Chapter 6 - Tour of the Cell

2. Describe the structure and function of the components of the endomembrane system

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How do lysosomes go about carrying out intracellular digestion in the cell?

Amoebas and many other protists eat by engulfing smaller organisms or food particles in a process called phagocytosis. The food vacuole formed in this way then fuses with a lysosome, whose enzymes digest the food.

What makes intermediate filaments more permanent fixtures of cells when compared to microfilaments and microtubules, which are often disassembled and reassembled in various parts of a cell?

Even after cells die, intermediate filament networks often persist; for example, the outer layer of our skin consists of dead skin cells full of keratin proteins. Chemical treatments that remove microfilaments and microtubules from the cytoplasm of living cells leave a web of intermediate filaments that retains its original shape. Such experiments suggest that intermediate filaments are especially sturdy and that they play an important role in reinforcing the shape of a cell and fixing the position of certain organelles. For instance, the nucleus typically sits within a cage made of intermediate filaments, fixed in location by branches of the filaments that extend into the cytoplasm.

Where are mitochondria found in nature?

Mitochondria are found in nearly all eukaryotic cells, including those of plants, animals, fungi and most protists.

How does the Golgi stack go about sort its products and delivering them to the necessary locations in the cell?

Molecular identification tags, such as phosphate groups added to the Golgi products, aid in sorting by acting like ZIP codes on mailing labels. Finally transport vesicles budded from the Golgi may have internal molecules on their membranes that recognize "docking sites" on the surface of specific organelles or on the plasma membrane, thus targeting the vesicles appropriately.

Where do most of the proteins made on free ribosomes function?

Most of them function within the cytosol. An example are enzymes that catalyze the first steps of sugar breakdown.

To understand the function of each cell structure requires the integration of cytology and __________

biochemistry

What is the nucleolus and where is it located?

The nucleolus is a prominent structure within the nondividing nucleus, which appears through the electron microscope as a mass of densely stained granules and fibers adjoining part of the chromatin.

What area of the cell contains most of the genes in the eukaryotic cell?

The nucleus. (Some genes are located in mitochondria and chloroplasts.)

What is sol?

it is a fluid suspension of a colloidal solid in a liquid.

What kind of cells do the domains Bacteria and Archaea consist of?

prokaryotic

What does interdigitated mean?

(of two or more things) interlock like the fingers of two clasped hands..

How do enzymes of the smooth ER help detoxify drugs and poisons?

Detoxification usually involves adding hydroxyl groups to molecules, making them more soluble and easier to flush from the body. Phenobarbital and other barbiturates are examples of drugs that are metabolized via the addition of hydroxyl groups.

What is a food vacuole?

It is a membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell.

What is a lysosome?

It is a membranous sac of hydrolytic enzymes that an animal cell uses to digest (hydrolyze) macromolecules.

What is a contractile vacuole?

It is a membranous sac that helps remove excess water out of certain freshwater protists. A contractile vacuole, helps maintain a suitable concentration of ions and molecules inside the cell.

What is a neurotransmitter?

It is a molecule that is released from the synaptic terminal of a neuron at a chemical synapse, diffuses across the synaptic cleft, and binds to the postsynaptic cell, triggering a response.

Define plastid

It is one of a family of closely related organelles that includes chloroplasts, chromoplasts, and amyloplasts. Plastids are found in cells of photosynthetic eukaryotes.

What is cytology?

the study of cell structure

Are vacuoles selective in transporting solutes?

Yes, like all cellular membranes, the vacuolar membrane is selective in transporting solutes; as a result, the solution inside a vacuole differs in composition from the cytosol.

How can you increase the rate of detoxification?

You can increase the rate of detoxification by increasing your intake of alcohol and other drugs. The intake of these drugs will induce the growth of smooth ER and its associated detoxification enzymes, which increases the rate of detoxification.

What is an organelle?

the membrane-enclosed structures within eukaryotic cells

What are vacuoles?

Vacuoles are large vesicles derived from the endoplasmic reticulum and Golgi apparatus. Thus, vacuoles are an integral part of a cell's endomembrane system.

What is an ovule?

An ovule is a structure that develops within the ovary of a seed plant and contains the female gametophyte.

What are chloroplasts known for?

Chloroplasts are known for being the site of photosynthesis, where the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar.

How do plant cells strengthen their walls?

When the cell matures and stops growing, it strengthens its wall. Some plant cells do this simply by secreting hardening substances into the primary wall. Others add a secondary cell wall between the plasma membrane and the primary wall.

What is the cortex?

(1) It is the outer region of cytoplasm in a eukaryotic cell, lying just under the plasma membrane, that has a more gel-like consistency than the inner regions due to the presence of multiple microfilaments. (2) In plants, ground tissue that is between the vascular tissue and dermal tissue in a root or eudicot stem.

1. Distinguish between the following pairs of terms: prokaryotic and eukaroytic cell; free and bound ribosomes; smooth and rough ER

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5. Compare the structure and functions of microtubules, microfilaments, and intermediate microfilaments

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6. Explain how the ultrastructure of cilia and flagella relate to their specific functions

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7. Describe the structure of a plant cell wall

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8. Describe the structure and roles of the extracellular matrix in animal cells

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9. Describe four different intercellular junctions

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Briefly explain the role of mitochondria and chloroplasts

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Describe the functions of the cytoskeleton

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Prokaryotic cells have which 4 distinguishing features?

