Chapter 13 & 14: How Cells Obtain Energy From Food

Question 1

Stages for the breakdown of food molecules?

Answer 1

3 stages

Question 2

Describe stage 1 of food breakdown

Answer 2

• breakdown of large food molecules to simple subunits (proteins to amino acids, polysaccharides to simple sugars, fats to fatty acids glycerol)

Question 3

Describe stage 2 of food breakdown

Answer 3

• breakdown of simple subunits to acetyl CoA
• limited amounts of ATP and NADH produced

Question 4

Describe stage 3 of food breakdown

Answer 4

• complete oxidation of the acetyl group in acetyl CoA to H2O and CO
• large amounts of ATP produced on the inner mitochondrial membrane

Question 5

Why do cells oxidize food in steps?

Answer 5

• activation energy smaller, and they can store energy in activated carriers (ATP, NADH)
• direct burning of sugar caues large activation energy overcome by the heat of fire, so all free energy released as heat(none stored)
• small activation energies overcome by enzymes that work at body temperature, some free energy stored in activated carriers

Question 6

Describe net result of oxidation of food molecules (redox rxn)

Answer 6

Food + O2 —-> ATP + NADH + CO2 + H2O

NADH activated carrier

Question 7

redox reaction

Answer 7

• process/reaction that involves transfer of electrons from one molecule to another
  -oxidation/reduction

Question 8

OIL RIG

Answer 8

• oxidation is loss of e-
• example: glucose oxidized in food molecules
• reduction is gain of e-
• example: NAD –> NADH

Question 9

Addition of electron

Answer 9

• often accompanied by addition of H+
• process called hydrogenation, so hydrogenation = reduction reaction

Question 10

Dehydrogenation

Answer 10

• these reactions or oxidation reactions, loss of e- and H+
• energy released

Question 11

Glucose food example: step 1

Answer 11

• aerobic respiration
• C6H12O6 +6O2 —> 6CO2 + 6H2O
• glucose and oxygen creates energy (heat and chemical)
• redox reaction: glucose oxidized, oxygen reduced (to water

Question 12

Glucose food example: step 2

Answer 12

• glycolysis
• occurs in cytoplasm
• anaerobic(no oxygen required)
• makes small amounts of energy
• net result: glucose —> 2 pyruvate + 2 ATP + 2 NADH

redox reactions, so taking up electrons and a proton at same time (NAD+ –> NADH)

Question 13

Fermentation

Answer 13

• NAD+ reformed when fermentation happens here
• instead of creating pyruvate, it creates lactate

Question 14

Mitochondria

Answer 14

• dynamic in structure, location, and number
• contains an outer membrane, intermembrane space, inner membrane, and two internal compartments
• large internal space called the matrix
• citric acid cycle within the matrix with NADH

Question 15

What is the origin of mitochondria?

Answer 15

• endosymbiosis
• prokaryote engulfed by endocytosis by anerobic eukaryotic cell
• one organism (endosymbiont) living inside of cell of another organism (host) for their mutual benefit

Question 16

Glucose example (final) Step 3

Answer 16

• citric acid cycle
• electron transport

Question 17

Citric acid cycle

Answer 17

• NADH carries electrons that are stripped off
• one turn of the cycle produces 3 NADH, 1 GTP, and 1 FADH2
• releases two molecules of CO2
• uses lots of carbon in order for all 8 steps to happen

Question 18

Electron transport chain

Answer 18

• high energy electrons are carried by NADH
• high energy since thare held weakly, making them reactive
• high energy electrons donated to electron transport chain complexes in the mitochondrial inner membrane
• NADH oxidized back to NAD+
• electrons held tigher and tighter down chain
• final electron acceptor O2 when O2 is reduced to H2O
• now electrons are lowest energy state
• they are held tightly by the O2

Question 19

How does NADH transfer electrons to oxygen?

Answer 19

• Through three large enzyme complexes embedded in the inner membrane

Question 20

Three large enzyme complex process to transfer electrons to oxygen from NADH explained

Answer 20

-High-energy electrons are transferred through three respiratory enzyme complexes in the inner mitochondrial membrane.
- During the transfer of electrons from NADH to oxygen, protons derived from water are pumped across the membrane from the matrix into the intermembrane space by each of the complexes
- Ubiquinone (Q) and cytochrome c (c) serve as mobile carriers that ferry electrons from one complex to the next.
- The three respiratory enzyme complexes associate to form a supercomplex that is thought to facilitate the passage of electrons.

Question 21

What can iron in a heme group provide?

Answer 21

• can serve as an electron acceptor within three complexes of the electron transport chain
• iron-sulfur centers also can carry electrons

Question 22

Chemiosmosis

Answer 22

• accumulation of protons in the intermembrane spaces drives protons into the matrix via diffusion
• membrane relatively impermeable to ions
• most protons can only reenter matrix through ATP synthase(uses energy of gradient to make ATP from ADP and Pi

most cells obtain most energy by membrane-based mechanism(s), like mitochondria and chloroplasts

Question 23

Describe how ATP synthase uses energy stored in electrochemical proton gradient to produce ATP

Answer 23

• ATP synthase converts mechanical energy (rotation of stalk) to chemical bond energy
• ADP +Pi –> ATP
• central stalk spins rapidly by electrochemical proton gradient
• when stalk not fully connected, can produce reverse reaction
• example of chemiosmosis

Question 24

What is uncoupling?

Answer 24

• electron transport can be uncoupled from ATP synthesis
• has H+ going out.in, O2 coverting to H2O in end
• electron transport will run at max capacity to reestablish H+ gradient

Question 25

uncoupling proteins (UCPs)

Answer 25

• made in brown fat-energy lost as heat
• put holes in inner membrane, so H+ proton gradient is lost
• so no ATP made

Question 26

Describe why mitochondria maintains a high ATP to ADP ratio in cells

Answer 26

• carrier protein in the inner mitochondrial membrane exchanges ATP for ADP
• molecules produced by ATP hydrolysis in the cytosol rapidly entemjtochondria for recharging
• ATP molecules formed in mito matrix by oxidative phosphorylation are rapidly pumped into the cytosol where they are needed
• ATP drives energetically unfavorable reactions, like a battery for an engine; if battery/mito blocked, ATP levels fall and battery runs down
• can cause cell to do die

Question 27

Mitochondrial disease

Answer 27

• mitchondrial defect is primary cause
• defect in mito encoded genes
• maternally inherited
• defects in respiration in high respiring tissues, skeletal muscle, neurons

Question 28

Mitochondira involved in Neurodegenerative diseases

Answer 28

• mitochondrial dysfunction secondary to disease process
• alzheimer’s
  -parkinson’s
• huntington’s
  multiple sclerosis

can be nuclear encoded mito genes or increases ROS

Question 29

How can Mitochondrial Respiration be measured?

Answer 29

Respirometry- O2 consumption inhibitors of the electron transport chain

roteonone and oligomycin

Question 30

Respiratory control

Answer 30

• electrochemical proton gradient inhibits rate of electron transport
• uncoupler can collapse the proton gradient, electron transport is free to run unchecked at the maximal rate
• this increases the proton gradient, which inhibits electron transport