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The nucleolus is a non-membrane bound structure composed of
proteins and nucleic acids that is located within the nucleus.
Ribosomal RNA (rRNA) is transcribed and assembled within the
nucleolus.
Nucleoli (plural for nucleolus) form around genetic loci termed
Nucleolar Organizing Regions (NORs).
NORs are composed of tandem repeats of rRNA
genes found in several different chromosomes.
Mitochondrion - 16,000 bp
Chloroplast - 120,000 bp
Eukaryote Nucleus - 3 billion bp
Four types of genes
Nuclear gene 1) Responds to regulatory signals - makes proteins for export.
Nuclear gene 2) Responds to internal signals - makes proteins for use in cytoplasm.
Nuclear gene 3) Makes proteins to be transported into an organelle.
Organelle gene 4) Makes proteins for use inside its own organelle.
Exported proteins are made on rough endoplasmic
reticula (ER). Rough ER is smooth ER that is
embedded with ribosomes.
Cytosolic or organelle - destined proteins are made on
free (unbound; not bound to ER) ribosomes. Proteins
destined for organelles are tagged and are targeted to
specific organelles. Only free ribosomes are found in
organelles.
External
signal
Protein-coding region of DNA
Noncoding region
Protein-coding region of RNA
Noncoding region
RNA-synthesizing enzyme
Regulatory proteins
Secreted protein
Proteins used in cell
Protein encoded by
mitochondrion or
chloroplast
Amino acid chain
Ribosome
Centrosomes surrounded by starlike webs of protein filaments are the master architects of cell division.
CENTRIOLES at the heart of the centrosomes in animal cells are tubelike structures.
Each one is formed from nine rods; each rod consists of three microtubules fused along
their length. A microtubule is a hollow fiber made of subunits that contain an alpha- and a
beta-tubulin protein. The cytoplasmic microtubules organized by the centrosome seem to
grow out of the pericentriolar material and not directly from the centrioles themselves.
STRUCTURE OF CENTRIOLE
Telomere – piece of DNA at the very tip of each cell’s chromosomes.
Telomerase – enzyme that helps restore a portion of the telomere
with each cell division.
Dyskeratosis congenita – genetic disease causing accelerated
shortening of telomeres. May result from lowered telomerase activity
1)Naked DNA
2)Nucleosome
3)Solenoid
4)Loop
5)Rosette
6)Coil
7)Chromatid
Interphase
Chromatin
M-Phase