Download Main differences between plant and animal cells: Plant cells have

Main differences
between plant and
animal cells:
Plant cells have: cell
walls, a large central
vacuole, plastids and
turgor pressure.
Animal cells have a
lysosome (related to
vacuole) and centrioles
(function in organizing
microtubules).
The Cell Wall
The primary cell wall is capable of rapid expansion during growth.
The secondary cell wall is deposited within the primary cell wall after
the cell reaches mature size.
From Biochemistry & Molecular Biology of Plants, Buchanan, Gruissem and Jones
Some cells have thick secondary walls such as stone cells in coconut shells (b)
Cell wall components:
Cellulose - a polysaccharide composed of 1,4-linked β-D-glucose
residues. Synthesized in the plasma membrane by cellulose synthase.
Hemicellulose - branched polysaccharides that are structurally
homolgous to cellulose because they have a backbone composed of
1,4-linked β -D-hexosyl residues (mannose, galactose, xylose, etc).
Synthesized in the Golgi.
Pectin - a family of complex polysaccharides that all contain 1,4-linked
α-D-galacturonic acid. Synthesized in the Golgi.
Structural proteins : hydroxyproline-rich glycoproteins (HRGPs),
proline rich proteins (PRPs) and glycine-rich proteins (GPGs).
Synthesized at rough endoplasmic reticulum (RER), modified
in the Golgi.
From: The Complex Carbohydrate Research Center http://www.ccrc.uga.edu
Plasma membrane serves as a semi-permeable barrier. Transporters (pumps,
channels, etc.) control what crosses the membrane.
Extracellular environment
Some are glycosylated
PHOSPHOLIPID
BILAYER
PUMPS AND
CHANNELS
Cytoplasm
The PM is the outermost surface of the protoplast.
SENSORY PROTEINS
RECEPTORS
STEROL
Cellulose synthase
is an integral
membrane protein
that uses cytosolic
UDP-glucose as a
substrate to
synthesize
cellulose that it
deposits
extracellularly.
Other cell wall components such as hemicellulose and pectin are synthesized in the
Golgi and delivered to the cell wall by exocytosis.
Exocytosis: fusion of a vesicle with the cell membrane, releasing the contents
of the vesicle to the cell exterior.
How do proteins get from the cytoplasm into the lumen of the ER? They are
translocated across the membrane either post translationally or co-translationally.
Then they can enter the secretory pathway.
ER, Endoplasmic Reticulum
- synthesis of the endomembrane
system (lipid synthesis)
- protein synthesis (on RER):
both membrane proteins and
soluble proteins
-  oil body synthesis, protein body
synthesis
-  ER is continuous with the
nuclear envelope
- ER is continuous through
plasmodesmata
-  RER has associated Ribosomes
that translate mRNA into protein
Plasmodesmata, connections between plant cells.
E.R. lumen
E.R.
plasma
membrane
Cytoplasm
Cell wall
plasmodesmal
proteins
Cytoplasm
Plasmodesmata connect the cytoplasm of adjacent cells,
the continuous cytoplasm is called the symplast.
The space outside of cells is called the apoplast or cell
wall space.
one pore
nuclear envelope
1 µm
0.2 µm
lipid bilayer facing
the nucleoplasm
nuclear
lipid bilayer facing
envelope the cytoplasm
pore complex that
spans both bilayers
Fig. 3-8, p. 37
Golgi (also called dictyosome):
- synthesis of cell wall polysaccharides
(you should know which ones)
- glycosylation of proteins
- preparation of secretory vesicles
destined for the plasma membrane
Camillo Golgi (1843-1926) was an Italian
cell biologist and microscopist who was the first to
identify the Golgi apparatus in 1898.
Proteins that are destined for the plasma
membrane are synthesized on rough ER
(RER) then can modified in the Golgi,
packaged into secretory vesicles and
sent to the PM.
Soluble secreted proteins are generally
synthesized on RER, inserted in to the
lumen of the ER, and then sorted to the
PM in secretory vesicles.
Cell Wall Polysaccharides
(hemicellulose, pectin) are synthesized in
the Golgi and sorted to the PM for
secretion.
Vacuoles
- vacuoles allow plant cells to be large (without making a large volume of cytoplasm).
-  storage of ions, sugars, amino acids, etc.
- digestion, the vacuole is analogous to the animal lysosome and contains proteases,
nucleases, glycosidases, lipases etc.
-  defense, sequestration of toxic compounds, pigments (flower color).
Figure 3.16: Vacuole pigments in petals.
The Cytoskeleton – two types of protein fibers: actin microfibers and microtubules.
They function in moving things around in cells.
Microtubules: composed of α and β
tubulin.
Actin microfibers composed of G-actin
Motor proteins use the energy of ATP hydrolysis to move directionally on
the cytoskeleton.
Myosin is a motor protein that moves
on actin microfibers.
Kinesin and Dynein motor proteins
move in different directions on
microtubules.
Example: actin functions in chloroplast orientation in response
to light quality.
Dim light
Bright light
Movie S1, Related to Figure 1. Chloroplast Movements in Response to a Blue-Light
Microbeam in Wild-Type Arabidopsis and thrumin1-1 Mutants. During exposure to a
blue-light microbeam (blue circle), chloroplasts (red) in wild-type mesophyll cells moved
away from the light and returned after the microbeam was turned off. Chloroplast
movement was impaired in the thrumin1-1 mutant in response to microbeam treatment.
Chloroplast structure
two outer
membranes
thylakoids
stroma
Mitochondria and chloroplasts are semi-autonomous:
- both divide by fission
- both contain circular chromosomal DNA, located in nucleoids
within the stroma/matrix.
- they contain ribosomes, tRNAs, etc.
- they depend on the import of nuclear encoded proteins
for many functions.
Chloroplast structure
A chloroplast
Close-up of stacked thylakoids and starch granules in the stroma.
Chloroplasts are one type of plastid
Dividing mitochondrion
Chloroplasts: function in photosynthesis: light reactions, dark reactions.
Starch synthesis and storage, chlorophyll and fatty acid synthesis.
Mitochondria: Main function is respiration (conversion of energy stored in
sugars to energy stored in ATP).