Tanveer Kurd Behramshahi Mastung Biology Concepts.
5000 Words
Factors affecting gene frequency
Many factors can alter gene frequency. Out of these five affect the proportion of homozygotes and heterozygote enough to produce significant deviations from the proportion claimed by Hardy Weinberg principle.
Mutation
The ultimate source of all changes; individual mutations occur so rarely that mutation alone does not change allele frequency much.
Migration
A very potent agent of change, migration locally acts to prevent evolutionary changes by preventing populations that exchange members from diverging from one another. Emigration and immigrations of members a population, cause disturbance in the gene pool.
Genetic drift
It is the change in frequency of alleles at a locus that occurs by chance. In small populations, such fluctuations may lead to the loss of particular alleles. This may occur in a small population when a few individual fail to reproduce and then genes are lost from the population.
Non-random mating
Inbreeding is the most common form; it does not alter allele frequency, but lessons the proportion of heterozygote individuals. Individuals with certain genotypes sometimes mate with one another more commonly than would be expected on a random basis. This is called non-random mating, causing the frequencies of particular genotypes to differ greatly from those predicted by the Hardy-Weinberg principle.
Selection
Some individuals leave behind more progeny than others, and the rate at which they do so is affected by their inherited characteristics. This is called selection. Selection can be artificial selection or natural selection. In artificial selection, the breeders select for the desired characters. In natural selection, the environment plays the role, thus affecting the proportions of gene in a population.
ENDANGERED SPECIES
Endangered species
Itis in imminent danger of extinction throughout its range (where it lives). Endangered species of plants have been recorded to more than 500.
In Pakistan Indus dolphin, Blackbuck, common leopard, Great Indian bustard, Houbara bustard, White-headed duck and Marbled teal are among the animal near to extinction.
Threatened species
It is likely to become endangered in the near future.
Extinct Species
It has been declared to be extinct from a locality .In Pakistan. Cheetah, tiger, Asian lion, Indian rhino, Cheer pheasant, Crocodile and Gavial have been declared extinct.
Cause of Extinction.
Fate of species.
Extinction has been the fate of most plant and animal species. It is a natural process of that will continue.
Habitat destruction.
In recent years, however, the threat to the welfare of wild plants and animals has increase dramatically--- mostly as a result of habitat destruction.
Tropical rain forests, the most threatened areas on the earth, have been reduce to 44% of their original extent.
In certain areas, such as Ecuador, forest coverage has been reduced by 95%. This decrease in habitat has resulted in tens of thousands of extinctions.
Habitats other that rain forest-grasslands, marshes, deserts, and coral reefs- are also being seriously threatened. Deserts, Sub-mountainous tract and Wetlands are habitats in peril. We must protect them rapidly.
Other Causes.
Other causes of extinction include climate change, population, and invasions from foreign species.
Estimation of Extinction
Accurately estimating the number of extinctions is impossible in areas like rain forests, where taxonomists have not even describe most species.
Effects of Extinction.
We are losing species that we do not know exist and we are losing resources that could lead to new medicines, foods, and textiles.
Multifaceted conservation plan
Saving species requires more that preserving a few remnant individuals is main task of this plan. It requires a large diversity of genes within species groups to promote species survival in changing environments. This genetic diversity requires large populations of plants and animals.
Components.
Preservation of endangered species depends on a multifaceted conservation plan that includes the following components:
A global system of national parks to protect large tracts of land and wildlife corridors that allow movement between natural areas.
Protected landscapes and multiple-use areas that allow controlled private activity but also retain value as a wildlife habitat.
Zoos and botanical gardens to save species whose extinction is imminent.
NTRODUCTION
ENZYMES
Definition
Enzymes are the most important group of proteins which are biologically active. They tremendously increase the efficiency of a biochemical reaction and are specific for each type of reaction.
Importance
Without these enzymes the reaction would proceed at a very slow speed making life impossible.
