8.2. DNA and Chromosomes

• Histone proteins allow DNA to fit into the nucleus
• Mitochondria and chloroplasts have DNA that is similar to prokaryotes in that it is circular and does not bind to histones
• The central nucleoid is an irregularly shaped region of a prokaryotic cell that contains all or most of its genetic information
• Accessory plasmids: Small, circular and contain helpful and even crucial genes
• Microsatellites: Where the DNA is outside of the nucleus
• Less than 2% of DNA codes for polypeptides. The rest are called non coding introns and these are found in between or at the ends of genes
• Non coding DNA corresponds to the portions of an organisms genome that do not code for amino acids.
• Exon = expressed sequence (coding)
• Intron = intervening sequence (non-coding)
• Non coding introns between genes are called intergenic regions. The purpose of non coding introns are not really known. Some non coding sequences have been known to regulate gene expression
• A gene is a small section of genetic material located at a position of a chromosome. This base sequence of DNA codes for the sequence of amino acids in a polypeptide or functional RNA.
• Locus: Position of a gene on a chromosome.
• Alleles: One of a number of alternate forms of a gene. Each individual inherits one allele from each parent. Any changes in the base sequence of that gene will result in a different allele.
• The P arms are short and the Q arms of a chromosome are longer
• Telomeres are found on the end of chromosomes like a cap to protect them from genetic replication
• Humans have 46 chromosomes in homologous pairs. They carry the same genes at the same loci, but may have different alleles of the same genes
• Telomeres can protect from:

  • Nucleolytic degradation
  • unnecessary recombination
  • interchromosomal fusion
• Telomere length can affect the pace of aging and onset of age related diseases. Telomere length shortens with age and shorter telomeres have been associated with poor survival.
• Chromosomes are only visible as distinct structures when a cell is dividing. For the rest of the time they are dispersed into the cell
• The considerable length of DNA found in each cell (2 metres in each human cell) is highly coiled and folded