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Structures and Functions
CELLS Structures and Functions
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Basic Parts of the Cell Plasma membrane – barrier between in and outside of cell Cytoplasm – region inside plasma membrane Cytosol – includes molecules and small particles but not organelles Genetic material Ribosomes
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Organelles! Eukaryotic Cell
Nucleus
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The Nucleus Most obvious structure (5μm)
Most eukaryotic cells contain a nucleus Function: Controls most functions of cell Houses and protects genetic information Structure: Nuclear envelope – double membrane layer contains genetic contents; porous – materials enter and exit Nucleoplasm – jelly like fluid filling nucleus Nucleolus – dense area where ribosomes are made
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Processes: Cell Division When cell is not dividing - DNA exists as chromatin: long, thin structures When cell is about to divide - DNA condenses to form chromosomes: structures made of DNA and protein Transcription – DNA converted to RNA in the nucleus
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Chromatin Cell Division Chromosome
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Mitochondria
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Mitochondria Size: 1-10 μm long Function:
Transfer energy from organic molecules to adenosine triphosphate (ATP) – powers most cellular reactions Structure: inner & outer membrane Outer – separates mitochondria from cytosol Inner – many folds (cristae) that capture and store energy Mitochondrial DNA – have own DNA THEORY: mitochondria originated from prokaryotic cells
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Processes: Cellular respiration – enzymes in matrix aid in formation of ATP by extracting energy from food sources
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Ribosomes
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Ribosomes small, spherical (< 25 nanometers) Function:
Build proteins Free ribosomes – make proteins used in cytosol (Ex: enzyme) Bound ribosomes – make proteins used in membranes, packaging, and elsewhere in body Structure: Manufactured partly in nucleolus (protein & RNA), completed in cytoplasm Have small and large subunit
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Endoplasmic Reticulum
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Endoplasmic Reticulum (ER)
System of cisternae - membranous tubes & sacs Continuous with nuclear membrane Function – moves molecules from one part of the cell to another Structure – Rough and Smooth Rough ER – covered with ribosomes; involved in making proteins Secretory proteins – secreted in vesicles (Ex: digestive enzymes) Membrane proteins – inserted in membranes Smooth ER – no ribosomes; builds lipids, produces steroid hormones, detoxifies drugs and poisons
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Golgi Apparatus
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Golgi Apparatus System of cisternae stacked up Function:
Manufacturing, warehousing, sorting, shipping Work with nearby vesicles coming from ER – vesicle contents modified, given “address label (carbohydrate label),” transported to other parts of cell Structure: Distinct polarity – membranes on opposite ends have different thickness & molecular composition Two poles: Cis (same side) – receives materials from ER Trans (opposing side) – vesicles bud off & are transported/exported
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Vesicles Small, spherical shaped sacs Function: Structure:
Migrate to and merge with cell membrane Release contents outside of cell Structure: Single membrane Different types (lysosomes, peroxisomes)
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Lysosomes Structure – bud from Golgi, contain digestive enzymes – each vesicle is specific! Function – Break down macromolecules (proteins, carbohydrates, nucleic acids) Processes: Autophagy – Digestion of worn-out organelles Autolysis – Digestion of damaged or extra cells when time for cell to die Phagocytosis – Cell eating Receptor-mediated endocytosis
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Vesicles
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Peroxisomes NOT produced in Golgi, contain different enzymes, such as Catalase Different types: Ex: Detoxify alcohol and other drugs Break down fatty acids
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Vacuole Membrane bound storage structures, contains fluid Types:
Food – stores nutrients Contractile – contract, dispose of excess water
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Vacuoles Centriole
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Centrioles Animal cells ONLY! Organize cell structure during division
2 short cylinders of microtubules
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Part of cytoskeleton
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Cytoskeleton Provides shape and support 3 structural elements
Microfilaments (Actin)- 2 strands intertwined; POLAR – can be used in cell movement, muscle contraction, cell division Intermediate fibers – NONPOLAR - anchor nucleus and other organelles in place, maintain shape Microtubules – hollow tubes made of maintain cell shape, hold organelles in place, POLAR – used in movement of chromosomes during division & organelles (like a railroad track) via the use of kinesins
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