Lecture Notes 10/16-11/15

cell structure and function

development of cell theory

• 1665 Robert Hooke-Royal Society of England
• dead cork cells
• "cell" from cellulae (Latin-"small room")
• 1838 Scheiden "Botanist" stated all plants made of cells
• Schwann "Zoologist" all animals made of cells
• derived that
1. all living things are composed of cells
2. cell is the basic unit of structure/function of life
• 1858 Virchow studied cell division
1. cells come only from preexisting cells
2. life comes from lie

methods of studying cells

• microscopes
• high speed centrifuge/differential centrifugation
• cell size (small) most human cells between 5-20 μ
• determined by surface area to volume ratio
• surface increases by the square (area)
• volume increases by the cube (volume)
• small size needed for volume (where life occurs)
• be able to acquire needed materials through its suface area
• size & shape determined by cell function
• strategies to increase surface area
• folding projections long & thin etc.

major cell types

• prokaryotic cells (before nucleus)
• very small (1-10 microns)
• no membrane bounded organelles
• have cytoplasm, cell membrane, nucleoid region, cell wall
• ex: bacteria, blue-green algae (uniform color)
• eukaryotic cells (true nucleus)
• 4 major cell lines (4 kingdoms)
• Plant, Animal, Fungi, Protista
• all have nucleus and membrane bounded organelles

organelle journey

1. nucleus
• nuclear membrane (double) has huge pores but smaller than DNA
• contains chromatin (DNA + protein)
• becomes chromatin at division
• stains easily (iodine, methylene blue)
  
2. nucleolus
• forms ribosomal DNA
• site of activity in nucleus
3. ribosomes
• RNA and protein
• 2 subunits
• cytoplasmic organelles
• endomembrane system
4. endoplasmic reticulum (ER)
• system of channels and saccules continous with outer layer of nuclear membrane
• rough ER-protein/lipid synthesis, products move to Golgi apparatus
• smooth ER-no ribosomes, may produce lipids and steroid hormones, detoxify drugs in liver (alcohol etc.), muscle cells store Ca⁺⁺, forms transport vehicles
5. Golgi apparatus
• stack of apparatus
• inner face towards ER
• outer face towards cell membranes
• protein filled vesicles from ER move to Golgi to be modified (2, 3, 4 levels of structure and/or lipo or glyco proteins formed here)
6. lysosomes (loose body)
• contain hydrolytic enzymes (40+) "suicide bags"
• digest worn out or foreign molecules
• common in white blood cells
7. microbodies
• similar to lysosomes
• contain specific enzymes-catalase
• peroxisomes-hydrogen peroxide H₂O₂ produced and destroyed by catalase
• glyoxysomes-leaves that photosynthesize germinating seeds to convert lipids into sugars for metabolism
8. vacuoles
• large membrane sac
• large in plants (central vacuole)
• reduces volume of living material
• so improves surface area to volume ratio
• filles with water osmosis-turgor pressure (turgid cells)
• smaller in animals
• storage area for cells
• pigments besides chlorophylls (flowers)
• toxic substances (chemical defense)
9. chloroplasts (anabolic rxns)
• contain pigments of photosynthesis
• double membrane contains thylakoid
• have own DNA, reproduce selves by division
• make some of own proteins
• theory-captured bacteria (symbionts)
10. mitochondria (catabolic rxns)
• double membrane system
• internal membrane folded into cristae
• intermembrane space critical to electron transport and ATP production
• has own DNA (eve theory)
• captured bacteria (symbionts)
• reproduce themselves by divison
11. cytoskeleton
• network of interconnected filaments and tubules from nucleus to plasma membrane maintains cell shape and moves organelles appear and disappear during cell cycle made up of monomers of actin, myosin, tubulin
12. actin and myosin (found in muscles as well as cytoskeleton)
• actin moves organelles around and forms pseudopodia in Amoeboid movement
13. intermediate filaments
• between actin filaments and microtubules
• take part in cell to cell junctions in skin protein keratin which is tough
14. microtubules
• tubulin subunits
• small hollow cylinder about 25 nm from 0.2 to 25 microns in length
• two forms (lambda and beta) forms dimer which is a lambda and beta pair
• forms strings of dimers (doublets) that coil to form tube
  
