IB Biology: Biomolecules

Carbohydrates & Lipids

Macromolecules

carbon compounds can be large molecules made from many small, repeating subunits

• have high molecular mass

• formed during condensation reactions

• often needs to be broken down into its monomers(e.g. in digestion)

Monomers

• smaller units from which larger molecules are made from

Polymers

molecules made from a larger number of monomers joined together in a chain

• polymers can be macromolecules, but not all macromolecules are polymers(e.g. lipids)

Condensation Reaction

• aka dehydration synthesis reactions

• requires energy(ATP)

• occurs when molecules combine, forming covalent bonds and resulting in polymers(polymerisation) or macromolecules

  • water is removed as part of the reaction

    • Polysaccharides(forms a glycosidic bond)

    • Polypeptides|(forms a peptide bond)

    • Nucleic Acids(form phosphodiester bond)

Hydrolysis

• means to break with water

• releases energy

• in the hydrolysis of macromolecules, covalent bonds are broken when water is added

  • hydrolysis of glycosidic bonds(produces monosaccharides)

  • hydrolysis of peptide bonds(produces amino acids)

  • hydrolysis of ester bonds(produces three fatty acids and glycerol)

Monosaccharides

• monomers of carbohydrates

  • disaccharide(two monosaccharides)

  • polysaccharaides(many monosaccharides)

• can join together via condensation reactions

  Different types of monosaccharides:

• Triose(e.g. glyceraldehyde)

• Pentose(e.g. ribose)

• Hexose(e.g. glucose)

Glucose

the main substrate used in respiration, releasing energy for the production of ATP

• produced during photosynthesis

• Isomers of glucose:

  • alpha(a) glucose

  • beta(B) glucose

• Starch and glycogen are made from alpha glucose

• Cellulose is made from molecules of beta-glucose

Properties of Glucose

• stable structure —covalent bonds

• Soluble in water due to its polar nature

• easily transportable due to its water solubility

• a source of chemical energy(when bonds are broken)

Starch

• the storage polysaccharide of plants

  • stored as granules in chloroplasts

• composed of alpha glucose monomers

• constructed from two different polysaccharides

  • Amylose(unbranched helix-shaped chain - more resistant to digestion)

  • Amylopectin(branched molecule - can be easily hydrolysed for cellular respiration or storage)

Glycogen

• a highly branched storage polysaccharide in animals and fungi

• liver and muscle cells contain glycogen as visible granules, enabling high rates of cellular respiration

  • can be broken down quickly, supplying the higher metabolic needs

Cellulose

• a structural carbohydrate found in the cell walls of plants

  • molecules are straight and unbranched

  • a polymer of B-glucose monomers

• cellulose molecules are joined by hydrogen bonds to form microfibrils; gives cellulose its structural strength

Glycoproteins

• when carbohydrates and polypeptides combine via covalent bonds

• forms part of the structure of cell surface membranes

• Acts as receptor molecules:

  • cell recognition & identification

  • receptors for cell signalling molecules

  • endocytosis

  • cell adhesion and stabilization

Glycoproteins & ABO Blood types

• glycoproteins can act as antigens which can identify cells as either “self” or “non-self”

  • cells that are recognized as non-self trigger immune responses

Lipids

(e.g. fats, oils, waxes, and steroids)

• Lipid macromolecules contain carbon, hydrogen, and oxygen atoms

• non-polar nature of lipid molecules means that lipids are insoluble in water or other polar solvents

• Can be improved through a combination

  • glycolipids

  • lipoproteins

Triglycerides

• formed when three fatty acids join to one glycerol molecule

  • fatty acids contain hydrocarbon chains that can be either saturated or unsaturated

• Formed by a dehydration synthesis reaction

  • formation of an ester bond is a condensation reaction

  • Three water molecules are released

• useful for long-term energy storage/ non-polar

Phospholipids

• formed from glycerol and fatty acids

• Phospholipids are amphipathic

  • polar hydrophilic head and non-polar hydrophobic fatty acid “tails”

• can have monolayers or bilayers when placed in water

• contains two fatty acids bonded to a glyercerol molecule with a phosphate ion

Properties of Triglycerides

• Lipids as an energy source

  • energy-dense due to a high # of C-H bonds

  • hydrolysis of triglycerides releases fatty acids and glycerol, forming useful respiratory substrates

  • insoluble — not easily transportable

• long-term energy storage

Fatty Acids

• Both triglycerides and phospholipids contain glycerol with fatty acids attached

• Fatty acids have long hydrocarbon ‘tails’

• Occurs in two forms:

  • saturated fatty acids

  • unsaturated fatty acids

    • can be monounsaturated or polyunsaturated

Saturated Fatty Acids

• carbon atoms in the hydrocarbon tail are all single bonds

  • ‘saturated’ with hydrogen bonds

• straight molecules; solid at room temperature

• storage molecules in animals(e.g. fats in meat and butter)

Unsaturated Fats

• bonds between carbon atoms in the hydrocarbon tail contain double bonds

  • double bonds cause the hydrocarbon tail to kink, or bend

• Monosaturated: a fatty acid with one C=C double bond; lower melting point

• Polyunsaturated: fatty acids with many C=C double bonds; low melting point