Download Cytoskeleton Provide shape and support for the cell Other functions

Chapter 4:
Cell Structure and Function
Cytoskeleton
• The cytoskeleton is a network
of fibers that organizes
structures and activities in the
cell.
Microtubules (the largest)
Intermediate fibers
Microfilaments (the smallest)
Think tube vs filaments – tubes are
always larger
Provide shape and support for the cell
Other functions of the cytoskeleton
MTs
MFs
IFs
• Provide movement
if the organism has flagellum or
cilia
• Intracellular movement
Transports organelles, proteins
and other cell components along
microtubule “rails”.
Nucleus
• Only present in eukaryotic cells
• Location of the organism’s
genome
DNA
• Nuclear envelope
Nucleolus
• Darkly stained regions within
the nucleus
• Ribosome assembly takes
place in this organelle.
Membrane that surrounds the
nucleus
Semipermeable
does not allow DNA out, but
messenger RNA does leave the
nucleus.
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Ribosomes
Endoplasmic reticulum (ER)
• Rough endoplasmic
reticulum
• Ribosomes
Protein factories
Place where most
ribosomes attach
Synthesizes most proteins.
Protein synthesis &
transportation
• Two types
Free ribosomes
Found in all cells
Ribosomes attached to the
endoplasmic reticulum (ER)
• Smooth endoplasmic reticulum
Lipid production, including
steroids.
In liver cells, it detoxify drugs and
alcohol
Also in liver cells, it breaks down
Golgi apparatus
• The warehouse of the cell
Stores, sorts, and transports
proteins and other molecules
within the cell
Directs transportation of
proteins and other molecules
to the outside of the cell.
Also synthesizes cellulose
and pectin (plants)
Vacuoles
Lysosomes
• Made by the golgi
apparatus
• Highly acidic
environments
Due to digestive enzymes.
• Digest waste particles &
malfunctioning
organelles.
Vacuoles
• Food vacuoles
Transport food from cell
membrane to other parts of
the cell.
This process is known as
phagocytosis.
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Contractile vacuoles
Central vacuoles
• Freshwater protists need these vacuoles to pump excess
water out of the cell.
Otherwise the cell continues to expand until it explodes.
• Found in plant cells
• Storage organelle
Water
May store proteins and
carbohydrates
Provides turgor, giving
plants strength
Wilted plants have little
turgor due to lack of water
Paramecium
Plant turgor
Mitochondria & chloroplasts
• Mitochondria are the
batteries of the cell.
Produces a lot of ATP, the
energy currency of most
metabolic functions.
• Chloroplasts
Found only in plants and
some protists
Plant needs water to fill
central vacuoles.
Normal plant
Chapter 5:
Membrane Structure and Function
Site of photosynthesis.
Plasma Membrane: Thin barrier separating inside of cell
(cytoplasm) from outside environment
Function:
1) Isolate cell’s contents from outside environment
2) Regulate exchange of substances between inside and
outside of cell
3) Communicate with other cells
Note: Membranes also exist within cells forming various
compartments where different biochemical processes occur
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The Fluid Mosaic Model of Cellular Membranes:
Phospholipid Bilayer: Double layer of phospholipids
• Hydrophilic ends form outer border
• Hydrophobic tails form inner layer
• Lipid tails of phospholipids
are unsaturated (C = C)
Cell Membrane Proteins:
1) Transport Proteins:
• Regulate movement of hydrophilic molecules through
membrane
A) Channel Proteins (form pores; e.g., Na+ channels)
B) Carrier Proteins (binding sites; e.g., glucose transporter)
2) Receptor Proteins:
• Trigger cell activity when molecule from outside
environment binds to protein
How are Substances Transported Across Membranes?
