Topic 5

Question 1

Aerobic Respiration

Answer 1

C6H12O6 + 6O2 –> 6CO2 + 6H2O + “Energy”

-aerobic respiration is a combustion reaction
-glucose is burned in oxygen to produce CO2 and H20, with the release of heat
-a series of coupled redox reactions that release the free energy of glucose
-transfers some of the released energy to other molecules

Question 2

Coupled Redox Reactions

Answer 2

-Non-polar covalent (C-C, C-H, Oxygen-Oxygen double bonds ) in the reactants are broken

-Polar covalent (Carbon-Oxygen double bonds, O-H) bonds in the products are formed

-Bonding electrons shared equally between the carbon atoms in glucose have moved farther away from the C nuclei in CO2, so glucose becomes oxidized

-Bonding electrons shared equally between the oxygen atoms in O2 have moved closer to the O nuclei in H2O, so oxygen becomes reduced

Question 3

Electron Carrier (Redox) Coenzymes

Answer 3

-Biological redox reactions generate reduction potential that is stored in electron carriers:

NAD+ + 2e- + 2H+ –> NADH + H+
NADP+ + 2e- + 2H+ –> NADPH + H+
FAD + 2e- + 2H+ –> FADH2

-Reduced electron carriers are energy transport molecules that move e- from one reaction to another

Question 4

Glycolysis: Overview

Answer 4

-partial oxidation of glucose

-10 connected reaction steps (some coupled)

-each step has its own enzyme

Question 5

Glycolysis: Simplified

Answer 5

What goes in :

Glucose (6 carbon)
-2 ATP
-4 ADP
-2 NAD+

What comes out :

-2 ADP
- 4 ATP
-2 NADH
2 Pyruvate (3 carbon)

Question 6

Electron Carriers in Glycolysis…

Answer 6

-are reduced

Question 7

What ATP is Generated By

Answer 7

Substrate-level phosphorylation

-an enzyme takes a PO4 from an organic molecule and adds it to ADP

Question 8

Glycolysis as Partial Glucose Oxidation

Answer 8

1. Not much ATP has been made
   - most Ep from glucose is in product molecule, pyruvate
2. The cell needs to remove pyruvate
   -to prevent equilibrium
3. We need to restore NAD+
   -too expensive to produce NAD+
   -much easier to oxidize the NADH

Question 9

Oxygen in Glycolysis

Answer 9

In eukaryotic and prokaryotic organisms, there is a checkpoint following glycolysis

-if oxygen is limiting; pyruvate is reduced
-if oxygen is present; pyruvate is oxidized

Question 10

Fermentation

Answer 10

• the anaerobic reduction of pyruvate

-if O2 is limiting, cells reduce pyruvate with NADH

Question 11

Lactate

Answer 11

-easier to get rid of than pyruvate

Question 12

Ethanol

Answer 12

-also easier to get rid of

Question 13

Where Oxidation Occurs in Eukaryotes

Answer 13

-in the mitochondrion

if there is O2, we will oxidize the pyruvate

Question 14

Layers of The Mitochondrion

Answer 14

1. cytosol
2. outer mitochondrial membrane
3. inter membrane space
4. inner mitochondrial membrane (e- transfer, ATP synthesis)
5. matrix (pyruvate oxidation and citric acid cycle)

Question 15

Pyruvate Oxidation (Bridge Reaction)

Answer 15

-Pyruvate is oxidized to Acetyl-CoA in the matrix

Pyruvate
CO2 (through decarboxylation)
NAD+ –> NADH
COA–> Acetyl CoA

Question 16

Citric Acid (Krebs) Cycle: Overview

Answer 16

-completes the oxidation of glucose

-8 connected (some coupled) reactions

• each step requires a unique enzyme

Question 17

Citric Acid Cycle- Other Products

Answer 17

• amino acids
  -lipids
  -nucleic acids

All feed into metabolic pathways

Question 18

Electron Transport System

Answer 18

• electrons move spontaneously down a potential energy gradient from one complex to the next
• the release of energy is used to pump protons into the inter membrane space

Question 19

Protein Complexes of the Electron Transport Chain (ETC)

