Different Cell Types. Lecture 1: Cell Bio THE PLASMA MEMBRANE. Cellular Similarities: Basic Cell Anatomy

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1 Lecture 1: Cell Bio Different Cell Types Humans have at least 200 different cell types. Yet, all cells share some basic components Cellular Similarities: Basic Cell Anatomy Plasma Membrane - lipid bilayer Cytoplasm Cytoskeleton - actin microfilaments, microtubules, IFs Nucleus - nuclear envelope,dna Ribosomes - protein synthesis Rough ER - protein synthesis, glycosylation Smooth ER - lipid and steroid synthesis/metabolism, receptor attachment,enzyme storage/prod, carb metab, Ca regulation, G6P (gluconeogenesis) Golgi Apparatus - sorting, modifying & packaging proteins, apoptosis Lysosomes - digests proteins with acidic enzymes Mitochondria - makes ATP, FA oxidation/synth, cholesterol steroids, apoptosis, Ca reg Centrosome with Centrioles anchor for microtubules esp during mitosis Composition, Permeability & Movement of substances accross THE PLASMA MEMBRANE 1

2 The Plasma Membrane The Plasma Membrane 1. The lipid bilayer is made of these lipids: 1. phospholipids (75%) 2. cholesterol (20%) 3. glycolipids (5%) 2. Proteins are embedded in the lipids Phospholipids, cholesterol, glycolipids, membrane proteins 75% (Amphipathic) Phospholipids Permeability of the Lipid Bilayer Freely Permeable to small, uncharged, nonpolar, molecules: Steroids, O2, CO2, N2 Fat-soluble vit: A,D,E,K Slightly Permeable to small, polar molecules: Urea, Water, Ethanol Phospholipids are an AMPHIPATHIC (ie both polar and non-polar) substance The Phosphate Heads are polar, or slightly charged, so it can form hydrogen bonds with water. They are attracted to water, or, Hydrophobic. The Fatty Acid Tails are non-polar, or uncharged. They are attracted to other lipids. They are repelled by water or Hydrophobic. Impermeable to charged, or large molecules such as sugar (Glucose), amino acids, nucleotides, proteins, Ions (Na+, Cl-) 2

3 FYI: Sizes of some molecules Channels, Carriers, Transporters, Active & Passive transport MEMBRANE PROTEINS Charged ions and Larger molecules cannot diffuse through the lipid bilayer. They cannot get into or out of a cell without assistance Integral & Peripheral Membrane Proteins Functions of Membrane Proteins 1. Integral (Transmembrane) Proteins: extend through lipid bilayer Receptors Ion channels Transporters Enzymes Cell Identity Markers Linkers 2. Peripheral Proteins: attached to inside or outside surface of plasma membrane 3

4 Passive vs. Active Transport :is energy required to cross the cell s membrane? 1. Passive Transport NO ENERGY IS REQUIRED Molecules flow from high concentration to low concentration or down their electrochemical gradients 2. Active Transport REQUIRES ENERGY (usually ATP) Molecules are pushed AGAINST their gradients 1. Passive Transport Its called PASSIVE because NO ENERGY IS REQUIRED for substances to diffuse down their gradients. A. In Simple DIFFUSION, substances pass directly through the lipid bilayer no protein is required B. Facilitated DIFFUSION the substance requires a channel protein or a carrier protein to enter the cell What drives the movement of the small uncharged molecules across a cell membrane? Concentration Gradient Substances or Solutes passively diffuse through a semipermeable membrane from high concentration to low concentration, seeking equilibrium B. Proteins that Facilitate Diffusion Channel Proteins eg ion channel DO NOT CHANGE SHAPE But, may be GATED ligand-gated voltage-gated stretch-gated Carrier = Transport Proteins eg glucose transporter Transport molecules down concentration gradient by BINDING & CHANGING SHAPE 4

5 For charged solutes, Electrochemical Gradient determines movement 2. Active Transport (Requires ENERGY) Electrical Gradient charged substances are drawn to areas of opposite charge + Concentration gradient - substances tend to go from high concentration to low concentration ç è = è Electrochemical gradient - net gradient for a substance depends on both concentration & charge ENERGY is needed to transport substances AGAINST their concentration or electrochemical gradients 1 Active Transport requires chemical energy (eg hydrolysis of ATP) to move a substance against its gradient 2 Active Transport uses electrochemical gradient of one substance (usually Na) to transport a second substance against its gradient Symport - 2 substances move in same direction Antiport - 2 substances move in opposite directions The Classic example of Active Transport: Na / K / ATPase pump Exocytosis & endocytosis Pumping Na & K, AGAINST their ELECTROCHEMICAL GRADIENTS requires energy. Binding of Na, triggers hydrolysis of ATP. Breaking ATP bonds releases Energy + ADP +Pi The energy changes the shape of the transporter to pump out the 3 Na VESICULAR TRANSPORT 3 Na+ out, 2 K+ in Net + charge outside cell 5

