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Cells
Chapters 7, 8, 11, and 12
A Tour of the Cell
Chapter 7
Cell Theory
1. All organisms are made up of cells.
2. New cells come only from old cells.
3. The cell is the basic unit of life.
Prokaryotic vs.
Eukaryotic Cells
• What is the major difference between the
two?
• Prokaryotes – “Before Nucleus”
• Contain no membrane bound organelles
• Limited to Nucleoid region, Ribosomes,
Plasma membrane, and cell wall
• Eukaryotes – “True Nucleus”
• Contains membrane bound organelles
Cellular Questions to
Ponder?
• Why are most cells microscopic?
• Do larger organisms have larger cells than
smaller ones?
• Cells need a large surface area to volume
ratio (in the ballpark of 6:1).
• Allows for cell to aquire more nutrients and
expel more waste
• Why do cells have folded membranes?
• Folded membranes allows for even more
surface area.
Internal Membranes
• Internal membranes compartmentalize the
functions of a eukaryotic cell:
• Partition cell into compartments
• Enzymes built into membranes because
compartments can provide separate
environments
Organelles
What do you know about the
organelles below?
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Nucleus
Endoplasmic Reticulum
Golgi Body (apparatus or complex)
Lysosomes
Mitochondria
Chloroplasts
Microtubules, Intermediate filaments, and microfilaments
Flagella and cilia
Centrioles
Cell Walls
Vacuoles
Peroxisomes
Nucleus contains
Genetic Library
• Contains DNA in form of chromosomes
• Surrounded by nuclear envelope
• Contains Nucleolus – portion of DNA that
manufactures components of ribosomes
which are then shipped to cytoplasm to
assemble amino acids
• Ribosomes – build a cell’s proteins
Endoplasmic Reticulum
(ER)
• Involved in production of various materials
• Rough ER – ribosomes attached;
involved in protein synthesis
• Smooth ER – no ribosomes; synthesis of
lipids and hormones
Golgi Apparatus
• Finishes, sorts and ships cell products
• Specifically… modify and package
proteins and lipids into vesicles
• Vesicles often move to and merge with
plasma membrane and release their
contents outside the cell
Lysosomes
• Digestive Compartments
• Contain digestive enzymes
• Phagocytosis – “eat vessel”
– A formed food vacuole fuses with lysosome
• Types of Vacuoles:
– Food Vacuoles
– Contractile Vacuoles: pump excess water out of
cell
– Central Vacuole: In plants; place to store organic
compounds and as disposal sites for metabolic
“wastes” – Provides “turgor pressure” keeping
plant cell rigidity so it doesn’t wilt
Mitochondria
• Aerobic Respiration (Creating ATP)
Chloroplasts
• Carry out photosynthesis
• Microtubules – provides support and
motility for cellular activities (part of
spindle fibers)
• Intermediate filaments: provides support
for maintaining shape of cell
• Microfilaments: involved in cell motility
(found in muscle cells and cels that move
by changing shape)
Flagella and Cilia
• Classified by their length and number per
cell…
• Flagella – long and few
• Cilia – short and many
• Both consist of microtubules arranged in a
“9+2” array – 9 pairs (doublets) of
microtubules arranged in a circle
surrounding a pair of microtubules
Cell Walls
• Found in plants, fungi, protists, and
bacteria
• Provide support for the cell
• Consists mostly of cellulose (in plants),
Chitin (in Fungi)
Peroxisomes
• Break down substnaces
• O2 combines with Hydrogen to form toxic
hydrogen peroxide (H2O2)
• Common in liver where they break down
toxic substances
Intercellular junctions
in animals
• Desmosome – Anchoring Junction
• Tight Junction – form a seal that
prevents leakage of extracellular fluid
across a layer of cells (i.e. keep the
contents of the intestine separate from the
body fluid on the oposite side)
• Gap Junction – Communicating junction
See image on page 126
Key differences between
plant and animal cells:
1.
2.
3.
4.
Plants have cell walls
Plants have chloroplasts
Plants have large central vacuoles
Animal cells have centrioles (microtubule
organizing centers)
Membrane Structure
and Function
Chapter 8
Evolution of Membrane
Models
• Original Davson-Danielli model – Globular
Protein sandwich a phospholipid bilayer
(proposed in 1935 and accepted until
1970)
• Currently explained by the fluid mosiac
model
Fluid Mosaic Model
• It is has mosaic nature of scattered
proteins within a flexible matrix of
phospholipid molecules.
Plasma Membrane
• Composed of a Phospholipid
Bilayer
• Selective Boundary between the cell
and its environment (Selectively
Permeable)
• Regulates functions of the cell
• Maintains Homeostasis
• Described by Fluid Mosaic model
What makes up the
Plasma Membrane?
• Phospholipid Bilayer – hydrophillic heads facing
out; hydrophobic tails facing in.
