Download Chapter 3 PowerPoint - Hillsborough Community College

Chapter 3 Part A
Cells:
The Living
Units
© Annie Leibovitz/Contact Press Images
© 2016 Pearson Education, Inc.
PowerPoint® Lecture Slides
prepared by
Karen Dunbar Kareiva
Ivy Tech Community College
Why This Matters
• Understanding the structure of the body’s cells
explains why the permeability of the plasma
membrane can affect treatment
© 2016 Pearson Education, Inc.
3.1 Cells: The Living Units
• Cell theory
– A cell is the structural and functional unit of life
– How well the entire organism functions depends
on individual and combined activities of all of its
cells
– Structure and function are complementary
• Biochemical functions of cells are dictated by shape of
cell and specific subcellular structures
– Continuity of life has cellular basis
• Cells can arise only from other preexisting cells
© 2016 Pearson Education, Inc.
3.1 Cells: The Living Units
• Cell diversity
– Over 200 different types of human cells
– Types differ in size, shape, and subcellular
components; these differences lead to
differences in functions
© 2016 Pearson Education, Inc.
Figure 3.1 Cell diversity.
Erythrocytes
Fibroblasts
Skeletal
muscle
cell
Smooth
muscle cells
Epithelial cells
Cells that connect body parts, form linings,
or transport gases
Cells that move organs and body parts
Macrophage
Fat cell
Cell that stores
nutrients
Nerve cell
Cell that fights
disease
Sperm
Cell of reproduction
© 2016 Pearson Education, Inc.
Cell that gathers information and controls
body functions
3.1 Cells: The Living Units
• Generalized cell
– All cells have some common structures and
functions
– Human cells have three basic parts:
1. Plasma membrane: flexible outer boundary
2. Cytoplasm: intracellular fluid containing organelles
3. Nucleus: DNA containing control center
© 2016 Pearson Education, Inc.
Figure 3.2 Structure of the generalized cell.
Chromatin
Nuclear envelope
Nucleolus
Nucleus
Plasma
membrane
Smooth endoplasmic
reticulum
Cytoplasm
Mitochondrion
Lysosome
Centrioles
Rough
endoplasmic
reticulum
Centrosome
matrix
Ribosomes
Golgi apparatus
Cytoskeletal
elements
• Microtubule
• Intermediate
filaments
© 2016 Pearson Education, Inc.
Secretion being
released from cell
by exocytosis
Peroxisome
Extracellular Materials
• Substances found outside cells
• Classes of extracellular materials include:
– Extracellular fluids (body fluids), such as:
• Interstitial fluid: cells are submersed (bathed) in this
fluid
• Blood plasma: fluid of the blood
• Cerebrospinal fluid: fluid surrounding nervous system
organs
– Cellular secretions (e.g., saliva, mucus)
– Extracellular matrix: substance that acts as glue
to hold cells together
© 2016 Pearson Education, Inc.
Part 1 – Plasma Membrane
• Acts as an active barrier separating
intracellular fluid (ICF) from extracellular
fluid (ECF)
• Plays dynamic role in cellular activity by
controlling what enters and what leaves cell
• Also known as the “cell membrane”
© 2016 Pearson Education, Inc.
3.2 Structure of Plasma Membrane
• Consists of membrane lipids that form a
flexible lipid bilayer
• Specialized membrane proteins float through
this fluid membrane, resulting in constantly
changing patterns
– Referred to as fluid mosaic (made up of many
pieces) pattern
• Surface sugars form glycocalyx
• Membrane structures help to hold cells together
through cell junctions
© 2016 Pearson Education, Inc.
Figure 3.3 The plasma membrane.
Extracellular fluid
(watery environment
outside cell)
Cholesterol
Polar head of
phospholipid
molecule
Glycocalyx
(carbohydrates)
Glycolipid
Glycoprotein
Nonpolar tail
of phospholipid
molecule
Lipid bilayer
containing proteins
Outward-facing
layer of
phospholipids
Inward-facing layer
of phospholipids
Functions of the
Plasma Membrane:
• Mechanical barrier: Separates two
of the body’s fluid compartments.
• Selective permeability: Determines
manner in which substances enter
or exit the cell.
• Electrochemical gradient:
Generates and helps to maintain
the electrochemical gradient required
for muscle and neuron function.
Filament of
cytoskeleton
Integral
proteins
• Communication: Allows cell-to-cell recognition
(e.g., of egg by sperm) and interaction.
