DNA, Genes and Chromosomes

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  • DNA, Genes and Chromosomes
    • Nuclear Eukaryotic DNA
      • 1) Eukaryotic cells contain linear DNA that exists as chromosomes- one long molecule of DNA. Found in nucleus
      • 2) DNA molecule really long, has to be wound up to fit into nucleus
      • 3) DNA wound around proteins called histones
      • 4) Histone proteins help to support DNA
      • 5) DNA coiled up tightly to make compact chromosome
      • 6) Mitochondria and chloroplasts have own DNA. Circular/ shorter, not associated with histone proteins
    • Genes
      • 1) Sequence of DNA bases that codes for a polypeptide/ functional RNA
      • 2) Sequence of amino acids forms primary structure of protein
      • 3) Different polypeptides have different order/ number of amino acids. Order of bases determines order of amino acids in polypeptide
      • 4) Each amino acid coded for by sequence of three bases: triplet
      • 5) To make polypeptide, DNA first copied into mRNA. First stage of protein synthesis
      • 6) Genes that don't code for polypeptides code for functional RNA- RNA molecules other than mRNA. Perform special tasks during protein synthesis e.g. tRNA and rRNA
      • Genome: Complete set of genes. Proteome: Full range of proteins cell able to produce
    • Coding
      • 1) Some genes dont code for polypeptides, code for functional RNA
      • 2) Eukaryotic DNA- genes that do code for polypeptides contain sections that dont code for amino acids
      • 3) These sections are introns. Several within a gene
      • 4) Genes that do code for amino acid are exons
      • 5)  Introns removed during protein synthesis- don't affect amino acid order. Prokaryotic DNA doesnt have introns
      • 6) Eukaryotic DNA contains multiple repeats outside genes
      • 7) DNA sequences that repeat e.g. CCTTCCTTCC
      • 8) These areas dont code for amino acids- non- coding repeats
    • Alleles
      • 1) Different forms of same gene
      • 2) Order of bases in alleles different- code for slightly different versions of same polypeptide
      • E.g. Gene that determines blood type has three alleles: O, A and B
      • In eukaryotic cell, DNA stored as chromosomes. Humans have 23 homologous pairs
      • Homologous pairs- both chromosomes same size/have same genes- could have different alleles.
      • Alleles coding for same characteristic found at same fixed position: locus on chromosome


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