Transcript Cell membrane - Aurora City Schools

Chapter 4
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Schwann, Schleiden and Virchow are credited
with coming up with the basics of the cell
theory
3 components:
◦ 1.All living organisms are made up of cells
◦ 2.Cells are the basic units of structure and function
in living organisms.
◦ 3.All cells come from cells that existed before them
by cellular reproduction.
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http://www.youtube.com/watch?v=AeygTtDx2W8
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Every cell has the following main
characteristics:
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Cell membrane
Cytoplasm
DNA
Ribosomes
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Antone von Leeuwenhoek assembled the first
microscope that was useful for scientific
research.
Compound light microscopes reflect light
through a set of lenses and the specimen to
magnify the specimen.
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See handout for the parts of the microscope – you must know it.
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http://www.youtube.com/watch?v=3emmlXcV-MU&feature=related
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Two important characteristics that determine
the quality of a light microscope:
◦ Magnification – an increase in the apparent size of
an object. We calculate magnification by the
following:
Magnification of eyepiece x magnification of
objective lens = total magnifying power
• Resolution – the measure of clarity of an image. As
the magnification increases, the resolution of the
image decreases.
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Some microscopes use beams of electrons for
magnification instead of light – electron
microscopes
Scanning electron microscope (SEM) – used to
study the detailed architecture of the surface
of the object. Forms a 3D image, but does
not show the inside of the object.
Transmission electron microscope (TEM) –
used to provide a detailed 2D image of the
inside structure of the object that is viewed.
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http://www.cellsalive.com/howbig.htm
Cells are microscopic, they are visible only
with light microscopes.
Most of their size ranges from 1-100 µm.
Cells are small, because they have to be
able to carry materials from one side of the
cell to the next in a short period of time.
Cells must have a large enough surface area
to be able to take in nutrients and oxygen
and release waste quickly.
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Prokaryotic cells –
◦ small cells (about 1-10 µm) that do not have a
nucleus and membrane-bound organelles
◦ Found in bacteria and archaebacteria
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Prokaryotic Cell Organelles:
◦ Nucleoid region – part of the prokaryotic cell where
the DNA is found
◦ Cell membrane – innermost covering of the cell
◦ Cell wall – outside of cell membrane, made up of a
special mix of polysaccharides and proteins
(antibiotics break it down)
◦ Capsule – outside of the cell wall, protective covering
(not all bacteria have it)
◦ Flagella (sing. Flagellum) – long, whiplike structure
that moves bacteria
◦ Pili – short, hair-like projection used to stick to other
surfaces and for conjugation (exchange of genetic
materials between bacteria)
◦ Cytoplasm – jelly-like fluid that dissolves substances
and holds organelles
◦ Ribosomes – organelles that make proteins in the
cytoplasm
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http://www.ted.com/talks/lang/eng/bonnie_bassler_on_how_bacteria_communicate.html
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Protists, Fungi, Plants, and Animals
Have nucleus and membrane-bound
organelles
Much larger and more complex than
prokaryotic cells.
Reproduce sexually and asexually
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Nucleus
◦ Control center of cell; contains most of the cell’s
DNA
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Nucleolus
◦ Location where ribosomes are synthesized
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Nuclear pore
◦ Allows RNA to move in and out of nucleus
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Ribosomes
◦ Protein synthesis
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Rough ER
◦ Comprised of a network of tubes and flattened
sacs.
◦ Continuous with plasma membrane and nuclear
membrane
◦ Site of protein synthesis (consists of ribosomes)
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Smooth ER
◦ Site of lipid and carbohydrate metabolism
◦ No ribosomes
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Golgi Apparatus
◦ Connected with ER; flattened disc-shaped sacs,
stacked one on top of the other
◦ Modification, storage, and packaging of proteins.
◦ “tags” proteins so they go to the correct
destination.
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Lysosomes (in animal cells and some protists)
◦ Digestion of nutrients, bacteria, and damaged
organelles; destruction of certain cells during
embryonic development
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Peroxisomes
◦ Diverse metabolic processes with breakdown of
H2O2 by-product
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Vacuoles
◦ Digestion (like lysosomes); storage of chemicals,
cell enlargement; water balance
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Chloroplasts
◦ Conversion of light energy to chemical energy of
sugars (site of photosynthesis)
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Mitochondria
◦ Conversion of chemical energy of food to chemical
energy of ATP
◦ “Power House” of cell
◦ Bound by double membrane
Mitochondria
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Cytoskeleton (including cilia, flagella, and
centrioles in animal cells)
◦ Maintenance of cell shape; anchorage for
organelles; movement of organelles within cells;
cell movement; mechanical transmission of signals
from exterior of cell to interior.
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Cell walls (in plants, fungi, and protists)
◦ Maintenance of cell shape and skeletal support;
surface protection; binding of cells in tissues
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We will be looking at:
◦ Cell Membranes
◦ Selective permeability of cell membranes
◦ The phospholipid bilayer that makes up cell
membranes
◦ The model that describes cell membrane, the Fluid
Mosaic Model
◦ Cell Transport Processes
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Membranes provide the structural basis for
metabolic order and surround the cell.
Most organelle’s are made from membranes
Semipermiability- Regulate the transport of
molecules in and out of the cell
Immune response
Attaches cells to other cells or surfaces.
