Organelles Flashcards
Site of synthesis of secretory (exported) proteins and of N-linked oligosaccharide addition to lysosomal and other proteins
Rough Endoplasmic Recticulum (RER)
Nissl bodies (RER in neurons) synthesize peptide neurotransmitters for ___
secretion
________ unattached to any membrane site of synthesis of cytosolic peroxisomal and mitochondrial protiens
Free Ribosomes
_____ glycosylation occurs in the eNdoplasmic reticulum
N-linked
Mucus secreting goblet cells of small intestine and antibody secreting plasma cells are rich in
RER
Proteins within organelles (eg., ER, Golgi bodies, lysosomes) are formed in ___
RER
Smooth Endoplasmic Reticulum (SER)
Site of steroid synthesis and detoxification of drugs and poisons. Lacks surface ribosomes
Location of glucose-6- phosphotase (last step in both glycogenolysis and gluconeogenesis.
SER
Hepatocyctes and steroid hormone-producing cells (lipids) of the adrenal cortex and gonads (sequesters store Ca+ from the cytosol) are rich in
SER
Post Translational modifications
1) Trimming- Removal of N or C terminal propedtides from zymogen to generate mature protein (ie.,trypsinogen to trypsin 2) Covalent alterations- phosphorylation, glycosylation, hydroxylation, methylation, acetylation, and ubiquitination
Chaperone protien
Intracellular protein involved in facilitating and maintaining protein folding. In yeast, heat shock proteins (eg. HS60) are constitutively expressed, but expression may increase with high temperatures, acidic ph, and hypoxia to prevent protein denaturing/misfolding
Proteasome
Barrel-shaped protein complex that degrades ubiquitin-tagged proteins. Defects in the ubiquitin-proteasome system have been implicated in some cases of Parkinson disease
____ is distribution center for proteins and lipids from ER to vesicles and plasma membrane
Golgi
Post-translational events in GOlgi include
modifying N-oligosacchraides on asparagine adding adding O-oligosaccharides on serine and threonine and adding mannonse-6-phosphate to proteins for lysosomal and other proteins.
_____ are sorting centers for material from outside the cell or from the Golgi, sending it to lysosomes for destruction or back to the membrane/Golgi for further use.
Endosomes
The endoplasmic reticulum (ER)
The endoplasmic reticulum (ER) is a single membrane-bound organelle that branches throughout the cell’s cytoplasm and encloses a lumen. It comes in two distinct yet continuous forms: rough ER (RER) and smooth ER (SER)
All cells have RER, but cells that make a lot of secretory proteins, such as antibody-secreting plasma cells, are rich in RER, making them appear darker, or basophilic, on hematoxylin and eosin (H&E) staining
True
In neurons particularly, the RER makes up Nissl bodies and synthesizes neurotransmitters.
True
The SER is responsible for:
The SER is responsible for:
- Synthesizing steroids and steroid hormones, fatty acids, and phospholipids
- Detoxifying drugs and metabolites
- Releasing calcium ions necessary for muscle contraction
The SER is small in most eukaryotic cells, but hepatocytes have large amounts of SER because one of their main roles is detoxification. When large amounts of toxic metabolites bombard the liver, the SER can even double its surface area in response to its increased workload!
True
What are the main functions of the rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER)?
The RER’s main functions are to fold, modify, and package proteins to be sent to the Golgi apparatus for further processing. The SER’s main functions are to synthesize steroid hormones, fatty acids, and phospholipids; detoxify drugs and metabolites; and release calcium ions for muscle contraction.
On H&E stain, the Golgi apparatus appears lighter than the RER and is sometimes termed the “Golgi ghost” in cells that are secreting a lot of protein
True
On H&E stain, the Golgi apparatus appears lighter than the RER and is sometimes termed the “Golgi ghost” in cells that are secreting a lot of protein
True
Golgi can be divided into three main sections based on the orientation of the cisternae
- Cis-Golgi: the receiving dock, where protein-containing vesicles from the RER fuse with the Golgi apparatus.