1. No nucleus 2. DNA in an unbound region called the nucleoid 3. No membrane-bound organelles 4. Cytoplasm bound by the plasma membrane

What are the 4 basic features of all cells?

1. Plasma membrane (selective barrier allows enough O, nutrients, & wastes to service entire cell) 2. Semifluid (jellylike) substance called cytosol (in which subcellular components are suspended) 3. Chromosomes (carry genes in form of DNA) 4. Ribosomes (tiny complexes make/synthesize proteins per instructions from genes)

What is a basal body?

A basal body is a eukaryotic cell structure consisting of a "9+0" arrangement of microtubule triplets. The basal body may organize the microtubule assembly of a cilium or flagellum and is structurally very similar to a centriole. In many animals (including humans) the basal body of the fertilizing sperm's flagellum enters the egg and becomes a centriole.

What is a centriole?

A centrosome has a pair of centrioles within it. Each centriole is composed of nine sets of triplet microtubules that are arranged in a ring. Before an animal cell divides, the centrioles replicate. Although centrosomes with centrioles may help organize microtubule assembly in animal cells, they are not essential for this function in all eukaryotes; fungi and almost all plant cells lack centrosomes with centrioles but have well-organized microtubules. Apparently, other microtubules organizing centers play the role of centrosomes in these cells.

What is another role that cilium play aside from being the means of locomotion for a cell.

A cilium may also act as a signal-receiving "antenna" for the cell. Cilia that have this function are generally nonmotile, and there is only one per cell. (In fact, in vertebrate animals, it appears that almost all cells have a cilium, which is called a "primary cilium"). Membrane proteins on this kind of cilium transmit molecular signals from the cell's environment to its interior, triggering pathways that may lead to changes in the cell's activities. Cilium-based signaling appears to be crucial in brain function and to embryonic development. (Wow the picture of the cross sections of the flagella and cilia are beautiful.)

What are the differences in the beating patterns of flagella and cilia?

A flagellum has an undulating motion that generates force in the same direction as the flagellum's axis, like the tail of a fish. In contrast, cilia work more like oars, with alternating power and recovery strokes generating force in a direction perpendicular to the cilium's axis, much as the oars of a racing crew boat extend outward at a right angle to the boat's forward movement.

What are lysosomes?

A lysosome is a membrane enclosed sac of hydrolytic (water breaking) enzymes found in the cytoplasm of animal cells and some protists.

What are the mechanics of dynein based bending that are involved in a process that resembles walking?

A typical dynein protein has two "feet" that "walk" along the microtubule of the adjacent doublet, one foot maintaining contact while the other releases and reattaches one step farther along the microtubule. Without any restraints on the movement of the microtubule doublets, one doublet, would continue to "walk" along and slide past the surface of the other, elongating the cilium or flagellum rather than bending it.

Define what microtubules are and give me a description of them.

All eukaryotic cells have microtubules, which are hollow rods measuring about 25 nm in diameter and from 200 nm to 25 microns in length. (Pill shaped - longer than they are wide.) The wall of the hollow tube is constructed from globular protein called tubulin. Each tubulin is a dimer (which is a molecule made up of two subunits). A tubulin dimer consists of two slightly different polypeptides, alpa-tubulin and beta-tubulin. Microtubules grow in length by adding tubulin dimers; They can also be dissembled and their tubulin used to build microtubules elsewhere in the cell.

What are some human cells that carry out phagocytosis?

Among the human cells that carry out phagocytosis are macrophages, a type of white blood cell that helps defend the body by engulfing and destroying bacteria and other invaders

What is an electron microscope?

An electron microscope is a microscope that uses a beam of electrons to illuminate a specimen and produce a magnified image.

How are the proteins of the inner surface of the lysosomal membrane and the digestive enzymes themselves spared from destruction?

Apparently, the three-dimensional shapes of these proteins protect vulnerable bonds from enzymatic attack.

Explain the process of how a polypeptide chain goes from the rough ER 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 the new polypeptide enters the ER lumen, it folds into its native shape. The polypeptide becomes classified as a secretory protein as carbohydrates are bonded to it in the ER lumen. The secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called transitional ER.

Where are the two cytoplasmic locales that ribosomes build proteins located?

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).

What is functions does the nucleolus carry out?

At the site of nucleolus, ribosomal RNA (rRNA) is synthesized from the instructions in the DNA. Also in the nucleolus, proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes.

What role do tight junctions play in animal cells?

At tight junctions, the plasma membranes of neighboring cells are very tightly pressed against each other, bound together by specific proteins (purple). Forming continuous seals around the cells, tight junctions prevent the leakage of extracellular fluid across a layer of epithelial cells. For example, tight junctions between skin cells make us watertight by preventing leakage between cells in our sweat glands.

Why is the ratio of surface area to volume critical for each square micrometer (µm) of membrane?

Because only a limited amount of a particular substance can cross per second

Where is the middle lamella located and what is its function?

Between the primary walls of adjacent cells is the middle lamella, a thin layer rich in sticky polysaccharides called pectins. (Pectin is used as a thickening agent in jams and jellies.)The middle lamella glues adjacent cells together.

What is current research on fibronectin, other ECM molecules, and integrins revealing about the influential role of the extracellular matrix in the lives of cells?

