Transcript V. CELL TRANSPORT, cont

UNIT III – CELL STRUCTURE & FUNCTION
• Hillis – Ch 4, 5
• Baby Campbell – Ch 4,5
• Big Campbell – Ch 6,7,11
Over 4 centuries ago von Leeuwenhoek and Hooke
Stacked glass lenses together and took the first look
At a world far too tiny for the naked eye to see
And forever changed our understanding of Biology! 
I. DISCOVERY OF CELLS
• History of Microscopes
 Anton van Leeuwenhoek
- Used lenses and looked at pond water
- described what he saw as small organisms
 Robert Hooke
- looked at cork under a primitive microscope
- described what he saw as “cells” which reminded him of
the rooms in the monastery
• Cell Theory
 All living things are made of cells.
 Cells are the smallest working unit.
 All cells come from pre-existing cells through cell division.
I. DISCOVERY OF CELLS, cont.
• Types of Microscopes
 Compound Light Microscope
 Magnification
 Resolution
 Advances in light microscopy
include
o
o
o
o
Confocal
Fluorescent
Phase Contrast
Super-resolution
 Electron Microscope
 Scanning Electron
Microscope (SEM)
 Transmission Electron
Microscope (TEM)
I. DISCOVERY OF CELLS, cont.
• Cell Size
o Metabolic needs impose
both upper & lower limits on
cell size
o How small?
 Must have enough space for
DNA, enzymes
 Mycoplasma sp. - < 1 μm
o How large?
 Surface Area to Volume Ratio
 Adaptations
II. CELL TYPES
• Prokaryotic Cells
 Typically smaller than
euks
 Bacteria
 Kingdom Archaebacteria
 Kingdom Eubacteria
 No true nucleus – DNA
found as a single
chromosome in region
called nucleoid
II. CELL TYPES, cont
• Prokaryotic Cells
1. Cell wall
2. Capsule
3. Cell membrane
4. Chromatin
5. Ribosomes
6. Pili
7. Flagella
II. CELL TYPES, cont
• Eukaryotic Cells
 Larger, more complex
 Contain true nucleus, membranebound organelles suspended in
cytosol
 Composed of
 Nucleus
 Ribosomes
 Endomembrane System
o
o
o
o
ER
Golgi Apparatus
Lysosomes
Vacuoles
 Mitochondria/Chloroplasts
 Peroxisomes
 Cytoskeleton
III. EUKARYOTIC CELL STRUCTURES
_Animal Cell
_Plant_ Cell
III. EUKARYOTIC CELL STRUCTURES, cont
• Nucleus
 Control center of
eukaryotic cell
 Nuclear Envelope
 Double membrane that
protects nucleus;
continuous with ER
 Contains pores
 Nucleolus
 Site of ribosome
production
 Chromatin
 DNA wrapped in
protein
III. EUKARYOTIC CELL STRUCTURES, cont
•
Ribosomes
 Suspended in cytosol or found on rough ER
 Site of protein production in a cell
III. EUKARYOTIC CELL STRUCTURES, cont
• Endomembrane System
 Endoplasmic Reticulum
 Interconnected network
continuous with nuclear envelope
 Rough ER
 modifies and transports
proteins to the golgi

 Smooth ER
 detoxifies drugs, alcohol,
poisons
 converts glycogen into
glucose
 synthesizes lipids
III. EUKARYOTIC CELL STRUCTURES, cont
Endomembrane System, cont
 Golgi Apparatus
 “Cell postmaster”
 Receives transport vesicles from ER; modifies, stores, and ships
products
 Receiving side is known as the cis face; shipping side is known as the
trans face
III. EUKARYOTIC CELL STRUCTURES, cont
Endomembrane System, cont
 Lysosomes
 Sacs containing hydrolytic enzymes
 Used for recycling cellular materials, destroying
pathogens
III. EUKARYOTIC CELL STRUCTURES, cont
Endomembrane System, cont
 Vauole
 Storage sac
 Plants typically have
large, central vacuole
surrounded by
membrane called
tonoplast. Absorbs
water and helps
plant cell to grow
larger
 Some protists have
contractile vacuole
to pump out excess
water
III. EUKARYOTIC CELL STRUCTURES, cont
• Mitochondria




Site of oxidative respiration
Contain own DNA, ribosomes
Found in virtually all euk cells
Enclosed by 2 membranes; inner membrane has folds called cristae
to increase surface area
III. EUKARYOTIC CELL STRUCTURES, cont
•
Chloroplast
 Type of plastid that carries out photosynthesis by converting solar energy
to chemical energy (glucose)
 Contain membranous system of flattened sacs called thylakoids – stack is