- Golgi stack/medial Golgi: the main processing area, where many protein modifications, including glycosylation and sulfonation, occur.
- Trans-Golgi: the exporting dock, it packs proteins into transport vesicles and sends them off to their final destination.
What is the main function of the Golgi apparatus?
The Golgi apparatus’ main function is to modify and package proteins it receives from the RER for transport to their final destination.
If a protein contains a signal peptide, a series of hydrophobic amino acids near the beginning (N-terminus) of the elongating peptide, it can be recognized by a_____
signal recognition particle (SRP)
Translation of all cellular proteins begins in the cytosol, with the exception of the few proteins made exclusively in mitochondria.
True
A ______ is a cytosolic ribonucleoprotein that traffics translating ribosomes and their products from the cytosol to the RER membrane, much like the forklift that takes your package from the production line to the warehouse.
SRP
If an SRP is absent or dysfunctional, proteins with a signal peptide accumulate in the _______, meaning they never make their way to the RER and cannot properly function.
cytoplasm
if a DNA mutation alters the signal peptide, the newly synthesized protein will remain in the _______
cytoplasm
Anti-SRP antibodies are associated with, but not specific for, ________, an inflammatory muscle disease. The presence of anti-SRP antibodies is associated with prominent muscle weakness and atrophy in these patients.
polymyositis
Once the SRP delivers the ribosome to the ___, the ribosome docks on the ___ membrane and becomes a membrane-bound ribosome.
RER
SRP tagged membrane-bound ribosomes continue translation and feed the growing peptide chain into the _____
RER Lumen
Inclusion cell disease (I-cell disease or mucolipidosis type 2) is a lysosomal storage disease caused by a defect in ___
N-acetylglucosaminyl-1-phosphotransferase.
This _______ enzyme phosphorylates mannose residues to form mannose-6-phosphate, the tag associated with lysosomal proteins.
Golgi apparatus
In I-cell disease, lysosomal proteins do not receive this tag and are secreted from the cell. As a result, lysosomes accumulate products they are supposed to break down. This unfortunately fatal childhood condition manifests in clinical signs and symptoms such as coarse facial features, gingival hyperplasia, corneal clouding, and restricted joint movements.
M6P
Proteins destined for peroxisomes contain a peroxisomal localization sequence, usually a serine-lysine-leucine sequence.
True
What role does the signal recognition particle (SRP) play in protein trafficking?
The SRP recognizes signal sequences on peptides early in translation and transports the ribosome to the RER membrane to continue translation of the peptide into the RER lumen.
Which of the following describes the flow of proteins through the Golgi apparatus?
The correct answer is Cis-Golgi to Golgi stack totrans-Golgi. After budding off the RER, protein-containing transport vesicles fuse with the cis-Golgi face. Proteins are then modified and processed in the Golgi stack before moving onto the trans-Golgi for transport to their final destinations.
A researcher wants to create a cell line with a mutation that alters the signal recognition particle (SRP). Which of the following abnormalities will result?
The correct answer is lysosomal proteins will be found in the cytosol. The SRP is important for recognizing the signal peptide and transporting ribosomes to the RER membrane. Proteins involved in this process include lysosomal, membrane, and secretory proteins. Without the SRP, these proteins will not be translated into the RER and will instead remain in the cytosol.
What toxic byproduct is formed by peroxisomal β-oxidation of very-long-chain fatty acids?
Hydrogen peroxide (H2O2).
The major function of peroxisomes is the breakdown of very-long-chain fatty acids through β-oxidation.
True
The primary function of the proteasome is to degrade ubiquitin-tagged proteins. The proteasome acts on signaling molecules, tumor suppressors, and anti-apoptotic molecules. It was previously thought that the proteasome’s targets were only damaged or misfolded proteins, but recent evidence shows that the proteasome is important for cell cycle regulation and cell survival. In fact, inhibition of the proteasome leads to programmed cell death, or apoptosis, whereas proteasome over activation has been linked to multiple cancers.
