-
8/10/2019 02 Cell Structure & Function
1/6
2Cellular Level of Organization
Detailed study of the cell began in the 1830s; some of the
scientists contributing tothe understanding of cell structure and
function were Robert Brown, MatthaisSchleiden, Theodor Schwann, and
Rudolph Virchow.
The cell theory states that all organisms are composed of cells,
that cells are thestructural and functional unit of organisms, and
that cells come only frompreexisting cells.
Prokaryotic VS Eukaryotic Cells
Prokaryotic cells lack a nucleus and are smaller and simpler
than eukaryotic cells(which have a nucleus). Prokaryotic cells are
placed in two taxonomic domains:Bacteria and Archaea. Organisms in
these two domains are structurally similar butbiochemically
different.
Eukaryotic cells are members of the domain Eukarya, which
includes the protists,fungi, plants, and animals. A
membrane-bounded nucleushouses DNA; the nucleusmay have originated
as an invagination of the plasma membrane. Eukaryotic cellsare much
larger than prokaryotic cells, and therefore have less surface area
per
volume. Eukaryotic cells are compartmentalized; they contain
small structures calledorganelles that perform specific functions.
Some eukaryotic cells (e.g., plant cells)have a cell wallcontaining
cellulose; plasmodesmata are channels in a cell wall thatallow
cytoplasmic strands to extend between adjacent cells.
The Structure of Eukaryotic Cells
o Plasma membrane-
porous, elastic structure that separates the contents of the
cell from its
surroundings;-
acts as a boundary layer to contain the cytoplasm (fluid in
cell)interlocking surfaces bind cells together
-
selectively permeable to select chemicals that pass in and out
of cells
Cell Structure & Function
page 1 of
-
8/10/2019 02 Cell Structure & Function
2/6
-
8/10/2019 02 Cell Structure & Function
3/6
o Endoplasmic reticulum-
sheets of unit membrane with ribosomes on the outside; forms a
tubulanetwork throughout the cell
-
transports chemicals between cells and within cells-
provides a large surface area for the organization of chemical
reactionsand synthesis
-
o Ribosomes-
non-membraneous, spherical bodies composed of RNA (ribonucleic
acidand protein enzymes
-
site of protein synthesis-
o Golgi Apparatus-
stacks of flattened sacs of unit membrane (cisternae) ; vesicles
pinch offthe edges
-
modifies chemicals to make them functional; secretes chemicals
in tinyvesicles ; stores chemicals ; may produce endoplasmic
reticulum
-
o Lysosomes-
membrane bound bag containing hydrolytic enzymes ; hydrolytic
enzyme =(water split biological catalyst)
-
main function of these microbodies is digestion; lysosomes break
downcellular waste products and debris from outside the cell into
simplecompounds, which are transferred to the cytoplasm as new
cell-buildingmaterials
-
o Mitochondria
-
composed of modified double unit membrane (protein, lipid) ;
innemembrane infolded to form cristae-
site of cellular respiration ie. the release of chemical energy
from foodGlucose + Oxygen ------> Carbon Dioxide + Water +
Energy (ATP)
-
o Peroxisomes-
membrane-bounded vesicles that contain specific enzymes. Their
actionresults in production of hydrogen peroxide.
-
Hydrogen peroxide (H2O2) is broken down to water and oxygen
by
catalase.Peroxisomes in the liver produce bile salts from
cholesterol andalso break down fats. Peroxisomes also occur in
germinating seeds where
they convert oils into sugars used as nutrients by the growing
plant.-
o Vacuoles-
a single layer of unit membrane enclosing fluid in a sac-
produces turgor pressure against cell wall for support ; stores
water andvarious chemicals ; may store insoluble wastes
-
page 3 o
-
8/10/2019 02 Cell Structure & Function
4/6
o Chloroplasts-
membranous organelles (a type of plastid) that serve as the site
ofphotosynthesis. The chloroplast is bound by a double membrane
organizedinto flattened disc-like sacs called thylakoids formed
from a thirdmembrane; a stack of thylakoids is a granum.
-
Chlorophyll and other pigments capture solar energy, and the
enzymes
which synthesize carbohydrates are located in the chloroplasts.
Othetypes of plastids, which differ in color, form, and function
fromchloroplasts, include chromoplasts and leucoplasts.
-
o Microfilaments-
solid rods made of globular proteins called actin- these
filaments are primarily structural in function and are an
importan
component of the cytoskeleton-
o Microtubules-
straight, hollow cylinders are found throughout the cytoplasm of
aleukaryotic cells (prokaryotes don't have them) and carry out a
variety offunctions, ranging from transport to structural
support
-
o Cilia and Flagella-
cilia and flagella are hair-like organelles that project from
the surface ofsome cells
-
they cause cells to move through their medium or cause fluids or
particlesto move over the cell surface
-
o Controsome and Centrioles
-
centrosome is the structure that occurs outside the nucleus of
animal cellsis composed of two centrioles set at right angles to
each other-
centrosome plays a critical role in organizing the tubule system
(mitoticspindle) that is involved in chromosome movement during
cell division
-
centrosomes also organize the array of microtubules and
microfilaments-
o Nucleus-
consists of the nuclear envelope, nucleolus, chromatin, and
nucleoplasm-
nuclear envelope is composed of two unit membranes with a
fluid-filledspace ; nuclear pores present ; outer membrane may be
continuous withendoplasmic reticulum ; selectively permeable to
control movement in o
out-
chromatin is composed of long thin strands of DNA ; contains
instructionsthat control cell metabolism and heredity
-
nucleolus is a composed of non-membraneous matrix of RNA
(ribonucleicacid) and protein ; instructions in DNA are copied here
; works withribosomes in the synthesis of protein
page 4 o
-
8/10/2019 02 Cell Structure & Function
5/6
page 5 of
-
8/10/2019 02 Cell Structure & Function
6/6
page 6 o
