Download Chapter 3 Cell Structure and Function 2013

 Cell - Basic unit of all living
things
 Plasma membrane – Outer
boundary of the cell
 Nucleus – Located centrally
 Directs cell activities
 Cytoplasm – Located
between plasma membrane
& nucleus
 Contains cytosol and
organelles
• Outermost component of cell
• Boundary that separates
substances Intracellular
(inside the cell) vs.
extracellular (outside the
cell) materials
• Selective permeable
• Allows some substances to
cross it more easily than
others
• Consists of lipids and
proteins
• Consists of 45-50% lipids
• 45-50% of protein
• 4-8% of carbohydrates
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Predominate lipids are:
Phospholipids and cholesterol
Phospholipids: lipid 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
• Determines fluid nature of the
membrane
• Provides stability
• Fluid-mosaic model:
• Plasma membrane is neither
rigid nor static
• Highly flexible
• Fluid nature of membrane
provides
– Distribution of molecules
within the membrane
– Phospholipids
automatically reassembled
if membrane is damaged
 Proteins are dispersed into the
phospholipid bilayer of
plasma membrane
 Integral or Intrinsic Proteins
– Embedded in the membrane
 Peripheral or extrinsic Proteins
– Attached to either the inner
or outer surfaces of the lipid
bilayer
 Membrane proteins function as:
Markers, attachment sites,
channels, receptors, enzymes,
or carriers
• Marker Molecules
• Allow cells to identify one
another or other molecules
• Are mostly glycoproteins
and glycolipids
• eg. Ability of immune
system to distinguish
between self and foreign
cells
• Organ transplant
• Attachment Proteins
• Integral proteins function
as attachment protein
• Allow cell to attach to
other cells
• Or to extracellular
molecule & intracellular
molecules
• Also function as cell
communication
Transport Proteins
Are integral proteins, allow ions or molecules
to move from one side of plasma membrane
to other
Transport proteins are:
 Channel proteins
 Carrier Proteins
 ATP-powered pumps
Channel Proteins
 Hydrophilic region of integral
protein faces inward
 Ions or small molecules of right
size, charge and shape can pass
through the channel
 Charge in hydrophilic part of
channel proteins determine
molecules can pass
 eg. Flow of H+ to inner
mitochondrial membrane for ATP
production
 Carrier Proteins (transporters)
 Are Integral proteins move
ions from one side of
membrane to the other
– Have specific binding sites
– Protein changes shape to
transport ions or molecules
– Resumes original shape after
transport
– eg. Transports sodium and
potassium ions across a nerve
cell membrane
• ATP-Powered Pumps
• Are transport proteins that
move specific ions and
molecules from one side
of plasma membrane to
the other
• Requires ATP
• Receptor Proteins
• Are Proteins or glycoproteins
in membranes with an
exposed receptor site
• Can attach to specific
chemical signal molecules
• Chemical signal can attach
only to cells with that specific
receptor
• Binding acts as a signal that
triggers a response
 Receptors Linked to Channel
Proteins
 Attachment of specific chemical signals
(e.g., acetylcholine) to receptors causes
change in shape of channel protein
 Causes channel opens or closes
 Changes permeability of plasma
membrane and some ions can pass
through ion channels
• Enzymes:
• Some membrane proteins
functions as enzymes
• Catalyze reactions at
outer/inner surface of
plasma membrane
• Eg. Surface cells of small
intestine produce enzymes
that breaks dipeptide into
amino acids
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Diffusion/Osmosis
• water diffuses through the membrane
• Lipid soluble substances go across
Filtration
• Moves particles with pressure difference
Passive Transport (= facilitated diffusion)
• No energy required
• selectively allow certain types of molecules
in and out through channel proteins
Active Transport
• Required energy = ATP
Endocytosis and Exocytosis
• Large mol. enters to cell by endocytosis
• Large mol. leaves cell via exocytosis
• Diffusion:
– net movement of molecules
down a concentration gradient
towards areas of lower
concentration
– Allows oxygen, carbon
dioxide, and lipids to cross
• Concentration Gradient
– Conc. Of ions/molecules on
one side not same as other
• Diffusion affected by different
conditions
– Temperature:
• High temp increases rate
of diffusion
– Size:
• Small molecules go down
conc. gradient faster
– Electronic gradient:
• charges of molecules/ions
affect diffusion rate
• Dropping a dye in a cup of water
– drop diffuses to the areas of
the cup w/out the dye
– goes down the concentration
gradient
– dye goes towards a uniform
mixture in water
– In osmosis, water molecules diffuse across a
selectively permeable membrane
• From an area of low solute concentration
• To an area of high solute concentration
• Until the solution is equally concentrated on both
sides of the membrane
• Osmotic concentration
– concentration of all molecules dissolved in a
solution
• Hypertonic solution
– solution with higher concentration of solutes
• Hypotonic solution
– Solution with lower conc. of solutes
• Isotonic solutions
– solutions with equal conc.
