Block 2. Biosynthesis
Unit 5. Laws of Thermodynamics and Metabolic Processes.
Cell Respiration
Cell respiration is the controlled release of energy from organic compounds to form ATP
Every living cell must carry out cell respiration in order to convert energy into a form that can be used
within the cell. Cells require energy for three main reasons:
a. Synthesizing large molecules like DNA, RNA and protein
b. Pumping molecules or ions across membranes by active transport.
c. Moving things around inside the cell, such as chromosomes, vesicles or in muscle cells the protein
fibers that cause muscle contraction.
The energy from these processes is supplied by ATP
(adenosine triphosphate). When ATP is split into ADP
(adenosine diphosphate) and phosphate, energy is
released:
ATP cannot usually be absorbed through plasma
membranes, so every cell must produce its own supplies.
Organic compounds containing energy are broken down by enzymes, in a careful and controlled way, so
that as much as possible of the energy released can be used to form ATP from ADP and phosphate.
Glycolysis and anaerobic cell respiration
Cell respiration can release energy from a variety of organic
compounds, but carbohydrates and lipids are the usual substrates. If
carbohydrates such as glucose are being used, almost all organisms
begin the process of cell respiration in the same way. A chain of
reactions takes place in the cytoplasm of cells, which converts the
glucose into a substance called pyruvate. This chain of reaction is called
glycolysis.
No oxygen is used in glycolysis and a small amount of ATP is produced.
If no oxygen is available then this is the only ATP that can be produced
in cell respiration.
In anaerobic conditions, glycolysis can
only continue if the pyruvate is
converted into other substances. In
humans, pyruvate is converted into
lactate (lactic acid). In contrast, yeast cells convert pyruvate into ethanol
(alcohol) and carbon dioxide. These substances are toxic in excess, so
must be removed from the cells that produce them, or be produced in
strictly limited quantities.
Aerobic cell respiration
If oxygen is available to a cell, pyruvate produced by glycolysis can be
oxidized to release more energy. In eukaryotic cells this happens inside
the mitochondrion. Energy released from pyruvate oxidation inside the
mitochondrion. Energy released from pyruvate oxidation is used to
produce ATP. The yield of ATP per glucose is much higher than from
glycolysis – more than ten times as much. Oxidation of pyruvate also
involves the production of carbon dioxide and water. In most organisms
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carbon dioxide is a waste product and has to be excreted, but the water is often useful. In humans about
half a liter is produced per day. Some desert animals never need to drink and eat only dry foods, because
cell respiration supplies almost all their water needs.
School
District
of Shell Lake
Questions:
1. Data Based Questions: production and consumption of ATP
The equation below summarizes the results of metabolic pathways used to produce ATP, using energy
from the oxidation of glucose.
Glucose + oxygen + (ADP+Pi)  Carbon dioxide + water + ATP
180 g
134.4 dm3
18.25Kg
134.4 dm3
108 g
18.25 Kg
Length of
race/m
1500
10,000
42,300
Volume of oxygen
consumed in cell
respiration during
the race/dm3
36
150
700
1. a) state the volume units that are shown in the equation (1)
b) state the mass units that are shown in the equation (2)
2. a) calculate the mass of ATP produced per dm3 of oxygen (2)
b) calculate the mass of ATP produced per race in Table 1 (4)
3. Explain how it is possible to synthesize such large masses of ATP during races. (3)
During a 100 m race, 80g of ATP is needed but only 0.5 dm3 of oxygen is consumed. Deduce how ATP is
being produced. (3)
2. Answer to the exercises of page 83 (22 to 27) Pearson
Sources
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Allot, A., & Mindorff, D. (2010). Biology Course Companion. New Yorl: Oxford University Press.
Damon, A., McGonegal, R., Tosto , P., & Ward, W. (2007). Biology Higher Level. New Jersey: Pearson.
Kent, M. (2000). Advanced Biology. En K. Michael, Advanced Biology (pág. 624). New York : Oxford University Press.
http://www.shelllake.k12.wi.us/parents/reflections44.cfm
SemOneAPBioFinalExamReview http://semoneapbiofinalexamreview.wikispaces.com/G.+Cellular+Respiration+(9)
Chasin, L. (2010), Lec. 8. Biol C2005/F2401, http://www.columbia.edu/cu/biology/courses/c2005/lectures/lec8_10.html
PBworks, http://torresbioclan.pbworks.com/w/page/22377237/Spikefish%20Mitochondrion
Yoga fitness http://www.themindbodyfitness.com/aerobic-cellular-respiration/aerobic-respiration-diagram-summary-14759/
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