Download Gated ion channels

Chapter 3
Cell Anatomy
Cell = Chamber/Compartment
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• Basic Structure of the Cell
– Plasma membrane
– Cytoplasm containing organelles (little organs)
– Nucleus
• Functions of the Cell
– Basic unit of life
– Protection and support through production and secretion of
various kinds of molecules
– Movement. Various kinds occur because of specialized
proteins produced in the cell (Flagella and Cilla)
– Communication. Cells produce and receive electrical and
chemical signals
– Cell metabolism and energy release
– Inheritance. Each cell contains DNA. Some cells are
specialized to gametes for exchange during sexual
intercourse
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Plasma Membrane (phospholipid bilayer)
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Plasma Membranes
• Fluid-mosaic model
• theory explaining how cell membranes
are constructed
– Molecules of the cell membrane are
arranged in a sheet
– The mosaic of molecules is fluid; that
is, the molecules are able to float
around slowly
• Chemical attraction is the force that holds
membranes together
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Membrane Lipids
• Primary structure of a cell membrane is a double
layer of phospholipid molecules
– Heads are hydrophilic (water-loving)
– Tails are hydrophobic (water-fearing)
– Molecules arrange themselves in bilayers in water
– Cholesterol molecules are scattered among the
phospholipids to allow the membrane to function
properly at body temperature
– Most of the bilayer is hydrophobic; therefore water or
water-soluble molecules do not pass through easily
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Membrane Lipids (cont)
What is it composed of?
• Phospholipids and cholesterol predominate
– Phospholipids: bilayer. Polar heads facing water in the
interior and exterior of the cell (hydrophilic); nonpolar
tails facing each other on the interior of the membrane
(hydrophobic)
– Cholesterol: interspersed among phospholipids.
Amount determines fluid nature of the membrane
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Membrane
Proteins
TYPES of Membrane
Proteins
• Integral / intrinsic
– Extend deeply into
membrane, often extending
from one surface to the
other
– Can form channels through
the membrane
• Peripheral / extrinsic
– Attached to integral proteins
at either the inner or outer
surfaces of the lipid bilayer
• Functioning depends on 3-D
shape and chemical
characteristics. Markers,
attachment sites, channels,
receptors, enzymes, or
carriers.
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1) Marker Molecules:
Glycoproteins
• Carbohydrates
attach to proteins
• Allow cells to
identify one another
or other molecules
– Immunity
– Intercellular
communication
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2) Attachment Sites
• Attachment sites
to other cells or
to
extra/intracellular
molecules.
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3) Channel Proteins (Integral):
hydrophilic
region faces inward; charge determines molecules that can
pass through
• Nongated ion channels:
always open
– Responsible for the
permeability of the plasma
membrane to ions when the
plasma membrane is at rest
• Gated ion channels can be
open or closed
– Ligand gated ion channel:
open in response to small
molecules that bind to proteins
or glycoproteins
– Voltage-gated ion channel:
open when there is a change in
charge across the plasma
membrane
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4) Receptor Molecules
• Proteins in membranes
with an exposed
receptor site
• Can attach to specific
ligand molecules and
act as an intercellular
communication system
• Ligand can attach only
to cells with that specific
receptor
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5) Enzymes and Carrier Protein
• Enzymes: some act to catalyze reactions at outer/inner surface of
plasma membrane.
• Carrier proteins: integral proteins move ions from one side of
membrane to the other
– Have specific binding sites
– Protein change shape to transport ions or molecules
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Cytoplasm
• Cytoplasm: gel-like internal substance of cells that includes
many organelles suspended in watery intracellular fluid called
cytosol
• Cellular material outside nucleus but inside plasma membrane
• Two major groups of organelles (Table 3-3)
– Membranous organelles are sacs or canals made of cell
membranes
– Nonmembranous organelles are made of microscopic
filaments or other nonmembranous materials
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Endoplasmic Reticulum
– 2 Types
 Smooth ER
 Rough ER
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Endoplasmic Reticulum
Smooth (SER):
• No ribosomes attached
• Synthesizes lipids and carbohydrates:
– phospholipids and cholesterol (membranes)
– steroid hormones (reproductive system)
– glycerides (storage in liver and fat cells)
– Storage of Ca++
– Fat metabolism and drug detoxification (liver)
Rough (RER)
-Has attached ribosomes
- Proteins produced and modified here
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Ribosomes
- Tiny round bodies in the
cytoplasm made of a large and
small subunit
- Build polypeptides in protein
synthesis
– Two types:
• Free ribosomes in
cytoplasm:
– manufacture proteins
for cell
• Fixed ribosomes attached
to ER membranes:
– manufacture proteins
for secretion
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Golgi Apparatus
• Flattened membrane
sacs stacked on each
other (cisternae)
• Modification,
packaging,
distribution of proteins
and lipids for
secretion or internal
use
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Function of Golgi Apparatus
Proteins made in the ER are packaged into tiny vesicles, which pinch
off and move towards the golgi apparatus.
