BIO 348 Chapter 15: Intracellular Compartments and Protein Transport

endosomal network

-Endocytic vesicles turn into endosomes, which are a network of tubes and vesicles *Early endosomes (near PM) *Late endosomes (closer to nucleus) -Endosomes sort endocytosed substances (e.g. recycle receptors back to PM, or sort internalized substances for degradation in lysosomes) -Endosomes maintain a low pH (~5-6) by an ATP-driven H+ pump in endosomal membrane

mitochondria

ATP synthesis by oxidative phosphorylation

Phagocytosis

-"Cell eating"; taking in large material from outside of cells -Usually performed by specialized cells such as phagocytes -Performed by unicellular organisms such as ameba as source of food *Ingest bacteria or other protists by phagocytosis, and then digest the cells by fusion with lysosomes -In multicellular animals, only specialized cells are capable of performing phagocytosis *E.g. macrophages and dendritic cells (white blood cells) *Ingest/digest bacteria and other pathogens to control infection *Ingest/digest cell debris (worn-out red blood cells, etc.) *Form sheet-like extensions called pseudopods from PM to surround the cell to be ingested and form vesicles around them

Pinocytosis

-"cell drinking"; picking up fluid and dissolved solutes from extracellular matrix *Performed by all eukaryotic cells -All eukaryotic cells take in fluid from the extracellular matrix (and dissolved substances) -A macrophage "swallows" 25% of its volume in liquid each hour; "takes in" the entire plasma membrane surface in ~1 hr -Compensated for by exocytosis *Cell surface area and internal volume remain the same -Allows the cell to indiscriminately take in dissolved substances from outside of cell, in concentrations similar to that found outside of cell

Other coated vesicles

-Another class of coat vesicles include COP-coated vesicles (COP = Coat proteins) -COP-coated vesicles are involved in transporting molecules from ER → Golgi and in different part of Golgi *Cis → Medial → Trans → Trans-Golgi network (TGN)

Constitutive exocytic pathways

-Any protein that enter the ER and doesn't contain any other signal sequence is automatically going to get released out of the cell -At the TGN, these proteins (or membrane proteins) get packaged into vesicles, which fuse with PM, releasing their content out of cell (or to PM) -Default pathway can be used to grow PM or to release proteins that are constantly needed out of the cell (SENT OUT IMMEDIATELY)

Golgi apparatus continued

-As proteins are sent through the different cisternae in the Golgi, they get modified in a sequential manner -Each face of the Golgi contains specific enzymes to modify the proteins in the proper order to go on to the next face (or out of cell) -All of the resident proteins/enzymes need to get sent back to the appropriate location as they (accidentally) travel into the next areas *E.g. cis-Golgi resident proteins may get into vesicles destined for medial-Golgi; they will get sent back (in new vesicles) to the cis-Golgi

Clathrin-coated vesicles

-Best studied coated vesicles -Form on Golgi apparatus for outward secretory pathway and on PM for inward endocytic pathway -Coat proteins assemble on cytosolic face of PM forming clathrin coated pits -Pits form vesicles, which bud off through the action of the dynamin bound at the neck of the forming vesicle -Dynamin and other factors cause the ring to constrict and pinch off, separating the vesicle from the rest of the membrane -Clathrin forms vesicle shape, but other proteins in coat called adaptins determine which proteins ("cargo") make it into the vesicles -Different types of clathrin coated vesicles have different types of adaptins to allow specific cargo to enter (e.g. clathrin coated vesicles originating from Golgi contain adaptin 1, and from PM contain adaptin 2)

Golgi apparatus

-Composed of stacks of flattened membrane enclosed sacs called cisternae (~3-20) -Usually located near the nucleus -# and size of cisternae depends on cell type -The Golgi Apparatus has distinct faces: *Proteins enter from ER through the cis-Golgi, travel through the medial-Golgi and then exit through the trans-Golgi into a network of interconnected tubes and vesicles called the Trans-Golgi Network (TGN) *Transport from ER to Golgi and through the different cisternae occurs via vesicles

Mitochondria and chloroplasts

-Contain their own genome/ribosomes to make specific proteins, but most of their proteins are imported from cytosol -Proteins contain an N-terminal signal sequence directing them to membrane -Translocated across both inner and outer membranes by protein translocators -Enter mitochondria unfolded; get refolded by chaperone proteins inside organelle -Signal sequence is cleaved; may contain more specific signal sequence to direct to specific location inside organelle