Composition
Enzymes are composed of hundreds of amino acids. These amino acids are brought closer and are arranged in a specific way by coiling and folding of the polypeptide chain within the globular symmetry of the enzyme
Active Site. The catalytic activity is restricted to a small portion of the structure known as the active site.
Substrate. The reactant called substrate is attached to the active site and converted into product.
Active site consisting of only a few amino acids. While rest of the bulk of the amino acids maintains the globular structure of the enzyme.
Cofactors
Definition.
Some enzymes consist solely of proteins. Others also have a non-protein part known as a co-factor, which is essential for the proper functioning of the enzymes.
Functions.
The cofactor usually acts as “bridge” between the enzyme and its substrate,
It contributes directly to the chemical reactions which bring about catalysis.
Sometimes the co-factor provides a source of chemical energy, helping to drive reactions which would otherwise be difficult of impossible.
specific in nature?
An enzyme is a three dimensional globular protein that has specific chemical composition due to its component amino acids and a specific shape. Every enzyme by virtue of its specificity recognizes and reacts with a special chemical substance called substrate. Any enzyme, therefore, reacts only with its specific substrate and transforms it into products(s). It is then released unaltered and thus can be used again and again.
Enzyme Chain to Chain Association
In certain cases enzymes act in a series of chemical reactions in a particular order to complete a metabolic pathway such as respiration or photosynthesis. The successive enzymes containing these reactions are normally present together in a precise order of reaction such that substrate molecules can be literally handed on’ from one enzyme to another forming an enzyme to enzyme chain. In this way the products from one step in pathway are transferred to the enzyme catalyzing the next step.
Reason
By increasing the enzyme molecules an increase in the number of active sites takes place. More active sites will convert the substrate molecules into product(s), in the given period of time. After a certain limiting concentration, the rate of reaction will no longer depend upon this increase.
Substrate Concentration
At low concentration of substrate the reaction rate is directly proportional to the substrate available.
At high concentration.
If the enzyme concentration is kept constant and the amount of substrate is increased, a point is reached when a further increase in the substrate does not increase the rate of the reaction any more. This is because at high substrate in the substrate all the active sites of the enzymes are occupied and further increase does not increase the reaction rate. This is said to be saturation.
said to be saturation.
Temperature
The rate of enzyme controlled reaction may increase with increase in temperature but up to a certain limit. Every 10 C rise in temperature doubles the enzymatic reaction.
Optimum Temperature
All enzymes can work at their maximum rate at a specific temperature called as optimum temperature. For enzymes of human body 37°C is the optimum temperature.
Effect of increase
Heat provides activation energy and therefore, chemical reactions are accelerated at high temperatures. Heat also supplies kinetic energy to the reacting molecules, causing them to move rapidly. Thus the reactants move more quickly and chances of their collision with each other are increased.
Denaturation. However, further increase in heat energy also increases the vibrations of atoms which make up the enzyme molecule. If the vibrations become too violent, globular structure essential for enzyme activity is lost and the enzyme is said to be denatured.
PH Value
Every enzyme function most effectively over a narrow range of pH known as the optimum pH. Some examples are
Ø Pepsin
Ø 2.00
Ø Sucrose
Ø 4.50
Ø Enterokinase
Ø 5.50
Ø Salivary amylase
Ø 6.80
Ø Catalase
Ø 7.60
Ø Chymotrypsin
Ø 7.00-8.00
Ø Pancreatic lipase
Ø 9.00
Ø Arginase
Ø 9.70
A slight change in pH can change the ionization of the amino acids at the active site. Moreover, it may affect the ionization of the substrates. Under these changed conditions enzyme activity is either retarded or blocked completely.
Extreme changes in pH cause the bonds in the enzyme to break, resulting in the enzyme denaturation.
Inhibitors
An inhibitor is a chemical substance which can react (in place of substrate) with the enzyme but is not transformed into product(s) and thus blocks the active site temporarily or permanently,
For example Poisons like cyanide, antibiotics, anti-metabolites and some drugs.