By communicating with a cell through integrins, the ECM can regulate a cell's behavior. For example, some cells in a developing embryo migrate along specific pathways by matching the orientation of their microfilaments to the "grain" of fibers in the ECM. Researchers have also learned that the ECM around a cell can influence the activity of genes in the nucleus (Awesome). Information about the ECM probably reaches the nucleus by a combination of mechanical and chemical signaling pathways. Mechanical signaling involves fibronectin, integrins, and microfilaments of the cytoskeletin. Changes in the cytoskeleton may in turn trigger chemical signaling pathways inside the cell, leading to changes in the set of proteins being made by the cell and therefore changes in the cell's function.

How are cells usually organized in animals or plants?

Cells in animals and plants are organized into tissues, organs, and organ systems. Neighboring cells often adhere, interact, and communicate via sites of direct physical contact.

What is chromatin?

Chromatin is the complex of DNA and proteins making up the chromosome.

What is the difference between the cytoplasm in a eukaryotic cell and the cytoplasm in a prokaryotic?

Cytoplasm in a eukaryotic cell refers only to the region between the nucleus and the plasma membrane which encloses (in cytosol) a variety of organelles of specialized form/function<--these membrane-bounded structures are not present in prokaryotic cells

Describe the process of cell motility.

Cytoskeletal elements and motor proteins work together with plasma membrane molecules to allow whole cells to move along fibers outside the cell. Motor proteins bring about the bending of cilia and flagella by gripping microtubules within those organelles and sliding them against each other. A similiar mechanism involving microfilaments causes muscle cells to contract. Inside the cell, vesicles and other organelles often use motor protein "feet" to "walk" to their destinations along a track provided by the cytoskeleton. (Haha this is very similiar to traintracks [cytoskeleton] and a train [motor proteins] and the passengers [vesicles and other organelles].)

What is cytosol?

Cytosol is the semifluid portion of the cytoplasm.

What are the functions of the plasmodesmata?

Cytosol passes through the plasmodesmata and joins the internal chemical environment of adjacent cells. These connections unify most of the plant into one living continuum. The plasma membranes of adjacent cells line the channel of each plasmodesma and thus are continuous. Water and small solutes can pass freely from cell to cell, and recent experiments have shown that in some circumstances, certain proteins and RNA molecules can also do this. The macromolecules transported to neighboring cells appear to reach the plasmodesmata by moving along fibers of the cytoskeleton. (Analogous to traveling to the border of states and going through the border control - How interesting).

What role do desmosomes play in animal cells?

Desmosomes (also called anchoring junctions) function like rivets, fastening cells together into strong sheets. Intermediate filaments made of sturdy keratin proteins anchor desmosomes in the cytoplasm. Desmosomes attach muscle cells to each other in a muscle. Some "muscle tears" involve the rupture of desmosomes.

Describe what happens during autophagy?

During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane and a lysosome fuses with the outer membrane of this vesicle. The lysosomal enzymes dismantle the enclosed material, and the organic monomers are returned to the cytosol for reuse. With the help of lysosomes, the cell continually renews itself. A human liver cell, for example, recycles half of its macromolecules each week.

What is extracellular matrix (ECM)?

ECM is the meshwork surrounding animal cells, akin to the walls of plant cells. The main ingredients of ECM are glycoproteins and other carbohydrate containing molecules secreted by the cells. (Recall that glycoproteins are proteins with covalently bonded carbohydrate, usually short chains of sugars.)

How many DNA molecules lie within a single chromosome?

Each chromosome contains one long DNA molecule that is associated with many proteins.

What is a motor protein?

It is a protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell.

What is a amoeba?

It is a protist grade characterized by the presence of a pseudopodia?

Describe some of the structural features of mitochondria and chloroplasts that make them similiar to prokaryotes.

First, rather than being bound by a single membrane like organelles of the endomembrane system, mitochondria and chloroplasts have two membranes surrounding them. Second like prokaryotes, they contain ribosomes, as well as circular DNA molecules attached to their inner membranes. The DNA in these organelle programs the synthesis of some of their own proteins, which are made on the ribosomes inside the organelles. Third, also consistent with their probable evolutionary origins as cells, mitochondria and chloroplasts are autonomous organelles that grow and reproduce within the cell.

How are the products of the ER modified during their transit from the cis region to the trans region of the Golgi apparatus.

For example, glycoproteins formed in the ER have their carbohydrates modified, first in the ER itself, then as they pass through the Golgi. The Golgi removes some sugar monomers and substitutes others, producing a large variety of carbohydrates. Membrane phospholipids may also be altered in the Golgi.

What are the mechanics of dynein based bending that involve the lateral movement of cilium or flagellum?

For lateral movement of a cilium or flagellum, the dynein "walking" must have something pull against, as when the muscles in your leg pull against your bones to move your knee. In cilia and flagella, the microtubule doublets seem to be held in place by the cross-linking proteins just inside the outer doublets and by the radial spokes and other structural elements. Thus, neighboring doublets cannot slide past each other very far. Instead, the forces exerted by dynein "walking" cause the doublets to curve, bending the cilium or flagellum.

What role do gap junctions play in animal cells?

Gap junctions (also called communicating junctions) provide cytoplasmic channels from one cell to adjacent cell and in this way are similar in their function to the plasmodesmata in plants. Gap junctions consist of membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass. Gap junctions are necessary for communication between cells in many types of tissue.

What are glycoproteins?

