Cell Organelles
Chapter 4
II Part
Cell walls
•
•
The exterior surface cells of some plants,
mushrooms and some protists have cell
walls.
Cell walls are made of polysaccarides like
cellulose and quitin.
– The cell walls support and protect the cells.
Since they are porous and fragile.
Cell walls
•
Cell walls can have several layers:
– The primary cell wall is in the extreme
exterior.
– The secondary cell walls are in the middle
between the primary cell wall and the plasma
membrane.
– The primary cell walls bond to each other by
intermediate lamella.
Plant cells
Cytoskeleton
• The cytoskeleton forms a proteic fiber net
inside the cytoplasm.
– It is composed of microtubules (thinner),
intermediate filaments and microfilaments
(thicker).
Cytoskeleton
Cytoskeleton
Cytoskeleton
• Main functions:
– Cell shape.
– Cell movement (examples: sperm cells or
contracting muscle cells).
– Organelle movement during endocytosis
(when large particles are engulfed by the
plasma membrane and pull the vesicles into the
cell) and exocytosis (vesicles budded off the
endoplasmic reticulum or Golgi apparatus).
– Cell division. In eukaryotic cells microtubules
move the chromosomes and separate them. In
animal cell division help the centrioles move.
Cilia and flagella
• They both are thin extensions of the plasma
membrane.
• They both surge from a basal body. Basal
bodies surge from centrioles.
• Cilia are numerous and smaller (10-25
microns).
• Flagella are unique and longer (50-75
microns).
Cilia and
flagella
Cilia and flagella
• Microtubules slide together (using ATP),
creating cillia and flagella´s movement.
• Functions:
– Cilia and flagella can move the cell or create
liquid currents arround the cell.
– Cilia rows resembling the arm of a swimmer
doing the breast stroke. (movement-cleaning)
– Flagella moves in a wavelike motion and helps
straight ahead movement.
Nucleus
• The nucleus has 3 main parts:
– Nuclear envelope
– Cromatin
– Nucleolus
Nucleus
• The nuclear envelope separates
chromosomes from the cytoplasm.
– It consists of a double membrane that has
nuclear pores to transport organic and
inorganic molecules (water, ions, proteins,
ribosome pieces and RNA).
– The exterior nuclear membrane has
ribosomes attached to it.
Nucleus
Nucleus
Nucleus
• The nucleus has DNA in different
presentations:
– As chromosomes easily seen with
microscope light. Are composed of genes and
provide the molecular code for a huge variety
of proteins.
– As cromatin directs DNA´s reactions with
RNA messenger to synthesize proteins.
Chromosomes and cromatin
Nucleus
• The region inside the nucleus that is
usually seen in a darker color is called the
nucleolus.
– The nucleolus is the place where ribosomes
are synthesized.
– Ribosomes synthesize proteins (amino acids).
Ribosomes
Membrane system
• The membrane system includes the plasma
membrane and other organelle membranes.
• Examples of organelles that have
membranes: nucleus, endoplasmic
reticulum, Golgi apparatus, lysosomes,
vesicles and vacuoles).
Membrane system
• The plasma membrane isolates the cell
and allows the transport regulation.
Membrane system
• The vesicles transport the membranes and
its content between the separated regions of
the membrane system (transport capsules).
• The ER forms channels inside the
cytoplasm.
• There are 2 kinds of ER:
– smooth
– rough
Endoplasmic reticulum
ribosomes
vesicles
Endoplasmic reticulum
Membrane system
• The Smooth Endoplasmic Reticulum (SER) has
no ribosomes.
• Functions:
• It has enzymes that eliminate the toxicity of certain
drugs (in the liver).
• It manufactures large quantities of lipids such as
steroid hormones made from cholesterol. Ex: sex
hormones in mammalian reproductive organs.
• It synthesizes lipids.
• It stores calcium ions.
vesicles
Smooth endoplasmic reticulum
Membrane system
• The Rough Endoplasmic Reticulum (RER) has
ribosomes attached to its exterior.
Functions:
– It produces proteins like digestive enzymes and
hormones.
– For example insulin (hormone that helps
metabolic utilization of nutrients, mainly with
carbs) Lack of it causes diabetes and too much
insuline causes hypoglycemia.
– It produces all the components of new
membranes.
Rough endoplasmic reticulum
Membrane system
•
The Golgi apparatus is a stack of flattened that
are connected to each other.
• Functions:
– It gets proteins from the ER through the
vesicles and classifies them.
– It modifies certain molecules. Example:
proteins into glycoproteins. Glycoproteins are
composed of 1 protein and carbohydrates.