Types of Inhibitors
Inhibitors can be divided into two types:
Irreversible
Reversible
Reversible
Definition
The inhibitors whose effects can be neutralized are said to be reversible inhibitors. Their effects are temporary in nature.
Mechanism of Action.
They check the reaction rate by occupying the active sites or destroying the globular structure. They occupy the active sites by forming covalent bonds or they may physically block the active sites.
Examples
An example of irreversible inhibitors in medicine is penicillin. Penicillin works by inhibiting the activity of the enzyme responsible for the creation of the bacterial cell wall.
Some poisons
Irreversible
Definition
The inhibitors whose effects cannot be neutralized and are said to be irreversible inhibitors. Their effects are permanent in nature
Mechanism of Action.
They form weak linkages with the enzyme so their effects can be neutralized completely or partly.
Examples
Succinate dehydrogenase is the enzyme that converts succinic acid into fumaric acid. Malonic acid competes with succinic acid for active site and product is not formed.
Reversible Inhibitors
They form weak linkages with the enzyme. Their effect can be neutralized completely or partly by an increase in the concentration of the substrate.
They are further divided into two major types
competitive
Non-competitive
Competitive inhibitors
Definition
Because of the structural similarity with the substrate they may be selected by the binding sites, but are not able to activate the catalytic sites. Thus product(s) are not formed.
Examples
Succinate dehydrogenase is the enzyme that converts succinic acid into fumaric acid. Malonic acid competes with succinic acid for active site and product is not formed
Competitive inhibition
Non competitive inhibitors
Definition
They form enzyme inhibitor complex at a point than the active site. They alter the structure of the enzyme in such a way that even if genuine substrate binds the active site, catalysis fails to take place.
Examples
Pyruvate kinase that catalyzes final step of glycolysis is non competitively inhibited by Alanine.
Non-competitive Inhibition.
In animals e.g.
muscle cell contract and relax,
nerve cells transmit impulses,
gland cells secrete,
red blood cell carry oxygen and
Some stomach cells secrete gastric juice.
In plants
Xylem cell conduct water and mineral salts from soil to the aerial parts of the plants.
Phloem cells translocate food.
Sclerenchymatous cell give support to surplus food and
Meristematic cells produce new cell for growth and development of the plant.
As they perform different functions they show great variation in shape and size. Despite the structural and functional diversity, the plant cells as well as animal cells have a common plan of organization.
Resolution and Magnification.
Resolution.
It is an ability of an instrument to distinguish two very close points apart.
For example, the human naked eye can differentiate between two points, which are at least 1.0mm apart. This is known as resolution of eye. The resolution can be increased with the aid of lenses.
Resolution of microscopes.
Compound microscope. In a typical compound microscope the resolution is 2.0um, which is about 500X that of naked eye. Compound microscope may have different magnification powers.The resolution will, however, remain the same, which is 500X that of the naked eye.
In electron microscope ranges between 2-4 Angstrom, which make it 500X greater than that of the compound microscope and 250,000X greater than that of the naked eye. This means that two points which are 2-4 Angstrom apart can be differentiated with the help of electron microscope.
Magnification.
It is an ability of optical instrument to enlarge the physical appearance of an image or something else.
A compound microscope is a typical laboratory microscope with at least different magnification powers.
Calculation of magnification Power.
The typical ocular lenses could be 5X and 10X but others also exist. Likewise different type of objective lenses viz. 20X, 40X, 100X etc. exist.
The magnification power of microscope is determined by multiplying X values of the ocular lenses with X values of the objective lenses.
Example. Therefore, a microscope with 10X ocular lens and 40X objective lens will have (10X X 40X) 400X magnification power.
Source of illumination.
The source of illumination of compound microscope is visible light.
The source of illumination of an electron microscope is beam of electron.
