B1.1 Carbohydrates and Lipids

B1.1.1—Chemical properties of a carbon atom allowing for the formation of diverse compounds upon which life is based

Students should understand the nature of a covalent bond. Students should also understand that a carbon atom can form up to four single bonds or a combination of single and double bonds with other carbon atoms or atoms of other non-metallic elements. Include among the diversity of carbon compounds examples of molecules with branched or unbranched chains and single or multiple rings.

NOS: Students should understand that scientific conventions are based on international agreement (SI metric unit prefixes “kilo”, “centi”, “milli”, “micro” and “nano”).

  • Carbohydrates are carbon-based molecules because carbon is good at forming 4 stable covalent bonds

    • Covalent bond - shared pair electrons with attraction to positive nuclei

    • Able to make stable and complex structures

    • Can form chains and rings

  • Condensation reactions form macromolecules - Uses monomers to create polymers

    • Condensation reactions: removes water to form a bond between two molecules (anabolic reactions)

      • Requires energy

      • The bond between two monosaccharides (simple sugars) are called glycosidic bonds

  • Disaccharides - two monosaccharides that are bonded together. ex. maltose (from two glucose)

  • Polysaccharides - many monosaccharides bonded together ex. amylopectin (form of starch)

  • Glucose is a 6 carbon sugar and is numbered from 1-5 clockwise (6 is not in the ring structure

    • Bonds between the 1st and 4th carbon of adjacent glucose molecules create 1-4 linkages; these create more linear structures

    • Bonds between the 1st and 6th carbon of adjacent glucose molecules create 1-6 linkages; results in branches of a molecule

    • All the bonds are created from condensation reactions

B1.1.2—Production of macromolecules by condensation reactions that link monomers to form a polymer

Students should be familiar with examples of polysaccharides, polypeptides and nucleic acids.

  • alpha-glucose: hydroxyl groups is on the bottom below hydrogen and is connected to C-1

  • beta-glucose: hydroxyl group is on the top above hydrogen and connected to C-1

B1.1.3—Digestion of polymers into monomers by hydrolysis reactions

Water molecules are split to provide the -H and -OH groups that are incorporated to produce monomers, hence the name of this type of reaction.

  • Hydrolysis - addition of water to split two molecules apart

  • Digestion: chemical breakdown of larger molecules into small molecules. Will always involve hydrolysis

B1.1.4—Form and function of monosaccharides

Students should be able to recognize pentoses and hexoses as monosaccharides from molecular diagrams showing them in the ring forms. Use glucose as an example of the link between the properties of a monosaccharide and how it is used, emphasizing solubility, transportability, chemical stability and the yield of energy from oxidation as properties.

  • Monosaccharide - one (mono) simple sugar

    • Triose sugars - 3 carbon sugars

    • Pentose sugars (ex. ribose) - 5 carbon sugars

    • 5-carbon and 6-carbon sugars form carbon rings with an oxygen atom

  • Glucose - C6H12O6

    • Polar molecules; soluble in water

    • Small

    • Stable (even when dissolved in water)

    • Yields energy when oxidized

B1.1.5—Polysaccharides as energy storage compounds

Include the compact nature of starch in plants and glycogen in animals due to coiling and branching during polymerization, the relative insolubility of these compounds due to large molecular size and the relative ease of adding or removing alpha-glucose monomers by condensation and hydrolysis to build or mobilize energy stores.

  • Polysaccharides - many saccharides bonded together

  • Similarities - Not soluble in water, do not have fixed size

  • Function of structural support: cellulose

  • Function of energy storage

    • Glycogen - energy storage molecule used in animals

      • Made of alpha-glucose, made of 1-4 and 1-6 linkages. Has more 1-6 linkages, making it highly branched

    • Starch (amylose and amylopectin) - energy storage molecule used in plants

      • Amylose: 1-4 glycosidic linkages/bond, made of alpha-glucose, makes a spiral chain (linear)

      • Amylopectin: 1-4 and 1-6 glycosidic linkages/bonds, made of alpha-glucose, spirals into branches

B1.1.6—Structure of cellulose related to its function as a structural polysaccharide in plants

Include the alternating orientation of beta-glucose monomers, giving straight chains that can be grouped in bundles and cross-linked with hydrogen bonds.

  • Cellulose - a polysaccharide made of glucose used as a structural component of plant cells

    • Made of beta-glucose and has 1-4 glycosidic bonds

    • Very straight chains

    • Can form hydrogen bonds with parallel chains of cellulose, making cellulose very strong

B1.1.7—Role of glycoproteins in cell–cell recognition Include ABO antigens as an example.

