Organic Compounds Study Guide

Biology

Organic Compounds

Big Picture

Our body is made out of four basic classes of organic compounds: carbohydrates, lipids, proteins, and nucleic acids. Each class performs a unique role and is vital for the function of life.

Key Terms

Organic Compound: A chemical substance created within an organism.

Carbohydrate: An organic compound containing carbon, hydrogen, and oxygen that supply the energy living systems need to survive.

Lipid: An organic compound produced for storing energy.

Protein: An organic compound making up muscles, enzymes, and other organs in the body.

Nucleic Acid: An organic compound used to store genetic information.

Fatty Acid: Molecule in which carbon atoms are bonded to hydrogen atoms or other groups of atoms.

Amino Acid: Small molecule that is a building block of proteins.

Nucleotide: Small molecule containing a sugar, phosphate group, and base that is a building block of nucleic acids.

Complementary Base Pair: Pair of nucleotide bases that bond together.

Four Main Types of Organic Compounds

There are four main types of organic compound responsible for cellular functions within cells. These are carbohydrates, lipids, proteins, and nucleic acids.

Types of Organic Compounds

Type of Compound

Examples

Functions

carbohydrates

sugars,
starches

provides energy to cells, stores energy, forms body structure

lipids

fats, oils

stores energy, forms cell membranes, carries messages

proteins

enzymes,
antibodies

helps cells keep their shape, makes up muscles, speeds up chemical reactions, carries messages and materials

nucleic acids

DNA, RNA

contains instructions for proteins, passes instructions from parents to offspring, helps make proteins

Carbohydrates

The most common type of organic compound.
Built of small, repeating units (monosaccharides) that can bind to make a larger molecule (poly-saccharide)

Lipids

Made up of fatty acids–either saturated (carbon bonded to as many hydrogen atoms as possible) or unsaturated (some carbon bonded to groups other than hydrogen atoms)
Lipids include:
triglycerides: the main form of stored energy in animals
phospholipids: the major components of cell membranes
steroids: serve as chemical messengers and have other roles

Notes

Biology

Organic Compounds cont.

Four Main Types of Organic Compounds (cont.)

Proteins

Made up of amino acids connected with peptide bonds
There are 20 amino acids, which, like the alphabet, can be arranged in any order and number to form a near-infinite number of polypeptides

Structure of a protein

The shape of a protein is important for function. There are four different structures that proteins can form in the body.

Figure: Protein structures

Image Credit: CK-12 Foundation, CC-BY-NC-SA 3.0

Nucleic Acids

Nucleic acids include DNA, which is double-stranded, and RNA, which is single-stranded. Nucleic acids are made up of nucleotides.
Nucleotides are made up of:
sugar
phosphate group
nitrogen base
Chemical bonds between the sugar of one nucleotide and the phosphate group of the next nucleotide hold together the backbone of all nucleic acid molecules.
There are five different types of nitrogen bases: cytosine, adenine, guanine, and either thymine (present in DNA) or uracil (present in RNA).
These bases pair up in a specific way, forming complementary base pairs. Adenine bonds only with thymine(uracil in RNA), and cytosine only with guanine.
Hydrogen bonding between base pairs holds together two strands of nucleic acid, forming the double helix in DNA molecules.

To remember DNA base pairing rules try using the mnemonic device: Grandama’s Cookies Taste Awesome.

Molecule

DNA

RNA

sugar

deoxyribose

ribose

bases

adenosine (A), thymine (T), cytosine (C), guanine (G)

adenosine (A), uracil (U), cytosine (C), guanine (G)

structure

double-stranded,
double helix

Single-stranded

Figure: Comparison of DNA and RNA molecules

Image Credit: Spoink, CC-BY-SA 3.0