Glycoproteins are proteins that have carbohydrates covalently bonded to them. The carbohydrates are attached to the proteins in the ER by enzymes built into the ER membrane.

What happens in Tay-Sachs disease?

In Tay-Sachs disease, a lipid digesting enzyme is missing or inactive in the lysosomes, and the brain becomes impaired by an accumulation of lipids in the cells. (An analogous situation would be a city (cell) that has all of its garbage pick up dudes on strike (lysosomes with impaired/missing enzymes) therefore overtime the city begins to fall apart).

What happens to the plant cell wall in actively growing plant cells?

In actively growing cells, the cellulose fibrils are oriented at right angles to the direction of cell expansion. Observations by researchers strongly support the idea that microtubules in the cell cortex guide cellulose synthase as it synthesizes and deposits cellulose fibrils. By orienting cellulose deposition, microtubules thus affect the growth pattern of the cells.

What is a dynein?

In cilia and flagella, dynein is a large motor protein extending from one microtubule doublet to the adjacent doublet. ATP hydrolysis drives changes in dynein shape that lead to bending of cilia and flagella. Dyneins are responsible for the bending movements of the organelle. A dynein molecule performs a complex cycle of movements by changes in the shape of the protein, with ATP providing the energy for these changes.

What makes microfilaments different from microtubules?

In contrast to the compression resisting role of microtubules, the structural role of microfilaments in the cytoskeleton is to bear tension (pulling forces). A three-dimensional network is formed by microfilaments just inside the plasma membrane (cortical microfilaments) helps support the cell's shape. (Ah these guys are kind of the underlying steel bars in buildings!). This network gives the outer cytoplasmic layer of a cell, called the cortex, the semisolid consistency of a gel, in contrast with the more fluid state of the interior cytoplasm. In animal cells specialized for transporting materials across the plasma membrane, such as intestinal cells, bundles of microfilaments make up the core of microvilli, delicate projects that increase the cell's surface area.

What are ovaries?

In flowers, the ovary, is the portion of a carpel in which the egg containing ovules develop. In animals, the ovary, is the structure that produces female gametes and reproductive hormones.

How does smooth ER store calcium ions?

In muscle cells, for example, the smooth ER membrane pumps calcium ions from the cytosol into the ER lumen. (I remember this from Sal's lecture!). When a muscle cell is stimulated by a nerve impulse (motor neuron that release acetylcholine!), calcium ions rush back across the ER membrane into the cytosol and trigger contraction of the muscle cell.

What is the function of a vacuole in plants and fungi?

In plants and fungi, certain vacuoles carry out enzymatic hydrolysis, a function shared by lysosomes in animal cells. (In fact, some biologists consider these hydrolytic vacuoles to be a type of lysosome.)

What is a primary cell wall?

In plants, it is a relatively thin and flexible layer that surrounds the plasma membrane of a young cell. A young plant cell first secretes this. In actively growing cells, the cellulose fibrils are oriented at right angles to the direction of cell expansion.

What are some other functions of vacuoles inside plants aside from carrying out enzymatic hydrolysis?

In plants, smaller vacuoles can hold reserves of important organic compounds, such as the proteins stockpiled in the storage cells in seeds. Vacuoles may also help protect the plant against herbivores by storing compounds that are poisonous or unpalatable to animals. Some plant vacuoles contain pigments, such as red and blue pigments of petals that help attract pollinating insects to flowers.

Where is the protein insulin synthesized in the body?

Insulin is synthesized in certain pancreatic cells, in the rough ER. From the rough ER insulin is secreted into the blood stream where it unlocks the door of cells in order to let glucose enter!

What are integrins?

Integrins are membrane proteins with two subunits, that bind to the ECM on one side and to associated proteins attached to microfilaments on the other side. This linkage can transmit signals between the cell's external environment and its interior and can result in changes in cell behavior. The name integrin is based on the word integrate.

What are some places in the human body, where intermediate filaments are found?

Intermediate filaments make up the nuclear lamina, which lines the interior of the nuclear envelope. By supporting a cell's shape, intermediate filaments help the cell carry out its specific function. For example, the long extensions (axons) of nerve cells that transmit impulses are strengthened by intermediate filaments. Thus, the various kinds of intermediate filaments may function together as the permanent framework of the entire cell.

What are the functions of a large central vacuole in mature plant cells?

The solution inside the central vacuole called cell sap, is the plant cell's main repository of inorganic ions, including potassium and chloride. The central vacuole plays a major role in the growth of plant cells, which enlarge as the vacuole absorbs water, enabling the cell to become larger with a minimal investment in new cytoplasm.

What does the membrane of the ER enclose?

It encloses a continuous compartment called the ER lumen (or cisternal space).

What is a microfilament?

It is a cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell. (This reminds me of a bunch of giant fiber optic cables lining the sea floor). Microfilaments make up part of the cytoskeleton and acting alone or with myosin to cause cell contraction; also know as an actin filament. Microfilaments are solid rods about 7 nm in diameter. A microfilament is a twisted double chain of actin subunits. Besides occurring as linear filaments, microfilaments can form structural networks when certain proteins bind along the side of an actin filament and allow a new filament to extend as a branch.

What is a pseudopodium?

It is a cellular extension of amoeboid cells used in moving and feeding.

What is hydrolysis?

It is a chemical reaction that breaks bonds between two molecules by the addition of water; it functions in the disassembly of polymers into monomers.

