Transcript Plasma Membrane

Chemistry and Cells
Important Definitions:
Define these terms (5 word definitions or less)
1. Elements
13. Steroid
25. Active transport
2. Isotopes
14. Mitochondria
26. Passive transport
3. Ions
15. Golgi apparatus 27. Endocytosis
4. -Carbohydrate
16. Rough E. R.
28. Phagocytosis
5. Protein
17. Smooth E. R.
29. Exocytosis
6. Enzyme
18. Lysosomes
30. Pinocytosis
7. Nucleic Acid
19. Peroxisomes
31. Tonicity
8. Deoxyribonucleic 20. Cytoskeleton
32. Isotonic
Acid
21. Centrioloes
33. Hypotonic
9. Ribonucleic Acid 22. A. T. P
34. Hypertonic
10. Lipid
23. Simple Diffusion
11. Saturated Fat
24. Facilitated
12. Unsaturated Fat
Diffusion
What are you made from?
Atom:
- smallest unit of
matter; unable to be
cut into smaller units
and still remain the
same.
But what do you get when you cut an atom in half?
Proton: -positively charged
+
Neutron: -neutral charge (no charge)
Electron:
- negative charge
-
What is an element?
Element:
- a group of atoms with
the same structure and
properties.
What happens when an
atom has more neutrons
than it is supposed to?
It creates an Isotope
Isotopes: - an isotope is an atom with more, or less
neutrons than other atoms of its element.
“Normal” Carbon 12
6 Protons
6 Neutrons
6 Electrons
Radioactive Carbon 14
6 Protons
8 Neutrons
6 Electrons
What happens when you put two elements together?
Compounds are formed.
Compound:
- two or more elements
that are combined in
specific proportions.
Ex - NaCl
a.k.a……….
Salt
Water, Water, Everywhere………….
Water: – the universal solvent
+
Polar (polarity) : having
a definite positive and
negative region on/in a
molecule.
That means that a water molecule
is like a little magnet!
Anything that is magnetic
(polar) will stick to water!!
Carbon Compounds
`
Carbon:
An element that is used
by organic life forms to
make molecules of the
body.
Macromolecule:
Macro = large or many
Molecule = arranged atoms
Def: a large molecule composed of many units, or
smaller molecules
Ex:
Glucose
A single 6
carbon ring
But if I add a lot of them together, I get:
Complex Carbs
A single unit is a MONOMER
Having multiple units is a
POLYMER
First Carbohydrates
What is a Carb?
Chemical Structure of a Carbohydrate:
Carbohydrates are
ALWAYS found in the
Ratio of :
O
H
1 Carbon to 2 Hydrogen
to 1 Oxygen
1:2:1
Glucose (simplest carb):
C6H12O6
Usually found in
a ring
C
H
What do we use Carbohydrates for?
Energy
Both short term
and long term
Long term
Complex carbs
like pasta
Short term
Simple Sugars
What can you eat that has more energy than Carbs?
Second Molecule:
Lipids (fats) can
store enough energy
that they can even
hold a flame!
Plants store fat as liquids.
Animals store fat as solids
Lipid Composition:
A Glycerin Molecule
This acts as a connector for:
Three Fatty acids
The fatty acids contain
several carbon groups that
store energy in their bonds.
What are the main types of Lipids?
Neutral Fats
Saturated and
Unsaturated fats
Used for long term energy storage!
Phospholipids
These make the cell
membrane
Steroids
These are messages carried
all about the body!
They are NOT only the
illegal drugs
Third Molecule:
Nucleic Acids: The cells Blueprint
DNA & RNA
DeoxyriboNucleic Acid & RiboNucleic Acid
The building block”
that makes nucleic
acids are
NUCLEOTIDES
Phosphate group
Ribose Sugar
Nitrogen Base
DNA:
Contains all the genetic material
that is needed by the cell.
It is found in a “Double Helix”,
two twists in a clockwise spiral.
RNA:
A single strand of Nucleotides that
carries genetic material out of the
nucleus to be processed.
Proteins
Forth Molecule:
Proteins are used as structural
components in all cells!
