2.4 : Proteins

Question 1

what are the main elements present in proteins?

Answer 1

carbon, hydrogen, oxygen, sulphur, nitrogen

Question 2

what are amino acids?

Answer 2

Amino acids are organic compounds that contain amine and carboxyl functional groups & combine to form proteins.

Question 3

what is the difference between polypeptides and proteins?

Answer 3

-polypeptides : two or more chains of covalently bonded amino acids held by peptide bonds.
(amino acids are linked by condensation reactions to form polypeptides)
-proteins : a chain of at least 50 amino acid residues covalently bonded together via peptide bonds.

Question 4

what is a dipeptide?

Answer 4

the combination of two amino acids via a condensation reaction.

Question 5

what occurs in the primary structure of proteins?

Answer 5

• this is the sequence of amino acids in a molecule
• determines the way that the chain will fold (depends on order, number, arrangement of amino acids - due to different chemical properties)

Question 6

what occurs in the secondary structure of proteins? what are the two shapes a protein can take up during this phase?

Answer 6

• this part develops when parts of the polypeptide chain take up a particular shape
• either coil up = a-helix or fold =b-sheets
• if there is no secondary structure = polypeptide chain will form a random coil

Question 7

what occurs in the tertiary structure? what are the 4 types of bond that can arise?

Answer 7

• this is when the precise, compact structure of the protein arises.
• arises when the molecule is folded further & held in a particular shape by either ionic, hydrogen, disulphide or van der waals bonds.

Question 8

what are ionic bonds?

Answer 8

electrostatic relation between ions that have opposing charges.

Question 9

what are hydrogen bonds?

Answer 9

weak bonds that stabilise a protein when a hydrogen atom is shared between two other atoms.

Question 10

what are disulphide bonds?

Answer 10

strong covalent bonds that are formed by the oxidation of -SH groups of two cysteine side chains.

Question 11

what are van der waals bonds?

Answer 11

weak forces of attraction that come into action when two or more electrically neutral molecules are close together.

Question 12

what occurs in the quaternary structure?

Answer 12

• arises when two or more proteins are held together, forming a complex and biologically active molecule.
• found in proteins that contain more than one polypeptide chain linked together or if they contain inorganic prosthetic groups.