Organelles

-Distinct membrane-bound compartments isolated from each other and the cytosol -Found only in Eukaryotic cells -Serve specific and particular metabolic functions within the cell

ER quality control continued

-ER size is determined by the amount of protein flowing through it -If the ER is too small, unfolded proteins accumulate and the ER becomes overwhelmed -Receptors in ER membrane then activate the unfolded protein response (UPR), which turns on transcription of ER resident proteins and other ER components -UPR prompts the cell to produce more ER -If cell is totally overloaded even with more and more ER produced, the UPR causes the cell to undergo apoptosis *E.g. Type-II diabetes

endocytic pathways

-Endocytosis enables cells to pick up material from the extracellular matrix Fluid Small molecules Large molecules Large particles Entire cells -Also allows for recycling of material sent to PM by exocytic pathway Lipids, proteins, etc. -Ingested material enters cell by formation of endocytic vesicles, which fuse with one another to form early endosomes. -Early endosomes mature to become late endosomes -Ultimately, endosomes fuse with vesicles containing lysosomal enzymes, maturing to become lysosomes

Vesicular Transport continued

-For proper function, each transport vesicle buds off from a specific organelle with the correct material to travel to the next organelle -The transport vesicle then fuses with the target membrane, releasing the contents of the vesicle into the target organelle (and membrane) -Example: A vesicle leaving from the Golgi to the PM must exclude Golgi-specific proteins (or lysosome, etc.) and fuse only with PM (not with lysosomal membrane, etc.) -Vesicular transport routes

vesicular transport

-Highly organized pathways between organelles of the endomembrane system -Secretory pathway: (Sends proteins/membranes to appropriate locations) ER → Golgi → PM (outside) by exocytosis; or ER → Golgi → lysosomes -Endocytic pathway: (Takes in material from out of cell for degradation) PM → endosomes → lysosomes (to degrade incoming material) -Note: " → " = transport vesicles

Target Membrane Identification

-How do vesicles know where to go and which membrane to fuse with? -Vesicles contain special membrane proteins called rab proteins, which will bind to tethering proteins on the target membrane - specifically tethers them to the right organelle -Also, vesicular membranes contain v-SNARE proteins, and target membrane contains t-SNARE proteins -Vesicles will only fuse with membrane that has matching tethering protein and t-SNARE

Protein sorting

-In order for each organelle to serve its particular function as well as grow, it must have the appropriate proteins and membrane proteins within -All proteins get made by ribosomes in the cytosol -There are different mechanisms by which specific proteins get transported to their appropriate intracellular location 1. Nuclear proteins get transported via nuclear pores 2. ER, Chloroplasts, Mitochondrial proteins are transported into the respective organelles via protein translocators located in the membranes 3.Endomembrane system

nuclear envelope is composed of two membranes studded with nuclear pores:

-Inner membrane contains chromosome-binding and lamina anchoring membrane proteins -Outer membrane contains same membrane proteins as ER (continuous)

Lysosomes

-Membranous sacs of hydrolytic enzymes -Controlled intracellular digestion of ingested extracellular material (endocytosis) and worn-out organelles -Low pH - ~5; hydrolytic enzymes (including proteases, nucleases, lipases) only functional at low pH *If lysosomal enzymes escape into cytoplasm (pH 7.2), won't be active -Lysosomal membranes contain transporters to allow products of digestion to enter cytosol (amino acids, nucleotides, etc.) -Lysosomal membranes also contain ATP-dependent H+ pump to maintain low pH -Interior of lysosome is coated heavily with sugars to protect lysosomal membrane proteins from getting degraded -Lysosomal proteins are marked with special phosphorylated sugar so that the Golgi can properly sort them

ER quality control

-Misfolded proteins are retained in the ER until they are properly folded -Chaperone proteins help misfolded proteins fold into the correct conformation -Misfolded proteins that can't properly fold get targeted for degradation (occurs in cytosol)

Protein Coat

-Most vesicles are formed by the formation of a protein coat around a membrane -Protein coat shapes the membrane into a bud, allowing it to eventually separate from the rest of the membrane to form a vesicle -Protein coat also allows for specific uptake of target molecules into the vesicles -Coated vesicles lose their coat before fusing with target membrane, and coat proteins get recycled

