Biology chapter 3

• RNA nucleotides form polymers in the same way as DNA nucleotides, through the formation of phosphodiester bonds in condensation reactions.
• Cells divide to produce more cells needed for growth or repair of tissues.
• When a cell prepares to divide, the two strands of DNA double helix separate and each strand serves as a template for the creation of a new double-stranded DNA molecule.
• After protein synthesis the RNA molecules are degraded in the cytoplasm.
• The strand that is unzipped from the 3' end can be continuously replicated as the strands unzip, this strand is called the leading strand and is said to undergo continuous replication.
• DNA polymerase always moves along the template strand in the same direction and can only bind to the 3' (OH) end, so travels in the direction of 3' to 5.
• DNA is contained within the cells of all organisms and scientists determined that this molecule was the means by which genetic information was passed from one generation to the next.
• The RNA polymers formed are small enough to leave the nucleus and travel to the ribosomes, where they are central in the process of protein synthesis.
• The base pairing rules still apply when RNA nucleotides bind to DNA to make copies of particular sections of DNA.
• The two daughter cells produced as a result of cell division are genetically identical to the parent cell and to each other.
• The phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused.
• The complementary base pairing rules ensure that the two new strands are identical to the original.
• DNA polymerase has to replicate each of the template strands in opposite directions due to the fact that DNA only unwinds and unzips in one direction.
• Sequences of bases are not always matched exactly, and an incorrect sequence may occur in the newly-copied strand, these errors occur randomly and spontaneously and lead to a change in the sequence of bases, known as a mutation.
• DNA replication involves the unwinding and separating of the two strands of the DNA double helix, catalysed by the enzyme DNA helicase.
• The instructions that DNA carries are contained in the sequence of bases along the chain of nucleotides that make up the two strands of DNA, the code in the base sequences is a simple triplet code.
• DNA replication is controlled by enzymes, a class of proteins that act as catalysts for biochemical reactions.
• DNA polymerase, another enzyme, catalyses the formation of phosphodiester bonds between free nucleotides and exposed bases on the template strands.
• DNA must code for a sequence of amino acids, this is called the genetic code.
• The other strand is unzipped from the 5' end, so DNA polymerase has to wait until a section of the strand has unzipped and then work back along the strand, this strand is called the lagging strand and is said to undergo discontinuous replication.
• Water has an unusually high boiling point.
• Amino acids join when the amine and carboxylic acid groups connected to the central carbon atoms react and the R-groups are not involved at this point.
• The resulting compound is a dipeptide.
• Reduced fat spreads contain the same quantity of energy gram for gram whether saturated or unsaturated, so butter and margarine have always had the same calorific value.
• Trans fats are produced as an unwanted byproduct of the hardening process and are unsaturated lipids in which the kinks that the double bonds naturally form have been reversed.
• When many amino acids are joined together by peptide bonds a polypeptide is formed and this reaction is catalysed by the enzyme peptidyl transferase present in ribosomes, the sites of protein synthesis.
• The very specific shapes of proteins are vital for the many functions proteins have within living organisms.
• Trans fats increase the shelf life of baked products and are usually removed from foods due to their link with the development of coronary heart disease.
• In thin layer chromatography, the stationary phase is a thin layer of silica gel (or another adhesive substance) applied to a rigid surface, for example a sheet of glass or metal.
• Amino acids are then added to one end of the gel and this end is then submerged in organic solvent.
• All amino acids have the same basic structure and different R-groups (variable groups) result in different amino acids.
• Twenty different amino acids are commonly found in cells, five of which are non-essential, nine are essential, and six are conditionally essential.
• This results in different amino acids moving different distances in the same time period resulting in them separating out from each other.
• The hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group of another amino acid and a peptide bond is formed between the amino acids and water is produced.
• The rate at which the different amino acids in the organic solvent move through the silica gel depends on the interactions (hydrogen bonds) they have with the silica in the stationary phase, and their solubility in the mobile phase.
• The different R-groups of the amino acids making up a protein are able to interact with each other forming different types of bond and these bonds lead to the long chains of amino acids (polypeptides) folding into complex structures (proteins).
• Peptides are polymers made up of amino acid molecules (the monomers) and proteins consist of one or more polypeptides arranged as complex macromolecules with specific biological functions.
• Thin layer chromatography (LC) is a technique used to separate the individual components of a mixture and can be used to separate and identify a mixture of amino acids in solution.
• The organic solvent then moves through the silica gel, this is known as the mobile phase.
• Water is a small molecule, much lighter than the gases carbon dioxide or oxygen, yet unlike oxygen and carbon dioxide, water is a liquid at room temperature.