Macromolecules

Page Contents

• Organic Compounds
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids

Organic compounds contain the element carbon. Carbon has the ability to form long chain molecules or ring structures. Carbon unites readily with H, O, N. Examples of organic compounds are carbohydrates, lipids, proteins and nucleic acids.

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Carbohydrates
Carbohydrates are optically active aldehyde or ketone compounds with two or more hydroxyl groups. Carbohydrates are an important source of energy for living organisms. In addition, they serve as metabolic intermediates, structural framework for DNA and RNA, structural supports in the cell walls of plants and bacteria, and as a linkage to many proteins and lipids.

Sugars
3 important types of carbohydrates are monsaccharides, disaccharides (common transport form of sugar) and polysaccharides (storage form). Monosaccharides are the simplest carbohydrates. When monosaccharides polymerize, they may form disaccharides and polysaccharides through dehydration reactions. Click here for a diagram illustrating the synthesis of a disaccharide. The resulting bonds between the subunits are termed glycosidic or ether bonds.

Monsaccharides	Disaccharides	Polysaccharides

Starches
Polysacccharides formed from glucose
Simplest structure: amylose Click here for picture
Amylopectin is a complicated variant of amylose (plant starch)
PECTINS: branched polysaccharides

1) Glycogen: highly branched animal starch
2) Cellulose: plant starch with alternating glucose subunit orientations
** Starch degrading enzyme cannot break the bond between two sugars in opposite orientation. Therefore cellulose cannot readily be broken down -- good structural material.
CHITIN: modified form of cellulose in which a N-group has been added to glucose units (i.e. crab shells)

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ROLE OF LIPIDS Fats provide 38kJ of energy compared with 17kJ for carbohydrates and proteins. - used when occasion arises
- excess carbohydrates are converted into fat
- beneath skin, around organs - exoskeleton of insects, skin of vertebrate
- sub-cutaneous fat - causes uterus to contract

Fats	Phospholipids	Steroids
Glycerol + 3 fatty acids	Glycerol + 2 fatty acids

FATS
- simple lipids containing C, H and O
- made up of glycerol and fatty acids

Trihydex alcohol (3 hydroxyl groups)

- long/short chains of hydrocarbons (C/H)
- carboxyl group at one end
- fatty acids used may be the same or different, unsaturated or saturated
a) Saturated fatty acids [Click here]
b) Unsaturated fatty acids [Click here]

Building up of Fats
Hydroxyl groups of glycerol interact with carboxyl groups of fatty acids
- water is eliminated
- ester bond results from the reaction between acid and alcohol
- fat formed depends on fatty acid used
[Click here for diagram illustrating building up of fats]

Unsaturated Fats
Formed from unsaturated fatty acids (has double bonds)
Lower melting points than saturated fats
Most are liquid at room temperature (oils)
Plants fats: cottoseed oil, peanut oil, sesame seed oil, olive oil

Saturated Fats
Formed from saturated fatty acids (ONLY single bonds)
More calories because it is richer in energy
Diet of saturated fats (red meat, lamb, lard) can lead to diseases of heart & major arteries
Animal fats: palmitic acid, stearic acid

PHOSPHOLIPIDS
- Complex lipids
- Amphiphilic lipids
- Glycerol + 2 fatty acids + PO + organic base:
Polar group is substituted for one of the three fatty acids in a fat molecule.
--> many cases, includes a phosphate group (PO)
--> most cases, the PO is combined with an organic base
- Most abundant phospholipid: phosphatidyl ethanolamine (cophalin)
*major constituent of cell membranes*

Role
- Structural
- Transport of fat in the blood (since phospholipids are soluble in water)
- Some are a source of choline

STEROIDS
Have certain properties like lipids.
-- insoluble in water, soluble in organic solvents

Structurally they differ from each other in:
a) location and nature of side group
b) location of certain double bonds
* skeleton of 4 rings (17 C-atoms)

General Structure:
OH attached to C-3
CH group attached to C-10, 13

In cholesterol, the branched hydrocarbon chain is attached to C-17.

Example of steroids

• Cholesterol
  • Synthesis of other steroids eg. bile salts, vitamin D
  • From diest and from carb/proteins.
  • Synthesis of sex hormones, adreno-cortical hormones
  • Manufactured by liver
  • Also taken in via foods i.e. dairy fat, egg yolk, organ meat
• Bile Salts
  • Synthesized and secreted by liver.
  • Emulsify fats in the intestine
• Sex hormones
  • estrogens
  • progesterone
  • testosterone

• Major structural material in animals
  • cell membranes
  • wall of cell organelles
  • connective tissues (collagen, elastin)
  • skeletal materials (collagen)
  • hair and nails (keratin)
  • muscle fibres (myosin)
• Control the chemical reactions and metabolic processes
  • enzymes (act as catalysts)
  • hormones (eg. insulin)
• Transport proteins
  • haemoglobin transports O and CO in the blood
• Protective proteins of bloods
  • clotting of blood (fibrinogen)
  • antibodies (inactivated foreign substances)
• Serve as food reserves
  • Ovalbumin (ingredient of egg white)
  • Casein (protein in mammalian milk)

AMINO ACIDS

Fundamental structural unit of proteins [Click here for illustration of the 20 a.a]
White, crystalline, soluble in water
Optically active except glycine
Optical isomers or stereoisomers
--> linkage of atoms are the same, differ only in the way that the constituent atoms are arranged in space
--> caused by presence of asymmetric C

Amino Acids are amphoteric substances ) - attracts protons In solution, NH and COOH interact together

Classes of amino acids:
Non-polar R groups (hydrophobic a.a.)
Polar R groups (hydrophillic a.a.)
Positively charged R group (NH)
Negatively charged R group (COO-)

Non-essential amino acids Essential amino acids
Remaining 10 cannot be synthesized and must be taken in diet. e.g. alanine, serine, lysine, aspartic acid

STRUCTURE OF PROTEINS
Insulin was the first protein to have its sequence determined by Frederick Sanger.

Primary Structure The sequence of amino acids in a protein together with the location of disulfide bridges. Single polypeptide chain.

Secondary Structure Polypeptide chains are not in the extended form but folded into sheets (fibrous) or wrapped into coils (globular). In many cases, folded into long spiral or helix maintained by S-S bridges and H-bonds between adjacent O-H atoms.

Tertiary Structure

Quaternary Structure Aggregate of subunits (eg. haemoglobin) Weak H-bonds keep the 4 polypeptide chains together.

CLASSIFICATION OF PROTEINS
Based on their physical characteristics
a) Fibrous
- polypeptide chains are arranged in parallel form to give physical toughness
- long & linear molecules
- insoluble in water
b) Globular
- polypeptide chains are tightly folded to form a spherical shape
- soluble in aqueous media

Based on their composition
a)Simiple proteins
- on hydrolysis, yield only a/a
b) Conjugated proteins
- on hydrolysis, yields a/a & non-protein compound (prosthetic grp.)
- eg. myoglobin has a heme prosthetic grp.

GENERAL CHARACTERISTICS OF PROTEINS IDENTIFICATION OF A/A IN A PROTEIN
Amino acids are separated and identified by paper chromatography.
Technique depends on the fact that different a/a have different solubility properties.
Amino acids travel at different speeds and separate on absorptive paper.
Treat paper with ninhydrin to stain, fluoresce under UV light, cut out, spot and dissolve.

[Link to website on protein sequencing]

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