Cells and Organelles Pro
What are the four main functions of the plasma membrane?
A) Physical barrier: partitions substances on the inside vs. outside B) Cell communications: think receptors!! C) Selective Structure: regulates ion and molecule flow D) Protection and Support: maintains cell integrity
What is the endomembrane system?
Cells have extensive sets of intracellular membranes, which together compose the endomembrane system. The endomembrane system includes the endoplasmic reticulum (ER), Golgi Apparatus, and lysosomes. Vescicles also allow exchange of membrane components with a cell's plasma membrane.
What is a chloroplast?
Chloroplast is a plant organelle and the site of photosynthesis. It contains the green pigment chlorophyll which absorbs light energy to convery carbon dioxide into water, oxygen, and sugar. Like the mitochondria, it contains their own circular DNA. Inside the chloroplast, we find flattened sacs called thylakoids. These thylakoids may be stacked like pancakes..each stack is called a grana. The fluid outside the thylakoids is called stroma, which as the DNA, enzymes, and ribosomes. Like the mitochondria, they have a double membrane. Thylakoids contain hundreds of different proteins and is still being investigated
Cells often communicate with each other and are not isolated. What are a few intracellular junctions?
Gap junctions, Rapid exchange, Plasmodesmata (in plants), Tight Junctions "Zona Occludens", and desmosomes.
What is a senescent cell?
It is a cell that no longer divides.
What is karyoplasm?
Karyoplasm simply forms the contents of the nucleus. It is the protoplasm that constitues the nucleus of the cell. Karyoplasm is also known as the nucleoplasm and it is the liquid content of the cell nucleus.
What are keratins?
Keratins represent a predominant type of intermediate fiber. Keratins are actually a diverse family of over 20 proteins that provide protection against abrasion and prevent water loss in epidermal cells.
What is phagocytosis?
Over 40 different enzymes are found and are particularily abundant in cells with high phagocytic activity. Phagocytosis is a type of endocytosis in which large particles are engulfed or eaten by the cell.
What is the rough endoplasmic reticulum?
Part of the rough endoplasmic reticulum is continous with the nuclear envelope. In an avergae liver cell, almost 15 million ribosomes are present. Ribosomes on the Rough ER are "membrane bound" and are involved in protein synthesis. Cells that make enzymes such as pancreas and those of the GI tract have abundant Rough ER. The rough ER works with the ribosome and continues the protein assembly. In most cases, proteins are moved to the Golgi complex for final modification and "finishing". They are either conveyed in vesicles or moved directly between the ER and Golgi complex befor ebeing delivered to their specific locations.
What is pinocytosis?
Pinocytosis is cell drinking...the cell takes in droplets of extracellular fluid which contains the solute molecules.
What is plasodesmata?
Plasmodesmata which are intracellular channels that connect plant cells. Water and small molecules can pass freely between the cells. These microscopic channgels traverse the cell wall of plants and some algal cells.
What is rapid exchange?
Rapid exchange occurs between gap junctions. Cyclic AMP which is involved with cell signal transduction can easily move. Gap junctions are responsible for the heart's coordinated beat.
There are three types of fibers that create a complex network in the cytoskeleton, what are they?
The Cytoskeletan is a complex network of: a) Microfilaments (actin) b) Microtubules c) Intermediate filaments They determine the shape of cells and play an important role in movement of organelles, vesicles, as well as entire cell movement. As you know, sperm cells can swim and white blood cells crawl across cell surfaces to destory invaders. These cells are powered and guided by the cytoskeleton. The cytoskeleton polymers are composed of many subunit proteins, and is always reorganizing itself. Sometimes it loses subunits, other times it gains subunits. Microtubules are involved with "molecular motors"...attaching to organelles and vesicles as well as chromosomes to help pull them apart.
Where does the material that went to the Golgi apparatus come from?
The material that went to the Golgi Apparatus comes from the endoplasmic reticulum. The endoplasmic reticulum is the largest membranous system in the cell. It occupies about 50% of the total membrane volume. It has two components: a) Smooth ER b) Rough ER
What is amphipathic?
having both hydrophilic and hydrophobic parts
What are connexins?
protein subunits of gap junctions
What is cytoplasm?
The cytoplasm involves the contents of the cell excluding the nucleus.
