Week 2-Cell structure Flashcards
What is the most charged membrane phospholipid?
phosphatidyl serine
What are the 4 major membrane phospholipids?
phosphatidyl-ethanolamine, phophatidyl-serine (both amino phospholipids)
phosphatidyl-choline, sphingomyelin (both choline phospholipids)
first 3 are all phosphoglycerides
Functions of cholesterol
stiffens membrane, reduces permeability, inhibits phase changes; head is hydrophilic and points outward
Where are glycolipids present on cell membranes?
non-cytosolic side
What is the main function of phosphatidylinositol phospholipids?
6 carbon ring can be phosphorylated/dephosphorylated differently to bind different proteins that take part in various intercellular functions
Where are phosphoglycerides made?
ER, but sphingosine synthesized in Golgi for sphingomyelin
What occurs during plasma membrane translocation to phospholipid distribution?
initially evenly distributed, choline-containing phospholipids are flipped to non-cytosolic leaflet, amino phospholipids shifted to cytosolic leaflet
What are the components of lipid rafts?
sphingolipids, cholesterol, proteins
What exactly comprises a glycocalyx? and what is its function?
It is made of membrane proteins that have sugars covalently attached; function in protection, identification, and adhesion
What are the four mechanisms to organize integral membrane proteins?
1- self-assembly into aggregates
2- tethered to extracellular molecules
3- tethered to intracellular molecules
4- bind to proteins on adjacent cells
What is the function of the rough ER?
protein synthesis of membrane bound proteins (not cytosolic proteins)
What are the functions of the smooth ER?
lipid synthesis, Ca++ regulation, detoxification
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
RER = B cells because they produce a lot of Abs SER = liver cells, detoxifying
What determines if a polyribosome is attached to an ER membrane?
polypeptide chain will possess an ER signal sequence, signaling polysome to remain attached
What determines if a polypeptide is released into the ER lumen or made into a single/multipass membrane protein?
determined by number and orientation of start/stop sequences in polypeptide chain; also determines which end is orientated toward which side
What is the directionality of vesicular transport through golgi?
products fuse with cis face, packaged and released through trans face
What are the three pathways for materials to enter the golgi?
endocytosis, phagocytosis, autophagy
How to endosomes mature before fusion with Golgi vesicles?
pump protons into lumen –> decrease pH –> activates hydrolyses –> condense and are now lysosomes
What is the signal to identify lysosomal enzymes?
phosphorylated mannose residues
What is the constitutive secretory pathway?
way for vesicles to leave golgi through direct exocytosis – lack of signal leads to this
Where does N-linked glycosylation of proteins occur and where is the sugar linked?
linked to asparagine, occurs in lumen of ER, modified in golgi
Where does O-linked glycosylation occur and where is the sugar linked?
linked to serine or threonine, occurs in golgi or outside of cell
What is the class of heavily O-linked glycosylated proteins and what are their sugar chains?
proteoglycans, made of glycosaminoglycan (GAG)
What gives the extracellular matrix its properties?
sugars on proteoglycans are sulfated, negative charge – attracts water to form hydragels
Where are misfolded proteins degraded?
misfolded proteins are ubiquinated and destroyed by proteosomes in the cytoplasm
What disease is associated with lysosomal dysfunction?
Tay-sachs
What are the three pathways out of the Golgi?
two secretory (constitutive and regulated) and one lysosomal pathway
What are caveolae and what is their purpose?
invaginations that can lead to uncoated vesicles –> vesicles can transport cargo from one side of cell to the other through transcytosis
What is characteristic of clathrin coated vesicles?
honeycomb look due to polymerization of clathrin proteins which are shapped like triskelions
What are coatamer (COP) 1 and 2 associated with?
transport back and forth between Golgi and ER
What is the main purpose of clathrin coated vesicles?
receptor mediated endocytosis; transport from Golgi to endosome/lysosome and from plasma membrane to endosome/lysosome
What removes the clathrin coat from vesicles?
