2 - Membranes & cell organelles
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2 - Membranes & cell organelles






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2 - Membranes & cell organelles 2 - Membranes & cell organelles Presentation Transcript

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