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Questions and Answers
What is the primary function of signal sequences in protein sorting within the cell?
What is the primary function of signal sequences in protein sorting within the cell?
- To facilitate protein degradation
- To direct proteins to specific cellular locations (correct)
- To enhance protein stability in the cytoplasm
- To bind proteins to ribosomes during synthesis
Which of the following correctly describes a mechanism utilized for the transport of proteins into the nucleus?
Which of the following correctly describes a mechanism utilized for the transport of proteins into the nucleus?
- Gated transport via nuclear pores (correct)
- Active transport through cell membranes
- Endocytosis through membrane invagination
- Simple diffusion through the cytoplasm
What is one key role of the rough endoplasmic reticulum (ER)?
What is one key role of the rough endoplasmic reticulum (ER)?
- Degradation of misfolded proteins
- Modification and folding of newly synthesized proteins (correct)
- Synthesis of lipids and steroids
- Synthesis of ATP
How do resident ER proteins maintain their location within the endoplasmic reticulum?
How do resident ER proteins maintain their location within the endoplasmic reticulum?
Which aspect of protein synthesis differs between free ribosomes and membrane-bound ribosomes?
Which aspect of protein synthesis differs between free ribosomes and membrane-bound ribosomes?
What type of ribosomes are responsible for synthesizing proteins destined for the endomembrane system?
What type of ribosomes are responsible for synthesizing proteins destined for the endomembrane system?
Which of the following proteins is NOT synthesized by free ribosomes in the cytosol?
Which of the following proteins is NOT synthesized by free ribosomes in the cytosol?
What is the primary method of transporting proteins to the mitochondria?
What is the primary method of transporting proteins to the mitochondria?
What is required for nuclear proteins to be imported into the nucleus?
What is required for nuclear proteins to be imported into the nucleus?
Which of the following statements about the function of free ribosomes is correct?
Which of the following statements about the function of free ribosomes is correct?
What type of proteins require vesicular transport for movement within the cell?
What type of proteins require vesicular transport for movement within the cell?
What is the significance of the signal sequence in protein synthesis?
What is the significance of the signal sequence in protein synthesis?
Which organelle’s proteins are encoded by nuclear DNA?
Which organelle’s proteins are encoded by nuclear DNA?
What is the role of the signal recognition particle (SRP) in protein synthesis?
What is the role of the signal recognition particle (SRP) in protein synthesis?
Which amino acid characteristic is associated with signal sequences for nuclear import?
Which amino acid characteristic is associated with signal sequences for nuclear import?
What is the primary function of the nuclear pore complex (NPC)?
What is the primary function of the nuclear pore complex (NPC)?
What features distinguish the outer membrane of the nuclear envelope?
What features distinguish the outer membrane of the nuclear envelope?
Which transport mechanism is employed for proteins entering the nucleus?
Which transport mechanism is employed for proteins entering the nucleus?
Which type of molecules are primarily transported via simple diffusion through the pore complex?
Which type of molecules are primarily transported via simple diffusion through the pore complex?
What characterizes co-translational import of proteins?
What characterizes co-translational import of proteins?
What are nucleoporins?
What are nucleoporins?
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Study Notes
Introduction to Compartments
- Cells contain internal membrane compartments that carry out specialized functions
- The endomembrane system consists of all internal compartments within a cell
- Compartments within the endomembrane system communicate with each other
Protein Synthesis and Sorting
- Ribosomes synthesize proteins
- Free ribosomes are located in the cytosol and produce soluble proteins
- Membrane-bound ribosomes are attached to the rough endoplasmic reticulum and produce proteins that are destined for the endomembrane system or for secretion from the cell
Protein synthesis
- Proteins destined for the cytosol are synthesized by free ribosomes
- Proteins destined for compartments within the endomembrane system or for secretion are synthesized by membrane-bound ribosomes
- The destination of a protein is determined by specific signal sequences
Signal Sequences
- Signal sequences are short stretches of amino acids that target proteins to specific cellular compartments
- ER signal sequences are rich in hydrophobic amino acids and signal proteins to the ER
- Nuclear localization sequences are rich in positively charged amino acids and signal proteins to the nucleus
Gated Transport - Nucleus
- The nucleus contains the cell's genetic information in the form of chromatin
- The nuclear envelope is a double-membrane bound organelle that separates the nuclear contents from the rest of the cell
- The inner membrane of the nuclear envelope is associated with the nuclear lamina, which provides structural support to the nucleus
- The nuclear pore complex (NPC) is a protein channel that allows selective transport of molecules in and out of the nucleus
- Nucleoporins are proteins that make up the nuclear pore complex
- Small hydrophilic molecules can diffuse passively through the NPC
- Larger molecules and macromolecules require active transport through the NPC
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