True
What is the main difference between proteasomal and lysosomal protein degradation?
Proteasomal degradation is specific and requires ubiquitin to recognize target proteins, whereas lysosomal protein degradation is less selective.
Ubiquitin is a highly conserved eukaryotic protein that is added post-translationally to proteins destined for proteasomal degradation. The ubiquitin conjugation cascade covalently adds ubiquitin to lysine residues on target proteins
- Ubiquitin activation enzyme (E1): activates and transfers ubiquitin to carrier protein E2
- Ubiquitin conjugating enzyme (E2): presents ubiquitin to E3
- Ubiquitin ligase (E3): binds and covalently attaches ubiquitin to target protein
What enzyme covalently attaches ubiquitin to its target protein?
Ubiquitin ligase (E3).
Which of the following pathways occurs in the peroxisome?
The correct answer is very-long-chain fatty acid β-oxidation. The peroxisome contains enzymes essential for β-oxidation of very-long-chain fatty acids that are longer than 22 carbons. This occurs when the fatty acids are too large to be broken down by mitochondria.
A cytosolic cellular structure with two subunits is observed to assemble and disassemble and to bind to mRNA and to associate, at times, with endoplasmic reticulum. The most likely identity of this structure is a/an
Ribosomes are composed of two subunits and exist within the cytosol, often bound to endoplasmic reticulum (ER). They participate in protein translation from mRNA and bind to mRNA during the process.
A single membrane-enclosed organelle is observed to be in close proximity to the plasma membrane. It appears to surround newly modified proteins in membrane-enclosed structures. The most likely identity of this organelle is
The Golgi complex is a series of membrane-enclosed tubules involved in protein processing. It is localized near the plasma membrane and places newly modified proteins within the vesicles that bud off from the Golgi.
Lysosomes are produced from the ____ and peroxisomes from the _______.
Golgi, endoplasmic reticulum
A membrane-enclosed intracellular structure is observed to release a protein through a pore into the cytosol. Following this release, biochemical reactions take place and result in the cell’s death by apoptosis. The most likely identity of this intracellular structure is
Mitochondria release cytochrome c into the cytosol, initiating a cascade of biochemical events that result in apoptotic cell death.
An organelle with DNA, distinct from genomic, chromosomal DNA and ribosomes is believed to have originally been a single-celled independent organism engulfed by ancestral eukaryotic cells. This organelle is
A mitochondrion is an organelle with its own DNA that is separate from the genomic DNA of the nucleus. Mitochondria are believed to have been engulfed by ancestral eukaryotic cells.
Nuclear lamina is composed mainly of
Nuclear lamina is composed mainly of intermediate filaments. The interior of the nucleus containing the nucleoplasm is organized by the nuclear lamina, the protein scaffolding of the nucleoplasm that is composed mainly of intermediate filaments, which are cytoskeletal components.
An organelle is bounded by a single membrane and contains hydrolytic enzymes that were synthesized on free ribosomes. From which structure was this organelle derived?
The organelle described is a peroxisome, which is derived from regions of the endoplasmic reticulum, and not from regions of the Golgi complex, which form lysosomes.
Two-cell types are compared for their ability to produce ATP from glucose, and while one produces only 2 ATP per glucose, the other has an ATP yield of 32 ATP from the glucose. The most likely difference between these cells that contributes to this finding is
The presence of mitochondria within a cell enhances the amount of ATP produced per glucose. One cell type was likely to be red blood cells, which lack mitochondria and produce only 2 ATP per glucose compared with 32 ATP per glucose in cells with mitochondria. This mitochondrial-dependent process of ATP production in mitochondria is oxidative phosphorylation.
