More biological molecules

• Differences between DNA & RNA?

  DNA- double-stranded, twisted into double helix. Held by hydrogen bonds between bases, longer, deoxyribose sugar, GCAT bases. RNA- single-stranded, ribose sugar, shorter, GCAU bases.
• Why is DNA a stable molecule?

  Phosphodiester backbone protects more chemically reactive organic bases inside double helix. Hydrogen bonds link bases forming bridges. 3 hydrogen bonds between G & C.
• How is a DNA double helix formed from 2 DNA polynucleotide strands?

  Hydrogen bonding between complementary base pairs. A-T (2 hydrogen bonds) & G-C (3 hydrogen bonds). Antiparallel strands twist round eachother to form DNA double helix. Purines = A & G pyrimidines = C,T & U.
• Semi-conservative replication:

  Involves separation of the DNA strands followed by replication of each strand separately to produce DNA half parental & half new.
• Role of DNA helicase:

  Causes 2 strands of DNA to separate by breaking hydrogen bonds that join complementary bases together.
• Role of DNA polymerase:

  Joins all nucleotides to form a complete polynucleotide chain- makes phosphodiester bonds. Moves in 5 prime to 3 prime direction. 2 identical molecules of DNA formed.
• Why is water a good solvent?

  Many important substances in biological reactions are ionic. Water is polar- slightly + charged end attracted to - ion & slightly - charged end attracted to + ion, so ions get surrounded by water & dissolve.
• Structure of ATP:

  Nucleotide base adenine, ribose sugar & 3 phosphate groups. Once made, ATP diffuses to part of cell that needs energy. Energy in ATP stored in high energy bonds between phosphate groups-released via hydrolysis.
• What is phosphorylation?

  Released inorganic phosphate can be added to another compound- often makes compound more reactive.
• How do nucleotides join to form a polynucleotide?

  Condensation reactions between phosphate & sugar of 2 nucleotides. Phosphodiester bond (phosphate group & 2 ester bonds). Sugar-phosphate backbone = chain of phosphates & sugars.
• Role of RNA?

  Transfers genetic info from DNA to ribosomes. Ribosomes read RNA to make polypeptides in translation. Ribosomes made from RNA & proteins.
• Why is ATP not a good long-term energy store?

  Unstable bonds between its phosphate groups. ATP is an immediate energy source as cells only need to store a few seconds' supply of it.
• Why does water have a high latent heat of vaporisation?

  Water vaporises when hydrogen bonds are broken. Lots of energy required to break hydrogen bonds- lots of energy used up when water evaporates. Therefore lots of heat used to change water from liquid to a gas. ( Lots of energy required to evaporate 1 gram of water).
• Why is water's high latent heat of vaporisation useful?

  Organisms can use water loss through evaporation to cool down without losing too much water. When water evaporates, it carries away heat energy from a surface, which cools surface & lowers temperature (sweating). Effective means of cooling as body heat used to evaporate water but not too much water lost.
• How is water an important metabolite?

  Many important metabolic reactions involve hydrolysis or condensation reactions. Metabolite= substance involved in metabolic reaction (chemical reaction in organism).
• How is ATP made?

  Condensation reaction between ADP & Pi. Catalysed by ATP synthase. Happens during respiration & photosynthesis.
• How is ADP broken down?

  Hydrolysis into ADP & Pi. Phosphate bond broken & energy released. Catalysed by ATP hydrolase.
• How is water cohesive?

  Stick together as they're polar- strong cohesion helps water flow (good for substance transport, e.g, xylem). High surface tension- when H20 in contact with air, molecules pulled back into body of H20 rather than escaping from it. H20 surface acts like skin & is strong enough to support small organisms.
• Why is water being a good solvent useful?

  Organisms can take up useful substances dissolved in water- substances can be transported around body (e.g, mineral ions). (Glucose dissolves in water as hydrogen bonds form between them and water).
• What substances does water readily dissolve?

  Gases, wastes, enzymes, inorganic ions & small hydrophilic molecules (e.g, ATP, amino acids & monosaccharides).
• What are inorganic ions?

  No carbon. E.g, iron ions in hb, H+ (pH), Na+ (co-transport of glucose & amino acids), phosphate ions ( ATP, DNA, RNA).
• Why might ATP hydrolysis be 'coupled' to other energy-requiring reactions in the cell?

  Energy released can be used directly to make coupled reaction happen, rather than being lost as heat.
• Why is water being transparent useful?

  Aquatic plants can photosynthesis.
• Water can't be compressed easily:

  Provides support, e.g, hydrostatic skeleton of animals such as earthworm & turgor pressure in herbaceous plants.