What is cytoplasmic streaming?

It is a circular flow of cytoplasm, involving interactions of myosin and actin filaments, that speeds the distribution of materials within cells. This movement is especially common in large plant cells, speeds the distribution of materials within the cell.

What is an intermediate filament?

It is a component of the cytoskeleton that includes filaments intermediate in size between microtubules and microfilaments. They are named for their diameter, which is 8-12 nm, larger than the diameter of microfilaments but smaller than that of microtubules. They are specialized for bearing tension (like microfilaments). They are a diverse class of cytoskeletal elements. Each type is constructed from a particular molecular subunit belong to a family of proteins whose members include keratins.

What is keratin?

It is a fibrous protein forming the main structural constituent of hair, feathers, hoofs, claws, horns, etc.

What is a thylakoid?

It is a flattened, membranous sac inside a chloroplast. Thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular "machinery" used to convert light energy to chemical energy.

What is the function of the pancreas?

It is a gland with exocrine and endocrine tissues. The exocrine portion functions in digestion (eating food), secreting enzymes and an alkaline solution into the small intestine via a duct; The ductless endocrine portion functions in homeostasis, secreting the hormones insulin and glucagon into the blood (Insulin are the keys that open up the doors in order to allow glucose into cells, which is then broken down into energy for us to use daily!)

What is actin?

It is a globular protein that links into chains, two of which twist helically about each other (similiar to DNA I think) forming microfilaments (actin filaments) in muscle and other kinds of cells.

What is collagen?

It is a glycoprotein in the ECM of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom. In fact collagen accounts for about 40% of the total protein in the human body. The collagen fibers are embedded in a network woven out of proteoglycans secreted by cells.

What is glucagon?

It is a hormone secreted by pancreatic alpha cells that raises blood glucose levels. It promotes glycogen breakdown and release of glucose by the liver. (I assume that this mechanism is used when someone has not eaten enough food, so the body must release glucagon to unlock the glycogen - the stored energy - in order for us to break down and use for energy to exist.)

What is a proteoglycan?

It is a large molecule consisting of a small core protein with many carbohydrate chains attached, found in the extracellular matrix of animal cells. A proteoglycan may consist of up to 95% carbohydrate.

What is a flagellum (plural flagella)?

It is a long cellular appendage specialized for locomotion. Like motile cilia, eukaryotic flagella have a core with nine outer doublet microtubules (like the centriole - but not triplet) and two inner single microtubules ensheathed in an extension of the plasma membrane. Prokaryotic flagella have a different structure.

Define vesicle

It is a membranous sac in the cytoplasm of a eukaryotic cell. (It can contain proteins).

What is phenobarbital?

It is a narcotic and sedative barbiturate drug used chiefly to treat epilepsy.

What is the cytoskeleton?

It is a network of microtubules, microfilaments, and intermediate filaments that extend throughout the cytoplasm and serve as a variety of mechanical, transport, and signaling functions. (The cytoskeleton is somewhat like a highway - which can be utilized by all the molecular machinery in the cell.)

What is a cilium (plural cilia)?

It is 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 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.

What is a transport vesicle?

It is a small membranous sac in a eukaryotic cell's cytoplasm carrying molecules produced by the cell.

What is a peroxisome?

It is a specialized metabolic compartment bounded by a single membrane. Peroxisomes contain enzymes that remove hydrogen atoms from various substrates and transfer them to oxygen, thus producing hydrogen peroxide, as a by product (This is how the peroxisome got its name!).

What is a granum (plural grana)?

It is a stack of membrane bounded thylakoids in the chloroplast. Grana function in the light reactions of photosynthesis. (It reminds me of a stack of green poker chips)

What is a centrosome?

It is a structure present in the cytoplasm of animal cells that functions as a microtubule organizing center and is important during cell division. A centrosome has two centrioles. These microtubules function as compression resisting girders of the cytoskeleton.

What is an oviduct?

It is a tube passing from the ovary to the vagina in vertebrates or to the uterus in vertebrates, where it is also known as a fallopian tube.

What is myosin?

It is a type of motor protein that associates into filaments that interact with actin filaments to cause cell contraction. Like dynein when it interacts with microtubules, myosin acts as a motor protein by means of projections that "walk" along the actin filaments. Contraction of the muscle cell results from the actin and myosin filaments sliding past one another in this way, shortening the cell. In other kinds of cells, actin filaments are associated with myosin in miniature and less elaborate versions of the arrangement in muscle cells. These actin-myosin aggregates are responsible for localized contractions of cells. For example, a contracting belt of microfilaments form a cleavage furrow that pinches a dividing animal cell into two daughter cells.

What is fibronectin?

It is an extracellular glycoprotein secreted by animal cells that help them attach to the extracellular matrix.

What is the cell wall?

It is an extracellular structure of plant cells that distinguishes them from animal cells. The wall protects the plant cell, maintains its shape, and prevents excessive uptake of water. On the level of the whole plant, the strong walls of specialized cells hold the plant up against the force of gravity. Prokaryotes, fungi and some protists also have cell walls.

What is a peroxisome?

It is an organelle that contains enzymes that transfer hydrogen atoms from various substrates to oxygen, producing and then degrading hydrogen peroxide.

What is a barbiturate drug?

It is any of a class of sedative and sleep-inducing drugs derived from barbituric acid.

What is a proteoglycan complex consisted of?

