Page 330 - Biology_F5

Gas exchange and respiration

Protein Metabolism protein synthesis and breakdown is
Proteins are crucial for building and regulated by various factors, including
repairing tissues, synthesising enzymes hormones, nutritional status, and physical
and hormones, and serving as a source activity.
of energy. Dietary proteins are broken
down into amino acids during digestion 6.3.5 Respiratory quotient (RQ)
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and absorbed into the bloodstream. Most
of the time, amino acids are recycled for Task 6.10
synthesis of new proteins or converted into From library and internet sources,
search for information about the
other compounds. In the time of energy Respiratory Quotients (RQ) and Basal
deficiency, amino acids can be oxidised Metabolic Rate (BMR). Note down
for energy through pathways like Kreb’s what you have observed.
cycle, gluconeogenesis, or ketogenesis.
The amino acids from proteins connect Respiratory quotient (RQ) is a measure
with glucose catabolism through pyruvate, of the ratio of carbon dioxide evolved by
acetyl CoA, and components of the citric an organism to that of oxygen consumed
acid cycle. Each amino acid must have its over a given period of time.
amino group removed prior to entry into
these metabolic pathways. RQ = Volume of CO evolved
2
Volume of O consumed
2
The carbon atoms of amino acids are For example, the equation for a complete
converted into intermediate compounds aerobic oxidation of hexose sugar is
associated with several alternative represented below:
pathways for energy production (Figure
6.15). The remaining amino group is C H O + 6O ⎯ →⎯ 6CO + 6H O
6
12
2
2
2
6
converted into ammonia. In mammals, the
liver synthesises urea from two ammonia RQ = 6CO 2 = 1
molecules and a carbon dioxide molecule. 6O 2
Thus, urea is the principal waste product
in mammals produced from the nitrogen However, it is difficult to have this
originating in amino acids, and it leaves theoretically calculated value, because a
substrate is rarely completely oxidised.
the body in urine. The balance between

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