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Date Created: 05/21/16
CELL BIOL 225 Lecture 15 Physiological Responses to Insulin • Stimulate glycogen synthase • Increase protein synthesis • Use glucose in lipid synthesis • Transfer glucose transporters to membrane o Need transporters to take glucose out of the blood stream • Activate Ras protein and stimulate cell growth and division o Ras – monomeric G protein involved n cell growth Figure above Explains: • Insulin binding stimulates PI3K which produces PIP3 and results in protein synthesis, glucose uptake and glycogen synthesis. • PI3K – phosphotidylinosital kinase • PDK1 = PI3K – dependent kinase • PKB = protein kinase B, more commonly called AKT Growth Factor Receptors • Growth factor receptors binds to RTK (Receptor Tyrosine Kinase) • Signal Trasmission • Activation of Ras o Ras activates the MAP Kinase Pathway • Activaion of MAPK pathway o MAPK – mitogen activated Protein Kinase ▯ Stimulates growth and reacts to growth factors. • The difference between G protein coupled receptors vs RTKs o RTKs go through the membrane once (one membrane spanning region) o G protein coupled receptors go through the membrane 7 times (spanning the membrane seven times) • Adaptor ptoeins bind to the phosphorylated RTK. They interact with Ras and convert it from its inactive form to its activated form. • Both GPCRs and RTKs can stimulate phospholipases and generate lipid second messengers. • Phospholipase C is being activated and DAG stays in the membrane and InsP3 foes to the InsP3 receptor channel where Ca+ is released The steps of a generalized MAP Kinase Cascade • Growth factors and hormones never enter the cell, they just bind to the receptor. • Growth factor binds to the RTK • GDP ▯ Ras GTP –GEF takes off (removed) GDP and puts on (replaces it with) GTP (GEF = G protein exchange factor) – activates Ras • Stimulate Raf • Transcription factor then goes to nucleus where the gene is, then transcription occurs. • It is a series of phosphorylations until the final step. • Active only when its phosphorylated. • Phosphorylations roles o Allows other proteins to bind o Changes protein conformation making of an enzyme for example. BIOL 225 Chapter 7 Interactions between cells and their environments • If you dissociate the cells and let them live, they will go back together, the ‘red’ cells will stay with the ‘red’ cells and the ‘blue’ will stay with the ‘blue’ cells. (from image below) Cell-‐Cell adhesive Interactions • Selectins • Certain members of immunoglobulin Super family (IgSF) and integrins. • Cadherins • Importance in development, inflammation, and metastasis Cell-‐Cell Adhesive Interactions • Cadherins – integral membrane proteins Selectins: • Selectins are a family of membrane glycoproteins that bind to specific oligosaccharides on the surfaces of neighboring cells. • “Lectin,” is a term for a compound that binds to specific carbohydrate groups. • Selectins have a small cytoplasmic segment, a single membrane-‐spanning domain, and a large extracellular portion. • Three cell-‐specific selectin types: • E-‐selectin, endothelial cells; • P-‐selectin, platelets and endothelial cells; L-‐selectin, leukocytes (white blood cells). • Just have different carbohydrate groups IgSF – immunoglobulin Super Family • Antibodies are immunoglobulin proteins with Ig domains, 70-‐110 amino acids organized into a tightly folded structure. • The human genome encodes 765 distinct Ig domains, making it the most abundant domain in human proteins. • These proteins are members of the immunoglobulin superfamily, or IgSF, and most are involved with mediating interactions of lymphocytes with cells required for an immune response (e.g., macrophages, lymphocytes, and target cells). • 2 membrane proteins and 2 cells interacting through these proteins Cadherins: • Cadherins include E-‐cadherin (epithelial), N-‐cadherin (neural), and P-‐cadherin (placental). • Cadherins have a large extracellular segment, a single transmembrane segment, and a small cytoplasmic domain. • The cytoplasmic domain is often associated with catenin proteins to tether the cadherins to the cytoskeleton and transmit signals. • Calcium ions maintain the extracellular portion of each cadherin in a rigid conformation required for cell adhesion. • Cadherins require calcium for a reaction Interactions of cells with other cells • Cadherins may mediate dynamic changes in adhesive contacts needed for morpheogenesis • During embryonic development, cells can change from an epithelium to a mesenchyme, or vice versa. Cell Junctions • Anchoring cells to other cells link epithelial cells together. o Desmosomes – made up of desmoplankin (outside) and desmoglein o Adherens Junctions – made up of cadherins and actin binding filaments. • Tight junctions – sealing the extracellular space o Tight junctions – (bladder and intestinal lining, blood brain barrier) – made up of two proteins – occludin and claudin proteins. (Mice lacking claudin die of dehydration, water leaves their body because they do not have tight junctions to keep water in their bodies) • Cell communications o Gap junctions o Plasmodesmata • Facilitated transporters on the basal surface (purple) Basal is where the capillaries meet (outside of the intestine in this case) Apical – the inside • The tight junctions help the cells maintain polarity. Without tight junctions there would be nothing to stop the Na+ Glucose transporters from slipping down the sides. • Glucose is at the surface because the glucose is at the lumen of the intestine. • Glucose comes in with Na+ because the delta G is positive so it must be coupled with the Na+ to get into the cell. The glucose leaves through facilitated diffusion out on the basal side. • Tight junctions PREVENT cell communication. Junctions for Communication • Gap Junctions – Animal cells o Made of connexin protein o Passage of ions o Communication o Hexomer o Gap junctions – protein molecules of about 1000Daltons can go through gap junctions o Defects in gap junctions can cause – deafness, blindness, cardiac problems (arrhythmia), nerve degeneration, and skin abnormalities (problems) o • Plasmodesmata –plant cells o Connects plant cells o Dilates for passage of macromolecules o Plasmodesmata are cytoplasmic channels passing through cell walls of adjacent plant cells. o Are lined by plasma membrane. o Contain a central structure, the desmotubule. o Serve as sites of cell-‐cell communication. o Dilate and up to 50 Kilo Daltons or 50,000 Dalton proteins can move through. o Both proteins and RNA (serving as a signaling molecule) move through Plasmodesmata. o Exam 2 Review Cell Biology Chapter 4 : The Structure and function of the plasma membrane 4.1 Overview of Membrane Functions 1. Compartmentalization • The plasma membrane encloses the contents of the entire cell. • The nuclear and cytoplasmic membranes enclose diverse intracellular spaces • Membrane compartmentalization allows specialized activities to proceed without external interference and enables cellular activities to be regulated independently of one another 2. Scaffold for Biochemical Activities • Because of their construction, membrane provide the cell with extensive frame work in which can be ordered for effective interaction. 3. Providing a selectively permeable barrier • Membranes prevent the unrestricted exchange of molecules from one side to the other. • Membranes provide the means of communication between the compartments they separate • Gated “Bridges” that promote the movement of select elements in and out of the enclosed space. 4. Transporting Solutes • Contains the machinery for physically transporting substances from one side of the membrane to the other. • *Genrally from a region where the solute is present at a low concentration to an area where the solute is at a higher concentration (NOT DIFFUSION) • Diffusion – going from the higher area of concentration to an area of lower concentration. • The plasma membrane is able to transport ions, thereby able to establish ionic gradients. (Which is important for nerve and muscle cells). 5. Responding to External Stimuli • Signal Transduction – Response of a cell to external conditions (external Stimuli) • Receptors – membranes posses receptors – they combine with specific molecules (ligands) or respond to other types of stimuli like light and mechanical tension. 6. Intercellular Interactions • Plasma membrane allows cells to recognize and signal one another to adhere (when appropriate) and exchange materials and information. • Proteins within the plasma membrane may also facilitate the interaction between extracellular materials and the intracellular cytoskeleton. 7. Energy Transduction • Energy transduction – the process by which one type of energy is converted to another • The most fundamental energy transduction occurs during photosynthesis – when – energy in the sunlight is absorbed by membrane bound pigments, converted to energy and stored as carbohydrates • In eukaryotes, the machinery for this energy is housed in the membrane of the chloroplast and mitochondria. 