chapter 3 definitions

• 5' to 3' is the direction of synthesis on a nucleotide strand
• Amino acid


  An organic compound that is a building block within a polypeptide or protein
• Anticodon

  A set of three consecutive nucleotides that is part of a tRNA molecule and is complementary to a codon; the three nucleotides consist of any of the four bases adenine, uracil, guanine or cytosine
• Apoptosis


  A programmed series of events that leads to cell death (as a result of the dismantling of the internal contents of the cell by various enzymes, including caspases)
• Cellular machinery


  ‘Biological machines’ that work to manufacture a biological molecule; e.g. transcription machinery includes RNA polymerase and binding factors or proteins; the translation machine is the ribosome
• Chromosome

  A structure composed of DNA and protein that contains linear arrays of genes carrying genetic information; prokaryotes generally have one circular chromosome, whereas eukaryotes have a number of linear chromosomes
• Coding DNA

  The sections of DNA that code for a protein; they contain instructions that determine the order of the codons in the mRNA, which in turn determines the order of the amino acids in a polypeptide or protein
• Codon table (amino acid table)

  • A translation table for determining the amino acid coded for by an mRNA codon; the three nitrogenous base letters can be looked up in the table to find the name of the specified amino acid
• Complementary base pairing


  The phenomenon whereby guanine always hydrogen bonds with cytosine and adenine always hydrogen bonds with thymine; guanine and cytosine share three hydrogen bonds, and adenine and thymine share two hydrogen bonds; the complementary pairing enables the helical structure of DNA to form
• DNA (deoxyribonucleic acid)


  The information-containing molecule present in all living things that contains the instructions, written in a chemical code, for the production of proteins by the cell; the information it contains is sufficient for the making and maintaining the organism; in addition, DNA is the genetic material that passes this information on to the next generation
• DNA helicase

  An enzyme that helps the two strands of the DNA double helix unwind and separate
• DNA ligase

  An enzyme used to catalyse the formation of a bond between two pieces of DNA
• DNA polymerase


  A member of a class of enzymes found in all living things, that synthesises new strands of DNA based on a template strand and according to complementary base-pair rules; DNA polymerases are important tools in biotechnology because they are capable of making exact copies of fragments of DNA, enabling efficient and accurate amplification of DNA templates
• DNA replication


  The process a DNA molecule undergoes to make a complete and identical copy of itself, readying a cell for cell division; it is a semi-conservative process, and the two daughter molecules contain exact copies of the genetic material in the parent molecule
• Double helix


  The structure formed by double-stranded molecules of nucleic acids such as DNA; two linear strands that run opposite to each other and twist together
• Enzyme

  A reusable, biological catalyst
• DNA replication


  The process by which a parent DNA molecule is copied to produce two daughter molecules containing exact copies of the genetic material
• Enzyme


  A reusable, biological catalyst that lowers the activation energy of a chemical reaction, making it proceed faster; it is a protein that is sensitive to factors such as temperature and pH
• Gene


  A unit of heredity that transmits information from one generation to the next; a segment of DNA that codes for a polypeptide
• Genetic code


  The way that the four nitrogenous bases of DNA (adenine, thymine, guanine, and cytosine) are ordered and contain information to direct the production of specific proteins
• Genome


  All of the genetic material contained in an organism or a cell; it includes the sequence of the DNA in the chromosomes within the nucleus, mitochondria, and chloroplasts
• Genome sequence


  The sequence of consecutive DNA ‘letters’ spanning all the chromosomes of a cell from start to finish
• Genomics


  The study of the genome – how genes interact with one another, the environment, and the resultant proteins produced; knowledge of an organism’s entire DNA sequence
• Heredity


  The study of inheritance, the genetic transmission of characteristics from one generation to another
• Lagging strand


  The DNA strand that is synthesized discontinuously in small fragments, called Okazaki fragments, in a 5' to 3' direction
• Leading strand


  The DNA strand that is synthesized continuously in a 5' to 3' direction
• Mature mRNA

  mRNA that has been processed after transcription; non-coding introns have been removed and the remaining exons joined
• mRNA (messenger RNA)


  The RNA molecule that carries the information from a gene to a ribosome for translation into a polypeptide; in eukaryotes it carries the message from the DNA in the nucleus out through a nuclear pore to a ribosome in the cytoplasm
• Nitrogenous base


  A structural component of the nucleotides that make up DNA or RNA
• Non-coding DNA


  All of the DNA sequences within a genome that are not found within mRNA-coding exons; examples include introns, promoters, and enhancers of genes; they have no known function
• Non-template/sense/coding strand


  The coding strand is also known as the sense strand; this strand has the same code as the mRNA strand, except uracil replaces thymine; it is not read during transcription
• Nuclear pore


  A small opening in the nuclear membrane through which relatively small single-stranded molecules such as mRNA can fit
• Nucleoid


  The region within a prokaryotic cell that contains the genetic material
• Nucleotide


  The basic building block of nucleic acids (DNA and RNA); nucleotides are linked together by phosphodiester bonds; each nucleotide is made up of a five-carbon sugar, a phosphate group, and a nitrogenous base
• Okazaki fragment


  A short fragment of DNA synthesized during DNA replication; multiple fragments are joined together to make the lagging strand during replication
• Organelle


  A specialized part of a cell that has its own specific function; a ‘little organ’
• Peptide bond


  A covalent bond that links amino acids in a polypeptide
• Phosphodiester bond


  A covalent bond that links a 3' carbon in one sugar to a 5' carbon in another sugar in DNA and RNA; it consists of a phosphate group, its covalent ester bond with the 3' carbon and its covalent ester bond with the 5' carbon; this bond connects nucleotides
• Covalent bond

  A chemical bond that involves the sharing of electron pairs between atoms
• Phosphodiester bond


  A covalent bond that links a 3' carbon in one sugar to a 5' carbon in another sugar in DNA and RNA; it consists of a phosphate group, its covalent ester bond with the 3' carbon and its covalent ester bond with the 5' carbon; this bond connects nucleotides, which form the backbone of a DNA or RNA chain