Basic Cellular Physiology and
Anatomy
The Breakdown of Organic Molecules
Takes the Place in Sequences of
Enzyme-catalized Reactions
• While your textbook is in a stable state, it
could burst into flames and exist in a more
stable state. It must have something that
provides energy of activation to move it from
its current state to a more stable state.
For living cells, the same end result
can be achieved in a less drastic way.
• Highly specific proteins catalysts, “enzymes”
can be used to control the “fire” in useful
ways. The fire changes to metabolism, the
“fire of life”, Max Kliber)
The enzyme provides the energy of
activation
The enzyme directs the order of
metabolism
Controlling the change in energy
form to do useful work
• Enzymes allow for useful work by controlling
the path and flow of energy change.
• Enzymes allow for the conversion of energy
from the sun to be converted into energy that
can be used to drive biological processes (ATP
adenosinetriphosphate - ATP). Used in the
manufacture of all proteins and enzymes.
• The majority of this ATP production by a nonphotosynthetic aerobic eukaryote cell takes
place in the mitochondria, which can make up
nearly 25% of the total volume of a typical
cell.
• It is the high energy bond of ATP that raises
the substrate plus the enzyme to a higher
level of activation allowing the metabolic
process to go.
Three distinct membrane systems
• These three structure can be visualized with
an electron microscope.
• The membranes are made of different
proteins
• Serve separate functions within the cell
• This is usually called ultrastructure.
The major membrane system
• The major membrane system extends from the nucleus to the
external surface of the plasma membrane.
• Includes:
– Nuclear envelope
– Endoplasmic reticulum: tubes, fibers, channels
– The Golgi apparatus
– Secretory granules
– Endosomes
– The plasma membrane that surrounds the cell
Lysosomes
• The second major membrane system that
breaks down proteins and lipids.
Mitochondria
• The third system is mitochondria (see below)
I Major membrane system
• Extends from the nuclear membrane to the
plasma membrane: contains 6 different parts
(1) Nuclear envelope
• Surrounds the nucleus of the neuron
(2) Endoplasmic reticulum
• A continuation of the nuclear membrane as a
set of extensive channels.
• In ultrastructure (electron microscopy)
appears in both a smooth membrane and a
rough membrane
3D drawing of rough and smooth endoplastic reticulum
• (3) Golgi apparatus
•
Flat disk shaped structures with no obvious
knobs.
• Packages the and distributes molecules with
the cell
3D drawing of the Golgi apparatus
Electronmicroscope photo of Golgi apparatus
Secretory granules
• (4) Secretory granules: A small subcellular vesicle,
surrounded by a membrane, that is formed from the
Golgi apparatus and contains a highly concentrated
protein destined for secretion. Secretory granules
move towards the periphery of the cell and upon
stimulation, their membranes fuse with the cell
membrane, and their protein load is exteriorized.
Processing of the contained protein may take place in
secretory granules. Comment Note that the term
'secretory vesicle' is sometimes used in this sense,
but can also mean 'transport vesicle.
Endosomes
• (5) Endosomes are granular membranes that
contains endolithic material pinched off from
the inside surface of the plasma membrane
for transport to the lysosomes for
degradation.
• Can be recycled if it is associated with the
Golgi apparatus
Plasma membrane bi-leaflet phospholipid
• Surrounding membrane of the cell
• Bi-leaflet structure:
– a hydrophobic head group: choline, phosphate
and glycerol
– A tail hydrophilic group: fatty acid
– The head ends are contiguous with the
extracellular and intracellular material
respectively.
– The tail end point to one another
1/2 of a bi-leaflet plasma
membrane
3D view of mitochondria and its constituent parts
Electronmicroscope photo of mitochondria
III Mitochondria.
• This is an independent system that has been
conserved evolutionary terms: low mutation
rate.
All membrane systems are imbedded
in the cytosol
• Cytosol: a gel like substance consisting of
water-soluble proteins and a variety of
insoluble filaments that form the
cytoskeleton.
Essentially all macromolecules of a
neuron are made in the cell body from
mRNA originating in the nucleus.
• Exception: some few are made in the
mitochondria.
Large folded macromolecules
• Proteins are very large molecules made of
serially places amino acids. All proteins are
made from directions situated in the nucleus
and brought to the ribosome by mRNA, which
is the “work bench” of protein manufacture.
Each neuron makes only three classes
of proteins
• 1. Proteins that are synthesized in the cytosol
and remain there.
• 2. Proteins that are synthesized in the cytosol
but are latter incorporated into the nucleus
and mitochondria.
• 3. Proteins that are synthesized in association
with the cell membrane system: 3
subcategories.
Proteins that remain attached to the
basic three types of membranes but
can latter be detached
• Membrane-spanning proteins – integral
proteins as they make up a part of the bileaflet structure of the plasma membrane
• Anchored proteins
• Associated proteins
• Unattached proteins that remain in the lumen
of the endoplasmic reticulum or Golgi sacs.
• Proteins that are transported by means of
vesicles that pinch off from the Golgi
apparatus and are distributed in secretory
vesicles (used in the release of
neurotransmitters) or other organelles –
lysosomes
• Class 1 and 2 proteins are translated on free
polyribosome (polysomes).
• Class 3 proteins are translated on polysomes
that become attached to the flattened sheets
of the endoplasmic reticulum
Microtubules
• Tubulin, subunits of microtubles, make up 10%
of total brain proteins.
• Neuronal microtubule have biochemical
specializations to meet unique demands
imposed by the size and shape of neurons.
Intracellular transport and cell
morphology are largley the
responsibility of microtubles.
• Microtubles, in vitro, are dynamic with polar
ends (plus and minus) that correspond to the
fast and slow growing ends respectively.
Slow Transport system (Squires et.al)
Fast axon Transport
• Results: Ochs found that the rate of fast
transport is about 410 mm (16.1 in) per day at
body temperatures. Fast anterograde
transport depends critically on the availability
of ATP for energy; is not affected by inhibitors
of protein synthesis; and is independent of the
cell body (Fig 5-10).
Fast transport system (Squires et. al.)