Download PR EUK CELL - Bioenviroclasswiki

IB BIOLOGY
2.3 EUKARYOTIC CELLS
2.3.1 Draw and label a diagram of the ultrastructure of a liver cell as
an example of an animal cell
http://www.youtube.com/watch?v=NiiLS_ovLwM&feature=related
video on eukaryotic cell.
2.3.2 Annotate the diagram from 2.3.1 with the functions of each
named structure
Organelles of eukaryotic cells
Common organelles include the following









Endoplasmic reticulum
Ribosomes
Lysosomes ( not usually in plant cells)
Golgi apparatus
Mitochondria
Nucleus
Chloroplasts
Centrosomes
Vacuoles
Cytoplasm
All eukaryotic cells have a region called the cytoplasm that occurs
inside the plasma membrane or the outer boundary of the cell. It is
in this region that the organelles occur.
Endoplasmic reticulum
The endoplasmic reticulum (ER) is an extensive network of tubules
or channels that extends almost everywhere in the cell from the
nucleus to the plasma membrane. The ER is of two types: smooth
and rough.
Smooth ER does not have any of the organelles called ribosomes on
its exterior surface. Rough ER has ribosomes attached to it.
Functions of RER
Helps in the synthesis of proteins.
Functions of SER
 Production of membrane phospholipids and cellular lipids
 Production of sex hormones such as testosterone and
estrogen
 Detoxification of drugs in the liver
 Storage of calcium ions needed for contraction in muscle
fibres.
 Transportation of lipid based compounds.
 To aid the liver in releasing glucose into the bloodstream
when needed.
Ribosomes
Ribosomes carry out protein synthesis in the cell. These
structures may be found free in the cytoplasm or maybe
attached to the surface of the endoplasmic reticulum.
They are always composed of a type of RNA and protein.
Lysosomes
Lysosomes are intracellular digestive centres that arise from the
Golgi apparatus.
The lysosomes lack any internal structures. They are sacs
bounded by a membrane that contains as many as 40 different
enzymes. These enzymes are hydrolytic and catalyze the
breakdown of proteins, nucleic acids, lipids and carbohydrates.
Functions:
Lysosomes fuse with the old or damaged organelles from within
the cell to break down so that recycling of the components
occur.
Lysossomes are also involved with the breakdown of materials
that are brought into the cell by phagocytosis.
The interior of a functioning lyssome is acidic which is suitable
for the enzymes to hydrolyse large molecules.
The newly formed lysosome is called the primary lysosome and
when it fuses with the food vacuole it is called the secondary
lysosome.
Golgi apparatus.
The Golgi apparatus consists of flattened sacs called cisternae
which are stacked upon one another .
Functions
This organelle functions in collection, packaging, modification,
and distribution of materials synthesized in the cell.
The side of the apparatus near ER is called the cis side. It
receives products from ER. These products move into the
cisternae of the Golgi apparatus. Movement then continues to
the discharging or opposite side, the trans side.
Small sacs called the vesicles can be seen coming off the trans
side. These vesicles carry modified materials to wherever they
are needed inside or outside the cell.
This organelle is prevalent especially in glandular cells such as
those in the pancreas, which manufacture and secrete
substances.
Mitochondria
Mitochondria are organelles that carry out cellular respiration in
nearly all eukaryotic cells, converting the chemical energy of foods
such as sugars to the chemical energy of a molecule called ATP(
Adenosine triphosphate).
Because of this the mitochondrion is often called the “cell
powerhouse”
Mitochondria are rod shaped organelles that appear throughout the
cytoplasm.
They have their own DNA. It also produces and contains its own
ribosomes.
They have a double membrane. The outer membrane is smooth, but
the inner membrane is folded into cristae.
Inside the inner membrane is a semi-fluid substance called matrix.
An area called inner membrane space lies between the two
membranes.
The cristae provide a huge surface area for the chemical reactions
(cellular respiration) to occur.
Cells that have high energy requirements, such as the muscle cells,
have large number of mitochondria.
.
An area called inner membrane space lies between the two
membranes.
The cristae provide a huge surface area for the chemical reactions
(cellular respiration) to occur.
Cells that have high energy requirements, such as the muscle cells,
have large number of mitochondria.
Mitochondria are organelles that carry out cellular respiration in
nearly all eukaryotic cells, converting the chemical energy of foods
such as sugars to the chemical energy of a molecule called ATP(
Adenosine triphosphate).
Because of this the mitochondrion is often called the “cell
powerhouse”
Mitochondria are rod shaped organelles that appear throughout the
cytoplasm.
They have their own DNA. It also produces and contains its own
ribosomes.
They have a double membrane. The outer membrane is smooth, but
the inner membrane is folded into cristae.
