the cell and plasma membrane
TRANSCRIPT
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The Cell and Plasma Membrane
http://www.youtube.com/watch?v=cj8dDTHGJBYhttp://www.youtube.com/watch?v=cj8dDTHGJBY
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Prokaryotes• Smallest Cells • Lack a nucleus – DNA is located in an area called
the nucleoid• Contain plasmids – small circular pieces of DNA
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Eukaryotes• Consists of: Plasma membrane• Barrier that surrounds the
cytoplasm of the cell
Organelles • Internal structures that
carry out specialized functions• Bounded by a membrane
(exception ribosome, centriole)
Cytosol• Liquid portion of the cell
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Examples of Cells
Amoeba Proteus
Plant Stem
Red Blood Cell
Nerve Cell
Bacteria
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Plant and Animal Cell
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Nucleus • Command centre of the cell
• Contains DNA blueprints for making proteins
• Surrounded by nuclear envoleope – Protects DNA from
chemical reactions • Nucelolus – Area of chromatin
(uncoiled DNA strands) that produces ribosomes
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Ribosomes • Assembled inside
nucleus • Made up of RNA and
proteins • Two Types – Free floating – found in
cytoplasm – Attached to ER
• Ribosomes make proteins
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Endoplasmic Reticulum • Continuous compartment
that folds repeatedly into flattened sacs and tubes Rough ER– Contains ribosomes
• Synthesis of proteins
– Once synthesized, proteins fold and take shape inside ER
Smooth ER– Contains no ribosomes – Synthesis of lipids – Transports vesicles to plamsa
membrane or Golgi body
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Golgi Bodies• Folded membrane (looks
like stack of pancakes) • Completion of proteins and
lipids making them fully functional
• use inside or outside of cell
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Mitochondria • Double bound
membrane organelle• Powerhouse of cell • Two compartments– Mitochondrial matrix– Intermembrane space
• Contain their own DNA and ribosomes– Synthesize ATP
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Vesicles • Transportation/destruction • Peroxisome – break down
fatty acids, detoxify alcohol• Vacuoles– Dispose of waste, debris and
toxic materials– Keep turgor pressure inside
plant cell• Lysosomes – fuse with
vacuole to dispose of worn out cell components (use of enzymes)
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Cytoskeleton• Made up of many protein
filaments– Gives shape to cell– Organizes organelles– Move cell structures
• Include – Microtubules
• form tracks that allow organelles to move
– Intermediate filaments• anchor organelles into regions of
cell• Support nuclear envelope and cell
membrane
– Actin filaments • Movement of membrane
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Centrosomes • Assembles and co-
ordinates activity of spindle fibres when the cell divides
• Contains centrioles
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Cilia, Flagella, Pseudopods• Organized array of microtubules• Flagella
– Whiplike structure – Propels cells (sperm)
• Cilia– Hair like structure – Sweeping action moves particles
(lining of airway)• Pseudopod (false feet)
– Lobe formations – Amoeba
• Prokaryotes – Contain pili – hollow appendages that
stick to other cells to swap information
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Cell Wall (Plant Cells)
• Located around plasma membrane
• Consists of cellulose fibres
• Protects supports and gives shape to the cell
• Waxy cuticle – Limits water loss on
hot/dry days
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Plastids (Plant Cells)• Chloroplasts– Double membrane bound
organelle– Stroma – semifluid interior,
contains enzymes and DNA– Specialize in photosynthesis – Contain chlorophyll
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Plasma Membranehttp://www.johnkyrk.com/cellmembrane.html
• Transports raw materials into the cell • Transport finished product and wastes out of cell • Prevent entry of unwanted matter into cell • Prevent matter needed to perform cellular
functions inside cell
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Plasma Membrane • Described by the Fluid Mosaic Model as:• Composed of a phospholipid bilayer• Semi-permeable – regulates substances in and out
of cell with the help of transport proteins
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Phospholipids
• Hydrophilic Head– Phosphate group– Polar group
• Hydrophobic Tail– Fatty acids
• Align themselves in aqueous solution
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Fluidity
• Cholesterol allows cells to function in a wide range of temperatures
• High temperature – Maintains rigidity in oily membrane
• Low temperature– Keeps membrane fluid/flexible – Prevents from freezing
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Membrane Protein : Integral/Peripheral
• Integral Membrane Proteins (transmembrane)– Exposed to aqueous environment on both sides of the
membrane – Transport, enzymatic activity, triggering signals,
attachment/recognition• Peripheral Membrane Proteins – Located on surface of a membrane – No interaction with hydrophobic core – Eg. Cytoskeleton
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Passive Membrane Transport
• No chemical energy required• Diffusion– Net movement of a substance from a region of high
concentration to a region of low concentration– Dynamic equilibrium between cells is met
• Molecule still randomly move through membrane but concentration remains same
• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/how_diffusion_works.html• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/diffusion_through_cell_membranes.html
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Simple Diffusion (Passive Transport)• Substances move across a membrane
unassisted• Size and charge affect the rate of diffusion
across the membrane
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Facilitated Diffusion
• Diffusion of larger molecules with the help of a transport protein (integral membrane protein)
• Stops when equilibrium is reached• Two types of Transport Proteins – Channel proteins– Carrier proteins
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Facilitated Diffusion
• Channel Proteins– Form hydrophilic pathways in the membrane – Water and certain ions can pass– Voltage-gated channels • Open or closed by changes in voltage across the
membrane or by binding molecules• Eg. Muscle contractions
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Facilitated Diffusion • Carrier Proteins – Form pathways
through the membrane
– Bind to a specific solute (glucose, amino acid)
– Carrier protein changes shape allowing solute to move from one side of the membrane to the other
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/how_facilitated_diffusion_works.html
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Simple vs Facilitated
• Simple Diffusion – Rate of diffusion
increases as difference in concentration gradient increases
• Facilitated Diffusion – Maximum rate is
reached but limited by number of transport protein in membrane
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Osmosis
• Passive diffusion of water across a membrane via aquaporins • Water always diffuses from an area of low solute
concentration (high water concentration) to an area of greater solute concentration (low water concentration)
• Three Solutions (Cell) – Hypotonic
• Solute concentration is high in cell (swells)
– Hypertonic• Solute concentration is low in cell (shrinks)
– Isotonic • Solute and water concentration is equal both in and outside cell
• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/animation_-_osmosis.html
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Osmosis
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Active Membrane Transport
• Substance carried across a membrane from an area of low concentration to an area of high concentration
• Use of pump• ATP used as energy source • Two Types – Primary Active Transport– Secondary Active Transport
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Primary Active Transport
• Pumps that moves positively charged ions across membranes (H⁺. Ca²⁺, Na⁺, K⁺)– ATP is hydrolyzed– Phosphate group attaches to pump allowing ion to bind to protein
transporter– Protein transporter undergoes a folding change exposing ion to
opposite side of membrane– Ion is released to side of higher concentration– Phosphate group is released
• This creates an electrochemical gradient– Effect of voltage and difference in ion concentration– Stored potential energy
• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/primary_active_transport.html
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Primary Active Transport
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Secondary Active Tranport • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/cotransport__symport_and_antiport_.html
• Uses concentration gradient of an ion as its energy source• This gradient was already established by primary pump. • Transport solute across membrane• Two ways
– Symport• Solute moves through channel in the same direction as ion
– Antiport• Solute moves in opposite direction as ion
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Exocytosis and Endocytosis
• Vesicles are used to transport• ATP is required• Exocytosis– Transport of proteins and waste material from
cytosol to exterior of cell • Endocytosis– Transport proteins and large molecules into cytosol
of the cell.
• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis