Download Nucleus, ribosomes and endoplasmic reticulum

Nucleus, ribosomes and endoplasmic reticulum
5/25/12
Cellular Uptake
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Major ways that cells acquire large samples from environment
Phagocytosis-”cell-eating” or engulfment
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Amoebae or macrophages
Cell produces pseudopod to surround large object
Pinocytosis-”cell drinking”
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Vesicle forms and brings in liquid
Endocytosis-receptor mediated
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A specific receptor-target interaction triggers
Forms coated pit and vesicle
Vesicle Nomenclature
Vesicles have specific names that are linked to their origin
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Phagocytosis=phagosome
Pinocytosis=pinosome or uncoated vesicle
Endocytosis=endocytic vesicle or coated vesicle
Nucleus
Command center of cell
Where DNA as chromosomes is located
Membrane bound
Site of transcription and RNA modification and maturation
Normally only one per cell unless cell is actively dividing
Nuclear membrane
Double membrane with perinuclear space in between
Very important for cell function
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Allow separation of mRNA from translational machinery
• Allows modification and maturation of mRNA before it is translated into proteins
Membrane is covered with octameric pores that allow mRNA out and nuclear proteins in
Ribosomes cover outer membrane and translate mRNA into proteins
Nucleolus
Very dense core of nucleus
Easy to see on EM
Responsible for synthesis of ribosomes
Essential for cell function
DNA Structure
In the nucleus, DNA exists as highly compact structures known as chromosomes
Many levels of compaction
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DNA is wound around Histone proteins like rope around a barrel
Histones associate and bring the complexes closer together
Looping and supercoiling compact DNA even further
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DNA would be larger than cell if not compacted
Ribosomes
Synthesize protein via translation
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Use mRNA as template
Comprises two subunits-60S and 40S
Very complex structures made up of many small proteins and rRNA molecules
Ribosome Location
Ribosomes perform one function but are found at several locations
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On outer surface of nuclear membrane
On Rough Endoplasmic Reticulum
Free in cytosol
Endoplasmic Reticulm
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Complex mass of membranes with cytoplasm of cell
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Complex structure with:
– Tubules-thin tubes of membrane
– Cisternae-large holding vats
Extension of nuclear membranes and perinuclear space
Two varieties
– Rough-coated with ribosomes
– Smooth-no ribosomes
Roles of ER
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Rough
Ribosomes synthesize excreted proteins
– Stored in cisternae or vesicle
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Modify proteins
– Glycosylation of proteins
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Delivery of membrane associated proteins
Often interacts with the Golgi
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Smooth
Tissue-specific uses
Storage of carbohydrates
Detoxification reactions in liver
Synthesizes much of the new membrane
material
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Modification of existing molecules