It is consisted of hundreds of proteoglycan molecules attached non covalently to a single long polysaccharide molecule.

What is acetylcholine?

It is one of the most common neurotransmitters; It functions by binding to receptors and altering the permeability of the postsynaptic membrane to specific ions, either depolarizing or hyperpolarizing the membrane.

What is the endomembrane system?

It is the collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.

What is stroma?

It is the dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; it is involved in the synthesis of organic molecules from carbon dioxide and water.

Define autophagy

It is the process by which lysosomes use their hydrolytic enzymes to recycle the cell's own organic material.

What is ovulation?

It is the release of an egg from an ovary. In humans, an ovarian follicle releases an egg during each uterine (menstrual) cycle.

Define homeostasis

It is the steady-state physiological condition of the body.

What is the endosymbiont theory?

It is 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 evolved into a single organism.

What are some of the macromolecules that the Golgi apparatus manufactures?

It manufactures many polysaccharides. For example pectins and certain other noncellulose polysaccharides are made in the Golgi of plant cells and then incorporated along with cellulose into their cell walls. Like the secretory proteins, nonprotein Golgi products that will be secreted depart from the "trans" face of the Golgi inside transport vesicles that eventually fuse with the plasma membrane.

What are protists?

The term protist is an informal term applied to any eukaryote that is not a plant, animal, or fungus. Most protists are unicellular, though some are colonial or multicellular.

What makes the cytoskeleton act like a "skeleton"?

Like a dome tent, the cytoskeleton is stabilized by a balance between opposing forces exerted by its elements. And just as the skeleton of an animal helps fix the positions of other body parts, the cytoskeleton provides anchorage for many organelles and even cytosolic enzyme molecules. The cytoskeleton is more dynamic than an animal skeleton, however. It can be quickly dismantled in one part of the cell and reassembled in a new location, changing the shape of the cell.

In what type of environment do lysosomal enzymes work best?

Lysosomal enzymes work best in the acidic environment found in lysosomes. If a lysosome breaks open or leaks its contents, the released enzymes are not very active. If the lysosome 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 lysosomes can destroy a cell by self-digestion.

What organisms have cilia or flagella and what do the cilia or flagella function as?

Many unicellular eukaryotes are propelled through water by cilia or flagella that act as locomotor appendages, and the sperm of animals, algae, and some plants have flagella. When cilia or flagella extend from cells that are held in place as part of a tissue layer, they can move fluid over the surface of the tissue. For example, the ciliated lining of the trachea (windpipe) sweeps mucus containing trapped debris out of the lungs. In a woman's reproductive tract, the cilia lining the oviducts help move an egg toward the uterus.

Why are microfilaments important in muscle cells?

Microfilaments are well known for their role in cell motility, particularly as part of the contractile apparatus of muscle cells. Thousands of actin filaments are arranged parallel to one another along the length of a muscle cell, interdigitated with thicker filaments of made of a protein called myosin.

What are the three main types of fibers that make up the cytoskeleton?

Microtubules are the thickest of the three types of fibers Microfilaments (also called actin filaments) are the thinnest. Intermediate filaments are the fibers with diameters in the middle range.

How do amoeba's take advantage of the localized contraction brought about by actin and myosin?

Movement brought about by actin and myosin plays a role in amoeboid movement. A cell such as an amoeba crawls along a surface by extending cellular extensions called pseudopodia (from the Greek "pseudes", false, and "pod", foot), and moving toward them. Pseudopodia extend by assembly of actin subunits into microfilament networks that convert cytoplasm from a sol to a gel inside these cell projections. Cell surface proteins on the pseudopodium make strong attachments to the "road". Next the interaction of microfilaments with myosin near the cell's trailing end causes the contraction of that region, loosening its cell-surface (table! or floor) attachments and pulling it forward toward the pseudopodia. Amoebae lacking myosin can still form pseudopodia, but forward movement is greatly slowed. Amoebas are not the only cells that move by crawling; so do many cells in the animal body, including some white blood cells.

Give some specific examples of how the cytoskeleton is utilized in cells.

One example is how vesicles containing neurotransmitter molecules migrate to the tips of axons, the long extensions of nerve cells that release these molecules as chemical signals to adjacent nerve cells. The vesicles that bud off from the ER travel to the Golgi along cytoskeletal tracks. The cytoskeleton also manipulates the plasma membrane, making it bend inward to form food vacuoles or other phagocytic vesicles. And the streaming of cytoplasm that circulates materials within many large plant cells is yet another kind of cellular movement brought about by the cytoskeleton. (The cell is analogous to a city, the tissues are like the state, the organ is like the nation, and the whole body is like the world)

What is microvillus? (plural, microvilli)

One of many fine, finger-like projections of the epithelial cells in the lumen of the small intestine that increase its surface area.

Give me some examples of the family of closely related plant organelles called plastids.

One type of plastid, the amyloplast, is a colorless organelle that stores starch (amylose), particularly in roots and tubers. Another is the chromoplast, which has pigments that give fruits and flowers their orange and yellow hues! (Does this mean that oranges and bananas have chromplasts that reside within them?) Chloroplasts is also apart of the family of plastids.

What are some characteristics of plant cell walls?