Nuclear transport continued

-Newly-made proteins containing nuclear localization signal bind to cytosolic nuclear import receptor proteins -nuclear import receptors direct nuclear proteins to pore complex and bind to fibrils extending from rim of nuclear pore -nuclear import receptors then pull nuclear proteins through pore and into nucleus, and get sent back into cytoplasm -requires energy - GTP hydrolysis -Proteins/ribosomal subunits get sent through pore fully folded

Proteins entering ER continued

-Proteins entering ER are sent there while they are being made -A ribosome synthesizing a protein destined for the endomembrane system will get sent to the surface of the endoplasmic reticulum creating Rough ER -Two populations of ribosomes -Membrane-bound ribosomes on surface of ER making proteins destined for endomembrane system/export -Free ribosomes in cytosol making all other proteins -Two types of ribosomes are identical except for the types of proteins they're making at that moment

Entry to ER

-Proteins entering ER may get sent to a variety of locations within the endomembrane system depending on specific localization signals -ER, Golgi, lysosomes, PM -Two types of proteins may enter ER: 1. Water soluble proteins fully enter lumen (interior) of ER to be sent out of cell or to lumen of other organelles 2. Membrane proteins partially enter lumen and are immediately embedded into ER membrane, to be sent to their final destination in endomembrane system

Nuclear pores direct traffic in and out of nucleus

-Ribosomal subunits and mature mRNA leave through nuclear pores -Proteins containing nuclear localization signals enter through nuclear pores

Secretory pathway

-Sends proteins/membranes to appropriate locations ER → Golgi → PM (outside) by exocytosis; or ER → Golgi → lysosomes

regulated exocytotic pathways

-Several cells produce secretory proteins that may be needed for specific functions (e.g. pancreatic cells producing insulin) -These proteins need to be delivered out of cell only when signaled -These proteins travel through the secretory pathway accumulate in secretory vesicles on the inner surface of the PM -When the appropriate extracellular signal comes (e.g. increase blood sugar levels), the vesicles fuse with PM releasing the secreted proteins into extracellular matrix (e.g. releasing insulin into blood stream to reduce blood sugar levels) (CONTROLLED, NOT ALL THE TIME)

Entry to ER continued...

-Signal sequence stays in translocation channel and get cleaved once protein is finished getting into ER, releasing the newly made protein into ER lumen -hydrophobic, allows it to be embedded in the hydrophobic region

Glycosylation

-Sugar chains (oligosaccharides) containing identical 14 branching sugars are attached onto specific asparagine (asn) a.a. residues on the growing polypeptide chain as it enters ER -Glycosylation occurs enzymatically by transferring pre-formed oligosaccharides from special glycolipid, dolichol phosphate onto Asn residues -Glycoslation begins in ER, but finishing touches, etc. are done in the Golgi -In ER, all oligosaccharides start off identical, in Golgi, monosaccharide subunits are changed, added and modified so that each protein has a specific oligosaccharide for its function (become specific and unique when brought here) -Oligosaccharides function in various ways: Protect proteins from degradation Retain protein in ER until properly folded Transport signal to get into appropriate organelle Cell-cell recognition, signaling and much, much more

Endocytic pathway

-Takes in material from out of cell for degradation PM → endosomes → lysosomes (to degrade incoming material)

Conclusions

-Vesicles are small structures within a cell consisting of a lipid bilayer and is involved in protein transport. -Certain types of protein transport to destinations such as the nucleus, ER, and mitochondria require signal sequences . -The Golgi is a series of flattened sacs that sorts and packages proteins. *Has a cis face on the ER side, trans face opposite the ER **The trans face secretes cargo into vesicles than fuses with the cell membrane for release. -The ER serves many general functions including the folding of proteins and the transport of proteins. -There are several vesicular transport pathways including various forms of endocytosis (cargo getting into the cell), phagocytosis, pinocytosis and exocytosis (cargo leaving the cell) via the secretory pathway. -Lysosomes contain hydrolases, that function at a more acidic pH, that help digest proteins and other molecules for degradation.

