DNA and Chromosomes

• What is a gene?

  A short section of DNA that codes for a polypeptide/protein.
• What do genes determine?

  The proteins of an organism.
• What is an allele?


  A different version of the same gene.
• What might genes differ in that make them alleles?

  They might have different base sequences.
• What are chromosomes?


  Tightly coiled-up DNA.
• What are homologous pairs of chromosomes?

  Chromosome pairs that have the same exact genes, but may have different alleles.
• What is a human karyotype?

  A picture of all the 23 homologous pairs of chromosomes in order.
• What is DNA like in eukaryotic cells?

  It's stored in the nucleus as a chromosome, it's linear, and associated with histones.
• What are histones?


  Proteins that DNA wounds around.
• Why is DNA wound around histones?

  So it fits in the nucleus and doesn't get tangled.
• What is DNA wrapped around a histone protein called?

  A nucleosome.
• What is DNA like in prokaryotic cells?

  It's much shorter, circular, is free in the cytoplasm, and isn't histone associated.
• What is a benefit of prokaryotic DNA being shorter?

  It doesn't have to get wrapped by histones, it supercoils to fit in the cell.
• Where is DNA also found?

  In mitochondria and chloroplasts.
• Why is DNA found in mitochondria and chloroplasts.

  To code for enzymes which are essential for their own reactions (respiration and photosynthesis).
• What is DNA in mitochondria and chloroplasts similar to?

  DNA in prokaryotic cells.
• What do histone proteins coil into?

  Chromosomes.