is Cell the minimum organization of living matter CELL MEMBRANE MODELS (plasma membrane): - All cells have a thin outer covering - Plasma membrane or cell membrane - Early models inferred the structure from chemical and permeability properties of the membrane - Cell membrane made up of phospholipids - Permeable to ions, water Fluid-Mosaic Model 2 layers of phospholipids as before, but now exposed proteins in a mosaic patterns, not a continuous layer pores bounded by protein as before fluidity: proteins and phospholipids can move (dynamic structure), evidence from hybrid cells - Phospholipid bilayer with a mosaic of associated proteins - Figure 7.7
Cell Coats: (not a separate entity from the cell membrane) glycocalyx composed of glycolipids, glycoproteins (short chain carbohydrates attached) - molecules that are part of the cell membrane - important feature for cell/cell recognition - Function: cell recognition Why do membranes exist ??? A) structural: need to keep contents of the cytoplasm inside of something; holds the cell together B) Functional properties: - Maintain concentrations of molecules and ions - Create free energy gradients - Orient molecules into functional complexes
Biological Systems: (with membranes)
Osmosis: net movement of water across (through) a semi-permeable membrane (ie permeable to water, but not to solutes) Relative Relationship: Which side does the water have the greatest free energy or is most concentrated? 1M sucrose OR Distilled water Distilled water In which direction will there be a net movement of water? Sodium chloride does dissociate in water, 1M Na+ & 1M Cl- (2 moles); NaCl has more material in solution, increasing the entropy of the water molecules making the water move from L to R 1M sucrose 1M NaCl Water permeable membrane In which direction will there be a net movement of water? To the RIGHT Equilibrium point would be 1.5 M on each side glucose 1M Sucrose 2M Glucose (1.5) 2.5 M 2M Sucrose 1M Glucose (1.5) 3.5 M
After water movement the glucose goes to equilibrium point** Membrane permeable to H20 and Glucose Terminology of Solutions Relative to one another: Hyperosmotic/ hypertonic: more concentrated Isosmotic/ isotonic: Equal Concentrated Hypoosmotic/ hypotonic: less concentrated Clicker ?: A single celled freshwater organism, such as a Paramecium, is transferred to saltwater. Which of the following would happen The cell will shrink Clicker ? Water will ___ the cells of a fish living in fresh water because of the process of osmosis. MOVE INTO Factors involved in the permeability * size and shape of molecules
- Really small molecules (like oxygen) will pass right through the membrance * solubility in lipids - Lipids are soluble in other lipids, non-polar things pass right through the membrane * net electric charge - typically not permeable through the cell membrane * chemical properties ------But water moves freely across the membrane-----* important to study the movement of water ** water is the universal solvent in biological systems
What is the relationship between the cytoplasm of the cells that line the passageways of the lungs and the extracellular fluid? Normally: Cytoplasm hypotonic Cystic fibrosis: cytoplasm hypertonic Cystic Fibrosis - Lack CL- channel cell membrane - Genetic Disorder - Based on a faulty protein - Symptoms: salty skin, mucus build up in lungs, causes breathing problems and increased lung infections - Cause: non- functional Cl- ion transporter - What is the chloride ion channel in individuals with Cystic Fibrosis? Chloride ions are moving from high to low concentrated, this is a facilitated diffusion transport. - How does the movement of Cl- out of the epithelial cells cause the mucus in the lungs to be less viscous? - How does the non-functional CFTR transporter result in thick mucus? - Treatment: diet high in protein Mucus build up is a simple problem of cell membrane permeability Movement of Substances Across Membranes: A) Many substances can move by diffusion, since the membrane is permeable to them (simple sugars, amino acids, lipids)
