Lecture3_080435 - Lecture 3 Lecture 3 Monomers and polymers...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Lecture 3 Lecture 3 September 23, 2010 Monomers and polymers Monomers and polymers Monomers: Small, single unit biomolecules that serve as the building blocks for the synthesis of larger molecules Polymers: Larger organic molecules, made by bonding together of smaller monomers – Complex carbohydrates, lipids, proteins, nucleic acids – Simple sugars, fatty acids, amino acids, nucleotides Hydrolysis and Dehydration Hydrolysis and Dehydration Synthesis The monomers of organic compounds join together by a chemical reaction known as dehydration synthesis to form polymers The reverse reaction of breaking up polymers is accomplished by a chemical reaction known as hydrolysis Chemical reactions Chemical reactions Processes in which chemical bonds are broken and/or formed A+B→C+D Reactants Products Balancing chemical equations Balancing chemical equations Law of conservation of mass: The total mass of all materials entering a reaction must equal the total mass of all the products – The total number of atoms of each element needs to be the same on each side of the equation C6H12O6 + 6O2 → 6CO2 + 6H2O glucose # of a particular atom within a molecule oxygen carbon dioxide water # of a independent (unjoined) atoms, ions, or molecules of that type Reversible and irreversible Reversible and irreversible reactions Reversible reactions: Reactions that go in both directions Irreversible reactions: Reactions that go in only one direction – Ex. An explosion – Usually represented by double arrows pointing in both directions Catalysts and enzymes Catalysts and enzymes Catalyst: A helper molecule that speeds up a reaction without being used up in the reaction – Enzymes: The catalysts used by living organisms Formula weight and the mole Formula weight and the mole Formula weight: The sum of the atomic weights of the atoms found in a formula – NaCl = 1 Na atom and 1 Cl atom Mole: The amount of material contained in a sample of the pure substance that has a mass in grams equal to the substance’s atomic or formula weight – Ex. 1 mole of NaCl would be a sample with a mass of 58.44 g – One mole of a substance contains 6.02 x 1023 particles (Avogadro’s number) 22.99 amu + 35.45 amu = 58.44 amu Mixtures Mixtures Consist of two or more types of elements or molecules physically blended together – Not linked by chemical bonds – Each retains its own properties Most common types of mixtures are between water and other substances Ex. Mixing sugar and salt Solutions Solutions Homogenous mixtures containing a relatively large amount of one substance (solvent = the dissolving medium) and smaller amounts of one or more substances (solutes = dissolved particles) – Ex. Salt water What is the solvent? What is the solute? Electrolytes and Nonelectrolytes Electrolytes and Nonelectrolytes Solutes that form ions in solution and conduct electricity are called electrolytes – Molecules that are ionically bonded form electrolytes Solutes that do not form conductive solutions are called nonelectrolytes Ex. NaCl breaks down into Na+ and Cl­ – Molecules that are covalently bonded form nonelectrolytes Ex. Sugar Measures of concentration Measures of concentration Concentration: Indicates the relationship between the amount of solute and the amount of solution – Molarity (M): The number of moles of solute in exactly 1 liter of solution Organic vs. Inorganic Organic vs. Inorganic Substances Organic substances generally contain carbon. Inorganic substances are all other substances Diamond and graphite (pure C) Carbon dioxide (CO ) 2 Carbon monoxide (CO) Carbonates (e.g. limestone (CaCO ) 3 Biocarbonates (e.g. baking soda (NaHCO ) 3 – Some exceptions to the “carbon­organic” rule Salts and neutralization Salts and neutralization reactions Salts can be produced by mixing solutions of appropriate acids and bases – They contain the positive ion for a base (NaOH) and the negative ion of an acid (HCl) 2 HCl + NaOH → NaCl + Formation of a salt allows aH O neutralization reaction to occur Hydrocarbons Hydrocarbons Ringed hydrocarbons, such as benzene, are called aromatic Hydrocarbon chains often form an inactive “backbone” to which reactive functional groups are attached, such as oxygen, nitrogen, phosphorus, etc. – Six­sided – Double bonds CHNOPS CHNOPS The six most abundant elements of life Most biological molecules are made from covalent combinations of these 6 elements Carbohydrates Carbohydrates Five important functions in living organisms: – Provide energy – Serve as stored form of chemical energy – Provide dietary fiber – Supply carbon atoms for synthesis of cell components – Form part of the structural elements of some cells Carbohydrates Carbohydrates Contain carbon, hydrogen, and oxygen Generalized formula = CH2o – Alcohol, ketone, aldehyde Commonly contain the functional groups: Simplest are simple sugars = monosaccharides – Consist of single units called saccharide – Glucose is an important monosaccharide Others include fructose, galactose, and ribose Carbohydrates Carbohydrates Disaccharides: Sugars formed by linking two monosaccharides through a covalent bond Polysaccharides: Contain many saccharides – Glycogen: Store carb of animals – Sucrose (glucose + fructose) – Lactose (glucose + galactose) – Starch: Storage carb of plants Highly branched – Cellulose: Structural carb of plants Amylose (long, unbranched network of glucose units) and amylopectin (highly branched network of glucose) Undigestible by humans—serves as fiber in our diet Classified by their solubility Insoluble in water; soluble in nonpolar solvents, such as alcohol Properties: Repel H2O, energy rich, low density Source of stored energy in plants and animals Provide protective coating on plants Structural component of plasma membrane Lipids Lipids Contain two components: fatty acids and alcohols Simple lipids Simple lipids – Fatty acids: Consist of a hydrocarbon chain with a carboxylic acid function group (­COOH) on the end Fatty acids with no double bonds in the hydrocarbon chain are saturated fatty acids Fatty acids with double bonds are unsaturated – Prevalent in plant products (grains, veggies, fruits) – Found in dietary animal products (meat, eggs, dairy) Consumption of a greater proportion of saturated than unsaturated fatty acids in linked to higher incidence of CVD Simple lipids Simple lipids Most common alcohol found in simple lipids is glycerol Simple lipids (fats and oils) are formed between the carboxylic acid group of three fatty acids and the three alcohol groups of glycerol – Resulting lipid is called a triglyceride – A 3­C alcohol that has 3 alcohol groups (­OH) Simple lipids Simple lipids Classified as fats or oils based on their melting points Their melting points goes down with increasing degree of unsaturation – Fats are solids at room temperature – Oils are liquids at room temperature When the body uses adipose tissue, the triglycerides react with water to release free fatty acids into the blood – Can be used as an immediate energy source – Oils contain more unsaturated fatty acids than fats do Complex lipids Complex lipids Have more than two types of components Usually have 3 or more of the following: – – – – – Glycerol Fatty acids A phosphate group An alcohol (other than glycerol) A carbohydrate Phospholipids: Complex lipids that contain phosphate Steroids: Composed of fused carbon rings – A major component of membranes – Amphipathic = hydrophilic head and hydrophobic tail – Three 6­member rings and a single 5­member ring Cholesterol: A steroidal alcohol Phospholipids Phospholipids The amphipathic nature of phospholipids (the fact that they have a polar and a nonpolar end) gives them unique behavior in water Polar regions face the water Nonpolar regions face each other Results in either bilayer (like cell membrane) or micelle (forms from single layer) Proteins Proteins Main structural components of cells Serve as enzymes, which catalyze chemical reactions Macromolecules made up of monomers called amino acids – 20 amino acids form all different combos Peptide bonds Peptide bonds Each amino acid molecule has three important parts – – – Chains form as a result of reactions between the amino group of one a.a. and the carboxyl group of another a.a. Covalent bond formed by this reaction is called a peptide bond Amino functional group (­NH2) Carboxyl functional group (­COOH) Characteristic side chain (R group) Levels of protein structure Levels of protein structure Primary structure: The order in which amino acids are bonded together to form the protein chain Secondary structure: Results when hydrogen bonding occurs between the amino hydrogen of one a.a. in the primary chain and the carboxyl oxygen of another a.a. Tertiary structure: Results when α­ helices and pleated sheets interact – Folded or spherical – α­helices, β pleated sheets, random coils Quaternary structure: Result when several polypeptides interact with each other – Ex. Hemoglobin—contains 4 highly folded polypeptide chains (globin portion) and 4 iron­containing heme groups, tucked into each of the folded polypeptides Hydrolysis and Denaturation Hydrolysis and Denaturation Hydrolysis: “Breakdown by H2O” Denaturation: When the bonds holding a protein chain in its 3o or 2o confirmation are broken – Addition of water to peptide bonds breaks them – It’s the means by which digestive enzymes break down ingested food so it can be absorbed by the blood – Can result from heating, exposure to extreme pH, or chemicals Nucleic acids Nucleic acids High MW macromolecules responsible for storing and using genetic info in living cells and passing it on to future generations Classified into 2 categories: – Deoxyribonucleic acid (DNA) – Ribonucleic acid (RNA) Found in primarily in cell’s nucleus Found primarily in the cytoplasm around the nucleus Composed of three