• Proteins – Some as channels to regulate passage
of molecules and others as enzymes.
• Cholesterol Molecules – reduce membrane
fluidity by reducing phospholipid movement at high
temps and hinders solidification at low temps.
• Membrane’s unique composition is suited to specific
functions (Mitochondria membranes are embedded with
enzymes that function in cellular respiration)
• Carbohydrates – Glycoprotein (protein w/ carb
attached) and Glycolipids designate if cell belongs
or not… these are called Oligosaccharides.
The fluidity of
Membranes:
• Phospholipids can move laterally
(frequent) or by the flip-flop (rare)
• Fluid contains unsaturated “tails” with
kinks while viscous contains saturated
“tails”
Important Components of
Plasma Membrane
(Important essay concept to
address chemistry, structure, and
components below)
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Transport Proteins
Enzymatic Proteins
Signal Proteins
Intercellular Joining Proteins
Cell-cell Recognition Proteins
Traffic Across Membranes
• Substances move in two ways:
• Bulk flow: overall movement of a group of
substances
Countercurrent Exchange – movement of
substnaces between two regions in which bulk flow
movement is in opposite directions. (i.e. blood in
fish gills moves opposite direction of surrounding
water running past them)
• Constant, Random Motion: motion of the molecules
independent from the motion of other molecules
Passive Transport
• Diffusion – movement of molecules from
High to low concentration
• Diffusion across a biological membrane is
called passive transport.
• Why is it considered passive?
• Cell doesn’t need energy to make it
happen
• When will this process stop?
• When Dynamic Equilibrium is reached
(Homeostasis)
Osmosis
• Osmosis is the passive transport of water
across a selectively permeable membrane.
• Osmotic conditions have 3 options:
Isotonic, Hypotonic, or Hypertonic
How many of you have every killed a plant? How?
Over watering or Under watering?
• Isotonic – same concentration of solutes
inside as outside cell, not net change
• Hypotonic – low solutes/ high H2O outside
cell; H2O moves in -- What does this do to
plant and animal cells?
• Animal cells burst; Plant cells swell
• Hypertonic – high solutes/ low H2O outside
cell; H2O moves out – What does this do to
plant and animal cells?
• Animal cell shrinks; Plant cell contents
shrink (loss of turgor pressure)
`
Osmosis
State
Isotonic
H2O
Solute [ ]
Movement Inside cell
Solute [ ]
Outside
Cell
none
[Same]
[Same]
Hypotonic
Into
the cell
[High]
[Low]
Hypertonic
Out of
the cell
[Low]
[High]
Osmosis Questions
• Which situation is best for animal cells?
Why?
• Which Situation is best for plant cells?
Why?
Passive Transport
• No energy is required to move particles
through the cell’s plasma membrane
• [high] to [low]
• Facilitated Diffusion
– Protein required to move particles
through membrane
– Move down concentration gradient by
random movement
– Channel proteins vs. carrier proteins
– How glucose enters the cell
Other passive
transports:
• Dialysis is the diffusion of solutes across
a selectively permeable membrane.
• Plasmolysis is the movement of water
out of a cell (osmosis) that results in the
collapse of the cell
• Facilitated diffusion – the movement of
solutes through channel proteins
Active Transport
• Movement of solutes against a gradient.
• [Low] to [High]
• Aided by transport proteins (pumps) –
each one is specific to a certain substance
• Requires the use of energy (typically ATP)
• 67% of energy used to transport Na+ and
K+ across membranes.
• See diagram of sodium-potassium pump
(Figure 8.14)
EXOCYTOSIS
• Process of removing large particles or
volumes of liquid
• Excretion – removal of waste products
• Secretion – removal of cell products
needed elsewhere
• Requires vesicle and energy
ENDOCYTOSIS
• Process in which the plasma membrane
engulfs substances from the environment
• Pinocytosis – “cell drinking” large drops
of liquid.
• Phagocytosis – “cell eating” large
particles are engulfed into a vesicle for
digestion
• This is how single celled protists capture
food and how white bloods cells work for
immunity
• Receptor-mediated endocytosis –
specific molecules in the fluid surrounding
the cell bond to specialized receptors in
the plasma membrane. This then triggers
a phagocytosis type process
Questions to look at on AP
regarding Membrane Traffic:
• Is the substance moving across a selectively
permeable membrane?
• Is the substance of interest water (solvent) or
substance (solute)?
• In which direction is the substance moving?
Down a gradient or the reverse?
• How does the concentration of solutes vary
from one region to another?
• Is energy required to move the substance?
Energy is required to go against the gradient
Cell Communication
Chapter 11
Paracrine Signaling
• Acts on nearby “target” cells
• Signal cell discharges molecules into
extracellular fluid
• Local signaling
Synaptic Signaling
• Nerve cell communication
• Neurotransmitters released into a synapse
• Local signaling
Hormonal Signaling
• Signals target cells at greater distances.
