Download Cell Structure PPT Part 2

The
Structure of
Cell:
Part II
Plastids
Plastids
• Chromoplasts
–Chloroplasts
responsible for
photosynthesis.
• Leukoplasts responsible
for storage of starch.
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Structure of Chloroplast
Chloroplasts have three
membranes. The outer
two are smooth and the
inner one makes stacks of
thylakoids or grana. The
chlorophyll and other
pigments are found in the
thylakoid membrane
where light energy is
converted into chemical
energy.
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Thylakoid
A stack of
thylakoids is a
granum. The matrix
found around the
thylakoid is called
the stroma. It
contains enzymes
for carbohydrate
synthesis.
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Ribosomes
Ribosomes are workbenches for
protein synthesis. They are made
from rRNA and proteins to form
two subunits. They do not
contain any membranes. Cells
can have thousands.
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Evolution of
Organelles
The endomembrane
system includes all
the organelles that
are derived from one
another, or are
continuous with one
another.
They have evolved from the folding in of the plasma
membrane over time. The membrane system includes the
nucleus, the E.R., the Golgi apparatus and the lysosomes.
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The Endomembrane System
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The Cytoskeleton
Gives the cell shape
Movement of organelles
Cytoplasmic streaming in plant cells
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Microtubules
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Cilia and
Flagella
Flagella and cilia are composed of ( 9 double + 2
single ) microtubules .
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Movement of Flagella
and Cilia
Both flagella and
cilia are covered
with the plasma
membrane.
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Difference Between Flagella and Cillia
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Centrioles and
Microtubules
Centrioles are
microtubule
organizing centers for
animal cells.
They are constructed
of nine triplet
microtubules.
Basal bodies anchor
cilia and flagella.
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Microfilaments
Microfilaments are made
from two intertwined
strands of actin subunits.
They are thinner than
microtubules.
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Muscle Contractions and Cytoplasmic Streaming
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Intermediate Filaments
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Cell Walls
Most cells have materials external to the
plasma membrane.
Cell walls are found in prokaryotes, plants,
fungi and some protists.
Cell walls of plants are made of cellulose;
in fungi they are made of chitin; in
prokaryotes they are murein (or muramic
acid) and in protists they vary.
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Plasmodesmata
Plasmodesmata are
channels between
plant cells that allow
direct flow from one
cell’s cytoplasm to
the cytoplasm in
adjacent cells.
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Glycocalyx or Extracellular Matrix
Animal cells lack cell walls but have an extra cellular matrix
(ECM) or glycocalyx. The ECM is made of glycoproteins such as
collagen, proteoglycan, and fibronectins. These glycoproteins
are connected to receptor proteins in the cell membrane called
integrins. Used for support, adhesion, movement and identity.
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Animal Cell Junctions
• There are several types of
intercellular junctions in animal cells
• Tight junctions- membranes of
neighboring cells are pressed
together
• Desmosomes-(anchoring junctions)
fasten cells together into strong
sheets
• Gap junctions-(communicating
junctions) provide cytoplasmic
channels between adjacent cells like
plasmodesmata in plant cells
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