Plant cell walls are much thicker than the plasma membrane, ranging from 0.1 micrometers to several micrometers. The exact chemical composition of the wall varies from species to species and even from one cell type to another in the same plant, but the basic design of the wall is consistent. Microfibrils made of the polysaccharide cellulose are synthesized by an enzyme called cellulose synthase and secreted to the extracellular space, where they become embedded in a matrix of other polysaccharides and proteins. This combination of materials, strong fibers in a "ground substance" (matrix), is the same basic architectural design found in steel-reinforced concrete and in fiberglass (Simply amazing, I wonder if we learned to build buildings by looking at nature?).

What is the purpose of proteins on a chromosome?

Proteins help coil the DNA molecule of each chromosome, reducing its length and allowing it to fit into the nucleus.

What are ribosomes?

Ribosomes, which are complexes made of ribosomal RNA and protein, are the cellular components that carry out protein synthesis.

What is Rough ER?

Rough ER is the part of the ER that is studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope.

What is smooth ER?

Smooth ER, is ER that lacks ribosomes on its outer surface. Smooth ER functions in diverse metabolic processes that include synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons. (Damn, then the cells of the liver must have a lot of smooth ER).

How many mitochondria can a eukaryotic cell have?

Some eukaryotic cells have a single large mitochondrion, but more often a cell has hundreds or even thousands of mitochondria; the number correlates with the cell's metabolic activity. For example, cells that move or contract have proportionally more mitochondria per volume than less active cells.

What are some of the different types of enzymes that exist within the mitochondrial matrix?

Some of the enzymes in the matrix catalyze some of the steps of cellular respiration. Other proteins that function in respiration, including the enzyme that makes ATP, are built into the inner membrane. As highly folded surfaces, the cristae give the inner mitochondrial membrane a large surface area, thus enhancing the productivity of cellular respiration. (This is another example of where form fits function). Loving it!

What are some of the steroids produced by the smooth ER in animal cells?

Some of the steroids that are produced are the sex hormones of vertebrates and the various steroid hormones secreted by the adrenal glands. The cells that synthesize and secrete these hormones - in the testes and ovaries, for example are rich in smooth ER, a structural feature that fits the function of these cells.

What are some of the functions that reactions in the peroxisome provide?

Some peroxisomes use oxygen to break fatty acids down into smaller molecules that are transported to mitochondria and used as fuel for cellular respiration. Peroxisomes in the liver detoxify alcohol and other harmful compounds by transferring hydrogen from the poisons to oxygen. The hydrogen peroxide formed by peroxisomes is itself toxic but the organelle also contains an enzyme that converts hydrogen peroxide to water.

What functions occur at the "cis" face?

The "cis" face is usually located near the ER. Transport vesicles move material from the ER to the Golgi apparatus. A vesicle that buds from the ER can add its membrane and contents of its lumen to the "cis" face by fusing with a Golgi membrane.

What functions of the cell occur at the "trans" face?

The "trans" face gives rise to vesicles that pinch off and travel to other sites.

How is the DNA organized within the nucleus?

The DNA is organized into discrete units called chromosomes within the nucleus. The chromosome is a structure that carries the genetic information of an organism.

What is the endoplasmic reticulum?

The ER is an extensive network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome studded (rough) and ribosome free (smooth) regions.

What does the Golgi apparatus look like?

The Golgi apparatus consists of flattened membranous sacs - cisternae - looking like a stack of pita bread. A cell may have many, even hundreds, of these stacks. The membrane of each cisterna in a stack separates its internal space from the cytosol.

Define carpel

The carpel is the ovule producing reproductive organ of a flower, consisting of the stigma, style, and ovary.

What is the endocrine system?

The endocrine system is the internal system of communication involving, hormones, the ductless glands that secrete hormones, and the molecular receptors on or in target cells that respond to hormones; functions in concert with the nervous system to effect internal regulation and maintain homeostasis.

Describe the the two internal compartments that the inner membrane divides the mitochondrion into.

The first of the two internal compartments is the intermembrane space, the narrow region between the inner and outer membranes. The second compartment, the mitochondrial matrix, is enclosed by the inner membrane. The matrix contains many different enzymes as well as the mitochondrial DNA and ribosomes.

What are the three compartments that make up the chloroplast?

The three compartments that make up the chloroplast are the: intermembrane space, the stroma, and the thylakoid space.

What is a side effect of increasing your intake of drugs?

The increase of drugs, which results in the rate of detoxification, can increase an individual's tolerance to drugs, meaning that higher doses are required to achieve a particular effect, such as sedation or (getting wasted I assume). Also, because some of the detoxification enzymes of relatively broad action, the proliferation of smooth ER in response to one drug can increase tolerance to other drugs. Barbiturate abuse (sedative abuse - in order to alter one's consciousness) for example can decrease the effectiveness of certain antibiotics and other useful drugs. (*** **** man, do not abuse drugs Daniel).

Describe the physical characteristics of mitochondria.

The mitochondrion is enclosed by two membranes, each a phospholipid bilayer with a unique collection of embedded proteins. The outer membrane is smooth, but the inner membrane is convoluted with infoldings called cristae.

What is the most abundant glycoprotein in the ECM of most animal cells?

The most abundant glycoprotein in the ECM of most animal cells is collagen.

What is the most obvious function of the cytoskeleton?

The most obvious function is to give mechanical support to the cell and maintain its shape. This is especially important for animal cells, which lack cell walls. This remarkable strength and resilience of the cytoskeleton as a whole is based on its architecture.

What is the nuclear envelope made up of?