components: Nucleotides Nucleotides The 3 components are chemically bonded, with the sugar molecule between the base and phosphate When nucleic acids bind to form chains, bonds form between the phosphate of one nucleotide and the sugar molecules – The bases extend out of the chain from each sugar molecule – An organic nitrogenous base – A sugar (DNA = deoxyribose; RNA = ribose) – A phosphate group ATP ATP Adenosine triphosphate A nucleotide Used as the body’s primary energy carrier It’s a modified RNA that has adenine as its base and two additional phosphates bonded in sequence to the original sequence – The high energy input used to create these high­energy phosphate bonds is “stored” – When energy is needed, the terminal phosphate is hydrolyzed off DNA DNA Double helix A­T G­C The pairing is the same in all DNA, but the sequence determining your genetic code – Determines what polypeptides you make DNA replication DNA replication Transcription Transcription DNA do not leave nucleus, so needs a messenger DNA uncoils Single­stranded mRNA is synthesized – mRNA Translation Translation DNA’s message is translated into protein from the mRNA at the ribosome Cell Structure and Function September 30, 2010 Cell Theory • The cell is the basic structural and functional unit of the body • The activities of our cells dictates the activities of our whole body • The biochemistry of the cell is controlled by what types of “subcellular” structures it contains • Basis for the “continuity of life” Cell Theory • All known living things are made up of cells • All cells are derived from pre-existing cells using the process known as cell division • Cells contain hereditary information, which is passed from cell to cell during division Cell Theory • All cells are basically the same in chemical composition • All energy flow (metabolism and biochemistry) of life occurs within cells Prokaryotic Cells • Cells that lack a membrane-bound nucleus – Genetic material is dispersed throughout the cytoplasm • No membrane-bound organelles • A simple internal structure • Most primitive type of cell • Examples include: – Bacteria – Blue-green algae Eukaryotic Cells • Many unicellular organisms are eukaryotic – Ex. Paramecium • All cells in multicellular organisms are eukaryotic • Possess a nuclear membrane surrounding the genetic material • Contain numerous membranebound organelles • Complex internal structure Common Features of Cells • Chemical composition – Contain roughly 24 of the naturally occurring elements • All contain plasma membrane, cytoplasm, and nucleus Common Features of Cells • All cells use nutrients and O2 to provide energy • Aerobic (cellular) respiration – Discharge CO2 and wastes products to the outside – Synthesize materials necessary for cell structure, growth, and repairs Common Features of Cells • Detect and respond to changes in the internal environment • There is a movement of materials within the cell • Maintain differences between intra- and extracellular fluid by controlling exchange of material • Reproduce Specialized Functions of Cells • The function depends on the particular type of cell • Depending on its particular specialization, the cell can modify a standard function • This specialized function occurs in addition to basic functions – All of the basic cell functions are aimed at maintaining cell survival • Cell structure also changes in conjunction with its specialization Basic Cell Plasma Membrane • Determines cell boundaries • Separates intra- and extracellular fluids • Gives the cell its form • Facilitates intercellular communication Plasma Membrane • Composition: – 55% protein – 25% phospholipid – 13% cholesterol – 4% lipids – 3% carbohydrates Plasma Membrane • Semipermeable • Controls movement of molecules into and out of cell Bulk Transport • Phagocytosis • Endocytosis – Receptor-mediated • Exocytosis Phagocytosis • Used to take in large, multimolecular particles • Only a few, specialized cells can perform phagocytosis • Involves the use of structures known as pseuodopods • Cells move by ameoboid movement • Contain vacuoles Phagocytic Cells • Neutrophil • Monocyte • Macrophage • http://academic.brooklyn.cuny.edu/biology/bio4fv/page/phago.htm Endocytosis • Two types: – Pinocytosis – Receptor-mediated endocytosis Pinocytosis • “Cell drinking” • Non-selective • Ingestion of dissolved particles • Extracellular fluid is taken into the cell • Cytoplasmic membrane invaginates and pinches off, placing small droplets of fluid into a pinocytic vesicle • Also way to retrieve extra plasma membrane Receptor-Mediated Endocytosis • Selective • Used for import of specific large molecules • Utilizes receptors on the cell surface • Mechanism by which the following are taken into the cell: – – – – Cholesterol Vitamin B12 Insulin Iron The Nucleus • Largest organized cell structure • Visible under a light microscope • Usually centrally located • Oval or round in shape • Control center of the