Differentiate between cytosol and ctyoplasm.
The cytoplasm is mainly water, and various organic and inorganic substances are disssolved or even suspended. The fluid suspension is the cytosol. The cytosol is the aqueous intracellular fluid, while the cytoplasm is everything within the cell (cytosol and organelles). If the cytoplasm were a stew, the cytosol would be the broth.
Which two types of phagocytotic cells are loaded with lysosomes?
Neutrophills and macrophages are loaded with lysosomes.
What is a catalase?
One enzyme in particular I want you to know about is known as a catalase. Catalase will break down H2O2, hydrogen peroxide, which is harmful to cells.
What are ribosomes?
Ribosomes are known as the "Protein Factories" that are made of rRNA and over 80 different proteins. This is the site of protein synthesis.
What are 3 places ribosomes can be found?
Ribosomes can be: a) Attached to the Endoplasmic Reticulum b) Attached to the Nuclear Envelope c) Freely suspended in the cytosol.
What are ribosomes made of?
Ribosomes consist of two subunits which are made in the nucleolus of the cell. The subunits are made separately in the nucleolus and exported to the cytoplasm for final assembly. The large and small subunit join together by binding an mRNA strand.
How do amoebas move and what type of microfilaments or microtubules does it involve for its movement?
Amoebas move by pseudopodia and this movement also involves actin and myosin.
What are centrioles and centrosomes?
Centrioles are found in animal cells, NOT PLANT cells. They are composed of 9 sets of microtubule triplets arranged in a cylinder. They have a "9+0" pattern. The "centrosome" is the most common microtubule-organizing center...MTOC within the cell. A pair of centrioles and associated proteins comprise the centrosome. The centriole pair is perpendicular to each other!! Before an animal cell divides, centrioles replicate. Recall during cell division, centrioles move to opposite ends of the cell. Microtubules extend from the centrioles to form the spindle. Some of the microtubules attach to the chromosomes by connecting to protein complexes called kinetochores that are present on each chromosome. The kinetochores control the metaphase/anaphase transition.
What are desmosomes?
Desmosomes remind me of "staples"...they fasten the cells together into strong sheets...some scientists call them a "spot-weld". They can attach muscle cells to one another. Desmosomes have intermediate filaments which are very strong, they are commin in epithelia that need to withstand abrasian such as skin. As a future doctor, you might be interested to known that some people produce antibodies against the proteins that make up the desmosome. In a skin disease called Pemphigus Vulgaris, we see a disruption of cell adhesion. Many blisters form and loss of extracellular fluid occurs. This can be fatal if not treated. Usually, a steroidal agent can control the pathology.
What are Gap Junctions?
Gap Junctions allows communication to occur between cells. We see membrane proteins that surround a pore that will allow substances such as small molecules, amino acids, and ions to pass. The proteins of gap junctions are called connexins. Many types of tissue such as muscle and heart contain these junctions. Gap junctions are responsible for the heart's coordinated beat.
What are intermediate fibers?
Intermediate fibers are more "permanent" structures than microtubules or the microfilaments. After cell death, they are often still seen. These fibers anchors the nucleus in place and provides much structural support for the cell. They alsomake up the framework of the nuclear envelope. Keratin is an example of a intermediate fiber.
Are ribosomes found in prokaryotes or eukaryotes?
Ribosomes are found in both prokaryotes and eukaryotes.
How is the Golgi apparatus like a warehouse?
The Golgi is like one big warehouse..where sorting and shipping occur. It reminds me of Mimeo...the company that ships our DAT destroyer books to you.
What are tight junctions aka "Zona Occludens"?
Tight junctions, also known as Zona Occludens, forms tight seals around cells to prevent contents from leaking. They allow skin cells, for example, to make us watertight, and maintain the integrity of the epithelial barrier. The intestinal barrier is maintained by tight junctions. The complex protein structures that regulate the permeability of the intestine is clearly one example of their importance. Chronic diseases such as Celiac disease or inflammatory bowel diseases involves a "leaky" intestinal barrier.
What are organelles?
Within cells, we find metabotically active structures that are involved in performing many functions. These structures are called organelles.
What is the cytoskeleton of the cell?
A microscopic network of actin filaments and microtubules in the cytoplasm of many living cells that gives the cell shape and coherence.
Properties of the plama membrane (plasmalemma)?
