Download THE CELL

SPSC2005 and HCSCGS17
Anatomy and Physiology of
Speech, Language and Hearing
THE CELL
Jennifer Linden
UCL Ear Institute
[email protected]
Seeley, R.R., P. Tate, and T.D. Stephens, Anatomy &
Physiology. 8th ed. 2008, McGraw-Hill: Chapter 3
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Case study: Jane
Jane has drooping eyelids and difficulty making
eye movements. Her vision is poor, and her
hearing is impaired. She also has cardiac
conduction abnormalities causing arrhythmia.
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Parts of a cell
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• Cell membrane, cytoplasm, nucleus
• No single cell includes all of the features seen in the
generalized cell.
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Basic structure of the cell
•
Cell membrane
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•
Lipid bilayer
Membrane proteins
Membrane permeability, gradients, transport
Diffusion, osmosis, active transport, exocytosis, endocytosis
Cytoplasm
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Organelles
Cytoskeleton, filaments & microtubules, cilia
Ribosomes, endoplasmic reticulum, Golgi complex
Lysosomes, mitochondria
Nucleus
– Function of nucleus, chromosomes
– Protein synthesis, transcription, translation
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Functions of the cell
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• Cell metabolism and energy use
• Synthesis of molecules
• Communication via electrical and chemical
signals
• Reproduction and inheritance. Each cell
contains DNA. Some cells are specialized as
gametes (eggs or sperm)
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Plasma membrane
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•
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Separation of intracellular vs. extracellular materials
Production of charge difference (membrane potential) across the membrane
by regulation of intracellular and extracellular ion concentrations
– Outside of membrane positively charged compared to inside
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•
Glycocalyx: combinations of carbohydrates and lipids (glycolipids) and
proteins (glycoproteins) on outer surface.
Fluid-mosaic model
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Membrane lipids
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•
Phospholipids and cholesterol predominate
– Phospholipids: bilayer. Polar (charged) 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
•
Fluid nature allows distribution of molecules within the membrane
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Membrane proteins
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•
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•
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Integral or intrinsic
– Extend deeply into membrane,
often extending from one surface
to the other
– Can form channels through the
membrane
Peripheral or 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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Marker molecules: Glycoproteins and glycolipids
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• Allow cells to identify
one another or other
molecules
– Immunity
– Recognition of oocyte by
sperm cell
– Intercellular
communication
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Channel proteins
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• 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 opened
or closed by certain stimuli
– 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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Receptors linked to channel proteins
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• Receptor molecules linked to
channel proteins (ligand-gated
channel)
• Attachment of receptor-specific
chemical signals (e.g.,
acetylcholine) to receptors
causes change in shape of
channel protein
• Channel opens or closes
• Changes permeability of cell to
some substances (e.g. cations
such as Na+, K+)
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Receptors linked to G protein complexes
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• Alter activity on inner
surface of plasma
membrane
• Leads to intracellular
chemical signals that affect
cell function
• Some hormones function in
this way
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Movement through the cell membrane
•
•
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Diffusion
Osmosis
Filtration
Mediated Transport
– Facilitated diffusion
– Active transport
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Diffusion
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• Movement of solutes from an area of higher
concentration to lower concentration in solution
– Concentration or density gradient: difference
between two points
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Osmosis
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• Diffusion of water (solvent) across a selectively
permeable membrane. Water moves from an
area of low concentration of solute to an area of
high concentration of solute
• Osmotic pressure: pressure required to prevent
water from moving across a membrane by
osmosis
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Osmosis - terms
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• Comparative terms
used to describe
osmotic pressures of
solutions
– Isosmotic: solutions with
the same concentrations
of solute particles
– Solution with a greater
concentration of solute is
hyperosmotic
– Solution with a lesser
concentration of solute is
hyposmotic
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Osmosis and cells
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• Important because large volume changes caused by water movement
disrupt normal cell function
• Cell shrinkage or swelling
– Isotonic: cell neither shrinks nor swells
– Hypertonic: cell shrinks (crenation)
– Hypotonic: cell swells (lysis)
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Filtration
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• Works like a sieve
• Depends on pressure difference on either side of
a partition
• Moves from side of greater pressure to lower
• Example: urine formation in the kidneys. Water
and small molecules move through the
membrane while large molecules remain in the
blood
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Mediated transport
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• Involves
– Carrier proteins
(transporters)
– ATP powered pumps
(active transport)
– Channel proteins (ion
channels)
• Characteristics
– Specificity: specific for a
single type of molecule
– Saturation: rate of
transport limited to number
of available carrier proteins
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Mediated transport – active transport
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• Active transport
– Use of energy allows the
cell to accumulate
substances. Requires ATP
– Rate of transport depends
on concentration of
substrate and on
concentration of ATP
– Example: Na+/K+ exchange
pump that creates electrical
potentials across
membranes (important in
nerve cells!)
