Cell and Its organelles

Principles of Genetics & Population Genetics AGB 121 2012-13

Dept. Of Animal Genetics and Breeding Veterinary College Hebbal, Bangalore -24

Cell and its Organelles Cell is the basic unit of organization of living matter.

It is the unit of biological activity delimited by a semi permeable membrane and capable of self reproduction in medium free of other living systems.

Cellular organisms have either prokaryotic or eukaryotic cells.

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Prokaryotic cells Composed of primitively organized cytoplasm and nucleus.

Nuclear substance is not separated by nuclear membrane from cytoplasm.

Cytoplasm does not have endoplasmic reticulum, Golgi complex. e.g: Blue green algae & Bacteria

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Eukaryotic cell Have true nucleus with nuclear membrane.

Nucleus has chromosomes, nucleolus and nucleoplasm.

The cytoplasm is enclosed in plasma membrane and has cell organelles Other organelles Mitochondria, Endoplasmic reticulum, Vacuoles, Lysosomes, Chloroplasts,Centrioles & Ribosomes.

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Features Size Cell wall Plastids

Vacuoles

Animal Cell Small Absent Absent except in Euglena Large numbers are present Single highly complex

Golgi apparatus Centrosomes Present. and centrioles 2/1/2013

Plant cell Large Rigid cell wall cellulose Present

Large single in the centre.

Simpler unit called dictyosomes.

Absent 7

PLASMA MEMBRANE

Consists of Lipids 20-40 %, Proteins-55-75% and Carbohydrates-1-5% 2/1/2013

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Plasma Membrane Functions:

• Protection of cells from injury.

• Passage of substances in and out of cell by selective permeability.

• Absorption, Secretory, Excretory and waste product removal.

• Determine antigen specificity • Helps in movement of unicellular organisms like Amoeba.

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Cytoplasm Is a Jelly like semi fluid mass of protoplasm excluding nucleus but includes all other components-cytoplasmic matrix, cell organelles & cell inclusions.

Contains water in liquid state and other particles like minerals, sugars, amino acids, tRNA, nucleotides, vitamins, proteins and enzymes in colloidal state.

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Functions of cytoplasm • Provides raw materials to cell organelles • Exchange of materials between cell organelles • Biosynthesis of fat, nucleotides, proteins, co-enzymes etc • Catabolic activities.

• Uniform distribution of various materials • Cytoplasmic streaming or cyclosis 2/1/2013

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Mitochondria

Power house of the cell (production of ATP) Cylindrical, length -5-10 micron, Diameter- 0.5-1.0 micron 2/1/2013

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Mitochondria • Two membranes-Outer membrane is smooth and permeable & Inner membrane is folded to from involutions called cristae • Two Chambers- Outer chamber contains enzymes and inner chamber contains proteins, ribosomes, RNA, mitochondrial DNA, enzymes of Kreb’s cycle, amino acid synthesis and fatty acid metabolism 2/1/2013

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Functions of Mitochondria • Oxidation of food materials • Matrix has enzymes for synthesis of fatty acids.

• Synthesis of amino acids

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Endoplasmic Reticulum Rough

Smooth

Provides surface for attachment of Ribosome's Helps in packaging of polypeptides to produce proteins & enzymes.

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Does not have Ribosome's.

Helps in synthesis of fat inside cells and adipose tissue.

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Endoplasmic Reticulum Inter connection of membrane linked channels that run through the cytoplasm.

Channels contain fluid called endoplasmic matrix.

Exists in three forms

Cisternae- Sac like formed bundles and lie parallel to one another actively involved in synthetic activity.

Vesicles- Oval rounded sacs also called as microsomes.

Tubules- Tube like structures connecting cisternae and Vesicles

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Function of EPR Synthesis of glycogen and glygenolysis in liver, sterols and hormones in testes and ovary, formation of Visual pigment from Vitamin A in retinal cells.

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GOLGI APPARUTUS

Golgi complex Camillo Golgi in 1898 2/1/2013

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GOLGI APPARATUS Complex protoplasmic structure made up of smooth membrane saccules or cisternae, a network of tubules with vesicles and vacuoles.

