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Biology 241 > 5.4 The Endomembrane System > Flashcards

5.4 The Endomembrane System Flashcards

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1
Q

vesicle

A

a small membrane-enclosed sac that transports substances within the cell

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2
Q

organelles inside cells are not isolated entities; they can communicate with each other through:

A

physical membrane “bridges” or transiently connected by vesicles - form by budding off an organelle, taking with them a piece of the membrane and internal contents of the original organelle and fusing with another organelle or the plasma membrane, re-forming a continuous membrane and unloading their contents.

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3
Q

endomembrane system

A

a cellular system that includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, the plasma membrane, and the vesicles that move between them

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4
Q

in plants, the endomembrane system is usually continuous between cells through…

A

plasmodesmata or connecting pores

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5
Q

molecules in the cytosol are in a different physical space than the inside of the endomembrane system and is physically separated by:

A

the membranes of the endomembrane system

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6
Q

the physical separation involved in the endomembrane system allows for:

A

specific functions to take place within the spaces defined by the membranes and also within the membrane itself

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7
Q

exocytosis

A

the process in which a vesicle fuses with the plasma membrane and empties its contents ion the extracellular space or delivers proteins to the plasma membrane

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8
Q

endocytosis

A

the process in which a vesicle buds off from the plasma membrane, bringing material from outside the cell into that vesicle, which can the fuse with other organelles

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9
Q

together, exocytosis and endocytosis provide a way to move material into and out of cells without….

A

passing through the cell membrane

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10
Q

nucleus (of a cell)

A

the compartment of the cell that houses the DNA in chromosomes

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11
Q

what is the innermost organelle of the endomembrane system?

A

the nucleus

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12
Q

nuclear envelope

A

the cell structure, composed of two membranes, inner and outer (both are lipid bilayers with associated proteins), that defines the boundary of the nucleus

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13
Q

nuclear pore

A

one of many protein channels in the nuclear envelope that act as gateways that allow molecules to move into and out of the nucleus and are thus essential for the nucleus to communicate with the rest of the cell

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14
Q

what can passively diffuse through the nuclear pores?

A

small molecules and ions, large proteins and RNA requires active transport

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15
Q

ribosome

A

a complex structure of RNA and protein, bound to the cytosolic face of the RER in the cytoplasm, on which proteins are synthesized

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16
Q

the outer membrane of the nuclear envelope is physically continuous with:

A

the endoplasmic reticulum (ER), an organelle bounded by a single membrane

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17
Q

what are the functions of the ER?

A

produces and transports many lipids&proteins in and out of cell (includes transmembrane proteins, proteins destined for Golgi apparatus, lysosomes, or export out of cell); site of production of most lipids that make up internal and external cell membranes

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18
Q

lumen

A

in eukaryotes, the continuous interior of the endoplasmic reticulum; in plants, a fluid-filled compartment enclosed by the thylakoid membrane; generally, the interior of any tubelike structure

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19
Q

rough endoplasmic reticulum (RER)

A

the part of the endoplasmic reticulum with attached ribosomes

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20
Q

role of RER:

A

synthesize transmembrane proteins, proteins that end up in the interior of organelles, and proteins destined for secretion

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21
Q

cells that secrete large quantities of protein have extensive….

A

rough ER (ex. cells in gut that secrete digestive enzymes)-all cells have some rough ER for production of transmembrane and organelle proteins.

22
Q

smooth endoplasmic reticulum (SER)

A

the portion of the endoplasmic reticulum that lacks ribosomes

23
Q

role of smooth ER

A

site of fatty acid and phospholipid biosynthesis

24
Q

SER predominates in cells specialized in the production of:

A

lipids

25
Q

Golgi apparatus is “connected” with the ER through:

A

vesicles that bud off the ER; vesicles carry lipids and proteins

26
Q

movement of vesicles from the ER to the Golgi apparatus and then to the rest of the cell is part of a biosynthetic pathway in which:

A

lipids and proteins are sequentially modified and delivered to their final destinations

27
Q

what are the three primary roles of the Golgi apparatus?

A
  1. further modified proteins and lipids produced in the ER
  2. acts as a sorting station as these proteins and lipids move to their final destinations
  3. site of synthesis of most of the cell’s carbohydrates
28
Q

cisternae (singular: cisterna)

A

the series of flattened membrane sacs that make up the Golgi apparatus

29
Q

what is the primary means by which proteins&lipids move through the Golgi apparatus to their final destinations (ex. plasma membrane, other organelles)

A

vesicles

30
Q

each region of the Golgi apparatus contain a different set of enzymes that catalyzes specific reactions so:

A

modifications of proteins and lipids take place in a sequence of steps, each performed in a different region of the Golgi apparatus

31
Q

glycosylation

A

a chemical modification that occurs predominantly in the Golgi apparatus in which sugars are covalently linked to lipids or specific amino acids of proteins.