– It packs material into vesicles to export it.
Golgi apparatus
The ER sends
vesicles with proteins
to the Golgi
apparatus.
Golgi apparatus
The modified proteins
leave the Golgi
apparatus inside other
vesicles.
Membrane system
•
What happens with substances that are
produced by the membrane system?
1. Option 1: The proteins that are secreted by
the RER, travle through the Golgi apparatus,
and are then exported by the plasma
membrane.
– On Figure 4-14 you can watch the process by
which antibodies (proteins produced by white
globules) attach to strange organisms and destroy
them.
FIGURA 4-14
How a protein
is synthesized
and exported?
Membrane system
2. Option 2: The digestive proteins produced by
the RER, travel through the Golgi apparatus
and are packed like lisosomes to be used by
the cell.
• The lisosomes mix with the food vacuoles
and digest the food into basic nutrients.
FIGURA 4-15
Lisosome and
food vacuole
synthesis and
fusion.
Memebrane system
3. Option 3: The proteins and lipids that are
produced in the ER flow through the Golgi
apparatusand enlarge the plasma membranes
and the organelle membranes.
Vacuoles
They are cellular membrane bags that
contain certain fluids.
• Functions:
– The sweet water organism´s contractile
vacuoles drain water.
Contractile vacuoles
Vacuoles
• Functions:
– The plant central vacuoles:
• They participate in the hydric equilibrium in
the cell.
• They store wastes, nutrients or toxic
pigments.
• They provide the turgent or turgor pressure
in the cytoplasm to keep the cell rigid.
Mitochondria
• The mitochondrias are rounded, oval or
tubular organelles that have a pair of
membranes.
– The interior membrane forms deep folds called
cristae.
– The intermembrane compartment is located
between the outer and inner membranes.
– The matrix is found between the interior
membrane folds.
Outer
membrane
Inner
membrane
Intermembrane
compartment
matrix
cristae
Mitochondria
Mitochondria
• The endosymbiotic hypothesis states that
mitochondria could have evolved from
prokaryotic bacteria.
Mitochondria
• They work like power plants inside the cell.
– Mitochondria extract energy from the food
molecules.
– This energy is stored like ATP.
– The process of energy extraction implies
anaerobic and aerobic reactions.
Chloroplasts
• The chloroplasts are specialized
organelles surrounded by a double
membrane:
- The outer membrane.
– The inner membrane; which locks a liquid
called stroma.
• The bunch of membrane empty and
interconnected sacks (granum) are inside
the stroma. They are called thylakoids.
Chloroplast
Outer
membrane
Inner membrane
stroma
thylakoid
Thylakoid
interconnect
ing channel
Granum
1 micra
Chloroplast
Chloroplasts
• The tilacoid membranes contain chlorophil
and other light-capturing pigments that
capture the Sun light and synthesize sugar
from CO2 and water (fotosynthesis).
Outer
membrane
Inner membrane
stroma
thylakoid
Channel
Granum
Chloroplast
Plastids
•
Plastids are found only in plants and
photosynthetic protists.
•
They are surrounded by a double
membrane.
Plastids
•
Functions:
– They store starch (synthesized from sugars
that were produced during photosynthesis).
– They store the molecules from the pigments
that give fruits their color.
Plastid
What are the major features of
prokaryotic cells?
– They are very small < 5 microns long.
– They have specialized surface features.
– They have less specialized structures in their
cytoplasm.
– They usually have a rigid cell wall.
Prokaryotic cells
Chromosome
Cell wall
Plasma
membrane
ribosomes
capsule
Prokaryotic cells
Prokaryotic cell
•
•
•
They do not have a defined nucleus and
many other organelles.
Some of them move because they have
a flagella.
Some common shapes are: rod, sphere
or helix.
Prokaryotic cells
•
Bacteria that infect other organisms,
posses surface features that help them
stick to specific hot tissues.
•
Examples: capsules, slime layers and
pili (made of polyssacharides).
Prokaryotic
cells
Prokaryotic cells
•
They have only 1 chromosome
composed of one long DNA fiber.
– This chromosome is located in the central
region of the cell (nucleoid region).
•
They also have small DNA rings called
plasmids (cytoplasm).
Prokaryotic cells
•
•
Some photosynthetic bacteria have
internal membranes with light-capturing
proteins and enzymes that catalyze the
synthesis of high-energy molecules.
Bacteria cytoplasm may contain
ribosomes (contain proteins) and food
granules that store energy-rich
molecules.
Prokaryotic cell
Photosynthetic
membrane