of solute
 The survival of a cell depends on its ability to
balance water uptake and loss
– Isotonic: cell neither shrinks nor swells
– Hypertonic: cell shrinks (crenation)
– Hypotonic: cell swells (lysis)
• Works like a sieve
• Depends on pressure difference on either
side of a partition
• Moves from side of greater pressure to
lower
• Eg: urine formation in the kidneys Blood
pressure moves water and small
molecules from the blood through the
filtration membrane while large molecules
remain in the blood
• Like diffusion, but uses
carrier or channel protein
• Selective Permeability
– Cell controls what comes in
and goes out
• Certain channel or carrier
proteins
– allow only certain molecule
types entry
• Molecules/ions go with
concentration gradient
• No energy required
– Active transport requires energy to move
solutes against a concentration gradient
• ATP supplies the energy
• Transport proteins move solute molecules across the
membrane
• Eg. Glucose, amino acids
• Macromolecules transported into or out of the
cell through plasma membrane by vesicle
formation
– Endocytosis – Cells engulf substances and plasma
membrane extends outward and surround food
particle and pinches off and forms the vesicle
• Phagocytosis
– Vesicle contains large
solid particles
• Pinocytosis
– Vesicle contains liquid
or small particle
• Receptor-Mediated
– Plasma membrane
contain specific
receptor that allows
certain substances to
be transported by
phagocytosis or
pinocytosis
• A vesicle may fuse with the membrane and expel its contents
outside the cell
• Examples
– Secretion of digestive enzymes by pancreas
– Secretion of mucous by salivary glands
– Secretion of milk by mammary glands
• Cytoplasm: Cellular
material outside nucleus
but inside plasma
membrane
• Composed of Cytosol,
Cytoskeleton,
Cytoplasmic Inclusions,
Organelles
• Cytosol: fluid portion
• Dissolved molecules
(ions in water) and colloid
(proteins in water)
• Is a network of fibers
extending throughout the
cytoplasm
• Gives mechanical support
to the cell
• Maintain cell shape
• Assists in cell movement
• Consists of three types of
protein fibers:
• Microtubules
• Actin or Microfilaments
• Intermediate filaments
 Microtubules
 Found in cytoplasm
 Hollow rods – 25 nm in
diameter, 0.25 m – 25 m in
length
 made up of protein – tubulin
 Shape and support the cell
 Guide movement of organelles
 Responsible for separation of
chromosomes during cell
division
 Essential components of
centrioles, spindle fibers, cilia
and flagella
 Actin filaments or Microfilaments
 Solid rods – 7 nm in diameter
 Twisted double chain of actin –
globular protein
 Mechanical support for microvilli
in intestinal cells
 Enable cells to change shape and
move
 Eg. Muscle cells, actin filaments
are responsible for muscle`s
contraction
Intermediate filaments
fibrous proteins supercoiled
into thicker cable
10 nm in diameter
larger than microfilaments but
smaller than microtubules
Support cell shape
Provide mechanical strength
to cells
eg. Support the extensions of
nerve cells
• Are aggregates of chemicals either produced
or taken in by cells
• For eg. Lipid droplets store energy-rich molecules
• hemoglobin in red blood cells transport oxygen
• melanin – skin color pigment
• Minerals, dye etc.- cytoplasm
• Small specialized structures
with particular functions
• Most have membranes that
separate interior of
organelles from cytoplasm
• Each organelle is
responsible for performing
specific function
• Nucleus is the largest
organelle of the cell
• The nucleus is the cell's genetic control center
• Contains the cell's DNA
• Forms long fibers of chromatin that make up chromosomes
• Human body cell has 46 chromosomes
• Nucleus is large, membrane-bound structure
• Consists of nucleoplasm and
surrounded by double membrane
nuclear envelope
• Pores in the envelope control
flow of materials in and out
• Nucleus contains ball-like
structure – nucleolus
• Ribosomes are synthesized in the nucleolus
• Chromosome Structure:
• Consist of chromatin, a complex
of DNA and histone proteins
• Before cell division, chromosome
duplication takes place
• Each chromosome consists of
two chromatids
• Chromatids are joined together
at the centromere
•Chromosome Structure:
• When the cell divides, the
sister chromatids separate
from each other
• Cell divides into two
daughter cells
• Each with a complete and
identical set of chromosomes
