2. CELL MEMBRANE 2
• Composed primarily of back-to-back phospholipids. Cholesterol is
present, contribute to fluidity of the membrane, various proteins are
embedded that have a variety of functions.
• Hydrophilic molecule – attracted to water.
• Hydrophobic molecule – repelled by water.
• Amphipathic – contains both hydrophilic and hydrophobic molecules.
Example: soap works to remove oil and grease stains because it has
amphipathic properties. Hydrophilic dissolves in water and
hydrophobic traps the grease and they get washed away.
3. CELL MEMBRANE – continued 3
• Intracellular fluid – fluid interior of the cell.
• Extracellular fluid – fluid environment outside the enclosure of the
cell membrane.
• Interstitial fluid – extracellular fluid not contained within blood
vessels.
4. Transport Across Cell Membrane 4
One of the great wonders of the cell membrane is the ability to
regulate the concentration of substances inside of the cell. Substances
such as Ca++, Na+, K+ and CL-, nutrients including sugars, fatty acids
and amino acids; and waste products, particularly CO2, which must
leave the cell.
• Selective permeability – cell membrane allows only substances
meeting certain criteria to pass through the membrane unaided.
5. Transport Across Cell Membrane 5
All substances that move through the membrane do so by one of two
methods.
Passive transport: movement of substances across the membrane
without the expenditure of cellular energy.
Active transport: movement of substances across the membrane
using energy from ATP (adenosine triphosphate)
6. PASSIVE TRANSPORT 6
In order to understand passive transport, we need to understand
concentration gradients and diffusion.
Concentration gradient: difference in concentration of a substance across
a space. Molecules (ions) will spread/diffuse from a higher concentration
to a lower concentration until they are equally distributed. When
molecules move in this way, they are said to move down their
concentration gradient)
Diffusion: movement of particles from an area of higher concentration to
an area of lower concentration. (Example – In a closed bathroom and a
bottle of perfume is sprayed. The scent molecules would naturally diffuse
from where it was sprayed to all corners of the room or until no more
concentration gradient remained
7. PASSIVE TRANSPORT – continued 7
• Diffusion – continued. (Example- spoonful of sugar placed in a cup of
tea. Eventually the sugar will diffuse throughout the tea until no
concentration gradient remains). If the room or tea was hotter, the
faster diffusion would take place.
9. FACILITATED DIFFUSION 9
Facilitated diffusion is the process used for those substances that
cannot cross the lipid bilayer due to their size or polarity. This type of
diffusion is helped by channel or carrier proteins.
Channel proteins: less selective than carrier proteins and usually
mildly discriminate between their cargo based on size and charge.
Carrier proteins: more selective, often allowing only one particular
type of molecule to cross.
Amino acids must undergo facilitated diffusion to move into a cell and
wastes must undergo facilitated diffusion to move out of a cell. Since
this is a passive process, it does not require energy expenditure.
10. FACILITATED DIFFUSION – continued 10
WATER CAN MOVE FREELY ACROSS THE CELL MEMBRANE OF ALL CELLS, EITHER THROUGH THE PROTEIN
CHANNELS OR BY SLIPPING BETWEEN THE LIPID TAILS OF THE MEMBRANE ITSELF
11. OSMOSIS 11
Osmosis is the diffusion of water through a semipermeable membrane down its
concentration gradient. Occurs when there is an imbalance of solutes outside of
the cell versus inside the cell.
Isotonic solution: (equal tension) – two solutions that have the same
concentration of solutes. Concentration of water molecules is the same outside
and inside the cells. Cells maintain normal shape. (solute concentration equal to
another solution)
Hypertonic solution: a solution that has a higher concentration of solutes than
another solution. Cells in a hypertonic solution will shrivel as water leaves the cell
via osmosis. (solute concentration higher than another solution)
Hypotonic solution: a solution that has a lower concentration of solutes than
another solution. Cells in a hypotonic solution will take on too much water and
swell with the risk of eventually bursting. (solute concentration lower than another
solution)
12. Osmosis – continued 12
Homeostasis in living things work to create an environment in which all
of the body’s cells are in an isotonic solution. The kidneys work to
maintain this homeostasis.
13. Passive transport – continued 13
Filtration: uses hydrostatic pressure gradient to push fluids and the
solutes within, from a higher pressure area to a lower pressure area.
(Example: Filtration pressure in the kidneys provides the mechanism
to remove wastes from the bloodstream)
In all of the passive transport mechanisms, the cell expends no
energy. They do not use ATP.
14. ACTIVE TRANSPORT 14
During Active Transport, ATP is required to move a substance across a
membrane, often with the help of protein carriers and usually against
the concentration gradient (from an area of low concentration to an
area of high concentration). Pumps are one of the most common types
of active transport.
Sodium-potassium pump: transport sodium out of cell while moving
potassium into the cell.
Active transport pumps can also work together with other active or
passive transport systems to move substances across the membrane.
15. ACTIVE TRANSPORT – continued 15
Endocytosis (bringing “into the cell”): process of a cell ingesting
material by enveloping it in a port of its cell membrane and then
pinching off that portion of membrane. Once it is pinched off it
becomes an independent, intracellular vesicle.
