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Cellular Level of
Organization
Introduction
 Two types of cells
1. Sex cells (haploid)
2. Somatic cells (diploid)
Cell Membranes
 4 main functions
1. Physcial Isolation
 Separates inside of cell from outside
2. Selectively Permeable
Membrane
 Regulates exchange with the
environment
3. Sensitivity
 Contains receptors
4. Structural Support
 The cell membrane can connect to other
cells or extracellular proteins
Cell Membrane Structure
 Hydrophilic head
 Hydrophobic tails
Cell Membrane Structure
 Ions and water soluble compounds
cannot cross the membrane
Cell Membrane Structure
 This separates the extracellular fluid from
the cytosol which is important for
homeostasis
What are in membranes?
1. Cholesterol
What are in membranes?
2. Integral proteins
What are in membranes?
3. Enzymes
 Catalyzes reactions
What are in membranes?
4. Receptor proteins
 Protein – lock
 Ligand - key
What are in membranes?
5. Carrier Protein
 Transports things across the membrane
What are in membranes?
6. Channels
 Allows continuous movements of ions
and water soluble materials
What are outside cell
membranes?
1. Peripheral proteins
2. Glycoproteins
3. Glycolipids
Glycoprotiens and
glycolipids
 Can tell if certain cells are normal or
abnormal by their glycoproteins and
glycolipids
Organelles
 Components of cells
1. Cytoskeleton


1.
2.
3.
Strength and flexibility
Composed of 3 main structures
Microfilaments ( actin )
Intermediate filaments ( collagen )
Microtubules ( tubulin )
2. Microvilli
 Increase surface area
 Finger-shaped projections of cell
membranes
3. Centrioles
 Their involved in cell division
 Not found in RBC, skel. muscle cells,
cardiac muscle cells, and neuron cells
4. Cilia
 Long slim extensions of the cell
membrane
 Found in trachea
5. Ribosomes
 Synthesize proteins
 Composed of two subunits ( one small
and one large)
 Free ribosomes
 Fixed ribosomes
6. Endoplasmic Reticulum
 Network within the cytoplasm attached to
the nucleus
6. Endoplasmic Reticulum
Two types
1. SER
2. RER
6. Endoplasmic Reticulum
 SER
 Detoxifies drugs or toxins
 Synthesizes lipids and carbs
6. Endoplasmic Reticulum
 RER
 Transports materials and synthesizes
proteins
7. Golgi Apparatus
 Proteins come from the ER into the golgi
for modification
8. Lysosome
 Breaks down and recycles organelles
 Breaks down bacteria and foreign
material
9. Peroxisomes
 Breaks down fatty acids and organic
compounds
10. Mitochondria
 Powerhouse of the cell
 Produces ATP – energy
 Contains two membranes (outer and
inner)
11. Nucleus
 Chromosomes are stored here
 Composed of DNA
Membrane Transport
 Membranes are selectively permeable
Membrane Transport
 Passive processes do not require energy
Membrane Transport
 Active processes require energy
Membrane Transport

3 major ways in which materials are
transported
1. Diffusion
2. Carrier-mediated transport
3. Vesicular transport
1. Diffusion
 Hypotonic solution – less concentrated
1. Diffusion
 Hypertonic – more concentrated
1. Diffusion
 Isotonic solutions – equal concentration
1. Diffusion
 Solutes move from hypertonic solution to
hypotonic solution
Ions and Water
 Remember ions and water must pass
through channels
Lipid Soluble Substances
 Alcohol, fatty acids, and steroids are lipid
soluble
O2 and CO2
 O2 and CO2 pass easily
Glucose
 Glucose to big to cross cell membrane
2. Carrier-Mediated
Transport
 Can be passive or active
2. Carrier-Mediated
Transport
 Proteins carry substances across
2. Carrier-Mediated
Transport
 Sometimes carries two things at once
(cotransport)
2. Carrier-Mediated
Transport
 Sometimes carries to things in opposite
directions (countertrasnport)
2. Carrier-Mediated
Transport
1. Fascilitated Diffusion
2. Active Transport
3. Secondary Active Transport
Facilitated Diffusion
 Passive
Facilitated Diffusion
 Carries substances such as glucose and
amino acids
Facilitated Diffusion
 Goes down conc. Gradient but limited to
number of carrier proteins
Active Transport
 Requires energy
Active Transport
 Not dependent on concentration gradient
Active Transport
 Ion pumps use active transport
Active Transport
 Exchange pumps move two kinds of ions
in different directions
Example: Na+/K+ Pump
Na+/K+ Pump
 Na higher in concentration outside cell
 K higher in cell
Na+/K+ Pump
 Sometimes Na diffuses into cell and K
leaves through leaky channels
Na+/K+ Pump
 Na+/K+ pump puts things back into order
Na+/K+ Pump
 Ejects on average 3Na+ and bringing in
2K+ ions
Secondary Active
Transport
 Does not require energy
Secondary Active
Transport
 Goes down a conc. gradient
Secondary Active
Transport
 It uses the concentration gradient of a
molecule as the driving force to move
another molecule against the
concentration gradient
3. Vesicular Transport
 Requires energy
3. Vesicular Transport
1. Endocytosis
2. Exocytosis
Endocytosis
 Imports substances into the cell
Endocytosis
1. Receptor mediated endocytosis
2. Pinocytosis
3. Phagocytosis
Receptor Mediated
Endocytosis
 Extremely selective
Receptor Mediated
Endocytosis
 Plasma membrane proteins bind only
with certain substances
Pinocytosis
 Cell drinking
Pinocytosis
 Dissolved proteins gather on the external
surface of the plasma membrane,
causing the membrane to invaginate and
to incorporate a droplet of fluid
Phagocytosis
 Cell eating
Phagocytosis
 Parts of the plasma membrane flow
around a relatively large or solid material
and engulf it.
Exocytosis
 Expels material out of the cell