cell • Genetic library • Protein czar • Most cells have a single nucleus, but some do have multiple nuclei (multinucleate) • Cells with no nuclei are considered anucleate – RBCs Nuclear Envelope • Double membrane – Outer membrane is continuous with rough endoplasmic reticulum – Inner membrane is lined with protein filaments • The two layers of the membrane fuse at certain points; pores form where this occurs • Encloses the nucleoplasm Nucleoli and Chromatin • There are usually 1-2 nucleoli per nucleus • This is the site where the subunits of ribosomes (protein factories) are assembled • The chromatin (the DNA) is coiled around proteins called histones DNA • Genetic blueprint for cell replication • Contains the directions for protein synthesis Transcription • Occurs in the nucleus • DNA to messenger RNA (mRNA) • mRNA enters cytoplasm Translation • • • Occurs in cytoplasm mRNA, rRNA, tRNA The mRNA carries genetic information encoded as a ribonucleotide sequence from the chromosomes to the ribosomes. – The mRNA is "read" by translational machinery in a sequence of nucleotide triplets called codons. Each of those triplets codes for a specific amino acid. • The ribosome and tRNA molecules translate this code into a specific sequence of amino acids. – – – – The ribosome is a multisubunit structure containing tRNA and proteins tRNAs are small, noncoding RNA chains that transport amino acids to the ribosome tRNAs have a site for amino acid attachment, and a site called an anticodon. The anticodon is an RNA triplet complementary to the mRNA triplet that codes for their cargo amino acid. Review of the Nucleus • Cell’s “control center” • Houses the cell’s genetic material – Deoxyribonucleic acid (DNA) • Serves as genetic blueprint for cell replication • Directs protein synthesis • DNA’s message is transcribed into messenger RNA (mRNA) – mRNA exits the nucleus through nuclear pores • In the cytoplasm, mRNA delivers the message to the ribosomal RNA (rRNA) – rRNA “reads” the code and translates it into the appropriate amino acid “map” • Transfer RNA (tRNA) transfers appropriate a.a.’s to their appropriate site on the “map” to make a protein DNA • • • Deoxyribonucleic acid Contains genetic instructions Backbone of DNA strand is made from alternating phosphate and sugar residues – The sugar is 2-deoxyribose, which is a pentose (5-carbon) sugar • Each strand of DNA has a direction--in a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand. This is called antiparallel. – The asymmetric ends of DNA strands are referred to as the 5′ (five prime) and 3′ (three prime) ends, with the 5' end being that with a terminal phosphate group and the 3' end that with a terminal hydroxyl group. • The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands. DNA • The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T) – These four bases are attached to the sugar/phosphate to form the complete nucleotide, as shown for adenosine monophosphate The following diagram illustrates a nucleotide, the building blocks of DNA • These bases are classified into two types; adenine and guanine are fused five- and six-membered heterocyclic compounds called purines, while cytosine and thymine are six-membered rings called pyrimidines – A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA http://www.biology-online.org/1/5_DNA.htm Chromosomes • Organized structures of DNA and proteins that are found in cells – Consist of a singular piece of DNA, which contains many genes, regulatory elements and other nucleotide sequences. • • • • • • • In eukaryotes, DNA exists in as chromatin, until the cell is ready to divide. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes may exist as either duplicated or unduplicated— unduplicated chromosomes are single linear strands, while duplicated chromosomes (copied during synthesis phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure 46 total 23 pairs Seen at the time of cell division Cytoplasm • Cellular material between nucleus and plasma membrane • Contains organelles = distinct, highly organized, membraneenclosed structures – “little organs” • Also contains inclusions = chemical substances stored within the cell – Pigments, lipofuscin, etc. • Organelles are dispersed within the cytosol = complex, gel-like liquid • Cytoskeleton = scaffolding Organelles • Similar in all cells, but have some variations depending on the specialization of the cell • Intracellular “specialty shops” • Each contains specific set of chemicals for carrying out a particular cellular function • Compartmentalization permits chemical activities that might not be compatible with each other to occur simultaneously within the same cell • Nearly ½ total cell volume occupied by organelles • 6 main types of organelles – – – – – – Endoplasmic reticulum Golgi complex Lysosomes Peroxisomes Mitochondria Vaults Cytosol • “Cell liquid” • Made up of a semi-liquid, gel-like mass laced with an elaborate protein network