Mol cell Bio exam 2 ch 15

all slides and notes from class done

Analogy for how protein synthesis in the side of soul find their way to membrane and organelles

Mail distribution: parcels find their way through ZIP Codes and addresses

Largest to smallest membrane in compartments by percentage volume (8)

Cytosol 54%, mitochondrion 22%, ER with membrane-bound poly ribosomes 12%, nucleus 6%, golgi apparatus 3%, endosome 1%, lysosome 1%, peroxisome 1%

Three functions of the cytosol

Signaling, cytoskeleton, protein synthesis

endosome function

Sorting of endocytosed material

peroxisome function

Oxidation of toxic molecules

What does this image show?

Electron micrograph of part of a liver cell, small black granules between the compartments are aggregates of glycogen and the enzymes that control its synthesis and breakdown

Label the top two

Nucleus, lysosomes

Label the bottom three

Peroxisome, mitochondrion, rough endoplasmic reticulum

Two advantages of compartmentalization

It separates processes, e.g. lysosomes can be extremely acidic, which would be detrimental for the rest of the cytoplasm, processes are able to be concentrated

how did compartmentalization arise? (3 steps)

Endo-symbiotic theory: aerobic prokaryotic cell was phagocytosed by an anaerobic prokaryotic cell, aerobic prokaryotic cell lost surrounding membranes derived from pre-eukaryotic cell, finally you have an early aerobic eukaryotic cell containing a mitochondria with a double membrane

 three ways of transport to organelles

Transport through nuclear pores, transport across membranes, transported by vesicles

label the transport ways top to bottom

Transport through nuclear pores, transport across membranes, transported by vesicles

what determines where a molecules is transported to, some examples of what signal they can have (3)?

Certain peptides (signal sequences), import into ER, retention in lumen of ER, import into mitochondria

what do proteins have to contain to be transported?

Signal peptides

What does this image show?

 depending on the red signal peptide a protein is either translocated to the ER or to the cytosol, scientists can use this to make proteins that will enter the ER (picture to the right)

why are nuclear pores important?

Many things have to enter and exit the nucleus

Label

nuclear pores

Label

Nuclear pore complexes

label bottom 4

nuclear basket, pore complex proteins, nuclear lamina, inner nuclear membrane

Label right 3 top to bottom

Cytosolic fibrils, outer nuclear membrane, nuclear envelope

steps of proteins migrating to the nucleus (1), what do they need (2)?

need nuclear localization signal, nuclear import receptor, together this will lead to delivery from cytoplasm to nucleus

label top three (left to right)

Perspective nuclear protein (cargo), nuclear localization signal, nuclear import receptor

Label bottom three (top then bottom left then bottom right)

cytosolic fibrils, nuclear basket, gel-like meshwork of nuclear fibrils

 what drives nuclear transport

Energy by GTP hydrolysis

label steps of how GTB hydrolysis provides energy for nuclear transport (start top left, following arrows)

ran hydrolyzes it's bound GTP, ran-GDP dissociates from receptor; protein binds to receptor; ran-GTP binds to receptor; protein delivered to nucleus

How does transport across membranes happen (6 steps)

precursor protein has a signal sequence which binds to import receptors, these receptors deliver the protein to a translocation apparatus at a contact site where mitochondrion’s two membranes are close together, precursor protein snakes in a unfolded state though two protein translocators (1 in each membrane), inside the mitochondrion chaperon proteins pull protein in and prevent backsliding back through the protein translocators, once inside signal peptidase cleaves signal sequence, chaperone proteins released and protein folds and matures

chaperone proteins two functions

prevents protein from preforming its function prematurely, prevents protein from backsliding

How is a protein transported into the ER?

proteins made in the cytoplasm/ER, it binds with an ER signal sequence to a signal receptor particle (SRP), this binds to a receptor in proximity to the protein translocator, SRP is displaced which causes the protein to be imported into the ER lumen

What does this image show?

How to transport into the ER happens

What happens with soluble proteins?

Their signal sequence is cleaved

What does this image show

How transport happens with soluble proteins, the signal sequence is cleaved

How does transport happen with membrane proteins? (3 points)

hydrophobic part has to be delivered into the membrane (has a stop transfer sequence and ends with hydrophobic part in membrane), signal peptide is recognized by the protein translator facilitating the import of the peptide, not all of it is transported in since it has a part spanning of the membrane

What does this image show?