• 13 rows of dimers
15. centrioles
• 9 triplents arranged in circle with no center
• animal cells have two at right cells
• plants have centrosomes but not centrioles
16. cilia and flagella
• differ by length but have a 9 + 2 circular arrangement
• the 2 are in the center of the 9 microtubule doublets
• eukaryotes have membranes surrounding them but prokaryotes don't

cell membrane

• unit membrane is composed of a phospholipid bilayer with proteins
1. by weight the membrane is 50% lipid and 50% protein
2. hydrophobic fatty acid face inwards
3. hydrophilic phosphate with many different groups attached faces outwards
• E for external environment
• C for cytosol or cytoplasm
4. produced by endoplasmic reticulum with inner face of similar or same composition as E face or outer face of membrane
• phospholipids freely rotate on their long axis in the membrane but seldom flip-flop between layers
• takes ATP energy to do this
• results in the membrane being asymmetrical with distinct inner and outer layers of different protein composition and function
• cholesterol molecules fit between the fatty acid tails
1. reduces permeability of membrane
2. increase stiffness of membrane
3. can flip-flop between layers
• two major methods used to study unit membrane
1. freeze fracture
• freeze a solution of cells (red blood) in liquid nitrogen
• take cube of "ice" and split it with a sharp edge
  
• by chance alone some membrane will be separated between the bilayer
• place sample in a leofelizer to "etch" (freeze dry) it to expose the edge of the membrane
• examine with a scanning electron microscope
• can readily see E face and P (or C) face with proteins embdedded within (E face has glycolipids and proteins, P face has cytoskeletal filaments
1. cell fusion with immunoglobins and florescent dyes
• from cell culture use cells from two different but related species (human and mouse)
• membranes fuse and at first proteins remain separate
• after 30-40 min membrane proteins have completely interspersed with each other
• can move at about 2 μm/sec laterally in membrane
  
• asymmetry makes/allows each side of the membrane to be functionally distinct from each other (mitochondria, chloroplasts), enzyme action one side vs. other side
• disulfide bridges, tertiary bonding, vanderwaal's forced, ionic interactions
  
• membrane proteins
• peripheral proteins (on outside and inside of membrane)
  
• integral proteins
• anchored by covalent bonds or molecular interactions
• pH change or shaking can disrupt them
• integral proteins within membrane
  
• hydrophilic on surfaces and hydrophobic within membranes
• channel proteins-form pores
• carrier proteins-phagocytosis or pinocytosis, selective
• receptor proteins-for protein hormones, vitamins, or lipoproteins that may need to gain entry
• enzymatic proteins-for photosynthesis or respiration, especially electron transport
• LAB-differential centrifugation, segregate parts
• reside: starch grains, provides energy for embryo
• digestion = hydrolysis
• H₂O₂ is an oxidizer
• peroxisomes reduce it to water and oxygen
• presence of oxidizing molecules cause aging
• vacuoles hard to see, mostly salt and water
• turgor pressure-tree roots
• chromoplasts-petals, not green/plastids
• large vacuoles broken into smaller
• different ratios of different colored chromoplasts
• insects-largest group of plant consumers
• plants develop defenses, i.e. caffeine
• anabolism-build up
• catabolism-break down
• chloroplast
• 2-outer eukaryotic, inner prokaryotic
• outer membrane-clear, thylakoid green
• endosymbion theory-mitochondria/chloroplasts-bacteria adapted symbiosis
• monochlonoantibodies
• glamuglobulims
• ave theory-chloroplasts and mitochondria have own DNA
• trace ancetry through mutations
• MTAC = microtubule organizing center
• centrioles produce microtubules
• filaments fasten cells together
• SPM = semipermeable osmosis
• Ψ_s = -iCRT
• microtubule-hollow, 9 sets of triplets
• plants lack centrioles
• centrosomes located in MTOC region
• shaft of glagellum-ring of 9 microtubule doulbets anchored to central pair
• ATP changes shape
• membrane is extension of cytoplasm
• basal body at the bottom, then doublets continue
• cytoplasmic streaming
• animal cell
• hypotonic-burst, lysis
• hypertonic-shrivels, crenation
• Singer and Nicolson-fluid-mosaic model, freeze-fracture of membrane
• asymmetrical phospholipid bilayer
• Gibbs' free energy
• endosymbiosis theory-membrane through invagination
• MMC-major histocompatibility complex
• faciliated diffusion-no ATP
• energy causes protein to change shape
• doesn't take very much
• solute is moving through diffusion until even with membrane
• sodium potassium pump-active transport mechanism
• gradient high → low
• diabetes
• type I-juvenile
• type II-obesity
  