4.3 The Chemical Composition of Membranes • Membranes are lipid-‐protein assemblies in which the components are held together in a thin sheet by non-‐covalent bonds. • The lipid bilayer serves as a structural backbone and to provide a barrier that prevents random movements of water soluble molecules over the membrane (in and out of the cell) Membrane Lipids • Contains a wide diversity of lipids – all are amphiapathic • Amphiapathi – contain both hydrophobic and hydrophilic regions. • There are three main types of membrane proteins o Phosphoglycerides o Sphingolipids o Cholesterol • Phosphoglycerides o Most membrane lipids have phosphate groups and are deemed phospholipids. o Since many have a glycerol backbone – theyre phosphoglycerides • Diglycerides o Phosphoglycerides – only have two of the hydroxyl groups of the glycerol that are esterifies to fatty acids. The third is esterified to a hydrophilic phosphate group. • Sphingolipids o Less abundant class of membrane lipids o All have two hydrophobic hydrocarbon chains at one end and a hydrophilic region at the other. • Cholesterol o Sterol (cholesterol) in certain animal cells that may constitute up to 50% of the lipid molecules in the plasma membrane. o Plant cells contain “cholesterol like” sterols The nature and important of the lipid bilayer • Membrane lipids also provide the precursors for highly active chemical messengers that regulate cellular function. The asymmetry of membrane lipids • All of the glycolipids of the plasma membrane are in the outer leaflet o They serve as receptors for extracellilar glands • Membrane Carbohydrates o The plasma membrane of eukaryotes also has carbohydrates present depending on the cell type, it can be 2-‐10% carbohydrate content in the membrane. o Most (90%0 of the carbohydrates in the membrane are covalently linked to proteins to form glycoproteins. o The remainder of the carbohydrates are linked to lipids to form glycolipids. o All of the carbohydrates of the plasma membrane face outward into the extracellular space. o The carbohydrates of the glycoproteins are present as short, branches hydrophilic oligiosaccharides (typically having less than 15 sugars) o Carbohydrate projections play an important role in mediating the interactions of a cell with its environment 4.4 The Structures And Functions of Membrane Proteins • A membrane may contain hundreds of different proteins • Each membrane protein has a defined orientation relative to the cytoplasm – this asymmetry is referred as “sidedness” 3 different classes distinguished by their intimacy with the lipid bilayer: • Integral Proteins o Penetrates the lipid bilayer o Are known as transmembrane proteins – they pass entirely through the lipid bilayer – have domains that protrude from both the extracellular and cytoplasmic sides of the membranes. • Peripheral Proteins o Located entirely outside of the lipid bilayer, on either the extracellular or the cytoplasmic side. (associated with the membrane surface by noncovalent bonds) • Lipid Anchored Proteins o Located outside the lipid bilayer on either the extracellular side or the cytoplasmic side o Covalently linked to a lipid molecule that is situated within the bilayer. • Integral Membrane Proteins o Function as receptors that bind specific substances at the membrane surface, as channels or transporters that are involved in the movements of ions and solutes across the membrane. o They are also amphiopathic • Freeze Fracture Analysis o The concept that proteins penetrate through membranes rather than remaining external to the bilayer was derived from the results of freeze fracture analysis o Cracks the lipid bilayer, leaves a “pit” in the bilayer where the proteins were. (Figure 4.15a represents this method of analysis) • Peripheral Membrane Proteins o Associated with the membrane by weak electrostatic bonds o These proteins provide mechanical support for the membrane and function as an anchor for integral membrane proteins. o Other peripheral proteins on the internal plasma membrane surface function as enzymes, specialized coats, or factors that transmit transmembrane signals. • Lipid-‐ Anchored Membrane Proteins o Numerous proteins present on the external face of the plasma membrane are bound to the membrane by a small, complex oligiosaccharided linked to a molecule of phosphatidylinositol. o Those containing this type of glycosyl-‐phosphatidylinositol linkages are called GPI-‐Anchored proteins. 