HYDROGEN BONDING
Water
Hydrogen bonds easily form between the hydrogen on one molecules and the oxygen on another.
Although individually they are weak, collectively they make it difficult to separate molecules from each othe
Cohesion
Water molecules attract each other and from hydrogen bonds between themselves. This allows water to be drawn up the xylem vessels of trees
Creates surface tension allowing insects such as pond skaters to be supported
Water
High Density
Water has a maximum density at 4°c as a result, ice floats, and acts as an insulator preventing water beneath from freezing completetly protecting the aquatic habitat
High Specific Heat Capacity
As a large amount of heat energy is needed to increase temperature of a body of water (due to large numbers of hydrogen bonds that need to be broken), large fluctuations in temperature are prevented. Aquatic environments are therefore relatively thermally stable
Proteins
Protein Structure
Primary Structure
The order of amino acids in a polypeptide chain. It is determined by the DNA sequence on one strand of DNA molecule
Secondary Structure
Folding of the primary structure into a 3D shape which is held together by hydrogen bonds between =O on the -COOH group and the H on NH2 groups.
- This creates 2 shapes: a-helix and B pleated sheet
Tertiary Structure
Folding of f the a-helix into a more compact shape - maintained by disulphide, ionic, hydrogen bonds and hydrophobic interactions
Quaternary Structure
Combination of 2 or more polypeptide chains in tertiary form combined
Dipolar molecule
Chemical reactions can take place - water acts as a transport medium (e.g. transports minerals up xylem)
Water as a "universal solvent": Due to its dipolar nature. It attracts charged particles (ions) and other polar molecules allowing them to dissolve.
Positively charged end (hydrogen) and a negatively charged end (oxygen)
Carbohydrates
Polysaccharides
Cellulose
Structural polysaccharide- present in plant cell walls
B-glucose units bonded together with adjacent molecules rotated by 180° forming long straight parallel chains that are cross-linked to each other by hydrogen bonds. These become tightly cross-linked to form bundles called microfibrils
Chitin Structural polysaccharide found in exoskeleton of arthropods
Similar structure to cellulose with many long parallel chains of B-glucose (with added acetylamine group/0 cross-linked to each other by hydrogen bonds forming microfibrils, due to adjacent glucose molecules which are rotated by 180° - similar to cellulose