Answer: Concentration Gradients
Concentration = Number of molecules in a given unit of
volume (e.g., grams / liter; moles / liter)
Gradient = Difference between two regions of space
such that molecules move from one region to
the other
3) Recognition Proteins:
• Allow cells to recognize / attach to one another
• Glycoproteins: Proteins with attached carbohydrate
groups
Diffusion: Movement of molecules from an area of high
concentration to an area of low concentration
Types of Movement Across Membranes (Table 4.1):
1) Passive Transport
• Requires no energy
• Substances move down concentration gradients
A) Simple Diffusion
• Small molecules pass directly through the phospholipid
bilayer (e.g., CO2, H2O, O2)
• Greater the concentration gradient, the faster diffusion occurs
• Diffusion will continue until gradient eliminated (dynamic equilibrium)
• Diffusion cannot move molecules rapidly over long distances
Rate depends on:
1) Molecule size
2) Concentration gradient
3) Lipid solubility
(Figure 4.3a)
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Channel and Carrier proteins
Types of Movement Across Membranes:
1) Passive Transport
• Requires no energy
• Substances move down concentration gradients
B) Facilitated Diffusion
• Molecules need assistance of channel proteins or
carrier proteins (e.g. ions, amino acids, sugars)
Channel Proteins
(Figure 4.3b)
Carrier Proteins
(Figure 4.3c)
Types of Movement Across Membranes:
1) Passive Transport
A) Simple Diffusion
• Requires no energy
B) Facilitated Diffusion
• Substances move down concentration gradients
C) Osmosis
Osmosis:
• Movement of water from an area of high [water] to area
of low [water] across semi-permeable membrane
water
water
In which direction will there be a net osmotic
movement of water?
out of the cell
into the cell
neither
0.05 M glucose
In which direction will there be a net osmotic
movement of water?
out of the cell
into the cell
neither
Permeable
only to
water
0.02 M glucose
0.01 M sucrose
0.05 M glucose
Permeable
only to
water
0.02 M glucose
0.03 M sucrose
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Osmosis and Living Cells:
Osmosis and Living Cells:
Isotonic Solution:
Isotonic Solution:
• Outside of cell has same [solute]
as inside of cell
• Outside of cell has same [solute]
as inside of cell
Hypertonic Solution:
Iso = same.
• Outside of cell has higher [solute]
than inside of cell
Isotonic = Same solute concentration
inside and outside of the cell.
• Hyper = higher
(net water movement
out of cell)
(no net water movement)
Osmosis and Living Cells:
Water balance in cells without walls
Isotonic Solution:
Solution is:
• Outside of cell has same [solute]
as inside of cell
hypotonic
isotonic
hypertonic
Hypertonic Solution:
• Outside of cell has higher [solute]
than inside of cell
Hypotonic Solution:
• Inside of cell has higher [solute]
than outside of cell
lyse
Hypo = lower
normal
shrivel
Tonicity is relative
to the inside of the cell
(net water movement into cell)
Water balance in cells with walls
hypotonic
isotonic
hypertonic
turgid
flaccid
shriveled
Types of Movement Across Membranes:
1) Passive Transport
2) Active Transport (aka pumps)
• Requires energy (ATP)
• Substances move against concentration gradients
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(Figure 4.7)
Types of Movement Across Membranes:
1) Passive Transport
Types of Movement Across Membranes:
1) Passive Transport
2) Active Transport
3) Endocytosis
2) Active Transport
3) Endocytosis
4) Exocytosis
• Movement of large particles into cells (vesicle formation)
1) Pinocytosis (“cell drinking”)
• Movement of large particles out of cells (e.g., hormones)
• Uptake of fluid droplets
2) Receptor-mediated Endocytosis
• Uptake of specific molecules via coated pits
3) Phagocytosis (“cell eating”)
• Uptake of large particles (e.g. bacteria)
(Figure 4.9)
Exocytosis
How are Cell Surfaces Specialized?
Answer: Junctions allow cells to connect and communicate
1) Connection Junctions:
A) Desmosomes: Hold cells together via protein filaments
(Figure 4.10a)
How are Cell Surfaces Specialized?
How are Cell Surfaces Specialized?
Answer: Junctions allow cells to connect and communicate
Answer: Junctions allow cells to connect and communicate
1) Connection Junctions:
B) Tight Junctions: Protein “seals” prevent leakage (cell →cell)
(Figure 4.10b)
2) Communication Junctions:
A) Gap Junctions: Protein channels allowing for signals to
pass between cells (animals)
(Figure 4.11a)
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How are Cell Surfaces Specialized?
Answer: Junctions allow cells to connect and communicate
2) Communication Junctions:
A) Plasmodesmata: Cytoplasmic bridges allowing for
signals to pass between cells (plants)
How are Cell Surfaces Specialized?
Answer: Cell walls offer support and protection
Cell Walls:
• Found in bacteria, plants, fungi, & some protists
• Composed of carbohydrates (e.g. cellulose, chitin),
proteins, or inorganic molecules (e.g. silica)
• Produced by the cell it protects/supports
(Figure 4.11b)
Exam on Thursday!
• Bring scantrons and 2 pencils in case one breaks
• Covers Chapters 1 – 5.
• Will be multiple choice, short answer, and 1 or 2
essay questions.
• Study Chapter 3 particularly carefully, it’s the
biggest chapter!
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