Proteins

Question 1

Proteins

Answer 1

• MONOMER= Amino acid
• POLYMER= Polypetide
• Polypeptides combine to form proteins
• 100 amino acids identified, but 20 amino acids occur naturally in proteins
• Made up of hydrogen, nitrogen, carbon & oxygen
• Have a specific shape to its function - change of shape leads to less function/protein to work differently

Question 2

Peptide bonds

Answer 2

• Formed during the combining of amino acids through a condensation reaction (rejects water)
• Bond forms between carboxyl group (COOH) and H
• When 2 amino acids join together they form a dipeptide
• Covalent

Question 3

Function of proteins

Answer 3

• Forms hair, nails and skin
• Hormones
• Enzymes
• Structural role in bones, tendons + muscles
• Antibodies

Question 4

Structure of proteins

Answer 4

1. Amino group (-NH2)- basic group from which the ‘amino’ from amino acid is derived
2. Carboxyl group (-COOH)- acidic group from which ‘acid’ is derived from amino acid
3. Hydrogen atom (-H)
4. R-group (variable)- a variety of different chemical group that varies in each amino acid
   * Split into primary, secondary, tertiary and quaternary structure to fold polypeptide into a specific shape for a specific function

Question 5

Primary structure

Answer 5

the order/sequence of amino acids
* change in the primary structure leads to a change in shape of a protein

Question 6

Secondary structure

Answer 6

the curling/folding of a polypeptide into a-helices + b-pleated sheets due to formation of H bonds
* there

Question 7

Tertiary structure

Answer 7

the overall 3-D shape of a protein, determined by interactions between R-group properties
* a-helices and b-pleated sheets twist and turn to give protein a complex, unique structure
* 3-D structure is determined by hydrophillic and hydrophobic R-groups also
* Compact ball shape for transport
* Complex structure is maintained by a number of different bonds:
1. Hydrogen bonds- formed between polar R-groups
2. Ionic bonds- formed between carboxyl (negative) and amino (positive) groups, aren’t involved in forming peptide bonds, 2nd weakest bond, easily broken down by changes in pH
3. Disulfide bonds- forms between sulfide atoms in R-groups, creates more folds to stabilise molecule, not easily broken down, fairly strong

Question 8

Quaternary structure

Answer 8

specific 3-D shape of a protein that is determined by multiple polypeptide/prosthetic groups bonded together
* Proteins are formed when multiple polypeptide chains link in various ways
* Non-protein (prosthetic) groups may associate with the polypeptide chains forming conjugated molecules e.g iron containing ‘haem’ group in haemoglobin

Question 9

Collogen

Answer 9

• FIBROUS PROTEIN
• Long polypeptide chain with repeating sequences of amino acids
• Insoluble- due to non-polar R-groups
• Form fibres that make them stronger due to cross-bridges
• Provides stength e.g. artery walls to prevent vessels from bursting from high pressure
• Found in tendons- connects muscles to bone to allow skeleton to move
• Found in skin-

Question 10

Haemoglobin

Answer 10

• GLOBULAR PROTEIN
• roughly spherical in shape + has specific shapes and function
• Used as transport, hormones + enzymes
• Protein found in red blood cells- transports oxygen from lungs to body tissue
• Quaternary structure- made up of 4 polypeptide chains
• Conjugated protein- has a prosthetic group attached to each polypeptide chain (haem- iron containing ions)
• Soluble