Metabolism: why do we need to eat and breathe?

Question 1

metabolism

Answer 1

the totality of an organism’s chemical reactions

Question 2

why do we need to eat?

Answer 2

• our cells require a constant supply of energy to support metabolism
  
  • this energy comes from the chemical bonds of food molecules
  • most important fuels are sugars and fats

Question 3

autotrophs

Answer 3

organisms that can create fuel molecules such as glucose from CO2 and H2O e.g. grass, trees

Question 4

heterotrophs

Answer 4

organisms that DO NOT create fuel molecules but obtain energy from external chemical fuels - dependent on autotrophs e.g. animals

Question 5

catabolism

Answer 5

metabolic pathways that release energy by breaking down complex molecules to simpler compounds (building blocks)

Question 6

anabolism

Answer 6

metabolic pathways that use energy to build complex molecules from the building blocks

Question 7

aerobic respiration

Answer 7

1. in both animals and plants, sugar molecules (C6H12O6) are broken down in many small steps (by enzymes) and oxidized with the help of oxygen
2. carbon dioxide and water are released as final products
3. energy is trapped
   - the energy released is captured in the form of “high-energy” chemical bonds in carriers such as ATP and NADH FADH2
   - these carriers in turn serve as portable sources of the energy and electrons needed for the synthesis of all molecules that form a cell

Question 8

electron carriers: NADH and FADH2

Answer 8

the oxidation of sugar molecules leads to the extraction of electrons, which are transferred to electron carriers

Question 9

oxidation

Answer 9

removal of electrons

Question 10

reduction

Answer 10

gain of electrons

Question 11

4 stages of food breakdown

Answer 11

1. breakdown of glucose to pyruvate (glycolysis in cytosol)
2. breakdown of pyruvate to acetyl CoA (in mitochondria)
3. complete breakdown (oxidation) or acetyl CoA to CO2 and H2O (in mitochondria)
4. oxidative phosphorylation and ATP synthesis (in mitochondria)

Question 12

glycolysis

Answer 12

a chain of reactions that splits glucose (6C) into two molecules of pyruvate (3C)

• in the cytosol
• produces 2 types of carriers - ATP and NADH
• 10 separate reactions, catalyzed by 10 different enzymes
• releases a small amount of the available chemical energy contained in glucose
• most of the energy remains stockpiled in the 2 molecules of pyruvate

Question 13

oxidation of pyruvate to acetyl CoA

Answer 13

pyruvate is transported into mitochondria and then oxidized, producing CO2, NADH and acetyl CoA

Question 14

the citric acid cycle

Answer 14

acetyl CoA (2C) enters the 8-steps of CAC in the mitochondrial matrix; it accounts for about 2/3 of the total oxidation of carbon compounds, producing NADH, FADH2, GTP, CO2 (waste product)

Question 15

oxidative phosphorylation

Answer 15

1. transfer of high-energy electron (sourced by NADH and FADH2) along an electron transport chain until a final acceptor (O2)
   
   1. creation of a H+ gradient over the inner mitochondrial membrane (between matrix and intermembrane space)
2. chemiosmosis
   
   1. backflow of protons (H+) down their electrochemical gradient through a protein complex - ATP synthase → synthesis of ATP
      
      • electrons are transferred from NADH and FADH, (INITIAL DONORS) to 0, (FINAL ACCEPTOR - this is why we need oxygen!) along the electron transport chain
      • the electron transport chain does not generate ATP directly!
        - instead, it creates a proton-motive force (gradient of protons H+)
        - H+ then flows back across the inner membrane through the ATP synthase → phosphorylation of ATP

Question 16

fermentation

Answer 16

for some anaerobic organisms, glycolysis is the main source of ATP; pyruvate is then converted by fermentation into simpler organic compounds, to regenerate NAD+

Question 17

ATP/GTP and NADH

Answer 17

the energy contained in the ATP/GTP molecule can be immediately spent; the energy contained in an NADH molecule will be used to regenerate ATP from ADP in stage 4

Question 18

chemical equation of aerobic respiration

Answer 18

glucose + oxygen > carbon dioxide + water + ATP