Protein Modifications Quiz

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Questions and Answers

What are some protein modifications that aid in proper-folding, stability, and activity of proteins?

Cleavage and hydroxylation

Phosphorylation and acetylation

Phosphorylation and glycosylation

Glycosylation and lipidation (correct)

Which two intracellular sites can proteins be targeted to?

Plasma membrane and nucleus

Cytosol and mitochondria (correct)

Plasma membrane and cytosol

Mitochondria and peroxisome

What is the signal peptide responsible for in protein synthesis?

Crossing and anchoring integral membrane proteins

Synthesizing proteins on free ribosomes

Completing N-linked glycosylation in the Golgi

Coupling between ribosomes and rough ER (correct)

What is the function of chaperones in protein folding?

Recognize exposed hydrophobic amino acids Signup and view all the answers

What is the role of the Golgi apparatus in protein sorting?

Sorting and packaging proteins from trans Golgi network Signup and view all the answers

What is the marker for lysosomal proteins?

Mannose-6P Signup and view all the answers

What is the cause of mucolipidosis II (I-cell disease)?

Defects in protein modifications and sorting Signup and view all the answers

Where can inclusion bodies be seen in patients with I-cell disease?

In the fibroblasts Signup and view all the answers

What are some protein modifications that aid in proper-folding, stability, and activity of proteins?

Glycosylation and lipidation Signup and view all the answers

Which two intracellular sites can proteins be targeted to?

Cytosol and mitochondria Signup and view all the answers

What is the signal peptide responsible for in protein synthesis?

Coupling between ribosomes and rough ER Signup and view all the answers

What is the function of chaperones in protein folding?

Recognize exposed hydrophobic amino acids Signup and view all the answers

What is the role of the Golgi apparatus in protein sorting?

Sorting and packaging proteins from trans Golgi network Signup and view all the answers

What is the marker for lysosomal proteins?

Mannose-6P Signup and view all the answers

What is the cause of mucolipidosis II (I-cell disease)?

Defects in protein modifications and sorting Signup and view all the answers

Where can inclusion bodies be seen in patients with I-cell disease?

In the fibroblasts Signup and view all the answers

What are some protein modifications for activation?

Cleavage, hydroxylation, phosphorylation, glycosylation, lipidation, and acetylation Signup and view all the answers

What is the function of chaperones such as heat shock proteins?

Aid in protein folding Signup and view all the answers

What is the function of the Golgi apparatus?

Responsible for various types of protein modifications and sorting Signup and view all the answers

Which type of proteins have KDEL sequence at their C-terminal end and are retained by the rER?

ER resident proteins Signup and view all the answers

What is the function of M6P-receptor in protein sorting?

Sorts lysosomal proteins Signup and view all the answers

What is the result of a mutated enzyme in I-cell disease?

Lysosomal enzymes do not carry M6P tag Signup and view all the answers

What is the function of glucosyl transferase and glucosidase II in protein modifications?

Recognizing and correcting misfolded proteins Signup and view all the answers

What is the function of SRP in protein synthesis?

Coupling between ribosomes and rough ER Signup and view all the answers

Study Notes

Mechanism and Significance of Protein Modifications

Genetic mutations can lead to mis-targeting of proteins, causing deficiencies and diseases.
Proteins undergo modifications for activation, including cleavage, hydroxylation, phosphorylation, glycosylation, lipidation, and acetylation.
Proteins can be targeted to different intracellular sites, including the plasma membrane, cytosol, nucleus, mitochondria, and peroxisome.
Targeting sequences and modifications aid in proper-folding, stability, and activity of proteins.
Proteins are placed into two categories based on their synthesis location and targets: Category-1 (synthesized on free ribosomes) and Category-2 (synthesized on rough ER).
Coupling between ribosomes and rough ER occurs via a signal peptide that binds to the signal recognition particle (SRP).
Integral membrane proteins require additional signals for crossing and anchoring into the lipid bilayer.
N-linked glycosylation occurs only in the ER and completes in the Golgi.
Protein folding is aided by chaperones such as heat shock proteins, which recognize exposed hydrophobic amino acids.
Quality control mechanisms in the ER allow only correctly folded proteins to move to the Golgi for further modifications.
Misfolded proteins are degraded in the proteasomes.
Glucosyl transferase and glucosidase II are involved in recognizing and correcting misfolded proteins.Protein Modifications and Sorting in Golgi Apparatus
Golgi apparatus is responsible for various types of protein modifications including terminal glycosylation and O-linked glycosylation.
O-linked glycosylation occurs at the -OH group of selected Ser/Thr amino acids in a primary protein.
Golgi apparatus also sorts and packages proteins from trans Golgi network and moves them to different targets such as cis Golgi (which receives proteins from ER).
Lysosomal proteins are sorted by a M6P-receptor and carry mannose-6P (M6P) as a marker.
M6P receptor (MPR) sorts proteins via clathrin coated vesicles which fuse with endosomes.
MPR is recycled to the Golgi in a lysosomal pH 4-5 in the early major pathway, and to the PM in a minor pathway which retrieves mannose-6-P.
ER resident proteins have KDEL sequence at their C-terminal end and are retained by the rER, while some escape to Golgi and are retrieved into rER in a pH-dependent manner.
Membrane proteins are synthesized as part of the ER membrane and become glycosylated in Golgi, with the glycosylated epitope facing the lumen of ER, Golgi, and vesicle.
Secretory proteins are exocytosed by default mechanism outside ER, Golgi, and vesicle.
Defects in protein modifications and sorting can result in mistargeting of proteins or enzymes, leading to diseases such as mucolipidosis II (I-cell disease).
In I-cell disease, lysosomal enzymes do not carry M6P tag due to a mutated enzyme, resulting in accumulation of mucopolysaccharidoses and inclusion bodies of proteins.
Inclusion bodies can be seen in the fibroblasts of patients with I-cell disease.

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Description

Test your knowledge on the mechanism and significance of protein modifications with this informative quiz! From genetic mutations to quality control mechanisms, learn about the different types of protein modifications, their roles in proper-folding and stability, and how they aid in the targeting of proteins to specific intracellular sites. Discover how the Golgi apparatus is responsible for various types of protein modifications and sorting, and how defects in these processes can lead to diseases such as mucolipidosis II. Take this quiz to enhance your understanding