4.7 The movement of Substances across Cell Membranes • The lipid bilayer of the membrane is ideally suited to prevent the loss of charged and polar solutes from the cell. o But – some special provisions must be made to allow the movement of nutrients, ions, waste products, and other compounds across the membrane. Two types of movement • Substances may move through the membrane passively by diffusion, OR actively by an d energy-‐couples transport process • Both movemenets lead to the net-‐flux of a particular ion or compound. • Net Flux – indicates that the movement of the substance into the cell and out of the cell is NOT balances, but exceeds the other. • Substances may move across the membrane by: o Simple Diffusion – Through the lipid bilayer o Simple Diffusion -‐ Through an aqueous protein lined channel (diffusion that is facilitated by a protein transporter) o Active Transport – Requires an energy driven protein pump that is capable of moving substances against a concentration gradient The energetics of solute movement • Diffusion -‐ The spontaneous process in which a substance moves from a region of higher concentration to a region of lowere concentration Diffusion of substances through membranes • Substances must be in higher concentration on one region and lower in the other. • Membrane must be permeable to the solute. • Must satisfy 1/both: o Solute can pass directly through bilayer -‐or-‐ o Solute can traverse through an aqueous pore that spans the membrane • Partition Coefficient – The ration of its solubility in a non polar solvent. • It is evident that the greater the lipid solubility, the faster the penetration. • Another factor determining the rate of penetration of a compound through a membrane is size. • IF two compounds have similar partition coefficients, the one with the smaller size will penetrate the membrane faster than that of the larger molecule. • Very small uncharged molecules penetrate very rapidly through the cellular membrane. • Membranes are highly permeable to small inorganic molecules such as O2, CO2, NO, and H2O, they are thought to slip between adjacent phospholipids. • Larger polar molecules, sugar, a.a’s and phosphoryared intermediates exhibit poor membrane permeability. • Materials that must enter from the blood stream, but exhibit poor permeability must enter through special mechanisms AND NOT by simple diffusion. The diffusion of Water through membranes • Membranes are said to be semi-‐permeable. • Water moves readily through a semi permeable membrane from a region of lower solute concentration to an area of higher solute concentration. • This process is known as osmosis -‐ the diffusion of water. • The area with a higher solute concentration is said to be hypertonic or hyperosmotic. • The area with a lower solute concentration is said to be hypotonic or hypoosmotic. (When a cell is palced into a hypotonic solution, the cell gains water by osmosis and swells (lysis)) • The cells volume is controlled by the difference between the solute concentration inside the cell and that in the extracellular medium. • Small integral proteins called aquaporins allow the passive movement of water from one side of the plasma membrane tot the other. The diffusion of ions through membranes • The lipid bilayer is highly impermeable to charged substances including ins such as Na+, K+. Ca+2 and Cl-‐ • The rapid movement (conductance) of these ions across membranes play a critical role in a large amount of cellular activities. • Ion Channels -‐ openings in the membrane that are permeable to certain (specific) ions. • Most ions channels are highly selective in allowing only one particular type of ion to pass through the pore. • Most ion channels that have been identified can exist in open or closed conformation or said to be gated. • The opening/closing of the gates are subject to complex physiological regulation. Lecture 15 Cell Biology Chapter 7 Interactions between cells and their environments Cell – Cell Adhesive Interactions Four distinct families of integral membrane proteins play a major role in mediating cell-cell adhesion. 1) selectins 2) certain members of the immunoglobulic superfamily (IgSF) 3) certain members of the integrin family, 4) Cadherins They are important in development, metastasis and inflammation. Cell – cell Adhesive Interactions Cadherins – integral membrane proteins Certain members of the IgSF and Integrins Selectins Selectins Selectins are a family of membrane glycoproteins that bind to specific oligiosaccharides on the surfaces of neighboring cells Lectin is a term for a compound that binds to specific carbohydrate groups. Selectins have a small cytoplasmic segment, a single membrane-spanning domain and a large extracellular portion. Three cell-specific selectin types: o E – Selectin – endotherlial cells o P – Selectin – platelets and endothelial cells o L – selectin – Leukocytes (white blood cells) Just have different carbohydrate groups attached The Immunoglobulin Super Family (IgSF) Antibodies are immunoglobulin proteins with Ig domains, 70 -110 a.a. organized into a tightly folded structure The human genome encodes 765 distinct Ig domains, making it the most abundant domain the human proteins. These proteins are members of the immunoglobulin super family, and most are involved with mediating interactions of