A 7-month-old girl who previously had a normal development now exhibits signs and symptoms of Tay-Sachs disease. Which of the following organelles is affected in this disorder?
Lysosomes. Tay-Sachs disease in an infant is acquired via autosomal recessive inheritance, with one mutant HEXA gene from each parent.
The child with Tay-Sachs disease, described in question 5.8, most likely acquired this disorder via
Inheritance of the same or different HEXA mutations from both her parents.
Tay-Sachs disease is a lysosomal storage disease. A mutant lysosomal hydrolase prevents the breakdown of certain macromolecules. In Tay-Sachs disease, gangliosides accumulate in the brain, causing the signs and symptoms. The other organelles listed are unaffected in Tay-Sachs disease.
A previously healthy 24-year-old male develops optic neuropathy and becomes blind. His mother’s brother has the same condition. The patient is told that while his condition is inherited, there is no chance that he will pass his mutant gene to any of his future children. What type of disorder most likely affects this patient?
Mitochondrial disease
This patient most likely has a mitochondrial disease. (He may have Leber hereditary optic neuropathy.) Mitochondrial diseases are inherited exclusively from the mother. Since sperms do not enter fertilized eggs, a male individual cannot pass on a defective mitochondrial gene to his children. This is the only type of condition that a male has no chance of passing on to any of his children.
______ genes require both parents to pass on a mutant gene in order for a child to be affected. In autosomal conditions though, an affected person would have a 50% chance of passing on a mutant gene to his children.
Autosomal recessive
Lysosomal storage diseases are often autosomal recessive.
True
Peroxisomal disorders are generally present at birth and affected individuals have a very short life expectancy.
True
Proteins that will function in the nucleus, mitochondria, or peroxisomes are synthesized on free ribosomes
_____ will remain free because the proteins lack an N-terminal signal sequence that causes a ribosome to bind to the ER.
Free ribosomes
Proteins are synthesized either on free ribosomes or on ribosomes bound to endoplasmic reticulum.
True
Ribosomes bind to endoplasmic reticulum when the proteins they are synthesizing contain an N-terminal signal sequence or leader sequence.
True
Ribosomes remain free when the proteins they are synthesizing lack a leader sequence.
True
The default pathway for proteins synthesized on bound ribosomes is to enter the lumen of the endoplasmic reticulum, then to move to the Golgi complex, and then to be secreted from the cell.
True
Proteins destined to function in lysosomes receive a mannose-6-phosphate tag in the Golgi.
True
Proteins secreted from the cell are released either in a constitutive or in a regulated manner.
True
Proteins synthesized on free ribosomes will remain in the cytosol unless they contain a tag to direct them to the nucleus, mitochondria, or peroxisomes.
True
A ribosome bound to endoplasmic reticulum is involved in translating a new protein. The final destination of that new protein may be
Lysosomal proteins are synthesized on ribosomes bound to endoplasmic reticulum.
The intended final destination of a new protein is within a peroxisome. However, the peroxisomal targeting signal is not properly incorporated into the precursor protein. The final destination of that protein will therefore be
Peroxisomal proteins are synthesized on free ribosomes, and the default pathway is to remain in the cytosol.
Lysosomal proteins are synthesized on bound ribosomes and traffic through the endoplasmic reticulum and Golgi complex.
True
Both mitochondrial and nuclear proteins are synthesized on free ribosomes. Both require tags different from peroxisomal targeting signals in order to enter into their destined organelles.
True
Secretion from the cell is the default pathway for proteins secreted on bound ribosomes.
True
A precursor protein intended to function within a lysosome fails to receive a proper lysosomal tag while it is being processed. The protein will therefore be sent to
Lysosomal proteins are synthesized on bound ribosomes, and the default pathway for them is to be secreted from the cell. If the mannose-6-phosphate lysosomal tag is not incorporated into an intended lysosomal precursor, then it will be sent outside the cell.
Which organelle is the next stop in the normal trafficking of a protein exiting the endoplasmic reticulum?
