(music) In this video we will address lipid
catabolism and protein catabolism. Lipids and proteins are molecules that
can be used by cells in addition to carbohydrates to meet
their energy needs and generate precursor metabolites for
anabolic reactions. We are going to address lipid
catabolism first. The most common type of lipid utilized by
cells to generate energy in the form of ATP and precursor
metabolites are the triglycerides. Triglycerides are
composed of a glycerol and three fatty acids as seen in the top
picture. Triglycerides may be separated into
their glycerol and fatty acid components via a hydrolysis reaction.
The reaction requires three water molecules and is catalyzed by an enzyme
known as a lipase. The glycerol component released from the
hydrolysis reaction can undergo further catabolism by entering glycolysis. In order to catabolize a glycerol molecule
via glycolysis, the glycerol molecule is converted to a
molecule of dihydroxyacetone-phosphate by
the addition of a phosphate derived from ATP. As
previously seen in carbohydrate catabolism, the dihydroxyacetone-phosphate
is converted into glyceraldehyde-3-phosphate and is then oxidized to pyruvic acid in order to produce ATP. The fatty acids
released from the hydrolysis reaction may also be catabolized further. The fatty acids are broken down through
a process known as beta-oxidation. During beta oxidation enzymes break the
carbon atoms of the fatty acid off in pairs that are joined to a
coenzyme-A, thereby producing acetyl-CoA molecules
that may enter the citric acid cycle. Carbons containing hydrogen are removed
two carbons at a time until all of the carbons of the fatty acid
have been converted into acetyl-CoA. Beta-oxidation will produce the reduced electron carriers
NADH and FADH in addition to many molecules of
acetyl-CoA for the citric acid cycle. Many organisms will utilize proteins to produce
their energy and precursor metabolites only if they do not have access to
carbohydrate or lipid sources. This is because proteins are important
structurally and functionally within cells. Cells such
as the pathogens we are studying this semester will catabolize proteins as an
important source of energy and metabolites. When you have an infection with an
organism such as a pathogenic bacteria or a pathogenic fungus, those organisms will catabolize your proteins to
meet their cellular needs. In laymen’s terms, we can say they are
eating your proteins to get their energy. Most proteins catabolized by such
organisms are too large to pass through their cell membranes, therefore these
organisms use exoenzymes to begin protein
catabolism. Exoenzymes are enzymes secreted
outside of the cell. The exoenzymes used to begin
protein catabolism are known as proteases. Proteases act to break a protein down
into its individual monomers, the amino acids by breaking the peptide
bonds that join them. The amino acids that are released from
the action of proteases are then small enough to pass through
the cell membrane into the cell. We will revisit exoenzymes in unit 3 when we explore virulence
factors in more detail. Once inside the cell the amino acids may
be further catabolized by removing the amino group in a process known
as deamination The molecules left after removing the
amino groups resemble the carbohydrates found
in the citric acid cycle and therefore may act as substrates in
the Krebs cycle to produce energy for the cell. (music)

One comment

  1. what bacterial test can be used to detect lipid metabolism. I read that petroleum can be degraded by these organisms, so can that be used as a test?

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