6 Vesicular Transport Vesicles (like bubbles) transport large or polar substances across the cell membrane. ALL REQUIRE ATP 1. Endocytosis - large substances (eg dead bacteria) enter the cell by invagination & pinching off a little bit of the plasma membrane Phagocytosis, pinocytosis, Receptor-mediated endocytosis 2. Exocytosis - large substances (eg neurotransmitters) exit the cell via vesicles that fuse with the plasma membrane. Movement of SOLVENT across membranes OSMOSIS 3. Transcytosis - cross cell. large substances enter one side of cell and leave the other side A special case of Diffusion OSMOSIS: Movement of WATER Movement of SOLVENT ie WATER through a semipermeable membrane Water moves towards areas with more solute (or higher osmolarity) Water moves by simple diffusion or through special membrane proteins, called aquaporins Osmosis & Tonicity Since water follows solute: if there is more solute is inside the cell, ie the interstitial fluid is hypotonic to the cell, water will enter the cell and it will swell or burst: hemolysis If there is more solute outside the cell, in the interstitial fluid ie interstitial fluid is hypertonic to the cell, water exits the cell and it crenates Under normal conditions, the osmotic pressure of the interstitial fluid = osmotic pressure of the cell s cytosol So water moves into and out of a cell at the same rate. 6

7 Summary of Movement across the Cell Membrane Movement of solutes across a cell membrane can happen by: Passive Transport Simple Diffusion directly across the lipid bilayer Facilitated Diffusion needs channel & carrier but no energy Active Transport 1 (requires ATP) 2 - symport & antiport (uses another substance s gradient) Vesicular Transport Endocytosis Exocytosis Transcytosis How a cell makes its proteins PROTEIN SYNTHESIS Movement of the solvent (not the solute) Osmosis (movement of water) Membrane Proteins & the Fluid Mosaic 2 Steps of Protein Synthesis Step 1: in Nucleus TRANSCRIPTION DNA is transcribed into mrna Step 2: in Ribosome TRANSLATION mrna is translated into a protein Ribosomes can be Protein positions and amounts are not static in the membrane but are constantly moving, changing places, adding or eliminating pieces like a mosaic that is fluid free in the cytoplasm or attached onto the Rough Endoplasmic Reticulum (RER) 7

8 The nucleus contains Chromatin In a non-dividing cell nucleus, the chromatin is loose and diffuse Chromatin is a thread of nucleosomes with linker DNA in between. A nucleosome is DNA wrapped around 8 histone proteins Only when a cell divides, the chromatin folds and packs tightly into Chromosomes TRANSCRIPTION: DNA codes for RNA DNA is made of nucleotides A Nucleotide consists of: a Phosphate group, a Deoxyribose Sugar, And a Base Adenine (A) Guanine (G) Thymine (T) Cytosine (C) The Base Pairs are: Adenine Thymine Cytosine Guanine RNA exits the Nucleus A gene is a section of DNA that codes for a protein. RNA polymerase binds to a gene s promoter region on the DNA. RNA pol. unwinds the double helix & pairs RNA nucleotides to DNA nucleotides from one strand When the RNA pol. reaches a terminator region, it falls off & transcription stops m/t/rrna exits the nucleus through a nuclear pore in the nuclear envelope Nuclear envelope is a double membrane of 2 lipid bilayers Nuclear envelope is continuous with rough endoplasmic reticulum The nucleus contains chromatin, RNA, proteins The Nucleolus is the part of DNA that codes for ribosomes 8

9 mrna leaves the Nucleus & enters Cytoplasm The Cytoplasm consists of: Cytosol mrna enters a Ribosome Ribosomes can be: 1. FREE - In the cytosol 2. Attached onto the Rough Endoplasmic Reticulum giving it its rough look 3. or in the mitochondria 75-90% water & dissolved substances: Cilia & flagella Ribosomes Rough Endoplasmic Reticulum Smooth E R Golgi complex Lysosome Peroxisome Proteosome ions glucose amino acids fatty acids proteins lipids ATP waste products Cytoplasm = Everything between the nucleus & the plasma membrane: Cytosol, Organelles & Cytoskeleton Organelles Centrosome Cytoskeleton Microfilaments Microtubules Intermediate Filaments Mitochondria TRANSLATION: RNA codes for PROTEIN mrna binds to a ribosome One amino acid is attached to each trna (transfer RNA) Each trna anticodon matches an mrna codon Amino acids bind together to form an elongating peptide chain 9

