level phosphorylation

Answer 22

When an enzyme transfers a phosphate group directly from a high energy “donor” molecule to ATP. This method of producing ATP does NOT require a proton gradient or the ATP synthase enzyme.

Question 23

Krebs cycle 1

Answer 23

• right before Krebs, a transition step further oxidizes each pyruvate molecule by removing a molecule of CO2, and NAD+ is REDUCED to NADH.
• remaining 2-carbon molecule is transferred to a coenzyme to form acetyl coenzyme A (Acetyl CoA). THIS is the compound that enters the Krebs cycle.

Question 24

Krebs cycle 2

Answer 24

-completes oxidation of each Acetyl group, RELEASING CO2 (Acetyl CoA sheds coenzyme, and combines with 4-carbon molecule). Resulting 6-carbon molecule is CITRATE. remaining steps REARRANGE and OXIDIZE citrate

Question 25

Krebs cycle 3

Answer 25

• 2 carbon atoms are released
• some transformations transfer electrons to NADH and FADH2
• others produce ATP by substrate-level phosphorylation
• 1 glucose molecule yields 2 acetyl CoA molecules

Question 26

Krebs cycle 4

Answer 26

• net output at this point in respiration is:
  4 ATP molecules
  10 NADH molecules
  2 FADH2 molecules
  all 6 carbon atoms are gone, released as CO2
• generates: ATP, CO2, NADH, and FADH2

Question 27

Electron Transport Chain 1

Answer 27

• cell ejects CO2 as waste and uses ATP to fuel processes
• NADH and FADH2 transfer their cargo to an electron transport chain in the inner mitochondrial membrane
• electron transport chain uses energy from NADH and FADH2 to establish a PROTON GRADIENT across the inner mitochondrial membrane. (gradient represents a form of potential energy)
• Mitochondrion harvests this potential energy as ATP, using the ATP synthase enzyme
• ATP synthase enzyme captures potential energy of proton gradient and saves it as ATP

Question 28

Chemiosmotic Phosphorylation

Answer 28

Protons move down their gradient through ATP synthase back into the matrix, and ADP is phosphorylated to ATP.

Question 29

breakdown of ATP, NADH, FADH2 yield:

Answer 29

• Glycolysis: 2 ATP
• Krebs: 2 ATP (1 ATP each from each of the two turns of the cycle - two turns, one for each glucose molecule). 6 NADH, 2 FADH2
• Electron transport: *should yield: 3 ATP’s PER NADH and 2 ATP’s PER FADH2
• Electrons from the 10 NADH’s from glycolysis, transition step, and Krebs yield up to 30 ATPs.
• Electrons from 2 FADH2 molecules yield 4 MORE
• ADD: 4 ATP from glycolysis + 2 ATP from Krebs + 30 from Electron transport = 36 ATP
  ACTUAL ATP yield is about 30 Per Glucose
• The rest of the potential energy is lost as HEAT in the reaction process

Question 30

Poisons that inhibit respiration:

Answer 30

• arsenic
• mercury
• cyanide
• carbon monoxide
• insecticide 2, 4-dinitrophenol (DNP)
• Oligomycin