Importance of Microscopy.
The revelation of complexity of structure of various cellular organelles is closely linked with the development of microscopy and improvement in the resolution power of the microscope.
Cell Fractionation.
Definition.
Cell fractionation is the separation and isolation of individual components of a cell.
Importance.
Structure of a cell can be studied under light microscope as well as electron microscope. The modern technology enables us to isolate various components of cells including its organelles by a process of cell fractionation and study their structure and function in detail.
Procedure.
It involves the techniques namely the homogenization and differential centrifugation.
Homogenization.
Homogenization is a process whereby a biological sample is brought to a state such that all fractions of the sample are equal in composition. During cell fractionation the tissues are homogenized or disrupted with special instruments.
Centrifugation.
The separation (fractionation) of various components of the homogenate is carried out by a density gradient centrifugations. The various cellular parts separate out in different layers depending upon their size and weight, and density of the medium.
Ultracentrifugation.
Some cellular components require very high speeds for separation from other parts of the cells. This is achieved through ultracentrifugation. Ultracentrifuges are electrically driven and are capable of speeds up to 60 000 rpm.
Structure of generalized Cell.
A cell consists of the following basic components:
Plasma membrane, also a cell wall in plant cell.
Cytoplasm, containing cell organelles.
Nucleus, with nuclear or chromatin material.
In the traditional system of classification
all organisms are divided into plants and animals. The cells of plants and animals can be distinguished by the presence or Absence of cell wall.
Eukaryotes.
Cells of animals and plants are complex and have a distinct nucleus (chromatin material is bounded by a membrane) and are called eukaryotic.
Prokaryotes.
On the other hand, the primitive type of cells, such as bacteria, lacks a definite nucleus and are said to be prokaryotic. In prokaryotes the nuclear material is directly submerged in the cytoplasm and is not separated from it by membranes.
The eukaryotic cells vary greatly in size.
They could be as big as an ostrich’s egg. Most of the cells are microscopic and are not visible to the naked
eye. Their size is measured in micrometer (µm). One µm is 0.000,001 meter or of a meter.
The use of modern technology has made it possible to study the following components of the cell in detail.
Plasma Membrane.
Location.
Plasma membrane or cell membrane is the outer most boundary of the cell. However, in most plant cells, it is covered by a cell wall.
Composition.
Cell membrane is chemically composed of lipids and proteins; 60 – 80% are proteins, while 20-40% are lipids. In addition there is a small quantity of carbohydrates.
Structure
Many biologists contributed to establish the structural organization of cell membrane.
Unit Model.
It was proposed earlier that cell membrane is composed of lipid bilayer sandwiched between inner and outer layers of protein. This basic structure is called the Unit membrane and is present in all the cellular organelles.
The modern technology has revealed that lipid bilayers are not sandwiched between two protein layers.
Fluid Mosaic Model.
The protein layers are not continuous and are not confined to the surface of the membrane but are embedded in lipid layers in a mosaic manner. This discovery led to the proposal of Fluid Mosaic Model. This model at present is the most accepted one. Cell membrane also contains charged pores through which movement of materials takes place, both by active and passive transport.
Functions of Cell membrane.
Transport of materials
This is one of the vital roles it plays for the cell. Therefore, it regulates the flow of materials and ions to maintain a definite gradient.
Selectively permeable membrane.
It offers a barrier between the cell contents and their environment, allowing only selective substances to pass through it, thus it is known as differentially permeable or selectively permeable membrane.
The substances which are lipid soluble cross it more easily than others,
Many small gas molecules, water, glucose etc. being neutral can easily cross.
While ions, being charged particles, have some difficulty in crossing.
There are certain mechanism to move material across the membrane.
Passive Transport.
The movement of a chemical substance across a cell membrane without expenditure of energy by the cell as in diffusion and osmosis etc. Many substances which are not needed, constantly enter the cell by passive transport.
Active Transport.