called a granum
 Fluid surrounding thylakoids is called stroma
 Contains DNA, ribosomes
III. EUKARYOTIC CELL STRUCTURES, cont
Endosymbiont Theory
III. EUKARYOTIC CELL STRUCTURES, cont
• Peroxisomes
 Membrane-bound compartments that use O2 to carry out metabolism
 H2O2 is produced; broken down by _perioxidase_
III. EUKARYOTIC CELL STRUCTURES, cont
• Cytoskeleton
 Provides structural support to cell
 Allows for movement
 Attachment site for organelles, enzymes
 More extensive in animal cells
 Composed of three types of proteins
 Microtubules
 Microfilaments
Actin
 Intermediate Filaments
More fixed
Keratin
Cytoskeleton
III. EUKARYOTIC CELL STRUCTURES, cont
Cytoskeleton, cont
IV. CELL BOUNDARIES
• Cell Wall
 Found in bacteria, fungi, and
plants
 Rigid structure; protects,
maintains shape of cells
 Prevents excess water uptake
 Plant cell wall
 Cellulose
 Pectin - Sticky polysaccharide
found between cell walls of
adjacent cells
 Plasmodesmata - Perforations
between adjacent cell walls
that allow for movement of
materials from one cell to
another
IV. CELL BOUNDARIES, cont
• Extracellular Matrix of Animal Cells
 Holds cells together, protects & supports cells
 Allows for communication between cells
 Composed primarily of glycoproteins – proteins with covalently-bonded
carbohydrate chains attached
 Must abundant glycoprotein in most animals is collagen
IV. CELL BOUNDARIES, cont
• Intracellular Junctions
in Animal Cells
 Tight Junctions – Press
membranes together very
tightly; prevents leakage of
fluid
 Desmosomes (Anchoring
Junctions) – Fasten cells
together in sheets
 Gap Junctions – Allow for
movement of cytoplasm
from one cell to another;
important in
communication between
cells
IV. CELL BOUNDARIES, cont
• Cell (Plasma) Membrane
 Selectively-permeable barrier found in all cells
 Composed primarily of phospholipid bilayer (amphipathic)
and proteins which are also amphipathic.
 Fluid Mosaic Model
 “Fluid” – Not a rigid structure. Organization due to high
concentration of water inside & outside cell
IV. CELL BOUNDARIES, cont
• Organization of Plasma Membrane
- membrane is held together by hydrophobic interactions; polar phosphate
heads face internal and external environments; non-polar fatty acid tails face
the interior of the bilayer.
- proteins and lipids can shift laterally, but flip-flopping is rare.
IV. CELL BOUNDARIES, cont
• Fluidity of Plasma Membrane
IV. CELL BOUNDARIES, cont
• Cell Membrane, cont
 Proteins - “Mosaic” – Assortment of different proteins embedded in
bilayer; determine most of membrane’s specific functions. Act as
channels, pumps, enzymes in metabolism, binding sites, etc
o Integral Proteins – Embedded in phospholipid layer
o Peripheral Proteins – Bound to surface of membrane
IV. CELL BOUNDARIES, cont
Membrane Proteins
IV. CELL BOUNDARIES, cont
• Cell Membrane, cont
 Carbohydrates
 “ID tags” that
identify cell.
 Enable cells to
recognize each
other and foreign
cells.
 May be bonded to
lipids (glycolipids)
or proteins
(glycoproteins)
IV. CELL BOUNDARIES, cont
V. CELL TRANSPORT
V. CELL TRANSPORT, cont
• Passive Transport – Movement of materials from high to low
concentration. No energy output required.
 Diffusion
Random movement of a substance across membrane down
concentration gradient
No net movement once equilibrium is reached
Diffusion
V. CELL TRANSPORT, cont
• Passive Transport, cont
 Facilitated Diffusion
 Passive transport of molecules across cell membrane with the help of
transport proteins
 Utilized by large molecules, charged particles, polar molecules
 Water
 Aquaporins
V. CELL TRANSPORT, cont
• Passive Transport, cont
 Osmosis – Diffusion of water across a membrane. Tonicity refers to
tendency of cell to gain or lose water. If the solution is
 Isotonic relative to the cell – Solute concentration is same on both sides of
membrane. No net movement of water.
