BIOL1130 Lecture Notes - Lecture 9: Ribosomal Rna, Symbiosis, Molecular Clock
7 Jun 2018
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The Universal Code
Abbreviations: k = kilo = 103, M = mega = 106, bp = base pairs
Conserved sequences are similar or identical sequences that occur within nucleic
acid sequences (such as RNA and DNA sequences), protein sequences, protein
structures or polymeric carbohydrates across species (orthologous sequences) or
within different molecules produced by the same organism.
The Genome - Prokaryotes
• The heritable DNA in a cell, the genome, is organized in the chromosomes
• Bacterial DNA may be in one or more circular or linear chromosomes
• There is one copy of each chromosome on average per cell, though rapidly
dividing cells have significant replicated sections
• The DNA is organized in large loops attached to a protein scaffold
• A bacterial genome is gene rich, usually less than 15% non coding
(repetitive) DNA
• The size of bacterial genomes varies from less than 600kbp up to 13Mbp
• Even for simple bacterial genomes, the functions of all the sequences are
not known.
• The diagram of a DNA sequence is called a map. Maps are drawn at
different scales and show different types of detail; when they describe
double stranded DNA this is usually drawn as a single line, either linear or
circular.
The Genome – Eukaryotes
• Nuclear genomic DNA is tightly coiled around histone proteins, and the
combination is called chromatin
• This winding massively reduces the length: width ratio of the DNA
molecules. 1.8m of DNA reduces to about 90 nanometers.
• The X shape is a temporary state during cell division where the two
copies of the chromosome (The sister chromatids) are held together at
the centromere prior to anaphase
• There maybe one, two, four or more copies of every chromosome in a cell
• The nuclear genome DNA is organized into linear chromosomes
o Generally….
• Centrosomes ensure that chromosomes are passed correctly during cell
division in eukaryotes
• Telomeres are highly repetitive sequences that protect the ends of the
eukaryote chromosomes.
• Repetitive DNA is spread throughout eukaryote chromosomes; it stains
more darkly and forms the dark bands called heterochromatin; we dont
know the function of many of these sequences
• The light stained bands are euchromatin; these regions contain genes.
Genome Structure – Eukaryotes
• Eukaryotic genomes are not just the nuclear DNA
• Large red and yellow structure is the nucleus of a eukaryote cell
• Tiny yellow dots are the mitochondria
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Document Summary
Abbreviations: k = kilo = 103, m = mega = 106, bp = base pairs. Conserved sequences are similar or identical sequences that occur within nucleic acid sequences (such as rna and dna sequences), protein sequences, protein structures or polymeric carbohydrates across species (orthologous sequences) or within different molecules produced by the same organism. Molecular phylogeny: dna sequence comparisons allow evolutionary relationships to be, dna melt curves inferred. If they are deleterious the fitness of the daughter cell is reduced. The order of the rrna genes in the rdna also is highly conserved in that category: however parts of the rdna are less conserved as they do not have a functional role in the ribosome. The its (red sequences = internal transcribed spacers) and the igs (aqua sequences intergenic spacer) are: some small parts of rdna sequences are observed to be universally conserved. So in every species where the genes have been sequence, these sequences are identical.