Secretory pathways

-Vesicular trafficking directs soluble proteins and membrane proteins from the ER through the secretory pathway: -ER→cis-Golgi→medial-Golgi→trans-Golgi→TGN→final destination (PM, lysosome, endosome, etc. -Transport through the secretory pathway is mediated by transport vesicles -As proteins enter ER and travel through the secretory pathway, they become modified and matured in various ways -Nucleus will only accept fully folded organelles

Entry to ER continued

-When a protein destined for ER is synthesize, the signal sequence is the first part to get made -A signal recognition particle (SRP) will then bind to signal sequence as soon as it comes out of ribosome (slowing down protein synthesis) -SRP transports the ribosome to ER membrane and binds to SRP receptor in membrane -SRP is then released, protein synthesis continues such that newly synthesized polypeptide chains snakes through Translocation channel in ER membrane (ER=unfolded)

evolution of the endomembrane system

-anaerobic archaeon to anaerobic eukaryotic cell -nuclear membrane, ER, nucleus

ER, Chloroplasts, Mitochondrial proteins are transported into the respective organelles via

-protein translocators located in the membranes -Proteins unfold to snake across the membrane

receptor-mediated endocytosis

-selectively taking in specific molecules from extracellular matrix -Allows cell to selectively take in specific molecules from extracellular matrix -Can increase the efficiency of internalization of particular substances by >1000 -fold compared to ordinary pinocytosis -Specific molecules bind to receptors in clathrin-coated pits on PM -Once enough molecules have bound to receptors, it triggers the clathrin coat to form vesicles, which pinch off from the PM

Membrane Fusion

-t-SNAREs and v-SNAREs not only determine specificity of vesicular trafficking, they also cause membrane fusion -When in close proximity (after rab protein and tethering protein interact), t- and v-SNARES form a coiled-coil motif, bringing the two membranes super close together, allowing membrane fusion to occur

Signal Sequences

-typically stretches of specific a.a. that range from 4-60 a.a. long -Often removed from finished protein after transport is complete -necessary and sufficient to direct protein transport to a specific organelle

Match

1) mitochondrion : provides cell with energy 2) lysosome: sac of digestive enzymes that degrades worn-out organelles 3) endoplasmic reticulum: synthesizing molecules 4) peroxisome contains enzymes that break down lipids 5) Golgi apparatus: receives proteins & lipids from the ER & dispatches 6) endosome sorts ingested molecules & recycles some back to the plasma membrane

Put the following steps used to transport proteins into mitochondria into the proper order.

1. Mitochondrial protein is synthesized in the cytosol 2. the receptor on the mitochondrial membrane binds the signal sequence on the protein 3. the protein delivered to the translocation apparatus on the mitochondria 4. the protein is passed through the translocation apparatus 5. the signal sequence is removed by signal peptidase and the protein folds into its final

Proteins allowed to enter ER

1. Water soluble proteins fully enter lumen (interior) of ER to be sent out of cell or to lumen of other organelles 2. Membrane proteins partially enter lumen and are immediately embedded into ER membrane, to be sent to their final destination in endomembrane system

Proper folding

: the ER contains chaperone proteins to ensure that proteins fold into proper conformation

Which is true of ribosomes? Choose one: Polyribosomes translate only those proteins that have an ER signal sequence. A special class of ribosomes attached to the ER membrane translates the proteins destined for that organelle. All ribosomes are attached to the ER when they begin synthesizing a protein. A common pool of ribosomes is used to synthesize both cytosolic proteins and proteins destined for the ER. Polyribosomes translate only cytosolic proteins.

A common pool of ribosomes is used to synthesize both cytosolic proteins and proteins destined for the ER

What happens to proteins with no signal sequence that are made in the cytosol? A. They remain in the cytosol. B. They are taken up by lysosomes. C. They are secreted. D. They are degraded by proteases. E. They are returned to their organelle of origin.

A. They remain in the cytosol.

Scientists have modified a clathrin molecule so that it still assembles but forms an open-ended lattice instead of a closed spherical cage. How would this clathrin molecule affect endocytosis in cells? Choose one: A. Vesicles cannot form properly without a clathrin cage, thus inhibiting endocytosis. B. All movement of molecules into and out of the cell would cease. C. Endocytosis would be unaffected, since adaptors and receptors can still interact. D. Vesicles would be larger, increasing the cargo endocytosed.

