Protein And Lipid

Question 1

Mention the functions of proteins and examples

Answer 1

• Act as enzymes (pepsin, DNA polymerase)
• Structural proteins (Keratin, collagen)
• Act as carrier and transport (Haemoglobin, aquaporin)
• Require for cell signalling (insulin & other hormones )
• Involve in defense mechanism (antibodies)
• As storage (bean seed proteins)

Question 2

What is the structure for proteins and what are the classes and number of amino acids

Answer 2

Made up of chain of amino acids that are joined together by peptide bonds.
Peptides: fewer than 50 aa
Dipeptides: 2 aa
Tripeptides: 3 aa
Polypeptides: more than 10 aa
Protein: more than 50 aa

Question 3

Describe the strcuture of amino acid

Answer 3

Amino acid consist of
central carbon atom which is alpha carbon
amino group
carboxyl group 
and a R group

The R group is a variable group that is different for each amino acid that gives unique chemical properties to each amino acid.

Question 4

How is a peptide bond formed between amino acid

Answer 4

During condensation reaction when a water molecule is removed, a covalent bond is formed between amine group of one amino group to a carboxyl group of another forming a C-N bond.
This bond is broken by hydrolysis

Question 5

Difference between essential, nonessential and conditional amino acids

Answer 5

Essential: Must be consumed in the diet

Nonesential: Can be synthesized in the body

Conditionally essential: Cannot be synthesized due to illness or lack of necessary precursors

Question 6

Give an example of conditionally essential amino acid

Answer 6

Arginine, premature infants lack sufficient enzymes required too create arginine.

Question 7

Why are the amino acids nonpolar and hydrophobic?

Question 8

Why are these amino acids polar and hydrophillic

Question 9

What is the name of the bond between sulfur and amino acid

Answer 9

Disulfide bridges

Question 10

Types of folding in secondary and tertiary protein structures.

Answer 10

Secondary: Local folding along short sections of polypeptide and interaction between adjacent amino acids.

Tertiary: Whole molecule folding interactions between distant amino acids

Question 11

Types of bonds in different levels of structure

Answer 11

Primary: Peptide bond

Secondary: Hydrogen bonds (weak bonds), alpha-helix and beta-pleated sheets.

Tertiary: Hydrophobic interactions, van der Waals interactions, hydrogen bonds, ionic bonds, disulfide bridges, covalent bonds between sulfurs in sulfhydryls.

Quaternary structures:
Hydrophobic interactions

Question 12

Conditions required for disrupting bonds of proteins (protein denaturation)

Answer 12

Heat
Acid
Bases
Salts 
Mechanical agitation

Question 13

What happens to the protein during protein denaturation

Answer 13

Unfavourable condition alter secondary and tertiary structure but does not change the primary strucutre. It alters 3D shape and destroys functionality.

Only some proteins can return to their functional shape.

Question 14

Protein strcuture obtained by what methods

Answer 14

X-ray crystallography

NMR- Nuclear Magnetic Resonance

Question 15

Is lipid a polymer like proteins, nucleic acids, polysaccharides?

Answer 15

NO

Question 16

Describe the importance of lipids

Answer 16

• Important constituent of the cell membranes
• Help in absorption of fat-soluble vitamins
• Maintain membrane fluidity
• Fat stored in adipose tissue: as a thermal insulator in subcutaneous tissues.
• Hormone synthesis
• Organ padding

Question 17

Major lipid of physiological significance

Answer 17

Fatty acid, Basic unit of fat composed of carbon atoms and hydrogen bonding

Question 18

Name two types of fatty acids

Answer 18

Saturated FA

Unsaturated FA

Question 19

Difference between unsaturated and saturated fatty acids

Answer 19

Saturated fatty acids have no double bonds, unsaturated contain one or more double bonds.

Saturated considered harmful. Unsaturated found in food from both plant and animal sources.

Saturated increases total cholesterol levels and triglycerde level. Unsaturated increase HDL level and lower total cholesterol levels

Saturated fatty acids are saturated with hydrogen since single bonds increase the number of hydrogens on each carbon unlike unsaturated due to double bonds.

Unsaturated are divided into monosaturated and polyunsaturated.

Question 20

Mention two hypercholestrolemic saturated fatty acids

Answer 20

• Myristic acid

- Lauric acid

Question 21

What are the divisions of unsaturated fatty acids

Answer 21

• Monounsaturated fatty acids
• Polyunsaturated fatty acids
• Eicosanoids

Question 22

Difference between monounsaturated and polyunsaturated fatty acids?

Answer 22

Monounsaturated: Contain one point of unsaturation (double bond) but polyunsaturated contain more than two points of unsaturation (double bond)

Monosaturated found in vegetable oil, polyunsaturated found in nuts and vegetable oil, soybean, sunflower, fatty fish.

Question 23

Similarity between monounsaturated and polyunsaturated

Answer 23

Beneficial for human consumption

Polysaccharide in particular has a protective role.

Question 24

Difference between Cis-unsaturated fatty acids and Trans unsaturated fatty acids

Answer 24

If hydrogens are present in the same plane, it is referred to as a cis fat; if the hydrogen atoms are on two different planes, it is referred to as a trans fat. The cis double bond causes a bend or a “kink” that prevents the fatty acids from packing tightly, keeping them liquid at room temperature.

Question 25

Significance of cos unsaturate fatty acids

Answer 25

• Decrease total cholesterol
• Decrease triglyceride level
• Increase HDL level