CELL STRUCTURE & FUNCTION
1.
2.
Recognize membrane systems and
organelles: RER, SER, Golgi body,
mitochondria, ribosomes, lysosomes,
chloroplasts, cell surface membrane,
nuclear envelope, centrioles, nucleus, and
nucleolus.
Outline their functions
Typical Eukaryotic Cell
 Plasma membrane/ cell surface membrane
defines cell boundary, retain contents
controls movement of substances
in/out of cell: maintain optimal
internal environment for cell f(x)ing.
 Nucleus
 Cytoplasm
Cytosol – (aq) soln of ions, organic
cmpds e.g. sugars, a.a, proteins
Organelles – sub cellular structures
(ribosomes, ER, golgi body,
lysosome, mitochondrion,
choloroplast, centriole
Cytoskeleton – framework of protein
filaments (fibrous proteins:
microtubules, immediate/micro
filaments)
 Cell wall
- plant cells, outside plasma membrane
Nucleus
 Largest organelle in eukaryotic cells,
spherical
 Nuclear envelope
- double membrane (phospholipids bilayer
x2)
- perforated by nuclear pores – ‘passage’
 hereditary material determines what
proteins are synthesized= controls cell
activity: regulate protein synthesis
(various enzymes needed for cell to
function optimally)
Chromosomes/Chromatin
hereditary material made of D.N.A.
when cell not dividing, genetic material=
thin elongated threads = chromatin (coil
-
around proteins/histones) Diffused mass_
microscope
b4 cell division, chromatin threads
condense to form thicker structures
called chromosomes
 heterochromatin ( tightly coiled, but
not as tight as chromosomes)
 euchromatin (loosely coiled chromatin,
dna is being further expressed)
Nucleolus
dark sphere, large amt DNA, RNA,
proteins
ribosomal RNA (component of ribosomes)
are synthesized
Ribosomes
 Site of protein synthesis (enzyme catalyses
peptide bonds/ linkages)
 Small+large subunit
 Floating in cytosol/ attched to ER
 Made of rRNA and protein
Endoplasmic Reticulum ER
 Extensive network of membranous tubules
and sacs (cisternae)
 Outer membrane of nuclear envelope
continuous with ER

-
Rough ER
ribosomes stud outer surface membrane
site of protein synthesis, meant for
secretion out of cell (digestive enzymes,
insulin, a hormone in pancreas: secrete
into bloodstream) OR insertion in plasma
membrane
1. proteins formed enter cisternal space,
fold into native configuration
2. vesicles bud off from ER, carrying
proteins to Golgi apparatus
3. contains enzymes on its membrane
that synthesis phospholipids
(transported to/ fuse with plasma
membrane (cell growth)

-
Smooth ER
smooth, > tubular
-
-
site: lipid synthesis (cholesterol,
membrane phospholipids; testosterone,
steroid hormones)
detoxification of drugs/poisons (alcohol;
liver cells rich in smooth ER)
site: carbohydrate synthesis
cisternal space stores Ca2+ (involves in
contraction by muscle cells)
Golgi Apparatus
 stack of flattened, membrane-bound sacs
called cisternae + associated with vesicles
called Golgi vesicles
 convex (forming/cis) face: new cisternae
formed by fusion of vesicles brought from
ER
 concave (trans/maturing) face: new
vesicles bud off
receives proteins + lipids from RER,
SER. Chemically modifies
(carbohydrate chain on glycoprotein
modified to give diff glycoprotein
products)
sorts/targets completed materials to
diff cell parts OR for secretion
vesicles bud off from Golgi fuse with
plasma membrane (cell membrane
repair)
form lysosomes
Lysosome
 single membrane, hydrolytic (disgestive)
enzymes : proteases, lipases, nucleases
 acidic! Enzyme contents synthesized on
RER,
transported via vesicles to G.A. cis-face
for processing, bud off trans face
=lysosomes
Digestion of material by endocytosis
- lysosome fuse with vesicles, digest
contents of food materials/ foreign
bacteria particles. Useful pdts of
digestion absorbed and assimilated
into cytoplasm; unwanted released to
external medium (exocytosis)
Autophagy
- breakdown unwanted old organelles
organic pdts frm breakdown process
returned to cytoplasm for reuse
Release of enzymes outside of cell
- sperm releases hydrolytic enzymes by
exocytosis to digest sheath of
nutrient cells surrounding ovum =
facilitate fertilization.
Autolysis
- release lysosome contents within cell
(metamorphosis of
tadpoles/caterpillars)

