B1.1 Carbohydrates and Lipids Exhaustive Study Guide

Chemical Properties of the Carbon Atom

• Carbon as the Backbone of Life: All organic compounds have carbon at their core. Carbon is considered special because its chemical properties allow for the formation of diverse compounds upon which life is based.

• Covalent Bonding: Students must 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. These bonds are formed by sharing electrons (covalent bonds).

• Structural Diversity: The ability of carbon to bond in multiple ways allows for the creation of:

  • Branched chains.

  • Unbranched (straight) chains.

  • Single or multiple ring structures.

• NOS (Nature of Science): Scientific conventions are based on international agreement. This includes the SI metric unit prefixes:

  • kilo ($10^{3}$)

  • centi ($10^{-2}$)

  • milli ($10^{-3}$)

  • micro ($10^{-6}$)

  • nano ($10^{-9}$)

Atomic Theory and Elements

• Understanding Atomic Numbers:

  • Top Number: Represents the number of protons.

  • Bottom Number: Represents the atomic mass, which is the number of protons plus the number of neutrons. This value is often an average, reflecting the distribution of isotopes.

• Essential Elements for Humans:

  • Essential: Hydrogen ($H$), Carbon ($C$), Nitrogen ($N$), Oxygen ($O$), Phosphorus ($P$), Sulfur ($S$), Chlorine ($Cl$), Sodium ($Na$), Magnesium ($Mg$), Potassium ($K$), Calcium ($Ca$), Iron ($Fe$), Iodine ($I$), Zinc ($Zn$), Copper ($Cu$), Manganese ($Mn$), Selenium ($Se$), Molybdenum ($Mo$).

  • Suggested Essential: Boron ($B$), Silicon ($Si$), Vanadium ($V$), Chromium ($Cr$), Cobalt ($Co$), Nickel ($Ni$), Tin ($Sn$), Fluorine ($F$), Arsenic ($As$).

  • Nonessential: Helium ($He$), Neon ($Ne$), Argon ($Ar$), Krypton ($Kr$), Xenon ($Xe$), etc.

Macromolecules: Synthesis and Digestion

• B1.1.2 Production of Macromolecules by Condensation Reactions: Monomers are linked together to form polymers (macromolecules). This process joins them and releases a water molecule ($H_2O$) in the process. Examples include:

  • Polysaccharides.

  • Polypeptides.

  • Nucleic acids.

  • Lipids.

• B1.1.3 Digestion of Polymers by Hydrolysis Reactions: Polymers are broken down into monomers through digestion. Water molecules are split to provide the $-H$ and $-OH$ groups which are then incorporated into the produced monomers.

Form and Function of Monosaccharides

• B1.1.4 Recognition and Properties: Monosaccharides can be recognized as pentoses (5-carbon) or hexoses (6-carbon) from molecular diagrams, typically shown in ring forms.

• Example: Glucose ($C_6H_{12}O_6$):

  • Solubility: High (highly soluble in water).

  • Transportability: High (easily transported within organisms).

  • Chemical Stability: High (stable molecule).

  • Energy Yield: High yield of energy from oxidation.

• Structural Variations:

  • Alpha ($\alpha$) Glucose: The hydroxyl ($-OH$) group on carbon-1 ($C_1$) is positioned downwards.

  • Beta ($\beta$) Glucose: The hydroxyl group on $C_1$ is positioned upwards.

Polysaccharides: Storage and Structure

• B1.1.5 Polysaccharides as Energy Storage compounds: These are made of alpha-glucose monomers linked together.

  • Starch (Plants): Includes amylose and amylopectin. It has a compact nature due to coiling and branching during polymerization.

  • Glycogen (Animals): Highly branched and compact.

  • Properties:

    • Relative insolubility due to large molecular size.

    • Compact and efficient storage system.

    • Ease of adding or removing monomers by condensation and hydrolysis to build or mobilize energy stores.

• B1.1.6 Structure of Cellulose: A structural polysaccharide in plants.

  • Composition: Beta-glucose monomers joined together.

  • Orientation: Alternating orientation of monomers ($180^{\circ}$ rotation relative to each other).