Inside the inner membrane is a semi-fluid substance called matrix.
An area called inner membrane space lies between the two
membranes.
The cristae provide a huge surface area for the chemical reactions
(cellular respiration) to occur.
Cells that have high energy requirements, such as the muscle cells,
have large number of mitochondria.
Electron micrograph of mitochondria.
Nucleus
Nucleus is bounded by a double membrane referred to as the
nuclear envelope. This membrane allows compartmentalization
of the eukaryotic DNA, thus providing an area where DNA can
carry out its functions and not be affected by processes
occurring in other parts of the cell. The nuclear membrane does
not provide complete isolation as it has numerous pores that
allow communication with the cell’s cytoplasm/
The DNA of eukaryotic cells often occurs in the form of
chromosomes. Chromosomes vary in number depending upon
the species.
Chromosomes carry all the information necessary for the cell to
exist.
DNA is the genetic material of the cell. It enables certain traits to
be passed to the next generation.
When the cell is not in the dividing process, the chromosomes
are not present as visible structures. The DNA is in the form of
chromatin. Chromatin is formed of strands of DNA and proteins
called histones.
Within the nucleus is nucleolus.
Function
Molecules of the cell ribosomes are manufactured in the
nucleolus.
Chloroplast
CHLOROPLAST:
Chloroplasts occur in plant cells.
The chloroplast contains a double membrane. The space enclosed by
the inner membrane, contains a thick fluid called stroma .
The chloroplast contains its own DNA and 70S ribosomes.
The interior of the chloroplast includes the grana, the thylakoids, and
the stroma.
The granum is composed of numerous thylakoids stacked like a pile of
coins.
The thylakoids are flattened sacs with components necessary for the
absorption of light.
Stroma contains many enzymes and chemicals necessary to complete
the process of photosynthesis.
Chloroplasts are capable of reproducing independently of the cell.
Function: Involved in the process of photosynthesis and helps in the
conversion of light energy to chemical energy stored in sugar
molecules.
Centrosome:
It occurs in all eukaryotic cells. It consists of a pair of centrioles
at right angles to one another.
Higher plant cells produce microtubules even though they do not
have centrioles.
The centrosome is located at one end of the cell close to the
nucleus.
Functions
These centrioles are involved in assembling microtubules which
are important to the cell in providing structure and allowing
movement.
Microtubules are important to cell division.
Vacuoles
Vacuoles are large storage organelles that usually form from the
Golgi apparatus. They are membrane bound organelles and
occupy a very large space inside the cells of most plants.
Functions
They store a number of different substances including potential
food, metabolic wastes and toxins to be expelled from the cell,
and water.
Vacuoles enable cells to have higher surface are to volume ratios
even at larger sizes.
In plants they allow an uptake of water that provides rigidity for
the organism.
2.3.3. Identify structures from 2.3.1 in electron micrographs of liver
cell
Electron micrograph of a liver cell
Look at electron micrographs in the internet to understand labeling.
2.3.4 Compare prokaryotic and eukaryotic cells
Feature
Type of genetic
material
Prokarytoic cells
A naked loop of DNA/
DNA in a ring form
without protein
Eukaryotic cells
Chromosomes
consisting of strands
of DNA associated
Location of genetic
material
In the cytoplasm in a
region called the
nucleoid/ DNA free in
the cytoplasm
Mitochondria
Ribosomes
Internal membranes
No mitochondria
Small sized- 70S
Few or none are
present
Size
0.5 – 1.0 micrometers
with protein.
In the nucleus inside a
double nuclear
membrane called the
nuclear envelope/DNA
enclosed within a
nuclear envelope
Always present
Larger sized -80S
Many internal
membranes that
compartmentalize the
cytoplasm including
ER, Golgi apparatus,
lysosomes
Size more than 10
micrometers.
2.3.5 State three differences between plant and animal cells.
Feature
Cell wall
Chloroplast
Vacuole
Plant cells
Cell wall and plasma
membrane are
present.
Chloroplasts are
present in the
cytoplasm.
Large fluid-filled
vacuole often present
Animal cells
No cell wall, only a
plasma membrane is
present.
There are no
chloroplasts
Not usually present
polysaccharide
Shape
Centriole
Store carbohydrate as
starch.
Fixed shape, usually
rather regular.
Do not contain
centriole within a
centrosome area
Store carbohydrate as
glycogen.
Able to change shape.
Usually rather regular.
Contain centriole
within a centrosome
area.
2.3.6 Outline two roles of extracellular components
Extracellular components and their functions:
The plant cell wall maintains cell shape, prevents excessive water
uptake, and holds the whole plant up against the force of gravity.
Cell wall protects the plants and provide the skeletal support that
keep plants upright on land. It consists of fibres of polysaccharide
cellulose embedded in a matrix of other polysaccharides and
proteins.