• Cell signaling: Plasma membrane proteins
interact with specific chemical messengers
and relay messages to the cell interior.
© 2016 Pearson Education, Inc.
Peripheral
proteins
Cytoplasm
(watery environment
inside cell)
Membrane Lipids
• Lipid bilayer is made up of:
– 75% phospholipids, which consist of two parts:
• Phosphate heads: are polar (charged), so are
hydrophilic (water-loving)
• Fatty acid tails: are nonpolar (no charge), so are
hydrophobic (water-hating)
– 5% glycolipids
• Lipids with sugar groups on outer membrane surface
– 20% cholesterol
• Increases membrane stability
© 2016 Pearson Education, Inc.
Membrane Proteins
• Allow cell communication with environment
• Make up about half the mass of plasma
membrane
• Most have specialized membrane functions
• Some float freely, and some are tethered to
intracellular structures
• Two types:
– Integral proteins; peripheral proteins
© 2016 Pearson Education, Inc.
Membrane Proteins (cont.)
• Integral proteins
– Firmly inserted into membrane
– Most are transmembrane proteins (span
membrane)
– Have both hydrophobic and hydrophilic regions
• Hydrophobic areas interact with lipid tails
• Hydrophilic areas interact with water
– Function as transport proteins (channels and
carriers), enzymes, or receptors
© 2016 Pearson Education, Inc.
Membrane Proteins (cont.)
• Peripheral proteins
– Loosely attached to integral proteins
– Include filaments on intracellular surface used for
plasma membrane support
– Function as:
• Enzymes
• Motor proteins for shape change during cell division
and muscle contraction
• Cell-to-cell connections
© 2016 Pearson Education, Inc.
Figure 3.4 Membrane proteins perform many tasks.
Enzymatic activity
Transport
• A protein (left) that spans the membrane
may provide a hydrophilic channel across
the membrane that is selective for a
particular solute.
• Some transport proteins (right) hydrolyze
ATP as an energy source to actively pump
substances across the membrane.
Enzymes
• A membrane protein may be an enzyme
with its active site exposed to substances
in the adjacent solution.
• A team of several enzymes in a membrane
may catalyze sequential steps of a
metabolic pathway as indicated (left to
right) here.
ATP
Signal
Receptors for signal transduction
Intercellular joining
• A membrane protein exposed to the
outside of the cell may have a binding site
that fits the shape of a specific chemical
messenger, such as a hormone.
• When bound, the chemical messenger
may cause a change in shape in the
protein that initiates a chain of chemical
reactions in the cell.
• Membrane proteins of adjacent cells may
be hooked together in various kinds of
intercellular junctions.
• Some membrane proteins (cell adhesion
molecules or CAMs) of this group provide
temporary binding sites that guide cell
migration and other cell-to-cell
interactions.
Receptor
CAMs
Cell-cell recognition
Attachment to the cytoskeleton
and extracellular matrix
• Some glycoproteins (proteins bonded to
short chains of sugars which help to make
up the glycocalyx) serve as identification
tags that are specifically recognized by
other cells.
• Elements of the cytoskeleton (cell’s internal
supports) and the extracellular matrix
(fibers and other substances outside the
cell) may anchor to membrane proteins,
which helps maintain cell shape and fix the
location of certain membrane proteins.
• Others play a role in cell movement or bind
adjacent cells together.
Glycoprotein
© 2016 Pearson Education, Inc.
Figure 3.4a Membrane proteins perform many tasks.
Transport
• A protein (left) that spans the membrane
may provide a hydrophilic channel across
the membrane that is selective for a
particular solute.
• Some transport proteins (right) hydrolyze
ATP as an energy source to actively pump
substances across the membrane.
ATP
© 2016 Pearson Education, Inc.
Figure 3.4b Membrane proteins perform many tasks.
Signal
Receptors for signal transduction
• A membrane protein exposed to the
outside of the cell may have a binding site
that fits the shape of a specific chemical
messenger, such as a hormone.
• When bound, the chemical messenger
may cause a change in shape in the
protein that initiates a chain of chemical
reactions in the cell.
Receptor
© 2016 Pearson Education, Inc.
Figure 3.4c Membrane proteins perform many tasks.
Attachment to the cytoskeleton
and extracellular matrix
• Elements of the cytoskeleton (cell’s internal
supports) and the extracellular matrix
(fibers and other substances outside the
cell) may anchor to membrane proteins,
which helps maintain cell shape and fix the
location of certain membrane proteins.