Some Substances are taken up against the concentration gradient (they move from the area of low concentration to the area of high concentration). This uphill movement of materials requires energy and is termed as active transport. The energy used for this movement is provided by ATP.
Endocytosis.
In many animal cells, the cell membrane helps to take in materials by in folding in the form of vacuoles. This type of intake is termed as endocytosis which can be either
Phagocytosis (to engulf solid particles) or
Pinocytosis (to take in liquid material).
Transmission of Impulses.
In neurons (nerve cells) the cell membrane transmits nerve impulses from one part of the body to the other to keep coordination.
Cell Wall
Location.
The outer most boundary in most of the plant cells is cell wall.
Secretion.
It is secreted by the protoplasm of the cell.
Variety.
The cell wall of plant cell is different from that of prokaryotes. Both in structure and chemical composition. Its thickness varies in different cells of the plant.
Structure and Composition of Plant Cell Wall
It is composed of three main layers: primary wall, secondary wall and the middle lamella.
The middle lamella
is first to be formed in between the primary walls of the neighboring cells. The middle lamella is a pectin layer which cements the cell walls of two adjoining plant cells together.
The primary wall
is composed of cellulose and some deposition of pectin and hemicelluloses. Cellulose molecules are arranged in a criss cross arrangement. The cellulose fibers are arranged in layers, with the fibers of each layer at right angle to those of other layers. The primary wall is a true wall and develops in newly growing cells.
Metabolism.
The smooth surfaced endoplasmic reticulum (SER) helps in metabolism of a number of different types of molecules particularly lipids.
Detoxification.
SER also help to detoxify the harmful drugs.
Transmission.
In some cells SER is responsible for transmission of impulses, e.g. muscle cells, nerve cells. In addition,
Transport.
SER also plays an important role in the transport of materials from one part of the cell to the other.
Ribosomes.
Cell contains many tiny granular structures known as ribosomes. Palade (1955) was the first person to study them.
Composition.
Eukaryotic ribosomes are compose of an almost equal amount of RNA and protein, hence they are ribonucleo-proteins particles. The RNA present in ribosome is called ribosomal RNA.
Location.
Ribosomes exist in two forms; either freely dispersed in cytoplasm or attached with RER as tiny granules.
Structure.
Each eukaryotic ribosome consists of two sub-units. The larger subunit sediments at 60S (S= Svedberg unit used in ultracentrifugation), while smaller subunit sediments at 40S. Two subunits on attachment with each other form 80S particle. This attachment is controlled by the presence of Mg2+ions.
Polysomes.
The ribosomes are attached to messenger RNA through small ribosomal subunit. A group of ribosomes attached to mRNA is known as Polysomes.
Synthesis.
New ribosomes are assembled in the nucleolus of the nucleus from where they are transported to the cytoplasm via the pores in nuclear membrane.
Function.
The factory of ribosome is the nucleolus, while that of protein synthesis is the ribosomes.
Golgi apparatus
Golgi apparatus was discovered by Italian physician Camillo Golgi in 1898. This apparatus, which was found virtually in all eukaryotic cells.
Structure.
It consists of stacks of flattened, membrane bound sacs, called cisternae. It is a complex system of interconnected tubules around the central stacks.
Their outer convex surface is the forming face, while the inner concave surface is the maturing face.
Formation.
Cisternae stacks are continuously formed by fusion of vesicles, which are probably derived by the budding of SER. Blebs from tips of SER fuse with Golgi apparatus cisternae at forming face, whereas secretory granules (transport vesicles) are pinched off at the maturation face of Golgi apparatus. The whole stack consists of a number of cisternae thought to be moving from the outer to the inner face.
Golgi complex.
These cisternae together with associated vesicles are called Golgi complex.
Functions.
Cell Secretion.
Golgi complex is concerned with cell secretions.
Formation.
Secretions are products formed within the cell on ribosomes and then passed to the outside through endoplasmic reticulum and Golgi apparatus.