Amino acids: - 20
different molecules that
combine to make all proteins
These are just two
Protein Uses:
Construction:
Proteins build components
inside and outside our cells
Enzyme reactions:
Enzymes are special proteins that
build or break down materials
inside or outside the cells
What happens to the food you eat?
Enzymes break
down the food by
acting as a
Catalyst
Enzyme
(catalyst)
Food particle
(substrate)
Catalyst – anything
The enzyme attaches
that makes a
to the food at the
reaction take place
“active site”
without being
changed itself The enzyme breaks the
food into smaller usable
pieces (products) and
releases them
Cells
 Cells are the basic units
of life
 All organisms are
composed of cells.
 The activity of the body’s
cells determines the both
the structure and the
function of the body.
 What we’ll be
concentrating on is how
things move in and out of
cells.
Plasma Membrane
 The membrane separates the
cell interior (the cytoplasm)
from the cell exterior
(extracellular or interstitial
fluid).
2 PM’s as seen w/ an electron microscope
 Both the cytoplasm and the
exterior are aqueous, or water Cartoon representation of the PM
based.
 The membrane is a bilayer
(double layer) of phospholipids.
 A phospholipid is a molecule
made of a glycerol backbone to
which 2 fatty acids and one
phosphorous-containing group
are attached.
 Because the cell has
water inside and water
outside, the
phospholipids have to
line up in two lines to
protect the fatty
(hydrophobic) tails
 This structure has
important implications
for how things travel
thru this membrane.
Plasma Membrane
 Notice that the membrane is
made up of more than just
phospholipids.
 Proteins are found either
embedded within the
membrane itself (membrane
proteins), or weakly associated
with either the interior or
exterior face of the membrane
(peripheral proteins).
 The membrane also has
molecules of cholesterol
embedded among the
phospholipids. Cholesterol
increases the temperature
range over which the
membrane can function.
 Some integral proteins protrude into the ECF and
have sugars attached. These are called glycoproteins.
 Glycolipids often function as markers that label the cell as “self,” i.e.,
not foreign.
 Other integral proteins function as:
Enzymes
Channels
Transport molecules
Structural supports
 The membrane is a fluid
structure. There is a lot of lateral
movement of phospholipids and
unanchored proteins.
 B/C of its gel-like nature and the
fact that it’s made up of many
different parts, we say the
membrane is a fluid mosaic.
Crossing the Membrane
 Nutrients must get in and
wastes must get out.
 Signaling molecules
received by a cell may
need to get in, while
signaling molecules sent
by a cell need to get out.
 Fluid must be able to get
in and out.
 Certain ions must be able
to get in and out.
Types of transport:
Passive Transport:
Requires NO Energy
Either by simple diffusion
or through a membrane
protein
Active Transport:
Requires Energy - ATP
Always happens through a
membrane protein and uses ATP
to force a molecule across a
membrane against concentration
grandient
Big Stuff?
 Membrane Proteins are adequate for bring small
molecules into the cell or out of the cell.
 However, a different kind of active transport is
necessary to move large things into/out of the
cell – vesicular transport.
There are 2 types of
vesicular transport:
exocytosis and
endocytosis
Exocytosis
 Exocytosis literally means “out of the cell”
 It accounts for hormone secretion, neurotransmitter
release, mucus secretion, and, sometimes, ejection of
wastes.
 Inside the cell, the substance to be exported is enclosed in a
membranous sac called a vesicle.
 The vesicle will migrate to the PM fuse with it, and then rupture,
spilling the contents into the extracellular space.
Endocytosis
 Reverse of exocytosis. Allows macromolecules to enter cells.
 The substance is progressively enclosed by an enfolding portion of
the plasma membrane.
 This forms a vesicle which will pinch off the plasma membrane and
enter the cytosol where it is typically digested.
 Types of endocytosis are:
 Phagocytosis
 Pinocytosis (a.k.a. bulk-phase endocytosis)
 Receptor-mediated endocytosis
 Literally “cell-eating.”
 Cytoplasmic extensions
called pseudopods “reach
out and grab” large, solid
material such as a clump of
bacteria or cell debris, and
then engulf it.
 The resulting vesicle is
called a phagosome.