32
Q

glycoproteins are important components of the eukaryotic cell surface by forming:

A

a relatively flexible and protective coating over the plasma membrane: sugars attached to the protein can protect the protein from enzyme digestion by blocking access to the peptide chain (result of glycosylation)

33
Q

glycoproteins and glycolipids are recognized specifically by other cells and molecules because of:

A

the distinctive shapes that sugars contribute to glycoproteins and glycolipids (ex. human blood types and their specific protein/lipids on the surface)

34
Q

what is the purpose of the reverse pathway from Golgi to ER?

A

functions in retrieving proteins that were accidentally moved forward and to recycle membrane components

35
Q

lysosomes

A

a vesicle derived from the Golgi apparatus that contains enzymes that break down macromolecules such as proteins, nucleic acids, lipids, and complex carbohydrates (degrades damaged or unneeded macromolecules)

36
Q

macromolecules destined for degradation are packaged by the Golgi apparatus into:

A

vesicles that then fuse with lysosomes, delivering their contents to the lysosome interior

37
Q

enzymes inside the lysosomes are synthesized in the:

A

RER, sorted in the Golgi apparatus and then packaged into lysosomes.

38
Q

Golgi apparatus also sorts and delivers specialized proteins that become embedded in lysosomal membranes such as:

A

proton pumps that keep internal environment at an acidic pH of 5 (optimum pH for activity of enzymes), other proteins transport the break down products of macromolecules across the membrane to the cytosol for use by the cell

39
Q

the function of lysosomes highlights the importance of having separate compartments of the cell bounded by selectively permeable membranes because…

A

lysosomal enzymes can’t function at pH7 (cell) and other cell enzymes/proteins would degrade in lysosome pH: by restricting the activity of these enzymes to the lysosome, the cell protects proteins and organelles in the cytosol from degradation

40
Q

protein sorting

A

the process by which proteins end up where they need to be in the cell to perform their function

41
Q

proteins are produced in two places, where?

A

free ribosomes in the cytosol and membrane-bound ribosomes on the rough ER

42
Q

signal sequence

A

an amino acid sequence that directs a protein to its proper cellular compartment

43
Q

proteins produced on free ribosomes are translated (signal sequences) and then sorted:

A

proteins with no sequence remain in the cytosol
proteins for mitochondria/chloroplasts have a signal sequence at their amino ends
proteins for nucleus have signal sequences located internally

44
Q

nuclear localization signal

A

the signal sequence for the nucleus that enables proteins to move through pores in the nuclear envelope

45
Q

proteins produced on the rough ER end up:

A

in the lumen of the endomembrane system, secreted out of the cell, or as transmembrane proteins. they are sorted as they are translated

46
Q

proteins produced on the rough ER begin translation on free ribosomes but a specific signal sequence at the amino terminal end directs the ribosome to the:

A

RER and into a membrane channel that leads into the ER lumen. continues into lumen if no other signal sequence. ends up in membrane if signal-anchor sequence present

47
Q

signal-anchor sequence

A

in protein sorting, an amino acid sequence in a polypeptide chain that embeds the chain in the membrane

48
Q

proteins destined for the ER lumen or secretion have an:

A

amino-terminal signal sequence which is recognized by SRP which binds to the signal sequence and the free ribosome and brings about a pause in translation. SRP binds with receptor on RER, SRP receptor brings ribosome to a channel in the membrane of the RER, SRP dissociates and translation continues allowing polypeptide chain to be threaded through the channel. specific protease cleaves the signal sequence as it emerges into the lumen of the ER and protein can remain in interior of ER, be transported by vesicles to interior of Golgi apparatus/organelles or secreted by exocytosis

49
Q

signal-recognition particle (SRP)

A

an RNA-protein complex that binds with part of a polypeptide chain and marks the molecule for incorporation into the endoplasmic reticulum (eukaryotes) or the plasma membrane (prokaryotes)

50
Q

proteins destined for cell membranes contain:

A

a signal-anchor sequence and an amino-terminal signal sequence

51
Q

after growing polypeptide chain and its ribosome are brought to the ER, it is threaded through the channel in the ER membrane until the signal-anchor sequence is encountered. The signal-anchor sequence is…

A

hydrophobic and diffuses laterally in the lipid bilayer. ribosome dissociates from the channel while translation continues. After translation, the carboxyl end of the chain remains on the cytosolic side of the ER membrane, the amino end is in the ER lumen, and the region between them resides in the membrane

Biology 241 (31 decks)

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