Biomolecules - 1 -

BIOMOLECULES (assigned readings: chapter 3, p.34-52)

[LG1: Explain why carbon is important in biological molecules.]

Carbon and Organic Compounds

recall that ~99% of an organism is composed of C H O N Ca P most of that is water (H2O) and other inorganic molecules, as well as a great variety of organic

molecules... carbon-based molecules

the simplest organic molecules are hydrocarbons that consist of only C and H atoms...

for example, the straight-chain hydrocarbons that consist of methylene groups (-CH2-) and chain-ending methyl groups (-CH3) except where carbon-carbon double or triple covalent bonds are

found

e.g. methane (see fig. above right), ethane, propane, butane,...

hydrocarbons are nonpolar, hydrophobic molecules only sparingly soluble in water

although they consist of only two types of elements, hydrocarbons can exhibit considerable structural diversity...

[table ref: Reece, J.B., Taylor, M.R. Simon, E.J, and J.L. Dickey, Campbell Biology: Concepts and Connections. 7

th edition, Benjamin

Cummings, Toronto, 2012; fig. 3.1]

Biomolecules - 2 -

Functional Groups and the Structural / Functional Variation of Organic Compounds

in addition to carbon and hydrogen, nitrogen and oxygen are commonly found in organic

molecules and contribute to the huge diversity

of biological molecules (biomolecules)

associated with life

note the covalent bonding patterns of these four atoms... (see text fig. 3-1)

these four elements are often found in a handful of functional groups common to many biomolecules...

knowledge of just a handful of common functional groups can help us predict the properties and even the functions of many

biomolecules note that all but one of the functional groups in table 3-1 are polar and thus lend polar

character to the biomolecules in which they are found

this polarity helps make many biomolecules (or those regions of large biomolecules) hydrophilic and thus water soluble

fig. 3-1 The covalent bonding patterns of C,

H, O and N, the four most common

elements in living organisms.

Biomolecules - 3 -

The Four Major Classes of Biomolecules

biomolecules... biological organic compounds; many are quite small, others can be extremely large...

macromolecules... extremely large organic molecules; most are polymers constructed of monomers...

monomers... the building block molecules of a polymer

polymers... large molecules made up of many monomers covalently linked together

the monomers used may all be the same (homopolymers) or different (heteropolymers)... monomers can be polymerized by condensation (dehydration) reactions to form polymers (see fig.

3-2) and polymers can be disassembled by hydrolytic reactions (hydrolysis)... (fig. 3-3 below)

fig. 3-2 (above left) Dehydration

synthesis (a condensation reaction.)

fig. 3-3 (above right) Hydrolysis (a

hydrolytic reaction.)

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Carbohydrates

simple sugars (monosaccharides) and their polymers (disaccharides and polysaccharides) main functions...

energy storage...

fuel molecules...

structural support...

molecular recognition...

e.g. as exposed parts of membrane glycoproteins andglycolipids that are used as receptors for extracellular signalling molecules

monosaccharides... see text figs. 3-5 (glucose), 3-6 (other hexoses), 3-7 (important pentoses)

major cell nutrients (esp. glucose) their carbon skeletons are often the raw material used for

building other organic molecule

monosaccharides with 3C are trioses; 4C tetroses, 5C pentoses, 6C hexoses, 7C heptoses, 8C octoses

fig. 3-7 (above) Important pentoses. fig. 3-6 (above) Hexose examples.

fig. 3-5 Various depictions of glucose,

a common hexose.

Biomolecules - 5 -

disaccharides...

2 monosaccharides linked covalently by a glycosidic bond

e.g. sucrose; table sugar (see text fig. 3-8, not

shown)

made from glucose + fructose

e.g. maltose (see fig. at right)

Formation of a disaccharide... maltose

Biomolecules - 6 -

many monosaccharides covalently linked together by glycosidic bonds may be just a few monomeric units in length (an oligosaccharide) or may be hundreds, thousands of

monomers linked together

e.g. storage polysaccharides...

e.g. glycogen, the principal storage polysaccharide of animals e.g. starch, the principal storage polysaccharide of plants (see text fig. 3-9, below...)

fig. 3-9 Starch

Biomolecules - 7 -

e.g. structural polysaccharides.. e.g. cellulose of plant cell walls... (see text fig. 3-10, below...) e.g. chitin of insect exoskeletons... (see text fig. 3-11, below...)

fig. 3-10 (above) Cellulose.

fig. 3-11 (below) Chitin.

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Lipids

a very diverse collection of generally hydrophobic, water-insoluble organic molecules

examples... fatty acids, monoglycerides, diglycerides, triglycerides (fats; see

lower half of text fig. 3-12,), phospholipids (see text fig. 3-15), glycolipids,

sterols (e.g. cholesterol; see text fig. 3-16a) and steroid hormones (e.g.

estrogen and testosterone; see text fig. 3-16b and c, respectively), waxes

e.g. fatty acids...

compounds with a hydrophilic carboxyl group & an unbranched, hydrophobic hydrocarbon chain

(see upper half of text fig. 3-12, below)

some commonly encountered fatty acids... myristic

acid, palmitic acid, and stearic acid

e.g. monoglycerides, diglycerides, and triglycerides

(see lower half of fig. 3-12)

glycerides are formed by one or more condensation (dehydration) reactions between glycerol (a 3-carbon alcohol) and fatty acids

although lipids are mostly nonpolar, many often have a polar functional group that makes them amphipathic (amphiphilic)...

amphipathic molecules have both polar regions and nonpolar regions

Biomolecules - 9 -

note that fatty acids or the fatty-acyl chains of glycerides, phospholipids, etc., may be saturated or

unsaturated...

the saturation state of a fatty-acyl chain is a contributing factor to the fluidity of the molecule (e.g. see the fat and the oil in text fig. 3-14)

some functions of lipid molecules...

energy storage and as fuel molecules...

very compact fuel reserve

membrane formation... (e.g. phospholipids, fig. 3-15, below, and sterols like cholesterol, fig. 3-16a)

the amphipathic nature of phospholipids and glycolipids (as well as sterols like cholesterol) is particularly important to the structure and function of membranes (see topic 3: Membranes)

fig. 3-14 A fat (a) and an oil (b).

fig. 3-15 A phospholipid.

Biomolecules - 10 -

communication (cell signalling)...

e.g. the steroid sex hormones, e.g. testosterone and estradiol which are derived from cholesterol (see text fig. 3-16, below)

cholesterol... cholesterol is the precursor for all of our steroid hormones

protection of organs... e.g. adipose tissue cushions many organs

thermal insulation...

e.g. adipose tissue decreases thermal conductivity of body coverings

fig. 3-16 Cholesterol and two steroid hormones.