All resources for B1.2 What happens in cells? GCSE OCR Biology Gateway 9-1. Triple and combined (Higher and Foundation) is covered in this material. Each PowerPoint is a whole lessons included with student activities and animated answers. DNA stands for deoxyribonucleic acid. DNA is found in the nucleus of cells. DNA is packaged into a thread-like structure called chromosomes. Humans typically have 46 chromosomes shared from their parents. Genes are sections of DNA that code for physical characteristics. The structure of DNA. DNA is comprised of monomers called nucleotides. A nucleotide consists of a phosphate group, a sugar (deoxyribose), and an organic base. There are four organic bases: Adenine, A. Thymine, T. Cytosine, C. Guanine, G. Hydrogen bonds in DNA. The role of proteins and AI Proteins as polymers Explaining transcription mRNA and complementary bases Explaining translation Enzymes are made of protein. Enzymes are biological catalysts. Catalysts speed up the rate of reaction without being used up themselves. Enzymes and the lock and key hypothesis. Enzymes breaking down and bonding substrates. Enzymes-catalysed reactions Rate of reaction Denaturing of enzymes and the active site Optimum temperature and optimum pH for enzymes Definition of concentration Increasing concentration of enzymes and substrates Saturation of substrates