– DNA Controls cellular activities
by directing protein synthesis
– Protein regulate most chemical
reactions
– DNA transfers its coded
information to RNA
• RNA carries the information
from nucleus to cytoplasm
to make proteins
– Sites for protein synthesis
– Assembled in nucleolus of
nucleus
– Then move through nuclear
pores into the cytoplasm
– Composed of a large and a
small subunit
– Consists of ribosomal
RNA (rRNA) & protein
– Some ribosomes are
suspended in cytosol, other
are attached to ER
– The endoplasmic
reticulum (ER)
• Main manufacturing
facilities within the cell
• A continuous network of
flattened sacs and tubes
in the cytoplasm
• Internal spaces of sacs
and tubes - Cisternae
• ER is composed of
• Rough ER
• Smooth ER
– Rough endoplasmic reticulum (rough ER) is studded
with ribosomes
• Are place where proteins are produced and modified
– Transported to other organelles
– Smooth endoplasmic reticulum (smooth ER)
lacks attached ribosomes
– Has variety of functions
• Synthesizes lipids, including fatty acids,
phospholipids and steroids
• Detoxify toxins and drugs in
liver cells
• Stores calcium ions that
function in muscle
contraction
• The Golgi apparatus consists
of stacks of flattened
membranous sacs
• Packaging and distribution
center
• Receives, modifies,
packages and distributes
proteins & lipids
manufactured by ER
• Ships modified products
to other organelles or the
cell surface via secretory
vesicles
– A lysosome is a membraneenclosed sac form from
Golgi apparatus
• It contains digestive enzymes
• The enzymes break down
macromolecules
• Lysosomes have several
types of digestive functions
• They fuse with food vacuoles
to digest the food
• Destroy bacteria that have
been ingested into white
blood cells
• Recycle damaged organelles
• Abnormal lysosomes can cause fatal diseases
– Lysosomal storage diseases
• Result from an inherited lack of one or more
digestive enzymes found in lysozymes
• Seriously interfere with various cellular functions
• eg. Pompe`s disease – lack of glycogen-digesting
enzyme
• Cause weakening of heart muscle
• Tay-Sachs disease – lack of lipid –digesting enzyme
• Accumulation of excess lipid damage brain
• Peroxisomes
– Smaller than lysosomes
– Contains two sets of enzymes
– One enzyme break down fatty
acids and amino acids
– Hydrogen peroxide is a byproduct of breakdown (toxic)
– Another enzyme Catalase
convert hydrogen peroxide into
water and oxygen
– More peroxisomes – kidney
and liver for detoxification
• Proteasomes
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Tunnel-like structure
not surrounded by membrane
Consist of large protein complexes
Found in nucleus and cytoplasm
Include several enzymes that break down and
recycle unneeded or damaged proteins in cell
• Major site of ATP synthesis
• Consists of two membranes
• Outer membrane – smooth
• Inner membrane
– Cristae: Infoldings of inner
membrane
– Matrix: Enzymes 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.
• Located in Centrosome:
specialized zone near nucleus
• Center of microtubule formation
• Contains pair of centriole
• Each with nine triplets of
microtubule – ring
• Before cell division – Centriole
replicate
• During cell division, centrioles
divide, move to ends of cell and
organize spindle fibers
• Facilitate the movement of
chromosomes during cell division
• Appendages projecting
from cell surfaces
• Capable of movement
• Cilia move in a coordinated
back-and-forth motion
• Occur in large no. on cell
surface
• Cylindrical in shape
• 0.25 m in diameter, 10 m
in length
• Moves materials over the
cell surface
• eg. Respiratory tract –
removes mucus
• Similar to cilia but longer (45 m)
• Usually only one per cell
• Move the cell itself in wave-like fashion
• Eg: sperm cell
Direction of swimming
1 µm
Motion of flagella
– The structure and
mechanism of cilia and
flagella are similar
• Ring of 9 microtubule
doublets surrounds a central
pair of microtubule
– 9 + 2 arrangement
– Extend into basal bodies
– Using energy from ATP, movement of dynein
arms ( motor proteins) produces microtubule
bending
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Extension of plasma membrane
Normally many microvilli on each cell
One tenth to one twentieth size of cilia
Do not move, supported by actin filaments
Increase the cell surface area
Found in kidney, intestine
Main function is absorption