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The Nucleus
The nucleus is made up of genomes
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This is known as DNA
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There is a limited number of genomes but they can be used differentially, which is how we get
phenotypic variation
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In protein synthesis, it is responsible for
the transcription of DNA into RNA, the processing of RNA into mRNA, the binding of ribosomes to
the mRNA to produce amino acids and the translation of the amino acids to produce the relevant
protein
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Small amount of DNA
are also found in mitochondria (plant and animal) and chloroplast (plant only)
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It is separated from the rest of the
cell and its cytoplasm by the nuclear envelope, a double membrane
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NUCLEAR ENVELOPE
This is a double membrane
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This separates the contents of the nucleus from the cytoplasm
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The average
diameter of the entire nucleus is about 6µm
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Proteins tend to enter the nucleus the most
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It is highly regulated as the material that enters is very specific and
controlled
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NUCLEAR LAMINA
This is a protein lattice that supports the nuclear envelope
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The envelope must
disappear transiently and this is able to happen due to the reversible disassembly of the lamina
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The cell can then be
looked at under an electron microscope
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They allow for 2-way passage across the
envelope
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If you look at the
structure of them, you can see that on the outside there are a number of small projections called
cytoplasmic filaments
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The nuclear pores are made of 100’s of different proteins in a very precise order and structure
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This includes things like
proteins, exiting RNA, specific amino acid sequences etc
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This is a short chain of amino
acids that label where the material is required to be
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DNA is arranged into chromosomes in the nucleus – in humans there are 46 chromosomes
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Individual chromosomes
can’t usually be seen unless the cell is undergoing division as they shorten and thicken themselves
for the process
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DNA is held in bundles called nucleosomes
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The nucleosomes are part of proteins
synthesis as they help to form the RNA
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These can exit the nucleus into the cytoplasm and perform translation as part of
protein synthesis
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As a result, not all DNA structures are the
same
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Decondensed DNA called EUCHROMATIN is
open DNA
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Condensed DNA is called
HETEROCHROMATIN and is a lot less accessible, meaning is cannot be transcribed
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The genes allow for mRNA synthesis
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