A. Vesicles cannot form properly without a clathrin cage, thus inhibiting endocytosis.

The movement of materials from the plasma membrane, through endosomes, and then to lysosomes describes which type of pathway? Choose one: A. endocytic pathway B. secretory pathway C. endolytic pathway D. endosomal pathway E. exocytic pathway

A. endocytic pathway

Which of the following components of receptor-mediated endocytosis of LDL is incorrectly matched with its function? Choose one: A. lysosome: releases LDL from the receptor B. clathrin: forms the coated vesicle C. LDL receptors: form bridges between the LDL particle and adaptin D. adaptin: binds to the specific receptors and recruits clathrin

A. lysosome: releases LDL from the receptor

Which of these organelles are surrounded by a double membrane? Choose one or more: A. nucleus B. chloroplast C. lysosome D. Golgi apparatus E. mitochondrion F. peroxisome

A. nucleus B. chloroplast E. mitochondrion

Which of the following correctly describe steps required for protein transport into the rough ER? Choose one or more: A. passing of the protein to a protein translocation channel in the ER membrane B. recognition and binding of the protein signal sequence by SRP C. initial transfer of the signal sequence to the inside of the rough ER D. cleavage of the signal sequence from the protein by signal peptidase

A. passing of the protein to a protein translocation channel in the ER membrane B. recognition and binding of the protein signal sequence by SRP D.cleavage of the signal sequence from the protein by signal peptidase

Which of the following is a role of the oligosaccharides on glycosylated proteins? Choose one or more: A. promoting cell-cell recognition B. forming part of the cell's glycocalyx, or carbohydrate layer C. acting as a signal sequence for proteins destined to remain in the cytosol D. protecting the protein from degradation and holding it in the ER until it is properly folded E. serving as a transport signal for packaging the protein into appropriate transport vesicles F. providing a source of energy for the cell

A. promoting cell-cell recognition B. forming part of the cell's glycocalyx, or carbohydrate layer D. protecting the protein from degradation and holding it in the ER until it is properly folded E. serving as a transport signal for packaging the protein into appropriate transport vesicles

Chloroplasts (in plant cells)

ATP synthesis and carbon fixation by photosynthesis

Which of the following is true of lysosomes? Choose one: Lysosomes contain around 40 types of hydrolytic enzymes, which are optimally active at pH 7.2. Most of the lysosomal membrane proteins have glycosylated regions on the cytosolic side of the membrane. An ATP-driven H+ pump in the lysosomal membrane maintains the organelle's pH. Lysosomes have a pH that is higher than that of the cytosol. The products of digestion in lysosomes leave the lysosome by transport vesicles.

An ATP-driven H+ pump in the lysosomal membrane maintains the organelle's pH.

Many viruses enter cells through receptor-mediated endocytosis. Which of the following strategies could be affective in blocking entry of this class of viruses into cells and could be used to treat viral infections? Choose one or more: A. Increase the activity of clathrin. B. Block the receptor with an antibody. C. Block the function of adaptin. D. Block the actin filaments.

B. Block the receptor with an antibody. C. Block the function of adaptin.

How do the interiors of the ER, Golgi apparatus, endosomes, and lysosomes communicate with each other? Choose one: A. by fusing with one another B. by small vesicles that bud off of one organelle and fuse with another C. They do not communicate with one another. D. by open pores that allow ions to exit and enter the organelles E. by excreting hormones and other small signaling molecules

B. by small vesicles that bud off of one organelle and fuse with another

As a polypeptide is being translocated across the membrane of the endoplasmic reticulum, a stop-transfer sequence can halt the process. What eventually becomes of this stop-transfer sequence? A. It is translocated into the lumen of the endoplasmic reticulum. B. It is cleaved from the protein. C. It forms an α-helical membrane-spanning segment of the protein. D. It stops protein synthesis and causes the ribosome to be released back to the cytosol. E. It remains in the cytosol.

C. It forms an α-helical membrane-spanning segment of the protein.

Phagocytosis is a process by which cells do which of the following? A. digest their own worn-out organelles B. ingest extracellular fluid and macromolecules C. consume large particles, such as microbes and cell debris D. engage in receptor-mediated endocytosis E. secrete hormones and neurotransmitters

C. consume large particles, such as microbes and cell debris

Fully folded proteins can be transported into which of the following organelles? A. chloroplasts B. endoplasmic reticulum C. nucleus D. mitochondrion

C. nucleus

Match the following structures used in receptor-mediated endocytosis with their functions.

