Download Plant Cell

Sources:
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lectures_f04am.htm
Lecture 6& 7 – Cell – structure and function
http://biology.tutorvista.com/animal-and-plant-cells/organelles.html
http://creationwiki.org/Cellular_organelle
http://www.ivyroses.com/Biology/Organelles/Organelle-Functions.php
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Plant Cell
Plant cells are eukaryotic cells or cells with membrane bound nucleus.
Generally, plant cells are larger than animal cells and are mostly similar in size and
shape. Most often they have a cube , polygonal shape - full all interior spaces
(parenchyma cells) or elongated cells with tapering ends - perform conductive and
roof function – prosenchyma cells. Plant cells are similar to animal cells in being
eukaryotic and they have similar cell organelles.
What is a Plant Cell?
Plant cells are eukaryotic cells i.e., the DNA inside the nucleus.
The most important distinctive structure of plant cell is the presence of the cell wall
- outside the cell membrane, vacuole and plastids.
Diagram of Plant Cell
Distinctive Features of Plant Cell
The features that are distinctive in plant cells are as follows:
 The cell wall forms the outer lining of the cell, with function to provide and
support rigidity.
 Plastids help in storage of plant product, participate in pollination and
reproduction - Exp: Chloroplasts aid in carrying out the process of
photosynthesis to produce food for the plants.
 Vacuoles are water-filled, membrane bound organelles which stores useful
materials.
Plants have specialized cells in order to perform certain functions for the
survival of plants . Some cells manufacture and store organic molecules, others
transport nutrients throughout the plant.
Some specialized plant cells include: parenchyma cells, collenchyma cells,
sclerenchyma cells, water conducting cells and food conducting cells. Plants cell
constitute of membrane bound nucleus and many cellular structures. These
organelles carry out functions that are necessary for the proper functioning and
survival of the cell. The cell organelles of the plant are enclosed by a cell wall and
cell membrane. The constituents of the cell are suspended in the cytoplasm or
cytosol.
The parts of the plant cell are as follows:
Cell wall is the outermost rigid covering of the plant cell. It is a salient
feature of plant cell.
Cell membrane or the plasma membrane is the outer lining of the cell inside
the cell wall.
Plants cells also contain many membrane bound cellular structures. These
organelles carry out specific functions necessary for survival and normal operation
of the cells.
There are a wide range of operations like producing hormones, enzymes, and
all metabolic activities of the cell.
Cytosol or cytoplasm is the gel-like matrix inside the cell membrane which
constitutes all other cell organelles.
Nucleus is the control center of the cell. It is a membrane bound
structure which contains the hereditary material of the cell - the DNA
Chloroplast is a plastid with green pigment chlorophyll. It traps light energy
and converts it to chemical energy by the process of photosynthesis.
Mitochondria carries out cellular respiration and provides energy to the cells.
Vacuoles are the temporary - временни storage center of the cell.
Golgi body is the unit where proteins are sorted and packed.
Ribosomes are structures that assemble- сглобяват, монтират proteins.
Endoplasmic reticulum are membrane covered organelles that transport materials.
Plant Cell Structure and Function
All parts of the plant play a significant role in the proper functioning of the cell.
Unlike animals, plant cells are surrounded by a rigid cell wall.
