Biological molecules - Water Flashcards
Biological uses of water
Water tension As a polar solvent Maintaining constant temperature Insulation Transport Metabolic functions Incompressibility
Structure of water
Two hydrogen atoms joined to an oxygen atom by a covenant bond, this makes a very stable molecule in a triangular shape.
The water molecule is dipolar- it has a slightly positive end and slightly negative end.
The dipolar ends have an attraction to each other to other water molecule. These form hydrogen bonds.
Water tension
This is important at the air-water interface where cohesive forces (hydrogen bonds) act in an inward direction
Water molecules hold together forming a thin skin of surface tension
Water boatman and other organisms exploit this phenomenon
As a Polar Solvent
The dipolar water molecule will dissolve other polar molecule e.g. salts, sugars and same alcohols
Other non-ionic compounds- alcohols and sugar have polar hydroxyl(OH) groups which allows them to dissolve
Non polar molecules- Lipids do not dissolve
Water is also very good at carrying other substance such as starch that form colloids
As a result of this, most chemical reaction within a cell occur in water (aqueous solutions)
Maintaining constant temperature
It is important to living organisms that sudden changes in temperature do not upset metabolic reaction in cells.
Thermoregulation (Thermoregulation is a process that allows your body to maintain its core internal temperature.)
Specific heat capacity
The hydrogen bond between molecules of water require a lot of energy to separate them as a result they tend to maintain a stable temperature throughout the year
Insulation
At 4°C water is at its maximum density (quantity of a substance within a given area)
Lower than 4°C and water molecules are more widely spread out
Unusually, in solid form (ice) water is less dense than as a liquid. This means that ice will float at the surface of a body of water
This layer of ice will insulate the water below, the water at the bottom will never freeze
This is particularly important for the survival of aquatic organisms
Transport
Adhesive (attraction between molecule and surface)
Cohesive (attraction between the same molecules)
Water molecule are attracted to other molecules as they are dipolar
This is important in the transport of soluble material in solution
Metabolic functions
Water is a reagent in metabolic processes e.g. reducing power in photosynthesis
Used to hydrolyse macromolecules to their subunits, in digestion
Also the medium in which all biochemical reactions take place
Incompressibility
As a liquid, water can’t be compressed
As a result it is often used in hydraulic mechanisms in living organisms
Important ANIONS
Nitrate: NO3- = Amino Acids and proteins, enzymes and DNA for example
Phosphate: (PO4)3- = Formation of ATP and ADP DNA and RNA
Chloride: Cl- = Nerve impulses and sweat
Hydrogencarbonate: (HCO3)- = Buffering blood
Important CATIONS
Sodium: Na+ = Nerve impulses and sweating
Calcium: C2+ = Calcium pectate, middle lamella, bone formation, muscle
Hydrogen: H+ = Cellular respiration, photosynthesis, pumps
Magnesium: Mg+ = Chlorophyll
ANIONS
Negative ions
CATIONS
Positive ions
Polar solvent
Polar solvent in which many metabolic reaction occur
Cohesion
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