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Cell membranes control what goes in and out
of the cell
It allows some substances to cross more
easily than others
Cell membrane is amazingly thin
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Lipids, mainly phopholipids, are the main
structural components of membranes
Phospolipid has a phosphate group and only
two fatty acids
◦ Head, with a charged phosphate group, is
hydrophillic
◦ Fatty acid tails are nonpolar and hydrophobic
◦ Thus, the tail end is pushed away by water, while
the head is attracted to water
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Hydrophobic interior of the bilayer is one
reason membranes are selectively permeable.
Nonpolar, hydrophobic molecules are lipidsoluble can easily pass through membranes
Polar molecules and ions are not lipid-soluble
◦ Ability to pass through membrane depends on
protein molecules in the phospholipid bilayer.
Phospholipid
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Phospholipids form a two-layer sheet called a
phospholipid bilayer.
◦ Hydrophillic heads face outward, exposed to the
water on both sides of a membrane
◦ Hydrophobic tails point inward, mingling together
and shielded from water.
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Hydrophobic interior of the bilayer is one
reason membranes are selectively permeable.
Nonpolar, hydrophobic molecules are lipidsoluble can easily pass through membranes
Polar molecules and ions are not lipid-soluble
◦ Ability to pass through membrane depends on
protein molecules in the phospholipid bilayer.
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Plasma membrane is described as a “Fluid
Mosaic”
Mosaic denotes a surface made of small
fragments, like pieces of colored tile
◦ A membrane is considered “mosaic” because it has
diverse protein molecules embedded in a
framework of phospholipids.
◦ A membrane mosaic is “fluid” in that most of the
individual proteins and phospholipids can can drift
literally in the membrane
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Tails of phospholipids are kinked.
◦ Kinks make the membrane more fluid by keeping
adjacent phospholipids from packing tightly
together.
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In animal cells, the steroid cholesterol
stabilize the phospholipids at body
temperature and also keep the membrane
fluid at lower temperatures.
◦ In a cell, phospholipid bilayer remains about as
fluid as salad oil at room temperature.
◦ Cell Membrane Proteins:
 Integral proteins – act as ion channels or molecular
channels
 Peripheral proteins – act as receptors
Cell membrane carbohydrates bonded to proteins
and lipids in the membrane:
 A protein with attached sugars is called a glycoprotein
 whereas a lipid with sugars is called a glycolipid.
 Function as cell identification tags that are recognized by
other cells.
 Significant for cells in an embryo to sort themselves to
tissues and organs.
 Also functions in the immune system to recognize and
reject foreign cells.
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Transport means the movement of molecules
from one side of the cell membrane to the
other
Transport is influenced by:
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The
The
The
The
size of substances
polarity of substances
concentration of substances
permeability of the cell membrane
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Passive
◦ Diffusion
◦ Osmosis
◦ Facilitated diffusion
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Active
Bulk
◦ Endocytosis
◦ Exocytosis
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Diffusion of a substance across a biological
membrane
Diffusion is the movement of particles from
high concentration to low concentration.
Moves with a concentration gradient
No energy input required
Eventually reaches equilibrium
◦ Molecules continue to move back and forth, but no
net change in concentration will occur
Small, nonpolar molecules that easily diffuse across
plasma membranes, such as O2 and CO2
Simple Diffusion
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Osmosis
◦ the diffusion of water across the cell membrane.
Especially important when the solute cannot move
through the membrane.
◦ Tonicity:
 Describes the tendency of a cell in a given solution to
lose or gain water.
 Isotonic, hypertonic, and hypotoni
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Osmosis (continued):
◦ Isotonic solution
 Equal concentration of solvent inside and outside of
cell; water goes in and out
 Cell’s volume remains the same; equilibrium
◦ Hypertonic solution
 Solute concentration is lower inside cell (solvent
concentration is higher inside cell) ;Water goes out
 Cell shrivels
 Causes plasmolysis in plant cells
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Osmosis (continued):
◦ Hypotonic solution
 Solute concentration is greater inside the cell (solvent
concentration is lower inside the cell); water goes in
 Cell swells and may lyse
 Causes cytolysis in animal cells
 Refer to figure 5.17
Osmosis
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Osmotic Pressure
◦ The pressure exerted by the flow of water through a
semipermeable membrane separating two solutions
with different concentrations of solute.
◦ Higher concentration of dissolved substances will
result in lower osmotic pressure and in the
movement of water into the area with more
dissolved substances.
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Facilitated diffusion
◦ Many substances can’t diffuse freely across
membrane because of their size, polarity, or charge
◦ Need the help of specific transport proteins in the
membrane to move across the membrane
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Transport processes that can move
substances from the lower concentration
area to the higher by using energy.
Energy is gained by using ATP molecules
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A type of active transport is the Na-K ion
pump
◦ 3 sodium ions move out of the cell with the help of
a transport protein, while 2 potassium ions move
into the cell.
◦ This process requires energy in the form of ATP.
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Type of active transport that involves movement of
large particles.
Endocytosis – a process by which large particles
can move into the cell by using membrane vesicles
Types of endocytosis:
◦ Phagocytosis – engulfing solid particles
◦ Pinocytosis – engulfing liquids, solutions
◦ Receptor-mediated endocytosis – moving into the
cell by first binding with receptor molecules on
the cell’s surface.
Receptor-mediated endocytosis
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Exocytosis – the process by which the cell
releases large molecules via vesicles through
its cell membrane