Answer 19

Peripheral Complex : complex 2

Integral Complexes: complex 1, 3, and 4

Question 20

Redox Driven Electron Flow

Answer 20

• e- flow toward increasingly electronegative prosthetic groups
• each time an e- transfer occurs, energy is given off to “do work”

-O2 is the final electron acceptor and is reduced to H2O

-all Ep turns to Ek

• e- move closer to a nucleus as they move down the chain

Question 21

ETC Proton Pump

Answer 21

-H+ are moved from the matrix to the inter membrane space

Question 22

Complexes 1 and 2

Answer 22

1. NADH in matrix donates e- to only complex 1
2. H+ are pumped from the matrix to inter membrane space by complex 1
3. FADH2 in matrix donates e- to only complex 2

-Complex 2 does not directly pump H+ across the membrane

Question 23

Ubiquinone (UQ) -a Hydrophobic Electron Taxi

Answer 23

-doesn’t exist in matrix of inter membrane, but in hydrophobic tails

1. UQ taxis e- from complex 1 to complex 3
2. UQ taxis e- from complex 2 to complex 3
3. When reduced, UQ takes H+ from the matrix

-when oxidized, UQ releases the H+ into the inter membrane system

Question 24

Complex 3, Cytochrome c, and Complex 4

Answer 24

1. e- flow from complex 3 to cytochrome c
2. cytochrome c is a hydrophilic e- taxi that moves e- to complex 4
3. e- flow through complex 4
   -the energy released is used to pump H+ from the matrix to inter membrane space
4. complex 4 donates e- to O2, which is reduced to H2O

Question 25

Electrochemical Gradient in The Electron Transport Chain

Answer 25

-H+ is lowered in the matrix when they are: 1. pumped or moved from matrix by complex 1, UQ, or complex 2 2. used to reduce O2 to H2O -The H+ electrochemical gradient is called: Proton Motive Force (PMF) - is a ratio of H+ across the inner mitochondrial membrane

Question 26

PMF Used for Chemiosmois

Answer 26

1. the PMF is used to power ATP synthsase 2. as H+ are allowed to flow down their concentration gradient, energy is used to add Pi to ADP -mechanical energy is generated

Question 27

Chemiosmosis

Answer 27

-ATP synthase catalyzes ATP synthesis using energy from the H+ gradient across the membrane

Question 28

ATP Synthase

Answer 28

Fo = proton channel F1= catalytic enzyme ADP + Pi ----> ATP 3H+ out ------> 3H+ in (highly endergonic process) (negative overall free energy)

Question 29

ATP Yields

Answer 29

-Total ATP made in aerobic respiration = about 32-38 ATP -not all our NADH/FADH2 goes to the electron transport chain -proton motor force is used more for chemiosmosis

Question 30

Metabolic Integration

Answer 30

If you don't need ATP: -glucose can be stored as a polymer (glucogen- animals or starch- plants) -triglycerides can be generated for even longer-term storage (acetyl- coA can be polymerized into fatty acids) -if you need ATP, these processes can be reversed

Question 31

Chemoorganoheterotroph

Answer 31

-Organisms need carbon for macromolecules (amino acids + nucleic acids + lipids) -Acetyl-CoA can be used to generate these macromolecules instead of going through the Krebs cycle

Question 32

Aerobic Respiration- Prokaryotes

Answer 32

-Prokaryotic organisms do not have membrane-bound organelles (no mitochondria) -All metabolism occurs in the cytosol and on the cell membrane -Otherwise it is "the same"

Question 33

What Occurs in The Cytosol

Answer 33

-pyruvate oxidation -krebs cycle -pyruvate reduction (fermentation) -Chemiosmosis

Question 34

Anaerobic Respiration

Answer 34

-only known to occur in prokaryotes -evolved at a time when oxygen was not abundant in the atmosphere -likely before aerobic respiration -uses final electron acceptors other than O2 (SO42-, NO3-) -otherwise it is "the same" -glycolysis, pyruvate oxidation, Krebs, NADH/FADH2 donate e- to ETC

Question 35

Chemolithotrophy

Answer 35

-only known to occur in prokaryotes -evolved in environments where organic molecules were not abundant -uses primary (initial) electron donors other than NADH or FADH2, but will use inorganic e- donors: SH2, Fe3+, H2, NH3 -does not require pyruvate oxidation or Krebs cycle -does require ETC and oxidative phosphorylation