B) membrane is impermeable to many other substances (ions, complex sugars, proteins, other large molecules) How do these molecules move across the membrane ?? permeases (enzyme-like proteins) in membrane act as carriers. Diffusion: Movement of small molecules as a consequence of thermal agitation (thermal energy) * physical property of matter * seeming contradiction: mvt of a given molecule random, but the net effect can be non random - Figure 7.11 - Molecules diffuse independently - spontaneous process (doing downhill energetically) What force causes the net movement? **movement from a region of Hi free energy to a region of low free energy (or down a free energy gradient) G = H - TS Movement of Substances other than Water Diffusion: (molecules that are permeable) Small Molecules Lipid soluble molecules Permeases: (molecules that are not permeable or that move slowly) Large molecules Charged molecules Permeases: Membrane bound proteins that facilitate the movement of molecules across the membrane Categorized by energy use Passive, use no energy Active, use energy The functions of permeases can be broken down by the use of energy Facilitated Diffusion Selective, but passive - Moves molecules down their free energy (concentration gradient) - Protein Carrier
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Protein channel Selective Figure (7.15)
Active transport Selective, but active, (require energy imput) - Moves molecules against their free energy (concentration gradient) - Protein carrier - Selective and requires energy (usually ATP) - Figure 7.16 Figure 7.17 Active and passive transport Other Movement: though technically not through the membrane (EUCARYOTES ONLY) Vesicle-mediated Transport a) Endocytosismovement of material into the cytoplasm; cell engulfs object, that becomes membrane bound vesicle Phagocytosis : large object Pinocytosis : small object Receptor-mediated : a more selective version of pinocytosis b) Exocytosismovement of material out of the cytoplasm; membrane bound vesicles fuse with cell membrane and expel contents
Cell Walls: composed of carbohydrates; separate entity from the cell - Plants, cellulose - Fungi, cellulose and chitin - Amino sugars - Bacteria, peptidoglycans (amino sugars, amino acids) Cell Adhesion: - Plants o Pectin (ripe fruit) o Lectin - Animals o Collagen - All proteins Glues: Junctions:
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Plants plasmodesmata (figure 6.28) Animals tight junctions, intermediary junctions, desmosomes figure 6.32 gap junctions: similar to plasmodesmata (cytoplasmic connections)
CELL TYPES: PROCARYOTIC EUCARYOTIC STRUCTURES WHAT THEY ARE WHAT ARE THEIR FUNCTIONS CELL: minimum organization of living matter; smallest unit capable of independent living existence A) B) important unifying generalization in biology! multicellular species built from these common building blocks
PROCARYOTIC VERSUS EUCARYOTIC Structures and functions PROCARYOTES Cell structure *Nucleoid: *Ribosomes: *Flagella: *Mesosome: EUCARYOTES: Organelles: active structures, typically with specific functions Nucleus: Endoplasmic Reticulum: two types of ER rough ER smooth ER
Golgi Apparatus: Lysosomes: Vacuoles and Vesicles: Membrane Movement: think in terms of the flow of membrane through the endomembrane system nuclear ER Golgi Lysosomes Cell Other Membrane Organelles
Actin filaments, Intermediate Filaments, and Microtubules Ribosomes: Sites of protein synthesis Plastids: (plants only) Mitochondria (all eucaryotes) Energy Transformations: 1. Cellular respiration (Figure 9.2): All organisms do cellular respiration - Breakdown glucose release energy then capture the energy in ATP o ADP + P + energy ATP (7.3 kcal/mole) endergonic reaction o Glucose + Oxygen CO2 + H2O + energy (-686 kcal/mole) exergonic reaction 2. Photosynthesis *Both of these must occur in the cell; laws of thermodynamics
Where and how is most of the ATP produced in your cells? Where: In the mitochondrion, ATP synthase (enzyme that synthesized ATP) How: Chemiosmosis or Oxidative Phosphorylation (Figure 6.17) Where does the energy required for ATP synthesis come from? Proton of hydrogen ion gradient Where does Hydrogen ion gradient come from?
Active transport of hydrogen ions powered by the flow of electrons along the ETC (Electron transport chain); Involved redox reactions
IMPORTANT REACTIONS AND MOLECULES: Redox Reactions: Figure 9.15 reduction: Addition of electrons or hydrogen to a molecule that adds energy (stores energy in reduced compounds) oxidation: Removal of electrons or hydrogen from a molecule reduing the energy (releases energy from reduced compounds **These reactions always occur together Energy Transporting Molecules: NAD NAD+ + 2H <------> NADH + H+ (NADox) (NADre) FAD FAD + 2H <------> FADH2 (FADox) (FADre) Local transport and the cells energy currency ATP (Adenosine Triphosphate) ADP + Pi --------------> ATP ( G = +7.3 Kcal/mole) Two mechanisms for phosphorylation 1) Substrate level Phosphorylation: 2) Oxidative Phosphorylation: CATABOLISM OF GLUCOSE: Summary equation: C6H12O6 + 6O2 ---------- 6CO2 + 6H2O G=-686 Kcal/mole oxidation of glucose: removal of electrons (hydrogen electrons, often w/protons H+) How Do you make ATP ATP Synthase The chemiosmotic gradient is both a concentration gradient and a voltage gradient .