Chapter 5-Membrane Structure and Function


5.1 Membrane Models

• lipid-soluble molecules enter cells more rapidly than water-soluble molecules
• sandwich/unit membrane model: the outer dark layer of the membrane contains protein plus the hydrophilic heads of the phospholipids, and the interior is the hydrophobic tails of these molecules
• fluid-mosaic model-introducted in 1972 by S. Singer and G. Nicolson proposing that the membrane is a fluid phospholipid bilayer in which protein molecules are either partially or wholly embedded. The proteins are scattered throughout the membrane in an irregular pattern that can vary from membrane to membrane

5.2 Plasma Membrane Structure and Function

• phosopholipids-molecules that form the bilayer of cell membranes, with polar hydrophilic heads bonded to two nonpolar hydrophobic tails
• the hydrophilic (polar) heads face the intracellular and extracellular fluids
• the hydrophobic (nonpolar) tails face each other
• glycolipids-lipid in plasma membranes that bear carbohydrate chains attached to hydrophobic tails
• cholesterol-lipid found in animal plasma membranes; related steroids are found in plant plasma membranes
• cholesterol reduces permeability of the membrane to most biological molecules
• peripheral proteins occur either on the outside of inside surface of the membrane or the inside surface; some are anchored to the membrane by covalent bonding, others by noncovalent interactions that can be disrupted by shaking or changing pH
• integral proteins are within the membrane; hydrophobic regions are embedded within the membrane and hydrophilic regions project from both surfaces of the bilayer
• many integral proteins are glycoproteins
• glycoproteins-proteins in plasma membranes that bear carbohydrate chains that project externally, "sugar-coated"
• plasma membrane is asymmetrical
• carbohydrate chains occur only on outside surface and cytoskeletal filaments attach to proteins only on inside surface
• at body temperature, phospholipid bilayer of plasma membrane has olive oil consistency
• the greater the concentration of unsaturated fatty acid residues, the more fluid is the bilayer
• in each monolayer, hydrocarbon tails wiggle, and entire phospholipid molecule can move sideways at a rage averaging about 2 m per second
• proteins are generally free to drift laterally in the fluid lipid bilayer
• fluidity of membrane is needed for the functioning of some proteins
• enzymes become inactive when the membrane solidies
• plasma mebranes of various cells and their organelles each have their own unique collections of proteins
• channel proteins-proteins through which a substance can simply move across the membrane
• carrier proteins-proteins that combine with a substance and help it to move across the membrane
• receptor proteins-proteins with shapes that allow specific molecules to bind to them
• binding molecules can cause proteins to change shape and bring about a cellular response
• enzymatic proteins-proteins that carry out metabolic reactions directly
• peripheral proteins stabilize and shape the plasma membrane
• carbohydrate chains of glycolipids and glycoproteins serve as the "fingerprints" of the cell
• cell-cell recognition
  

