BIOL 3110 Lecture Notes - Interphase, Cell Nucleus, Reading Frame

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Published on 7 Oct 2012
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Oct 29, 2009
How Did Interrupted Genes Evolve
-Exon duplication and shuffling; the presence of exons has always been a part of
the genes early on in life. The existence of introns allow for the exons to be
shuffled and reorganized
-The size of an exon is usually smaller than an intron; when exons are shuffled
they tend to be flanked on either side by introns, the most important criteria for
successful insertion is to ensure that the reading frame is the same as before.
-Do some exons represent distinct protein domains?
-Immunoglobulin proteins are made of 2 protein chains, the light and
heavy “chains”. The variable region is used for attaching onto the antigen
and the constant is used for binding onto the pathways to remove it.
-Do distinct genes share exons?
-There are certain proteins or receptors that share exons with out genes,
such as the LDL receptor and EGF precursor.
-As proteins increases in length the genes have a greater number of exons to code
for them, not larger exons
-Site in protein (represented by the intron/exon boundaries of the gene) is located
at the surface of the protein.
DNA Packaging
-All genetic information from bacteria or eukaryotes is highly condensed to fit all
the information of the genome into the nucleus; the DNA is also usually
complexed with RNA and proteins.
-The actual size of the genome is usually much greater than the size of the
organism itself, however, due to the thinness of DNA and its highly compacted
forms it can be fitted in.
Compartment
Shape
Dimensions
DNA length
E. coli cell
Cylinder
1.7 x 0.65 um (L x
diameter)
1.43x10 um
Human cell nucleus
Sphere
6um diameter
~2m (diploid) =
2x10
um
-There is approximately 100 mg/mL of liquid in the nucleus, how the cell is able
to sort through all this dense information for reading is still unknown.
-Another important feature of packaging is that it must be flexible.
-Packing Ratio = length of DNA / length of unit containing it.
Ex. DNA length is ~ 14000 µm and chromosome length is 2 µm therefore
the ratio is 7000.
-Lightly lysed bacteria DNA is packaged in the nucleoid body, this structure takes
up about 1/3 of the entire volume of the cell and is attached to a proteinaceous
scaffold that holds it together, if this structure is lysed then the entire cell will
burst.
Eukaryotic DNA Packaging
-Loops and scaffold similar to bacteria structures hold the DNA together; during
interphase DNA is in a more diffused state called a chromatin per loop, which is
about 85kb long with one negative supercoil/200bp
-In metaphase the chromatin condense into chromosomes (about 5-10x denser
than a chromatin) which is ~ 30-90kb long per loop and is attached to a
proteinaceous scaffold.
-refer to previous notes
Overall Chromatin & Chromosome Structure With Histones
-The basic structure of the chromosome is shaped like an X and has histones
dotting the structure that forms a 30nm fiber
-Metaphase chromosomes are folded <???>
-G-banding is a method to stain for metaphase chromosomes and it will highlight
the AT-regions. This is a useful test for identifying defects in the chromosome
structure.

Document Summary

Exon duplication and shuffling; the presence of exons has always been a part of the genes early on in life. The existence of introns allow for the exons to be shuffled and reorganized. Immunoglobulin proteins are made of 2 protein chains, the light and heavy chains . The variable region is used for attaching onto the antigen and the constant is used for binding onto the pathways to remove it. There are certain proteins or receptors that share exons with out genes, such as the ldl receptor and egf precursor. As proteins increases in length the genes have a greater number of exons to code for them, not larger exons. Site in protein (represented by the intron/exon boundaries of the gene) is located at the surface of the protein. All genetic information from bacteria or eukaryotes is highly condensed to fit all the information of the genome into the nucleus; the dna is also usually complexed with rna and proteins.