• Others play a role in cell movement or bind
adjacent cells together.
© 2016 Pearson Education, Inc.
Figure 3.4d Membrane proteins perform many tasks.
Enzymatic activity
Enzymes
© 2016 Pearson Education, Inc.
• A membrane protein may be an enzyme
with its active site exposed to substances
in the adjacent solution.
• A team of several enzymes in a membrane
may catalyze sequential steps of a
metabolic pathway as indicated (left to
right) here.
Figure 3.4e Membrane proteins perform many tasks.
Intercellular joining
• Membrane proteins of adjacent cells may
be hooked together in various kinds of
intercellular junctions.
• Some membrane proteins (cell adhesion
molecules or CAMs) of this group provide
temporary binding sites that guide cell
migration and other cell-to-cell
interactions.
CAMs
© 2016 Pearson Education, Inc.
Figure 3.4f Membrane proteins perform many tasks.
Cell-cell recognition
• Some glycoproteins (proteins bonded to
short chains of sugars which help to make
up the glycocalyx) serve as identification
tags that are specifically recognized by
other cells.
Glycoprotein
© 2016 Pearson Education, Inc.
Glycocalyx
• Consists of sugars (carbohydrates) sticking out
of cell surface
– Some sugars are attached to lipids (glycolipids)
and some to proteins (glycoproteins)
• Every cell type has different patterns of this
“sugar coating”
– Functions as specific biological markers for cellto-cell recognition
– Allows immune system to recognize “self” vs.
“nonself”
© 2016 Pearson Education, Inc.
Clinical – Homeostatic Imbalance 3.1
• Glycocalyx of some cancer cells can change so
rapidly that the immune system cannot recognize
the cell as being damaged.
• Mutated cell is not destroyed by immune system so
it is able to replicate
© 2016 Pearson Education, Inc.
Cell Junctions
• Some cells are “free” (not bound to any other
cells)
– Examples: blood cells, sperm cells
• Most cells are bound together to form tissues
and organs
• Three ways cells can be bound to each other
– Tight junctions
– Desmosomes
– Gap junctions
© 2016 Pearson Education, Inc.
Cell Junctions (cont.)
• Tight junctions
– Integral proteins on adjacent cells fuse to form
an impermeable junction that encircles whole
cell
– Prevent fluids and most molecules from moving
in between cells
– Where might these be useful in body?
© 2016 Pearson Education, Inc.
Figure 3.5a Cell junctions.
Plasma membranes
of adjacent cells
Microvilli
Intercellular
space
Basement membrane
Interlocking
junctional
proteins
Intercellular
space
Tight junctions: Impermeable
junctions that form continuous
seals around the cells prevent
molecules from passing through
the intercellular space.
© 2016 Pearson Education, Inc.
Cell Junctions (cont.)
• Desmosomes
– Rivet-like cell junction formed when linker
proteins (cadherins) of neighboring cells interlock
like the teeth of a zipper
– Linker protein is anchored to its cell through
thickened “button-like” areas on inside of plasma
membrane called plaques
– Keratin filaments connect plaques intercellularly
for added anchoring strength
– Desmosomes allow “give” between cells,
reducing the possibility of tearing under tension
– Where might these be useful in body?
© 2016 Pearson Education, Inc.
Figure 3.5b Cell junctions.
Plasma membranes
of adjacent cells
Microvilli
Intercellular
space
Basement membrane
Intercellular space
Plaque
Intermediate
filament (keratin)
Linker
proteins
(cadherins)
Desmosomes: Anchoring junctions
that bind adjacent cells together act
like molecular “Velcro” and also help
form an internal tension-reducing
network of fibers.
© 2016 Pearson Education, Inc.
Cell Junctions (cont.)
• Gap junctions
– Transmembrane proteins (connexons) form
tunnels that allow small molecules to pass from
cell to cell
– Used to spread ions, simple sugars, or other
small molecules between cells
– Allows electrical signals to be passed quickly
from one cell to next cell
• Used in cardiac and smooth muscle cells
© 2016 Pearson Education, Inc.
Figure 3.5c Cell junctions.
Plasma membranes
of adjacent cells
Microvilli
Intercellular
space
Basement membrane
Intercellular
space
Channel
between cells
(formed by
connexons)
Gap junctions: Communicating
junctions that allow ions and small
molecules to pass are particularly
important for communication in
heart cells and embryonic cells.
