Protein folding in the endoplasmic reticulum Protein synthesis

Biology Multiple Choice Questions and Answers for Different Competitive Exams

The term "cytosol" was first introduced in 1965 by H

Whey is the richest natural source of BCAAs (branch powder, or Epic Protein Chocolate.
Organelles Mitochondrium The It synthesises secretory proteins, What organelle is being digested by the secondary lysosome shown in picture above.
The guard cell opens when potassium ions move into the vacuoles, The ribosome is the organelle that makes or synthesises proteins.
Start studying Cell Organelles.

Intracellular trafficking - WormBook

ER stress and the unfolded protein response - …

For the most part, eukaryotes do not secrete proteins directly across the plasma membrane. Instead, the newly synthesized proteins are translocated from the cytoplasm into an intracellular organelle, the endoplasmic reticulum (ER). The ER is a series of membranous cisternae and tubules that spread throughout the cytoplasm and is continuous with nuclear membrane. As we shall see, the mechanisms for translocating proteins across ER membranes and bacterial membranes both involve a transmembrane pore. Why have an ER? A common speculation on the evolutionary advantage of the ER is that it provides a controlled milieu in which exported proteins can fold and oligomerize, without being exposed to the rigors of the extracellular world. In this regard, the lumen of the ER resembles the periplasmic space in gram-negative bacteria.

When E. coli makes a protein that is destined for export, it is made as a preprotein containing a signal sequence (4). In most proteins, these signal sequences are a stretch of contiguous amino acids at the amino terminus of a protein, with a positively charged amino terminus, at least six sequential hydrophobic amino acids, and a cleavage site for the signal peptidase that removes the signal after translocation. The presence of the signal sequence in a newly synthesized protein causes a protein chaperone to bind to it, retarding its folding. There appear to be at least two major chaperone systems in E. coli. One involves the tetrameric cytosolic protein secB, which binds to newly synthesized proteins that contain a signal sequence. It binds throughout the length of the newly synthesized polypeptide chain, keeping it from adopting its native conformation (2). A different class of chaperones binds to the nascent chain as the secreted protein is being synthesized on the ribosome. An example of such a chaperone is a ribonucleoprotein, the signal recognition protein (SRP). In E. coli SRP consists of a 4.5 S RNA molecule and a single protein, Ffh, which is a GTPase; that is, it hydrolyzes guanosine triphosphate (5).


Introduction to Biological Membranes

Endocytosis is the vesicle-mediated process used by all cells to internalize extracellular macromolecules, plasma membrane lipids, and plasma membrane proteins (). There are several endocytic pathways that utilize different mechanisms to internalize portions of the plasma membrane. The best studied endocytosis pathway in worms () and mammalian cells () is the clathrin-coated pit pathway (). Many receptors and their associated ligands cluster into clathrin-coated pits by association with clathrin adaptor proteins such as the four-subunit complex AP2. Clathrin adaptors in turn bind to the clathrin lattice which is thought to provide the force required to deform the membrane into a curved bud. The large GTPase dynamin is then involved in pinching off the coated pit to form a clathrin-coated vesicle. Such vesicles are then uncoated by the chaperone hsc70 and the DNA-J domain co-chaperone auxillin. Uncoated endocytic vesicles then fuse with one another and with early endosomes in a reaction requiring the small GTPase Rab5. In early endosomes some ligand-receptor complexes dissociate due to the reduced pH of the endosomal lumen. Many receptors then recycle to the plasma membrane either directly or indirectly via recycling endosomes. Many ligands do not recycle but instead are transported from early to late endosomes and eventually to lysosomes for degradation. Early to late endosome transport may be mediated by small vesicular intermediates, or may be a maturation process whereby early endosomes lose components through recycling pathways and gain components through fusion with vesicles derived from the secretory pathway. Late endosomes are then thought to fuse with pre-lysosomes to form “hybrid” organelles, which mature back into lysosomes through sorting and fission.

intro to cell ch 7 Flashcards | Quizlet

1958 Radioactive proteins are followed after their synthesis as they progress towards their secretory fate; this allows the definition of not only trafficking pathways but of the organelles that lie along that pathway.