5.3 Permeability of the Plasma Membrane

• differentially-selectively
• permeable-can move across the membrane
• macromolecules cannot diffuse across the membrane because they are too large
• ions and charged molecules cannot cross the membrane because they are unable to enter the hydrophobic phase of the lipid bilayer
• noncharged, lipid-soluble molecules such as alcohols and oxygen can cross the membrane with ease by slipping between the hydrophilic heads of the phospholipids and pass through the hydrophobic tails of the membrane
• concentration gradient-gradual decrease in concentration over distance
• oxygen is more concentrated outside because a cell uses oxygen during cellular respiration
• carbon dioxide is more concentrated inside because it is produced when a cell carries out cellular respiration
• macromolecules can cross through vesicle formation
• ions and molecules (amino acids and sugars) cross through transport proteins
• carrier proteins combine with an ion/molecule and then transport it
• channel proteins form a channel that allows ions/charged molecules to pass through
• passive transport does not use chemical energy
• diffusion
• facilitated transport
• active transport requires chemical energy
• active transport
• endocytosis
• exocytosis
• diffusion-movement of molecules from a higher to a lower concentration until equilibrium is achieved and they are distributed equally
• diffusion is a physical process that can be observed with any type of molecule
• solution-fluid (solvent) that contains a dissolved solid (solute)
• solvent-liquid portion of a solution that dissolved the solute
• solute-substance dissolved in a solvent, forming a solution
• gases can diffuse through lipid bilayer (oxygen and carbon dioxide)
• after inhaling, the concentration of oxygen in alveoli is higher than that in blood, so the oxygen diffuses into the blood
• osmosis-diffusion of water into and out of cells
• a thistle tube containing a 10% sugar solution is covered at one end by a differentially permeable membrane and placed in a beaker containing a 5% sugar solution
1. a differentially permeable membrane separates 2 solutions, does not permit passage of solute
2. beaker has more water (lower percentage of solute) and thistle tube has less water (higher percentage of solute) per volume
3. membrane permit passage of water, there is net movement of water from the beaker to the inside of thistle tube
4. concentration of solute in thistle tube is less than 10% because there is now less solute per volume and the concentration of solute in the beaker is greater than 5% because there is now more solute per volume
• osmotic pressure-pressure that develops in a system due to osmosis
• the greater the possible osmotic pressure, the more likely water will diffuse in that direction
• due to osmotic pressure, water is absorbed from the human large intestine, retained by the kidneys, and taken up by capillaries from tissue fluid
• tonicity-degree to which a solution's concentration of solute versus water causes water to move into or out of cells
• isotonic solutions-solute concentration is same on both sides of membrane, no net gain or loss of water
• hypotonic solutions-solutions that cuse cells to swell or burst due to an inake of water, lower of percentage of solute
  
• any concentration of a salt solution lower than 0.9% is hypotonic to red blood cells
• lysis refers to disrupted cells
• hemolysis is disrupted red blood cells
• turgor pressure-swelling of a plant cell in a hypotonic solution
• hypertonic solutions-solutions causing cells to shrink or shrivel due to a loss of water, solution with a higher percentage of solute
• crenation-shrunken red blood cells
• plasmolysis-shrinking of cytoplasm due to osmosis
• carrier proteins-protein that combines with and transports a molecule or ion across the plasma membrane, required for faciliated transport and active transport
• facilitated transport-passage of molecules such as glucose and amino acids across plasma membrane even though they are not lipid-soluble
• active transport-use of a plasma membrane carrier protein to move a molecule/ion from a region of lower to higher concentration, opposing equilibrium and requiring energy ; molecules or ions move through the plasma membrane, accumulating on either side
• sodium-potassium pump-carrier protein in the plasma membrane that moves sodium ions iout of and potassium into animal cells, important in nerve and muscle cells
• passage of salt (NaCl) across plasma membrane is important
• Cl^- crosses plasma membrane because it is attracted by Na⁺
• sodium ions are pumped across and chloride follows
• exocytosis-vesicles formed by the Golgi apparatus carrying a specific molecules fuse with the plasma membrane as secretion occurs
• insulin
• during cell growth, exocytosis is used as a means to enlarge the plasma membrane, whether or not secretion is taking place
• endocytosis-cells take in substances by vesicle formation, a portion of the plasma membrane invaginates to envelop the substance and then the membrane pinches off to form an intracellular vesicle
• phagocytosis-when the material taken in by endocytosis is large (e.g. food particle, another cell)
• phagocytosis is common in unicellular organisms like amoebas and in amoeboid cells like macrophages
• pinocytosis-vesicles form around a liquid or very small particles (blood cells, cells lining kidney tubules or intestinal walls, plant root cells)
• receptor-mediated endocytosis-form of pinocytosis that is specific because it involves use of a receptor protein shaped in such a way that a specific substace (ligand) can bind to it (vitamins, peptide hormones, lipoproteins)
• receptors gather at a coated pit (layer of fibrous protein on the cytoplasmic side). Once the vesicle is formed, the fibrous coat is released and the vesicle appears uncoated
• coated pits are also involved in the transfer and exchange of substances between cells
• receptor-mediated endocytosis is important, ex: in familial hypercholesterolemia, cholesterol is transported in blood by a complex of lipids and proteins called low-density lipoprotein (LDL). Individuals with familial hypercholesterolemia inherit a gene causing them to have a reduced number and/or defective receptors for LDL in their plasma membranes. Instead of cholesterol enterng cells, it accumulated in aterial blood vessel walls, leading to high blood pressure, occluded arteries, and heart attacks