The nuclear envelope is made up of two membranes, that are each a lipid bilayer with associated proteins, that are separated by a space of 20 to 40 nm.

Where is the nuclear lamina located and why is it important?

The nuclear lamina is located on the nuclear side of the envelope. It is a netlike array of protein filaments. It is important because it maintains the shape of the nucleus by mechanically supporting the nuclear envelope.

How does the nucleus direct protein synthesis?

The nucleus directs protein synthesis by synthesizing mRNA according to the instructions provided by the DNA. The mRNA is then transported to the cytoplasm via the nuclear pores. Once an mRNA reaches the cytoplasm, ribosomes translate the mRNA's genetic message into the primary structure of a specific polypeptide.

How come the pancreas has such high rates of protein synthesis?

The pancreas has high rates of protein synthesis because it's cells have large numbers of ribosomes, relative to other cells. It has a few million ribosomes inside its cells (*** **** that is a lot of cells - A few million in something so damn small - no wonder understanding the human body is so difficult.) A cell that is active in protein synthesis, not surprisingly has prominent nucleoli ( the place on the chromatin that produces a lot of rRNA).

Where is the protein structure pore complex located and what is its function?

The pore complex lies on the surface of the nuclear envelope. It plays an important role in the cell by regulating the entry and exit of proteins and RNAs as well as large complexes of macromolecules.

Where do the proteins that are produced by the bound ribosomes go?

The proteins are destined for insertion into membranes, for packaging within certain organelles such as lysosomes or for export from the cell. (Ah I see so the proteins go inside the lysosome, and the lysosomes are the ones that breakdown particles that enter the cell. The lysosome is similar to a garbage man.) Cells that specialize in protein secretion - for instance, the cells of the pancreas that secrete digestive enzymes, frequently have a high proportion of bound ribosomes.

What are some characteristics of the secondary cell wall?

The secondary wall, often deposited in several laminated layers, has a strong and durable matrix that affords the cell protection and support. Wood for example, consists mainly of secondary walls. Plant cell walls are perforated by channels between adjacent cells called plasmodesmata.

What are the three main types of cell junctions in animals?

The three main types are "tight junctions", "desmosomes", and "gap junctions". (Gap junctions are most like the plasmodesmata of plants, although gap junction pores are not lined with membrane.) All three types of cell junctions are especially common in epithelial tissue, which lines the external and internal surfaces of the body.

What is the uterus?

The uterus is a female organ where eggs are fertilized and/or development of the young occurs.

What are chloroplasts?

These organelles are found in plants and algae, and are the sites of photosynthesis. These organelles convert solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water.

What makes up the endomembrane system?

These parts include, the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, and vacuoles.

What is the name for "specialized" peroxisomes?

They are called glyoxysomes and they are found in the fat-storing tissues of plant seeds. The glyoxysomes also contain enzymes that initiate the conversion of fatty acids to sugars, which the emerging seedling uses as a source of energy and carbon until it can produce its own sugar by photosynthesis.

Where is the peroxisome located in leaf cells of plants?

They are located in the cytosol and they live in the same neighborhoods as chloroplasts and mitochondrion. These organelles cooperate with peroxisomes in certain metabolic functions.

What are plasmodesmata's?

They are open channels through the cell wall that connects the cytoplasm of adjacent plant cells, allowing water, small solutes, and some larger molecules to pass between the cells.

What are the two sides of a Golgi stack referred to as?

They are referred to as the "cis" face and the "trans" face; these act, respectively, as the receiving and shipping departments of the Golgi apparatus.

What are mitochondria?

They are the sites of cellular respiration, the metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels.

After leaving the ER, do many transport vesicles travel to?

They travel to the Golgi apparatus, which acts as a warehouse for receiving, sorting, shipping, and even manufacturing. Here, the products of the ER, such as proteins, are modified and stored and then sent to other destinations.

What is the importance of arranging the chloroplast into three compartments?

This compartmental organization enables the chloroplast to convert light energy to chemical energy during photosynthesis.

Define phagocytosis

This is a type of endocytosis in which large particulate substances or small organisms are taken up by the a cell. It is carried out by some protists and certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells.)

Why are the two ends of a microtubule slightly different?

This is because of the orientation of tubulin dimers. One end can accumulate or release tubulin dimers at a much higher rate than the other, thus growing and shrinking significantly during cellular activities. (This is called the "plus end," not because it can only add tubulin proteins but it's the end where both "on" and "off" rates are much higher.

What does the term "cell motility (movement)" encompass?

This term encompasses both changes in cell location and more limited movements of parts of the cell. Cell motility generally requires the interaction of the cytoskeleton with motor proteins.

Where do transport vesicles bud off from?

Transport vesicles bud off from a region of the rough ER called transitional ER and travel to the Golgi apparatus and other destinations.

How does the chromatin appear before division and after it?

When the organism is not dividing the chromatin appears as a diffuse mass in micrographs. When the cell prepares to divide, the chromosome condense further, becoming thick enough to be distinguished as separate structures.

What kind of cells do the domains fungi, animals, plants and also protists, consist of?

eukarotic

In prokaryotic cells DNA is concentrated in a region that is not membrane-enclosed, called the ________

nucleoid

In eukaryotic cells most DNA is in an organelle called the _______

nucleus (which is bounded by a double membrane)

What is biochemistry?

the study of the chemical processes (metabolism) of cells