Week 2-Cell structure

Question 1

What is the most charged membrane phospholipid?

Answer 1

phosphatidyl serine

Question 2

What are the 4 major membrane phospholipids?

Answer 2

phosphatidyl-ethanolamine, phophatidyl-serine (both amino phospholipids)
phosphatidyl-choline, sphingomyelin (both choline phospholipids)
first 3 are all phosphoglycerides

Question 3

Functions of cholesterol

Answer 3

stiffens membrane, reduces permeability, inhibits phase changes; head is hydrophilic and points outward

Question 4

Where are glycolipids present on cell membranes?

Answer 4

non-cytosolic side

Question 5

What is the main function of phosphatidylinositol phospholipids?

Answer 5

6 carbon ring can be phosphorylated/dephosphorylated differently to bind different proteins that take part in various intercellular functions

Question 6

Where are phosphoglycerides made?

Answer 6

ER, but sphingosine synthesized in Golgi for sphingomyelin

Question 7

What occurs during plasma membrane translocation to phospholipid distribution?

Answer 7

initially evenly distributed, choline-containing phospholipids are flipped to non-cytosolic leaflet, amino phospholipids shifted to cytosolic leaflet

Question 8

What are the components of lipid rafts?

Answer 8

sphingolipids, cholesterol, proteins

Question 9

What exactly comprises a glycocalyx? and what is its function?

Answer 9

It is made of membrane proteins that have sugars covalently attached; function in protection, identification, and adhesion

Question 10

What are the four mechanisms to organize integral membrane proteins?

Answer 10

1- self-assembly into aggregates
2- tethered to extracellular molecules
3- tethered to intracellular molecules
4- bind to proteins on adjacent cells

Question 11

What is the function of the rough ER?

Answer 11

protein synthesis of membrane bound proteins (not cytosolic proteins)

Question 12

What are the functions of the smooth ER?

Answer 12

lipid synthesis, Ca++ regulation, detoxification

Question 13

Give an example of a cell that would have a lot of rough ER and a cell that would have a lot of smooth ER

Answer 13

RER = B cells because they produce a lot of Abs
SER = liver cells, detoxifying

Question 14

What determines if a polyribosome is attached to an ER membrane?

Answer 14

polypeptide chain will possess an ER signal sequence, signaling polysome to remain attached

Question 15

What determines if a polypeptide is released into the ER lumen or made into a single/multipass membrane protein?

Answer 15

determined by number and orientation of start/stop sequences in polypeptide chain; also determines which end is orientated toward which side

Question 16

What is the directionality of vesicular transport through golgi?

Answer 16

products fuse with cis face, packaged and released through trans face

Question 17

What are the three pathways for materials to enter the golgi?

Answer 17

endocytosis, phagocytosis, autophagy

Question 18

How to endosomes mature before fusion with Golgi vesicles?

Answer 18

pump protons into lumen –> decrease pH –> activates hydrolyses –> condense and are now lysosomes

Question 19

What is the signal to identify lysosomal enzymes?

Answer 19

phosphorylated mannose residues

Question 20

What is the constitutive secretory pathway?

Answer 20

way for vesicles to leave golgi through direct exocytosis – lack of signal leads to this

Question 21

Where does N-linked glycosylation of proteins occur and where is the sugar linked?

Answer 21

linked to asparagine, occurs in lumen of ER, modified in golgi

Question 22

Where does O-linked glycosylation occur and where is the sugar linked?

Answer 22

linked to serine or threonine, occurs in golgi or outside of cell

Question 23

What is the class of heavily O-linked glycosylated proteins and what are their sugar chains?

Answer 23

proteoglycans, made of glycosaminoglycan (GAG)

Question 24

What gives the extracellular matrix its properties?

Answer 24

sugars on proteoglycans are sulfated, negative charge – attracts water to form hydragels

Question 25

Where are misfolded proteins degraded?

Answer 25

misfolded proteins are ubiquinated and destroyed by proteosomes in the cytoplasm

Question 26

What disease is associated with lysosomal dysfunction?

Answer 26

Tay-sachs

Question 27

What are the three pathways out of the Golgi?

Answer 27

two secretory (constitutive and regulated) and one lysosomal pathway

Question 28

What are caveolae and what is their purpose?

Answer 28

invaginations that can lead to uncoated vesicles --> vesicles can transport cargo from one side of cell to the other through transcytosis

Question 29

What is characteristic of clathrin coated vesicles?

Answer 29

honeycomb look due to polymerization of clathrin proteins which are shapped like triskelions

Question 30

What are coatamer (COP) 1 and 2 associated with?

Answer 30

transport back and forth between Golgi and ER

Question 31

What is the main purpose of clathrin coated vesicles?

Answer 31

receptor mediated endocytosis; transport from Golgi to endosome/lysosome and from plasma membrane to endosome/lysosome

Question 32

What removes the clathrin coat from vesicles?