5.4 Modification of Cell Surfaces

• cell wall-structure that surrounds a plant, protistan, fungal, or bacterial cell and maintains the cell's shape and rigidity
• primary cell wall contains cellulose fibrils in which microfibrils are held together by noncellulose substances
• pectins allow the wall to stretch when the cell is growing, noncellulose polysaccharides harden the wall when the cell is mature
• pectins are abundant in the middle lamella (layer of adhesive substances that holds cells together)
• some cells in woody plants have secondary walls, which have greater quantities of cellulose fibrils and layers of cellulose fibrils are laid down at right angles to one another
• lignin is a common ingredient in secondary cell walls
• plasmodesmata-numerous narrow membrane-lined channels passing through the cell wall connecting the cytoplasm of neighboring cells
• an extracellular matrix is a meshwork of insoluble proteins with carbohydrate chains (glycoproteins) that are produced and secreted by animal cells, influences development, migration, shape, and function of cells
• collagen (strength) and elastin fibers (resistance)
• fibronects and luminins are two adhesive proteins that play a dynamic role in influencing the behavior of cells, directing cell migration during development, necessary for production of milk by mammary gland cells, bind to receptors in the plasma membrane and permit communication between the extracellular matrix and cytoplasm
• proteoglycans are glycoproteins whose carbohydrate chains contain amino sugars, providing a rigid packing gel that joins various proteins in the matrix, regulating the activity of signaling sequences that bind to receptors in the plasma protein
• adhesion junctions-internal cytoplasmic plaques
• tight junctions-where plasma membrane proteins actually attach to each other, producing a zipperlike fastening
• gap junction-allows cells to communicate

Chapter 4-Cell Structure and Function


4.1 Cellular Level of Organization

• 1830s Mathias Schleiden stated that all plants are composed of cells and Theodor Schwann stated that all animals are composed of cells
• cell-smallest unit of living matter
• a cell is not only the structural unit but also the functional unit of organs, and, therefore, organisms
• once a cell gets to a certain size, it divides (multicellular organisms grow, unicellular organisms reproduce)
• Rudolf Virchow concluded "every cell comes from a preexisting cell"
• cell theory-all living things are composed of cells, and cells come from other cells
• most cells are smaller than one millimeter
• cells need surface areas large enough to allow adequate nutrients to enter and to rid itself of wastes
• small cells have greater surface area per volume than large cells
• cells that specialize in absorption have modifications that greatly increase the surface area per volume of the cell
• columnar cells along the surface of the intestinal wall have surface foldings called microvilli that increase their surface area

4.2 Bacterial Cells

• bacteria-prokaryotic cells in the domain Bacteria
• prokaryotic cells-lacking a membrane bound nucleus and organelles
• main features of bacterial anatomy: cell wall, capsule or slime layer, flagellum, plasma membrane, cytoplasm, cytosol, ribosomes, nucleoid, plasmids, thylakoids
• cell wall-contains peptidoglycan
• capsule-surrounds cell wall
• slime layer-gelatinous sheath in lieu of a capsule
• flagellum-long, very thin appendages possessed by motile bacterium
• some also have fimbriae, short appendages that help attach them to appropriate surfaces
• plasma membrane-membrane that regulates the movement of molecules into and out of the cytoplasm
• cytoplasm-the interior of the cell, consisting of cytosol and ribosomes
• cytosol-semifluid medium
• ribosomes-small bodies that coordinate the synthesis of proteins
• nucleoid-where innumerable enzymes and chromosome (loop of DNA)/genes are located
• plasmids-small accessory rings of DNA
• thylakoids-(cyanobacteria) membranes of flattened discs containing light-sensitive pigments
• cytoplasm is the site of thousands of chemical
• bacteria are adapted to living in almost any kind of environment and are diversified to the extent that almost any type of organic matter can be used as a nutrient for some particular bacterium

