Cell bio lecture 14: Endomembrane System

How do proteins become embedded in the membrane of the endoplasmic reticulum?

via stop- and start-transfer sequences that stop and start translocation of a polypeptide through the ER membrane, resulting in transmembrane proteins

The endoplasmic reticulum is a site for

N-linked glycosylation of polypeptides

For each statement, indicated if it is true of the rough ER only, smooth ER only, of both RER and SER, or neither

Rough ER only: - has ribosomes attached to its outer (cytosolic) surface - is the site for biosynthesis of secretory prpoeins - is the site for the folding of membrane-bound proteins - usually consists of flattened sacs Smooth ER only: - is involved in the detoxification of drugs - is involved in the breakdown of glycogen - tends to form tubular structures Both: -Contains less cholesterol than does the plasma membrane -visible only be electron microscopy Neither: N/A

A student is studying cotranslational import into the ER lumen in a cell-free system. What would be the expected result if the student were to replace all of the GTP in the system with a nonhydrolyzable analog of GTP?

The SRP would remain bound to the SRP receptor on the ER surface.

Ribosomes that do not anchor on the surface of the rough endoplasmic reticulum during translation most probably

are synthesizing cytoplasmic proteins.

In comparing stop-transfer and internal start-transfer sequences in proteins it can be said that ______.

both are hydrophobic

A researcher is attempting to isolate rough ER microsomes using ultracentrifugation. Which of the following would indicate contamination of the rough ER with another organelle?

catalase

The transfer of polypeptides into the ER is called

cotranslational import

In which of the following organelles would you expect to first find a protein destined to be secreted from a cell?

endoplasmic reticulum

Each of the following is part of the core oligosaccharide side chain in the ER except: -N-acetyl glucosamine. -mannose. -glucose. -erythrose. -All are part of the core oligosaccharide.

erythrose.

Which of the following proteins are synthesized by bound ribosomes? insulin ribosmal protein actin DNA polymerase lysosomal enzyme ER protein

insulin lysosomal enzyme ER protein

Comparing cells synthesizing proteins and cells secreting steroid hormones, the cells synthesizing the steroid hormones have

more Smooth ER

Each of the following is part of the endomembrane system except: lysosomes. Golgi complex. zymogen granules. peroxisomes. endosomes.

peroxisomes

cytosolic polypeptides are transported to a target organelle via

post-translational import

Rough ER function

protein synthesis

Drag each label to identify the path a secretory protein follows from synthesis to secretion.

protein synthsis > endoplasmic reticulum > cis golgi cisternae > medial golgi cisternae > trans golgi cisternae > plasma membrane > extracellular space

Golgi Apparatus functin

-cisternal maturation -protein modification and sorting

Smooth ER Function

-poison detoxification -calcium ion storage -lipid synthesis

Each of the following is an endoplasmic reticulum function except ... -addition of carbohydrate to proteins to make glycoproteins. -the export of protein that cannot be folded into the cytoplasm for destruction. -the assembly of multimeric proteins. -peptide folding. -All are endoplasmic reticulum functions.

All are endoplasmic reticulum functions.