How does transport across membranes happen with membrane proteins?

two types of vesicular transport

endocytosis (from outside cell to inside) and exocytosis (buds from inside cell to outside)

Steps post endocytosis (4)

Endocytosis, early endosome (also includes vesicles from golgi apparatus), late endosome, lysosome

Steps pre-exocytosis (3)

Golgi apparatus, transport vesicles, exocytosis

what is vesicular budding driven by?

assembly of a protein coat

what does this image show?

vesicular budding

what are the components and functions of the protein coat parts (4)

cargo receptor - holds cargo molecules and connects them to adaptin
adaptin - between the cargo receptor and clarithin
clarithrin - assembles into a basketlike lattice structure that distorts the membrane and drives vesicle budding
dynamin - cuts the internally budding vesicle from the membrane

vesicular budding: label the red top row 4 going from left to right

cargo receptor, adaptin, clarithin coat, coated vesicle

vesicular budding: label the red bottom row 4 going from left to right

cargo molecules, dynamin, adaptin, naked transport vesicle

label the orange (steps of what is happening)

vesicle formation, uncoating

what is important for membrane fusion?

snares

proteins involved in exocytosis (4) + functions)

cargo protein (protein to be released after exocytosis), v-snare (on vesicle combines with T snare), receptor (holds docking protein), t-snare (in target membrane, combines with v-snare)

exocytosis: label the processes (orange) (top left to bottom right)

tethering, docking, fusion, cargo protein delivered

exocytosis: label the top 3 proteins on right (top to bottom)

Receptor, cargo protein, v-snare

exocytosis: label the lower 3 proteins on left (top to bottom)

Rab, tethering protein, t-snare

how can movement of molecules be visualized in vivo

using green fluorescent protein

2 types of secretory pathways w/ descriptions

Constitutive of secretion: without external signals
Regulated exocytosis: extra cellular stimulus is needed for release of cargo of the vesicles that are in the cytoplasm

constitutive exocytosis pathway steps from movie (9 steps)

fluorescently labeled membrane proteins synthesized in ER, dispersed through extensive membrane network of ER, move to exit sites that form in random locations in the membrane network, at each of these sites membrane proteins concentrated and packaged in transport vescicles, clusters of transport vesicles fuse to form transport intermediates, transport intermediates move along microtubule track to golgi, exit golgi moving on transport vesicles that are pulled outward on microtubules, delivered to plasma membrane, there it fuses and contents are dispersed

secretory pathways: label the red top two and then bottom (unregulated exocytosis)

newly synthesized soluble proteins for constitutive secretion, newly synthesized plasma membrane lipids, newly synthesized plasma membrane protein

secretory pathways: label the orange left to right (regulated exocytosis)

Secretary vesicles storing secretory proteins, signal transduction, extracellular signal such as hormone or neurotransmitter

endocytosis- “eating and drinking” of the cell, name and describe

pinocytosis- drinking, fluid containing smaller vesicles (<150nm)
phagocytosis- eating, larger particles (>250nm), bacteria, RBCs/defective cells

What does this image image show?

phagocytic white blood cell phagocytosing a bacterium

how does cholesterol enter cells, from where

it circulates in the bloodstream, then enters through receptor mediated endocytosis

in what form does cholesterol circulate?

cholesterol molecules are derivatized and packed inside LDL particles, they are surrounded by a protein and phospholipid layer

Steps of receptor, mediated endocytosis with cholesterol (9 steps)

protein of cholesterol recognized by LDL receptors in plasma membrane, adaptin (adaptor molecule) binds to tail of LDL receptor that protrudes into the cytosol, adaptin recruits clarithin which starts coating the membrane, assembly of the clarithin coat causes the membrane to bend inward forming a vesicle that buds off inside the cell taking with it cholesterol, once inside cell vesicle uncoats and fuses with endosome, endosomes low pH causes LDL receptors to release their cargo, (empty LDL receptors are recycled: bud off and return to membrane), endosome fuses with lysosome and LDL particles disassembled, free cholesterol is released to be used in synthesis of new membranes

endosome function

intracellular compartment that first receives all endocytosed material, has low pH

how often do LDL receptors make round trips from plasma membrane to endosome?

every 10 mins

receptor mediated endocytosis: label processes, left top to bottom

Endocytosis, uncoating, fusion with endosome

receptor mediated endocytosis: label processes, right top to bottom

return of the LDL receptors to plasma membrane, budding off of transport, vesicles, delivery of LDL to lysosome

what is the fate of endosomes (3)

recycling, degradation (in lysosome), transcytosis

function of lysosomes, how does it achieve that?

degradation, using many acid hydrolyses and a very acidic environment, H+ pump keeps acidity inside

autophagy description

cell eats itself and obsolete parts are removed

label the three processes top to bottom

phagocytosis, endocytosis, autophagy