Plant organelles - Summary
Organell type
Nucleus
Mitochondria
Chloroplasts
Endoplasmic
reticulum : rough
Endoplasmic
reticulum : smooth
Golgy apparatus
Components
Function
Double membrane organelles
Nucleolus
Ribosome subunit assembly
Nuclear lamina
Structural support
Chromosomes
Iunformation
storage
and
trasmission
Enzymes that harvest energy ATP production - oxidative
from molecules to make phosphorylation
ATP
Pigments and enzymes thet Production of sugars via
use light energy for sugars photosynthesis
–
making
photosinthetically
phosphorylation
One membrane organelles
Network of branching sacs;
Protein
synthesis
and
Ribosomes associated
processing
Network of branching sacs;
Lipid synthesis and processing
Enzymes for synthesizing or
breaking down lipids
Stack of flattened, distinct Protein, lipid and carbohydrate
Lysososmes*
Vacuoles
Peroxisomes
(in motochondria)
Plasma membrane
Ribosomes
Cytoskeleton
Cell wall
cisternae
Acid hydrolases (catalyze
hydrolysis reactions)
Contains
transporters for
selected molecules
processing
Digestion
and
recycling,
conteins protein pumps
Varies – coloration,storage of
oils, carbohydrates, water or
toxins
Contains enzymes, thet Oxidation of faty acids, ethanol
catalyze oxidation reactions or other compounds
Phospholipid bilayer with Selective
permeability
–
transort and receptor proteins maintains
intracellular
environmenmt
Non membraned organelles
Complex of RNA and Protein synthesis
proteins
Actin filaments, intermediate Structural support; movement
filaments and microtubutles of materials
Carbochydrate
fibers Protectio9n, structural support
running
trought
carbochydrate or protein
matrix
Lysososmes * - in plants there no found typical lysososmes (one membraned structures) , but in
plant vacuole (or in extracellular spaces, and in other organelles) were found are enzymes with
lytic activities - proteases, nucleases, phosphatases, and other degradative enzymes. Plant
vacuoles were therefore seen as fulfilling the role of the animal lysosomal system (Boller and
Wiemken 1986; Matile 1978 ; Wink 1993. This is just one paper of many reporting plant cell
lysosomes. The first such report appeared more than 30 years ago: Matile (1968) "Lysosomes of
root tip cells in corn seedlines." Planta 79: 181-196.
Protoplasm
Protoplasm refers to the living content that animals and vegetable cells are formed
of, surrounded by a plasma membrane (the outer surface of a cell; aka cell
membrane). A cell is the smallest, most basic unit of life, that is capable of existing
by itself. Protoplasm is sometimes used as a term term for all of the materials found
inside a cell. In eukaryotes (organisms whose cells contain complex structures
inside membranes), protoplasm surrounding the cell nucleus (control center) refers
to cytoplasm, a gel-like substance found inside the cell. In such cases, the
protoplasm inside the nucleus is referred to as the nucleoplasm.
Protoplasm is typically divided into cytoplasm and multiple organelles. Organelles
are a name for all of the small bodies in the cell that perform necessary roles
regarding the chemical reactions inside a cell. The liquid aspect of protoplasm is
transparent. Depending on the functional state of the cell, protoplasm can take a
liquidy and slightly gel-like form (like egg whites), a semi-solid form (like jelly), or
a solid form. The more liquid form is known as a sol. Protoplasm was once
considered a mysterious substance but nowadays it is recognized that it is made of
an assortment of small organic and inorganic molecules. Organic molecules contain
the element, carbon, whereas inorganic molecules do not. Ninety percent of
protoplasm is made up of inorganic substances such as water, inorganic salts (e.g.,
mineral salts such as sodium chloride), and gases (e.g., oxygen and carbon dioxide.
Organic substances include fat cells, amino acids, nucleic acids, and
polysaccharides (types of carbohydrates).
Chemical functions of the cell take place within the protoplasm such as
responding to environmental stimuli. The protoplasm is capable of moving
(expanding and contracting) and growing (as the cell divides). Movement of the
protoplasm is referred to as protoplasmic streaming.
Protoplasm is also known as plasmogen. The term, protoplasm, has become
relatively unpopular among biologists these days as the specific substances inside
the cell tend to be named individually. Protoplasm comes from the Greek word
"protos" meaning "first" and the Greek word "plasma" meaning "thing formed." Put
the two words together and you have "first thing formed."
The term, protoplasm, was first used by a physiologist (Jan Pukinje) in 1840
when describing the formative material of animal embryos. A physiologist is
someone who studies the functions of human organisms and their parts. An
embryo is a fertilized egg from the time of conception until the 8th week
of pregnancy. A German botanist (plant biologist), Hugo von Mohl, is often
credited with being the first to use the term protoplasm, although this is incorrect as
noted above. He did, however, describe protoplasm as a"tough, slimy, granular,
semi-fluid" material inside plant cells, distinguishing it from the wall and nucleus
of the cell and the sap within the vacuoles (sacs in the cytoplasm that are filled with
fluid). Some people state that the term protoplasm originated in 1835 with a
zoologist named F lix Dujardin but he actually referred to it as “sarcode.”