1. Allows the cell to maintain homeostasis (steady state of equilibrium) 2. Allows ions and other solutes to be transported in or out and contains ion channels and many proteins 3. This plasma or cell membrane contains phosphilipids, cholesterol, proteins, glycoproteins. This selective barrier regulates materials from passing into or out of the cell.
How is a phagosome formed?
A phagosome is formed by the fusion of the cell membrane around a microorganism or senescent cell ( a cell that no longer divides). This phagosome fuses with the lysosome and the enzymes begin digestion.
Are leaked lysosomes dangerous to the cell?
Any leaked lysosomes are normally harmless to the cell since the cytosol has a pH of about 7.2 and will make lysosomal enzymes inactive.
What is the Endosymbiotic Theory?
Although most DNA is packaged in chromosomes, mitochondria and chloroplasts have a small amount of their own DNA. Mitochondrial DNA is double-stranded, but circular. This has led scientists to believe that mitochondria originated from an ancestral aerobic prokaryotic bacterium...This bacterium adapted to a symbiotic relationship with an ancestral host cell. This is the Endosymbiotic Theory. Mitochondria are self-replicating too, with an average life span of about 10 days. The endosymbiotic theory deals with the origins of mitochondria and chloroplasts, two eukaryotic organelles that have bacteria characteristics. Mitochondria and chloroplasts are believed to have developed from symbiotic bacteria
Cells have shape, can move and have the ability to communicate. A system of tubules and filaments comprise the cytoskeleton. The cell organelles can be membranous such as the mitochondria or lysosome or be non-membranous such as the ribosomes.
Cells have shape, can move and have the ability to communicate. A system of tubules and filaments comprise the cytoskeleton. The cell organelles can be membranous such as the mitochondria or lysosome or be non-membranous such as the ribosomes.
What kind of cells would contain lots of ribosomes?
Cells making an enzyme will have a lot of ribosomes.
What types of cells show an abundance of smooth ER?
Cells that are active in the synthesis of cholesterol, triglycerides, and steroids show an abundance of smooth ER.
What organs contain the most mitochondria?
Cells usually possess a high number of mitochondria, but kidneys and heart have enormous numbers of mitochondria!! Heart has the most; kidneys are second for those who are curious. A liver cell might have 2,000, but a heart cell has 5,000 mitochondria.
Chromatin can be either heterochromatin or euchromatin, what's the difference?
Chromatin can be either heterochromatin or euchromatin. Heterochromatin is dark-staining and much is found near the nuclear envelope. It is condensed and not actively transcribed. The euchromatin is the light area...less dense...less compact and has genes that are actively transcribing. In most cells, more of the DNA is found in euchromatin than heterochromatin.
What is cilia and flagells composed of?
Cilia and flagella are composed of microtubules and motor proteins are used for movement.
What are cilia and flagella?
Cilia and flagella are projections from the cell. They are made up of microtubules , as shown in this cartoon and are covered by an extension of the plasma membrane. They are motile and designed either to move the cell itself or to move substances over or around the cell.
What is clathrin?
Coat protein on cell membrane receptors, it provides the mechanism to covert a planar membrane into a spherical structure (vesicle), the receptor provides the specificity. It plays a major role in the formation of coated vesicles.
What are cyanobacteria?
Cyanobacteria give us oxygen! They represent the only form of oxygenic photosynthetic bacteria known to date. These bacteria contain chlorophyll, and perform photosynthesis similar to plants. Cyanobacteria are mainly found in water, but can be found on corals, rocks, and even land. Cyanobacteria used to be called blue-green algae, but we try to avoid it. Remember, these cyanobacteria are from Kingdom Monera and represent prokaryotes. Prokaryotes are unicellular, and lack a membrane-bound nucleus, mitochondria, and other membrane-bound organelles.
What is cytoplasmic streaming?
Cytoplasmic streaming is the movement of the cytoplasm in plants or animals, it is also believed to involve actin and myosin.
What is colchicine?
Drugs such as colchicine disrupts the microtubules and is used to treat gout. Microtubules disruptions blocks white blood cell migration which is responsible for inflammation. Gout is a painful inflammation of the big toe and foot caused by defects in uric acid metabolism resulting in deposits of the acid and its salts in the blood and joints. Make sure you understand that colchicine is a "Mitotic poison"...it messes up the microtubules. Thus, I hope you can see that mitosis would be halted!!
