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Definition
- All eukaryotes have a large nucleus surrounded by a double-membrane nuclear envelope (Figure 7.7).
- The nucleus contains the linear eukaryotic chromosomes in the form of chromatin. The nuclear lamina anchors chromosomes and maintains the overall shape and structure of the nucleus.
- Ribosomal RNA synthesis occurs in a distinct region of the nucleus called the nucleolus.
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Definition
- Eukaryotic ribosomes are made of RNA and protein, and have a large and a small subunit (Figure 7.8). Many ribosomes are found in the cytosol, the fluid part of the cytoplasm.
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Term
| Rough Endoplasmic Reticulum |
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Definition
- The rough endoplasmic reticulum (rough ER) is a network of membrane-bound tubes and sacs studded with ribosomes for protein synthesis (Figure 7.9) and is continuous with the nuclear envelope.
- As proteins are made, they move inside the rough ER where they are folded and otherwise modified.
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Definition
- The Golgi apparatus, formed by a series of stacked flat membranous sacs (cisternae), receives products from the rough ER and sends finished products to the cell surface in vesicles (Figure 7.10).
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Term
| Smooth Endoplasmic Reticulum |
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Definition
- The smooth endoplasmic reticulum (smooth ER) lacks ribosomes and is responsible for fatty acid and phospholipid synthesis, as well as for breakdown of hydrophobic toxins (Figure 7.11).
- The endomembrane system, composed of the smooth and rough ER and the Golgi apparatus, is the primary center for protein and lipid synthesis.
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Definition
- Peroxisomes are single–membrane–bound globular organelles where oxidation reactions occur (Figure 7.12).
- Different types of peroxisomes specialize in different types of oxidation reactions.
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Definition
- Lysosomes are single–membrane–bound centers for storage and/or waste processing (Figure 7.13).
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Definition
| In phagocytosis, the plasma membrane of a cell surrounds a smaller cell or food particle and engulfs it. The resulting structure is delivered to a lysosome, where it is taken in and digested |
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Definition
| In autophagy, damaged organelles are surrounded by a membrane and delivered to a lysosome. There the components are digested and recycled. |
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Term
| receptor–mediated endocytosis |
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Definition
| In receptor–mediated endocytosis, macromolecules outside the cell bind to membrane proteins that act as receptors. The plasma membrane folds in and pinches off to form an early endosome. Early endosomes then undergo a gradual maturation process that leads to formation of a late endosome and eventually a fully functioning lysosome (Figure 7.15). |
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Definition
| Endocytosis is a process by which the cell membrane can pinch off a vesicle to bring outside material into the cell. In addition to phagocytosis and receptor–mediated endocytosis, a third type of endocytosis called pinocytosis brings fluid into the cell. Pinocytotic vesicles do not go to lysosomes. |
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Definition
| Plants and fungi have very large vacuoles that function primarily as water and/or ion storage and help the cell maintain its normal volume (Figure 7.16). |
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Definition
- Mitochondria have two membranes; the inner one is folded into cristae that contain the mitochondrial matrix (Figure 7.17). ATP production is a mitochondrion's core function.
- Most of the enzymes and molecular machines responsible for synthesizing ATP are embedded in the membrane or the cristae, or suspended in the matrix.
- Mitochondria have their own DNA and their own ribosomes. They grow and divide independently of nuclear division and cell division.
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Term
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Definition
- Most plant and algal cells have chloroplasts that, like mitochondria, grow and divide independently, have a double membrane, and contain chloroplast DNA. Chloroplasts contain everything required to convert light energy to chemical energy (photosynthesis) (Figure 7.18).
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Definition
- The cytoskeleton gives the cell shape and structural stability, and aids cell movement and transport of materials within the cell.
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Definition
| Fungi, algae, and plants have a stiff outer cell wall that protects the cell (Figure 7.19). |
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| How Does Cell Structure Correlate with Function? |
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Definition
- An organelle's membrane and its enzymes correlate with its function (Summary Table 7.2), and cell structure (e.g., the type, size, and number of organelles) correlates with cell function.
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Term
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Definition
- Biologists study the structure and function of organelles and cells using a combination of tools and approaches, including light and transmission microscopy and differential centrifugation.
- Cells are dynamic living things with interacting parts and constantly moving molecules.
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