BSC 310 Lecture Notes - Lecture 10: Acetaldehyde, Electrochemical Gradient, Prokaryote
Cellular Respiration
Microorganisms such as cyanobacteria can trap the energy in sunlight through the
process of photosynthesis and store it in the chemical bonds of carbohydrate
molecules. The principal carbohydrate formed in photosynthesis is glucose. Other types
of microorganisms such as nonphotosynthetic bacteria, fungi, and protozoa are unable
to perform this process. Therefore, these organisms must rely upon preformed
carbohydrates in the environment to obtain the energy necessary for their metabolic
processes.
Cellular respiration is the process by which microorganisms obtain the energy available in
carbohydrates. They take the carbohydrates into their cytoplasm, and through a complex
series of metabolic processes, they break down the carbohydrate and release the energy.
The energy is generally not needed immediately, so it is used to combine ADP with
phosphate ions to form ATP molecules. During the process of cellular respiration, carbon
dioxide is given off as a waste product. This carbon dioxide can be used by
photosynthesizing cells to form new carbohydrates. Also in the process of cellular
respiration, oxygen gas is required to serve as an acceptor of electrons. This oxygen gas is
identical to the oxygen gas given off in photosynthesis.
The overall mechanism of cellular respiration involves four subdivisions: glycolysis, in which
glucose molecules are broken down to form pyruvic acid molecules; the Krebs cycle, in
which pyruvic acid is further broken down and the energy in its molecule is used to form
high-energy compounds such as NADH; the electron transport system, in which electrons are
transported along a series of coenzymes and cytochromes and the energy in the electrons is
released; and chemiosmosis, in which the energy given off by electrons is used to pump
protons across a membrane and provide the energy for ATP synthesis.
Glycolysis. The process of glycolysis is a multistep metabolic pathway that occurs in the
cytoplasm of microbial cells and the cells of other organisms. At least six enzymes operate
in the metabolic pathway.
In the first and third steps of the pathway, ATP is used to energize the molecules. Thus, two
molecules of ATP must be expended in the process. Further along in the process, the six-
carbon glucose molecule is converted into intermediary compounds and then is split into two
three-carbon compounds. The latter undergo additional conversions and eventually
form pyruvic acid at the conclusion of the process.
During the latter stages of glycolysis, four ATP molecules are synthesized using the energy
given off during the chemical reactions. Thus, four ATP molecules are synthesized and two
ATP molecules are inserted into the process for a net gain of two ATP molecules in
glycolysis.
Also during glycolysis, another of the reactions yields enough energy to convert NAD
toNADH. The reduced coenzyme (NADH) will later be used in the electron transport system,
and its energy will be released. During glycolysis, two NADH molecules are produced.
find more resources at oneclass.com
find more resources at oneclass.com
As glycolysis does not use oxygen, the process is considered to be anaerobic. For certain
anaerobic organisms, such as certain bacteria and fermentation yeasts, glycolysis is the sole
source of energy. It is a somewhat inefficient process because much of the cellular energy
remains in the two molecules of pyruvic acid.
The Krebs cycle. Following glycolysis, the mechanism of cellular respiration then involves
another multistep process called the Krebs cycle, also called the citric acid cycle and the
tricarboxylic acid cycle. The Krebs cycle uses the two molecules of pyruvic acid formed in
glycolysis and yields high-energy molecules of NADH and FADH and some ATP and carbon
dioxide (Figure 1 ).
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Microorganisms such as cyanobacteria can trap the energy in sunlight through the process of photosynthesis and store it in the chemical bonds of carbohydrate molecules. The principal carbohydrate formed in photosynthesis is glucose. Other types of microorganisms such as nonphotosynthetic bacteria, fungi, and protozoa are unable to perform this process. Therefore, these organisms must rely upon preformed carbohydrates in the environment to obtain the energy necessary for their metabolic processes. Cellular respiration is the process by which microorganisms obtain the energy available in carbohydrates. They take the carbohydrates into their cytoplasm, and through a complex series of metabolic processes, they break down the carbohydrate and release the energy. The energy is generally not needed immediately, so it is used to combine adp with phosphate ions to form atp molecules. During the process of cellular respiration, carbon dioxide is given off as a waste product. This carbon dioxide can be used by photosynthesizing cells to form new carbohydrates.