© 2016 Pearson Education, Inc.
How do substances move across the plasma
membrane?
• Plasma membranes are selectively permeable
– Some molecules pass through easily; some do
not
• Two ways substances cross membrane
– Passive processes: no energy required
– Active processes: energy (ATP) required
© 2016 Pearson Education, Inc.
3.3 Passive Membrane Transport
• Passive transport requires no energy
• Two types of passive transport
– Diffusion
• Simple diffusion
• Carrier- and channel-mediated facilitated diffusion
• Osmosis
– Filtration
• Type of transport that usually occurs across capillary
walls
© 2016 Pearson Education, Inc.
Diffusion
• Collisions between molecules in areas of high
concentration cause them to be scattered into
areas with less concentration
– Difference is called concentration gradient
– Diffusion is movement of molecules down their
concentration gradients (from high to low)
• Energy is not required
• Speed of diffusion is influenced by size of
molecule and temperature
© 2016 Pearson Education, Inc.
Figure 3.6 Diffusion.
Dye pellet
© 2016 Pearson Education, Inc.
Diffusion occurring
Dye evenly distributed
Diffusion (cont.)
• Molecules have natural drive to diffuse down
concentration gradients that exist between
extracellular and intracellular areas
• Plasma membranes stop diffusion and create
concentration gradients by acting as selectively
permeable barriers
© 2016 Pearson Education, Inc.
Clinical – Homeostatic Imbalance 3.2
• If plasma membrane is severely damaged,
substances diffuse freely into and out of cell,
compromising concentration gradients
• Example: burn patients lose precious fluids,
proteins, and ions that weep from damaged
cells
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Nonpolar, hydrophobic lipid core of plasma
membrane blocks diffusion of most molecules
• Molecules that are able to passively diffuse
through membrane include:
– Lipid-soluble and nonpolar substances
– Very small molecules that can pass through
membrane or membrane channels
– Larger molecules assisted by carrier molecules
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Simple diffusion
– Nonpolar lipid-soluble (hydrophobic) substances
diffuse directly through phospholipid bilayer
– Examples: oxygen, carbon dioxide, fat-soluble
vitamins
© 2016 Pearson Education, Inc.
Figure 3.7a Diffusion through the plasma membrane.
Extracellular fluid
Lipidsoluble
solutes
Cytoplasm
Simple diffusion
of fat-soluble
molecules directly
through the
phospholipid bilayer
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Facilitated diffusion
– Certain hydrophobic molecules (e.g., glucose,
amino acids, and ions) are transported passively
down their concentration gradient by:
• Carrier-mediated facilitated diffusion
– Substances bind to protein carriers
• Channel-mediated facilitated diffusion
– Substances move through water-filled channels
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Carrier-mediated facilitated diffusion
– Carriers are transmembrane integral proteins
– Carriers transport specific polar molecules, such
as sugars and amino acids, that are too large for
membrane channels
• Example of specificity: glucose carriers will carry only
glucose molecules, nothing else
– Binding of molecule causes carrier to change
shape, moving molecule in process
– Binding is limited by number of carriers present
• Carriers are saturated when all are bound to
molecules and are busy transporting
© 2016 Pearson Education, Inc.
Figure 3.7b Diffusion through the plasma membrane.
Lipid-insoluble solutes
(such as sugars or
amino acids)
Shape
change
releases
solutes
Carrier-mediated facilitated
diffusion via protein carrier
specific for one chemical; binding
of substrate causes transport
protein to change shape
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Channel-mediated facilitated diffusion
– Channels with aqueous-filled cores are formed by
transmembrane proteins
– Channels transport molecules such as ions or water
(osmosis) down their concentration gradient
• Specificity based on pore size and/or charge
• Water channels are called aquaporins
– Two types:
• Leakage channels
– Always open
• Gated channels
– Controlled by chemical or electrical signals
© 2016 Pearson Education, Inc.
Figure 3.7c Diffusion through the plasma membrane.
Small lipidinsoluble
solutes
Channel-mediated
facilitated diffusion
through a channel
protein; mostly ions
selected on basis of
size and charge
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Osmosis
– Movement of solvent, such as water, across a
selectively permeable membrane
– Water diffuses through plasma membranes
• Through lipid bilayer (even though water is polar, it is
so small that some molecules can sneak past
nonpolar phospholipid tails)
• Through specific water channels called aquaporins
(AQPs)
– Flow occurs when water (or other solvent)
concentration is different on the two sides of a
membrane
© 2016 Pearson Education, Inc.
