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TOC#_____ Carbon in Macromolecules Reading Why do all the Macromolecules of Life Contain Carbon? Read the following article. Highlight important information and take notes on the right side. ​
Keep in mind this bullet point from your proficiency scale: ​
Describes the unique bonding properties of carbon that permits the formation of proteins, carbohydrates, lipids, and nucleic acids. Carbon is the fourth most abundant element in the universe and is the building block of life on earth. On earth, carbon circulates through the land, ocean, and atmosphere, creating what is known as the Carbon Cycle. Part of this cycle is photosynthesis and cellular respiration. In its ​
metabolism​
of food and ​
respiration​
, an animal consumes ​
glucose​
(C​
H​
O​
), which combines with oxygen 6​ 12​ 6​
(O​
) to produce carbon dioxide (CO​
), water (H​
O), and energy, 2​
2​
2​
which is given off as heat. The animal has no need for the carbon dioxide and releases it into the atmosphere. A plant, on the other hand, uses the opposite ​
reaction​
of an animal through photosynthesis. It intakes carbon dioxide, water, and energy from sunlight to make its own glucose and oxygen gas. The glucose is used for ​
chemical energy​
, which the plant metabolizes in a similar way to an animal. The plant then emits the remaining oxygen into the environment. Carbon is Important to Life Cells​
are made of many ​
complex​
​
molecules​
called macromolecules, which include proteins, nucleic acids (RNA and DNA), carbohydrates, and lipids. The macromolecules are a subset of organic molecules (any carbon­containing liquid, solid, or gas) that are especially important for life. The fundamental component for all of these macromolecules is carbon. The carbon atom has unique properties that allow it to form ​
covalent bonds​
to as many as four different atoms, making this versatile element ideal to serve as the basic structural component, or "backbone," of the macromolecules. What is it about carbon that makes it so important? The answer lies with carbon’s unique properties. Carbon has an exceptional ability to bond with a wide variety of other elements. Carbon atoms can form multiple stable bonds with other small atoms, including hydrogen, oxygen, and nitrogen. Carbon atoms can also form stable bonds with other carbon atoms. In fact, a carbon atom may form single, double, or even triple bonds with other carbon atoms. This allows carbon atoms to form a tremendous variety of very large and complex molecules. Nearly 10 million carbon­containing organic compounds are known. Types of carbon compounds in organisms include carbohydrates, lipids, proteins, and nucleic acids. Structure of Carbon Individual carbon atoms have an incomplete outermost ​
electron shell​
. With an atomic number of 6 (six electrons and six protons), the first two electrons fill the inner shell, leaving four in the second shell. Therefore, carbon atoms can form up to four covalent bonds with other atoms to satisfy the ​
octet rule​
. The methane molecule provides an example: it has the chemical formula CH​
. Each of its 4​
four hydrogen atoms forms a single covalent bond with the carbon atom by sharing a pair of electrons. This results in a filled outermost shell. Take away message: Carbon can form 4 covalent bonds because it has 4 electrons in its outer shell. It can form the following number of bonds. Notice that in each case below, there is a total of four bonds. ●
4 single bonds ●
two double bonds ●
one double bond and two single bonds ●
one triple and one single bond These bonds allow all the bond in carbohydrates, proteins, lipids, and nucleic acids to form.