2 - Membranes & cell organelles


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2 - Membranes & cell organelles

  1. 1. The Plasma Membrane
  2. 2. Quick Facts <ul><li>Primary purpose is to maintain the internal environment of cells by regulating what goes in and what comes out. </li></ul><ul><li>Average width: 0.01 μ m </li></ul><ul><li>Primary components: </li></ul><ul><ul><li>Phospholipid bilayer </li></ul></ul><ul><ul><li>Protein molecules </li></ul></ul><ul><ul><li>Glycoproteins and glycolipids </li></ul></ul><ul><ul><li>Cholestrol: steroid that stabilizes the membrane </li></ul></ul>
  3. 3. Phospholipids
  4. 4. Carbohydrate groups and Proteins <ul><li>Carbohydrate groups on glycoproteins and glycolipids </li></ul><ul><li>Form antigen (label identifying cell as “self”) </li></ul><ul><li>Proteins </li></ul><ul><li>Facillitate the movement of substrate across the membrane </li></ul>
  5. 5. <ul><li>7-9nm thick (nucleus & ER membranes = 5-7nm) </li></ul><ul><li>All biological membranes are the same : fluid-mosaic model </li></ul><ul><ul><li>phospholipid bilayer, proteins, carbohydrates and cholesterol </li></ul></ul><ul><li>Membranes are fluid structures - individual lipid molecules & some proteins move about within the layers </li></ul><ul><li>Phospholipids </li></ul><ul><ul><li>Hydrophobic tails will face away from water to form a monolayer or micelle (if tails are short) </li></ul></ul><ul><ul><li>Therefore membrane is impermeable to water soluble (polar) molecules </li></ul></ul><ul><li>Proteins carry out most other membrane functions, </li></ul><ul><ul><li>they are located throughout the membrane (hence the term mosaic) </li></ul></ul><ul><ul><li>can cross both layers OR be confined to one </li></ul></ul><ul><ul><li>Provide channels for water-soluble molecules & ions to pass </li></ul></ul><ul><li>Cholesterol (between the phospholipid molecules) </li></ul><ul><ul><li>makes the membrane less fluid & more stable </li></ul></ul><ul><li>Carbohydrates are usually on the outer surface & linked to protruding proteins </li></ul>Membranes
  6. 6. How does it regulate molecular transport? <ul><li>Passive Transport </li></ul><ul><ul><li>Diffusion </li></ul></ul><ul><ul><li>Osmosis </li></ul></ul><ul><ul><li>Facilitated diffusion (channel & carrier mediated) </li></ul></ul><ul><li>Active Transport </li></ul><ul><ul><li>Primary (uses chemical energy) </li></ul></ul><ul><ul><li>Secondary (uses electrochemical gradient) </li></ul></ul>
  7. 7. Passive transport: Diffusion <ul><li>Relies on molecules being small enough to pass through the semi-permeable membrane … </li></ul><ul><li>or in the case of channel-mediated diffusion, can be through a protein channel </li></ul><ul><li>Movement of molecules governed by the concentration gradient (high to low) </li></ul><ul><li>Diffusion ceases when balance is achieved </li></ul><ul><li>Diffusion animation </li></ul>
  8. 9. Passive transport: Osmosis <ul><li>Occurs when molecules of a substrate are too large to pass through the semi-permeable membrane </li></ul><ul><li>Substrate molecules do not move, instead water crosses the membrane in order to achieve balance (low to high) </li></ul><ul><li>Diffusion ceases when balance is achieved </li></ul><ul><li>Osmosis animation </li></ul>
  9. 11. Solute Solvent (eg. Water)
  10. 12. Passive transport: Facilitated diffusion <ul><li>Molecules of substrate are unable to permeate the membrane but are instead transported through specialised protein channels. </li></ul><ul><li>Proteins change shape to facilitate movement </li></ul><ul><li>Molecules are transported along the concentration gradient (high to low) </li></ul><ul><li>Diffusion ceases when balance is achieved </li></ul><ul><li>Facilitated diffusion animation </li></ul>
  11. 13. Facilitated diffusion
  12. 14. Primary active transport <ul><li>Active transport involves molecules moving against the concentration gradient </li></ul><ul><li>Molecules are transported along protein channels, proteins change shape to facilitate movement </li></ul><ul><li>Requires the input of energy in the form of ATP (Adenosine triphosphate) </li></ul><ul><li>Allows cell to retain ideal intracellular environment even when concentration of required ions in extracellular environment is low. </li></ul><ul><li>Primary active transport animation </li></ul>
  13. 15. Secondary active transport <ul><li>Same purpose as in primary active transport except … </li></ul><ul><li>ATP is not required to power the protein pump. </li></ul><ul><li>Instead, energy is gained by moving another substance in or out of the cell, but along the concentration gradient. </li></ul><ul><li>A bit like a wind-up toy, an input of energy will result in the output of energy, </li></ul><ul><li>Secondary active transport animation </li></ul>