Cargo Molecules packaged into vesicle for transport Receptor Captures the correct cargo molecules Adaptin Mediates contact between the receptor and another component Clathrin Shapes the forming vesicle

Which best describes a pathway that a protein might follow from synthesis to secretion? Choose one: Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane ER → Golgi apparatus → secretory vesicle → plasma membrane ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane Cytosol → ER → secretory vesicle → plasma membrane Cytosol → ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane

Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane

Which best describes a pathway that a protein might follow from synthesis to secretion? A. ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane B. ER → Golgi apparatus → secretory vesicle → plasma membrane C. Cytosol → ER → secretory vesicle → plasma membrane D. Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane E. Cytosol → ER → Golgi apparatus → transport vesicle → endosome → secretory vesicle → plasma membrane

D. Cytosol → ER → transport vesicle → Golgi apparatus → transport vesicle → plasma membrane

ATP is important for chaperone protein function. Why would protein import into mitochondria be disrupted if ATP were depleted from inside mitochondria? Choose one: A. The translocation apparatus would be unable to function without ATP hydrolysis. B. The signal sequence would not be recognized on the mitochondrial protein. C. The protein would be blocked from entering the translocation apparatus. D. The protein could slip back out of the mitochondria during transport.

D. The protein could slip back out of the mitochondria during transport.

The outer membrane of the nucleus is continuous with the membrane of which other organelle? Choose one: A. endosome B. Golgi apparatus C. mitochondrion D. endoplasmic reticulum E. peroxisome

D. endoplasmic reticulum

In the unfolded protein response, the accumulation of misfolded proteins in the ER serves as a signal for the cell to do which of the following? A. send the misfolded proteins to the Golgi apparatus for modification and folding B. glycosylate the misfolded protein C. destroy the misfolded proteins D. produce more ER E. export the misfolded proteins to the cytosol

D. produce more ER

In which process do Rab proteins function? Choose one: A. vesicle docking B. cargo protein delivery C. vesicle fusion D. vesicle tethering

D. vesicle tethering

Investigators have engineered a gene that encodes a protein bearing an ER signal sequence followed by a nuclear localization signal. What would be the likely fate of that protein? A. The protein will be recognized by a nuclear import receptor and escorted into the nucleus. B. Because of its conflicting signals, the protein will be sent to a lysosome for destruction. C. Because of its conflicting signals, the protein will remain in the cytosol. D. Because of its conflicting signals, the protein will be degraded in the cytosol. E. The protein will be recognized by an SRP and enter the ER.

E. The protein will be recognized by an SRP and enter the ER.

Lysosomal enzymes are directed to lysosomes by which of the following? A. their ability to fold properly and function at high pH B. an N-terminal signal sequence C. a C-terminal hydrophobic membrane-spanning amino acid sequence D. their ability to fold properly and function at low pH E. a phosphorylated sugar group

E. a phosphorylated sugar group

How do the interiors of the ER, Golgi apparatus, endosomes, and lysosomes communicate with each other? A. by open pores that allow ions to exit and enter the organelles B. by excreting hormones and other small signaling molecules C. by fusing with one another D. They do not communicate with one another. E. by small vesicles that bud off of one organelle and fuse with another

E. by small vesicles that bud off of one organelle and fuse with another

Most mitochondrial and chloroplast proteins are made within which part of the cell? A. Golgi apparatus B. mitochondrion or chloroplast itself C. endoplasmic reticulum D. peroxisome E. cytosol

E. cytosol

Endocrine cells that synthesize lipid hormones, such as steroids, contain extensive amounts of which of the following? A. nucleus B. Golgi apparatus C. rough ER D. cytosol E. smooth ER

E. smooth ER

Proteins destined for the Golgi apparatus, endosomes, lysosomes, and even the cell surface must pass through which organelle? Choose one: peroxisome nucleus ER mitochondrion

ER

Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell? Choose one: Golgi apparatus endosome mitochondrion nucleus peroxisome

Golgi apparatus

The ER signal sequence on a growing polypeptide chain is recognized by a signal-recognition particle (SRP) in the cytosol. What does this interaction accomplish? Choose one: It guides the ribosome and its polypeptide to the ER. It speeds the synthesis of the polypeptide chain. It releases the polypeptide chain from the ribosome. It returns the ribosome to the pool of free ribosomes in the cytosol. It cleaves the ER signal sequence from the polypeptide chain.

It guides the ribosome and its polypeptide to the ER.