What is responsible for the bending movement of cilia and flagella?
Dynein, one of the molecular motors, is responsible for the bending movements of the cilia and flagella.
Over 40 different enzymes are found and are particularily abundant in cells with high phagocytic activity. What are some types of enzymes found in phagocytototic cells?
Enzymes include proteases, nucleases, phosphotases, and sulfatases, etc.
What is exocytosis?
Exocytosis require ATP. It is when molecules are secreted by the fusion of vesicle with the plasma membrane. The release of the contents goes to the extracellular space without compromising cell membrane (plasma membrane) integrity. Beta cells of the pancrease make insulin and secrete it into the blood by exocytosis. Exocytosis is triggered in many cells by a brief release of Ca2+ ions in the cytosol. Neurotransmitters released into the synaptic cleft is done by exocytosis.
What is a feulgen stain?
Feulgen stain is a staining technique discovered by Robert Feulgen and used in histology to identify chromosomal material or DNA in cell specimens. It is darkly stained. The principle of Feulgen stain is to dissociate the two strands of DNA through hydrolysis by a solution of molar HCl which destroys the purine bases. HCl separates the two purine bases of DNA: adenine, guanine
What is the important pattern seen in flagella and cilia and what is an axoneme?
Flagella and Cilia have a "9+2" pattern. This entire picture of the 9+2 arrangement along with the proteins constitutes what is called an axoneme.
What is freeze fracture?
Freeze fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer. In this technique, e can study the bilayer. The interior and exterior are surely NOT symmetrical. The freeze-fracture studies provided the first direct evidence of integral proteins in many biological membranes.
What does the Smooth ER do in the liver and what is cytochrome 450?
In the liver, the Smooth ER contains a large amount of cytochrome 450 and participates in detoxifying certain drugs. The cytochrome 450 catalyzes reactions to decrease drug toxicity. The hepatocyte (liver cell) is involved with drug detoxification, thus has a high % of smooth ER.
What is the Tay-Sachs disease?
In Tay-Sachs disease, a critical lysosomal enzyme is deficient...lipids cannot be digested, and cells become "engorged" and neuronal function suffers...the child dies before age 4.
what is the glycoclayx?
In a transmission electron microscope study, we would see the external of the cell showing a "fuzzy" area. This is the glycocalyx. It essentially is the carbohydrate chains covalently linked to the transmembrane proteins and/or phospholipids on the outer portion. It has many negatively charged sulfate and carboxyl groups. They are involved with making up receptors that participate in functions such as cell recognition, hormone response, and adhesion.
What is cell-Mediated Endocytosis?
In cell-mediated endocytosis, we see the capture of macromolecules using receptor proteins in the cell membrane. These receptor molecules associate with the macromolecules and then become associated intracellularly as well using a molecule called clathrin. Hormones, growth factors, antibodies, even antigens are bound at the cell surface. A region of the cell membrane called a coated pit is lined by a later of proteins. Upon binding, the coated pit forms a vesicle!! You need not to know any details, but clathrin is a major player in cell-mediated endocytosis.
What is endocytosis? What are the three types of endocytosis?
In endocytosis we see a uptake of a molecule and produce a new vesicle from the plasma membrane. Phagocytosis, pinocytosis, and cell-mediated endocytosis. All require ATP.
In plants, hemicellulose and pectin are made by what?
In plants, hemicellulose and pectin are made by the Golgi apparatus. Both hemicellulose and pectin contribute to the plant cell wall.
What is an inclusion?
Inclusion are the nonliving components of a cell. Inclusions include: a) pigments-melanin pigment in skin and hair b) Lipid droplets in fat cells c) Glycogen granules in liver and skeletal muscle cells d) Vacuoles..membrane bound vecles..more prominent in plants. They can be used for storage e) crystals..likely remnants of certain proteins
In cancer cells, the nucleolus is hypertrophic, what does this mean?
Interestingly, in cancer cells, the nucleolus is often hypertrophic meaning increased in size. But, be careful. Large nucleoli are not only encountered with rapidly growing malignant tumors, but are found in cells that are actively synthesizing proteins.
What are intermediate filaments?