  14. 16. Bulk transport <ul><li>Substrate can be moved in bulk by packaging it in a vesicle that either merges with the plasma membrane or breaks off from it. </li></ul><ul><li>Substrate exits the cell via EXOCYTOSIS </li></ul><ul><li>Substrate enters the cell via ENDOCYTOSIS , of which there are 3 types: </li></ul><ul><ul><li>Phagocytosis (taking in solids) </li></ul></ul><ul><ul><li>Pinocytotsis (taking in liquids) </li></ul></ul><ul><ul><li>Receptor mediated endocytosis </li></ul></ul><ul><li>Bulk transport animation </li></ul>
  15. 17. Endocytosis
  16. 18. Exocytosis
  17. 19. <ul><li>Isotonic: ( iso - same) surrounding fluid and cells internal fluid are of equal concentration </li></ul><ul><li>Hypotonic: ( hypo - lower) surrounding solution has a lower concentration than the cells. </li></ul><ul><li>Water will diffuse through the membrane into the cells </li></ul><ul><li>Hypertonic: </li></ul><ul><li>( hyper - higher) surrounding solution has a higher concentration than the cells </li></ul>
  18. 20. Mitochondrion Golgi apparatus Centriole smooth ER Lysosome Cytoplasm/Cytosol Plasma membrane Cell Wall Ribosome rough Endoplasmic Reticulum (ER) Nucleus nuclear pore nucleolus nuclear membrane
  19. 21. <ul><li>Eukaryote’s nuclear envelope is a double membrane </li></ul><ul><li>Prokaryotes lack a nuclear envelope </li></ul><ul><li>DNA contains encoded instructions for every aspect of an organisms existence; structure , function and behaviour </li></ul><ul><li>DNA granular until mitosis, then DNA becomes organised into chromosomes </li></ul><ul><li>Nucleolus/nucleoli = aggregation of RNA </li></ul><ul><li>Nuclear pores to allow movement between nucleus and cytoplasm </li></ul><ul><li>Control centre </li></ul>Nucleus
  20. 22. <ul><li>Produces chemical energy in the form of adenosine triphosphate (ATP) through the process of cellular respiration </li></ul><ul><li>Outer & inner membrane </li></ul><ul><li>The inner membrane contains many folds to provide a larger surface area for energy production </li></ul><ul><li>ATP produced by reactions on inner membrane </li></ul><ul><li>Only in eukaryotes </li></ul><ul><li>Energy supplying organelle </li></ul>Mitochondrion
  21. 23. <ul><li>Synthesize proteins through the addition of amino acids </li></ul><ul><li>Receive coded instructions via mRNA </li></ul><ul><li>Composed of protein and rRNA (ribosomal RNA) </li></ul><ul><li>Free ribosomes in the cytosol make proteins for local use </li></ul><ul><li>Ribosomes connected to the ER make proteins for other parts of the cell or for export </li></ul><ul><li>Protein factories </li></ul>Ribosomes
  22. 24. Ribosomal products Exported Digestion Pepsin Stomach Both Speed up reaction Catalaze Liver Kept Movement Actin / Myocin Muscle Exported Control glucose levels Insulin Pancreas Kept Carry O2 Haemoglobin RBC Kept / exported Function Protein Cell Type
  23. 25. <ul><li>Network of intracellular membranes </li></ul><ul><li>Prior to transport, packages substances in a transport vessicle </li></ul><ul><li>Production, processing, transport & storage of materials within a cell </li></ul><ul><li>Links with plasma membrane and other membranous organelles </li></ul><ul><li>Intracellular transport </li></ul>Endoplasmic Reticulum
  24. 26. <ul><li>Stack of flat membrane sacs </li></ul><ul><li>Collects identical proteins and condenses them in to a single export unit </li></ul><ul><li>Packages protein bundles in to excretory vessicles </li></ul><ul><li>Concentration and packaging </li></ul>Golgi Apparatus
  25. 27. Organelles in action
  26. 28. <ul><li>Large membrane-bound vessicles containing digestive enzymes </li></ul><ul><li>Used for breaking down unwanted structures or substances within the cell </li></ul><ul><li>Malfunction results in build up of toxic substances within the cell </li></ul><ul><li>Animation </li></ul><ul><li>Controlled destruction </li></ul>Lysosome
  27. 29. <ul><li>Peroxisomes </li></ul><ul><ul><li>Prevent the dangerous build-up of hydrogen peroxide (a byproduct of some cellular processes) </li></ul></ul><ul><li>Endosomes </li></ul><ul><ul><li>pass newly ingested material to lysosomes for digestion </li></ul></ul><ul><li>Cilia & Flagella </li></ul><ul><ul><li>used for movement in many prokaryotic cells & some eukaryotes </li></ul></ul><ul><ul><li>covered by an extension of the cell membrane </li></ul></ul><ul><ul><li>made up of 9 doublet microtubules & 2 single, central microtubules </li></ul></ul>Other organelles
