proteins

Question 1

what are amino acids?

Answer 1

• basic building blocks of proteins
• around 20 in proteins

Question 2

structure of amino acids

Answer 2

• consists of an amino (-NH2) group and a carboxyl (-COOH) group
• α carbon in the middle
• α carbon bonded to a hydrogen atom, a carboxyl (-COOH) group, an amino (-NH2) group and a R group
• amino acids differ only in R group

Question 3

formation of polypeptide chain

Answer 3

1. condensation reaction occurs between an amino (-NH2) group of one amino acid and a carboxyl (-COOH) group of another, removing a water molecule and forming a dipeptide joined by a peptide bond
2. dipeptide can be joined to other amino acids via the same reaction to form a polypeptide
3. polypeptide chain is folded into unique 3-dimensional shape due to chemical bonds occuring between R groups of amino acids
4. polypeptide chain has 2 different ends - amino (-NH2) end and carboxyl (-COOH) end
5. Amino (-NH2) / N terminal is beginning of polypeptide chain. sequence of amino acids in chain is written starting from N terminal.

Question 4

proteins can be made up of either:

Answer 4

1. ONE polypeptide chain folded into a unique 3-dimensional shape, held by chemical bonds ( myoglobin - oxygen binding protein in muscles)
2. SEVERAL polypeptide chains folded into a unique 3-dimensional shape, held by chemical bonds (haemoglobin - oxygen-binding protein in red blood cells)

Question 5

primary structure of a protein

Answer 5

• variety, sequence and number of amino acids in a polypeptide chain
• bond : peptide bond only

Question 6

secondary structure of a protein

Answer 6

• localised, repetetive folding of polypeptide chains
• bonds : hydrogen bonds between peptide bonds of polypeptide backbone

types of secondary structures:

1. α-helix
   * extended spiral spring
   * stablised by hydrogen bonds between -C=O and -NH groups in polypeptide backbone
   * keratin
2. β-pleated sheet
   * 2 or more regions of polypeptide chain lie parallel to one another in flat zigzag sheets
   * stabilised by hydrogen bonds between -C=O and -NH groups in one part of backbone and -C=O and -NH groups in adjacent part of parallel regions
   * may run in same (parallel) or opposite direction (anti-parallel)
   * fibroin (found in silk, high tensile strength)

Question 7

teritary structure of proteins

Answer 7

• polypeptide chains bend and fold to form a precise, compact, globular 3 dimensional shape unique to the protein
• bonds : intramolecular R-group interactions (HHID- hydrogen bond, hydrophobic interactions, ionic bonds, disulfide bonds)

Question 8

quarternary structure of proteins

Answer 8

• combination of a number of polypeptide chains, involves non-protein groups into a large, complex and functional protein molecule
• bonds : HHID hydrogen bonds, hydrophobic interactions, ionic bonds and disulfide bonds + non protein groups
• haemoglobin (4 polypeptide chains each contaning a heme group which has iron ion in the center)

Question 9

functions of proteins

Answer 9

1) homeostatic

2) enzymatic

3) hormonal

4) transport
* haemoglobin transports oxygen
* lipoproteins transports cholesterol

5) storage
* ferritin stores iron in liver
* myoglobin stores oxygen

6) protection
* antibodies
* blood clotting

7) support
* keratin - hair
* collagen - muscles and bones

8) source of energy for extreme starvation

Question 10

test for proteins

Answer 10

Biuret test
1. To 2cm³ of the test sample, add an equal volume of 5% sodium hydroxide (NaOH) solution
2. add 2 drops of 1% copper sulfate (CuSO4) solution and mix.
3. observe any color change

present = light blue –> violet
absent = stays light blue