Shape is not fixed depending on the physiological state the shape varies.

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Structure of Golgi Complex Cisternae: 4-8 membrane bound saccules or cisternae. They have two side -convex side called forming face & concave side called maturing face.

Tubules: In the form of network towards the periphery and maturing face of golgi apparatus.

They inter connect different cisternae.

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Vesicles: Small sacs of Smooth (containing secretary substance called secretion vesicles) & coated vesicles have rough surface and elaborate membrane proteins) Vacuoles-modified form of cisternae.

Some function as lysosomes.

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Function of Golgi complex Secretion vesicles contain zymogen granules, are sent out of the cells through exocytosis or reverse pinocytosis.

Transformation of membrane: Convert one type of membrane to another and recycling of plasma membrane.

Form glycoprotein from protein of EPR Synthesis of complex carbohydrates such as pectin, mucoploysaccharaids, hemicellulose,cellulose etc.

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Function of Golgi complex Hormones: Production of hormones by endocrine glands, formation of matrix of connective tissue, synthesis of retinal pigments in chick embryo.

Formation of acrosome.

Vitelogenesis- formation of oocytes and development of yolk.

Formation of lysosomes Store house of digestive enzymes.

Membrane vesicles join the region of cytokinesis and produce new plasmalemma 2/1/2013

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LYSOSOMES- Suicidal bags

•Small vesicles bounded by a single membrane.

•Contain hydrolytic enzymes in the form of minute crystalline or semi crystalline granules.

•Important enzymes- Phosphatases, sulphatases, proteases, nucleases, liposases and glycosidases.

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Types of Lysosomes Primary –Newly pinched of vesicles from golgi apparatus.

Secondary- Fusion of primary lysosomes with phagosomes and also known as digestive vacuoles.

Residual bodies or tertiary lysosome- throw out the residues and undigested food materials into the external environment by exocytosis Autophagic vaculoes- formed by fusion of primary lysosomes and worn out organelles 2/1/2013

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Functions of Lysosmes • Intracellular digestion of food • Lysosomes of leucocytes eliminate foreign proteins, toxic substances, bacteria and other microorganisms.

• Provide nutrition during starvation by hydrolyzing organic food.

• Removal of old ,aged and useless organelles.

• Provide enzymes for sperm penetration 2/1/2013

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Functions of Lysosmes- contd Essential for cell division by overcoming agents that cause repression of mitotic cycles.

Lysosome related nucleases might result in mutation, breakage of chromosomes and blood cancer.

Lysosomes remove carcinogens by engulfing and separating them.

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ENDOSOMES & ENDOCYTOSIS Membrane-bound vesicles, formed via a complex family of processes collectively known as endocytosis.

The basic mechanism involves the invagination (folding inward) of a cell's plasma membrane to surround macromolecules or other matter diffusing through the extracellular fluid.

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Sphaerosomes Small cell organelles bounded by single membrane take part in storage and synthesis of fat.

They arise from endoplasmic reticulum and have some lysosome activity.

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Peroxisomes or Microbodies

Small cell organelles with single membrane which absorbs molecules of oxygen and take part in oxidation other than those involved in respiration.

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Types of Microbodies Peroxisomes- contain enzymes for peroxidase synthesis.

Glycoxysomes-contains enzymes for beta oxidation of glyoxylate.

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RIBOSOMES • Tiny organelles composed of approximately 60 percent RNA and 40 percent protein.

• In eukaryotes, ribosomes are made of four strands of RNA. • In prokaryotes, they consist of three strands of RNA. • Protein and RNA complex responsible for protein synthesis.

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Ribosomes Organelle ribosome- found in mitochondria Cytoplasmic ribosome - remain attached to Endoplasmic reticulum.

Size of ribosome is measured in Svedberg Unit.

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Ribosomes May occur in linear or helical groups called as polyribosome and connected with thick strand of mRNA. Polyribosomes are found during active protein synthesis.

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Functions of Ribosome Protein synthesis Storage of rRNA Temporary storage of protein and finally transfer it to the cytoplasmic reticulum.

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Microfilaments

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Microfilaments Ultra microscopic rods or protein filaments made of actin like lobule protein molecule.