10 mrna Codons & trna Anticodons Review: from DNA to Cytosolic protein A Codon on the mrna is made of 3 nucleotides The Anticodon is a set of 3 nucleotides on the matching trna Transmembrane vs Secretory proteins a signal sequence on the amino acid chain complexes with Signal Recognition Particle (SRP). Together, they guide the ribosome towards the ER. SRP Receptors on the ER, bind the SRP & remove it so that the signal sequence can enter a Translocation channel. Secretory proteins will cross the RER membrane completely to enter the lumen of the RER Transmembrane proteins will cross the RER membrane partially and remain membrane-bound ** The Golgi Apparatus, or Post Office Proteins from the RER move to the golgi apparatus via vesicles. Golgi apparatus modifies the proteins (eg adding a sugar for plasma membrane glycoproteins) Golgi then sorts the proteins headed for the same destination (eg lysosomes) into vesicles 10

11 Protein moves from RER to Golgi Apparatus The Secretory Pathway If a protein is made in the RER, then moves to the golgi apparatus it will not stay in the cytosol, but, rather, will be secreted Protein modification & sorting 3 possible places for a protein to end up: 1. Membrane Vesicle: As a plasma transmembrane protein 2. Secretory Vesicle: Secreted out of the cell 3. Transport Vesicle: Intracellular destination eg lysosome This protein will end up in the membrane or out of the cell or in a vesicle (vs in the cytosol if made on a free ribosome) Smooth ER OTHER ORGANELLES The Smooth Endoplasmic Reticulum has no ribosomes Synthesizes fatty acids & steroids (like estrogen, testosterone) Detoxifies lipid-soluble drugs, pesticides, alcohol, Helps release glucose into blood (cleaves P from G6P) In muscle cells, it stores & releases Ca2+ 11

12 Lysosomes digest Proteosomes Contains the cell s digestive enzymes Autophagy - breaks down its own damaged organelles Phagocytosis - digests external substances like bacteria Autolysis - destroys the entire cell that contains the lysosome Enzymes only work at extremely acidic ph (5) Proton transporter imports H+ to keep ph low inside Barrel-shaped organelles that degrade cytosolic proteins, coated with ubiquitin, into peptides. Proteins targeted for degradation may be non-functional, misfolded or Peroxisome Contain oxidases - enzymes that oxidize organic substances like fatty acids, amino acids & toxic substances like alcohol Numerous in liver cells where toxic substances accumulate for detoxification. By-product of oxidation is hydrogen peroxide, H 2 O 2 (toxic) Contain catalase enzyme to degrade H 2 O 2 THE CYTOSKELETON 12

13 ACTIN MICROFILAMENTS CYTOSKELETON The cytoskeleton organizes and moves components of the. Made of Actin & Myosin Proteins It is made up of: 2. Enables Cell movement 1. Responsible for Cell shape Forms nonmotile Microvilli Creates cell polarity ie Apical vs basolateral surfaces Muscle contraction Cell locomotion 1. MICROFILAMENTS 2. INTERMEDIATE FILAMENTS 3. MICROTUBULES 3. Requires ATP to assemble 4. The associated motor molecule is Myosin Microfilaments & cell movement MICROTUBULES & the Centrosome Myosin is the motor molecule that moves the actin Cell movement is a result of actin microfilaments extending forward & pushing the cell in that direction Emanate from centrioles within the centrosome Minus (-) end is anchored at centriole Plus (+) end grows Requires GTP to assemble Motor proteins: Kinesin & Dynein move vesicles along microtubule in opposite directions (VESICULAR TRANSPORT) Align & pull apart chromosomes during Mitosis Make up cilia & flagella 13

14 Cytoskeleton Assembly & Disassembly INTERMEDIATE FILAMENTS Microfilaments are made of ACTIN Myosin is the motor molecule MICROTUBULES Kinesin moves things towards (+) end Dynein moves things towards (-) end (at the centriole) Scaffolding/Stability Eg Nuclear lamina Not Dynamic Cell-type specific Eg keratin Mitochondrial Energy Production Krebs Cycle, Electron Transport Chain and ATP production THE MITOCHONDRIA Fatty acids, amino acids and sugars enter the Citric Acid Cycle within the mitochondria, to produce NADH, a source of electrons and H+ ions. and The electrons enter the Electron Transport Chain while the H+ ions power oxidative phosphorylation by ATP synthase complex to make ATP. 14

