Textbook: Chapter 8: ER/Golgi Flashcards
Some enveloped viruses, such as the herpes virus, fuse directly with the plasma membrane, depositing the genome-laden capsid inside the cell. A larger proportion of viruses, however…
hijack endocytic pathways to enter the cell, thereby leaving few traces on the cell surface to alert the attention of roving immune cells. In these cases, viruses are internalized into vesicles known as endosomes and later release their genome into the cell.
endomembrane system includes
endoplasmic reticulum, Golgi complex, endosomes, lysosomes, and vacuoles
peroxisomes
organelles that sequester diverse oxidative reactions
Transport vesicles move through the cytoplasm in a directed manner, often …….. When it reaches its
destination,…….
- pulled by motor proteins that operate on tracks formed by microtubules and microfilaments of the cytoskeleton
- a vesicle fuses with the membrane of the acceptor compartment, which receives the vesicle’s soluble cargo as well as its membranous wrapper
Materials follow the biosynthetic (or secretory) pathway from the endoplasmic reticulum, through the Golgi complex, and out to various locations including (6):
lysosomes, endosomes, secretory vesicles, secretory granules, vacuoles, and the plasma membrane.
endocytic pathway organelle order:
Materials follow the endocytic pathway from the cell surface to the interior by way of endosomes and lysosomes, where they are generally degraded by lysosomal enzymes.
constitutive secretion (2)
What it is+ contribites to
- materials are transported in secretory vesicles from their sites of synthesis and discharged into the extracellular space in a continual manner.
- Most cells engage in constitutive secretion, a process that contributes not only to the formation of the extracellular matrix, but also to the formation of the plasma membrane itself.
regulated secretion + ex (2)
- materials are stored as membrane-bound packages and discharged only in response to an appropriate stimulus.
- Regulated secretion occurs, for example, in endocrine cells that release hormones, in pancreatic acinar cells that release digestive enzymes, and in nerve cells that release neurotransmitters
Proteins, lipids, and complex polysaccharides are transported through the cell along the —- or —- pathway
- biosynthetic
- secretory
Biosynthetic organell order:
- A biosynthetic pathway can be discerned in which
proteins are synthesized in the endoplasmic reticulum, modified during passage through the Golgi complex, and transported from the Golgi complex to various destinations, such as the plasma membrane, a lysosome, or the large vacuole of a plant cell
These various types of cargo—secreted proteins, lysosomal enzymes, and membrane proteins—are routed to their appropriate cellular destinations by virtue of specific “addresses” or sorting signals. Explain how this works:
sorting signals that are encoded in the amino acid sequence of the proteins or in the attached oligosaccharides. The sorting signals are recognized by specific receptors that reside in the membranes or surface coats of budding vesicles, ensuring that the protein is transported to the appropriate destination.
Autoradiography provides a means to visualize biochemical processes by allowing …..
an investigator to determine the location of radioactively labeled materials within a cell.
Autoradiography steps (4):
- To determine the sites where secretory proteins are synthesized, slices of pancreatic tissue are incubated in a solution containing radioactive amino acids for a brief period of time. During this period, labeled amino acids were taken up by the living cells and incorporated into the digestive enzymes as they were being synthesized on ribosomes.
- The tissues were quickly fixed, and the locations of proteins that had been synthesized with labeled amino acids during the brief incubation were determined autoradiographically. Using this approach, the endoplasmic reticulum was discovered to be the site of synthesis of secretory proteins
- After incubating the tissue for a brief period in radioactive amino acids, they washed the tissue until it was free of excess isotope and transferred it to a medium containing only unlabeled amino acids.
- the movements of newly synthesized molecules can ideally be followed by observing a wave of radioactive material moving through the cytoplasmic organelles of cells from one location to the next
What Pulse and Chase refers to
The pulse refers to the brief incubation with radioactivity during which labeled amino acids are incorporated into protein. The chase refers to the period when the tissue is exposed to the unlabeled medium, a period during which additional proteins are synthesized using nonradioactive amino acids
The longer the chase, the ……
farther the radioactive proteins manufactured during the pulse will have traveled from their site of synthesis within the cell.
rough endoplasmic reticulum (RER) (5)
presence of+composed of+continous+the synthesis of+starting
- presence of ribosomes bound to its cytosolic surface
- composed of a network of flattened sacs (cisternae)
- continuous with the outer membrane of the nuclear envelope, which also bears ribosomes on its cytosolic surface
- the synthesis of proteins and the synthesis of most of the lipids of a cell’s membranes
- The RER is the starting point of the biosynthetic pathway
smooth endoplasmic reticulum (SER) (4)
lacks+ membrane+extensively developed in+ functions
- lacks associated ribosomes
- the membranes of the SER are highly curved and tubular, forming an interconnecting system of pipelines traversing the cytoplasm
- extensively developed in a number of cell types, including those of skeletal muscle, kidney tubules, and steroid-producing endocrine glands
- They sequester calcium ions within the cytoplasm of cells. The regulated release of Ca2+ from the SER of skeletal and cardiac muscle cells (known as the sarcoplasmic reticulum in muscle cells) triggers contraction
The two types of ER in terms of their membranes are….
not ribosomes.
their membranes are continuous
Further experiments revealed that polypeptides are synthesized at two distinct locales within the cell:
- on ribosomes attached to the cytosolic surface of the RER membranes
- free ribosomes
Proteins synthesized on ribosomes attached to the cytosolic surface of the RER membranes (2):
released into+ process is called+ includes what type of protein?
- released into the ER lumen in a process called co translational translocation
- include (1) secreted proteins, (2) integral membrane proteins, and (3) soluble proteins that reside within compartments of the endomembrane system, including the ER, Golgi complex, lysosomes, endosomes, vesicles, and plant vacuoles
Protein synthesized on free ribosomes (2):
released in+includes what type of proteins
- released into the cytosol
- includes (1) proteins destined to remain in the cytosol (such as the enzymes of glycolysis and the proteins of the cytoskeleton), (2) peripheral proteins of the cytosolic surface of membranes (such as spectrins and ankyrins that are only weakly associated with the plasma membrane’s cytosolic surface), (3) proteins that are transported to the nucleus, and (4) proteins to be incorporated into peroxisomes, chloroplasts, and mitochondria.
Secretory proteins contain a signal sequence at their ……. that….
- N-terminus
- directs the emerging polypeptide and ribosome to the ER membrane.
Co-translational translocation
signal sequence:
a stretch of 6–15 hydrophobic amino acid residues
Steps for Co-translational translocation (10)
- Begins on a free ribosome
- Signal sequence (directs ribosome to membrane) usually at N-terminal end is 6-15 hydrophobic amino acids
- Signal secognition particle (SRP) binds to the signal sequence and the ribosome
- Polypeptide synthesis is halted temporarily
SRP directs this complex to the ER membrane by interaction with the SRP receptor (ribosome+peptide) - Ribosome/polypeptide then are transfered from the SRP once it docs to the receptor to the translocon (a protein pore in the ER membrane with a plug to prevent ion diffusion)
- Contact with the signal sequence displaces the plug
SRP released from the SRP receptor - Translocation through the pore: Polypeptie enters the ER lumen
- Upon termination, ribosome is released
- Signal sequence is removed by an enzyme: signal peptidase
- Protein chaperones (Eg: BiP) aid in protein folding