Cell compartmentalization and transport (Lec 14) Flashcards
(41 cards)
Why do eukaryotic cells contain membrane-enclosed organelles?
Membrane-enclosed organelles increase the surface area of the plasma membrane and provide optimal conditions for specific reactions to occur on the surface of lipid membranes.
How do membrane-enclosed organelles promote optimal conditions for specific reactions?
Membrane-enclosed organelles promote optimal conditions for specific reactions occurring on the surface of lipid membranes by providing:
1) high [substrate] for specific enzymes
2) optimal biochemical environment (pH, salt, oxidative, penitential)
3) High [used enzymes]
What are the basic features of membrane-enclosed organelles?
Membrane-enclosed organelles are differentially abundant and serve the same basic function in different cells.
Membrane-organelles have additional properties in specialized cells
Topological relationship of organelles may be explained by?
evolutionary origins
Based on topological classification, how are the cytoplasmic content divided?
Cytoplasmic division classified into different spaces.
Inside (acronym- CNC): nucleus, cytoplasm, cilium
Outside: secretory/endocytic system, cell exterior; ER, golgi, endo, lyso, peroxisomes
Endosymbiont: mitochondria and plastids
How can proteins move between different compartments?
Protein synthesis starts at the cytosol (except proteins translated in mitochondria or plastids) and a signal sequence determines the movement of proteins. Through signal sequences, proteins can remain in the cytosol or move to different compartments through gated, transmembrane, or vesicular transport.
Where does protein synthesis start? What are the exceptions?
Protein synthesis starts at the cytosol (except proteins translated in mitochondria or plastids)
What are the three types of transport that allow proteins to move between cell compartments?
1) gated
2) transmembrane
3) vesicular
Can organelles be constructed de novo? Why or why not?
No, information is required in the organelle itself.
During protein synthesis, what is the general role of signal sequences and sorting receptors?
Directs protein movement between different cell compartments
Signal sequence (targeting) Signal receptors (shuffling)
What do signal sequences do?
Determines fate of protein movement-Targeting, function remains unaffected even if transplanted to other proteins
What do signal receptors do?
Signal receptors can be reused for shuttling similar protein classes
Inner nuclear membrane
Involved in transport between nucleus and cytosol, and makes contact with nuclear lamina and chromosomes
Outer nuclear membrane
Continuous with ER filled with ribosomes and is involved in transport between nucleus and cytosol
Role of nuclear pores during transport
Mediate import/export from nucleus
Nuclear pores are formed by?
Nuclear pore complex
Nuclear pore complex formed by?
nuclear porins (4 major classes)
Nuclear pore complex
Formed by nuclear porins, the nuclear pore complex is composed of ~30 distinct proteins forming the nuclear pores in the nuclear envelope
Has an 8-fold rotational symmetry with reflection symmetry at the center
125X 106 Da molecular weight (vertebrates)
What are the four major classes of nuclear porins and what are their general characteristics or functions?
Membrane ring: interact with nuclear envelope
Scaffold: have domains related to clathrin or COPII vesicle coats
Channel: FG-repeat domains, forming a gel that blocks the channel
Fibrils and nuclear basket
NPC contributes to ______ transport.
gated
Describe transport of molecules with the size of >5 kDA, >60 kDa, <60 kDa through nuclear pore complex.
5 kDA: free passage, aqueous channel
<60 kDA: size-dependent ungated entry- bigger the slower
>60 kDA: bound ‘entry receptor’ through karyopherin needed for entry
Nuclear localization signal (NLS)
directs nuclear proteins to nucleus
Nuclear localization signals are localized….?
somewhere on the surface of a protein in loops or patches
How are NLS regulated?
masked or displayed