Packaging. The secretions are converted into finished product and are packed inside membrane, before export.
For example in mammals, the pancreas secretes granules containing enzymes that help in digestion. The Golgi complex has a role in formation of these granules.
Transport.
The proteins or enzymes which have to be transported out of the cell pass through the Golgi apparatus.
Formation of Conjugated molecules.
The most important function of this apparatus is to modify the proteins and lipids by adding carbohydrates and converting them into glycoproteins or glycolipids.
LYSOSOMES.
Lysosomes are cytoplasmic organelles and are different from others due to their morphology.
Discovery.
These were isolated as a separate component for the first time by de Duve (1949).
Occurrence.
Lysosomes (lyso = splitting; soma = body) are found in most eukaryotic cells. They are most abundant in those animal cells which exhibit phagocytic activity.
Structure
They are bounded by a single membrane and are simple sacs rich in acid phosphatases and several other hydrolytic enzymes.
Formation.
These enzymes are synthesized on RER and are further processed in the Golgi apparatus.
Primary Lysosomes.
The processed enzymes are budded off as Golgi vesicles and are called as primary lysosomes. Lysosomes contain those enzymes which can digest the phagocytosed food particles.
Secondary Lysosomes.
A lysosome formed by the combination of a primary lysosome and digestive vacuoles and in which lysis takes place through the activity of hydrolytic enzymes.
Functions.
Phagocytosis.
Any foreign object that gains entry into the cell is immediately engulfed by the lysosome and is completely broken into simple digestible pieces. The process is known as phagocytosis (eating process of a cell).
Importance. Lysosomes protect the cells from invading organisms or any other foreign object, (food) which are engulfed in the cell as phagocytic vacuoles.
Autophagy.
They are also involved in the autophagy (self-eating). The lysosomes which eat parts of their own cell are known as autophagosomes. The digestive vacuoles and autophagosomes are also known as secondary lysosomes.
Importance.
Renewal of material. During this process some old, worn out parts of cell, such as old mitochondria are digested. In this way, materials of cell may be recycled and cell may be renewed.
Sometimes, under abnormal circumstances, e.g. starvation the parts of the cell are engulfed by primary lysosomes and digested to generate energy.
Degeneration.
Their enzymes can also result in degeneration of cell, as may occur during some developmental processes.
Extracellular Digestion.
Lysosomes also release enzymes for extra cellular digestion.
Lysosomal Diseases.
Storage Diseases.
Several congenital diseases have been found to be due to accumulation within the cell of substances such as glycogen or various glycolipids. These are also called storage diseases
Cause.
These are produced by a mutation that affects one of the lysosomal enzymes involved in the catabolism of a certain substance.
About twenty such diseases are known these days, which are because of absence of a particular enzyme.
Glycogenosis type II disease.
The liver and muscle appear filled with glycogen within membrane bound organelles. In this disease, an enzyme that degrades glycogen to glucose is absent.
Tay-sach’s disease
is because of absence of an enzyme that is involved in the catabolism of lipids. Accumulation of lipids in brain cells lead to mental retardation and even death.
Peroxisomes.
Discovery.
De-Duve and coworkers isolated in 1965 particles from liver cells and other tissues which were enriched with some other enzymes such as peroxidase, catalases, glycolic acid oxidase and some other enzymes. They have also been found in protozoa, yeast and many cell types of higher plants.
Etymology.
The name peroxisome was applied because this organelle is specifically involved in the formation and decomposition of hydrogen peroxide in the cell.
Structure.
These are single membrane enclosed cytoplasmic organelle found both in animal and plant cells. These are characterized by containing H2O2 – producing oxidases and catalase. They are approximately 0.5 µm in diameter.
Function.
In plants, peroxisomes play important role in both catabolic and anabolic pathways.
Glyoxysomes
Occurrence
Plants contain an organelle, which in addition to glycolic acid oxidase and catalase also possess a number of enzymes that are not found in animal cells.
