Title: Metabolism of the Cell
1Metabolism of the Cell
2Metabolism
- 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
3Cellular 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.
4Major 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
5Metabolism 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
6Metabolism 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)
7Metabolism 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)
8Glycolysis
9Glycolysis
- 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)
10Glycolysis - Overview
- 3 Phases
- sugar activation
- sugar cleavage
- sugar oxidation and formation of ATP
Fig. 25.6, p. 966
11Phase 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
12Phase 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
13Phase 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
14Phase 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
15Glycolysis 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
16From 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
17Krebs Cycle
18Krebs 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
19Krebs 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
20Acetyl-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
21Acetyl-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
22Total 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)
23Oxidative Phosphorylation
- Electron Transport System (ETS)
- and Chemiosmosis
24Electron Transport System
- Utilizes the NADH and FADH2 produced in
Glycolysis and Krebs. - Occurs in the inner membrane of the mitochondria.
- Cannot occur without oxygen
25Electron 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
26Electron 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
27Electron 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
28Electron 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
29Electron 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!
30Electron 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
31Total 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