CELL STRUCTURE : PART TWO
Golgi Body or Golgi Apparatus
- Stack, of a half dozen or more flattened sacs.
- On one side, protein-filled vesicles are received
from the E.R.
- Responsible for sorting/modifying proteins and
packaging them into vesicles over at the other
side.
- From here the vesicles move to different
locations in the cell.
Vacuoles
- Storage areas for water, sugars, and salts.
Vessicles
- Very small vacuoles
- Act as storage sites for various kinds of
molecules, but most often used for
transporting materials.
- Can be formed either by the Golgi
Apparatus/ER or from an in-folding of the
cell membrane.
VESICLE FORMATION ILLUSTRATED
BELOW:
Lysosomes
- Special vacuoles formed by the Golgi body.
- Contains powerful hydrolytic enzymes used
to digest substances entering the cell. These
enzymes may also be used to digest organelles
that are of no further use. (Autodigestion).
Ribosomes
- Bean-shaped structures.
- Each contains two - rRNA and protein
subunits.
- Function as the site for protein synthesis
(translation).
- Found on E.R. (proteins for export), or by
themselves out in the cytoplasm. (Proteins for
use within the cell).
- Several ribosomes together in a line, all
producing the same protein, form what is
called a polyribosome (polysome)
- Produced in the nucleolus of the nucleus
when rRNA and Proteins combine, then move
out of nucleus.
Ribosomes
on E.R. =
Rough ER
Mitochondria
- React glucose with oxygen to release energy,
this energy is stored in ATP molecules and
then used by the cells to carry out specialized
functions eg. Movement, cell transport.
- During cellular respiration oxygen is used
up and carbon dioxide is given off.
- C6H12O6 + 6O2  6CO2 + 6H2O + Energy
- Considered the powerhouse of the cell.
- Structurally it consists of two membranes.
- The inner membrane loops back and fourth
through the inner fluid (matrix) of the
mitochondria. This increases its surface area
and allows it to form shelf-like structures
(folds) called cristae.
- This inner membrane is the site of cellular
respiration.
Cytoskeleton
- Provides internal structure to maintain the
cell’s shape, also anchors the organelles and
allows them to move when such movement is
required.
- Composed of microfilaments and
microtubules.
Microfilaments – (Actin)
- Extremely thin protein fibers usually found
in bundles.
- Similar in composition to the protein in
muscle (allows for contraction).
- Associated with cell movement such as :
“Cyclosis”, cytoplasmic streaming, amoeboid
movement and the “pinching off” process
that occurs during cell division.
Microtubules
- Thin cylinders which are several times
larger than microfilaments.
- Each cylinder contains 13 rows of a globular
protein (tubulin) which is arranged in a spiral
fashion.
- Found in both cytoplasm and in certain
organelles.
- Used to construct materials essential for the
formation of cilia, flagella and centrioles.
Microtubule
Centrioles
- Very short cylinders with a 9 + 0
arrangement of microtubules.
- Give rise to basal bodies which in turn
direct the formation of cilia and flagella.
- Also used to help direct movement of
material through the cell.
Cilia
- Short, numerous, hair-like projections that
are used for locomotion by many unicellular
organisms.
- Membrane–bound collections of
microtubules (9 pairs arranged around a
central pair, giving rise to a (9 + 2 pattern).
- Each pair of outer microtubules (doublet)
also has pairs of arms projecting toward a
neighboring doublet and spokes extending
toward the central pair of microtubules.
Flagella
- Like cilia but can be very much longer.
- Also used for the locomotion of organisms
and gametes (sperm). See diagrams below