15 The Electron Transport Chain Other mitochondrial functions H+ ions from NADH are pumped into, and collect in the mitochondrial intermembrane space. The H+ concentration gradient is used as 2 active transport energy source to turn ATP synthase which makes ATP H+ entering the mitochondrial matrix attaches to O2 to make H2O 1. Steroid synthesis (pregnenolone, cortisol, aldosterone) 2. Triggers Apoptosis (cell death) Back to the Beginning Nucleus - Trasncription of DNA to mrna which goes out nuclear pores of nuclear envelope Free ribosome - mrna translation for cytosolic protein synthesis RER - studded with ribosomes. mrna Translation & Translocation for secretory or transmembrane proteins. Golgi Apparatus - modifies proteins & tags for destination, apoptosis Lysosomes - acidic enzymes Centriole - microtubules attach, mitosis (cell division), vesicle shuttle Cytoskeleton- actin microfilaments, microtubules, Intermediate filament Mitochondria - ATP generation from FA oxidation,protein, carb. cholesterol steroids, apoptosis SER - lipid & steroid synthesis/ metab, receptor attachment, G6P, enzyme storage/prod, carb metab, Ca regulation Peroxisome - oxidative enzymes, detoxes Cell division & Cell death THE CELL CYCLE, APOPTOSIS, AND CANCER 15

16 Cells have 3 possible states of existence: The Cell Cycle 1. Remain alive and functional without dividing (G 0 ) 2. Grow & Divide = The Cell Cycle Interphase (G 1, S, G 2 ) Mitosis Nuclear division: Prophase, Metaphase, Anaphase, Telophase Cytokinesis: cytoplasmic division 3. Die (Apoptosis) Consists of 2 major periods: 1. Interphase: the cell is replicating itself but not dividing 2. Mitotic phase: the nucleus is dividing Is the period from cell reproduction to the next reproduction Interphase: (growth & replication) G1, S, G2 S phase of Interphase: DNA replication DNA replicates during S (synthesis) phase. The majority of a cell s lifespan is spent in Interphase: G1 - normal cell functions, duplication of organelles & cytosol components S - DNA replicates G2 (Gap2) - centrosome duplication completes. DNA strands separate and new DNA is synthesized along each strand 16

17 Mitotic Phase (Division) 23 Pairs of Chromosomes Mitotic phase: a cell s nucleus and cytoplasm are dividing. Includes: Mitosis Prophase Metaphase Anaphase Telophase Prophase: chromosomes are visible, nucleus disappears Everyone has 23 homologous pairs of chromosomes with with unique banding patterns. One member in each pair is inherited from each parent Cell Cycle Interphase & Mitotic Cell Division Metaphase: chromosomes align Anaphase: chromosomes split Telophase: chromosomes uncoil, 2 nuclei form 17

18 Cell division: Mitosis vs Meiosis There are 2 major kinds of cells - somatic cells and germ cells Somatic Cell Division ie Mitosis produces 2 identical diploid daughter cells for: Healing: replaces dead or injured cells Growth: adds new cells Reproductive Cell Division ie Meiosis produces haploid gametes: Turning on cell division CDK s Cyclin Dependent protein Kinases will turn on G1, then turn it off, and continue an orderly progression through S, G2, etc Cyclins - turn CDKs on & off sperm or oocytes Apoptosis vs. Necrosis APOPTOSIS Apoptosis - Regulated, genetically programmed cell death (suicide) that does not produce inflammation. Cell is destroyed from within, shrinks & is engulfed by phagocytes. Necrosis - pathological cell death resulting in cell swelling, bursting, spilling contents & inflammation 18

19 CANCER Proto-oncogenes & Oncogenes Disease state characterized by uncontrolled, or abnormal cell division = CANCER excess tissue resulting from uncontrolled cellular division = TUMOR or NEOPLASM A cancerous neoplasm is called a malignant tumor. Most malignant tumors spread to other parts of the body, or, metastasize. Genes are sections of DNA that code for proteins Proto-oncogenes are normal genes that code for proteins that tend to deal with growth or cell division, such as growth factors If these proto-oncogenes should mutate, they become oncogenes and cell division becomes uncontrolled Tumor Suppressor Genes Tumor suppressor genes are genes that code for proteins that stop cell division, or induce apoptosis eg BRCA. Loss of these genes lead to uncontrolled cell division. 19