Because of its rigidity, it only allows only a certain amount of water
to enter the cell. In plants, when adequate amount of water is inside
the cell, there is pressure against the cell wall. That pressure helps
to support the plant’s upright position.
Cell
Bacteria
Fungi
Yeasts
Algae
Plants
Animals
Outermost part
Cell wall of peptidoglycan
Cell wall of chitin
Cell wall of glucan and mannan
Cell wall of cellulose
Cell wall of cellulose
No cell wall; plasma membrane
secretes a mixture of sugar and
proteins called glycoproteins
that forms the extracellular
matrix.
Animal cells secrete glycoproteins that form the extracellular
matrix. This functions in support, adhesion and movement. This
layer helps hold cells together in tissues and can have protective
and supportive functions.
The extracellular matrix (ECM) of many animal cells is composed
of collagen fibres plus a combination of sugars and proteins called
glycoporteins. These form fibre-like structure that anchor the
matrix to the plasma membrane. This strengthens the plasma
membrane and allows attachment between adjacent cells.
The ECM allows for cell-to-cell interaction, and bringing about coordination of cell action within the tissue.
ADDITIONAL INFORMATION
CYTOSKELETON:
Eukaryotic cells contain a network of protein fibers, collectively called
the cytoskeleton, extending throughout the cytoplasm.
Functions: they provide structural support, and are involved in various
types of cell movement.
Three main types of fiber make up the cytoskeleton:
Microfilament(the thinnest type of fiber)
Microtubules ( the thickest type pf fiber)
And Intermediate filaments.
Microfilaments, also called actin flilaments. It is made of globular
protein called actin. Present inside the plasma membrane and helps
support cell’s shape. It interacts with other kinds of protein filaments to
make cells contract.
Intermediate filaments are made of fibrous proteins and have a rope
like structure.
Function: reinforcing cell shape and anchoring certain organelles, for
example nucleus is held in place with the help of intermediate
filaments.
Microtubules are straight hollow tubes composed of globular proteins
called tubulin.
Functions: Provide rigidity and shape.
Provide anchorage for organelles and to act as tracks for organelle
movement within the cytoplasm. Lysosomes might move along a
microtubule to reach a food vacuole.
Guide the movement of chromosomes when cells divide
CILIA AND FLAGELLA:
Cilia are short and numerous appendages that helps in movement in
organisms such as Paramecium.
Flagella are longer, generally less numerous appendages seen in
protists such as Euglena
Cilia lining the upper respiratory tract in multicellular organisms.
Flagellum on a sperm cell.
Both flagella and cilia are composed of microtubules wrapped in an
extension of the plasma membrane. A ring of nine microtubules
doublets surrounds a central pair of microtubules. This arrangement
seen in cilia and flagella is called 9+2 pattern.
The anchoring structure is called a basal body.
Bending movement of cilia/flagella involves protein called dynein
arms that are attached to each microtubule doublet.
Dynein arms are powered by ATP, move neighbouring doublets of
microtubules relative to one another. Because they are anchored
within the organelle, the doublets bend instead of sliding past one
another.
CELL WALL:
Cell wall protects the cells in plants and provide the skeletal support
that keeps plants upright on land.
Plant cell wall consists of fibers of the polysaccharide cellulose
embedded in a matrix of other polysaccharides and proteins.
Cell walls are multilayered.
Between the walls of adjacent cells is a layer of sticky polysaccharide
that glues the cells together.
Cell walls of certain plants are made of lignin.
Plasmodesmata channels between adjacent plant cells. It forms a
communicating system connecting the cells in plant tissues. Plasma
membrane and the cytoplasmic fluid of the cells extend through the
plasmodesmata, so that water and other molecules can readily pass
from cell to cell.
It helps the cells of the plants to share water, nourishment and
chemical messages.
Animal cells do not have cell wall but most of them secrete a sticky
layer of glycoprotein called the extracellular matrix.
These form fibre-like structures that anchor the matrix to the plasma
membrane. This strengthens the plasma membrane and allows
attachment between adjacent cells.
Researchers have discovered that ECM helps regulate cell behavior,
probably through contact with proteins in the plasma membrane.
Adjacent cells in many animal tissues also connect by cell junctions.
There are three general types.
Tight junction: Binds cells together, forming a leak proof sheet. It is
seen lining the digestive tract, preventing the contents from leaking
into the surrounding tissues.
Anchoring junctions:
Rivet cells together with cytoskeletal fibers, forming strong sheets.
Seen in skin and heart muscle.(stretching and mechanical stress )
Gap junctions: They allow small molecules to flow between
neighboring cells. For example, flow of ions through gap junctions in
the cells of heart muscle coordinates their contraction.