BSCI 1510 Gated Transport Lecture

What are the three mechanisms through which proteins are transported to organelles?

Gated transport, translocation, and vesicular transport.

What roles do signal sequences play in protein transport?

Signal sequences help target proteins to their correct organelle by indicating where they should be delivered.

What is the main function of the nucleolus?

The nucleolus is the site of ribosome biogenesis, where ribosomal RNA is combined with proteins to form ribosomal subunits.

How do proteins enter the nucleus?

Proteins enter the nucleus through nuclear pores that recognize specific nuclear localization signals (NLS).

What characterizes gated transport?

Gated transport allows fully folded proteins to pass through a large pore into the nucleus or peroxisomes.

How are peroxisomal proteins imported?

Peroxisomal proteins are delivered to the organelle through a peroxisome targeting signal (PTS) and are recognized by specific receptors.

What is the structure of the nuclear envelope?

The nuclear envelope is a double membrane system with nuclear pores that allow material to move in and out of the nucleus.

What happens to the nuclear localization signal (NLS) during nuclear import?

The NLS of a nuclear protein is recognized by importins which help transport the protein through the nuclear pore.

What is the function of Ran protein in nuclear transport?

Ran protein, in its GTP-bound form, binds to import receptors, causing them to release their cargo proteins in the nucleus.

How do signal sequences differ in their characteristics?

Signal sequences can differ in their position (N- or C-terminal, internal), some are cleaved after use, and others remain uncleaved.

What specialized transport mechanism do peroxisomal proteins use?

Peroxisomal proteins utilize a gated mechanism similar to gated transport, allowing fully folded proteins to enter through specific receptors.

Why are peroxisomes considered essential for eukaryotic life?

Peroxisomes are necessary for various metabolic processes, including fatty acid beta-oxidation and hydrogen peroxide decomposition.

What structural feature allows nuclear pore complexes to selectively regulate entry/exit?

The disordered protein complexes within the nuclear pore complex prevent the free passage of large molecules while allowing small molecules to pass.

What is the significance of the SKL sequence in protein targeting?

The SKL sequence is a peroxisomal targeting signal that directs fully folded proteins to the peroxisome.

What consequences arise from PEX1 and PEX6 mutations in humans?

Mutations in PEX1 and PEX6 lead to Zellweger Syndrome, which results in severe abnormalities in organs such as the liver and kidneys.

What evidence supports the idea of evolutionary invagination in nuclear membranes and ER?

The structure of modern bacteria and archaea, with DNA attached to the plasma membrane, suggests that the nuclear envelope may have formed through membrane invagination.

How do transcription factors utilize nucleocytoplasmic transport?

Transcription factors often have both a nuclear localization signal (NLS) and a nuclear export signal (NES) to facilitate shuttling between the nucleus and cytoplasm.

What function do peroxins play in peroxisomal protein import?

Peroxins are proteins that facilitate the import of peroxisomal proteins into the organelle.