Intermediate filaments are about 10 nm diameter and provide tensile strength for the cell.
What is myosin?
Like the motor protein dynein, myosin is another motor protein that loves to walk. However, it is a microfilament-based and not microtubule-based like dynein. Myosin "walks" along the actin filaments. Recall, this is seen in muscle contraction. I hope you remember that actin and myosin filaments slide past one another.
How are lysosomes formed?
Lysosomes are formed by budding from the Golgi Complex.
What are lysosomes?
Lysosomes are membrane bound organelles that contains hydrolytic enzymes used to digest macromolecules. Neutrophils and macrophages are loaded with lysosomes.
What do lysosomes do?
Lysosomes break down macromolecules into their constituent parts, which are then recycled. These membrane-bound organelles contain a variety of enzymes called hydrolases that can digest proteins, nucleic acids, lipids, and complex sugars. The lumen of a lysosome is more acidic than the cytoplasm. This environment activates the hydrolases and confines their destructive work to the lysosome. In plants and fungi, lysosomes are called acidic vacuoles. Lysosomes are formed by the fusion of vesicles that have budded off from the trans-Golgi. The sorting system recognizes address sequences in the hydrolytic enzymes and directs them to growing lysosomes. In addition, vesicles that bud off from the plasma membrane via endocytosis are also sent to lysosomes, where their contents — fluid and molecules from the extracellular environment — are processed. The process of endocytosis is an example of reverse vesicle trafficking, and it plays an important role in nutrition and immunity as well as membrane recycling. Lysosomes break down and thus disarm many kinds of foreign and potentially pathogenic materials that get into the cell through such extracellular sampling
What is the pH of a lysososome and what shape are lysosomes?
Lysosomes have a pH of about 5 within lysosomal lumen, and they are usually spherical in shape.
What are some things lysosomes will digest?
Lysosomes will digest: a) Microorganisms like fungi or bacteria b) Cellular debris such as old cells c) Old organelles such as mitochondria
Polysaccharides and glycosaminoglycans are made by what?
Many of the cells polysaccharides are made by the Golgi and most of the glycosaminoglycans of the extracellular matrix.
When are membrane phospholipids most stable? What is the structure of a phospholipid?
Membrane phospholipids are most stable when organized in a lipid bilayer. As you can see, each phospholipid molecule of the lipid bilayer is made up of this polar head group and two long nonpolar fatty acyl traits projecting inward. The phospholipid is composed of both a hydrophilic area and a hydrophobic area. Therefore, the molecule is amphipathic. Hopefully you can see that the protein components can span the entire length (integral) or are simply attached to the cytosolic side (peripheral). Since most integral proteins span the entire length, we refer to them often as transmembrane proteins. These transmembrane proteins are often quite long and can fold while forming channels that allow the passage of specific ions or molecules.
How are cell membranes synthesized?
Membranes and their constituent proteins are assembled in the ER. This organelle contains the enzymes involved in lipid synthesis, and as lipids are manufactured in the ER, they are inserted into the organelle's own membranes. This happens in part because the lipids are too hydrophobic to dissolve into the cytoplasm. Similarly, transmembrane proteins have enough hydrophobic surfaces that they are also inserted into the ER membrane while they are still being synthesized. Here, future membrane proteins make their way to the ER membrane with the help of a signal sequence in the newly translated protein. The signal sequence stops translation and directs the ribosomes — which are carrying the unfinished proteins — to dock with ER proteins before finishing their work. Translation then recommences after the signal sequence docks with the ER, and it takes place within the ER membrane. Thus, by the time the protein achieves its final form, it is already inserted into a membrane The proteins that will be secreted by a cell are also directed to the ER during translation, where they end up in the lumen, the internal cavity, where they are then packaged for vesicular release from the cell. The hormones insulin and erythropoietin (EPO) are both examples of vesicular proteins.
Microfilaments are built from what?
Microfilaments are built from actin (a globular protein)
What are microfilaments?
Microfilaments are fine, thread-like protein fibers, 3-6 nm in diameter. They are composed predominantly of a contractile protein called actin, which is the most abundant cellular protein. Microfilaments' association with the protein myosin is responsible for muscle contraction. Microfilaments can also carry out cellular movements including gliding, contraction, and cytokinesis.
There are microtubule motor proteins and microfilament motor proteins, what are they?