The English biologist, Thomas Huxley, later referred to protoplasm as “the
physical basis of life.” He believed that life resulted from molecules being spread
within the protoplasm. Failed attempts were made to manually reproduce it is the
laboratory to study the beginnings of life as protoplasm as it was traditionally
considered responsible for all living processes.
Cell wall: - It is located outside the cell membrane whose main function is to
provide rigidity, strength, protection against mechanical stress and infection. Cell
wall is made up of cellulose, pectins,glycoproteins, hemicellulose and lignin.
The primary cell wall is characterized by a high proportion of pectin
substances - 50-60% cellulose - 30% structural proteins - up to 10%. Rarely, it can
participate, and lignin. It is characteristic of young cells in which the celulose is
relatively small amounts. flexible and extensible and allowing the cell to grow.
Primary walls are the major textural component of plant-derived foods. The
ripening (maturating) of fruits and vegetables is associated with changes in wall
structure and composition. Plant-derived beverages often contain significant
amounts of wall polysaccharides. Some wall polysaccharides bind heavy metals,
stimulate the immune system or regulate serum cholesterol. Wall polysaccharides
are used commercially as gums, gels, and stabilizers in food industry.
However, the primary cell wall, can be defined as composed
of cellulose microfibrils aligned at all angles. Microfibrils are held together by
hydrogen bonds to provide a high tensile strength.
Gradually, the amount of cellulose and lignin increases at the expense of the
pectin so that the mature cells in the ratio between the structural components is 35 50% cellulose, 25-30% lignin, 10-25 % hemicellulose, pectin - 0%. The outer part
of the primary cell wall of the plant epidermis is usually impregnated with cutin
and wax, forming a permeability barrier known as the plant cuticle.
Deposition of lignin greatly reduces the mobility of fiber, cell wall becomes
thicker and stops growing - its formed secondary cell wall. (incorporation the lignin
betwin the fibers) . The secondary cell wall, a thick layer formed inside the primary
cell wall after the cell is fully grown . It is not found in all cell types.
The evolution of conducting tissues - xylem fibers, tracheids, and sclereids
with rigid secondary cell walls was a critical adaptive event in the history of land
plants, as it facilitated the transport of water and nutrients and allowed extensive
upright growth. Secondary walls also have a major impact on human life, as they
are a major component of wood and are a source of nutrition for livestock. In
addition, secondary walls may help to reduce our dependence on petroleum, as they
account for the bulk of renewable biomass that can be converted to fuel.
Secondary walls - especially in grasses - may also contain microscopic silica
crystals, which may strengthen the wall and protect it from herbivores.
Cells with secondary cell walls are rigid. Cell to cell communication is
possible through pits in the secondary cell wall that allow plasmodesma to connect
cells through the secondary cell walls.
Cell walls in some plant tissues also function as storage depots for
carbohydrates that can be broken down and resorbed to supply the metabolic and
growth needs of the plant. For example, endosperm cell walls in the seeds of cereal
grasses, nasturtium, and other species, are rich in glucans and other polysaccharides
that are readily digested by enzymes during seed germination to form simple sugars
that nourish the growing embryo. Cellulose microfibrils are not readily digested by
plants, however.
In contrast to animal cell division in plants starting from the middle of the
cell.
The middle lamella, a layer rich in pectins. This outermost layer forms the
interface between adjacent plant cells and glues them together and forms during the
cell division.
The middle lamella is laid down first, formed from the cell
plate during cytokinesis, and the primary cell wall is deposited inside the middle
lamella after that.
Cell Membrane (plasma membrane) - the biological membrane, which is
present in both eukaryotic and prokaryotic cell. It is also called as cell membrane as
it is works as a barrier between the inner and outer surface of a cell. In animal cells,
the plasma membrane is present in the outer most layer of the cell and in plant cell
it is present just beneath the cell wall.
Structure of Plasma Membrane
Plasma membrane can be defined as a biological membrane or an outer
membrane of a cell, which is composed of two layers of phospholipids and
embedded with proteins. It is a thin semi permeable membrane layer, which
surrounds the cytoplasm and other constituents of the cell.
