lecture 3

Question 1

intracellular compartments

Answer 1

mitochondria, golgi apparatus, ER, nucleus, plasma membrane, free ribosomes, peroxisome, cytosol, lysosome, endosome

volumes will differ from cell to cell

half the volume of cells is cytosol

Question 2

rough er

Answer 2

membrane-bound ribosomes
synthesis of soluble proteins and transmembrane proteins for the endomembrane

Question 3

smooth ER

Answer 3

phospholipid synthesis, detoxification

Question 4

organelles

Answer 4

a discrete structure or subcompartment of a eukaryotic cell that is specialized to carry out a particular function

Question 5

protein sorting

Answer 5

proteins are nuclear encoded

mRNA arrived in the cytoplasm (translatioon starts on ribosomes in cytosol)

cytosolic proteins dont have a sorting signal their default location is the cytosol

proteins that are sorted have a sorting signal called signal sequence

Question 6

signal sequence

Answer 6

stretch of amino acid sequence in a protein
specifies where protein will go in the cell

signal sequences are recognized by sorting receptors

Question 7

post-translational sorting

Answer 7

proteins are nuclear encoded, they are fully synthesizied in cytosol before sorting

when folded:nucleus, peroxisomes
- targeted by a signal sequence for import into nucleus/peroxisomes

when unfolded: mitochondria, plastids

Question 8

co-translational sorting

Answer 8

proteins are nuclear-encoded
they have ER signal sequence

associated with ER during protein synthesis in the cytosol

Question 9

sorting proteins to peroxisomes

Answer 9

containes enzymes for oxidative reactions
enzymes imported in through the transmembrane protein complex

Question 10

sorting proteins to mitochondria/chloroplasts

Answer 10

have their own genomes and ribosomes

most proteins for these cells are nuclear-encoded

they are translated into the cytosol and targeted by a signal sequence for import

proteins are UNFOLDED for import

Question 11

sorting proteins to the ER

Answer 11

co translational sorting

proteins are nuclear encoded

proteins have an ER sequence
ER signal sequence is hydrophobic

proteins that enter the ER are soluble proteins and transmembrane proteins

Question 12

cotranslational translocation: soluble protein

Answer 12

1. translation starts, N-terminal ER signal sequence emerges
2. recognized by SRP, elongation arrest by SRP
3. SRP-ribosome complex> SRP receptor> translocon
4. transolocon opens
5. protein synthesis resumes with protein transfer into ER lumen
6. signal peptidase cleaves ER signal sequence
7. protein is released into ER lumen
8. translocon closes

destination: lumen of endomembrane of organemme or secretion at PM

Question 13

cotranslational translocation: transmembrane protein

Answer 13

1-5 same
6. stop transfer sequence enters translocon (internal hydrophobic segment)
7. protein transfer stops and transmembrane domain is released into lipid bilayer
8. signal peptidase cleaves ER signal sequence and translocation closes
9. protein is completed

destination: membrane of an endomembrane organelle or in the plasma membrane

Question 14

ER signal sequences

Answer 14

N-terminal ER signal sequence
at N-terminus of protein, stretch of hydrophobic amino acids, removed by signal peptidase

internal ER sequence
start-transfer sequence, stretch of hydrophobic amino acids, NOT removed, they remain part of the protein

Question 15

endomembrane system

Answer 15

ER, golgi, endosomes, lysosomes

Question 16

secretory pathway

Answer 16

-proteins and lipids are made in ER

delivered to other compartments
ER>outside is exocytosis
ER>lysosomes via endosomes

Question 17

endocytic pathway

Answer 17

contents move into cell
endocytosis

Question 18

retrieval pathway

Answer 18

retrieval of lipids, selected proteins for reuse

Question 19

exocytosis

Answer 19

vesicle conetents are delivered to extracellular space

vesicle membrane becomes part of pm

Question 20

Endocytosis

Answer 20

vesicle luminal contents come from extracellular space

plasma membrane forms vesicle membrane

Question 21

vesicle

Answer 21

small, membrane-enclosed organelle in cytoplasm of eukaryotic cell
shuttles components back and forth in the endomembrane system

Question 22

maintenance of membrane protein asymmetry

Answer 22

each membrane protein has a specific oreintation, resule of insertation in ER

protein assymmetry is maintaied through vesicular transport

Question 23

golgi

Answer 23

recieves proteins and lipids from the ER, modifies them and then dispatched them to other destinations in the cell

Question 24

protein glycosylation

Answer 24

starts in the ER, single type of oligosaccharide is attatched to many proteins

complex oligosaccharide processing occirs in golgi

Question 25

endosomes

Answer 25

membrane bound organelles
contain material ingested by endocytosisl

Question 26

lysosomes

Answer 26

membrane bound organelles, contain hydrolytic enzymes to digest worn-out proteins, organelles, other waste

main site of intracellular digestion