Download Lecture 13

METABOLISM
The net sum of all chemical reactions
taking place in a cell!
CATABOLISM
•  Breakdown/hydrolysis reactions
•  Usually liberate energy
•  We will study one example:
–  Glycolysis and Fermentation
ANABOLISM
•  Synthesis/condensation reactions
•  Usually require energy
•  Examples include protein synthesis and
DNA replication
FOCUS ON: Carbohydrate Catabolism
•  Glucose is the most popular reactant,
although other sugars will work.
•  Also, fats and proteins can be oxidized for
energy, but we will not focus on them.
•  THE BEGINNING SET OF
REACTIONS IS ALWAYS
GLYCOLYSIS!!!!!
Glycolysis in a nutshell
•  A molecule of glucose (6 carbons) is split into
two molecules of pyruvic acid (3 carbons).
This is an oxidation event.
•  A net gain of two ATP molecules is produced
by substrate-level phosphorylation.
•  Two molecules of the coenzyme NAD+ are
reduced to NADH. This is a reduction event.
GLYCOLYSIS NEVER
STANDS ALONE!!!!
•  After glycolysis, there are two choices:
•  Pyruvic acid may enter a fermentation
pathway, or
•  It may enter a respiration pathway
•  Respiration may be aerobic or anaerobic;
•  Anaerobic respiration is not the same as
fermentation!!!! (although fermentation
requires no oxygen).
The Fermentation Option:
Lactic acid or ethanol
•  No ATP is produced during fermentation;
why must these reactions take place?
•  NADH must be oxidized back to NAD+ so
that glycolysis can continue!!!!!!!!!
•  Ethanol fermentation is most popular in
microorganisms, especially yeast - beer,
alcohol, bread, etc.
Fermentation in a nutshell
•  Pyruvic acid is converted to
– Lactic acid (3 carbons) OR
– Ethanol and carbon dioxide
•  NO ATP is produced
•  NADH is oxidized to NAD+.
Respiration involves
•  The Krebs Cycle (also called the TCA or citric
acid cycle), and
•  A series of electron transfer agents (an electron
transport chain), with an inorganic terminal
electron acceptor (TEA). •  If the TEA is oxygen, respiration is aerobic.
•  If the TEA is not oxygen, it is anaerobic (e.g.,
some bacteria can use nitrate or sulfate as the
TEA.)
Organisms can be grouped according to
the way they obtain ENERGY and
CARBON
(two fundamentals of life!). We call
this their nutritional pattern.
•  Heterotrophs - obtain carbon in an organic
form and thus are dependent on other
organisms.
•  Autotrophs - obtain carbon in inorganic
form (carbon dioxide), and thus are not
directly dependent on other organisms for
their carbon needs.
Organisms can be grouped according to
the way they obtain ENERGY and
CARBON
(two fundamentals of life!). We call
this their nutritional pattern.
•  Phototrophs - obtain energy from light;
in other words, they are capable of
photosynthesis.
•  Chemotrophs - obtain energy from the
oxidation of chemical compounds.
So, to get a more complete and accurate picture of
an organism’s nutritional pattern, we can combine
these terms:
•  Chemoheterotrophs - use reduced organic
compounds for both carbon and energy. Most
heterotrophs are of this type. Examples of this type
include E.coli and human beings.
•  Chemoautotrophs - oxidize reduced inorganic
compounds for energy (e. g. H2S, NH3, Fe), use CO2
as a carbon source. Examples include deep-sea vent
bacteria and less exotic types such as many soil
bacteria involved in decomposition and nutrient
recycling. Also known as lithoautotrophs (“rock
feeders”)
So, to get a more complete and accurate picture of
an organism’s nutritional pattern, we can combine
these terms:
•  Photoautotrophs - use light as an energy
source and CO2 as a carbon source. These
are the most common ecological
“producers” and include the cyanobacteria. •  Photoheterotrophs - use light as an energy
source and organic compounds for carbon.
Examples include the green and purple
nonsulfur bacteria.