2.1.2 Biological Molecules Flashcards
Hydrogen bonding
Water is a polar molecule with regions of partial positivity and negativity.
The difference in electronegativity between the oxygen and the hydrogen means the oxygen attracts a greater share of electrons in the covalent bond, giving it a slightly negative charge.
Interactions of opposite charges within water molecules form relatively weak bons called hydrogen bonds
Break and reform as water molecules constantly moving
Main Properties of Water
Solvent properties Surface tension High specific heat capacity Freezing properties Transparent
Water as a Solvent
Polarity- regions of partial electropositivity (hygrogens) and electronegativity (oxygen) due to hydrogen bonds
Molecules in cells that are either charged (salt ions) or polar can interact with the charges in water molecules, as water hydrates polar ions
- essential elements required by organisms are obtained in ionic form
- acts as the transport medium (via blood, lymph) in multi-cellular organisms
- removes metabolic waste e.g. urea, ammonia in urine
- secretion (via digestive juices, tears)
- allows movement of minerals to lake and sea
Cohesion
Cohesion- attractive forces that hold the molecules of the liquid together
In water there is cohesion due to the hydrogen bonds.
High surface tension when the surface of a liquid contracts so that it occupies the least possible area. This occurs as water molecules on the surface have fewer surrounding molecules to bond with, so they form stronger bonds with the ones they do have.
High surface tension allows organisms e.g. pond skaters to sit on the surface of the water, allows spherical droplets to form
Adhesion
Adhesion- Attraction of molecules of one kind to molecules of a different kind
Adhesion is strong for water, especially with other charged/polar molecules
Capillary action- adhesion enables water molecules to climb upwards in capillary tubes in an upward motion against gravity
Water molecules are more strongly attracted to glass walls of a tube compared to other water molecules (due to glass being more polar than water).
Meniscus- curved surface formed by liquid in a cylinder. Water extends higher where it contacts the edge of the tube and dips lower in the middle.
Important for:
- secretion of tears from tear ducts
- transpiration of water up the xylem tube in plants
Transparency
The transmission of light into depth of water is important for the role of water as a habitat
- sun is the primary source of energy for biological organisms (light required for photosynthesis)
- allows visibility for aquatic creatures
- can be used as an indicator for water quality
Lubricant
Water acts as a lubricant
- during digestion water in saliva lubricates the food molecules to make the passage to the small and large intestine easier
- water around eyeballs, in synovial fluid (joints) and muscles move without friction
Latent Heat of Vaporisation
Water has a high latent heat of vaporisation - the amount of energy needed to change one gram of a liquid substance to a gas at constant temperature
Water acts as a coolant
- evaporation of water from the surface of the body e.g. sweat, panting, transpiration
Specific Heat Capacity
Water has a high specific heat capacity - energy required to raise the temperature of a substance by one degree Celsius (4.18 joules/gram C in water)
- can minimise changes in temperature (e.g. Cars, warm-blooded animals)
- Water is a metabolite that takes part in many reactions in the body, allows enzymes to function correctly
- organisms can se less energy on temperature control
- provide thermally stable environment for aquatic organisms
Freezing Properties
water forms hydrogen bonds
When water freezes - water molecules form a crystalline structure where they are in fixed positions further apart than in liquid water
Water expands when frozen so ice has a lower density than water
- water can act as an insulating layer protecting aquatic organisms
Monomer
Single/individual unit that bonds with other monomers to form a polymer
Polymer
Multiple individual monomers bonded in a repeating pattern to form a larger molecule.
Chemical elements in biological molecules
Carbohydrates
C, H, O
Lipids
C, H, O
Proteins
C, H, O, N, S
Nucleic Acids
C, H, O, N, P
Condensation reaction
Reaction between 2 molecules resulting in the formation of a larger molecule and the release of a water molecule. Reverse of the hydrolysis reaction.
Hydroxyl groups interact and a new bond is formed
Hydrolysis
The breakdown of a molecule into 2 smaller molecules requiring the addition of a water molecule. Reverse of the condensation reaction.
Glucose structure + properties
Hexose monosaccharide 6 carbons in a ring shaped single unit Mono - monomer Saccharide - sugar a.k.a carbohydrates Polar Soluble in water due to hydrogen bonds
Ribose structure
Pentose monosaccharide
Contains 5 carbon atoms in a ring shaped single unit
Present in RNA nucleotides
Glucose synthesis
Condensation
2 monosaccharides side by side so hydroxyl groups at carbon 1 and 4 interact. Bonds break to release a water molecule and a new bond forms between the 2 glucose molecules to form a disaccharide. The covalent bond formed is called a (1,4) glycosidic bond
Hydrolysis
Addition of water molecules catalysed by enzymes
Converts polysaccharides/disaccharides into monosaccharides by breaking the glycosidic bonds
E.g. starch/glycogen converted to glucose for respiration