Answer 32

ATPases (members of heat shock protein family)

Question 33

What proteins functions as molecular switches and take part in COP1 and COP2 vesicle coating?

Answer 33

G proteins; become active and unactive through GTPases (active=GTP, inactive=GDP)

Question 34

What is KEDL?

Answer 34

an amino acid sequence on ER proteins that allows them to be returned to ER if they end up in the Golgi

Question 35

What proteins play an important role in delivery and fusion of vesicles?

Answer 35

Rabs, Rab effectors, SNAREs

Question 36

What is the system by which SNAREs work?

Answer 36

the vesicle has a v-SNARE protein and the target has a corresponding t-SNARE; must recognize each other

Question 37

How do Rab proteins know which membranes to bind to?

Answer 37

inositol phospholipids -- specificity in their phosphorylation leads to recognition of membrane for Rab binding

Question 38

Where do mitochondria tend to localize?

Answer 38

near site of high ATP utilization and along microtubules; often close connection to ER

Question 39

How are proteins brought into mitochondria from cytoplasm?

Answer 39

through translocator complexes that recognize alpha-helical protein structure with hydrophobic residues along one side (for TOMS and TIMS)

Question 40

What are TOMS and TIMS?

Answer 40

transporters of outer mitochondrial membrane or inner, respectively

Question 41

What is OXA?

Answer 41

transports protein from matrix OUT of mitochondria

Question 42

What inserts lipids into the mitochondrial membrane?

Answer 42

exchange proteins remove lipids from ER to insert into mitochondrial membranes

Question 43

What are the functions of peroxisomes?

Answer 43

detox, beta-oxidation of some fatty acids, formation of myelin phospholipids

Question 44

What is the outer edge of the nuclear matrix lined with?

Answer 44

lamins make up the scaffolding of the nuclear matrix; they are part of the intermediate filament family

Question 45

What exactly is the nucleolus?

Answer 45

ribosome producing factory; contains the chromosomes that have the duplicated genes of rRNA –tons of transcription and production of rRNA

Question 46

What size proteins can diffuse through nuclear pores?

Answer 46

5000 daltons - 60K daltons

Question 47

What type of protein will most quickly be transported to the nucleus?

Answer 47

any protein with a nuclear localization signal (NLS)

Question 48

How do proteins larger than 60kDaltons get into the nucleus?

Answer 48

through active transport that uses energy and receptor proteins

Question 49

What are the characteristics of imported proteins (to nucleus)?

Answer 49

Bind import receptors in the presence of GDP, and dissociate in the presence of GTP

Question 50

What are the characteristics of exported proteins (to nucleus)?

Answer 50

Bind export receptors in the presence of GTP, and dissociate in the presence of GDP

Question 51

What controls the directionality of transport of proteins to and from the nucleus?

Answer 51

small G-protein called Ran

Question 52

Where are Ran-GEF and Ran-GAP found?

Answer 52

Ran-GEF (exchange factor) - nucleus | Ran-GAP (activating protein) - cytoplasm

Question 53

What is the protein microfilament and what are its functions?

Answer 53

actin; cell shape, division and motility, also support/organize plasma membrane

Question 54

What is the microtubule protein and what are its functions?

Answer 54

tubulin; organize cytoplasm, intracellular transport (railroad), cell division, cilia/flagellae motility

Question 55

What are the functions of intermediate filaments?

Answer 55

strengthen cytoplasm/tissues, support nucleus, epidermal appendages

Question 56

Where are microtubules localized?

Answer 56

near nucleus by spanning out from their centrosome

Question 57

How are actin filaments constructed/deconstructed?

Answer 57

remove monomers from - end and add to the + end

Question 58

How are tubulin filaments constructed/deconstructed?

Answer 58

ossicilations of slow growth and rapid breakdown (called dynamic instability) – determined by whether the end units have hydrolyzed their GTP; occurs on + end

Question 59

What regulates polymerization of intermediate filament proteins?

Answer 59

polymerize when unphosphorylated, depolymerize when phosphorylated; do NOT have an inherent polarity

Question 60

What is the arrangement of tubulin filaments?

Answer 60

alpha-beta dimers form protofilaments, 13 protofilaments form hollow cylinder

Question 61

What is the arrangement of intermediate filament proteins?

Answer 61

two alpha helices wrap together to form coil-coil --> two dimers form tetramer (doesn’t have an inherent polarity to it due to opposite association of dimers)

Question 62

How do actin filaments move forward?

Answer 62

polymerization causes the head to move forward ; associated with myosin for muscle contraction

Question 63

What does the Rho family of proteins do?

Answer 63

activate various actin-binding proteins for microfilament organizaton; includes Rho, Rac, and Cdc42

Question 64

What microtubule-associated (tubulin) proteins are motor proteins?

Answer 64

dynein, kinesin

Question 65

What family of cytoskeleton proteins connect epithelial cells at cell-cell junctions?

Answer 65

intermediate filaments; also found in nucleus to support nuclear envelope