DNA Genes and chromosomes

• what is DNA like in prokaryotes

  single circular chromosomal DNA molecule

  contain plasmids that contain few genes

  plasmids more accessible for proteins required for gene expression

  not associated with proteins
• Chromosome structure 


  Long condensed DNA molecules made up of a series of genes.

  wrapped tightly around histone globular protein that organises and condenses DNA tightly so it fits into nucleus

  other proteins and enzymes used in copying and repairing DNA

  tightly coiled combination of DNA and proteins called chromatin ( what chromatids and chromosomes made up of )

  have telomeres that protect protein ends
• DNA in mitochondria and chloroplast 


  Small circular pieces of mitochondrial DNA and ribosomes found in matrix for protein synthesis of proteins and enzymes needed for aerobic respiration , photosynthesis and replication
• definition of a gene

  Base sequence of DNA that codes for amino acid sequence of a polypeptide or functional RNA molecule
• types of RNA molecules and function

  mRNA:base sequence of messenger RNA , used by ribosomes to form polypeptide chains for protein synthesis

  tRNA :carries amino acids to ribosomes

  rRNA:ribosomal RNA molecules form part of ribosome structure
• what us a locus

  position of a gene on a chromosome and can exist in different forms called alleles

  different alleles of a gene have slightly different nucleotide sequences but still in same position on chromosomes
• What is triplet code 


  Sequence of 3 bases that code for one amino acid also known as a codon
• importance of stop and start codons

  tell cells where individual genes start and stop and that cell reads DNA correctly
• what does non overlapping mean in genetic code

  each triplet only read once and triplets don’t share bases
• what does degenerate mean in triplet code

  that more than one triplet code can code for certain amino acids reduces number of mistakes in mutations
• what does it mean when genetic code is universal

  all organisms use same code to code for amino acids
• what are introns 


  Non coding parts of DNA that separate exons (coding parts of DNA)
• what is splicing 


  before Pre mRNA exits nucleus , non coding sections (introns) are removed and coding sections (exons) joined together in process called splicing