Biology - genetic information, variation relationships

• What is a gene?

  A section of DNA that contains a code for making a polypeptide and functional RNA
• What is a locus?


  The location of a particular gene on a chromosome
• What is an allele?

  A different version of the same gene
• What is a chromosome?

  A threadlike structure composed of tightly coiled DNA wrapped around histones (in eukaryotic cells)
• What is a centromere?

  The region of a chromosome where the two sister chromatids are joined
• What are homologous chromosomes?

  A pair of chromosomes that have the same genes and are the same size
• How is DNA stored in eukaryotic cells?

  As linear chromosomes inside the nucleus
• How is prokaryotic DNA structured?

  As shorter and circular DNA molecules that are not wound around histones
• What is a codon?

  Three bases on mRNA that code for an amino acid
• What is a start codon?

  Three bases at the start of an mRNA sequence that help to initiate translation
• What is a stop codon?

  Three bases at the end of every gene that do not code for an amino acid and cause ribosomes to detach
• What is meant by the genetic code being a "triplet code"?

  An amino acid is coded for by three DNA bases
• What does it mean that the genetic code is degenerate?

  Each amino acid is coded for by more than one triplet of bases
• What is the advantage of the genetic code being degenerate?

  If a substitution mutation occurs, the new triplet of bases may still code for the same amino acid, having no impact on the final protein produced
• What is the advantage of the genetic code being universal?

  Genetic engineering is possible, allowing a human gene to be inserted into another organism, such as bacteria to produce insulin
• What is the advantage of the genetic code being non-overlapping?

  If a point mutation occurs, it will only affect one codon and therefore one amino acid
• What is an intron?

  A non-coding sequence of DNA
• What is an exon?

  A sequence of DNA that codes for amino acids
• What is splicing?

  Post-transcription modification that removes introns
• What is a genome?

  The complete set of genes in a cell
• What is a proteome?


  The full range of proteins that a cell is able to produce
• What is an anticodon?

  Three bases on the tRNA which are complementary to the codon on mRNA
• What is the structure of mRNA?

  Single-stranded structure made up of codons and a copy of one gene
• What is the function of mRNA?

  To carry the copy of the genetic code of one gene from the nucleus to a ribosome in the cytoplasm
• What is the structure of tRNA?

  Single-stranded, folded to create a cloverleaf shape, held in place by hydrogen bonds, with an anticodon and amino acid binding site
• What is the function of tRNA?

  To transfer a specific amino acid to the ribosome to create the polypeptide chain
• What is transcription?

  The first stage in protein synthesis where one gene in DNA is copied into mRNA, occurring in the nucleus
• What enzymes are involved in transcription?

  DNA helicase and RNA polymerase
• What is the role of DNA helicase in transcription?

  It catalyzes the breaking of hydrogen bonds between the two strands of DNA
• What is the role of RNA polymerase in transcription?

  It joins adjacent RNA nucleotides together, forming a phosphodiester bond
• What is pre-mRNA?

  mRNA in eukaryotes that still contains the introns
• How is pre-mRNA modified?

  The introns are removed by a protein called a spliceosome, leaving just the exons
• What is ATP used for in translation?

  Forming the peptide bond between amino acids
• What is a haploid cell?

  A cell with one copy of each chromosome
• What is a diploid cell?

  A cell with two copies of each chromosome
• What is meiosis?

  Cell division that creates genetically different gametes, involving two nuclear divisions and resulting in four haploid daughter cells
• What is independent segregation?

  Homologous pairs of chromosomes randomly line up opposite each other at the equator of the cell, creating a large number of possible combinations of chromosomes in the daughter cells produced
• What is crossing over?

  Homologous pairs of chromosomes line up opposite each other at the equator in meiosis 1, twisting, breaking, and recombining with another chromatid, resulting in new combinations of alleles in the gametes
• What are gametes?

  Sex cells (sperm and egg)
• How does meiosis introduce variation?

  Through crossing over and independent segregation