 Hypertonic relative to the cell – Concentration of solute is greater outside
cell → water moves out of cell until equilibrium is reached. Cell may shrivel.
 Hypotonic relative to the cell – Concentration of solute is lower outside cell
→ water moves into cell until equilibrium is reached. Cell may swell to
bursting point.
Osmosis
V. CELL TRANSPORT, cont
• Passive Transport / Osmosis, cont
 Water Potential
 Used to predict the passive movement of water
 Designated as Ψ (Greek letter psi)
 Water always moves from an area of higher water potential →
lower water potential
 Ψ = ΨP + ΨS
ΨS = -iCRT
i = ionization constant (if NaCl, i = 2 because Na+ and Cl-)
C = molar concentration
R = pressure constant (R = .0831 liter bars/mole –K)
T = temp K (273 + C)
- Increase in solute lowers the water potential
ΨP = 0 at atmospheric pressure; an increase in positive
pressure raises the pressure potential, which raises water
potential.
Practice
• Determine the water potential of a cell if ΨP =
0.3 MPa and ΨS = - 0.5 MPa.
Ψ = ΨP + ΨS
Ψ=
Calculate the pressure potential in a cell if
ΨW = 0 and ΨS = - 0.2.
A dialysis bag is filled with sucrose solution of unknown
concentration and then placed in a 0.6 M sucrose solution. The
bag’s initial mass is 24 grams and the final mass is 22 grams.
– What does this tell you about the molarity of the unknown
solution in the dialysis bag?
– Initially, is the unknown solution hyper, hypo, or isotonic
relative to the solution in the beaker?
– Calculate the initial water potential of the sucrose solution
in the beaker. Assume the temperature is 28 degrees
Celsius. Show your work!
Ψ = ΨP + ΨS
• Ψ = 0 + ΨS
• ΨS
• http://www.bozemanscience.com/waterpotential/
V. CELL TRANSPORT, cont
• Passive Transport/Osmosis, cont
 Osmoregulation
 Cells must have mechanism to prevent excess loss, uptake of water
 Cell wall, contractile vacuole
 Plasmolysis – Seen in plants; excessive water loss causes cell
membrane to pull away from cell wall
V. CELL TRANSPORT, cont
(crenated)
V. CELL TRANSPORT, cont
• Active Transport
• Movement of materials against concentration gradient. Requires energy
output by cell
 Carrier Proteins – Na+ / K+ Pump
V. CELL TRANSPORT, cont
• Active Transport, cont
 Proton Pump
V. CELL TRANSPORT, cont
• Active Transport,
cont
 Exocytosis
 Secretion of
biomolecules by
fusion of vesicles
with cell
membrane.
Biomolecules “spit
out”.
 Hormones,
neurotransmitters,
etc
V. CELL TRANSPORT, cont
• Active Transport, cont
 Endocytosis – “Sucking In”. Cell membrane surrounds, engulfs
particle or biomolecule, pinches in to form vesicle.
Phagocytosis – “Sucking in” food particles
Pinocytosis – “Sucking in” fluid droplets
Receptor-mediated Endocytosis – Very specific
Endocytosis
VII. CELL SIGNALING
VII. CELL SIGNALING, cont
• Coordinates cell activities, development
• Typically involves 3 steps:
 Reception – Target cell’s detection of signal molecule due to binding of
signal molecule to receptor protein in cell membrane
 Transduction – Binding of signaling molecule changes receptor protein;
triggers a sequence of events within cell
 Response – Results in specific cellular response; for example, activation of
genes, enzyme catalysis, etc.
VII. CELL SIGNALING, cont
• Reception
 Typically involves G Proteins
VII. CELL SIGNALING, cont
• Transduction
 Typically multi-step pathway
 Relay molecules are usually protein kinases
VII. CELL SIGNALING, cont
• Transduction
 Non-protein
molecule known as
cAMP is often
second messenger
VII. CELL SIGNALING, cont
• Response
 Nuclear
May “turn on” or “turn off” genes
 Cytoplasmic
May regulate enzyme activity
 Apoptosis
Controlled cell suicide
VI. CELL SIGNALING, cont
• Regulation