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Endocytosis
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• Internalization of
substances by
formation of a
vesicle
• Types
– Phagocytosis
(shown)
– Pinocytosis
– Receptormediated
endocytosis
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Exocytosis
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• Accumulated vesicle secretions expelled from cell
• Examples
– Secretion of digestive enzymes by pancreas
– Secretion of mucus by salivary glands
– Secretion of milk by mammary glands
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CYTOPLASM
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• Cellular material outside nucleus but inside plasma membrane
• Cytosol
• Cytoskeleton
• Inclusions
• Organelles
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Cytoskeleton
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• The cytoskeleton is a network
of several kinds of protein
filaments that extend
throughout the cytoplasm and
provides a structural
framework for the cell
(Seeley 8 p76).
• It consists of
– microfilaments
– intermediate filaments
– microtubules
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Organelles
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• Small specialized structures with particular
functions
• Most have membranes that separate interior
of organelles from cytoplasm
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Ribosomes
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• Sites of protein
synthesis
• Composed of a large
and a small subunit
• Types
– Free
– Attached (to endoplasmic
reticulum)
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Endoplasmic reticulum (ER)
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• Rough ER
– Has attached ribosomes
– Proteins produced and modified here
• Smooth ER
– No attached ribosomes
– Manufactures lipids
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Golgi apparatus
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• Modification,
packaging,
distribution of proteins
and lipids for
secretion or internal
use
• Flattened membrane
sacs stacked on each
other
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Function of Golgi apparatus
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• Proteins produced by
ribosomes of rough ER
• Proteins encapsulated
by vesicle formed by ER
• Vesicle moves from ER
to Golgi apparatus
• Golgi apparatus repackage proteins into
secretory vesicles
• Secretory vesicles travel
to cell membrane where
proteins are secreted by
exocytosis
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Action of lysosomes
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Mitochondria
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• 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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Cilia and flagella
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• Cilia
– move materials across the
surface of the cell
– stiff during power stroke but
flexible during recovery
– many coordinated together
– airways & uterine tube
• Flagella
– move an entire cell
– single flagella wiggles in a
wavelike pattern
– propels sperm forward
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Microvilli
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Extension of plasma membrane
Increase the cell surface area
Normally many on each cell
One tenth to one twentieth size of cilia
Do not move
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NUCLEUS
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• Parts of the nucleus include:
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•
•
•
nuclear envelope with nuclear pores
nucleolus
genetic material (DNA) - chromatin or chromosomes
genes are arranged in single file along chromosomes
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Function of the nucleus
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• Non-dividing cells contain nuclear chromatin
– loosely packed DNA
• Dividing cells contain chromosomes
– tightly packed DNA
– it doubled (copied itself) before condensing
• Genes found on chromosomes
– each gene contains directions for a specific protein
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Chromosomes
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• Each chromosome is a
long molecule of DNA
that is coiled together
with several proteins.
• Human somatic cells
have 46 chromosomes
arranged in 23 pairs.
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Case study: Jane
Jane has Kearns-Sayre Syndrome (KSS), a rare
disease caused by a mutation in mitochondrial
DNA that interferes with mitochondrial function.
Energy production in cells is therefore impaired.
The cellular energy deficit has greatest impact
where cells burn a lot of energy, such as in eye
muscles, sensory neurons, and cardiac muscle.
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