known as the cytoskeleton – Gives cell its shape, provides internal organization, and regulates its movements • Many chemical reactions conducted in cytosol Endoplasmic reticulum (ER) • Elaborate fluid-filled membrane system distributed evenly through cytosol • Primarily a protein- and lipid-manufacturing factory • Two types – Smooth ER: Meshwork of tiny interconnected tubules – Rough ER: Projects outward from the smooth ER as stacks of flattened sacs • Relative amount of smooth and rough ER varies between cells, depending on the activity of the cell Rough ER • Outer surface is studded with small, dark-staining particles = ribosomes – Ribosomal RNA-protein complexes that synthesize proteins • Most abundant in cells specialized for protein secretion (e.g. digestive cells) or cells that require extensive membrane synthesis (e.g. egg cells) Rough ER • For exam: – Ribosomes on outer surface – Protein manufacturing – “Membrane factory” – Proteins – Phospholipids – All secreted proteins Rough ER • Ribosomes produce proteins and they’re released into the ER lumen • These proteins serve two functions – Export to exterior as secretory products (hormones or enzymes) – Transport within cell for construction of new membrane (PM or organelle membrane) • Membranous walls also contain enzymes essential for lipid synthesis Ribosomes • Granules of protein and RNA • Protein synthesis • Free = Produce globular proteins in cytosol • Membrane-bound = Produce proteins destined for membranes or for export Link between smooth and rough ER • After proteins are synthesized and released into the ER lumen, it can’t pass through ER membrane Smooth ER • Does not contain ribosomes – Not involved in protein synthesis • Sparse in most cells • Serves primarily as central packaging and discharge site for proteins of RER • Proteins and lipids pass from RER to SER • Portions of smooth ER then “bud off” into transport vesicles – These are then transported to Golgi • Abundant SER in muscle (sarcoplasmic reticulum) – Stores calcium needed for muscle contraction Smooth ER • For exam… – Continuous w/ rough ER – Contains enzymes involved in – Lipid metabolism, cholesterol synthesis – Steroid hormone synthesis – Absorption, transport of fats – Detoxification – Glycogen breakdown – Forms transport vesicles Golgi complex • Closely associated with ER • Each complex consists of a stack of flattened, slightly curved, membrane-enclosed sacs – Stacks not physically connected to one another • Stacks are thin in middle but have dilated (bulging) edges • Number of stacks differs per cell, with increased numbers found in cells highly specialized for protein secretion Golgi complex • ER transport vesicle fuses with Golgi membrane sac closest to cell center • Vesicle membrane opens up and integrates into Golgi membrane – Contents released into interior of Golgi sac • “Raw” proteins from ER modified into final form • The “finished” products are then sorted and segregated according to their function and destination Golgi “Post office” • Finished products collected in dilated ends of sacs • Outermost end pinches off to form membrane-enclosed vesicle – Cargo destination determines the wrapping – Each different surface marker serves as specific docking marker (like an address on an envelope) – Vesicle can then only “dock and unload” at the appropriate docking-marker acceptor (house address) Golgi in Secretory Cells • In secretory cells, numerous large secretory vesicles bud off from stacks – These include endocrine cells that secrete digestive enzymes • Secretory proteins remain stored within the vesicles until the cell is stimulated by a specific signal indicating the need for release • Upon appropriate stimulation, vesicles move to cell’s periphery • Contents are quickly released to cell’s exterior as vesicle fuses with PM = exocytosis (secretion) Exocytosis • Process by which a cell directs secretory vesicles out of the cell • Membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane • Involves 5 steps: – – – – – Vesicle trafficking Vesicle tethering Vesicle docking Vesicle priming Vesicle fusion Lysosomes • Membrane-enclosed sacs containing powerful hydrolytic enzymes – Catalyze hydrolysis reactions • Break down organic molecules of cell debris and foreign material (e.g. bacteria) – “lyse” = breakdown – “some” = body • Similar to hydrolytic digestive enzymes • Vary in size and shape, depending on the contents they are digesting – Usually oval or spherical • Autolysis = self-digestion • • • “Cell eating” Way that large mutimolecular particles are internalized Only a few cells are capable of this Phagocytosis – White blood cells = “professional phagocytes” • • When foreign object (bacterium) is encountered, phagocyte extends pseudopods (“false feet”), surrounding and trapping it Lysosome fuses with the membrane of the internalized vesicle and releases hydrolytic enzymes into it – These attack the bacterium/foreign object, without