4.3 Eukaryotic Cells

• eukaryotic cells-cells that have a true nucleus, a membrane-bounded structure where DNA is housed with threadlike structures called chromatin
• a membrane is a phospholipid bilayer with embedded proteins
• organelles-small bodies each with a specific structure and function, many are membrane-bounded
• the cytosol, which is a semifluid medium outside the nucleus, is divided up and compartmentalized by the organelles
• compartmentalization keeps the cell organized and keeps its various functions separate from one another
• the cytosol has an organized lattice of protein filaments called the cytoskeleton
• some eukaryotic cells, notably plant cells, have cell walls
• cell wall-supports and protects the cell but does not interfere with the movement of molecules across the plasma membrane; plant cell walls contain cellulose fibris and therefore has a different composition than the cell wall of bacteria
• endosymbiotic relationship (suggested by Lynn Margulis and others)
1. mitochondria and chloroplasts are similar to bacteria in size and in structure
2. both organelles are bounded by a double membrane--the outer membrane may be derived from the engulfing vesicle, and the inner one may be derived from the plasma membrane of the original prokaryote.
3. mitochondria and chloroplasts contain a limited amount of genetic material and divide by splitting. Their DNA is a circular loop like that of bacteria
4. although most of the proteins within mitochondria and chloroplasts are now produced by the eukaryotic host, they do have their own ribosomes and they do produce some proteins. Their ribosomes resemble those of bacteria
5. the RNA (ribonucleic acid) composition of their ribosomes suggests a eubacterial origin for chloroplasts and mitochondria
• nucleus-has a diameter of about 5 µm, prominent structure in eukayotic cell, containg chromatin in nucleoplasm
• chromatin-looks grainy, a network of strands that undergoes coiling into rodlike structures
• chromosomes-rodlike structures containing DNA and much protein, and some RNA
• nucleolus-dark regions of chromatin where ribosomal RNA is produced and where rRNA joins with proteins to form the subunits of ribosomes
• nuclear envelope-double membrane with pores separating the nucleus from the cytoplasm
• nuclear pores-100 nm, permits the passage of proteins into the nucleus and ribosomal subunits outside of the nucleus
• ribosomes are found in both prokaryotes and eukaryotes
• ribosomes are 20 by 30 nm in eukaryotes and slightly smaller in prokaryotes
• ribosomes are composed of two subunits, one large and one small, and each has its own mix of proteins and RNA
• polyribosomes-groups of ribosomes
• in eukaryotic cells some occur free within the cytosol either single or in groups, or attached to the endoplasmic reticulum
• ribosomes are sites of protein synthesis; they receive mRNA from the nucleus and synthesize proteins
• vesicle-tiny membranous sacs where ribosomes are secreted out of the cell
• ribosomes bind to endoplasmic reticulum through receptor proteins which act as docking sites for a particular molecule
• the endomembrane system consists of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, and several vesicles
• this system compartamentalizes the cell so that particular enzymatic reactions are restricted to specific regions
• membranes that make up the endomembrane system are connected by direct physical contact and/or by the transfer of vesicles from one part to the other
• endoplasmic reticulum-system of membranous channels and saccules (flattened vesicles), physically continuous with the outer membrane of the nuclear envelope
• rough ER-studded with ribosomes on the side of the membrane that faces the cytoplasm, synthesizes and moders proteins
• smooth ER-does not have attached ribosomes, continuous with rough ER, synthesizes phospholipids, steroids, fatty acids; in the testes it produces testosterone, in the liver it detoxifies drugs
• Camillo Golgi discovered the Golgi apparatus in 1898
• Golgi apparatus-stack of three to twenty slightly curved saccules whose appearance can be compared to a stack of pancakes
• in animal cells one side of the stack is directed toward the ER and the other toward the plasma membrane
• Golgi apparatus contains enzymes that alter the carbohydrate chains first attached to proteins in the rough ER
• the Golgi apparatus packages its products in vesicles that depart at the outer face
• some of these vesicles are lysosomes
• lysosomes-membrane bounded vesicles produced by the Golgi apparatus that have a very low pH and powerful hydrolytic digestive enzymes
• lysosomes sometimes break down macromolecules, fusing with these vesicles and being engulfed by white blood cells
• autodigestion is when parts of a cell are digested by its own lysosomes
• apoptosis-programmed cell death
• peroxisomes-membrane-bounded desicles that contain specific enzymes imported from the cytosol
• have enzymes for oxiding small organic molecules with the formation of hydrogen peroxide
