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Biology for Advanced Level Secondary Schools

on the number of carbons each has. The cells. After being ingested, carbohydrates
portions with 3 carbons are converted are broken down into glucose, which
into pyruvate; those with 4 carbons form enters the bloodstream. The simple sugars
oxaloacetate while those with 5 carbons are catabolised during glycolysis. Insulin,
are converted into α-ketoglutarate. a hormone produced by the pancreas,
For example aspartate and glutamate helps to regulate blood glucose levels
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enter directly into the Kreb’s cycle by facilitating the uptake of glucose into
at oxalaoacetate and α-ketoglutarate cells for energy or storage. Excess glucose
respectively. can be stored in the liver and muscles as
glycogen, or converted to fat for long-
Glucose, Lipids, and Protein term energy storage. During the time of
Metabolism fasting or low glucose availability, stored
glycogen is broken down into glucose
Task 6.9 through the process called glycogenolysis,
Search for information from library while gluconeogenesis allows the body to
and internet sources on glucose, produce glucose from non-carbohydrate
lipids, and protein metabolism. Note sources like amino acids and glycerol.
down the alternative intermediate
compounds that enter in the metabolic
pathways of each molecule. Lipid Metabolism
Lipids, including fats and cholesterol,

Glucose, lipids, and protein metabolism are are essential for various physiological
fundamental processes that are essential functions, such as energy storage,
for energy production, cellular function, insulation, and cell membrane structure.
and maintaining an overall metabolic Dietary fats are broken down into fatty

balance of the body. The breakdown and acids and glycerol in the digestive system
synthesis of carbohydrates, proteins, and and absorbed into the bloodstream. The
lipids connect with the pathways of glucose fatty acids from fats connect with glucose
catabolism. Glucose metabolism involves catabolism through acetyl CoA (Figure
its conversion to energy or glycogen for 6.15). Within cells, fatty acids can be
storage. Lipid metabolism includes the oxidised for energy through beta-oxidation
synthesis, breakdown, and transport of fats or re-esterified into triglycerides for
for energy and cellular function. Protein storage in the adipose tissue. Cholesterol,
metabolism encompasses the synthesis, another type of lipid, is essential for cell
breakdown, and utilisation of amino acids membrane integrity and the synthesis of
for various physiological processes and steroid hormones and bile acids. Excess
tissue maintenance. cholesterol can be stored in cells or
transported to the liver for excretion as
Glucose Metabolism bile or conversion into bile salts.
Glucose is the primary source of energy for

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