• Specialized cells secrete hormones into
bodily fluid (typically blood).
• Can reach all body cells
• Only specific “target” cells act and
respond.
• Plants also use to signal from one part of
plant to another
Three stages of cell
signaling…
1. Reception – target cell detects an incoming signal
from outside cell
2. Transduction:
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Changes protein in some way
Converts change to form that can bring specific cellular
response.
Often requires sequence of changes in a series of
different molecules (signal transduction pathway)
3. Response – signal finally triggers cell response
(i.e. catalysis by enzyme, rearrangement of
cytoskeleton, activation of specific genes…)
• Process ensures the crucial activities occur in
the right cells, at the right time, and in proper
coordination with other cells
Examples Pathways
• G-protein-linked receptor (11.6 and 11.7)
• Tyrosine-kinase receptor (11.8)
• Ligand-gated ion-channel receptor (11.9)
Signal Transduction
Pathways
• Relay signals from receptors to cellular
responses
• Protein phosphorylation is a major
mechanism of signal transduction (11.10)
• Small molecules and ions are key
components of signaling pathways (2nd
messengers)
– cAMP (11.12)
– IP3 (11.14)
Cellular-Responses to
Signals
• In response to signal, a cell may regulate
activities in the cytoplasm or transcription
in the nucleus.
• Elaborate pathways amplify and specify
the cell’s response to signals
• Nuclear Response (Figure 11.16)
• Specificity of cell signaling (Figure 11.17)
The Cell Cycle
Chapter 12
Key Roles of Cell
Division:
• Functions in reproduction, growth, and
repair
How do daughter cells compare to original
cell?
• Division distributes identical sets of
chromosomes to daughter cells
• Somatic Cells – All body cells except
reproductive cells.
• Gametes – sperm and eggs
Important Terms:
• Chromatin:
DNA protein fiber organized into long thin
fibers
• Sister Chromatids:
Two chromatids containing identical sets of
DNA that are initially attached.
• Centromere:
Location of sister chromatid attachment.
The Cell Cycle
• Occurs in Eukaryotic Cells
• Regular pattern of:
– Growth
– DNA duplication
– cell division
• 4 Stages in the cell cycle:
Gap 1 (G1), Synthesis, Gap 2 (G2), Mitosis
• Enzymes control the transfer through the
stages
Gap 1 (G1)
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First Stage (Growth)
Cell carries out normal functions
Cell increases in size
Organelles increase in number
Synthesis
• Second Stage
• Growth and Duplication of DNA
Gap 2 (G2)
• Third Stage
• Similar to G1 phase
• Growth and preparation for cell
division.
• Includes a critical checkpoint … the
cell will only reproduce if everything
is in order.
Mitotic Cycle (Mitosis)
Interphase precedes Mitosis and includes
G1,S, and G2
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Prophase
1. Nucleoli
disappears and
chromatin
becomes visible
chromosomes.
2. Nuclear envelope
breaks down.
3. Mitotic spindle is
assembled
• Spindle attached
to Kinetochore
Metaphase
1. Chromosomes
move to the
equator
2. Each sister
chromatid is
attached to its own
spindle fiber
3. Spindle fibers are
attached to
centromere at
kinetochore
Anaphase
1. Centromeres are
split
2. Sister Chromatids
are pulled apart
becoming
chromosomes
Telophase and
Cytokinesis
1. Chromosomes reach
opposite poles of the
cell
2. Two distinct daughter
cells are formed
3. Processes of
prophase are reversed
 Cleavage Furrow –
groove the forms as
“purse strings”
tightened
 Cytokinesis = division
of the cytoplasm
Mitosis of a White Fish
Blastula Cell
Regulation of the Cell
Cycle
Cell-Cycle Control System:
• Cyclically operating set of molecules in the
cell the both triggers and coordinates key
events in the cell cycle.
Cell-cycle Checkpoints:
• Stop and go-ahead signals regulate the cycle.
• Enzymes drive this process
Cues to regulate Cell
Cycle
Internal Signals:
• M-phase checkpoint is the gatekeeper
• Signal that delays anaphase originates at
the kinetochores that are not yet attached
to spindle microtubules
• External Signals:
• Growth factors are required to stimulate
growth
• Density-dependent inhibition – crowded
cells stop dividing (12.15)
• Anchorage dependence – to divide,
animal cells must be attached to
substratum.
Cancer…
• Early in life, cells divide frequently
while later in life, cells only grow and
divide to replace old cells or repair
injuries.
• Cells continue to be regulated by cell
cycle and regulation cues
• Cancer cells have escaped cell
cycle controls
Key cancer terms
• Metastasis – spread of cancer cells
beyond their original state.
• Tumor – mass of abnormal cells within
otherwise normal tissue
• Benign tumor – most likely wont cause a
serious problem.
• Malignant tumor – invasive enough to
impair functions of one or more organs
(cancerous tumor)