  • Result: Formation of straight chains that group into bundles and cross-link with hydrogen bonds.

  • Function: Forms plant cell walls that are rigid and strong.

Glycoproteins and Cell Recognition

• B1.1.7 Role of Glycoproteins: These consist of proteins with carbohydrate chains attached. They are found in cell membranes, sticking out into the extracellular space.

• Function: Crucial for cell-to-cell recognition.

• Example: ABO antigens (located on the surface of red blood cells) serve as a primary example of this recognition system.

Lipids: Properties and Classification

• B1.1.8 Hydrophobic Properties: Lipids are substances in living organisms that dissolve in non-polar solvents and are mostly insoluble in aqueous (water-based) solvents.

• Types of Lipids:

  • Fats and Oils: Triglycerides.

  • Waxes: Single chain lipids.

  • Steroids: Four-ring structures.

• Reason for Hydrophobicity: Lipids contain long chains of carbon sharing electrons equally, making the molecule non-polar.

Formation of Triglycerides and Phospholipids

• B1.1.9 Condensation Reactions in Lipids:

  • Triglycerides: Formed by linking one glycerol molecule to three fatty acid molecules.

  • Phospholipids: Formed by linking one glycerol molecule to two fatty acid molecules and one phosphate ($PO_4$) group.

Fatty Acids: Structure and Health

• B1.1.10 Types of Fatty Acids:

  • Saturated Fatty Acids: No double bonds between carbons; the chain is "full" of hydrogens. They are straight chains and typically found in animals. They are solid at room temperature with high melting points (e.g., $32\,^{\circ}C$).

  • Unsaturated Fatty Acids:

    • Monounsaturated: One double carbon bond ($C=C$).

    • Polyunsaturated: Multiple double carbon bonds ($C=C$).

    • Cis-unsaturated: Hydrogens are on the same side of the double bond, causing a "kinked" chain. They are liquid at room temperature with low melting points (e.g., $-5\,^{\circ}C$). Found primarily in plants and fish (e.g., Salmon).

    • Trans-unsaturated: Hydrogens are on opposite sides of the double bond.

• Saturated vs. Unsaturated Content in Sources:

  • Animal Fats: High saturated acid content (e.g., Butter: $15\%$ palmitic; Lard: $25\%$ palmitic, $15\%$ stearic; Human fat: $25\%$ palmitic).

  • Plant Oils: High unsaturated content (e.g., Olive oil: $80\%$ oleic; Corn oil: $52\%$ linoleic; Safflower: $76\%$ linoleic).

  • Exceptions: Coconut oil and Palm oil are high in saturated fats compared to other plants.

• Temperature Adaptations:

  • Organisms seek the most tightly packed fatty acids that remain liquid at their body temperature.

  • Endotherms: Use saturated fatty acids because high body temperatures keep them liquid.

  • Ectotherms (e.g., Cold-water fish): Use cis-unsaturated fatty acids to maintain liquidity at low temperatures.

  • Plants: Generally possess liquid oils (cis-unsaturated) as they cannot control their temperature.

Role of Triglycerides in Adipose Tissue

• B1.1.11 Energy Storage and Insulation:

  • Energy Storage: Triglycerides are used for long-term energy storage. They are twice as energy-dense as carbohydrates but more difficult to digest and transport because they are non-polar.

  • Thermal Insulation: Triglycerides have low thermal conductivity.

  • Case Study: Aquatic mammals (e.g., "Fat Neal the Seal") have thick layers of blubber (adipose tissue) to reduce heat loss from the core to the aquatic environment.

Phospholipid Bilayers and Steroids

• B1.1.12 Formation of Bilayers: Phospholipids are amphipathic, meaning they have both a hydrophilic head (phosphate group) and a hydrophobic tail (fatty acids).

  • In water, the tails cluster together while heads face the water, forming a bilayer. This is the fundamental structure of the plasma membrane.

• B1.1.13 Steroids: Non-polar steroids can pass directly through the phospholipid bilayer to affect the cell.

  • Examples: Oestradiol and Testosterone.

  • Identification: Steroids can be identified by their distinctive four-ring molecular structure.