Cell Organelles and Protein Sorting

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Questions and Answers

Which organelle is the primary site for protein synthesis and intermediary metabolism?

  • Cytosol (correct)
  • Golgi Apparatus
  • Endoplasmic Reticulum
  • Mitochondria

What is the primary function of the endosomes within a cell?

  • Sorting and recycling of endocytosed material (correct)
  • Aerobic respiration
  • Protein modification and sorting
  • Intracellular digestion

Which of the following organelles is responsible for oxidative reactions and the breakdown of long-chain fatty acids?

  • Lysosomes
  • Peroxisomes (correct)
  • Mitochondria
  • Endoplasmic Reticulum

Which transport mechanism involves the movement of cargo between topologically equivalent spaces without crossing a membrane?

<p>Vesicular Transport (A)</p> Signup and view all the answers

What distinguishes topologically equivalent compartments from others within a cell?

<p>Molecules can move between them without crossing a membrane. (C)</p> Signup and view all the answers

Which type of sorting signal directs proteins from the cytosol to specific organelles like the ER or mitochondria?

<p>Signal Peptides (B)</p> Signup and view all the answers

What is the role of signal patches in protein sorting?

<p>Directing enzymes and proteins to the correct compartments (B)</p> Signup and view all the answers

Which of the following is NOT a component of the nuclear envelope?

<p>Endoplasmic Reticulum Lumen (D)</p> Signup and view all the answers

Which component of the nuclear envelope is continuous with the endoplasmic reticulum?

<p>Outer Nuclear Membrane (D)</p> Signup and view all the answers

What is the function of nuclear pore complexes (NPCs)?

<p>To allow bidirectional movement of proteins and RNA (A)</p> Signup and view all the answers

What type of transport occurs through nuclear pore complexes for small molecules (

<p>Passive Transport (A)</p> Signup and view all the answers

Which of the following statements accurately describes the movement of molecules between the cytosol and the nucleus?

<p>Small molecules can freely diffuse through nuclear pore complexes. (D)</p> Signup and view all the answers

What is the role of the nuclear lamina?

<p>To provide structural support to the nuclear envelope (B)</p> Signup and view all the answers

How does transmembrane transport differ from gated transport?

<p>Transmembrane transport requires crossing a membrane, while gated transport occurs through a channel. (D)</p> Signup and view all the answers

Which organelle sorts and recycles endocytosed material?

<p>Endosome (C)</p> Signup and view all the answers

What distinguishes signal peptides from signal patches?

<p>Signal peptides are linear sequences of amino acids, while signal patches are conformational. (A)</p> Signup and view all the answers

What is the primary function of the lysosomes?

<p>Intracellular digestion (B)</p> Signup and view all the answers

Which of the following organelles is NOT involved in protein modification and sorting?

<p>Mitochondria (A)</p> Signup and view all the answers

If a protein is destined for the mitochondrial matrix, where would you expect its signal sequence to direct it initially?

<p>Across both the outer and inner mitochondrial membranes (B)</p> Signup and view all the answers

How do proteins enter the endoplasmic reticulum (ER) lumen?

<p>Co-translationally through a protein translocator (B)</p> Signup and view all the answers

Which of the following processes primarily occurs in the Golgi apparatus?

<p>Final protein modifications and sorting (C)</p> Signup and view all the answers

What is the consequence of a mutation that disrupts a signal peptide on a protein normally targeted to the ER?

<p>The protein will remain in the cytosol. (C)</p> Signup and view all the answers

In vesicular transport, how do vesicles recognize and fuse with their target membrane?

<p>They use complementary SNARE proteins. (A)</p> Signup and view all the answers

How does a protein destined for the lysosome acquire its specific targeting signal in the Golgi?

<p>Addition of a mannose-6-phosphate (M6P) tag (C)</p> Signup and view all the answers

What is the function of the outer nuclear membrane's ribosomes?

<p>Synthesizing proteins destined for secretion or the ER (A)</p> Signup and view all the answers

Which of the following describes the correct order of compartments a protein might encounter if it is synthesized in the ER and ultimately functions in the lysosome?