Vesicles fuse with the golgi membrane and release the proteins.
Enzymes within the golgi modify the proteins
The processed molecules eventually pinch off and move towards the
plasma membrane where they are secreted.
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Function of Golgi Apparatus
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Lysosomes
• Powerful enzyme containing vesicles
• Functions of Lysosomes
– Clean up inside cells:
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Break down large molecules
Attack bacteria
Recycle damaged organelles
Eject wastes by exocytosis
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Proteasomes
– Hollow protein cylinders found throughout the
cytoplasm
– Break down abnormal or misfolded proteins and
normal proteins no longer needed by the cell (and
that may cause disease)
– Break down protein molecules one at a time by
tagging each one with a chain of ubiquitin molecules,
unfolding the protein as it enters the proteasome, and
then breaking apart peptide bonds
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Proteasomes
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Peroxisomes
• Peroxisomes
– Smaller than lysosomes
– Detoxify harmful substances in cell
– Contain enzymes to break down fatty acids
and amino acids
– Contain peroxidase and catalase
– Hydrogen peroxide is a by-product of
breakdown
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Mitochondria
• Major site of ATP
synthesis
• Membranes
– Cristae: Infoldings of inner
membrane
– Matrix: Substance located
in space formed by inner
membrane
• Mitochondria increase in
number when cell energy
requirements increase.
• Mitochondria contain DNA
that codes for some of the
proteins needed for
mitochondria production.
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Nucleus
- The cell’s control center
– Contains genetic material (DNA)
– Three distinct regions:
1. Nuclear Membrane
2. Nucleoli
3. Chromatin
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Nuclear Structure and Content
• Nuclear Membrane
- double membrane connected by nuclear pores
-encloses nucleoplasm
• Nucleoli
- site of ribosome formation
• Chromatin
-carries cells DNA
-condenses into Chromosomes during cell
division
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Cytoskeleton
• Supports the cell but has to allow for
movements like changes in cell
shape and movements of cilia
• Cell fibers:
– Microfilaments: “cellular mm”
• Made of thin, twisted strands of
protein molecules that lie
parallel to the long axis of the
cell
• Can slide past each other and
cause shortening of the cell
• Actin and myosin are
subcategories
– Microtubules: hollow, made of
tubulin.
• Internal scaffold, transport, cell
division, move things around cell
– Intermediate filaments:
mechanical strength
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Cell Fibers
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Centrosome
An area of the cytoplasm near the nucleus that
coordinates the building and breaking apart of
microtubules in the cell
Nonmembranous structure also called the
microtubule organizing center
Center of microtubule formation
Before cell division, centrioles divide, move to
ends of cell and organize spindle fibers
– General location of the centrosome is
identified by the centrioles
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Cell Extensions
Cilia
• Appendages projecting from
cell surfaces
• Capable of movement
• Moves materials over the cell
surface
• Shorter and more numerous
than flagella
• Coordinated oar like
movements
• Respiratory tract
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Flagella
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Similar to cilia but longer
Usually only one per cell
Move the cell itself in wave-like fashion
Human Example: sperm cell
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Microvilli
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Extension of plasma membrane
Line intestines
Increase the cell surface area for absorption
Normally many on each cell
One tenth to one twentieth size of cilia
Do not move
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Cell Connections
Membrane junctions
1. Tight junctions – Adjacent plasma
membranes fused together
tightly
2. Desmosomes – Anchoring
junctions that prevent cells
subjected to mechanical stress
from being pulled apart
3. Gap junctions - Allow
communication between cells
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