The Golgi complex is the next stop in the trafficking of a protein that is exiting the endoplasmic reticulum. Proteins within the endoplasmic reticulum are synthesized on bound ribosomes. Free ribosomes synthesize proteins in the mitochondria, nucleus, and peroxisomes. None of them enter the endoplasmic reticulum. The lysosome is the final destination for some proteins synthesized on bound ribosomes that are in the endoplasmic reticulum. After leaving the Golgi complex, lysosomal proteins are sent to the lysosome. Lysosomes are not, however, on the main trafficking route for proteins synthesized on bound ribosomes.
A 3-month-old male child has a defect that results in failure to add mannose-6-phosphate to certain proteins within the Golgi complex. This defect will result in abnormal proteins in
Mannose-6-phosphate is the tag added to lysosomal proteins.
In order to be secreted constitutively from a cell, a newly synthesized protein must contain which of the following during some point in its production and processing?
An N-terminal signal peptide will be contained within a protein that is destined to be secreted from a cell. This signal sequence directs the ribosome translating the protein to bind to the endoplasmic reticulum. From there, the nascent polypeptide will traffic through the Golgi and then to the outside of the cell.
The C-terminal tripeptide is a sequence that directs a protein to a peroxisome.
True
Clathrin is a coat protein that is found transiently on regions of Golgi membrane involved in concentrating particular types of proteins.
True
________ is a modification made to most acid hydrolase precursors, allowing their trafficking to lysosomes.
Mannose-6-phosphate
the TOM complex is the translocase of outer mitochondrial membrane complex that imports new mitochondrial proteins across the first or outer mitochondrial membrane.
True
A nascent polypeptide being translated on a ribosome bound to the endoplasmic reticulum contains the sequence Asn-X-Thr. This sequence will direct the protein to be
Nascent polypeptides that contain the consensus sequence Asn-X-Thr are glycosylated in an N-linked manner upon entry into the lumen of the ER.
4-month-old male is evaluated for muscle weakness and poor muscle tone. Physical examination reveals hepatomegaly (enlarged liver) and further testing reveals the presence of heart defects. Excess glycogen is found within cells of his muscles, heart, and liver. Deficiency of acid maltase is suspected. Based on this information, glycogen accumulation has occurred in which location in the affected cells?
A lysosomal storage disorder is described by the findings in this scenario. Acid hydrolases, including acid maltase, normally function within lysosomes to degrade excess macromolecules of particular types. In this instance, glycogen is accumulating because it is not being degraded by acid maltase. This scenario describes Pompe disease, an autosomal storage disorder. Excess of a particular macromolecule such as glycogen would not be found in any of the other intracellular locations listed because degradative enzymes are not normally localized to these organelles.
Precursors to lysosomal β-glucocerebrosidase bind to the protein LIMP-2 during their trafficking to lysosomes. It has been shown that neither LIMP-2 nor β-glucocerebrosidase is a substrate of GlcNAc-IP. Based on this information, trafficking of β-glucocerebrosidase to its functional location
Occurs independently of mannose-6-phosphate.
As described, the process is independent of mannose-6-phosphate, the usual tag on lysosomal precursor proteins. Since neither the enzyme nor its LIMP-2 binding protein are acted on by GlcNAc-IP, they will not contain mannose-6-phosphate.
A protein destined to be localized within nuclei will gain access into that organelle when its nuclear localization signal binds to which of the following molecules in order to facilitate its entry?
Proteins that gain access to the nucleus have nuclear localization signals that bind to importin, to facilitate entry into the nucleus.
Autophagy refers to
Autophagy is a process by which organelles or cytoplasmic proteins are degraded in the lysosomal compartment. This process usually proceeds through the formation of an autophagosome, which then fuses with the lysosomal membrane causing the release and degradation of the contents. Autophagy is also activated when the cell is under stress and requires raw materials such as amino acids and energy.
