Download File - Mr. Shanks` Class

G. Related pathways
pg 117
1] CARBOHYDRATES
- Cells first choice for ‘food’ or energy
broken down by simple aerobic cellular respiration
2. PROTEINS
H
Proteins breakdown into amino acids
H2N—C—COOH
R
deaminase removes the amino [NH2] group
The remainder enters the energy cycle at various points, eg:
leucine  acetyl-CoA
alanine  pyruvate
proline  into Kreb’s
3. LIPIDS
triglycerides 
glycerol + 3 fatty acids
glycerol   3-phosphoglycerate
3 fatty acids  beta-oxidation
beta oxidation
most fatty acids are 18 carbons long
[into glycolysis]
What does and 18-carbon fatty acid look like?
H H H H H H H H H H H H H H H H H OH
H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C=O
HHHHHHH HHHHHHHHHH
How many carbons in acetyl-CoA? 2 carbons
How many times do we have to cut the 18 carbon fatty acid?
C-C C-C C-C C-C C-C C-C C-C C-C C-C
8 cuts
To calculate the energy released by lipid breakdown, there
are two steps.
Step One: beta-oxidation step that converts a long chain of
carbons into a series of acetyl-CoA
The oxidation of fatty acids into acetyl-CoA molecules
requires the breaking of bonds, always one less bond
that the number of acetyl-CoA.
To break bonds, we must add water and ATP. When these
fatty acid bonds are broken,
1 FADH2 and 1 [NADH + H+] are produced.
Given these steps, the beta-oxidation of an 18 carbon fatty
acid is shown below.
18 carbon + 9 CoASH
fatty acid
+ 8 ATP + 8 FAD + 8 NAD+ + 8 H2O
9 acetyl-CoA + 8 ( ADP + Pi ) + 8 FADH2 + 8 ( NADH + H+ )
Step two: the breakdown of the acetyl-CoA
through the normal Kreb’s cycle.
One turn through Kreb’s cycle produces
1 ATP:
1 FADH2:
3 [NADH + H+].
To determine the total number of high energy compounds
produced this way, we must multiply these base numbers
by the number of acetyl-CoA’s.
#
1
1 acetylCoA
ATP
#
9
9 acetylCoA
ATP
3
NADH+H+
27
NADH+H+
1
FADH2
9
FADH2
#
9
9 acetylCoA
ATP
#
-8
OXIDATION
ATP
27
NADH+H+
8
NADH+H+
9
FADH2
8
FADH2
#
NET
1
ATP
35 NADH+H+
17
FADH2
#
NET
1
ATP
35
NADH+H+
17
FADH2
#
1
NET
3
x
GLUCOSE
ATP
105
ATP
34
ATP
140
ATP
3 x
36 ATP
total
108 ATP
Comparing 18 carbons of fatty acid with 18 carbons of glucose
18 carbons fatty acid  140 ATP
18 carbons of glucose  108 ATP
Therefore we get 140 ATP / 108 ATP
or 130 % energy from the lipid compared
to glucose
This is why we store energy on our bodies as fat!
Now try the two examples based on
12 carbons
and 20 carbons