 Usually, the phagosome
fuses with a lysosome, a
membranous organelle that
contains digestive enzymes,
and its contents are
digested.
 Macrophages and white
blood cells are the most
phagocytic cells in the
body.
Phagocytosis
Pinocytosis
 Literally means “cell-drinking.”
 A bit of infolding plasma membrane surrounds
a droplet of extracellular fluid containing
dissolved molecules. This creates a tiny
membranous vesicle.
 Most cells routinely perform this.
 Unlike phagocytosis, pinocytosis is unselective!
Diffusion
 Many molecules have the capacity to
diffuse right through the phospholipid
bilayer.
 Nonpolar molecules move thru w/ ease b/c
they do not mind the hydrophobic interior of
the plasma membrane.

Such molecules include O2, CO2, steroid hormones,
fat soluble vitamins, and alcohol.
 What governs whether these molecules will
move into or out of a cell?

Its CONCENTRATION GRADIENT.
 Hydrophilic molecules must diffuse thru
special protein channels in order to get
thru the cell membrane.
 This type of transport through the plasma
membrane is termed simple diffusion.
 Based on the concept of
diffusion.
 Random molecular
movement (due to KE)
results in molecules moving
from areas where their
concentration is high to
where their concentration is
low.
 Note: Concentration is
defined as how many
molecules of a substance
are present in a certain
volume of liquid.
 The dissolved particles are
the solutes while the fluid
in which they’re dissolved
is the solvent. Together,
they create a solution.
Note that in the above diagram,
molecules are moving down their
concentration gradient!
Diffusion
 Some polar molecules enter cells via diffusion. They cannot go
straight through the nonpolar lipid bilayer, so they require the
assistance of proteins that act as carrier molecules.
 These carriers bind the substance (glucose and other simple
sugars are the best examples) on one side of the plasma
membrane and then change their conformation and release the
substance on the other side of the PM.
This is known as
facilitated diffusion.
Osmosis
 Osmosis is the diffusion of water
through a semipermeable membrane.
 A membrane that is semipermeable
allows some molecules to pass thru,
but does not allow others.
 Water will diffuse from an area of high
concentration to an area of low conc.
 It’s important that you understand the
following:
 An area that has a high [water] has a low
[dissolved particles].
 An area that has a low [water] has a high
[dissolved particles].
Right: Water molecules (black dots)
move to the right since they are high in
conc. on the left and low on the right.
 Water will diffuse from
a solution with low a
concentration into a
solution of high
concentration if they
are separated by a
semipermeable
membrane.
 This is simply
another way of
saying that water
will flow down its
concentration
gradient.
(Permeable to water only)
Tonicity
 Tonicity is defined as the ability of a solution to
change the shape of a cell immersed in it due to
changes in the cell’s water volume.
 A solution with the same concentration of nonpenetrating solutes as those found in cells are
isotonic, i.e., “the same tonicity.”
 Cells exposed to such solution retain their normal
shape and exhibit no net gain or loss of water.
 Most intravenous solutions are isotonic (e.g., 0.9%
saline or 5% glucose).
 Why is this necessary?
Red Blood Cells in
an Isotonic Solution
 Suppose you placed a
cell in a solution, and
the cell shrank (the
Tonicity
technical term is
crenated):
 The cell must have lost
water which means
that, the [nonpenetrating solutes]
was higher outside the
cell.
 Thus, the solution was Red blood
hypertonic (hyper
cells in a
means greater than
hypertonic
usual).
environment
 Suppose you put a cell
in solution and the cell
burst (lysed):
Tonicity
 The cell must have
gained water which
means that the [nonpenetrating solutes] was
higher inside the cell.
 Thus the solution was
hypotonic (hypo means
less than usual).
 Do you think pure water
is hypertonic to cells or
hypotonic to cells?
RBC’s in a hypotonic
environment
Cell Junctions:
How do cells connect?
Gap Junctions:
These are the way cells communicate
with cells adjoining them. They are
semi-permeable and allow many
things across the boundary
Desmosomes:
Anchors holding cells to neighboring cells.
Tight Junctions:
Creates a water-tight bond between
the cells like rivets.