3.13- Proteins are made from amino acids linked by peptide bonds

How are amino acids linked to form polymers? What is a peptide bond? What is a dipeptide, and what is a polypeptide?

By DEHYDRATION REACTIONS: Carboxyl group of 1 amino acid links to amino group of other amino acid, and a water molecule is removed. Peptide bond= the covalent linkage between amino acids. Dipeptide= 2 amino acids bonded together. Polypeptide= a chain of amino acids.

What determines whether the amino acids are hydrophilic or hydrophobic?

R group determines (if R group is polar/charged, it's hydrophilic, and vice versa).

What all plays a role in determining a protein's 3-dimensional shape?

-R group interactions -Eg: hydrophobic amino acids may cluster together in center of globular protein, while hydrophilic amino acids face outside, helping proteins dissolve in aqueous solution of cell. -Hydrogen bonds between hydrophilic R groups -Ionic bonds between hydrophilic R groups -Disulfide bridges between sulfur atoms of some R groups.

How are there so many kinds of proteins from just 20 amino acids?

-Sequence of polypeptides can be ANY COMBINATION and ANY LENGTH (analogy: just 26 letters of alphabet but can make thousands of words). -Most polypeptides at least 100 amino acids in length, and some more than 1,000.. -Each polypeptide has unique sequence of amino acids.

How do proteins exist in a cell?

-The functional groups r ionized at cellular pH. -If R groups contain acidic or basic groups, they are charged at the pH of a cell.