This organelle is present only during a short period in the germination of the lipid-rich seed and is absent in lipid-poor seed such as the pea.
Functions
This organelle, called glyoxysomes are most abundant in plant seedlings, which rely upon stored fatty acids to provide them
with the energy and
Material to begin the formation of a new plant.
In seeds rich in lipids such as castor bean and soybeans, glyoxysomes are the sites from breakdown of fatty acids to succinate.
Glyoxylate Cycle.
One of the primary activities in these germinating seedlings is the conversion of stored fatty acids to carbohydrates. This is achieved through a cycle, glyoxylate cycle, the enzymes of which are located in the glyofilaments.
Vacuoles
Location.
Although vacuoles are present both in animal and plant cells,
They are particularly large and abundant in plant cells often occupying a major portion of the cell volume and forcing the remaining intracellular structures into a thin peripheral layer.
These vacuoles are bounded by a single membrane and are formed by the coalescence of smaller vacuoles during the plant’s growth and development.
Functions.
Vacuoles serve to expand the plant cell without diluting its cytoplasm
It also functions as sites for the storage of water and cell products or metabolic intermediates.
The plant vacuole is the major contributor to the turgor that provides support for the individual plant cell and contributes to the rigidity of the leaves and younger parts of the plants.
Cytoskeleton
Cytosol contains cytoskeletal fabric formed of microtubules, microfilaments and intermediate filaments.
Composition.
The main proteins that are present in cytoskeleton are tubulin (in microtubules), actin, myosin, tropomyosin and others which are also found in muscles.
Microtubules are long. Unbranched, slender tubulin protein structures.
Function.
very important functions of microtubules are
Their role in the assembly and disassembly of the spindle structure during mitosis.
Several cell organelles are derived from special assemblies of microtubules, for examples cilia, flagella, basal bodies and centrioles.
Intermediate filaments
These have diameter in between those of microtubules & microfilaments.
Function.
Intermediate filaments are involved in determination of cell shape and integration of cellular compartments
Microfilaments
These are considerably more slender cylinders made up of contractile actin protein, linked to the inner face of the plasma membrane.
Function.
They are involved in internal cell motion (cyclosis) and amoeboid movements are because of microfilaments,
Centrioles.
Occurrence.
Animal cells and cells of some microorganisms and lower plants contain two centrioles located near the exterior surface of the nucleus. They are absent in higher plants.
Structure.
In cross section each of the nine microtubules is further composed of three tubules the two centrioles are usually placed at right angle to each other.
Functions.
Just before a cell divides, its centrioles duplicate and one pair migrates to the opposite side of the nucleus. The spindle then forms between them.
Centrioles play important role in the location of furrowing during cell division, and
Centrioles play important role in the formation of cilia.
Mitochondria are very important organelles of eukaryotic cells, because they are involved in the manufacture and supply of energy to the cell. They are also known as powerhouses of the cell. The size and number of mitochondria varies and depends on the physiological activity of the cell
Morphology and structure.
The mitochondrial membranes are similar in structure to other cell membranes.
Under compound microscope.
they appear to be vesicles, rods or filaments.
Under an electron microscope,
they show complex morphology and structure.
Membranes.
A mitochondrion is bound by two membranes, the outer membrane is smooth, while the inner membrane forms infoldings into the inner chamber called mitochondrial matrix. These infolds are called cristae. A crista is made of lipoprotein membrane containing different enzymes as well as F1 particles embedded in it.
F1 particles.
The inner surface of cristae in the mitochondrial matrix has small knob like structures known as F1 particles. After a special processing the inner
mitochondrial membrane is ruptured and the F1 particles come out on the surface.
Mitochondrial Matrix.
It is present inside the inner membrane. Mitochondrial matrix contains in it a large number of enzymes, coenzymes and organic and inorganic salts which help in several vital metabolic processes.
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