BIO 2960 HW 6 - Problem Set#6 KEY Bio2960 Spring 2012 1 The...

1
Problem Set #6
KEY
Bio2960; Spring 2012
1. The teacher of Bio2960 did not ask you to memorize a whole lot of chemical
structures. However, he wanted you to know the structures of glyceraldehyde 3-
phosphate, pyruvate and acetyl CoA (not CoA though) because these
intermediates are major metabolic crossroads in cellular metabolism. Draw the
chemical structures of these compounds and list the biochemical
pathways/processes that are linked to each of these compounds. Also, indicate the
cellular compartments (in an eukaryotic cell) where these pathways/processes
take place. [Name of sub-organelle compartments should be mentioned in your
answer.
Glyceraldehyde 3-phosphate Pyruvic acid (pyruvate) Acetyl CoA
Glyceraldehyde 3 phosphate: glycolysis (cytosol), gluconeogenesis (cytosol),
Calvin cycle (stroma [matrix] of chloroplasts), glycerol synthesis (cytosol).
Pyruvate: glycolysis (cytosol), gluconeogenesis (cytosol), fermentation
(cytosol), pyruvate oxidation (matrix of mitochondria), alanine synthesis
(cytosol)
Acetyl CoA: pyruvate oxidation (matrix of mitochondria), fatty acid
degradation (matrix of mitochondria), fatty acid synthesis (cytosol), citric
acid cycle (matrix of mitochondria), glyoxylate cycle (glyoxysomes in plants).
2. Based on the discussions we had in class, estimate how many ATP molecules are
produced when one molecule of glucose is fully oxidized in CO
2
. How many
ATP molecules are produced if oxygen supply is rather limited?
The table below outlines accountings of the energy gain from the metabolism
of a single glucose molecule.

2
This scenario uses the figures cited in lecture (see PPT file): 2.5 ATPs per
NADH and 1.5 ATPs per FADH
2
.
Step Anaerobic (low
oxygen)
Aerobic (plenty of
oxygen)
Glycolysis
ATP invested - 2 ATP - 2 ATP
2 cytoplasmic NADH (see below)
ATP generated by substrate level phosphorylation + 4 ATP + 4 ATP
Pyruvate Oxidation
2 mitochondrial NADH + 5
Oxidative Phosphorylation
6 mitochondrial NADH + 15
2 mitochondrial FADH
2
+ 3
GTP generated by substrate-level phosphorylation + 2 GTP (ATP)
2 cytoplasmic NADH from glycolysis (whose
electrons are shuttled into the mitochondria and
donated to FADH
2
)
(because of the mitochondrial membranes being a
physical barrier for the transport of NADH from
cytosol to mitochondria)
+ 3
Total 2 30
3. Explain why most fatty acids contain even-numbered carbon chain.
Because the building block of a fatty acid is the two-carbon acetyl CoA.
4. Based on the information/answer in Q2 above, try to figure out how many ATPs
are generated if a molecule of palmate (16 carbons), a saturated fatty acid
enriched in palm oil, is fully oxidized.
One palmitate with 16 carbons can be cleaved 7 times by the β -oxidation
process to generate 8 molecules of acetyl CoA, which will then further
metabolized in the citric acid cycle.
Initially, palmitate has to be converted to palmityl CoA consuming one
molecule of ATP (of course, this steps requires one molecule of HS-CoA as
well).