• RH2 + O2 → R + H2O2
• in plants, peroxisomes oxidize fatty acids into molecules and carry out a reaction in leaves that releases carbon dioxide that can be used for photosynthesis
• vacuole-large membranous sac
• plant cells have a large central vacuole so filled with a watery fluid that it gives added support to the cell
• vacuoles store substances
• plant vacuoles contain water, sugar, salt, pigments, toxic molecules
• chloroplasts and mitochondria are two eukaryotic membranous organelles that specialize in converting energy to a form that can be used by the cell
• chloroplasts-use solar energy to synthesize carbohydrates
• mitochondria-where broken down carbohydrate-derived products to produce ATP molecules
• photosynthesis is the process by which solar energy is converted to chemical energy within carbohydrates
• solar energy + carbon dioxide + water → carbohydrate + oxygen
• carbohydrate + oxygen → carbon dioxide + water + energy
• when a cell needs energy, ATP supplies it
• chloroplasts, which are about 4-6 μm in diameter and 1-5 μm in length, are plastids
• stroma-fluid enclosed by two membranes bounding the chloroplast containing DNA, enzymes, ribosomes
• thylakoids-interconnected flattened sacs in grana
• grana-stacked up structures containing thylakoids
• mitochondria are 0.5-1.0 μm in diameter and 2-5 μm in length
• mitochondria are also bounded by two membranes
• cristae-invagination of inner membrane, providing a greater surface area to accommodate the protein complexes and other participants in cellular respiration
• matrix-where the cristae project, inner space filled with semifluid membrane that contains enzymes that break down carbohydrate products, releasing energy that is used for ATP production on the cristae, also contains DNA and ribosomes
• cytoskeleton-network of interconnected filaments and tubules that extends from the nucleus to the plasma membrane in eukaryotic cells
• cytoskeleton change into spindles, contain three types of elements: actin filaments, intermediate filaments, microtubules
• actin filaments are long, thin fibers (7 nm in diameter) containing two chains of globular actin monomers twisted about one another in a helical manner
• they form a dense complex web just under the plasma membrane to which they are anchored by special proteins, they are seen in microvilli that project from intestinal cells, their presence most likely accounts for the ability of microvilli to alternately shorten and extend into the intestine; in plant cells they form the tracks along which chloroplasts circulate or stream in a particular direction; the presence of a network accounts for the formation of pseudopods, extensions that allow certain cells to move in an amoeboid fashion
• motor molecules-proteins that can attach, detach, reattach along an actin filament
• in the presence of ATP, myosin pulls actin filaments along
• intermediate filaments (8-11 nm in diameter) are a ropelike assembly of fibrous polypeptides, but the specific type varies according to the tissue
• some support the plasma membrane and take part in the formation of cell-to-cell junctions
• in the skin filaments made of keratin give mechnanical strength
• need to have phosphate added by soluble enzymes
• microtubules-small hollow cylinders 25 nm in diameter and 0.2-25 μm in length made of a globular protein called tubulin
• when assembly occurs, and tubulin molecules come together as dimers and arrange themselves in rows
• regulation of microtubule assembly is under control of a microtubule organizing center/MTOC
• centrosome-the main MTOC, near the nucleus, radiates microtubules that help maintain the shape of the cell and act as the track along which organelles can move
• centrioles-short cylinders with a 9 + 0 pattern of microtubule triplets
• in animal cells and most protists, a centrosome contains 2 centrioles lying at right angles to each other
• before an animal cell divides, the centrioles replicate and the members of each pair are at right angles to one another. Then, each pair becomes part of a separate centrosome that moves apart and organizes the mitotic spindle
• plant and fungal cells have centrosome equivalents but no centrioles, which means they may not be necessary to the assembly of cytoplasmic microtubules
• in cells with cilia and flagella, centrioles give rise to basal bodies that direct microtubule organization
• a basal body may function for a cilium/flagellum like a centrosome does for a cell
• cilia/flagella-hairlike projections that can move either in an undulating fashion (whip) or stiffly (oar)
• cellular paramecia move by cilia, sperm cells have flagella, our respiratory tract has cilia
• in eukaryotic cells, cilia and flagella have 9 microtubule doublets arranged in a circle around 2 central microtubules called the 9 + 2 pattern, moving when the microtubules slide past one another
• each cilium and flagellum has a basal body lying in the cytoplasm at its base and have the same arrangement of microtubule triplets