Cell Parts (Chapter 6)

microtubules

A hollow rod composed of tubulin proteins that makes up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella. main functions: maintainence of cell shape (compression-resisting girders), cell motility as in cilia or flagella, chromosome movements in cell division, organelle movements (biggest)

vacuoles

A membrane-bounded vesicle whose specialized function varies in different kinds of cells. derived from the ER and GA. integral part of a cell's endomembrane system. This membrane is selective in transporting solutes; as a result the solution inside a vacuole differs in composition from the cytosol. 3 diff types are food, contracile, and central.

smooth ER

That portion of the endoplasmic reticulum that is free of ribosomes. Outer surface lacks them. Functions in diverse metabolic processes, which vary with cell type. These processes include synthesis of lipids, metabolism of carbohydrates, detoxification of drugs and poisions, and storage of calcium ions.

rough ER

That portion of the endoplasmic reticulum with ribosomes attached. Many types of cells secrete proteins produced by ribosomes attached to rough ER. For ex, certain pancreatic cells synthesize the protein insulin in the ER and secrete this hormone into the bloodstream. As a polypeptide chain grows from a bound ribosome, the chain is threaded into the ER lumen through a pore formed by a protein complex in the ER membrane. As a new polypeptide enters the ER lumen, it folds into its native shape. Most secretory proteins are glycoproteins, proteins that have carbs covalently bonded to them. The carbs are attached to the proteins in the ER by enzymes built into the ER membrane. After secretory proteins are formed, the ER membrane keeps them separate from proteins that are produced by free ribosomes and that will remain in the cytosol. Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called transitional ER. Vesicles in transit from one part of the cell to another are called transport vesicles. In addition to making secretory proteins rough ER is a membrane factory for the cell. It grows in place by adding membrane proteins and phospholipids to its own membrane. As polypeptides destined to be membrane proteins grow from the ribosomes they are inserted into the ER membrane itself and anchored there by their hydrophobic portions. Like the smooth ER, the rough ER also makes membrane phospholipids; enzymes built into the ER membrane assemble phospholipids from precursors in the cytosol. The ER membrane expands and portions of it are transferred in the form of transport vesicles to other components of the endomembrane system.

intermediate filaments

a component of the cytoskeleton that includes filaments intermediate in size between microtubules and microfilaments. specialized for bearing tension . each type is constructed from a particular molecular subunit belonging to a family of proteins whose members include the keratins. ______ are more permanent fixtures of cells than are microfilaments and microtubules which are often disassembled and reassembled in various parts of a cell. 8-12 nanometers

flagella

a long cellular appendage specialized for locomotion. like motile cilia eukaryotic flagella have a core with 9 outer doublet microtubules and two inner single microtubules (the 9+2 arrangement) ensheathed in an extension of the plasma membrane. Prokaryotic flagella have a different structure.

peroxisomes

an organelle containing enzymes that transfer hydrogen atoms from various substrates to oxygen, producing and then degrading hydrogen peroxide. specialized metabolic compartment bounded by a single membrane.

Golgi apparatus

an organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and routeproducts of the endoplasmic reticulum and synthesize some products, notably noncellulose carbohydrates. After leaving the ER, many transport vesicles travel here. A warehouse for receiving, sorting, shipping, and even some manufacturing. Here, products of the ER, such as proteins, are modified and stored and then sent to other destinations. Not surpisingly, the ____ is especially extensive in cells specialized for secretion. Consists of stacks of flattened sacs, or cisternae, which, unlike ER cisternae, are not physically connected. A __(first word)__ stack receives and dispatches transport vesicles and the products they contain. A __(first word)___ stack has a structural and functional directionality, with a cis face that recieves vesicles containing ER products and a trans face that dispatches vesicles. The cisternal maturatin model proposes that the Golgi cisternae themselves "mature" moving from the cis to the trans face while carrying some proteins along. In addition, some vesicles recycle enzymes that had been carried forward in moving cisternae, transporting them "backward" to a less mature region where their functions are needed.

endomembrane system

as the membrane moves from the ER to the GA and then elsewhere, its molecular comp and metabolic functins are modified along with those of its contents. The _____ is a complex and dynamic player in the cell's compartmental organization.

endosymbiosis

the theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by an ancestral eukaryotic cell. The engulfed cell and its host cell then involved into a single organism (eventually the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont - a cell living within another cell). The endosymbiont theory of the origin of mitochondria and chloroplasts in eukaryotic cells. According to this theory, the proposed ancestors of mitochondria were oxygen-using nonphotosynthetic prokaryotes, while the proposed ancestors of chloroplasts were photosynthetic prokaryotes.

Nucleolus

(plural, nucleoli) a specialized structure in the nucleus, consisting of chromosomal regions containing ribosomal RNA (rRNA) genes along with ribosomal proteins imported from the cytoplasm; site of rRNA synthesis and ribosomal subunit assembly. a prominent structure within the nondividing nucleus. Appears through the electron microscope as a mass of densely stained granules and fibers adjoining part of the chromatin. Here a type of RNA called ribosomal RNA (rRNA) is synthesized from instructions in the DNA. Also in the _______, proteins imported from the cytoplasm are assembled with the rRna into large and small units of ribosomes. These subunits then exit the nucleus through the nuclear pores to the cytoplasm, where a large and a small subunit can assemble into a ribosome. Sometimes, there are two or more nuclei; the number depends on the species and the stage in the cell's reproductive cycle.

nucleus

1) an atom's central core, containing protons and neutrons. 2) the organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made up of chromatin. 3) a cluster of neurons. contains most of the genes in the eukaryotic cell. (Some genes are located in mitochondria and chloroplasts). It is generally the most conspicuous organelle in a eukaryotic cell, averaging about 5 micrometers in diameter. It is enclosed by the nuclear envelope.