A protein with a short half-life
Proteins with short half-lives are usually degraded through the proteosome pathway after tagging them with ubiquitin. Proteins with N-terminus serine have a long half-life and are preferentially degraded by the lysosomes.
A proteosome is a(n)
Proteolytic complex consisting of ATPases and other enzymes to degrade proteins.
Proteosomes are barrel-like structures that are made of several protein subunits with an ability to degrade intracellular ubiquitinated proteins. This process requires ATP. It selectively degrades intracellular proteins with short half-lives, and these proteins have to be ubiquitinated. Proteosomes remove ubiquitin from the target proteins and are composed of a central core and two regulatory regions. Proteosomes are present in the cytosol of cells and are distinct from the lysosomal pathway of protein degradation.
Kinesin and dynein are families of microtubule motor proteins that facilitate intracellular transport along microtubules.
TAKEAWAY: A kinesin is a protein belonging to a class of motor proteins found in eukaryotic cells. Kinesins move along microtubule filaments and are powered by the hydrolysis of adenosine triphosphate (ATP).
COP I
COP I – This is not the correct answer. COP-I coats vesicles involved in retrograde transport from Golgi → RER.
COP-II
COP-II is the coat protein for vesicles transported in an anterograde direction from the RER → Golgi.
Spectrin
Spectrin heterodimers form tetramers that interact with actin and provide flexibility and support for the membrane.
Actin is
Actin is the protein found in thin filaments in the RBC cytoplasm. Intermediate filaments are important cytoskeletal elements with specificity that depends on the origin of the cells in question.
Southwestern blot
Southwestern blot identifies DNA-binding proteins (transcription factors) using labeled double-stranded DNA probes. These transcription factors are involved in controlling gene expression.
TAKEAWAY: Southwestern blot mapping” is a time-efficient way of identifying DNA-binding proteins and specific sites on the genomic DNA that they interact with.
Southwestern blot
Southwestern blot identifies DNA-binding proteins (transcription factors) using labeled double-stranded DNA probes. These transcription factors are involved in controlling gene expression.
TAKEAWAY: Southwestern blot mapping” is a time-efficient way of identifying DNA-binding proteins and specific sites on the genomic DNA that they interact with.
Spectrin
Spectrin heterodimers form tetramers that interact with actin and provide flexibility and support for the membrane.
Endosomes
Endosomes are sorting centers for material from outside the cell or from the Golgi, sending it to lysosomes for destruction or back to the membrane/Golgi for further use
During a laboratory experimentation involving the herpesvirus (HSV-1). Eukaryotic cells are cultured and infected with HSV-1. Observation of these cells reveal transport of the herpesvirus capsids along microtubules to the nucleus mediated by a cytoplasmic motor protein complex.
Which of the following proteins may be involved in catalyzing this retrograde transport of HSV-1 from the cellular membrane to the nucleus?
Dynein – Transport of herpesvirus capsids along microtubules to the nucleus is mediated by the cytoplasmic dynein-dynactin complex.
TAKEAWAY: A dynein is a protein belonging to a class of motor proteins found in eukaryotic cells. Dynein move along microtubule filaments and are powered by the hydrolysis of adenosine triphosphate (ATP). HZV utilizes actin and microtubules for both retrograde transports from the plasma membrane and along axons during virus entry and for anterograde transport during virus assembly and exit using dynein and kinesin-mediated transport of herpesvirus capsids along microtubules.
A 64-year-old woman visits her physician with complaints of a rash on the right side of her face. Physical examination reveals a vesicular rash following a dermatomal pattern on the patient. The physician suspects herpes zoster ophthalmicus of the CN V1 branch and diagnoses her with Shingles. The physician explains to the patient that this virus remains latent in dorsal root or trigeminal ganglia and can be triggered by stress to travel anterograde to the skin where eruptions occur as in this case.
Which of the following proteins may be involved in catalyzing this anterograde transport of this virus?
