Nucleic acids Flashcards
What is the dipolar water molecule?
A water molecule is made up of two atoms of hydrogen and one of oxygen.
Although the molecule has no overall charge, the oxygen atom has a slight negative charge, while the hydrogen atoms have a slight positive charge.
The water molecule therefore has positive and negative poles so is dipolar.
How are water molecules bonded?
Different poles attract, and therefore the positive pole of one water molecule will be attracted to the negative pole of another molecule.
The attractive force between these opposite charges is called a hydrogen bond.
Although each bond is fairly weak, together they form important forces that cause the water molecules to stick together, giving water its unusual properties.
Why does water have a high specific heat capacity of water?
Because water molecules stick together, it takes more energy to separate them than would be needed if they did not bond together.
The boiling point of water is therefore high.
Without its hydrogen bonding, water would be a gas at the temperature commonly found on earth.
So it takes more energy to heat a given mass of water.
What is specific heat capacity?
The heat energy needed to raise the temperature of 1kg of water by 1°c.
It takes a lot of energy to raise the temperature of water.
Why is a high specific heat capacity of water important to living organisms?
Water acts as a buffer against sudden temperature variations, making the aquatic environment a temperature-stable one.
As organisms are mostly water, it also buffers them against sudden temperature changes especially in terrestrial environments.
The bodies of living organisms are mainly water, the water in and around our cells absorbs a lot of heat energy without its temperature increasing much.
What is the latent heat of vaporisation of water?
Hydrogen bonding between water molecules means that it requires a lot of energy to evaporate 1 gram of water.
What is the importance of large latent heat of vapourisation?
Animals that are able to sweat can keep cool as the water in sweat evaporates off the surface of the animal.
Plants are also cooled when water evaporates from their leaves.
What is cohesion and surface tension in water?
Cohesion of water is the tendency of molecules to stick together.
With its hydrogen bonding, water has large cohesive forces and these allow it to be pulled up through a tube, such as a xylem vessel in plants.
Surface tension is where water molecules meet air they tend to be pulled back into the body of water rather than escaping from it.
What is the importance of strong cohesion to water molecules?
In plants, water moves up the xylem vessels as a continuous stream.
This allows the water to move from the roots to the top of the tallest trees.
Water cohesion leads to surface tension.
This means water behave as if there is a skin where the water meets the air.
This allows small animals to live on the surface of water bodies, e.g. pond skaters.
What is the importance of water to living organisms?
Water is the main constituent of all organisms:
Up to 98% of a jellyfish is water and mammals are typically 65% water.
Water is also where life on earth arose and it is the environment in which many species still live.
How is water used in metabolism?
Water is used to break down many complex molecules by hydrolysis, for example proteins to amino acids.
Water is produced in condensation reactions.
Chemical reactions take place in an aqueous medium.
Water is a major raw material in photosynthesis.
What is the importance of water in metabolic reactions to living organisms?
Hydrolysis reactions are important in digestion of large molecules in animals.
Condensation reactions are important in synthesis of important molecules such as proteins in living organisms.
How is water used as a solvent?
Water readily dissolves other substances:
Gases such as oxygen and carbon dioxide.
Wastes such as ammonia and urea.
Enzymes, whose reactions take place in solutions.
Inorganic ions and small hydrophilic molecules such as amino acids, monosaccharides and ATP.
What is the importance of water as a solvent to living organisms?
The metabolic reactions that happen inside all living organisms can only happen when the reactants are dissolved in water.
Substances being dissolved in water also allows them to be transported around the bodies of living organisms.
What are other important features of water?
Its evaporation cools organisms and allows them to control their temperature.
It is not easily compressed and therefore provides support, for example the hydrostatic skeleton of animals such as the earthworm and turgor pressure in herbaceous plants.
It is transparent and therefore aquatic plants can photosynthesise and also light rays can penetrate the jelly-like fluid that fills the eye and so can reach the retina.
Where are inorganic ions found?
In organisms where they occur in solution in the cytoplasm of cells and in body fluids and as well as part of larger molecules.
They may be in concentrations that range from very high to very low.
What are the functions of inorganic ions?
The specific function a particular ion performs is related to its properties.
For example, iron ions are found in haemoglobin where they play a role in the transport of oxygen.
Other examples include the phosphate ions that form a structural role in DNA molecules and a role in storing energy in ATP molecules.
Hydrogen ions are important in determining the pH of solutions and therefore the functioning of enzymes.
Sodium ions are important in the transport of glucose and amino acids across plasma membranes.
What is the structure of ATP?
Adenosine triphosphate is a phosphorylated macromolecule with three parts:
Adenine - a nitrogen-containing organic base.
Ribose - a pentose sugar molecule that acts as the backbone to which other parts are attached.
Phosphates - a chain of three phosphate groups.
How does ATP store energy?
The bonds between the phosphate groups are unstable and so have a low activation energy, which means they are easily broken.
When they do break they release a considerable amount of energy.
Usually in living cells it is only the terminal phosphate that is removed.
What is the equation for converting ATP into ADP?
ATP + H2O = ADP + Pi + energy.
Adenosine triphosphate + water = adenosine diphosphate + inorganic phosphate + energy.
As water is used to convert ATP to ADP, it is a hydrolysis reaction.
The reaction is catalysed by the enzyme ATP hydrolase.
