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Metabolism of the Cell

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Title: Metabolism of the Cell


1
Metabolism of the Cell
  • Energy Production

2
Metabolism
  • Refers to all chemical reactions necessary to
    maintain life.
  • Anabolic processes (anabolism) build from smaller
    molecules
  • for example, building of proteins from amino
    acids
  • anabolic processes generally require energy input
  • Catabolic processes (catabolism) break down
    larger molecules into smaller ones.
  • for example, breakdown of glucose into carbon
    dioxide and water
  • catabolic processes generally release energy

3
Cellular Respiration
  • Describes the series of reactions that break down
    glucose to release ATP.
  • Includes glycolysis, Krebs cycle, and oxidative
    phosphorylation within the electron transport
    system.

4
Major Stages of Metabolism
  • I. Glycolysis
  • II. Krebs Cycle (a.k.a., tricarboxylic acid
    cycle, TCA cycle, citric acid cycle)
  • III. Oxidative Phosphorylation
  • Electron Transport System and Chemiosmosis
  • Digestion, the breakdown of food into usable
    molecules such as glucose, is required before
    metabolism can occur

5
Metabolism Terms
  • ATP Adenosine triphosphate - simplest storage
    form of cellular energy
  • Glucose main substrate for ATP production a
    monosaccharide (simple sugar).
  • NAD coenzyme that accepts hydrogen derived
    from niacin
  • NADH (more accurately NADHH) reduced form of
    the coenzyme includes two additional electrons
    and one hydrogen.
  • FAD another coenzyme that accepts hydrogen
    derived from riboflavin.
  • FADH2 reduced form including two hydrogens and
    their electrons

6
Metabolism Terms(cont.)
  • Oxidation - reactions within cellular respiration
    that occurs due to a loss of electrons (usually
    seen as hydrogen) or a gain in oxygen.
  • Oxidation-reduction (redox) reactions coupled
    reactions in which one substance donates (loses)
    electrons (i.e., is oxidized) and another then
    gains those electrons (i.e., is reduced).
  • Reduction reaction in which a substrate gains
    electrons (usually seen as hydrogen)

7
Metabolism Terms(cont.)
  • Phosphorylation addition of phosphate group to
    a molecule resulting in addition of energy to the
    molecule e.g., ADP Pi ?ATP
  • substrate-level phosphorylation direct transfer
    from one molecule to another
  • e.g., bisphophoglycerate ADP ? ATP
    phosphoglycerate
  • moves phosphate from bisphosphoglycerate (which
    has 2 phosphates) to ADP to make ATP and
    phosphoglycerate (which has one phosphate)
  • oxidative phosphorylation more complex method
    of ATP production involving electron transport
    chain (series of redox reactions)

8
Glycolysis
9
Glycolysis
  • Breakdown of glucose into pyruvic acid
  • Glucose comes from the food that we eat
  • Occurs in the cytoplasm of the cells
  • Results in a net production of 2 ATP and 2
    reduced electron carriers (NADH)

10
Glycolysis - Overview
  • 3 Phases
  • sugar activation
  • sugar cleavage
  • sugar oxidation and formation of ATP

Fig. 25.6, p. 966
11
Phase 1 Sugar Activation
  • Glucose (6-carbon) gains phosphate (and energy)
    from each of two (2) ATP molecules and becomes an
    unstable 6-carbon molecule (fructose-1,6-diphospha
    te)
  • Adenosine triphosphate (ATP) becomes adenosine
    diphosphate (ADP)

Fig. 25.6, p. 966
12
Phase Two Sugar Cleavage
DHAP
G3P
  • Unstable 6-carbon molecule, (fructose-1,6-diphosph
    ate), is broken into 2 3-carbon molecules (DHAP
    and G3P)
  • no additional energy required

Fig. 25.6, p. 966
13
Phase Three Sugar Oxidation
  • 2 3-carbon molecules (DHAP and G3P) are each
    oxidized resulting in release of energy used to
    make 4 ATP (2 from each) and formation of 2
    pyruvate (1 from each)
  • ATP produced by substrate-level phosphorylation

Fig. 25.6, p. 966
14
Phase Three Sugar Oxidation (cont)
  • oxidation of these 2 3-carbon molecules (DHAP and
    G3P) also results in formation of 2 molecules of
    NADH (one from each 3-carbon molecule), the
    energy from which will be used in the
    mitochondria during oxidative phosphorylation
  • when oxygen is present, pyruvate diffuses into
    the mitochondria for the next steps of cellular
    respiration
  • when oxygen is not present, pyruvate is reduced
    using the NADH and becomes lactic acid

15
Glycolysis Energy Summary
  • Net ATP production 2
  • 4 produced 2 used
  • two (2) ATP are utilized in phase 1, so 2 are
    subtracted from the total produced
  • 2 NADH produced total (one per G3P)
  • will be used in electron transport chain /
    oxidative phosphorylation in mitochondria when
    oxygen is present

