general properties of proteins

Question 1

what are amino acids?

Answer 1

monomers from which proteins are made

Question 2

what is the structure of an amino acid?

Answer 2

look up

Question 3

what are the 3 groups in the amino acid structure and what do they consist of?

Answer 3

• amino group
• r group
• carboxylic acid group

Question 4

what is the r group?

Answer 4

a carbon containing side chain

Question 5

what is the bond that forms between two amino acids?

Answer 5

peptide bond

Question 6

what reaction forms the peptide bond between two amino acids and what is given off?

Answer 6

condensation reaction, water

Question 7

what is formed by the condensation of two amino acids?

Answer 7

a dipeptide

Question 8

draw a dipeptide

Answer 8

look up

Question 9

how are peptide bonds broken?

Answer 9

hydrolysis reaction

Question 10

what are polypeptides?

Answer 10

formed by the condensation of many amino acids, a long chain of them

Question 11

what is the test for proteins?

Answer 11

biuret test

Question 12

explain the biuret test.

Answer 12

1. place sample of solution to be tested in a test tube and add an equal volume of SODIUM HYDROXIDE solution at room temp
2. add a few drops of very dilute (0.05%) COPPER (II) SULFATE solution and mix gently
3. PURPLE colouration indicates the presence of peptide bonds and so a protein, remains blue if not

Question 13

what are the 5 types of proteins?

Answer 13

structural 
catalytic 
signalling
fibrous proteins 
globular

Question 14

what are fibrous proteins?

Answer 14

proteins formed from parallel polypeptide chains and held together by cross links

these form long, rope like fibres, with high tensile strength and are generally insoluble in water

Question 15

3 examples of fibrous proteins.

Answer 15

• collagen
• keratin
• silk

Question 16

what are globular proteins? and how are they structured?

Answer 16

have a spherical shape caused by tightly folded polypeptide chains

the chains are usually folded so that the hydrophobic groups are on the inside and the hydrophilic groups are on the outside, makes them soluble in water

Question 17

3 examples of globular proteins.

Answer 17

• transport proteins (haemoglobin)
• enzymes (lipase)
• hormones (oestrogen)

Question 18

what is the primary structure of a protein?

Answer 18

the sequence of amino acids found in its polypeptide chains -determines its properties and shape

Question 19

what is the secondary structure of a protein?

Answer 19

the shape which the polypeptide chain forms as a result of hydrogen bonding

ALPHA HELIX, BETA PLEATED SHEET

Question 20

how are hydrogen bonds formed in secondary structure (or all structures) of proteins?

Answer 20

hydrogen atoms have a small positive charge and the oxygen and nitrogen atoms have a small negative charge, opposite attract to form hydrogen bonds

Question 21

what is the tertiary structure of a protein?

Answer 21

due to the bending and twisting of the polypeptide helix into a compact structure

hydrogen, ionic & disulfide bonds

Question 22

what is the quaternary structure of proteins?

Answer 22

comes from the combination of a number of different polypeptide chains and prosthetic groups into a large, complex protein molecule