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85 Cards in this Set
- Front
- Back
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What are 4 benefits of post-translational modifications? |
1) Controls protein activation 2) Guides protein transport 3) Alters protein-protein or protein-DNA interactions 4) Targets proteins for degradation |
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Many hormones are synthesized as one large protein and cleaved into what? |
Separate smaller peptides |
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Describe the cleavage and removal of amino acid residues in the protein |
-Start methionine -Removal of signal sequence -Removal of sequence to form "active" protein |
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What are Zymogens? |
Inactive proteins needing processed to become active |
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What are protein kinases? |
Enzymes responsible for adding a phosphate group to a protein. |
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What are Phosphatases? |
Enzymes responsible for removing phosphate groups |
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How does phosphorylation work? |
Works as an on/off switch |
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What residues can be phosphorylated? |
Serine, Threonine, tyrosine, aspartate, histidine and lysine |
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What is Glycosylation? |
The addition of oligosaccharides to proteins via a glycosidic bond to the hydroxyl (O-linked) or amino group (N-linked) of a amino acid side chain |
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Where does Glycosylation occur? |
In the ER and Golgi |
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Describe methylation and Acetylation |
Addition and removal of methyl and acetyl groups at specific lysine and arginine residues control gene expression. |
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What is Myristoylation? |
-(C14) is added to the N-terminus at a glycine residue -Requires cleavage of start methionine -Results in protein association with intracellular vesicles |
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What is Palmitoylation and Prenylation? |
-Addition of a lipid on a cysteine side chain. -Palmitoyl groups (C16) anchor proteins to the cell surface -Farnesyl (C15) and geranylgerany (C20) are found on the cell surface proteins used in regulation (cell signaling) |
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What are 3 types of Fatty Acid/Lipid addition? |
1) Myristoylation 2) Palmitoylation 3) Prenylation |
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What is hydroxylation? |
-The addition of a hydroxyl group to an amino acid -Proline and lysine residues are hydroxylated on the α-chains of collagen |
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What is carboxylation? |
-Carboxyl groups are added to glutamate residues by a vitamin K-dependent carboxylation -Important for blood clotting factors |
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What is Ubiquitination? |
The addition of the small polypeptide ubiquitin to a protein via a lysine residue to target proteins for degradation in the proteasome |
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What are the 3 steps of protein sorting? |
1) Transport through nuclear pores 2) Transport across membranes 3) Transport by vesicles |
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Where are all proteins made? |
In the cytosol (except proteins synthesized from mitochondrial DNA |
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What is protein sorting/trafficking? |
The transport of the proteins to various compartments of the cell |
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What directs the protein transport? |
The amino acid sequence of the protein directs its transport |
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What are 3 modes of protein sorting? |
1) Gated transport 2) Transmembrane transport 3) Vesicle transport |
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What is gated transport? |
The nuclear pore complex facilitates protein transport from cytosol to nucleus |
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What is transmembrane transport? |
-Membrane-bound protein translocators that directly transport specific proteins across the membrane -Proteins are usually unfolded to undergo this transport |
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What is vesicle transport? |
Membrane enclosed transport intermediates pinch off from the other membrane-enclosed compartments |
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What are 2 things that contribute to signal sequences? |
1) Signal patches 2) Sorting receptors |
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What is a signal sequence? |
-A short (15-60 amino acids) sequence in the protein that is used to direct proteins to the correct compartment of the cell. -The sequence can be cleaved from the protein once transport has occured |
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What are signal patches? |
-3-D arrangement of amino acids on the proteins surface that forms after the protein is folded. -Can be used for gated transport |
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What do sorting receptors do? |
Recognize corresponding signal sequences or patches and guide the protein to the correct location |
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Hydrophobic signal sequences are important for what function? |
Import into the ER |
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Positively charged signal sequences are important for what function? |
Import into the nucleus |
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What are some proteins that are transported into the nucleus? |
Histones, transcription factors and polymerases |
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The transport of proteins in/out of the nucleus utilize what? |
Nuclear pore |
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What is the Nuclear Pore Complex? |
-Large complex of over 50 proteins (nucleoporins) arranged in an octagonal shape -Transport requires energy (GTP) |
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What is a Nuclear Localization Signal (NLS)? |
Signal sequence or signal patch that is rich is positively charged amino acids |
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What are nuclear import receptors? |
Soluble cytosolic proteins that bind the NLS as well as nucleoporins |
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Describe mitochondria |
-Mitochondria are double-membrane bound organelles -Not all mitochondrial proteins are encoded by mitochondrial DNA, many proteins need to be transported from the cytosol |
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How are proteins transported to (and into) the mitochondria? |
-Proteins are transported into the cytosol after they have completed translation. -The proteins remain unfolded until transported by the help of chaperone proteins. |
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What are 3 mitochondrial translocators? |
1) TOM complex 2) TIM complex 3) OXA |
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What is the TOM Complex? |
Translocase for the outer membrane |
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What is the TIM Complex? |
Translocases for the inner membrane (TIM23 and TIM22) |
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What is OXA a translocase for? |
Translocase for inner membrane |
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What powers the transport of proteins through the mitochondrial membranes? |
ATP and the H+ gradient in the mitochondria |
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What is the role of ER during the transportation of proteins? |
-Translocation into the ER is a co-translational process, it occurs while the protein is being synthesized -The ER has an important role in posttranslational modification |