Microfilaments associate to form hexagonal bundle are contractile.

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Microfilaments-Functions • Cytoplasmic streaming • Microvilli are maintained through support provided by microfilaments.

• Spindle apparatus formation.

• Movement of fibroblast to undulation of microfilaments.

• Associated with cleavage furrow at the time of cytokinesis.

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MICRO TUBULES • Straight, hollow cylindrical organelles.

• Functions, ranging from transport to structural support (Cytoskeleton) • Help in movement of cilia and flagella • Movement of nuclei during cell division 2/1/2013

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CILIA AND FLAGELLA Are essential for the locomotion of individual organisms in unicellular organisms.

In multicellular organisms, cilia function to move fluid or materials past an immobile cell as well as moving a cell or group of cells..

Passage of eggs in oviduct Conjugation and fusion of gametes 2/1/2013

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CENTRIOLES • Self-replicating organelles made up of nine bundles of microtubules and are found only in animal cells.

•They appear to help in organizing cell division, but aren't essential to the process.

•Complex formed of centrioles and cytoplasm is called centrosome or central apparatus.

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Centrioles Prior to nuclear division the two centrioles present in a centrosome move to opposite poles.

Centrioles possess a whorl of nine peripheral fibrils and each fibril is made up of three sub fibrils called triplet fibril.

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Functions-Centriole Formation of nucleating centres.

Forming poles of the spindle • The distal centrioles give rise to axial filament or tail in spermatozoa • Basal bodies formed from centrioles give rise to cilia and flagella.

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CHLOROPLAST[PLASTIDS]

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CHLOROPLAST Surrounded by a double membrane, containing stacked membranes.

Responsible for photosynthesis, the trapping of light energy for the synthesis of sugars.

Contains DNA, and like mitochondria is believed to have originated as a captured bacterium.

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VACUOLES

Membrane surrounded "bags" that contain water and storage materials in plants.

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NUCLEUS

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Nucleus (Robert brown in 1831) It is a specialized double membrane bound protoplasmic body, which contains all the genetic information for controlling cellular metabolism and transmission of posterity.

Cells have single nucleus.

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Nuclear envelope or Karyotheca • Made of two lipoproteins and trilaminar membrane.

Contains large number pores or perforations.

• Inner membrane is smooth

•Outer membrane may be smooth or may be rough on the cytoplasmic surface.

•Two membranes are separated by a electron transparent perinuclear space.

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Nucleoplasm or Nuclear sap or Karyolymph • Transparent semifluid colloidal substance which fills nucleus.

• Contains nucleosides and number of enzymes (DNA polymerase, RNA polymerase and nucleoside phosphorylase) • For synthesis and function of DNA, RNA, nucleoproteins etc.

• Some proteins are essential for spindle formation.

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Chromatin Hereditary DNA-protein fibrillar complex Chromatin is in the form of overlapping and coiled fibres which appear to produce a network of chromatin reticulum.

Chromatin fibres are disrtibuted through out the nucleoplasm.

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Euchromatin and Heterochromatin Euchromatin contains functional genes.

Heterochromatin is a condensed region believed to be genetically inert.

During prophase the chromatin fibres condenses to form chromosomes 2/1/2013

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Nucleolus (Fontana in 1781) Is a naked round structure which is attached to the chromatin at specific region called Nucleolar organizer region.

NOR regions of chromosome associated with nucleolus and containing genes for rRNA. Commonly 1-4 nucleoli are found in a nucleus.

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Nucleolus Has four components Amorphus matrix – homogenous ground substanceprotein Granular part- Granules of Protein, RNA Fibrillar portion- made of protein-RNA to be precursor of granules.

Chromatin portion- that part of chromatin associated with nucleolus 54

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Nucleolus- Function Principle site of development of ribosomal RNA Centre of formation of ribosomes

Forms nucleo proteins Essential for formation of spindle fibres during nuclear division.

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Functions of Nucleus • Possess genetic information • Controls all cellular activities.

• Variations are caused due to changes in genetic material • Helps in cell growth and membrane development.

• For cell differentiation by allowing certain sets of genes.

• Cell replication

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Thank you 2/1/2013

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