lymphocytes with cells required for an immune response. (Macrophages, Lymphocytes, and target cells) 2 membrane proteins and 2 cells interacting through these proteins Cadherins Cadherins include 3 different types as well: o E – Cadherin – epithelial o N – Cadherin – Neural o P – Cadherin –Placental Cadherins have a large extracellular segment, a single transmembrane segment, and a small cytoplasmic domain The cytoplasmic domain is often associated with catenin proteins to tether the cadherins to the cytoskeleton and transmit signals Calcium ions maintain the extracellular portion of each cadherin in a rigid conformation required for cell adhesion Cadherins require calcium for a reaction. Interactions of cells with other cells Cadherins may mediate dynamic changes in adhesive contacts needed for morphogenesis. During embryonic development, cells can change from an epithelium to a mesenchyme or visa versa. This epithelia mesnechymal transition (EMT) is found during mesoderm formation. Migrating mesenchymal cells with eventually give rise to medodermal tissues such as blood, muscle and bone. Cell Junctions Anchoring cells to other cells – link epithelial cells together o Desmosomes o Adherens Junctions Tight junctions – sealing the extracellular space Cell communication o Gap junctions o Plasmodesmata Junctions for Communication Gap junctions – animal cells o Made of connexin protein o Passage of ions o Communication o Gap junctions – protein molecules of about 1000 Daltons can go through gap junctions. o Defects in gap junctions can cause deafness, blindness, cardiac problems, nerve degeneration and skin abnormalities. Plasmodemata – plant cells o Connect plant cells o Dilates for passage of macromolecules o Plasmodesmata - are cytoplasmic channels passing through cell walls of adjacent plant cells o Lined by the plasma membrane o Contain a central structure, the desmotubule o Dilate and up to 50 Kilo Daltons (50,000 Dalton) proteins can move through. o Both proteins and RNA (serving a signal molecule) move through plasmodesmata Cell Biology Lecture 19 (4/14/16) Actin Based Movement • Polymerization/depolymerization of actin and cell migration • Actin Binding proteins • Actin and myosin based movement o Muscle cells o Cell division • Actin receptor proteins react to a signal Structure of Muscles • Muscle are attached to bond • Muscles are composed of muscle fibers • A muscle fiber = muscle cells o Multi nucleated cells that are fused • Myoblasts fuse to give muscle cells • The contractile component of muscles is the sarcomere Inside the muscle cell • Myofibrils – contractile elements • Unit of contraction = sarcomere o Thin filaments – actin fiber o Thick Filaments -‐ myosin motor o Sarcomere – extends z line to z line o Titin – largest protein known, it is greater than 3.5 million Å (3500 kÅ). Has more than 38 thousand amino acids joined together • contraction = shortening of the sarcomere • Distance between the z bands will get shorter • The driving force behind this is ATP hydrolysis Molecular Mechanism – Actinomyosin Contractile Cycle • In step 1 – ATP binding to myosin breaks the cross bridge between the myosin and actin • In step 2 – ATP hydrolysis – energy is conserved in the myosin head. • In step 3 – Myosin binds weakly to the actin filament • In step 4 – release of Pi (loss) causes a tighter binding, myosin undergoes a large conformational change (motion) pulling against the actin causes a power stroke – contraction • Power stroke moves the actin filament towards the center of the sarcomere. • In step 5 – ADP is removed (lost) from the myosin head, cross bridge still formed. Refer to picture below. • Power stroke – myosin moves the actin filament towards the center of the sarcomere • 70 degree rotation of myosin head = ▯ moves actin filament 10nm Regulation of Muscle Contraction Troponin and Tropomyosin complex • Low ca2+ the myosin can not bind to the actin • High Ca2+ the myosin binds to actin • Tropmyosin prevents myosin from binding to actin under low ca2+ concentration Control of Calcium • Transverse tubules and nervous impulse • Voltage gates channel in tubules -‐-‐ release of Ca2+ • Sarcoplasmic Reticulum – release of Ca2+ • Sarcoplasmic reticulum – ER (Endoplasmic Reticulum) in sarcomere (muscle cell) Cell Biology Lecture 19 (4/14/16) Actin Based Movement Polymerization/depolymerization of actin and cell migration Actin Binding proteins Actin and myosin based movement o Muscle cells o Cell division Actin receptor proteins react to a signal Structure of Muscles Muscle are attached to bond Muscles are composed of muscle fibers A muscle fiber = muscle cells o Multi nucleated cells that are fused Myoblasts fuse to give muscle cells The