-
MEMBRANES

Specific way in which proteins insert into
lipid bilayer (bifacial characteristic)

Extracellular face and cytoplasmic face
differ in lipid protein composition because
of endomembrane system’s synthesis,
transport.

Vesicle fuse with plasma membrane =
inner surface because part of
extracellular face
Mitochondrion (sgl)
 Spherical/rod-shaped, double membrane
(2 p.b)
 Intermembrane space (outer, inner
membrane)
 Outer membrane smooth, inner membrane
highly folded to form numerous cristae
 Cristae project into semi-fluid matrix,
containing ribosomes, circular DNA and
various enzymes involved in aerobic
respiration
 site: aerobic respiration, forming ATP
Chloroplast
 Lens-shaped, double membrane, inner
membrane
continuous with series of flattened sacs
within chloroplasts, called thylakoids (use
in photosynthesis)
1 stack thylakoids = granum
≥2 granum = grana
 Chlorophyll located on thylakoid
membrane

Fluid within chloroplast – stroma (circular
DNA, ribosomes, enzymes, ~starch grains)
Vacuole
 Fluid-filled sac, single membrane
 Animal cells have smaller, numerous
vacuoles
Plant cells – large central vacuole
surrounded by membrane called tonoplast.
Contains cell sap – soln: mineral salts,
sugars, enzymes, pigments, waste pdts
- conc. cell sap draws H2 O into vacuole
(maintain turgor pressure, support
herbaceous plants)
- (growth) as cell increase size, vacuole
enlarge (take water) with minimal
cytoplasm increase
- contain pigments (anthocyanins – colors
in flowers, fruits) attract animals
pollination, seed dispersal
- after cell death, hydrolytic enzymes in
vacuole released to cause autolysis of
cell
- store waste (calcium oxalate crystals,
latex)/ food
Cytoskeleton

network of protein fibres extendg thru’
cytoplasm

structural support, control cell movement
(white
blood cells carrying out phagocytosis,
movement by amoeba, muscle cell
contraction), anchorage for organelles and
directs their movement within cell
(vesicles move from ER to Golgi)
1. Microtubules
- hollow tubes of protein tubulin
- responsible for beating of flagella, cilia
- help separate chromosomes during cell
division
- microtubules grow out from centrosome,
the
microtubule organizing center of cell
2. Microfilaments
- 2 intertwined strands of protein actin
- contraction of muscle cells
- allows animal cell division (cleavage
furrow)
3. Intermediate Filaments
- diverse proteins within keratin family
- anchorage (e.g. cage of 3 nucleus sits in)
Centrioles

pair of cylindrical structures positioned at
right angles

(each) 9 triplets of microtubules in a ring

found within centrosome region, near
nucleus

centrioles replicate, move to opp. ends of
cell

found in animal/ lower plants.
(X plants w seed pdtn)
nuclear divisioin, organize icrotubules
on which chromosomes move
Endocytosis: Uptake of material by cell; small
part of plasma membrane folds inwards,
pinches off from rest of membrane, leaving a
vesicle (containing engulfed material) inside
cell.
Eukaryotic cell: Cell with membrane bound
nucleus and membrane-bound organelles,
includes plants and animal cells.
Hgih Plants: Plants that produce seeds,
including anglosperms (flowering plants).
Lower plants include ferns and mosses (spores)
Prokaryotic Cell: Cell lacking a membrane
bound nucleus and membrane-bound
organelles (bacteria and archaea).