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细胞质
细胞质是由细胞器和悬浮在水溶液（胞质溶胶）中称为细胞骨架的蛋白质支架所组成的。胞质溶胶是由富含水、离子、盐和各种有机分子所组成的胶体。
蛋白质折叠和错误折叠
细胞质是进行多个细胞过程（包括蛋白质的合成和折叠）的场所。胞质溶胶中的水性促进了蛋白质的折叠过程，从而使得疏水性氨基酸侧链埋在蛋白质的核心中，…
在真核细胞中，细胞质是位于质膜与核膜之间的区域。
由于原核细胞没有细胞核，细胞质指的是质膜内所包含的所有内容。
在这两种细胞类型中，细胞质空间均被一种称为胞质溶胶的凝胶状基质所充满。
细胞质溶胶是一种水溶液，含有许多可溶性离子、小分子和大分子。
真核细胞的细胞质中还包含许多执行特定细胞功能的膜包被细胞器，例如线粒体、内质网和高尔基体。
存在于细胞质中的一套蛋白质纤维结构——细胞骨架，赋予细胞其形态和结构。它还参与细胞内运输和细胞运动。
此外，许多非细胞器的细胞功能，例如蛋白质合成，也发生在细胞质中。细胞质的水性环境通过将疏水性氨基酸侧链排斥至蛋白质内部，从而促进蛋白质的正确折叠。
一些细胞还会以包涵体的形式在细胞质中储存不溶性代谢产物，如糖原。
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Q1: What is the difference between cytoplasm in eukaryotic and prokaryotic cells?
In eukaryotic cells, cytoplasm is the area between the plasma membrane and nuclear envelope, while in prokaryotic cells it refers to everything within the plasma membrane since they lack a nucleus. Both contain cytosol, a gel-like aqueous matrix filled with ions and molecules. Eukaryotic cytoplasm additionally contains membrane-bound organelles like mitochondria and the endoplasmic reticulum that perform specialized functions.
Q2: What is the cytosol and what does it contain?
The cytosol is a gel-like aqueous matrix that fills the cytoplasmic space in all cells. It is an aqueous solution containing soluble ions, small molecules, and macromolecules. The aqueous nature of the cytosol facilitates protein folding by repelling hydrophobic amino acid side-groups into the protein core while hydrophilic amino acids face outward toward the water.
Q3: How does the cytoskeleton contribute to cell structure and function?
The cytoskeleton is a framework of protein fibers that gives cells their shape and structure. It consists of three types of filaments: microtubules made of tubulin, microfilaments composed of actin, and intermediate filaments. Beyond structural support, the cytoskeleton facilitates intracellular transport, enables cell motility, and plays a crucial role in cell division by guiding chromosomes to opposite ends.
Q4: What are the three types of cytoskeletal filaments and their functions?
Microtubules, the largest filaments made of tubulin, provide structural stability and act as tracks for transporting proteins and vesicles. Microfilaments, composed of actin, enable rapid cell motility and muscle contraction. Intermediate filaments, made of proteins like keratin or desmin depending on cell type, provide structural support. All three types work together to maintain cell integrity and facilitate cellular processes.
Q5: What causes protein misfolding in the cytoplasm and what are the consequences?
Cellular stresses such as aging, pH changes, temperature fluctuations, or osmolarity shifts can cause protein misfolding in the cytoplasm. Misfolded proteins may accumulate to form insoluble protein aggregates. These aggregates are implicated in neurodegenerative disorders like Alzheimer's and Parkinson's disease, making protein folding quality critical for cellular health.
Q6: What cellular processes occur in the cytoplasm?
The cytoplasm is the site of protein synthesis and protein folding, where the aqueous environment supports proper protein structure formation. Additionally, many non-organelle cellular functions take place here. Some cells also store insoluble metabolic products like glycogen in the cytoplasm as inclusions, making it a hub for both biosynthetic and storage activities.
Q7: How do microtubules and microfilaments differ in their dynamic properties?
Microtubules are highly dynamic structures that can grow or shrink by adding or removing tubulin molecules from their ends. Microfilaments, composed of actin, can assemble and disassemble rapidly, enabling quick responses to cellular signals. In contrast, intermediate filaments are less dynamic but still provide essential structural support, offering stability where rapid changes are not required.