Microtubule motor proteins: Dynein and kinesins Microfilament motor proteins: Myosin is the motor, actin filaments are the tracks along which myosin moves, and ATP is the fuel that powers movement.
Rank the diameter sizes between microfilaments, intermediate filaments, and microtubules from largest to smallest.
Microtubules > intermediate filaments > microfilaments.
What are microtubules?
Microtubules are cylindrical tubes, 20-25 nm in diameter. They are composed of subunits of the protein tubulin--these subunits are termed alpha and beta. Microtubules act as a scaffold to determine cell shape, and provide a set of "tracks" for cell organelles and vesicles to move on. Microtubules also form the spindle fibers for separating chromosomes during mitosis. When arranged in geometric patterns inside flagella and cilia, they are used for locomotion.
Which of the three cytoskeletal polymers is the strongest?
Microtubules are the strongest of the cytoskeletal polymers. Most cells would lose their shape if microtubules are depolymerized!! Microtubules are organized to suit the needs of each cell. A mature neuron for example, uses microtubules for strenth, while a young neuron uses microtubules to help with movement.
What is special about mitochondria and chloroplasts?
Mitochondria and chloroplasts were once likely prokaryotes that got ingested by larger cells...this was the Endosymbiont Theory.
What are Dyneins and kinesins?
Molecular motors are enzymes that will walk along microtubules and they include dyneins and kinesins. These molecules can generate enough force to literally walk across the microtubule. Dynein "walking" is responsible for the bending movement of the cilia and flagella.
What are molecular motors and what do they include?
Molecular motors are enzymes that will walk along microtubules. These molecular motors include Dyneins and kinesins. These molecules can generate enough force to literally walk across the microtubules.
What do the pores of the nuclear envelope do?
Nuclear envelopes contains pores used for importing and exporting materials such as proteins or RNA.
What are osteoclasts?
Osteoclasts are cells that break down bone, these are a fine example of a multinucleated cell. Multinucleated cells can often be found under pathological conditions such as in a malignant (cancerous tumor).
What are examples of cells that are multinucleated and cells that have no nucleus?
Osteoclasts, skeletal muscle cells, and hepatocytes (liver cells) are examples of multinucleated cells. Red blood cells, platelets (thrombocytes)-which are involved with blood clotting, are examples of cells with no nucleus.
What plays a role in the aging process?
Oxidative damage to mitochondria has been proposed to play a role in the aging process.
What are peroxisomes?
Peroxisomes contain enzymes that oxidize certain molecules normally found in the cell, notably fatty acids and amino acids. Those oxidation reactions produce hydrogen peroxide, which is the basis of the name peroxisome. Peroxisomes are spherical organelles that are membrane-bound and contain over 40 oxidative enzymes including catalase. Peroxisomes contain enzymes involved with lipid metabolism. The beta oxidation of long chained fatty acids, of 18 carbons or longer, are done by peroxisomal enzymes. These enzymes are different from those of the mitochondria. These fatty acids are made shorter, then subsequently shuttled to the matrix of the mitochondria for oxidation. Interestingly, the peroxisome also makes H2O2, hydrogen peroxide. H2O2 detoxifies substances such as ethanol and even kills microorganisms. The excess H2O2i broken down by catalase. This is often a very confusing point that I find student don't clearly understand. They do self-replicate, but unlike the mitochondria lack their own DNA. Hence, they must import the needed proteins for self-replication. Also, mitochondria generate ATP, peroxisomes do not.
What is phagocytosis?
Phagocytosis is cell eating..such as engulfing of microorganisms, cellular debris, old, worn-out cells (for example macrophages and neutrophils) Over 40 different enzymes are found and are particularily abundant in cells with high phagocytic activity. Phagocytosis is a type of endocytosis in which large particles are engulfed or eaten by the cell.
What is the fluid mosaic model?
Proteins in the phospholipid bilayer can floate in this bilayer sea much like an iceberg. This model is called the fluid mosaic model. Proteins literally float in a lateral motion along the plane of the membrane. Lipids and many membrane proteins are in constant lateral motion.
What are enzymes?
Proteins that speed up chemical reactions. A substance produced by a living organism which acts as a catalyst to bring about a specific biochemical reaction.
What is protoplasm? And what does it include?
