B2 nucleic acids

• ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) are nucleic acids, which are made up of multiple nucleotides joined together by phosphodiester bonds
• individual nucleotides are made up of three components:

  • pentose sugar
  • phosphate group
  • nitrogen-containing organic base
• the 5 organic bases are; adenine, cytosine, guanine, thymine, uracil
• adenine binds to thymine or uracil
• cytosine binds to guanine
• RNA is a single, short, polynucleotide chain, joined by phosphodiester bonds
• an RNA nucleotide is made up of ribose, a phosphate group, and either adenine, cytosine, guanine or uracil
• RNA is important as it transfers genetic information to the ribosomes, is a component in ribosomes themselves, and is involved in protein synthesis
• DNA is two polynucleotide chains joined by hydrogen bonds between specific complementary bases, and phosphodiester bonds between nucleotides, forming a double helix
• a DNA nucleotide is made up of deoxyribose, a phosphate group, and either adenine, cytosine, guanine or thymine
• DNA is important as it passes genetic information from cell to cell, and between generations, and its variety of combinations of bases provides genetic diversity
• ATP is adenosine triphosphate, a nucleotide derivative
• ATP has three components; adenine, ribose, and three phosphate groups
• the bonds between phosphate groups in ATP are unstable and have a low activation energy so can be easily broken by hydrolysis, releasing a lot of energy
• the equation for ATP hydrolysis is:

  ATP + H2O -> ADP + Pi + E
• ATP hydrolysis is catalysed by ATP hydrolase, ATP synthesis is catalysed by ATP synthase
• ATP is a good energy source because each molecule releases a small amount of energy, so the quantities are more manageable, and because the hydrolysis is a single reaction that releases immediate energy
• ATP cannot be stored so must be continuously made in the mitochondria
• ATP has 5 main uses: metabolic processes, movement, active transport, secretion, activation of molecules
• ATP is used for metabolic processes as it provides energy needed to build molecules from basic units
• ATP is used for movement as it provides energy for muscle contraction, for the filaments of muscle to slide past eachother, shortening the length of the fibre
• ATP is used for active transport as it provides energy to change the shape of carrier proteins in plasma membranes, allowing molecules to be moved against the concentration gradient
• ATP is used for secretion as it is needed to form the lysosomes necessary for secretion of cell products
• ATP is used for activating compounds as the inorganic phosphate released during hydrolysis can be used to phosphorylate other compounds to make them more reactive
• water is a major component of cells as it has many useful properties; metabolite, solvent, high specific heat capacity, high specific latent heat, cohesion and tension
• water is a metabolite in many reactions, such as condensation and hydrolysis
• water readily dissolves other substances such as inorganic ions, waste, enzymes, gases, making it an important solvent where reactions occur
• because of hydrogen bonding, water has a high specific heat capacity, so it takes more energy to heat a given mass of it, this means it acts as a temperature buffer, making both the aquatic environment and organisms themselves more stable
• because of hydrogen bonding, water has a high latent heat of vaporisation, so it takes more energy to evaporate a given mass of it, this means it is a very effective means of cooling, eg animals by sweat, as the heat is used to evaporate the water
• water molecules have a tendency to stick together, hydrogen bonds create cohesive forces allowing water to be pulled up through a tube eg the xylem, water also has surface tension which means it is strong enough to support small organisms, and be pulled back into the body of an organism instead of escaping
• inorganic ions are found in organisms, in solution in the cytoplasm and bodily fluids, they can be in very high or very low concentrations, depending on the type of ion
• each inorganic ion has a specific role, depending on its properties