Cell Biology (Cell Structure)
PLO A1, A2 (pages 45 61, 67-77)
The Cell
Theory
·
The
cell is the basic unit of structure and function in organisms.
·
All
organisms are made of one or more cells (unicellular/multicellular)
·
All
cells come from pre-existing cells
Cells are
extremely diverse:
·
among
forms of life (ex. plant cells versus animal cells versus cells of protists)
·
within
a single form of life (ex. muscle cells versus nerve cells versus epithelial
cells)
Cells can
be categorized as:
·
prokaryotic have cell walls, plasma membrane, ribosomes, thylakoids, enzymes,
chromosome (DNA only). DO NOT HAVE
nucleus or any membrane bound organelles
·
eukaryotic
nucleus present, many visible membrane bound organelles
defn : organelles tiny specialized structures performing specific cellular functions.
Cellular
structures
·
cell
membrane (plasma membrane)
-
a phospholipid bilayer in which protein molecules are embedded.
-
proteins
can act as channels for various particles (from individual atoms to large
macromolecules like proteins)
-
contains
the cytoplasm (a gel-like/semifluid medium
between the plasma membrane and the nucleus)
-
is a semi-permeable
layer that controls what enters and leaves the cell.
-
membranes in general allow separation of various
metabolic processes whether its separate from outside (extracellular)
of cell or inside (intracellular)
·
nucleus
-
A
prominent organelle separated from cytoplasm by the nuclear envelope (a double
membrane with many nuclear pores that allow macromolecules like proteins and
ribosomal subunits through). This membrane is continuous with encoplasmic reticulum membrane.
-
contains chromosomes which carry code for the
production of proteins. (chromatin is visible with an electron microscope)
-
semi-fluid
interior of nucleus is the nucleoplasm
-
contains the nucleoli (sing., nucleolus). Ribosomes are made
here.
·
chromosomes
-
found
inside the nucleus
-
hold the genetic code for the production of
proteins which in turn determine the characteristics and metabolic functioning
of a life form.
-
Chromosome
structure has many levels: (see page 84
in your text)
1. DNA helix is wrapped around histone proteins (a nucleosome)
2. nucleosome chain is coiled (chromatin)
3. chromatin is looped (euchromatin)
4. euchromatin is condensed (heterochromatin)
5. heterochromatin is condensed (chromosome)
·
ribosomes
-
composed of two subunits, 1 large & 1 small. Each subunit made of protein and rRNA
-
site
of protein synthesis
-
float freely by themselves or in groups (polyribosomes) in cytoplasm. Proteins made here stay in the cell
-
OR
found attached to endoplasmic reticulum.
Proteins made here are secreted from the cell or become integrated in
the plasma membrane.
·
smooth
and rough endoplasmic reticulum (ER)
-
membranous channels and saccules
(continuous with outer membrane of the nuclear envelope.
-
rough ER is studded with ribosomes. proteins enter channels and are modified
(clipped by enzymes or tagged with a sugar chain to make glycoproteins)
-
smooth ER is continuous with rough ER. SER functions to produce phospholipids and
vesicles in which proteins move to the Golgi. Various other functions also exist (ex.
testosterone production, detoxifies drugs)
·
Golgi Apparatus
-
stack
of 3 to 20 slightly curved saccules
-
positioned between the ER and the plasma membrane.
-
receives
vesicles full of protein or lipids from the ER
-
produces secretory vesicles
that fuse with plasma membrane releasing their contents to the outside of the
cell.
-
maturation/stationary saccule
models ???
-
involved in processing, packaging, and secretion.
-
forms
lysosomes (vesicles that contain proteins but stay in
the cell)
-
glycoprotein
tag put on at the ER determines final destination
·
lysosomes
-
membrane
bound vesicles made by Golgi
-
contain
hydrolytic digestive enzymes
-
will fuse with vesicles that pinch off from the
plasma membrane containing extracellular
molecules. Digested products then enter
the cytoplasm. Ex. white blood cells
engulf a bacterium (endocytosis) and the vesicle
fuses with a lysosome and the bacterium is destroyed.
-
will fuse with other organelles in the cytoplasm (autodigestion).
Rejuvenation occurs as result
-
Absence
of a digestive enzyme results in lysosomal storage
disease. ex.
Tay Sachs disease. Myelin cells cannot
break down a type of lipid.
·
vacuoles
-
large membranous sac that generally stores water,
sugars, salts, and even pigments & toxic molecules.
-
large in plant cells, small in animal cells.
-
protists have developed contractile vacuoles
to rid the cell of excess water.
·
mitochondria
-
0.5-1.0
μm diameter
-
2-5
μm length
-
double membrane bound organelle, therefore has an
outer and inner membrane.
-
inside
of the inner membrane is the matrix which contains DNA, ribosomes
and enzymes
-
carbohydrates
are broken down in matrix releasing energy for ATP production (CELLULAR
RESPIRATION)
-
cristae are folds of inner membrane that go
deep into the matrix to increase surface area.
-
positioned throughout the cytoplasm.
·
vesicles
-
any membrane bound spherical body in the cytoplasm
of a cell.
-
used for storage or transport of many different
molecules.
-
usually associated with transport, secretion or
ingestion.
·
peroxisomes
-
vesicle whose enzymes are made from free ribosomes and whose digestive actions in combination with O2
results in H2O2 being made.
-
found
in liver cells that are producing bile salts from cholesterol
·
cytoskeleton
-
microfilament
lattice that is found throughout the cytoplasm
-
built
from three filament types: actin
filaments, microtubules and intermediate filaments
-
holds
all organelles in place and moves them appropriately
-
a
dynamic system/always moving
-
can
disassemble and reassemble quickly during cell division to form the spindle
-
centrosome is a structure near the nucleus
that controls microtubule assembly. It
consists of two centrioles lying at right angles to
each other.
-
centrosomes are thought to be precursors to basal bodies
·
Cilia/Flagella
-
membrane bound cylinders enclosing a matrix area.
-
at base of each is a basal body which directs the
movement of fibres in cilia and flagella.