Protoplasm is the living substance of the cell and it includes: a) Cytoplasm b) Karyoplasm (aka Nucleoplasm)
How are organelle membranes maintained?
The ER, Golgi apparatus, and lysosomes are all members of a network of membranes, but they are not continuous with one another. Therefore, the membrane lipids and proteins that are synthesized in the ER must be transported through the network to their final destination in membrane-bound vesicles. Cargo-bearing vesicles pinch off of one set of membranes and travel along microtubule tracks to the next set of membranes, where they fuse with these structures. Trafficking occurs in both directions; the forward direction takes vesicles from the site of synthesis to the Golgi apparatus and next to a cell's lysosomes or plasma membrane. Vesicles that have released their cargo return via the reverse direction. The proteins that are synthesized in the ER have, as part of their amino acid sequence, a signal that directs them where to go, much like an address directs a letter to its destination. Soluble proteins are carried in the lumens of vesicles. Any proteins that are destined for a lysosome are delivered to the lysosome interior when the vesicle that carries them fuses with the lysosomal membrane and joins its contents. In contrast, the proteins that will be secreted by a cell, such as insulin and EPO, are held in storage vesicles. When signaled by the cell, these vesicles fuse with the plasma membrane and release their contents into the extracellular space.
What is the function of the Golgi Apparatus?
The Golgi apparatus functions as a molecular assembly line in which membrane proteins undergo extensive post-translational modification. Many Golgi reactions involve the addition of sugar residues to membrane proteins and secreted proteins. The carbohydrates that the Golgi attaches to membrane proteins are often quite complex, and their synthesis requires multiple steps. In electron micrographs, the Golgi apparatus looks like a set of flattened sacs. Vesicles that bud off from the ER fuse with the closest Golgi membranes, called the cis-Golgi. Molecules then travel through the Golgi apparatus via vesicle transport until they reach the end of the assembly line at the farthest sacs from the ER — called the trans-Golgi. At each workstation along the assembly line, Golgi enzymes catalyze distinct reactions. Later, as vesicles of membrane lipids and proteins bud off from the trans-Golgi, they are directed to their appropriate destinations — either lysosomes, storage vesicles, or the plasma membrane
What is the golgi apparatus?
The Golgi apparatus is responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations. It is located in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus. The golgi apparatus is stacks of membranous "sacs" that is involved with the synthesis of carbohydrates and in the modification of proteins. For example, carbohydrates are added to the protein by Golgi enzymes. In other words, post translational modification and "packaging" of proteins occur here. Some proteins are glycosylated...we add sugars, while other proteins have sugars removed.
What are cells?
The basic functionl units of complex organisms are cells.
What is the cytoskeleton?
The cytoskeleton is unique to eukaryotic cells. It is a dynamic three-dimensional structure that fills the cytoplasm. This structure acts as both muscle and skeleton, for movement and stability. The long fibers of the cytoskeleton are polymers of subunits. The primary types of fibers comprising the cytoskeleton are microfilaments, microtubules, and intermediate filaments.
What is the drug Taxol often used for?
The drug often used for ovarian and breast cancer is Taxol. This drug will bind to the microtubules and prevent them for disassociating. Another clever way to stop mitosis. Recall, a cancer or malignancy represents an uncontrolled mitosis.
How does the golgi apparatus and the endoplasmic reticulum work together?
The endoplasmic reticulum is a series of membranes found throughout the cell that are connected to the nucleus. The endoplasmic reticulum can be smooth or rough. A smooth endoplasmic reticulum (SER) does not have ribosomes attached whereas a rough endoplasm reticulum (RER) does. The membranes of the endoplasmic reticulum form sacs called cisternae. Proteins are folded in the cisternae spaces called lumen. Additionally, the smooth endoplasmic reticulum forms lipids and steroids. When enough proteins have been created a vesicle is pinched off of the membrane. This transition vesicle then moves through the cytoplasm from the endoplasmic reticulum to the Golgi apparatus. The Golgi apparatus then packages, transports, distributes, or stores the contents of the vesicle. After the Golgi apparatus does its work on the contents of the vesicle, a secretory vesicles is created and pinched off into the cytoplasm. The contents of the secretory vesicle are delivered to where they are needed within the cell.
What is the mitochondria?