Function of Plasma Membrane - it separates the contents of the cell from its
outside environment and it regulates what enters and exits the cell.
Plasma membrane plays a vital role in protecting the integrity of the interior
of the cell by allowing only selected substances into the cell and keeping other
substances out.
It also serves as a base of attachment for the cytoskeleton in some organisms
and the cell wall in others. Thus the cell membrane supports the cell and helps in
maintaining the shape of the cell.
The cell membrane is primarily composed of proteins and lipids. While lipids
help to give membranes their flexibility and proteins monitor and maintain the
cell's chemical climate and assist in the transfer of molecules across the membrane.
The lipid bilayer is semi-permeable, which allows only selected molecules to
diffuse across the membrane.
Characteristics of Plasma Membrane: The plasma membrane (cell
membrane) is made of two layers of phospholipids - a stable barrier between two
aqueous compartments., has many proteins embedded in it – act as pumps,
channels, receptors, enzymes or structural components, regulates the entry and exit
of the cell. Many molecules cross the cell membrane by diffusion and osmosis. The
lipid bilayer is a thin polar membrane made of two layers of lipid molecules. These
membranes are flat sheets that form a continuous barrier around all cells.Phospholipids - hydrophilic phosphate head - polar (water loving), and a
hydrophobic tail , consisting of two fatty acid chains - non-polar (water fearing).
Plasma Membrane Structure
Proteins in Plasma Membrane
In plasma membrane, a protein helps in providing the support and shape to the cell.
There are three types of proteins in plasma membrane, which includes:
Cell membrane receptor proteins - It helps in communication of a cell with their
external environment with the help of hormones, neurotransmitters and other
signaling molecules.
Transport proteins - It helps in transporting molecules across cell membranes
through facilitated diffusion. For example: globular proteins.
Glycoprotein - It helps in cell to cell communications and molecule transport across
the membrane.
Biological membranes typically include several types of molecules other than
phospholipids. A particularly important example in animal cells is cholesterol,
which helps strengthen the bilayer and decrease its permeability. Cholesterol also
helps regulate the activity of certain integral membrane proteins.
Other organelles:
Plastids:
Chloroplasts: It is an elongated or disc-shaped organelles, containing chlorophyll.
They have two membranes - inside is folded and have structures that look like stack
of coins. Chloroplasts' main role is to conduct photosynthesis, where the
photosynthetic pigment chlorophyll captures the sunlight energy and converts it in
some energy-storage molecules ATP and NADPH. That compaunds the cell use to
make organic molecules from carbon dioxide in a process known as the Calvin
cycle, fatty acid synthesis, amino acid synthesis, and the immune responses in
plants. The number of chloroplasts per cell varies from 1 in algae up to 100 in
plants like Arabidopsis and wheat.
Chloroplasts are highly dynamic - they circulate and are moved around within plant
cells, and occasionally pinch in two to reproduce. Their behavior is strongly
influenced by environmental factors like light. Chloroplasts, like mitochondria,
contain their own DNA, which is thought to be inherited from their ancestor - a
photosynthetic cyanobacterium that was engulfed by an early eukaryotic cell.
Chloroplasts can be found in an extremely wide set of organisms, some not even
directly related to each other - a consequence of many secondary and even tertiary
endosymbiotic events.
Structure and Function of Chloroplasts - Plant chloroplasts are large organelles (5
to 10 μm long) that, are bounded by a double membrane called
the chloroplast envelope
In addition to the inner and outer membranes of the envelope, chloroplasts
have a third internal membrane system, called the thylakoid membrane.
The thylakoid membrane forms a network of flattened discs called thylakoids,
which are frequently arranged in stacks of coins called grana. Internal space called
stroma.
Chemiosmotic generation of ATP in chloroplasts and mitochondria
In mitochondria, electron transport generates a proton gradient across the
inner membrane, which is then used to drive ATP synthesis in the matrix.
In chloroplasts, the proton gradient is generated across the thylakoid
membrane and used to drive ATP synthesis in the stroma.
The different types of plastids are frequently classified according to the kinds
of pigments they contain.
