Summary Molecular Biology of the Cell 2 (book) (WBFA007-04)
Summary Regenerative Medicine
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Molecular Biology Of The Cell (WBFA00604)
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Chapter 12: Intracellular Compartments and Protein Sorting
Eukaryotic cells contain organelles
organelle = functionally distinct,
membrane-enclosed compartment
o contains its own characteristic
set of enzymes and other
specialised molecules, and
complex distribution systems
transport specific products
from one compartment to
another
cytosol = space of the cytoplasm
outside the membrane-enclosed
organelles – aqueous solution
o intermediary metabolism
cytoplasm = cytosol + cytoplasmic
organelles
All eukaryotic cells have the same basic set of membrane-enclosed organelles
o transport hydrophilic molecules – lipid bilayer of cell membranes is
impermeable to most of these molecules
o also specific molecules which make the organelle unique
nucleus contains the genome; principal site of DNA and RNA synthesis
endoplasmic reticulum (ER)
o smooth ER – regions of the ER which lack ribosomes
o rough ER has many ribosomes bound to its cytosolic surface
ribosomes synthesise both soluble and integral membrane proteins, most of which
are destined either for secretion to the cell exterior or for other organelles
o not enclosed by a membrane
ER sends many of its proteins and lipids to the Golgi apparatus receives lipids and
proteins from the ER and dispatches them to various destinations, usually covalently
modifying them en route
o golgi cisternae – organised stacks of disclike compartments
mitochondria and chloroplasts generate most of the ATP that cells use to drive
reactions requiring an input of free energy
o chloroplasts are a specialised version of plastids
plastids storage of food or pigment molecules
lysosomes contain digestive enzymes that degrade defunct intracellular
organelles, as well as macromolecules and particles taken in from outside the cell by
endocytosis
peroxisomes small vesicular compartments that contain enzymes used in various
oxidative reactions
Invagination and pinching off of the plasma membrane of an ancestral cell creation
of membrane-enclosed organelles with an interior or lumen that is topologically
equivalent to the exterior of the cell
transport vesicles bud off from one organelle and fuse with another
, mitochondria and plastids contain their own
genomes – suggest that mitochondria and
plastids evolved from bacteria
o symbiosis endosymbiotic theory
Four distinct families of intracellular
compartments in eukaryotic cells:
o 1) nucleus and cytosol –
communicate though nuclear pore
complexes; are topologically
continuous
o 2) all organelles that function in the
secretory and endocytic pathways
ER, Golgi apparatus,
endosomes, and lysosomes,
peroxisomes, transport
vesicles etc.
o 3) mitochondria
o 4) plastids (in plants only)
Proteins can move between compartments
in different ways
sorting signals direct
proteins’ delivery to
locations outside the cytosol
or to organelle surfaces
Secretory and endocytic
pathways in eukaryotic
cells
o cargo molecule
doesn’t need to pass
a membrane – is
inside the vesicle organelle fuses with another
organelle
Three fundamental ways by which proteins move from one
compartment to another:
o 1) gated transport – selective gates that actively
transport specific macromolecules and allow free
diffusion of smaller molecules
between cytosol and nucleus
o 2) transmembrane transport – in protein
translocation transmembrane protein translocators
directly transport specific proteins across a membrane
from the cytosol into a space that is topologically distinct
transported protein molecule usually most unfold
to snake through the translocator
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