contractile component of muscles is the sarcomere Inside the muscle cell Myofibrils – contractile elements Unit of contraction = sarcomere o Thin filaments – actin fiber o Thick Filaments - myosin motor o Sarcomere – extends z line to z line o Titin – largest protein known, it is greater than 3.5 million Å (3500 kÅ). Has more than 38 thousand amino acids joined together contraction = shortening of the sarcomere Distance between the z bands will get shorter The driving force behind this is ATP hydrolysis Molecular Mechanism – Actinomyosin Contractile Cycle In step 1 – ATP binding to myosin breaks the cross bridge between the myosin and actin In step 2 – ATP hydrolysis – energy is conserved in the myosin head. In step 3 – Myosin binds weakly to the actin filament In step 4 – release of Pi (loss) causes a tighter binding, myosin undergoes a large conformational change (motion) pulling against the actin causes a power stroke – contraction Power stroke moves the actin filament towards the center of the sarcomere. In step 5 – ADP is removed (lost) from the myosin head, cross bridge still formed. Refer to picture below. Power stroke – myosin moves the actin filament towards the center of the sarcomere 70 degree rotation of myosin head = moves actin filament 10nm Regulation of Muscle Contraction Troponin and Tropomyosin complex Low ca2+ the myosin can not bind to the actin High Ca2+ the myosin binds to actin Tropmyosin prevents myosin from binding to actin under low ca2+ concentration Control of Calcium Transverse tubules and nervous impulse Voltage gates channel in tubules -- release of Ca2+ Sarcoplasmic Reticulum – release of Ca2+ Sarcoplasmic reticulum – ER (Endoplasmic Reticulum) in sarcomere (muscle cell) Cell Biology BIO 225 Lecture 17 Chapter 8 – Endomembrane System Components: o ER – endoplasmic reticulum o Golgi Apparatus o Endosomes o Lysosomes o Vacuoles Budding and fusion of vesicles from one compartment to the next Adding carbohydrates to proteins and lipids Transfer proteins Transfer of membrane lipids Insertion of membrane proteins and lipids Proteins stop transfer sequences Models for protein orientation in the membrane o C terminus in cytoplasm o C terminus in lumen of ER Lipid synthesis in ER Lipid delivery to endomembranes and plasma membranes Asymmetry of membrane proteins Synthesized in ER Orientation of protein in vesicle Orientation of protein in membrane Degradation of abnormal proteins Abnormal proteins are translocated out of the ER Tagged in cytoplasm with ubiquitin protein Sent to proteasome and degraded Lysosomes: Single membrane bound organelles Lysosomes contain acid hydrolases which can digest every type of biological molecule. The low pH optimum of these enzymes is maintained by a proton pump (H+ ATPase) Targeting enzymes to the lysosome: Tag is mannose-6-phospahe Receptor for mannose-6-P tagged proteins in the trans golgi Deliver proteins to endosome lysosome Defects and diseases o I-cell disease – no tag so lysosomal proteins secreted from the cell o Lysosomal storage diseases – no enzyme to digest sphingolipid compounds. Lysosomal malfunctions can have serious effects on human health Lysosomal storage disorders result from the absence of specific lysosomal enzymes thus allowing undigested material to accumulate. Treatment for these diseases may include- enzyme replacement therapy Endocytosis: Receptor mediated endocytosis Clathrin coated pits Early endosomes Late endosomes Lysosome- terminal component of endocytic pathway Different coats bring vesicles to different locations Clathrin coats for endocytosis and transport of lysosomal enzymes to the lysosome. COPII coated vesicles go from ER to golgi COPI – coated recycling vesicles bring back to the ER Targeting and Fusing Vesicles: Movement of the vesicle toward specific target compartment Tethering vesicles to the target compartment o Process mediated by g-proteins called rabs. o Rabs play a key role in vesicles targeting by recruiting specific tethering proteins Docking vesicles to target organelle – paring v-SNARE to t-SNARE Fusion – pairing lead to pulling the two lipid bilayers together Post-transitional Localization Proteins synthesized in the cytoplasm on free ribosomes Proteins remain in the cytoplasm Proteins directed to organelles o Unfold proteins and transport into mitochondria and chloroplasts o Folded proteins transported into peroxisome by unknown mechanism. Intermembrane space – between inner and outer membrane The tags for the chloroplasts are much more complex The tags once they’re in their proper destination, they get “cut” off Peroxisomes: Membrane bound vesicles 0.1-10um in diameter Contain oxidases and generate H2O2, but they also contain catalase to break