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What proteins are transported into the ER? |
-Transmembrane proteins -Proteins found in the lumen of the ER or other membrane-bound organelles -Excreted proteins |
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What are free ribosomes? |
-Ribosomes that remain in the cytoplasm -Synthesize proteins used in the cytoplasm |
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What are membrane-bound ribosomes? |
Ribosomes that start in the cytoplasm and are recruited to the surface of the ER during translation |
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What is the ER signal sequence? |
Contains a section of hydrophobic/nonpolar amino acids |
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What are signal-recognition particles (SRPs)? |
Bind the ER signal sequence, temporally stalls translation |
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What is the signal-recognition particle receptor (SRP-receptor)? |
-An integral membrane receptor on the cytosol side of the ER membrane -Bring SRP-ribosomes to the surface of the ER |
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What is the Sec61 complex? |
-ER protein translocator -Donut-shaped -Contains binding site for the ER signal sequence |
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Where are Polysomes found? |
-Found on the ER surface -As ribosomes bind to the mRNA and create a polysome, they are also recruited to the ER translocator |
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What are the steps of translation of ER or secreted (soluble) proteins? |
-As the protein is translated the polypeptide chain is threaded through the translocator and is bound by chaperone proteins -The signal sequence is bound to the translocator and is cleaved by the signal peptidase -After translation is complete the protein is folded in the lumen of the ER by chaperone proteins -These proteins are utilized in the ER lumen, other membrane-bound organelle or secreted from the cell |
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Describe creating transmembrane proteins |
-Similar to translating a soluble protein on the ER except with the addition of the Hydrophobic stop sequence -The hydrophobic stop sequence is transferred laterally in the membrane from the translocator |
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What is the job of Chaperone proteins? |
To aid in the folding of proteins as they are translated |
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What happens when proteins are misfolded? |
They are degraded in the cytosol |
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What happens when proteins are misfolded in the ER? |
-They must be transported to the cytosol for degradation -Glycosylation is the trigger for all export od the ER, this prevents new proteins in the process of folding to be marked as "misfolded" -Once in the cytosol the proteins are ubiquitinated and marked for degradation |
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What is a cellular response to the accumulation of unfolded proteins in the ER? |
Unfolded protein response |
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How does the unfolded protein response work? |
-Activates transcription factors that increase the transcription of genes for chaperone proteins -The chaperone proteins contain ER signal sequences and will be transported into the ER to help protein folding -The increase in ER chaperone proteins may not resolve problem and cell will undergo programmed cell death (apoptosis) |
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Where does Glycoslyation occur? |
In the ER and golgi |
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What happens to most proteins made in the ER? |
The are glycosylated -N-glycosylation is more common than O-glycosylation |
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The precursor oligosaccharide is synthesized in the ER and attached to what? |
The lipid, dolicol |
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Oligosaccharyl transferase does what? |
The precursor oligosaccharide is transferred to the asparagine residue of the protein by this process. |
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What occurs right after the protein is being pushed through the translocator, prior to folding? |
Glycosylation |
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Membrane bound vesicles are utilized to transfer components to and from where? |
The ER, Golgi, lysosomes, endosomes, and plasma membranes |
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Where are many modifications made to the proteins that help direct the sorting of the protein to the correct location? |
In the Golgi |
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All O-linked glycosylation and proteoglycan assembling occurs where? |
In the Golgi |
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What are the 4 processes within the Golgi? |
1) Glycosylation 2) Sulfation 3) Phosphorylation 4) Proteolysis |
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What is Glycosylation? |
The addition of a carbohydrate |
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What is Sulfation? |
The addition of a sulfur |
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What is Phosphorylation? |
Addition of a phosphate |
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What is Proteolysis? |
The cleavage of peptide bonds |
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What 3 proteins bind to the cytosol side of the vesicle used to transport proteins to/from/within the Golgi? |
1) Clathrin 2) COPI 3) COPII |
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Describe the advanced mechanism used by Clathrin, COPI and COPII. |
-Associated with many other proteins to form "cage-like" structures to surround the vesicle for transport -Utilize specific receptors that select the appropriate proteins for transport (selective) |
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How do SNAREs work? |
-In order for two membranes to fuse they must be in very close proximity. -V-SNAREs (vesicle) and t-SNAREs (target membrane) interact and wrap around each other, pulling the two membranes together -The SNAREs interaction catalyzes the fusion of the two membranes |
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Tetanus and botulism toxins enter neurons and cleave what? |
SNAREs |
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What does the attachment of mannose 6-ohosphate to a protein do? |
Targets the protein for the lysosome |
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What is I-cell disease caused by? |
A deficiency of the ability to phosphorylate mannose |
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What is I-cell disease characterized by? |
Skeletal abnormalities, restricted joint movement, coarse facial features, and severe psychomotor impairment. Death usually occurs by 8 years of age |
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What is Mucolipidosis II? |
A mutation in gene encoding GlcNAc-phophotranserase found in domestic shorthair cats |
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What is Mucolipidosis II characterized by? |
-Abnormal facial features -Retarded growth -Progressive hindlimb paresis -Skeletal abnormalities |
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What is constitutive secretion? |
Secretory vesicle travels from Golgi directly to the membrane |
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What is regulated secretion? |
Secretory vesicles remain in the cytoplasm until a signal triggers the fusion and release of contents |
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What transports macromolecules bound to specific receptors for import into the cell? |
Clathrin-coated vesicles |
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What is the following an example of? |
Vesicle transport during endocytosis |