  28. 30. <ul><li>A ribosome on the ER assembles around the mRNA, every 3 nucleotides codes a particular amino acid </li></ul><ul><li>The protein is packaged in a transport vessicle and transported through the cell along the ER </li></ul>How it all comes together <ul><li>Protein production to excretion </li></ul><ul><li>An mRNA copy of a gene on the DNA is made. This copy then travels out in to the cytosol </li></ul><ul><li>Proteins are concentrated and then packaged in to a secretory vessicle. </li></ul><ul><li>Vessicle floats through the cytosol before merging with the plasma membrane </li></ul>Cytoplasm Nucleus Ribosome ER Golgi Body
  29. 31. <ul><li>Here is the description of the table. You may change or delete this text as you wish. </li></ul><ul><li>This chart is compatible with PowerPoint 97 to 2007. </li></ul><ul><li>Here is a placeholder for more text and description of the chart. Changing this text will not interfere with the formatting of this template. </li></ul>Summary <ul><li>Of structures and functions </li></ul>
  30. 32. c c c c
  31. 33. <ul><li>Membrane bound (called a tonoplast in plants), liquid filled spaces </li></ul><ul><li>food vacuoles (intracellular digestion) </li></ul><ul><li>contractile vacuoles (water balance) </li></ul><ul><li>plant cells typically have large ones filled with sap (turgidity & storage) </li></ul><ul><li>Present in plants, fungi, some protists, bacteria & animals </li></ul>Vacuole
  32. 34. <ul><li>Double membrane, inner membrane contains many inner folds </li></ul><ul><li>Contains DNA, free ribosomes, starch grains and lipid droplets </li></ul><ul><li>Folded inner membrane forms thylakoids, stacks of these are called grana </li></ul><ul><li>The light-dependent reaction occurs in the chlorophyl containing grana </li></ul><ul><li>The light-independent reaction occurs in the fluid around the grana called the stroma </li></ul><ul><li>Only plants cells contain chloroplasts. Photosynthetic bacteria contain chlorophyll, but it is free-floating within the cell. </li></ul><ul><li>Sunlight trappers </li></ul>Chloroplasts
  33. 35. <ul><li>Only in plant, fungi & bacterial cells </li></ul><ul><li>Primary cell wall made of non-living cellulose (chitin in fungi and bacteria) </li></ul><ul><li>Plants have secondary cell walls made of lignin </li></ul><ul><li>The walls of two cells are connected by a sticky pectin layer </li></ul><ul><li>Provides support, strength & prevents expansion </li></ul><ul><li>Freely allows water & dissolved substances through </li></ul><ul><li>Rigidity and support </li></ul>Cell Wall
  34. 36. The cell skeleton <ul><li>Maintain the shape of the cell </li></ul><ul><li>Provide a support structure for the components of the cell </li></ul><ul><li>Movement of materials within cell </li></ul><ul><li>Movement of the cell itself - if required </li></ul>Maintain the shape of the cell Provide a support structure for the components of the cell Movement of materials within cell Movement of the cell itself - if required <ul><li>Microtubules </li></ul><ul><li>Hollow </li></ul><ul><li>Composed of tubulin </li></ul><ul><li>Microfilaments </li></ul><ul><li>Solid </li></ul><ul><li>Thinner </li></ul><ul><li>More flexible </li></ul><ul><li>Intermediate filaments </li></ul><ul><li>Very tough </li></ul><ul><li>Composed of proteins </li></ul>
  35. 37. Occluding (tight) junctions <ul><li>Cell membranes “come together” </li></ul><ul><li>Function: </li></ul><ul><ul><li>hold cell together </li></ul></ul><ul><ul><li>help to maintain polarity of cell </li></ul></ul><ul><ul><li>prevent passage of molecules </li></ul></ul><ul><li>NO movement of material between cells </li></ul>
  36. 38. Communicating (gap) junctions <ul><li>Aligned protein channels in the membranes of adjoining cells </li></ul><ul><li>Permit the passage of: </li></ul><ul><li>amino acids, sugars, salt ions, and other small molecules </li></ul>
  37. 39. Anchoring junctions (Desmosomes) <ul><li>Dense plaques of protein anchoring intermediate filaments that protrude in to the cytosol of neighbouring cells </li></ul><ul><li>Serve as a bridge connecting the actin cytoskeleton of neighbouring cells </li></ul>
  38. 40. Connections between plant cells: plasmodesmata
  39. 41. <ul><li>Signal to apoptose may come from inside or outside the cell </li></ul><ul><li>Cell death via apoptosis is a normal part of the cell cycle </li></ul><ul><li>Failure to apoptose will result in uncontrolled growth and reproduction. </li></ul><ul><li>Invasion in to healthy cells represents a malignant tumour </li></ul><ul><li>Cancer is the second highest cause of death in humans after heart disease </li></ul><ul><li>Animation of difference between apoptosis and necrosis </li></ul><ul><li>Programmed cell death </li></ul>Apoptosis
  40. 42. Apoptosis <ul><li>The sequence of events </li></ul>