3.1.4.1 General Properties of Proteins

Question 1

what are proteins also referred to as?

Answer 1

polypeptides

Question 2

what are polypeptides made from (ie. monomers?)

Answer 2

amino acids

Question 3

how many amino acids are there and how many of these are naturally occurring?

Answer 3

100 identified, 20 of which are naturally occuring

Question 4

describe the general structure of an amino acid and draw it

Answer 4

(check diagram against notes)
amine group (NH₂)
carboxyl group (COOH)
central carbon (C)
hydrogen atom (H)
R group (R)

Question 5

what can 2 amino acids bond together to form and which mechanism does this involve?

Answer 5

two amino acids can bond together to form a dipeptide, and this happens through a condensation reaction, (molecule of H₂O removed and a bond is made.)

Question 6

what sort of bond is formed when a dipeptide is made and where is it?

Answer 6

peptide bond forms between the C-N

Question 7

if condensation reactions are repeated after a dipeptide then what is formed?

Answer 7

polypeptide

Question 8

place in order of decreasing strength: ionic, hydrogen, covalent bonds

Answer 8

STRONGEST
covalent
ionic
hydrogen
WEAKEST

Question 9

give 3 examples of tertiary proteins

Answer 9

enzymes, antibodies and hormones

Question 10

give 4 examples of quaternary proteins and 2 of their prosthetic groups (PG)

Answer 10

chlorophyll (PG = Mg)
haemoglobin (PG = Fe)
collagen
antibodies

Question 11

what is an R group?

Answer 11

an R group is a carbon containing side chain
it is what differs between amino acids

Question 12

state the 5 functions of polypeptides within an organism and give examples

Answer 12

1. STRUCTURE eg. collagen, keratin, actin
2. ENZYMES eg. carbohydrase, protease
3. TRANSPORT eg. haemoglobin
4. HORMONES eg. oestrogen, testosterone
5. ANTIBODIES

Question 13

name and describe the chemical test for proteins

Answer 13

BIURET TEST:
- place sample of solution into test tube
- add equal volume of sodium hydroxide
- add few drops of copper (II) sulphate
- mix gently

+ve result = purple/mauve
-ve result = remains blue

Question 14

describe the differences between globular and fibrous proteins

Answer 14

fibrous: elongated shape, insoluble, structural roles eg. collagen, keratin, myosin, actin

globular: spherical shape, soluble in water, metabolic roles eg. haemoglobin, enzymes, hormones

Question 15

describe the primary structure of a protein (3 points)

Answer 15

• a singular polypeptide chain
• only contains peptide bonds
• the order and number of amino acids in the chain determines the structure and function of a protein

Question 16

describe the secondary structure of a protein (3 points)

Answer 16

• hydrogen bonding between H⁺ and O⁻
• causes the polypeptide chain to fold and twist into a 3D structure
• results in the formation of an alpha helix or a beat pleated sheet

Question 17

where do the H⁺ and O⁻ originate from when forming a secondary protein?

Answer 17

hydrogen in -NH is delta positive and oxygen in C=O is delta negative

Question 18

give 2 examples of secondary structure proteins

Answer 18

keratin and collagen

Question 19

describe the structure of a tertiary structure protein (3 points)

Answer 19

• further twisting and folding of a secondary structure
• results in a 3D SPECIFIC structure
• the number and location of ionic, covalent and hydrogen bonds determine and maintain this structure of the tertiary protein

Question 20

describe the strength of hydrogen bonds and what they can be broken by?

Answer 20

numerous and weak so easily broken by temperature changes

Question 21

describe the strength of ionic bonds and what they can be broken by?

Answer 21

formed between the carboxyl and amine groups that are not involved in the peptide bond. easily broken by pH and are weaker than covalent but stronger than hydrogen

Question 22

describe the strength of covalent bonds and what they can be broken by? given an example

Answer 22

a sulphide bridge is a very strong covalent bond caused by interactions between the R group of the amino acid and cysteine. not easily broken

Question 23

describe the structure of a quaternary protein (2 points)

Answer 23

• a protein consisting of more than one polypeptide chain linked together
• possible prosthetic group