Proteins Flashcards
What are the 4 classes of amino acids?
Acidic, basic, polar, non-polar.
What is the structure of an amino acid?
All amino acids have central carbon which has four groups attached to it; a hydrogen; an NH2 amine group at one end; a COOH carboxylic acid group at the other end; and a variable component, called an R group.
How are these classes defined?
By the R group attached to the central carbon.
Which if the groups are hydrophilic?
Acidic, basic, polar.
Which of the groups are hydrophobic?
Non-polar.
How are amino acids linked?
Amino acid monomers are linked together during translation of mRNA at the ribosome. An enzyme causes a condensation reaction between two adjacent amino acids. Water is removed by joining the OH group of the COOH of one amino acid to the hydrogen from the NH2 of the other amino acid. The bond that links the amino acids is called a peptide bond.
What is the primary protein structure?
This is the sequence of amino acids that make up a polypeptide chain. Each amino acid is linked to the next by a peptide bond to form a chain of amino acids. The chain has an N-terminus at one end and a C-terminus at the other end.
What is the secondary structure?
It is stabilised by hydrogen bonds between atoms of different peptide bonds in the chain. The hydrogen of the N-H has a weak positive charge so it is electrically attracted to the weak negative charge on the oxygen of the C=O of another peptide bond.
What are the two types of secondary structure?
The alpha-helix is a spiral with the R groups sticking outwards.
The beta-sheet has parts of the polypeptide chain running alongside each other to form a corrugated sheet, with the R groups sitting above and below. The polypeptide chains are usually antiparrallel (chains in opposite directions with respect to N-C polarity) but they can also be parallel (chains in the same direction with respect to N-C polarity).
What is the tertiary structure?
The final 3-dimensional shape of the protein. It is stabilised by interactions between R groups of amino acids. The R groups were far apart in the primary structure, but folding at the secondary level bring R groups close enough to interact.
What is a hydrophobic interaction?
Non-polar R groups are mostly arranged to the inside of the protein. The polar, acidic and basic R groups are mostly arranged on the outside.
What is the van der waals interaction?
Very weak attractions between the electron clouds of atoms.
What hydrogen bonding?
The weak negative charge of the oxygen of C=O is attracted to the weak positive charge on a hydrogen of an OH or NH2 group.
What is ionic bonds?
The COOH and NH2 groups ionise to become COO- and NH3+. These groups are strongly charged and can attract each other.
What is a disulphide?
Covalent bonds form due to reactions between the sulphur-containing R groups of cysteines.