Kinesin – This is the correct answer. Kinesin-mediated transport of herpesvirus capsids is likely involved in the transport of capsid/tegument structures to sites of secondary envelopment in the TGN and in the trafficking of enveloped virus particles, contained within a vesicle, to the cell periphery causing the eruption of the patient’s vesicular rash seen in shingles.
TAKEAWAY: A kinesin is a protein belonging to a class of motor proteins found in eukaryotic cells. Kinesins move along microtubule filaments and are powered by the hydrolysis of adenosine triphosphate (ATP). HZV utilizes actin and microtubules for both retrograde transports from the plasma membrane and along axons during virus entry and for anterograde transport during virus assembly and exit using dynein and kinesin-mediated transport of herpesvirus capsids along microtubules.
Fluorescence in situ hybridization (FISH)
Fluorescence in situ hybridization (FISH) – This is the correct answer. FISH is used for specific localization of genes and direct visualization of chromosomal anomalies at specific gene loci at the molecular level. You may not have covered FISH, and you may not cover it. I would suggest learning about it as the immunofluorescent component of FISH is a technique that translates to other uses, and you might see some results at some point in medical school when they discuss immunofluorescent results in cell biology or other assays.
TAKEAWAY: FISH is often used for finding specific features in DNA for use in genetic counseling such as detection of microdeletions such as in DiGeorge syndrome. DiGeorge syndrome is typically due to the deletion of 30 to 40 genes in the middle of chromosome 22 at a location known as 22q11.
A medical student is studying the effects of chromatin structure on gene regulation. She isolates a class of proteins that when bound to DNA appear as a “bead-like” form when viewed with an electron microscope.
These proteins are most likely rich in which of the following?
Lysine and Arginine. DNA is negatively charged due to a high portion of anionic phosphate groups. Lysine and arginine are amino acids that have positively charged side groups. The positive charge of the nucleosome (“Bead- like” form; also known as beads on a string) forms ionic bonds with DNA. The linker histone H1 protein noncovalently binds to stabilize the chromatin fiber by binding to the nucleosome and linker DNA.
TAKEAWAY: DNA is negatively charged. Therefore, proteins that associate closely with DNA typically have abundant positively charged compounds. Phosphate groups are what give DNA their negative charge. Lysine and Arginine give histones the positive charge, resulting in aiding towards stabilization of the chromatin fiber by binding to the nucleosome and linker DNA.
Endosomes
are vesicles that have taken up extracellular debris by budding off the cellular membrane into the cell.
Proteasomes
play a role in protein degradation.
The _______ is a site of protein synthesis and enzymatic modifications.
The rough endoplasmic reticulum is a site of protein synthesis and enzymatic modifications.
The ________ is the site of lipid synthesis and detoxification of drugs and poisons.
The smooth endoplasmic reticulum is the site of lipid synthesis and detoxification of drugs and poisons.
The _______ is the destination of secreted proteins.
The extracellular space is the destination of secreted proteins.
________ encode enzymes involved in oligosaccharide assembly or the covalent bonding of oligosaccharides to the N-terminus of a polypeptide.
N-linked oligosaccharides
First-year medical students are studying cellular and molecular biology pertaining to various protein modalities. They observe a 3-D animation showing a ribosome bound to endoplasmic reticulum is involved in translating a new protein. Which of the following structures is the final destination of that new protein?
A lysosome – This is the correct answer. Lysosomal proteins are synthesized on ribosomes bound to endoplasmic reticulum. TAKEAWAY: Protein trafficking is the transport of proteins to their correct subcellular compartments or to the extracellular space (“secretory pathway”). Endo- and exocytosis describe vesicle budding and fusion at the plasma membrane and are by most authors not included in the term protein trafficking.
RNase H - RNase H removes the RNA primer from Okazaki fragments in _——————
mammalian cells.
(SRPs) signal Recognition Particles