doing damage to the rest of the cell • Broken-down objects get recycled and re-used (amino acids, glucose, fatty acids) • Can also fused with aged or damaged organelles to remove them from the cell – “selective digestion” Lysosomes • People can be missing various lysosomal enzymes – Tay-Sachs is a lysosomal storage disease • Characterized by abnormal accumulation of complex molecules found in nerve cells • Causes progressive nervous system degeneration Peroxisomes • 1/3 to ½ the average size of lysosomes • Like lysosomes, in that they are membrane-enclosed sacs of enzymes • Instead of hydrolytic enzymes, peroxidases contain oxidative enzymes – Use O2 to strip hydrogen from certain molecules = oxidation • Detoxifies various wastes and neutralizes free radicals Mitochondria and ATP • Rod-shaped or oval • Enclosed by double membrane – Smooth outer membrane – Inner membrane that forms a series of infoldings/shelves called cristae, which project into an inner cavity filled with gel-like matrix • Cristae contain electron transport proteins • Folds greatly increase surface area • Matrix contains citric acid cycle enzymes that prepare nutrient molecules for final extraction of energy by cristae proteins Vaults • • • • “Cellular transport vehicles” 3x as large as ribosomes Shaped like octagonal barrels – Have multiple arches (“vaults”) and a hollow interior • • • Sometimes seen open, like unfolded flowers, with each half bearing 8 “petals” attached to a center ring Do not show up with ordinary staining techniques Nuclear pores are also octagonal shaped, so vaults may serve as “cellular trucks”, docking at or entering nuclear pores, picking up synthesized molecules, and delivering them elsewhere Cargo may be mRNA or ribosomal subunits Cytosol: Not just a liquid • Important in: – Regulation of intermediary metabolism • Large set of chemical reactions inside the cell that involve the degradation, synthesis, and transformation of small organic molecules such as simple sugars, amino acids, and fatty acids • Critical for capturing energy for cell activities and providing raw materials for structure and growth – Ribosomal protein synthesis • Free ribosomes for synthesis of proteins needed in the cytoplasm – Storage of fat, carbohydrate, and secretory, transport, and endocytic vesicles • Excessive nutrients not immediately used for ATP production are converted into cytosolic storage forms called inclusions – Not surrounded by membrane • Adipose tissue (fat) = most important storage product • Glycogen = Storage form of glucose • Secretory vesicles processed and packaged by the ER and Golgi remain in cytosol until signaled to empty Cytoskeleton • Cell “bone and muscle” • Intracellular protein scaffolding network • Organizes cell components and controls cell movement • Three elements: – Microtubules – Microfilaments – Intermediate filaments Microtubules • Largest cytoskeletal elements • Long, slender, hollow tubes composed of tubulin molecules • Maintain asymmetric cell shapes and coordinate complex cell movements • Also play an important role in coordinating the following complex cell movements: – Transport of vesicles = “highways” – Distribution of chromosomes during cell division – Movement of specialized cell projections such as cilia and flagella Cilia and Flagella • Cilia = Numerous tiny, hairlike protrusions – “Eyelashes” – Beat in concert – Found on respiratory, digestive, brain, reproductive tract cells • Flagellum = Single, long, whiplike appendage – “Whip” – Only human cells that have them are sperm Microfilaments • Smallest elements of the cytoskeleton • Most obvious are actin • Unlike the hollow tube formed by tubulin, actin is assembled into two strands twisted around each other to form a helical microfilament – In muscle, myosin protein forms another type of microfilament • Two functions: Microfilaments – Play vital role in various cell contractile systems (actin/myosin in muscle; pseudopods in amoeboid movement) – Act as mechanical stiffness for cell projections (microvilli) • Also increase surface area Intermediate filaments • Intermediate in size between microtubules and microfilaments • Irregular, threadlike proteins • Help resist mechanical stress • Different types of IFs for different cell types, depending on their structural or tensionbearing needs – Skin contains keratin IFs Cytoskeleton Review #/Cell Microtubules Many Structure Long, slender hollow tubes compos ed of tubulin Intertwined helical chains of actin;als o myosin Irregular, threadlike proteins Function Maintain cell shape and coordinate complex cell movements Microfilaments Many Contractile systems; mechanical stiffener for microvilli Intermediate filaments Many Resist mechanical stress Centrosome and Centrioles • Centrosome = region near nucleus – Microtubule organizing center • Centrioles – 27 microtubules forming tube – Play role in cell division ...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online