Chromoplasts - Chromoplasts lack chlorophyll but contain carotenoids;
they are responsible for the yellow, orange, and red colors of some flowers and
fruits, although their precise function in cell metabolism is not clear. Chromoplasts
are found in fruits, flowers, roots, and stressed and aging leaves, and are
responsible for their distinctive colors. This is always associated with a massive
increase in the accumulation of carotenoid pigments. The conversion of
chloroplasts to chromoplasts in ripening is a classic example.
The main evolutionary purpose of chromoplasts is probably to attract
pollinators or eaters of colored fruits, which help disperse seeds. However, they are
also found in roots such as carrots and sweet potatoes. They allow the accumulation
of large quantities of water-insoluble compounds in otherwise watery parts of
plants.
When leaves change color in the autumn, it is due to the loss of green
chlorophyll, which unmasks preexisting carotenoids.
Leucoplasts are nonpigmented plastids, which store a variety of energy
sources in nonphotosynthetic tissues - such as roots, bulbs and seeds. They may be
specialized for bulk storage of starch - amyloplasts, lipid - elaioplasts or protein proteinoplasts (also called aleuroplasts . In many cell types, leucoplasts do not have
a major storage function and are present to provide a wide range of essential
biosynthetic functions - synthesis of fatty acids \palmitic acid\ , many amino acids,
and tetrapyrrole compounds such as heme. In general, leucoplasts are much smaller
than chloroplasts and have a variable morphology, often described as amoeboid.
Amyloplasts and elaioplasts are
examples
of
leucoplasts
that
store starch and lipids, respectively.
Plastid differentiation is not permanent, in fact many interconversions are
possible. Chloroplasts may be converted to chromoplasts, which are pigment-filled
plastids responsible for the bright colors seen in flowers and ripe fruits . Starch
storing amyloplasts can also be converted to chromoplasts, and it is possible for
proplastids to develop straight into chromoplasts. Chromoplasts and amyloplasts
can also become chloroplasts, like what happens when a carrot or a potato is
illuminated. If a plant is injured - наранено, or something else causes a plant cell to
revert to a meristematic state, chloroplasts and other plastids can turn back into
proplastids. Chloroplast, amyloplast, chromoplast, proplast, etc., are not absolute
states-intermediate forms are common.
Mithochondria - These structures are described as "the powerhouse of the cell"
because they generate most of the cell's supply of adenosine triphosphate (ATP),
used as a source of chemical energy.
Mitochondrion ultrastructure
A mitochondrion has a double membrane; the inner one contains
its chemiosmotic apparatus and has deep grooves which increase its surface area.
While commonly depicted as an "orange sausage with a blob inside of it" (like it is
here), mitochondria can take many shapes and their intermembrane space is quite
thin. A mitochondrion contains outer and inner membranes composed of
phospholipid bilayers and proteins. The two membranes have different properties.
Because of this double-membraned organization, there are five distinct parts to a
mitochondrion.
The outer mitochondrial membrane, which encloses the entire organelle, is
60 to 75 angstroms (Å) thick. It has a protein-to-phospholipid ratio similar to that
of the eukaryotic plasma membrane (about 1:1 by weight). It contains large
numbers of integral membrane proteins called porins. These porins form channels
that allow molecules of 5000 daltons or less in molecular weight to freely diffuse
from one side of the membrane to the other. The mitochondrial outer membrane
can associate with the endoplasmic reticulum (ER) membrane, in a structure called
MAM (mitochondria-associated ER-membrane).
The intermembrane space is the space between the outer membrane and the
inner membrane. It is also known as perimitochondrial space.
The inner mitochondrial membrane contains proteins with five types of
functions - those that perform the redox reactions of oxidative phosphorylation;
ATP synthase, which generates ATP in the matrix; Specific transport proteins that
regulate metabolite passage into and out of the matrix; Protein import machinery;
Mitochondrial fusion and fission protein. Mitochondria can transiently store
calcium.
Cytoskeleton: It is a network of fibers made up of micro-tubule and microfilament. They maintain the shape and gives support to the cell.
Microtubules: They are hollow cylinder like structures found in the cytoplasm of
the cells. Its function is transport and structural support.
Microfilaments: Microfialments are solid rod like structures whose primary
function is structural support.
