Exam 3 - Lecture 6 Flashcards
The endomembrane system is an_____and what are its 3 functions?
internal membrane system within the eukaryotic cell that
carries out a variety of functions such as:
Synthesis of proteins and their transport
Metabolism and movement of lipids
Detoxification
“DMs”
membrane communication
The membranes of the system are either directly in contact with each other or can communicate through the formation of vesicles
What are the functions of The endoplasmic reticulum and the Golgi complex are sites for
protein synthesis, processing, and sorting
what is the function of Endosomes
carry and sort material brought into
the cell
what is the function of the Lysosomes
digest ingested material and unneeded cellular
components
describe the ER compositon/ appearance
The endoplasmic
reticulum (ER) is a
continuous network of flattened sacs, tubules, and
vesicles through the
cytoplasm of a eukaryotic
cell
The membrane-bound sacs
are called ER cisternae,
and the space inside them is the lumen
is the ER lumen
The endoplasmic
reticulum (ER) is a
continuous network of
flattened sacs, tubules, and
vesicles through the
cytoplasm of a eukaryotic
cell
ER cisternae
membrane bound sacs
ER lumen
space inside the cisternae
Rough ER is characterized by
ribosomes on the cytosolic
side of the membrane
form large flattened sheets
Smooth ER lacks
ribosomes
and form tubular structures
2 different ribosome locations
in the cytosol - responsible for protein
ER - membrane proteins come from ER
The lumenal spaces of rough and smooth ER are
continuous
Rough ER Functions
Biosynthesis of proteins: Ribosomes on the cytosolic side of the
rough ER membrane synthesize both membrane-bound and
soluble proteins for the endomembrane system
Rough ER is the site for
The initial steps of addition of carbohydrates to glycoproteins
The folding of polypeptides
Recognition and removal of misfolded proteins
Assembly of multimeric proteins
C.R.A.P
- Carb addition to gylcoprotiens
- Recognition and removal of misfolded proteins
- Assembly of multimeric Protein
- Polpeptide folding
Funtions of the ER
- Synthesis of proteins for Incorporation into the
plasma membrane,Organelles of the
endomembrane system, and Export from the cell - Synthesis of lipids
- Plays a Central Role in the
Biosynthesis of Membranes
Smooth ER Functions
- Drug Detoxification:
involves hydroxylation: adding hydroxyl groups to hydrophobic drugs increases
their solubility, making them easier to excrete from the body - Carbohydrate Metabolism:
involved in breakdown of stored glycogen using glucose-6-phosphatase
enzyme (unique to smooth ER) - Calcium Storage
Example: calcium ions stored in ER lumen of
muscle cells and released when needed for muscle
contraction. - Steroid Biosynthesis
large amounts of smooth ER are found in cells that synthesize cholesterol and steroid hormones
Both types of ER are present in _________ but________
most eukaryotic cells, but there is variation in the relative amounts
Cells involved in synthesis of secretory proteins have prominent rough ER networks
Cells producing steroid hormones tend to have extensive networks of smooth ER
Be able to differentiate look, funciton, structure
see slides
After the ER Glycoproteins and membrane lipids from the ER undergo
further processing and are sorted and packaged for transport IN the Golgi complex
the golgi complex plays a central role
in membrane and protein trafficking in eukaryotic cells
Golgi stack
a series of 3-8 of cisternae is called a Golgi stack
what is the function of vesicles
carry lipids and proteins from the ER to the
Golgi complex and then to various destinations in the cell
what are the two faces of the Golgi Complex called
The cis face is oriented toward the ER, and the Golgi compartment on this side is called the
cis-Golgi network (CGN)
The opposite side is called the trans face, and the compartment on this side is called the trans-Golgi network (TGN)
The cis face is oriented toward
the ER, and the Golgi compartment on this side is called the
cis-Golgi network (CGN)
Proteins and lipids leave the Golgi in
transport vesicles that continuously bud from the tips of the TGN
medial cisternae location and function
Between the TGN and CGN
where much of the processing of proteins occurs
2 models have been proposed
Flow of Lipids and Proteins Through the Golgi Complex
The stationary cisternae model
The cisternal maturation model
Explain The stationary cisternae
model:
each cisterna in the Golgi stack is a stable structure
Transport from one cisterna to another is mediated by shuttle vesicles
These bud off from one cisterna and fuse with the next cisterna in a cis-to- trans sequence
The cisternal maturation model
the Golgi cisternae are transient compartments
They gradually change from CGN through medial cisternae to TGN
Enzymes not needed in later compartments are returned to earlier compartments in vesicles
Anterograde transport:
movement of material toward the plasma membrane
As a secretory granule fuses with the plasma membrane and discharges its contents (exocytosis), a bit of membrane from the ER becomes part of the plasma membrane
Retrograde transport
the flow of vesicles from Golgi cisternae back to the ER
allows the cell to balance the flow of lipids toward the plasma membrane
ensures a supply of materials for forming new vesicles
Two methods (unique to eukaryotes) for transporting materials across the plasma membrane are
exocytosis and endocytosis
how can proteins be tracked
Proteins were radioactively labeled briefly and tracked through time using electron microscopy and autoradiography
Exocytosis
the process by which secretory vesicles release their contents outside the cell
Adds lipids and proteins to the plasma membrane
Animal cells secrete hormones, mucus, milk proteins, and digestive enzymes
this way
Plant and fungal cells secrete enzyme and structural proteins for the cell wall
Endocytosis
the process by which cells internalize external materials
Removes lipids and proteins from the plasma membrane
The Process of Exocytosis
- Vesicles containing products for secretion move to the cell surface
- The membrane of the vesicle fuses with the plasma membrane
- Fusion with the plasma membrane discharges the contents of the vesicle
- The membrane of the vesicle becomes part of the cell membrane
Endocytic vesicles develop into early
endosomes, which fuse with vesicles from the TGN
They acquire digestive enzymes and form new lysosomes
In phagocytosis
solid particles are ingested
In pinocytosis
liquids are taken up
The lysosome is an organelle of the endomembrane system that contains
digestive enzymes
lysosome function
It is capable of degrading all the major classes of biological macromolecules
Isolate digestive enzymes from the rest of the cell
lysosome size
Vary in size and shape but are usually ~0.5 μm in diameter, bounded by a single membrane
how is the lysosome protected form its digestive enzymes
The lumenal side of the membrane is coated with glycoproteins to protect the membrane from degradation
Lysosomes Properties
Lysosomes maintain an acidic environment (pH 4.0–5.0) inside
due to ATP-dependent proton pumps in the membrane There are numerous enzymes inside lysosomes; all are
acid hydrolases
Heterophagic lysosomes
contain substances that originated outside the cell
Autophagic lysosomes:
Those with materials that originated inside the cell