  • glycoprotein: a protein with an attached carbohydrate chain

    • embedded in cell membranes with chains facing outwards

    • Used in cell recognition

    • Each cell will have a unique pattern of monosaccharides/glycoproteins

  • Four blood types in humans: A, B, AB, O

    • Recognized by different antigens

      • Antigens: recognition features on the outside of cells (and viruses or other particles. There are type A, B, and O antigens

      • Antigens are the glycoproteins

    • If someone has a type B blood, the body will recognize the type B antigens

    • However, if that person received type A blood, the immune system would not recognize the antigens and will attack it

B1.1.8—Hydrophobic properties of lipids

Lipids are substances in living organisms that dissolve in non-polar solvents but are only sparingly soluble in aqueous solvents. Lipids include fats, oils, waxes and steroids.

B1.1.9—Formation of triglycerides and phospholipids by condensation reactions

One glycerol molecule can link three fatty acid molecules or two fatty acid molecules and one phosphate group.

  • Hydrophobic (water-hating) molecules; this is because they are non-polar and non-soluble in water

    • Include fats, oils, waxes, and steroids

  • Fatty Acids: A carbon chain with a carboxyl group and methyl group on opposite sides

  • Triglyceride: made of glycerol combined with three fatty acid chains

    • These bonds are formed by condensation reactions

    • Entirely hydrophobic (non-polar, non-soluble in H2O)

  • Phospholipids: made of glycerol, 2 fatty acid tails, 1 phosphate group head

    • The phosphate group and glycerol head is polar/hydrophilic

    • The fatty acid tails are non-polar/hydrophobic

    • Are amphipathic molecules, meaning they have both hydrophilic and hydrophobic parts

B1.1.10—Difference between saturated, monounsaturated and polyunsaturated fatty acids

Include the number of double carbon (C=C) bonds and how this affects melting point. Relate this to the prevalence of different types of fatty acids in oils and fats used for energy storage in plants and endotherms respectively.

  • Monounsaturated fatty acids: contain one double bond, which creates a kink/bend in the chain

    • When all of the hydrogens are on one side, they repel each other, creating a bend in the chain

  • Polyunsaturated fatty acid: contains more than one double bonds in one chain (multiple kinks)

  • Trans fatty acid: the hydrogens are on opposite sides of the chain, causing equal repelling force.

  • Cis-unsaturated fatty acids (naturally occurring fatty acids)

    • Hydrogen atoms are on the same side of the chain

    • Most natural fatty acids

    • Oils

    • Have bends/kinks

  • Trans-unsaturated fatty acids

    • Hydrogen atoms on opposite sides of the chain

    • Straightens out the chain

    • Usually manmade, helps to solidify fatty acids (more stable)

    • Health concerns as they are easily metabolized in the cholesterol

B1.1.11—Triglycerides in adipose tissues for energy storage and thermal insulation

Students should understand that the properties of triglycerides make them suited to long-term energy storage functions. Students should be able to relate the use of triglycerides as thermal insulators to body temperature and habitat.

  • Adipose tissue: fatty tissue under the skin and around organs made mostly of triglycerides

    • Triglycerides are very good at storing energy long term

    • Stable

    • Insoluble, so they do not affect osmolarity or concentration gradients

    • Very energy dense (9 cal/g whereas carbs have 4 cal/g)

    • Have thermal insulation; not good heat conductors so they help keep organism warm (ex. ringed seal and their blubber)

    • Good for absorber shock, which is great for the protection of organs

B1.1.12—Formation of phospholipid bilayers as a consequence of the hydrophobic and hydrophilic regions

Students should use and understand the term “amphipathic”.

  • Phospholipids form in watery solutions form a bilayer with tails pointing inwards and heads pointing outward

B1.1.13—Ability of non-polar steroids to pass through the phospholipid bilayer

Include oestradiol and testosterone as examples. Students should be able to identify compounds as steroids from molecular diagrams.

  • Help determine permeability of the bilayer

  • Polar molecules (ex. glucose) cannot pass because of their charges

  • Steroids are made of non-polar lipids

    • Ex. Testosterone

      • Made of 3 6-sided rings and 1 5-sided ring

      • Hydrophobic lipid-based molecules, allowing it to pass through lipid bilayer

      • Steroid hormones can go directly into the cells