Cell bio quiz 3 Flashcards
Where is N-linked glycosylation initiated?
N-linked glycosylation is initiated in the endoplasmic reticulum (ER).
What is the role of GPI anchors?
GPI anchors are used to attach some proteins to the plasma membrane, as opposed to having membrane-spanning regions.
Why are many proteins synthesized in the ER rapidly degraded?
Many proteins synthesized in the ER are rapidly degraded because they fail to fold correctly.
What triggers the unfolded protein response?
The unfolded protein response is triggered by an excess of unfolded proteins in the endoplasmic reticulum.
Where are membrane lipids primarily synthesized?
Membrane lipids are primarily synthesized in the ER
What are the three main types of lipids in eukaryotic cell membranes?
The three main types are phospholipids, glycolipids, and cholesterol.
How are proteins and lipids transported along the secretory pathway?
They are transported in transport vesicles, which bud from the membrane of one organelle and fuse with another.
What is the role of the Golgi apparatus?
The Golgi apparatus functions as a factory where proteins received from the ER are further processed and sorted for transport to their eventual destinations.
How are lysosomal proteins targeted?
Lysosomal proteins are targeted by the addition of a phosphate group to mannose residues, which is recognized by the mannose-6-phosphate receptor in the trans Golgi network.
What is the significance of the COP II coat in vesicular transport?
COP II-coated vesicles carry proteins from the ER to the ER-Golgi intermediate compartment and then on to the Golgi.
How is the specificity of vesicular transport established?
The specificity is established by the localization of Rab proteins on the correct membrane, which facilitates the formation of v-SNARE/t-SNARE complexes.
What is autophagy?
Autophagy is the process by which the cell digests its own parts, including cytoplasm or internal organelles, through the formation of autophagosomes that fuse with lysosomes.
How do both proteins and phospholipids travel along the secretory pathway?
Both proteins and phospholipids travel along the secretory pathway in transport vesicles which bud from the membrane of one organelle and then fuse with the membrane of another.
What are ERES and ERGIC?
ERES=ER exit side. From there they go to the ERGIC=ER Golgi intermediate compartment and then on to the Golgi.
How are resident ER proteins destined to remain in the lumen of the ER marked?
Resident ER proteins destined to remain in the lumen of the ER are marked by KDEL or KKXX retrieval sequences at their carboxy terminus.
What functions as a factory in which proteins received from the ER are processed and sorted?
The Golgi apparatus or Golgi complex functions as a factory in which proteins received from the ER are further processed and sorted for transport to their eventual destinations—endosomes, lysosomes, the plasma membrane, or secretion from the cell.
Where are the complex polysaccharides of the cell wall synthesized in plant cells?
In plant cells, the Golgi apparatus further serves as the site at which the complex polysaccharides of the cell wall are synthesized.
What distinguishes the processing of the N-linked oligosaccharide of lysosomal proteins from that of secreted and plasma membrane proteins?
The processing of the N-linked oligosaccharide of lysosomal proteins differs from that of secreted and plasma membrane proteins. Lysosomal proteins are specifically recognized and modified by the addition of a phosphate group to the number 6 position of mannose residues.
What role does the Golgi apparatus play in lipid metabolism?
In addition to its activities in processing and sorting glycoproteins, the Golgi apparatus functions in lipid metabolism— in particular in the synthesis of glycolipids and sphingomyelin from ceramide (which is synthesized in the ER).
How are proteins, as well as lipids and polysaccharides, transported from the Golgi apparatus?
Proteins, as well as lipids and polysaccharides, are transported from the Golgi apparatus to their final destinations through the secretory pathway.
What distinguishes the constitutive secretory pathway?
The constitutive secretory pathway, which operates in all cells, leads to continual unregulated protein secretion. In the absence of specific targeting signals, proteins carried to the plasma membrane by constitutive secretion.
What mediates the fusion of a transport vesicle with a target membrane?
The SNARE hypothesis states that vesicle fusion is mediated by pairs of transmembrane proteins (v-SNARE and t-SNARE on the vesicle and target membranes respectively).
What are some clinical symptoms of laminopathies and other nuclear envelopathies?
Laminopathies and other nuclear envelopathies have a large variety of clinical symptoms including skeletal and/or cardiac muscular dystrophy, lipodystrophy (degenerative conditions of the body’s adipose tissue), diabetes, dysplasia (epithelial anomaly), dermo- or neuropathy, leukodystrophy (degeneration of the white matter), and progeria (premature aging).
What are B-type lamins and where are they expressed?
B-type lamins are present in every cell. B-type lamins B1 and B2 are expressed from the LMNB1 and LMNB2 genes.
When are A-type lamins expressed, and what are the most common A-type lamins?
A-type lamins are only expressed following gastrulation. Lamin A and C are the most common A-type lamins and are splice variants of the LMNA gene.
What gene is mutated in patients with classical laminopathy?
Patients with classical laminopathy have mutations in the gene coding for lamin A (LMNA gene).
What are some mutations implicated in nuclear envelopathies?
Mutations implicated in other nuclear envelopathies were found in genes coding for lamin-binding proteins such as lamin B receptor (LBR gene), emerin (EMD gene), LEM domain-containing protein 3 (LEMD3 gene), and prelamin-processing enzymes.
What are the earliest features of Emery-Dreifuss muscular dystrophy, and what genes cause it?
Among the earliest features of Emery-Dreifuss muscular dystrophy are joint deformities called contractures, which become noticeable in early childhood and most often involve the elbows, ankles, and neck. Mutations in the EMD (Emerin, a lamin-binding protein) and LMNA genes cause Emery-Dreifuss muscular dystrophy.
What is progeria, and how many known cases are there currently in the world?
Progeria, narrowly referring to Hutchinson-Gilford Progeria Syndrome, is an extremely rare genetic condition that causes physical changes resembling greatly accelerated aging in sufferers. Currently, there are 51 known cases in the world.
What causes Gaucher’s disease, and how common is it?
Gaucher’s disease is caused by a deficiency of the enzyme glucocerebrosidase, leading to an accumulation of glucocerebroside. It is the most common of the lysosomal storage diseases and occurs in approximately 1 in 50000 live births, most often among persons of Ashkenazi Jewish heritage.
What enzyme activity is insufficient in Tay-Sachs disease, and what does it lead to?
Tay-Sachs disease is caused by insufficient activity of an enzyme called hexosaminidase A, which catalyzes the biodegradation of gangliosides. Insufficient activity of this enzyme leads to the accumulation of lipids in the brain, causing problems.
What does the structure of a cell membrane function to do?
The structure of a cell membrane functions to separate the interior of the cell from its environment and to define the internal compartments of eukaryotic cells including the nucleus and cytoplasmic organelles.
How do lipid bilayers behave?
Lipid bilayers behave as two-dimensional fluids in which individual molecules are free to rotate and move in lateral directions.
Who gave the cell membrane its “fluid mosaic” description, and why?
“Fluid mosaic” was the description Jonathan Singer and Garth Nicolson gave the cell membrane when they observed that proteins are inserted into a lipid bilayer.
