. SCIENTIFIC INQUIRY Imagine protein X, destined to span the...

Name: Problem 8, Chapter 6: Campbell Biology
Uploaded: 2019-05-02T22:24:06-08:00
Duration: 2 min 30 s
Channel: Yinghui Xin
Description: . SCIENTIFIC INQUIRY Imagine protein X, destined to span the plasma membrane. Assume that the mRNA carrying the genetic message for protein X has already been translated by ribosomes in a cell culture. If you fractionate the cells (see Figure 6.4), in which fraction would you find protein X? Explain by describing its transit through the cell

. SCIENTIFIC INQUIRY Imagine protein X, destined to span the plasma membrane. Assume that the mRNA carrying the genetic message for protein X has already been translated by ribosomes in a cell culture. If you fractionate the cells (see Figure 6.4), in which fraction would you find protein X? Explain by describing its transit through the cell

. SCIENTIFIC INQUIRY Imagine protein X, destined to span the
plasma membrane. Assume that the mRNA carrying the genetic
message for protein X has already been translated by ribosomes
in a cell culture. If you fractionate the cells (see Figure 6.4), in
which fraction would you find protein X? Explain by describing
its transit through the cell

Key Concepts

Signal Peptide and Signal Recognition Particle (SRP)

Proteins destined for secretion or membrane insertion generally carry an N-terminal signal peptide that directs them to the endoplasmic reticulum. The signal recognition particle (SRP) binds to this peptide as it emerges from the ribosome, pausing translation and targeting the ribosome-protein complex to the ER membrane for co-translational translocation.

Co-Translational Translocation

Co-translational translocation is the process in which a nascent polypeptide is fed into the endoplasmic reticulum while still being synthesized by the ribosome. This mechanism ensures that proteins destined for the secretory pathway or membrane localization are properly inserted into or across the ER membrane.

Endoplasmic Reticulum (ER) and Golgi Apparatus

The endoplasmic reticulum is the initial site where membrane and secretory proteins are inserted and folded. After their synthesis and initial processing in the ER, these proteins are transported to the Golgi apparatus, where they undergo further modifications and sorting before being directed to their final destinations such as the plasma membrane.

Vesicular Transport and Membrane Integration

Following processing in the Golgi apparatus, proteins are packaged into vesicles that carry them to various cellular compartments, including the plasma membrane. This vesicular trafficking is essential for ensuring that membrane proteins are correctly delivered and integrated into the appropriate cellular membranes.

Cell Fractionation

Cell fractionation is a laboratory technique used to separate cellular components such as organelles based on differences in density and size. This method enables the isolation and analysis of specific organelles like the endoplasmic reticulum or plasma membrane, which is critical for tracking the cellular transit and localization of proteins.

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