Which is true of the constitutive exocytosis pathway? Choose one: It replaces the regulated exocytosis pathway in cells specialized for secretion. It operates continually in all eukaryotic cells. It packages proteins that form aggregates in the conditions present in the trans Golgi. It packages proteins that carry a signal sequence that marks them for secretion. It packages proteins in secretory vesicles that accumulate near the plasma membrane.

It operates continually in all eukaryotic cells.

If a signal sequence is removed from an ER protein, what happens to the altered protein? It can enter any organelle other than the ER. It remains in the cytosol. It is escorted to the ER by chaperone proteins. It is immediately degraded. It is unable to exit the ER.

It remains in the cytosol.

What would happen to a protein that is engineered to contain both a nuclear localization signal and a nuclear export signal? Choose one: It would spend most of its time in the cytosol. It would spend most of its time in the nucleus. It would shuttle in and out of the nucleus. It would be unable to fold properly and would be targeted for destruction. It would bind to nuclear import receptors and nuclear export receptors, forming a nonfunctional complex.

It would shuttle in and out of the nucleus.

Which of these organelles are surrounded by a double membrane? Choose one or more: A. peroxisome B. mitochondrion C. lysosome D. nucleus E. Golgi apparatus F. chloroplast

Mitochondrion nucleus chloroplast

A certain membrane protein is found on the ER membrane with the N-terminus on the ER side of the membrane and the C-terminus on the cytosol side of the membrane. The protein contains three transmembrane domains. What would be the orientation of the protein across the ER membrane if the gene were mutated such that the third transmembrane domain coded for hydrophilic amino acids? Choose one: Orientation A Orientation B Orientation C Orientation D

Orientation B **look at image**

endomembrane system

Proteins (and membranes) entering the ER may be sorted and transported via transport vesicles to other organelles within the endomembrane system

Which proteins play a central role in the fusion of a vesicle with a target membrane? Choose one: SNAREs Rab proteins clathrin tethering proteins adaptin

SNAREs

cleavage

Some proteins need to be cleaved by proteases to become activated

Relocated signal sequence

The proteins switch places but the signal sequence remains in the same area

What distinguishes proteins destined for regulated secretion? Choose one: They have a series of amino acids that act as a tag that marks them for packaging into secretory vesicles. They are cleaved from membrane domains in the Golgi apparatus prior to being packed into secretory vesicles. They are produced in small amounts and then concentrated in secretory vesicles. Their surface properties allow them to form aggregates that are packaged into secretory vesicles. They bind to clathrin in order to interact directly with the proteins to be packed into secretory vesicles.

Their surface properties allow them to form aggregates that are packaged into secretory vesicles.

What enables proteins destined for nuclear import to pass through the nuclear pore? Choose one: Their nuclear localization signal interacts with the cytosolic fibrils that extend from the pore. Their nuclear localization signal interacts with the unstructured meshwork of proteins lining the pore. They promote the hydrolysis of GTP, which provides the energy needed for their transport. They are recognized by receptors that interact with repeated amino acid sequences in proteins lining the nuclear pore. They are unfolded to allow them to snake through the meshlike network of proteins lining the nuclear pore.

They are recognized by receptors that interact with repeated amino acid sequences in proteins lining the nuclear pore.

How are proteins destined to function in the ER retained there? Choose one: They contain a C-terminal ER retention signal. They are embedded in the ER membrane by a transmembrane α helix. They are anchored to dolichol in the ER membrane. They bind to chaperones within the ER. They retain their N-terminal ER signal sequence.

They contain a C-terminal ER retention signal.

Nuclear pores are composed of

a complex of about 30 different proteins

Lysosomal enzymes are directed to lysosomes by which of the following? Choose one: an N-terminal signal sequence a C-terminal hydrophobic membrane-spanning amino acid sequence their ability to fold properly and function at low pH their ability to fold properly and function at high pH a phosphorylated sugar group

a phosphorylated sugar group

I-cell disease

absent enzyme marker in Golgi apparatus (mannose 6-phosphate); empty lysosomes

chaperone protein

advise and make sure protein folds

Vesicle budding is driven by which of the following? Choose one: hydrolysis of ATP by dynamins assembly of a protein coat interactions of v- and t-SNAREs capture of Rabs by tethering proteins binding of a cargo molecule

assembly of a protein coat

Which mechanism is used for degrading obsolete parts of a cell, such as a defective mitochondrion? Choose one: apoptosis exocytosis autophagy pinocytosis phagocytosis

