L4// Biology: Carbohydrates and Lipids - Structure, Function, and Diversity

Organic Compound

A compound containing carbon

Carbon Valence

Carbon (valence = 4) can form four covalent bonds with other atoms

Methane

Molecular formula: CH4

Ethane

Molecular formula: C2H6

Ethene (ethylene)

Molecular formula: C2H4

Hydrocarbons

Organic molecules consisting of only carbon and hydrogen

Polymers

Macromolecules built from monomers

Monomers

The small building-blocks of molecules

Dehydration Reaction

Occurs when two monomers bond together through the loss of a water molecule

Hydrolysis

The reverse of dehydration reaction, breaking down a polymer into monomers

Monosaccharides

The simplest carbohydrates, or simple sugars

Glucose

The most common monosaccharide, molecular formula: C6H12O6

Hexoses

6-carbon sugars

Triose

3-carbon sugars

Pentose

5-carbon sugars

Disaccharide

Formed when a dehydration reaction joins two monosaccharides

Glycosidic Linkage

The covalent bond formed between two monosaccharides

Starch

A storage polysaccharide of plants, consisting entirely of glucose monomers

Glycogen

A storage polysaccharide in animals, mainly stored in liver and muscle cells

Cellulose

A major component of the tough wall of plant cells, a polymer of glucose

Chitin

A structural polysaccharide found in the exoskeleton of arthropods and cell walls of fungi

Energy Storage in Carbohydrates

Carbohydrates have more free energy than CO2

Fatty Acids

Components of fat molecules with a higher ratio of C-H and C-C bonds to C-O bonds

Lipid

What is a Lipid?

Lipid Characteristics

Largely nonpolar and hydrophobic

Lipids

Do not dissolve in water due to their hydrocarbon components.

Saturated Fatty Acid

Fatty acid chains that consist of only single bonds between the carbons.

Unsaturated Fatty Acid

Fatty acid chains that contain one or more double bonds, causing kinks in the chains.

Highly Saturated Fats

Solid at room temperature and more common in animals than in plants.

Highly Unsaturated Fats

Liquid at room temperature.

Triacylglycerols

Fats composed of three fatty acids linked to glycerol.

Ester Linkage

The bond formed between the hydroxyl group of glycerol and the carboxyl group of a fatty acid.

Steroids

A family of lipids distinguished by a bulky, four-ring structure.

Cholesterol

A steroid that is an important component of plasma membranes in many organisms.

Phospholipids

Membrane-forming lipids that contain a polar, hydrophilic region and a nonpolar, hydrophobic region.

Lipid Micelles

Structures formed when phospholipid heads face the water and tails face each other.

Phospholipid Bilayers

Two sheets of phospholipid molecules that align with hydrophilic heads facing a surrounding solution.

Selective Permeability

The ability of membranes to allow some substances to pass while excluding others.

Permeability Scale

A measure of how easily different substances can cross phospholipid bilayers.

Fluidity of the Membrane

Refers to how individual phospholipids can move laterally within the lipid bilayer.

Fluid-Mosaic Model

Describes the structure of membranes as a dynamic mosaic of phospholipids and proteins.

Integral Proteins

Proteins that span the membrane and can affect membrane permeability.

Transmembrane Proteins

Integral proteins that span the membrane and are involved in the transport of selected ions and molecules.

Peripheral Proteins

Proteins found only on one side of the membrane, often attached to integral proteins.

Hydrophobic Interactions

Interactions that reduce the permeability of membranes by preventing close packing of hydrocarbon tails.

Cis Double Bonds

Double bonds in unsaturated fatty acids that introduce kinks into hydrocarbon chains.

Hydrophilic Region

The part of phospholipids that contains highly polar covalent bonds.

Hydrophobic Region

The part of phospholipids that consists of nonpolar fatty acid or isoprene chains.

Biological Role of Lipids

Lipids serve various functions including energy storage, membrane structure, and signaling.

Physical State of Lipids

Affected by bond saturation; saturated fats are solid, while unsaturated fats are liquid at room temperature.

Membrane Function

To keep damaging materials out of the cell and allow entry of materials needed by the cell.

Hydrophobic Tails

The nonpolar parts of phospholipids that face each other inside the bilayer.