뒤로Eukaryotic Cell Structure and Protein Trafficking
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Chapter 7.3 – Eukaryotic Cell Structure and Protein Movement
Learning Objectives
Differentiate cell movement with flagella and cilia.
List the major cytosolic organelles and their functions.
Describe how proteins are imported to the nucleus.
Explain how proteins are exported out of the cell via the plasma membrane.
Understand the endomembrane system and protein trafficking.
Animal Cell Structure
Major Organelles and Their Functions
Eukaryotic animal cells contain specialized organelles that perform distinct functions necessary for cellular life.
Nuclear Envelope: Double membrane that encloses the nucleus, separating genetic material from the cytoplasm.
Chromosomes: Structures composed of DNA and proteins; DNA is tightly packed to fit within the nucleus.
Nucleolus: Dense region within the nucleus responsible for manufacturing ribosomes and processing rRNA.
Mitochondria: Organelles that generate ATP through cellular respiration.
Endoplasmic Reticulum (ER): Network of membranes involved in protein and lipid synthesis. Divided into rough ER (with ribosomes) and smooth ER (without ribosomes).
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes: Contain digestive enzymes for breaking down macromolecules and cellular debris.
Nuclear Transport
Import and Export of Proteins Through Nuclear Pores
The nucleus is separated from the cytoplasm by the nuclear envelope, which contains nuclear pores that regulate the movement of molecules.
Nuclear Pore Complex: Large protein structures that allow selective transport of proteins, RNA, and other molecules.
Import: Proteins destined for the nucleus contain a nuclear localization signal (NLS), a specific amino acid sequence recognized by import proteins.
Export: RNA and ribosomal subunits are exported from the nucleus to the cytoplasm through nuclear pores.
Example: Pyruvate kinase with an NLS is imported into the nucleus, while without NLS it remains in the cytosol.
Endomembrane System and Protein Trafficking
Pathways for Protein Movement
The endomembrane system is a network of membranes within the cell that work together to modify, package, and transport proteins and lipids.
Endoplasmic Reticulum (ER): Proteins destined for secretion or for certain organelles are synthesized in the rough ER.
Signal Sequence: A 20-amino acid ER signal sequence directs the growing polypeptide to the ER.
Signal Recognition Particle (SRP): Binds to the signal sequence and guides the ribosome to the ER membrane.
Golgi Apparatus: Proteins are further modified and sorted for their final destinations.
Vesicle Transport: Proteins are packaged into vesicles for delivery to the plasma membrane or other organelles.
Example: Secretory proteins follow the pathway: ribosome → ER → Golgi apparatus → vesicle → plasma membrane.
Cell Movement: Flagella and Cilia
Structure and Function
Flagella and cilia are cellular appendages that enable movement and are composed of microtubules arranged in a characteristic pattern.
Flagella: Long, whip-like projections that move cells by undulating or rotating. Found in sperm cells and some protists.
Cilia: Short, hair-like projections that move fluid or cells over surfaces. Found in respiratory tract cells.
Microtubule Arrangement: Both structures have a "9 + 2" arrangement of microtubules—nine doublets surrounding two central microtubules.
Motor Proteins: Dynein and other proteins generate force for movement by sliding microtubules against each other.
Comparison Table: Flagella vs. Cilia
Feature | Flagella | Cilia |
|---|---|---|
Length | Long | Short |
Number per cell | Few (1-2) | Many |
Movement | Undulating/rotating | Beating/back-and-forth |
Function | Cell locomotion | Move fluid/cells |
Key Equations and Concepts
Protein Import Rate: The rate at which proteins are imported into the nucleus depends on the number of nuclear pores and the presence of NLS.
Signal Sequence Recognition:
Microtubule Arrangement: pattern in cilia and flagella
Additional info: The notes infer standard textbook details about organelle functions, protein trafficking, and cytoskeletal structures to provide a complete study guide for General Biology students.