This results in a large free energy gradient Where do the reduced molecules come from? Kreb's Cycle (Citric Acid Cycle) Where does the pyruvic acid come from? Where does the Hydrogen ion gradient come from? - Active transport of hydrogen ions powered by the flow of electrons along with ETC (Electron Transport Chain) - Involved redox reactions - Figure 9.15 Clicker ?: In an atively respiring mitochondrion where would you expect to find the lowest pH? Intra- mitochondrial membrane space
How does the flow of electrons provide energy to pump hydrogen ions? - Each transfer of electrons is downhill energetically - Figure 9.13 What happens to the electrons at the end of the ETC? - The electrons combine with oxygen and hydrogen ions and make water Where do the reduced NADH+ H+ and FADH2 come from? - Most of the NADH + H+ and all the FADH2 comes from the Krebs or citric Acid cycle. - Figure 9.11 Oxidative Level Phosphorylation - Uses the exergonic flow of electrons form the food (glucose) to oxygen to drive the endergonic synthesis of ATP - Chemiostasis Substrate Level Phosphorylation - Direct transfer of phosphate to ADP from an organic molecules with a high energy phosphate bond Where does the Acetyl- CoA come from? - The breakdown of pyruvic acid - Figure 9.10
Where does the pyruvic acid come from? - the breakdown of glucose (glycolysis) - figure 9.08 9-27 Clicker: Bears have a tissue known as brown fat. In these cells the mitochondria have a special protein known as thermogenin. This is a facilitated diffusion channel for H+, with no associated ATP catalytic site. Based on the model of the mitochondria what will happen to the ATP production?
How many molecules of ATP are produced from 1 molecule of glucose in the presence of oxygen? Figure 9.6
GL YCOL YSIS:
FERMENT A TION: if no oxygen is present Fermentation as an alternative to most of this pathway What happens if there is no oxygen present? - IF there is no oxygen then nothing inside the mitochondrion can work, only glycolysis can work - In fermentation, take the pyruvic acid and turn it to lactic acid or
ATP YIELD FROM GLUCOSE BREAKDOWN: 1) Single molecule: anaerobic aerobic Interconversion of Food Stuffs: Other Sugars and Carbohydrates: Lipids: Proteins:
Clicker: If you begin with 1 molecule of Acetyl CoA how many oxidative level ATPs will be produced in a mitochondrion with only one hydrogen ion pump in the ETC (near the end) PHOTOSYNTHESIS: Summary Equation (low energy) 6CO2 + 12H2 0 + LIGHT 6O2 + C66H12O6 + 6H20 (high energy) - Convert 2 low energy molecules into a high energy molecule Clicker: What is the fate of oxygen in water? Becomes part of ? Figure 10.4 Reduction of CO2: redox reactions Photosynthetic Reactions: a long series of steps, several basic questions Fate of specific atoms? Two basic stage to photosythesis light dependent reactions (Light Reactions): Capture light energy in chemical energy light-independent reactions (Dark Reactions): Use the chemical energy to convert CO2 into glucose [Calvin Cycle] figure 10.5 Photosynthetic structures (Eucaryotes): takes place inside a chloroplasts Thylakoids granum stroma DARK REACTIONS: CALVIN-BENSON CYCLE Takes place in the stroma What are the inputs and outputs? - CO2, ATP, NADPH (inputs); Sugar (output) - figure 10.18
Where does the energy come from to drive these reactions? - Light Reactions (photosystems) - Cyclic and Non- cyclic photophosphorylation Photosystem: A collection of several hundred pigment molecules in the thylakoid membrane Figure 10.12; PHOTOSYSTEM 1: Composition: antenna pigments
200 molecules chlorophyll a and 50 b 50 molecules carotenoid 1 molecule special chlorophyll a (P700)
reaction center pigments
Why have so many different types of pigments as antenna pigments? All absorb different wave lengths of light; Figure 10.9;
NON-CYCLIC PHOTOPHOSPHORYLATION: source of electrons for photosystem 2 H20 Photosystem 2 Cytochrome complex Photosystem 1 NADPH Calvin Cycle Inputs and Products to non-cyclic Inputs: Light, H20, ADP, NADP+ Outputs: Oxygen, ATP, NADPH + H+ CYCLIC PHOTOPHOSPHORYLATION Photosystem 1 Cytochrome complex Photosystem 2 Inputs and Products Inputs: Light, ADP Outputs: ATP
SUMMARY OF ENERGY TRANSFORMATIONS: (This will not be covered in lecture) Catabolic Pathways: release stored energy 1) glycolysis 2) fermentation: anaerobic conditions 3) Citric Acid Cycle (in mitochondrial matrix) 4) Electron Transport Chain (in inner mitochondrial membrane) in procaryotes no mitochondria all processes take place in the cytoplasm or as part of the cell membrane Anabolic Pathways: store energy 1) photophosphorylation: oxygen as by product (in thylakoid membrane) 2) Calvin-Benson Cycle: production of G3P (in stroma) Similarities in Anabolic and Catabolic Pathways 1) similar molecules and pathways PGA, G3P, oxaloacetic acid, etc. Production of G3P leading to glucose 2) Membrane bound electron transport chains Step-wise release of energy 3) Extensive use of redox reactions 4) Energy transfer and storage molecules NAD or (NADP), FAD, ATP 5) Proton (H+) chemiosmotic gradient F1 complex (or ATP synthetase) phosphorylates ADP SUMMARY: Photosynthesis: H2O + CO2 stores energy (reduction) Cellular Respiration: C6H12O6 + O2 releases energy (oxidation) Photosynthesis and respiration questions: