Biol 1551 Sep 13^th lecture notes

 

Chapter 3 Biological molecules (continued)

 

3. Four major classes of biological molecules
1. carbohydrate
2. lipid
3. protein
4. nucleic acid

 

 

4. Overview of biological polymers

 

type of organic molecule	polymer	monomer unit
carbohydrates	polysaccharide	monosaccharide
proteins	protein (polypeptide)*	amino acid
nucleic acids	nucleic acid (polynucleotide)*	nucleotide

* Although I did not use this terminology at this point of lecture, but these terms have been mentioned in the later lectures (Sep 16 and 18).

 

 

5. Carbohydrates

 

1. Monosaccharide (simple sugar)

·        Monosaccharide has chemical structure of (CH₂O)n. Although n can be any number between 3 and 7, 5 and 6 are common.

 

·        Examples of six-carbon monosaccharides are glucose and fructose (Fig 3.4B, p37).  The chemical formula of these sugars are the same (C₆H₁₂O₆).  But the structures are different.

 

·        Monosaccharides forms ring structure in solution.  (Fig 3.4C, p37)

Glucose – six-sided ring

Fructose – five-sided ring

 

 

2. Disaccharide – combination of two monosaccharides (Fig. 3.5, p38)

ex.

glucose + glucose = maltose

            glucose + fructose = sucrose (table sugar)

 

 

 

3. polysaccharide (Fig 3.7, p39)

                                                              i.      Starch

·        glucose unit with / without branching

·        plant storage polysaccharide

-hydrolysed to release glucose, which provides chemical energy

 

                                                            ii.      Glycogen

·        glucose unit with/without branching (more branching than starch)

·        animal storage polysaccharide

-hydrolysed to release glucose, which provides chemical energy

 

                                                          iii.      Cellulose

·        Most abundant organic molecules on earth!

·        glucose unit without branching

·        linked in a different orientation

·        extensive hydrogen bonds

·        structural support

- major component of cell wall, wood – used to produce paper

- Cotton fibers are made of cellulose.

·        Cannot be digested by animals – dietary fibers

- Cows get help from microorganisms in their stomach.

 

 

 

 

6. Lipids – made only with C and H linked by non-polar covalent bonds, hydrophobic (water insoluble)

 

“Water and oil doesn’t mix.” because water is polar and oil is non-polar.

 

1. fat/oil (oil is the liquid form of fat)

structure (Fig 3.8C, p40)

            glycerol + (fatty acid)x3

            Fat is also known as triglyceride.

function – energy storage in animals

 

Presence and absence of double bonds in fatty acid chain determines physical characteristics of fat.

 

                                                              i.      saturated fat

·        no double bonds in fatty acid chain

·        solidify easily

·        animal fat such as butter and lard

·        regular intake of saturated fat leads to increased risk of heart disease

 

                                                            ii.      unsaturated fat

·        double bond(s) in fatty acid chain-kink in the chain

·        stays liquid at room temperature

·        vegetable oil, fish oil

 

                                                            iii.      “not all fat is bad for you”

·        Regular intake of fish oil is associated with a reduced risk of heart disease.

 

                                                           iv.      “not all vegetable oil is better for you”

hydrogenated vegetable oil – Hydrogen is added to vegetable oil to make saturated fat.  Found often in margarine.  Regular intake of margarine containing hydrogenated vegetable oil increases the risk of heart disease

 

2. phospholipids

·        structure (Fig 5.11 A, p79)

 

·        consists of three parts

o       phosphate containing portion

o       glycerol

o       two fatty acid chains

 

·        one end is hydrophilic (phosphate containing portion)

·        one end is hydrophobic (fatty acid chains)

·        main component of plasma membrane (cell membrane)

phospholipid bilayer (Fig 5.11, p79)

 

 

3. wax

                                                               i.      fatty acid + alcohol

                                                             ii.      more hydrophobic than other lipids

                                                            iii.      makes natural coating to prevent water loss

·        fruits

·        insects

 

 

4. steroids

 

four-ring structure (Fig 3.9, p41)

 

<cholesterol>

·        integral part of animal cell membrane (Fig 5.12, p80)

·        starting material for other steroids

 

<steroid hormones>

·        testosterone – male sex hormone

·        estradiol – female sex hormone

“anabolic steroid” – synthetic variants of testosterone

-         promote muscle growth / sports performance

-         serious health hazard – banned