down H2O2. Oxidize fatty acids (24-26 carbon chains) Synthesize special phospholipids called plasmalogens found in the myelin sheath of nerves. Plasmalogens have an ether linkage between the fatty acids and glycerol rather than an ester linkage. Peroxisomes = glyoxysomes in plant seedlings. Are a specialized type of peroxisome that converts fatty acids to carbohydrates o Only plant seedlings can do this Peroxisome targeting signal MPTS – for the membrane Cell Biology BIOL 225 Lecture 16 Interactions of Mammalian Cells with Extracellular Matrix • In culture • In the body • Components of the Extracellular matrix • Cell signaling • Focal Adhesions – contacts when the cell starts making contact. Allows cells to attach to the substratum ( Surface of a flask, cover slip) seen invitro • Invitro – in a lab, in class, tissue culture. • Normal human cells can not grown in a suspension (in liquid). Normal human cells require a surface to grow on. • Cancer cells however can grow in suspension, like a bacteria or yeast cell. How cells interact with their extracellular environment • Extracellular matrix – scaffolding, support for tissues o Fibrous for support • Connective tissue • Basement membrane underneath the plasma membrane (basement membrane does not contain cells. • Basement membrane prevents cancer cells from entering tissues. Components of the extracellular matrix • Integrins – integrated through the membrane • Integrin transmembrane proteins bind to components of the ECM in their active form. o Can transmit signals • Integrins transmit signals from ECM to cell interior • Collagen o Trip helix of 3 polypeptides (alpha) o Has a lot of prolines + lysines (get hydroxylated – adding OH – gives opportunity for hydrogen bonds) o Hydroxylated prolines and lysines form hydrogen bonds to join the three alpha polypeptides into a collagen fiber o 1mm fiber can hold 22 pounds (10 Kilograms) without breaking o For hydroxylation to occur, you need vitamin C (as a cofactor for hydroxylations) (ascorbic Acid) o Lack of vitamin C = Scurvy o Collagen associated Diseases ▯ Fibrosis of the lungs and liver (liver = cerosis) ▯ Type 1 defect – osteogenesis imperfect + fragile bones ▯ Type 4 – kidney disease – alport o Talin – adaptor protein that links integrins to the cytoskeleton • Proteoglycan • Fibronectin o Polypeptide o Held together by disulfide bonds o RGD – binding site for the integrins o Defects in fibronectin ▯ Development – cells must migrate and fibronectin directs their migration ▯ The lung and kidney develop from branching structure and need to form clefts. • Laminin • Changing in the ECM are conveyed by binding to our receptor and activates the kinases and causes changes in the cell. Hemidesmosomes Anchor Cells to ECM • Hemidesmosomes – anchor the cells to the ECM • Integrins – found only in animals, theres 18 different alphas an 8 different beta chains. Heterodimer. About 24 different integrins • You need integrins to interact with the basement membrane and the ECM tissues + substratum in tissue cultures. • Because of integrins, normal cells do not grow in suspension, you need substratum contact to generate signals for cell viability. • Hemidesmosomes – cant attach in some auto immune diseases to the basement membrane (causes severe blistering) • Defects in integrins, collagen or laminin 5 also disrupt the basement membrane Junctions for communication • Gap Junctions – animal cells o Connexin o Passage of ions • Plasmodesmata – plant cells o Connect plant cells o Dilates for passage of macromolecules • Plasmodesmata – cytoplasmic channels passing through cell walls of adjacent plant cells. o Are lines by a plasma membrane o Contain a central structure, the desmotubule. o Serves as a site of cell-‐cell communication Plant Cell Wall • Extracellular • Function o Shape o Support, protection against mechanical abrasion, pathogens and osmotic stress. • Components o Cellulose arranged in microfibrils to provide rigidity o Matrix contains hemicellulose, pectin and glycoproteins. o Matrix keeps the plants hydrates • Assembly of cellulose Synthesis of plant cell walls • Cell walls arise as a cell plate that forms between the plasma membranes of newly formed daughter cells. • The walls of growing cells are primary walls and allow flexibility lacking in the thicker secondary walls of mature cells. CELL BIOL CHAPTER 8 Cytoplasmic Membrane Systems: Structure, function, and membrane trafficking Endomembrane System • Components • Budding and fusion of vesicles from one compartment to next • Tranfer of proteins • Transfer of membrane lipids • Coated vesicles – COP Proteins An overview of the biosynthetic/ secretory pathways
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