The mitochondria is the powerhouse of the cell. It contains enzymes specialized in making ATP and carrying out aerobic respiration. They can have a shape that is round or elongated. Animals and plants contain mitochondria. Often can be visible with a light microscope. In the picture you can see that this is a 2D picture, thus it was taken with a TEM (transmission electron microscope). Note the cristae...foldings of the inner membrane, which greatly increases the surface area.
What is the nucleus?
The nucleus is the largest organelle of the cell. In the eukaryotic organism, most of the genes are found here ( a small smount is found in the mitochondria and chloroplasts.) It is enclosed by the nuclear envelope, which is a double membrane. Inside the nucleus, DNA is organized into units called chromosomes. The chromosomes are made of proteins and DNA called a chromatin complex. For humans we have 46 chromosomes in the nucleus, normally. The germ cells...sperm and eggs, have 23 chromosomes.
What are the three major compounds of the nucleus?
The nucleus, bounded by a pair of lipid membranes has three major components: A) Nucleolus: rRNA synthesis B) Chromatin: genetic material C) Nucleoplasm: the content of the nucleus, excluding the nucleolus
Explain the parts of a mitochondria.
The outer membrane allows the passage of small molecules and ions. The inner membrane is higly folded and is a closed space, even to small ions! The inner mitochondrial matrix is where the electron transport chain that makes up almost 90% of the ATP is found. The matrix of mitochondria is enclosed by the inner membrane. This might sound confusing so lets have a look in the picture. Matrix: Kreb Cycle (TCA cycle) and Fatty Acid Oxidative processes occur...contains many enzymes, ribosomes, and mitochondrial DNA. Very gel-like and viscous.
What is the plasma membrane (plasmalemma)?
The plasma membrane also known as plasmalemma, seperates the cytoplasm from its extracellular environment.
What is the smooth ER?
The smooth ER...outer surface lacks ribosomes. It is involved with lipid biosynthesis such as phospholipids. The Smooth ER is also involved with holding and releasing Calcium ions in a controlled manner, and released when needed. It is specialized in skeletal muscles and called the sarcoplasmic reticulum. The Smooth ER is also involved in steroid biosynthesis and detoxification of drugs and poisons.
What are the two main functions of the rough endoplasmic reticulum?
The two main functions of the rough endoplasmic reticulum are the production of A) mitochondria and proteins secreted by the cell. B) hydrogen peroxide and steroid hormones secreted by the cell.
What are the three main destinations for the material being shipped out of the trans-Golgi?
There are three main destinations for the material being shipped out of the trans Golgi: Inside the cell...many are released in vesicles destined to be delivered to the lysosomes. The Plasma Membrane...many molecules are shipped to be used for repair to the membrane, for cell signaling purposes, etc. Outside the cell...such as the release of the hormone insulin
What is actin?
Thin filament protein. Twisted into a double helix and appears like a double-stranded chain of pearls. Contains the myosin-binding site. Actin plays a critical role in cytokinesis and phagocytosis. In most eukaryotic cells, actin is the most abundant protein, and participates in more protein-protein interactions than any other protein.
What are the three main sections of the golgi apparatus?
Three main sections of the golgi apparatus: 1. Cis Golgi: molecules go in 2. Main Golgi: molecules get processed 3. Trans Golgi: molecules go outward The apparatus has three primary compartments, known generally as "cis" (cisternae nearest the endoplasmic reticulum), "medial" (central layers of cisternae), and "trans" (cisternae farthest from the endoplasmic reticulum).
What is the nucleolus?
a small dense spherical structure in the nucleus of a cell during interphase, it works to make ribosomes so it is also known as the ribosome production factory. It is a non-membranous organelle. One or more may be found within the nucleus, but rarely beyond three. In addition to rRNA synthesis, the assembly of large and small ribosomal subunits occurs here. Small amounts of DNA are present, but not stain with Feulgen stain.
What are proteosomes?
proteosomes are protein complexes found in the cytoplasm about the size of a ribosomal subunit (small). They degrade denatured or unneeded proteins. Think of proteosomes as the quality control protein department. Lysosomes do the bulk of the job, but these organelles assist with primarily individual proteins. Recent studies have shown that they remove abnormal or misfolded proteins and use ATP to drive the needed conformational changes in their subunits. It has a very cool structure, note the four stacked rings!