ATPases (members of heat shock protein family)
What proteins functions as molecular switches and take part in COP1 and COP2 vesicle coating?
G proteins; become active and unactive through GTPases (active=GTP, inactive=GDP)
What is KEDL?
an amino acid sequence on ER proteins that allows them to be returned to ER if they end up in the Golgi
What proteins play an important role in delivery and fusion of vesicles?
Rabs, Rab effectors, SNAREs
What is the system by which SNAREs work?
the vesicle has a v-SNARE protein and the target has a corresponding t-SNARE; must recognize each other
How do Rab proteins know which membranes to bind to?
inositol phospholipids – specificity in their phosphorylation leads to recognition of membrane for Rab binding
Where do mitochondria tend to localize?
near site of high ATP utilization and along microtubules; often close connection to ER
How are proteins brought into mitochondria from cytoplasm?
through translocator complexes that recognize alpha-helical protein structure with hydrophobic residues along one side (for TOMS and TIMS)
What are TOMS and TIMS?
transporters of outer mitochondrial membrane or inner, respectively
What is OXA?
transports protein from matrix OUT of mitochondria
What inserts lipids into the mitochondrial membrane?
exchange proteins remove lipids from ER to insert into mitochondrial membranes
What are the functions of peroxisomes?
detox, beta-oxidation of some fatty acids, formation of myelin phospholipids
What is the outer edge of the nuclear matrix lined with?
lamins make up the scaffolding of the nuclear matrix; they are part of the intermediate filament family
What exactly is the nucleolus?
ribosome producing factory; contains the chromosomes that have the duplicated genes of rRNA –tons of transcription and production of rRNA
What size proteins can diffuse through nuclear pores?
5000 daltons - 60K daltons
What type of protein will most quickly be transported to the nucleus?
any protein with a nuclear localization signal (NLS)
How do proteins larger than 60kDaltons get into the nucleus?
through active transport that uses energy and receptor proteins
What are the characteristics of imported proteins (to nucleus)?
Bind import receptors in the presence of GDP, and dissociate in the presence of GTP
What are the characteristics of exported proteins (to nucleus)?
Bind export receptors in the presence of GTP, and dissociate in the presence of GDP
What controls the directionality of transport of proteins to and from the nucleus?
small G-protein called Ran
Where are Ran-GEF and Ran-GAP found?
Ran-GEF (exchange factor) - nucleus
Ran-GAP (activating protein) - cytoplasm
What is the protein microfilament and what are its functions?
actin; cell shape, division and motility, also support/organize plasma membrane
What is the microtubule protein and what are its functions?
tubulin; organize cytoplasm, intracellular transport (railroad), cell division, cilia/flagellae motility
What are the functions of intermediate filaments?
strengthen cytoplasm/tissues, support nucleus, epidermal appendages
Where are microtubules localized?
near nucleus by spanning out from their centrosome
How are actin filaments constructed/deconstructed?
remove monomers from - end and add to the + end
How are tubulin filaments constructed/deconstructed?
ossicilations of slow growth and rapid breakdown (called dynamic instability) – determined by whether the end units have hydrolyzed their GTP; occurs on + end
What regulates polymerization of intermediate filament proteins?
polymerize when unphosphorylated, depolymerize when phosphorylated; do NOT have an inherent polarity
What is the arrangement of tubulin filaments?
alpha-beta dimers form protofilaments, 13 protofilaments form hollow cylinder
What is the arrangement of intermediate filament proteins?
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)
How do actin filaments move forward?
polymerization causes the head to move forward ; associated with myosin for muscle contraction
What does the Rho family of proteins do?
activate various actin-binding proteins for microfilament organizaton; includes Rho, Rac, and Cdc42
What microtubule-associated (tubulin) proteins are motor proteins?
dynein, kinesin
What family of cytoskeleton proteins connect epithelial cells at cell-cell junctions?
intermediate filaments; also found in nucleus to support nuclear envelope