Microfilaments

A cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction; also known as an actin filament. Structural role of microfilaments is to bear tension (pulling forces). Well-known for their role in cell motility. 7 nanometers

ribosomes

A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucelolus. complexes made of ribosomal RNA and protein. They are the cellular components that carry out protein synthesis. Cells that have high rates of protein synthesis have particularly large numbers of ribosomes. For example, a human pancreas cell has a few million ribosomes. Not surprisingly, cells active in protein synthesis also have prominent nuclei. Ribosomes build proteins in 2 cytoplasmic locales. At any given time, free ribosomes are suspended in the cytosol, while bound ribosomes are attached to the outside of the endoplasmic reticulum or nuclear envelope. Bound and free ribosomes are structurally identical, and ribosomes can alternate between the two roles. Most of the proteins made on free ribosomes function within the cytosol; examples are enzymes that catalyze the first steps of sugar breakdown. Bound ribosomes generally make proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes or for export from the cell (secretion).

lysosomes

A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists. A membranous sac of hydrolytic enzymes that an animal cell uses to digest (hydrolyze) macromolecules. ______ enzymes work best in the acidic environment found in found in ______. If a _____ breaks open or leaks its contents, the released enzymes are not very active because the cytosol has a neutral pH. However, excessive leakage from a large number of _____ can destroy a cell by self-digestion. Hydrolytic enzymes and _____ membrane are made by rough ER and then transferred to the GA for further processing. At least some ____ probably arise from budding from the trans face of the GA. ____ carry out intracellular digestion in a variety of circumstances. ____ also use their hydrolytic enzymes to recycle the cell's own organic material, a process called autophagy.

cell wall

A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists; protects the cell and helps maintain its shape. polysaacharides such as cellulose (in plants and some protists), chitin (in fungi), and peptidoglycan (in bacteria) are important structural components of cell walls. also prevents excessive uptake of water. much thicker than plasma membrane. parts are primary cell wall, middle lamella, secondary cell wall

centriole

A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a 9 + 0 pattern. A centrosome has a pair of _______ s.

chloroplasts

Capture energy from sunlight and use it to produce food for the cell. contain green pigment chlorophyll. Found in leaves and other organs of plants and in algae. contents of chloroplast partitioned from the cytosol by an envelope consisting of 2 membranes separated by a very narrow intermembrane space. Chloroplasts contain thylakoids, granum, and stroma.

cytoskeleton

a network of microtubules, microfilaments, and intermediate filaments that extend throughout the cytoplasm and serve a variety of mechanical, transport, and signaling functions. composed of three types of molecular structures: microtubules. microfilaments, and intermediate filaments. gives mechanical support to cell and maintains its shape. provides anchorage for many organelles and even cytosolic enzyme molecules. several types of motility aka movement involve it. cell motility involves its interaction with motor proteins. _____ elements and motor proteins work together w plasma membrane molecules to allow whole cells to move along fibers outside of the cell. Inside cell vesicles and other organelles often use motor protein feet to walk to their destinations along a track provided by the cytoskeleton. The _____ also manipulates the plasma membrane, making it bend inward to form food vacuoles or other phagocytic vesicles.

cilia

a short appendage containing microtubules in eukaryotic cells. a motile cilium is specialized for locomotion or moving fluid past the cell. It is formed from a core of nine outer doublet microtubules and two inner single microtubules (the 9+2 arrangement) ensheathed in an extension of the plasma membrane. A primary cilium is usually nonmotile and plays a sensory and signaling role; it lacks the two inner microtubules (the 9+0 arrangement).

Prokaryotic cells

a type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with ___________ (bacteria and archaea) are called prokaryotes. In this type of cell, the DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid. This type of cell evolved before eukaryotic cells.

Eukaryotic cells

a type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with _____ (protists, plants, fungi, and animals) are called eukaryotes. In this type of cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane.

mitochondria

found in nearly all eukaryotic cells, including those of plants animals fungi and most protists. Some cells have a single large one, but more often a cell has hundreds or thousands of mitochondria. number correlates with cell's level of metabolic activity. For ex, cells that move or contract have proportionally more mitochondria per volume than less active cells. 1) outer membrane-smooth inner membrane-convoluted w/ infoldings called cristae. Inner membrane divides it into 2 internal compartments 2) first compartment - intermembrane space that is narrow region between inner and outer membranes. second compartment- mitochondrial matrix, enclosed by inner membrane.

endomembrane system

the collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, and vacuoles. This carries out a variety of tasks in the cell, including synthesis of proteins, transport of proteins into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons. The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles. Despite these relationships, the various membranes aren't identical in structure and function. Moreover, the thickness, molecular composition, and types of chemical reactions carried out in a given membrane are not fixed, but may be modified several times during the membrane's life. Having already discussed the nuclear envelope, we will now focus on the endoplasmic reticulum and the other endomembranes to which the endoplasmic reticulum gives rise.

extracellular matrix

the meshwork surrounding animal cells consisting of glycoproteins, polysaccharides, and proteoglycans synthesized and secreted by the cells. although animals lack walls like plant cells, they have _____. _____ of most animals is collagen. embodied in a network woven out of proteoglycans secreted by cells.