Figure 3.7d Diffusion through the plasma membrane.
Water
molecules
Lipid
bilayer
Aquaporin
Osmosis, diffusion of
a solvent such as water
through a specific
channel protein
(aquaporin) or through
the lipid bilayer
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Osmolarity: measure of total concentration of
solute particles
• Water concentration varies with number of
solute particles because solute particles
displace water molecules
– When solute concentration goes up, water
concentration goes down, and vice versa
• Water moves by osmosis from areas of low
solute (high water) concentration to high areas
of solute (low water) concentration
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• When solutions of different osmolarity are
separated by a membrane permeable to all
molecules, both solutes and water cross
membrane until equilibrium is reached
– Equilibrium: Same concentration of solutes and
water molecules on both sides, with equal
volume on both sides
© 2016 Pearson Education, Inc.
Figure 3.8a Influence of membrane permeability on diffusion and osmosis.
Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients in
opposite directions. Fluid volume remains the same in both compartments.
Left
compartment:
Right
compartment:
Solution with
lower osmolarity
Solution with
greater osmolarity
H2O
Solute
Freely
permeable
membrane
© 2016 Pearson Education, Inc.
Solute
molecules
(sugar)
Both solutions have the
same osmolarity: volume
unchanged
Diffusion (cont.)
• When solutions of different osmolarity are
separated by a membrane that is permeable
only to water, not solutes, osmosis will occur
until equilibrium is reached
– Same concentration of solutes and water
molecules on both sides, with unequal volumes
on both sides
© 2016 Pearson Education, Inc.
Figure 3.8b Influence of membrane permeability on diffusion and osmosis.
Membrane permeable to water, impermeable to solutes
Solute molecules are prevented from moving but water moves by osmosis.
Volume increases in the compartment with the higher osmolarity.
Left
compartment
Right
compartment
H2O
Selectively
permeable
membrane
© 2016 Pearson Education, Inc.
Solute
molecules
(sugar)
Both solutions have identical
osmolarity, but volume of the
solution on the right is greater
because only water is
free to move
Diffusion (cont.)
• Movement of water causes pressures:
– Hydrostatic pressure: pressure of water inside
cell pushing on membrane
– Osmotic pressure: tendency of water to move
into cell by osmosis
• The more solutes inside a cell, the higher the osmotic
pressure
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• A living cell has limits to how much water can enter
it
• Water can also leave a cell, causing cell to shrink
• Change in cell volume can disrupt cell function,
especially in neurons
© 2016 Pearson Education, Inc.
Diffusion (cont.)
• Tonicity
– Ability of a solution to change the shape or tone
of cells by altering the cells’ internal water
volume
• Isotonic solution has same osmolarity as inside the
cell, so volume remains unchanged
• Hypertonic solution has higher osmolarity than
inside cell, so water flows out of cell, resulting in cell
shrinking
– Shrinking is referred to as crenation
• Hypotonic solution has lower osmolarity than inside
cell, so water flows into cell, resulting in cell swelling
– Can lead to cell bursting, referred to as lysing
© 2016 Pearson Education, Inc.
Figure 3.9 The effect of solutions of varying tonicities on living red blood cells.
Isotonic solutions
Cells retain their normal size and
shape in isotonic solutions (same
solute/water concentration as
inside cells; water moves in
and out).
© 2016 Pearson Education, Inc.
Hypertonic solutions
Cells lose water by osmosis and
shrink in a hypertonic solution
(contains a higher concentration
of nonpenetrating solutes than
are present inside the cells).
Hypotonic solutions
Cells take on water by osmosis
until they become bloated and
burst (lyse) in a hypotonic
solution (contains a lower
concentration of nonpenetrating
solutes than are present
inside cells).
Clinical – Homeostatic Imbalance 3.3
• Intravenous solutions of different tonicities can
be given to patients suffering different ailments
– Isotonic solutions are most commonly given
when blood volume needs to be increased
quickly
– Hypertonic solutions are given to edematous
(swollen) patients to pull water back into blood
– Hypotonic solutions should not be given because
they can result in dangerous lysing of red and
white blood cells
© 2016 Pearson Education, Inc.