autophagy

Oligosaccharide chains added in the ER can undergo further modification in which organelle(s)? Choose one: lysosomes only the trans Golgi network both the cis and trans Golgi networks endosomes only the cis Golgi network

both the cis and trans Golgi networks

The low pH inside endosomes leads to what outcome? Choose one: causing all cargo proteins to bind to their receptors destroying most internalized receptors destroying all internalized cargo proteins causing many internalized receptors to release their cargo

causing many internalized receptors to release their cargo

Which type of protein binds to improperly folded or improperly assembled proteins in the ER, holding them there until proper folding occurs? Choose one: ER retention signals antibodies tethering proteins chaperones oligosaccharyl transferase

chaperones

What protein can assemble into a basketlike network that gives budding vesicles their shape? adaptin clathrin Rab protein dynamin SNARE

clathrin

Phagocytosis is a process by which cells do which of the following? Choose one: consume large particles, such as microbes and cell debris secrete hormones and neurotransmitters ingest extracellular fluid and macromolecules digest their own worn-out organelles engage in receptor-mediated endocytosis

consume large particles, such as microbes and cell debris

nucleus

contains main genome; DNA and RNA synthesis

Cytosol

contains many metabolic pathways; protein synthesis; the cytoskeleton

Exocytosis vs endocytosis

endocytosis takes IN molecules, exocytosis puts OUT molecules.

Which organelle is the major site of new membrane synthesis in a cell? Choose one: peroxisome endoplasmic reticulum Golgi apparatus nucleus mitochondrion

endoplasmic reticulum

Proteins have to be unfolded to cross the membranes of which of these organelles? Choose one or more: endoplasmic reticulum nucleus mitochondria chloroplasts

endoplasmic reticulum mitochondria chloroplasts

Which cellular compartment acts as the main sorting station for extracellular cargo molecules taken up by endocytosis? Choose one: clathrin-coated vesicles Golgi apparatus transport vesicles lysosomes endosomes

endosomes

disulfide bridge formation

enzymes in the secretory pathway oxidize cysteine residues to form disulfide bridges

endosymbiosis

evolution of mitochondria and chloroplasts

Nucleus is

folded

Mycobacterium tuberculosis, the microbe responsible for tuberculosis, can avoid being killed by macrophages by inhibiting what process? Choose one: formation of phagosomes receptor-mediated endocytosis antibody production growth of pseudopods fusion of phagosomes with lysosomes

fusion of phagosomes with lysosomes

Exocytosis

how the proteins are released: vesicle carrying, docking, fusion

lysosomes

intracellular degradation

Which organelle is essentially a small sac of digestive enzymes that functions in degrading worn-out organelles, as well as macromolecules and particles taken into the cell by endocytosis? Choose one: nucleus lysosome peroxisome Golgi apparatus endosome

lysosome

Golgi apparatus

modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle

Aqueous pores allows

nonselective transport of small, water soluble molecules, and VERY selective transport of larger proteins, mRNA, etc.

Nuclear proteins get transported via

nuclear pores -Membrane proteins creating the pores can selectively let nuclear proteins which contain a special signal a.a. nuclear localization sequence

Proteins enter which organelle through pores in its membrane? Choose one: mitochondria ER nucleus lysosome peroxisome

nucleus

Peroxisomes

oxidative breakdown of toxic molecules

Which organelle contains enzymes used in a variety of oxidative reactions that break down lipids and destroy toxic molecules? Choose one: lysosome peroxisome endoplasmic reticulum endosome mitochondrion

peroxisome

Main types of endocytosis

phagocytosis, pinocytosis, receptor-mediated endocytosis

Protein modifications in the secretory pathway

proper folding glycosylation disulfide bridge formation cleavage chaperone protein

endosomes

sorting of endocytosed material

Endoplasmic Reticulum (ER)

synthesis of most lipids; synthesis of proteins for distribution to many organelles and to the plasma membrane

Glycosylation

the addition of oligosaccharide chains onto proteins; start in ER, modified/matured in the Golgi

Which membrane-enclosed organelles most likely evolved in a similar manner? Choose one: chloroplasts and peroxisomes the nucleus and the ER mitochondria and the Golgi apparatus mitochondria and the nucleus mitochondria and the ER

the nucleus and the ER

mitochondria and chloroplasts are

unfolded