biological molecules - 3.14 (proteins)

Question 1

what do amino acids combine to make?

Answer 1

polypeptides

Question 2

what do polypeptides combine to make?

Answer 2

proteins

Question 3

what are the four chemical groups in an amino acid that attach to a central carbon atom?

Answer 3

-amino group (NH2)
-carboxyl group (-COOH)
-hydrogen atom (H)
= R group- every amino acid has a different R group

Question 4

how is a dipeptide formed?

Answer 4

2 amino acid monomers combine by the removal of a water molecule in a condensation reaction, forming a peptide bond between the C atom of one amino acid and the N atom of the other.

Question 5

what is the primary protein structure?

Answer 5

the sequence of amino acids in a polypeptide chain

Question 6

what is the secondary protein structure?

Answer 6

The linked amino acids that make up a polypeptide possess both -NH and -C=O groups on either side of every peptide bond.
- The hydrogen of the -NH group has an overall positive charge, while the O of the -C=O has an overall negative charge. These 2 groups therefore readily form weak hydrogen bonds. This causes the chain to twist into an alpha helix.

Question 7

what is the tertiary protein structure?

Answer 7

The alpha-helices can be twisted and folded even more to give the complex, 3D structure of each protein.
-This structure is maintained by a number of different bonds:
-disulphide bridges (fairly strong and not easily broken)
-ionic bonds (formed between any carboxyl and amino groups that aren’t involved in forming peptide bonds. They are weaker than disulphide bonds are easily broken by a change in pH)
-hydrogen bonds (have collective strength, but are easily broken.)

Question 8

what is the quaternary protein structure?

Answer 8

large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways.
-There may also be non-protein (prosthetic) groups associated with the molecules.

Question 9

what is the test for proteins?

Answer 9

biuret reagent, colour change = blue to purple/lilac.

Question 10

what are globular proteins?

Answer 10

• they are round and complex, and carry out metabolic functions, such as enzymes and haemoglobin.

Question 11

what are fibrous proteins?

Answer 11

• they are long and narrow chains, such as collagen, and have structural functions.