Phagocytosis (“cell eating”): endocytosis of large particles that must be
broken down or digested.
Pinocytosis (“cell drinking”): brings fluid containing dissolved
substances into a cell through membrane vesicles.
Exocytosis (taking “out of the cell”): process of the cell exporting
material using vesicular transport.
18. Cytoplasm and Cellular Organelles 18
Cytosol: jelly-like substance within the cell, provides the fluid
medium necessary for biochemical reactions.
Organelle (“little organ”): one of several different types of
membrane-enclosed bodies in the cell, each performing a unique
function.
Cytoplasm: composed of organelles and cytosol
Nucleus: cell’s central organelle, contains the cell’s DNA
19. Endomembrane System of the Cell 19
Set of three major organelles that form a system within the cell to work
together to perform various cellular jobs, including the task of
producing, packaging, and exporting certain cellular products.
Endoplasmic Reticulum (ER): series of winding thoroughfares similar
to waterway canals in Venice. The ER provides passages throughout
much of the cell that function in transporting, synthesizing and
storing materials. It supports many functions.
There are two forms of ER:
• Rough ER: so-called because its membrane is dotted with embedded
organelles called ribosomes, giving the RER, a bumpy appearance.
Primary job of rough ER is the production of proteins.
20. Endomembrane System of the Cell 20
• Ribosomes: organelle that serves as the site of protein synthesis.
• Smooth ER: contains no ribosomes. Synthesis of lipids. Cells that
produce large quantities of steroid hormones (female ovaries and
male testes), contain large amounts of smooth ER.
Golgi apparatus: looks like stacked flattened disks, almost like oddly
shaped pancake stakes. Responsible for sorting, modifying, and
shipping off products that come from the rough ER, (like the post-
office). It has 2 sides. One side receives products in vesicles. The
other side releases the product after repacking into new vesicles.
21. Endomembrane System of the Cell 21
Lysosomes: organelle that contains enzymes that break down and
digest unneeded cellular components. Similar to a wrecking crew
that takes down old and unsound buildings. They also break down
foreign material.
• Autophagy: “self-eating”- process of a cell digesting its own
structures.
• Autolysis: “self-destruct mechanism”- in the case of damaged or
unhealthy cells, the lysosomes can be triggered to open up and
release their digestive enzymes into the cytoplasm of the cell thus
killing the cell. Apoptosis – process of cell death controlled.
22. Organelles for Energy Production and
Detoxification 22
• Mitochondria (plural): membranous, bean-shaped organelle that is
the “energy transformer” of the cell. The inner membrane of the
mitochondria is where a series of proteins, enzymes, and other
molecules perform the biochemical reactions of cellular respiration.
These reactions convert energy stored in nutrient molecules (Glucose)
into adenosine triphosphate (ATP), providing usable cellular energy to
the cell. Oxygen molecules are also required during cellular
respiration. Cells use ATP constantly and so the mitochondria are
constantly working.
23. Cytoskeleton 23
Cytoskeleton – group of fibrous proteins that provide structural support
for cells, but this is only one of the functions. These components are
critical for cell motility, cell reproduction and transportation of
substances within the cell.
• Microtubules – thickest of the protein-based filaments. Maintain the
cells shape and structure, helps resist compression of the cell and
play a role in positioning the organelles within the cell. They have
two cellular appendages: cilia(lines the airways of the respiratory
system and flagella(specialized for cell locomotion, sperm cell).
• Microfilament – thinner type of cytoskeletal filament.
25. Nucleus 25
• Nucleus is the largest and most prominent of the cell’s organelles.
Considered the control center of the cell because it stores all of the
genetic instructions for manufacturing proteins. Nucleus of living
cells contains the genetic material that determines the entire
structure and function of the cell.
• Inside the nucleus lies the blueprint that dictates everything a cell will
do and all of the products it will make. This information is stored
within DNA.
• The following structures are in order from least to most complex in
organization: DNA, nucleosome, chromatin, chromosome.
26. Cellular Differentiation 26
• Stem Cells: unspecialized cell that can divide without limit as needed
and can, under specific conditions, differentiate into specialized cells.
The first embryonic cells that arise from the division of the zygote are
the ultimate stem cells.
oTotipotent: stem cells that have the potential to differentiate into any
of the cells needed to enable an organism to grow and develop.
oPluripotent: develop from totipotent stem cells and are the
precursors to the fundamental tissue layers of the embryo. It has the
potential to differentiate into any type of human tissue but cannot
support the full development of an organism.
27. Cellular Differentiation – continued 27
oMultipotent: stem cell that are slightly more specialized and has the
potential to differentiate into different types of cells within a given
cell lineage or small number of lineages, such as red blood cell or
white blood cells. In the process of hematopoiesis, it involves the
differentiation of multipotent cells into blood and immune cells.
These hematopoietic stem cells give rise to many different cell types
including red and white blood cells and platelets.
oOligopotent: limited to becoming one of a few different cell types.
oUnipotent: fully specialized cell and can only reproduce to generate
more of its own specific cell type.