Plasmodesmata: They are microscopic channels which traverse the cell walls of
plant cells and enables transport and communication between them.
Vacuole: Vacuoles are known as cells storage center. Plant cells have large
membrane bound chamber called vacuole. Its main function is storage. Vacuoles
are found in the cytoplasm of most plant cells. They are membrane bound
organelles,
they
perform
functions
of
secretion,
excretion
and
storage. Tonoplast: A vacuole that is surrounded by a membrane is called tonoplast.
Golgi complex: The Golgi bodies look like the endoplasmic reticulum and are
situated near the nucleus. They are found in almost all eukaryotic cells. Their main
function is to process and package macromolecules synthesized from other parts of
the cell. The Golgi apparatus is referred to as the cell's packaging center.
Ribosomes: Ribosomes are smallest and the most abundant cell organelle.
It comprises of RNA and protein. Ribosomes are sites for protein synthesis. They
are found in all cells because protein are necessary for the survival of the cell. The
ribososomes are known as the protein factories of the cell.
Endoplasmic reticulum: Endoplasmic reticulum is a membrane bound
compartment, which look like flattened sacs lined side by side. It is a large network
of interconnecting membrane tunnels. It is composed of both rough endoplasmic
reticulum and smooth endoplasmic reticulum.
They are responsible for protein translation, and protein transport to be used in the
cell membrane. They also aid in sequestration of calcium, and production and
storage of glycogen and other macromolecules.
Lysosome: Lysosome contain digestive enzymes. They digest excess or worn out
organelles, food particles and any foreign bodies.
Cytoplasm: It is a gel-like matrix inside enclosed by the cell membrane. The
cytoplasm supports cell organelles and also prevents the cell from bursting or
shrinking.
Protoplasm is the living content of a cell that is surrounded by a plasma
membrane. It is a general term for the cytoplasm.[1] Protoplasm is composed of a
mixture of small molecules such as ions, amino acids, monosaccharides and water,
and macromolecules such as nucleic acids, proteins, lipids and polysaccharides.[2]
In eukaryotes the protoplasm surrounding the cell nucleus is known as the
cytoplasm and that inside the nucleus as the nucleoplasm
Nucleus: It is the control center of the cell. It is bound by a double membrane
known as the nuclear envelope. It is a porous membrane, it allows passage of
substances and is a distinctive characteristic of the eukaryotic cell. Most of the
genetic material is organized as multiple long linear DNA molecules. The nucleus
directs all the activities of the cell and also help in protein formation.
Cell nuclei contain most of the cell's genetic material, organized as multiple
long linear DNA molecules in complex with a large variety of proteins, such as
histones, to form chromosomes. The genes within these chromosomes are the cell's
nuclear genome. The function of the nucleus is to maintain the integrity of these
genes and to control the activities of the cell by regulating gene expression—the
nucleus is, therefore, the control center of the cell.
The nucleus provides a site for genetic transcription that is segregated from
the location of translation in the cytoplasm, allowing levels of gene regulation that
are not available to prokaryotes. The main function of the cell nucleus is to control
gene expression and mediate the replication of DNA during the cell cycle.
In plants, the cell wall provides support to individual cells by containing the
pressure created in the central vacuole and protecting the plant cells against
invading bacteria and fungi.
The wall consists of cellulose fibers (cellulose microfibril), which provides
tensile strength, embedded in a network of highly branched carbohydrates. These
cellulose fibers are bound by polysaccharides called hemicelluloses. The initial cell
wall, the primary cell well, is relatively soft and flexible. As the cell grows and
matures, this layer expands and additional layers of cellulose fibers and branched
carbohydrates are laid down between the primary cell wall and the plasma
membrane of the cell creating a new wall layer, more rigid and thicker than the first.
This is called the secondary cell wall. The secondary cell wall can be
reinforced by lignin, a hard substance assembled for alcohols, surrounded by
cellulose fibers. It is commonly found in plants and trees, hence why, wood is
useful to make strong structures like houses and furniture. The walls of adjacent
primary cell walls are held together by a layer of gel-like polysaccharides, called
pectin. This polysaccharide material forms the middle lamella.