<p>ER → Golgi → Endosome → Lysosome (B)</p> Signup and view all the answers

How does the cell ensure that proteins targeted to the ER are translocated into the ER lumen rather than remaining embedded in the ER membrane?

<p>Hydrophobic stop-transfer sequences halt translocation, leading to membrane insertion. (B)</p> Signup and view all the answers

What is the significance of protein glycosylation in the Golgi apparatus?

<p>It aids in protein folding and sorting. (B)</p> Signup and view all the answers

Which of the following mechanisms is NOT directly involved in protein sorting?

<p>Protein degradation by proteasomes (D)</p> Signup and view all the answers

Flashcards

Nucleus

Site of DNA and RNA synthesis within eukaryotic cells.

Cytosol

Location of protein synthesis and intermediary metabolism.

Endoplasmic Reticulum (ER)

Organelle involved in protein modification and sorting, also lipid synthesis.

Golgi Apparatus

Organelle responsible for further protein modification and sorting, also involved in the synthesis of complex polysaccharides.

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Endosomes

Vesicles involved in sorting and recycling endocytosed material.

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Lysosomes

Organelles responsible for intracellular digestion.

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Mitochondria

Organelles where aerobic respiration occurs, producing ATP.

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Peroxisomes

Organelles involved in oxidative reactions and breakdown of long-chain fatty acids.

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Gated Transport

Movement of proteins and RNA between the cytosol and nucleus through nuclear pore complexes.

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Transmembrane Transport

Transport of specific proteins across membranes from the cytosol into distinct spaces.

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Vesicular Transport

Movement of cargo from one topologically equivalent space to another via vesicles.

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Topologically Equivalent Compartments

Compartments that can exchange molecules without crossing a membrane.

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Signal Peptides

Amino acid sequences that direct proteins to specific cellular compartments.

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Signal Patches

Specific arrangement of amino acids on a protein's surface which directs proteins to correct compartments.

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Inner Nuclear Membrane

The part of the nuclear envelope that binds to chromosomes and the nuclear lamina.

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Outer Nuclear Membrane

The part of the nuclear envelope that is continuous with the ER and studded with ribosomes.

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Nuclear Pore Complexes (NPCs)

Structures within the nuclear envelope that allow bidirectional movement of proteins and RNA.

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Study Notes

  • Organelles have distinct functions within the cell.
  • The nucleus is responsible for DNA and RNA synthesis.
  • The cytosol is the site of protein synthesis and intermediary metabolism.
  • The endoplasmic reticulum (ER) is involved in protein modification and sorting.
  • The Golgi apparatus also functions in protein modification and sorting.
  • Endosomes are key for sorting and recycling endocytosed materials.
  • Lysosomes facilitate intracellular digestion.
  • Mitochondria are the site of aerobic respiration.
  • Peroxisomes carry out oxidative reactions and break down long-chain fatty acids.

Mechanisms for Sorting Proteins

  • Gated transport moves proteins and RNA between the cytosol and nucleus via nuclear pore complexes.
  • Transmembrane transport moves specific proteins across membranes.
  • Vesicular transport moves cargo between topologically equivalent spaces without crossing a membrane.

Topologically Equivalent Compartments

  • Compartments are topologically equivalent if molecules can move between them without crossing a membrane.
  • The ER and Golgi apparatus are topologically equivalent.

Types of Sorting Signals

  • Signal peptides direct proteins from the cytosol to specific compartments like the ER or mitochondria.
  • Signal patches direct enzymes and proteins to the correct compartments, such as from the Golgi to lysosomes.

Components of the Nuclear Envelope

  • The inner nuclear membrane binds to chromosomes and the nuclear lamina.
  • The outer nuclear membrane is continuous with the ER and is studded with ribosomes.
  • Nuclear pore complexes (NPCs) allow bidirectional movement of proteins and RNA.

Function of Nuclear Pore Complex

  • Nuclear pore complexes allow small molecules to pass through passively.

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