The covalent bond between two amino acids is called a peptide bond. This is formed by positioning two amino acids so the carboxyl group of one is adjacent to the amino group of another. An enzyme then joins the two via a dehydration synthesis reaction. Ester bonds link fatty acids to glycerol heads, and phosphodiester bonds are formed between the sugar and phosphate backbone of a nucleic acid.

The primary structure of a protein is its amino acid sequence. The coils and folds of a protein are its secondary structure. Irregular contortions in the protein structure due to interactions between amino acid side chains is the tertiary structure. The overall structure when two or more polypeptides aggregated is the quaternary structure.  

Conformation is the the term for the three dimensional structure of proteins. Though the types of proteins are incredibly diverse they are all polymers made up of the same set of 20 amino acids. A protein's molecular weight involves the sum of all the atoms and their abundances, molecular weight is often used to approximate the size of a protein when determining if it will pass through a pore or channel in a membrane. The amino acid sequence is the primary structure, and is held together by peptide bonds.

Disulfide bonds may be formed in both tertiary and/or quaternary structures of a protein. These bonds result from the oxidation of the R-group (side chain) of the amino acid cysteine.

The linear sequence of amino acids in a polypeptide chain gives rise to the protein's primary structure.

The formation of disulfide bridge occurs in the tertiary and/or quaternary level of protein structure. This involves two sulfur atoms sharing a lone pair of electrons to form a covalent bond, which enhances the integrity of the protein's structure. The amino acid that is involved in forming disulfide bridges is cysteine.

Proteins consist of the elements nitrogen, carbon, hydrogen, and oxygen.  They are polymers of molecules called amino acids.  Lipids are made up of glycerol and fatty acid chains.

All amino acids have an amino group and a carboxyl group.  Amino acids do not have glycerol.  The side chain called an R-group is what differentiates amino acids from each other in their chemical properties and functions.

Primary structure takes advantage of covalent bonding to form a peptide bond between amino acids. Secondary structure takes advantage of hydrogen bonding to form alpha helices and beta-pleated sheets. The tertiary structure takes advantage of all these forms of bonding and interactions to fold into the overall shape of the protein and the quaternary structure is formed by using these interactions to connect multiple polypeptides.

Proteins preform multiple functions in the body. Carrier proteins move molecules from place to place. Sometimes the molecules they carry relay signals between cells. Proteins can bind to substrates to bring the ingredients of key reactions together, catalyzing those reactions. Certain proteins integrate into cell membranes providing structural elements. Fatty acids store energy, while proteins do not. They lack the highly reduced carbon-hydrogen bonds of fatty acids.