16
From Glycolysis to Krebs
  • Pyruvate created in glycolysis diffuses from the
    cell cytoplasm into the matrix of the
    mitochondria to be further broken down
  • Going from glycolysis to Krebs involves an
    intermediate step in which pyruvate is reduced
    and reworked into a 2-carbon molecule called
    acetyl-CoA by removing one CO2 group and addition
    coenzyme A this also produces 1 molecule of NADH
    for each pyruvate

17
Krebs Cycle
18
Krebs Cycle
  • Begins when the acetyl group of acetyl-CoA
    combines with oxaloacetate (4-carbon molecule) to
    form citrate (6-carbon molecule) and release the
    CoA.
  • Remaining reactions involve oxidizing the
    molecule and regenerating oxaloacetate
  • reactions also produce carbon dioxide (CO2),
    which will be released from the cell reduced
    electron carriers, which will be used in the next
    stage and GTP, which can be used to produce an
    equivalent amount of ATP

Fig. 25.7, p. 968
19
Krebs Cycle (cont)
  • Each citrate is rearranged during this cycle to
    produce two (2) CO2 molecules, three (3) NADH,
    one (1) FADH2, and one (1) ATP.

Fig. 25.7, p. 968
20
Acetyl-CoA and Krebs Cycle Energy Summary
  • ATP Production One (1) per cycle of Krebs.
  • NADH Production
  • one (1) NADH created with the formation of Acetyl
    CoA
  • three (3) NADH created during Krebs cycle
  • FADH2 Production One per cycle of Krebs
  • REMEMBER Krebs goes through 2 times for each
    glucose that started the process

21
Acetyl-CoA and Krebs Cycle Energy Summary
  • REMEMBER Krebs goes through 2 times for each
    glucose that started the process, therefore, the
    total is
  • 2 ATP created during the Krebs cycle
  • 2 NADH created with the formation of Acetyl CoA
  • 6 NADH created during Krebs cycle
  • 2 FADH2 created during Krebs cycle

22
Total Energy Summary, Through Krebs Cycle
  • From one (1) molecule of glucose
  • 4 ATP 2 (Glycolysis) 2 (Krebs)
  • 10 NADH 2 (Glycolysis) 2 (Acetyl CoA
    formation) 6 (Krebs)
  • 2 FADH2 2 (Krebs)

23
Oxidative Phosphorylation
  • Electron Transport System (ETS)
  • and Chemiosmosis

24
Electron Transport System
  • Utilizes the NADH and FADH2 produced in
    Glycolysis and Krebs.
  • Occurs in the inner membrane of the mitochondria.
  • Cannot occur without oxygen

25
Electron Transport System Step 1
  • Molecules within the inner membrane of the
    mitochondria take the two (2) electrons from
    NADH and the two (2) from FADH2 and pass them
    from one to another. (i.e., redox reactions)

Fig. 25.8, p. 969
26
Electron Transport System Step 2
  • The transfer of electrons moves hydrogen atoms
    (H) into the intermembrane compartment of the
    mitochondrion.

Fig. 25.8, p. 969
Fig. 25.8, p. 969
27
Electron Transport System Step 3
  • When enough H atoms collect in the compartment,
    they travel down their concentration gradient
    into the mitochrondrial matrix in a process
    called chemiosmosis.
  • Movement occurs through ATP synthase enzyme that
    uses the energy of H movement to create ATP from
    ADP

Fig. 25.8, p. 969
28
Electron Transport System Step 4
  • Once the electrons have moved to the end of the
    molecules in this chain, two(2) electrons combine
    with one (1) oxygen atom (formed from the
    breakdown of molecular oxygen, or O2) and two (2)
    hydrogen atoms to make water.
  • Oxygen is a KEY component to this process.
  • If oxygen is not present to combine and make
    water, then the electron transport system backs
    up, no H atoms are released and ATP cannot form.
  • Krebs cycle cannot be run because NAD and FAD are
    not regenerated

29
Electron Transport System ATP Totals
  • Each pair of H moved results in formation of 1
    ATP
  • ATP from NADH each NADH moves 3 pairs of H
  • 6 NADH from Krebs ? 18 ATP
  • 2 NADH from Acetyl CoA ? 6 ATP
  • 2 NADH from Glycolysis ? 6 ATP
  • BUT there is a cost to move the NADH in from the
    cytoplasm at 1 ATP each, so the net total in most
    cells is 4 ATP.
  • This loss DOES NOT OCCUR IN HEART CELLS OR LIVER
    CELLS. In these cells movement is more
    efficient, and the ATP production is 6 ATP!

30
Electron Transport System ATP Totals
  • ATP from FADH2
  • FADH2 transfers its H pairs at a different
    point, resulting in only 2 ATP per molecule
  • 2 FADH2 from Krebs ? 4 ATP.
  • Total ATP
  • ATP from NADH 18 6 (4 or 6) 28 (or 30)
  • ATP from FADH2 4
  • TOTAL from ETS 32 (or 34) ATP

31
Total ATP Production through the Entire System
  • 2 ATP (Glycolysis) 2 ATP (Krebs) 32-34 ATP
    (from ETS) 36-38 ATP

Fig. 25.10, p. 972
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