Protein Targeting: PTS1R and Peroxisome Membrane

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Questions and Answers

What is the primary function of the Pex14p receptor on the peroxisome membrane?

To facilitate the transport of the PTS1R complex across the membrane

To unfold proteins so they can fit through the membrane

To provide the energy required for protein targeting

To recognize and bind the PTS1R complex (correct)

What is the role of chaperons in protein targeting to mitochondria?

To provide the energy required for protein transport

To facilitate the transport of the protein across the mitochondrial membrane

To bind to the protein in the cytoplasm and ensure it reaches the correct organelle (correct)

To remove the signal sequence from the protein

What is the purpose of ATP hydrolysis in protein targeting to peroxisomes?

To recognize and bind the PTS1R complex

To allow the recycling of the PTS1R receptor (correct)

To provide the energy required for protein unfolding

To facilitate the transport of the PTS1R complex across the membrane

What is the function of signal peptidase in mitochondrial protein targeting?

To remove the signal sequence from the protein Signup and view all the answers

What is the role of the PTS1R complex in peroxisome targeting?

To recognize and bind to the Pex14p receptor on the peroxisome membrane Signup and view all the answers

What is the purpose of the protein translocator complex in mitochondrial protein targeting?

To transport the protein across the mitochondrial membrane Signup and view all the answers

What is the purpose of chaperons in the mitochondrial protein targeting pathway?

To prevent premature folding of the protein Signup and view all the answers

What is the primary function of the signal recognition particle (SRP) during protein targeting?

Recognizing the signal peptide and the ribosome during protein targeting to the ER Signup and view all the answers

What is the destination of the PTS1R complex in peroxisome targeting?

The peroxisome membrane Signup and view all the answers

During co-translational insertion of membrane proteins, what sequence allows hydrophobic amino acids to associate with the lipid membrane?

Anchor sequence Signup and view all the answers

What is the primary site of protein synthesis for secretory proteins and membrane proteins?

Endoplasmic reticulum (ER) Signup and view all the answers

What is the role of the signal sequence in protein targeting?

Binding to the SRP to facilitate protein targeting to the ER Signup and view all the answers

Which of the following is NOT a characteristic of signal sequences?

C-terminal sequence Signup and view all the answers

What is the primary mechanism of protein targeting to the ER?

Co-translational insertion Signup and view all the answers

What is the primary cause of osteogenesis imperfecta, a family of genetic disorders that affect the bones?

Mutations in COL1A1 and COL1A2 genes that prevent the production of type I collagen Signup and view all the answers

What is the role of signal sequences in collagen synthesis?

Directing polypeptide chains into the ER lumen Signup and view all the answers

What is the fate of the procollagen molecules after they are secreted into the extracellular matrix?

They are cleaved by collagen peptidases to form tropocollagen Signup and view all the answers

What is the characteristic of collagen fibrils in Ehlers-Danlos syndrome?

Increased extensibility and decreased rigidity Signup and view all the answers

What is the term for the breaking of peptide bonds to remove part of a protein?

Proteolytic cleavage Signup and view all the answers

What is the destination of proteins synthesized by ribosomes on the rough ER?

Plasma membrane Signup and view all the answers

What is the peroxisome targeting sequence (PTS) typically located on?

C-terminus of the protein Signup and view all the answers

What is the receptor that recognizes the peroxisome targeting sequence (PTS)?

PTS1R Signup and view all the answers

What is the requirement for protein sorting that is intrinsic to the protein?

A signal Signup and view all the answers

What is the term for the synthesis of polypeptides on ribosomes at the border of the ER?

Co-translational insertion Signup and view all the answers

Study Notes

Protein Targeting to Peroxisomes

Peroxisome targeting sequence (PTS) is a signal intrinsic to the protein, usually present on the C-terminus
Cytosolic receptor protein PTS1R binds to the SKL signal and directs it to the correct membrane
14 Pex proteins create a transport channel through the peroxisomal membrane, facilitating the transport of the PTS1R complex across the membrane
ATP hydrolysis is needed to allow recycling of the PTS1R receptor

Protein Targeting to Mitochondria

Proteins contain a signal sequence to ensure they go to the right organelle
Chaperons become associated with protein in cytoplasm (requires ATP), unfolding proteins to fit through the membrane
Protein attaches to the “Protein Translocator Complex” and moves into mitochondria
Chaperons are released, and another class binds to prevent premature folding
Signal peptidase removes signal sequence, and protein is folded into final shape for its function

Collagen Biosynthesis

Occurs in fibroblast cells
Signal sequences direct polypeptide chain into the ER
Hydroxylation of Proline and lysine residues (requires ascorbate + vitamin C)
Glycosylation of selected hydroxylysine residues
Assembly of 3 polypeptide chains into a procollagen triple helix
Procollagen is processed into secretory vesicles, and secreted into extracellular matrix
Procollagen’s terminal ends are cleaved by Collagen Peptidases, forming tropocollagen
Tropocollagen molecules are covalently linked via aldol covalent cross-links, forming collagen fibrils by Lysyl Oxidase

Scurvy and Ehlers-Danlos Syndrome

Scurvy is caused by insufficient hydroxylation of Proline and lysine residues due to lack of vitamin C and ascorbic acid
Results in fatigue, weakness, poor wound healing, anaemia, and gum disease
Connective tissue becomes defective, leading to instability of collagen
Treatment involves vitamin C intake
Ehlers-Danlos syndrome (EDS) is caused by mutations in genes affecting extracellular peptide cleavage and altering collagen fibril cross-linking
Results in altered stability and functionality of fibers, making them more extensible and losing their rigidity

Protein Synthesis and Sorting

Proteins synthesised on free ribosomes are destined for cytosol or post-translational import into organelles
Proteins synthesised by ribosomes on the rough ER are destined for the plasma membrane or secretory pathway via co-translational insertion
Co-translational insertion is the synthesis of polypeptides on ribosomes at the border of the ER, resulting in the polypeptide being contained within the ER
The 4 requirements for Protein Sorting are: a signal intrinsic to the protein, a receptor that recognizes the signal, a translocation machinery, and energy

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Description

This quiz covers the role of PTS1R in protein targeting, its interaction with the Pex14p receptor, and the translocation machinery involved in transporting the PTS1R complex across the peroxisomal membrane.