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An animal cell, the organelles are small, membranous cellular inclusion, floated in the cytosol.

They keep various cellular activities separated from one to another.

Organelles

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Nucleus

Nucleus is a largest organelle, has a dia meter of about 5 μm.

Prominent organelle in eukaryotic cell

Stores genetic information

Separated from the cytoplasm by nuclear

envelope.

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Nuclear envelope or nuclear membrane consists of inner membrane and outer membrane.

The space between inner and outer membrane is continues with the lumen of rough endoplasmic reticulum.

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The two nuclear membranes fuse at the

nuclear pores.

Nuclear pores are constructive of specific set of membrane protein.

It functions as channel between the nucleus and the cytosol.

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It regulates the movement of the material from and to the nucleus.

Protein fibers associated with the inner membrane of the nuclear envelope

Protein fibers maintain the shape of nucleus and provide chromatin attachment.

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The nucleus contains the nucleoplasm, the nucleolus, fibrous matrix, DNA-protein complex, chromatine-chromosome.

Chromatine looks grainy, but actually it is thread like material.

Chemical analysis shows that chromatine and chromosomes contain DNA, protein and some RNA

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Chromatin undergoes coiling into chromosome just before the cell divides

It is immersed in the nucleoplasm

Nucleoplasm is sugested has a different composition from cytosol

The DNA of all chromosomes is packaged into a compact structure with the aid of specialized proteins.

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It is traditional to divide the DNA-binding proteins in eucaryotes into two general classes: the histones and the nonhistone chromosomal proteins.

The complex of both classes of proteins with the nuclear DNA of eucaryotic cells is known as chromatin.

Histones are unique to eucaryotes.

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DNADNA is the hereditary or genetic material.

DNA stores information regarding its own replication and the order in which amino acid are to the joined to make protein

Nucleotide is a molecular complex of three types of molecule: phosphate, pentose sugar and a nitrogen containing base.

DNA is double stranded, the two strands twisted about each other in the form of double helix.

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The sugar in DNA is deoxyribose → deoxy ribonucleic acid.

The bases in DNA consist of purine (two rings) and pyrimidine (one ring).

The purine: Adenine (A) and Guanine (G)

The pyrimidine:Thymine (T) and Cytosin (C)

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The sugar and phosphate as the backbone of the strand and the bases project to one side of the backbone.

Between the strands, Thymine (T) always paired with Adenine (A) and Guanine (G), with Cytosin (C).

It is called complementary.

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NUCLEOLUS

Usually one nucleus has one nucleolus, but sometime one nucleus has more than one nucleolus or nucleoli.

Nucleolus is the one or two dark regions of

the chromatine, where ribosomal RNA (rRNA) is produced.

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rRNA joints with protein to form subunits of the ribosomes.

The subunits of the ribosome leave the nucleus enter the cytoplasm.

The subunits joint together in the protein synthesis.

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Endoplasmic Reticulum

ER is an interconnected network of internal membrane

Has a number of functions in synthesis of many membrane lipid and proteins

Smooth ER (sER) it lacks ribosomes. Rough ER (rER) are studded with ribosomes

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The smooth ER is the site of synthesis and metabolism of fatty acids and phospholipids.

The rough ER synthesize certain membrane protein and organelle proteins

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Secretory polypeptide from ribosom, passes through rER, accumulate in the lumen of rER before transported.

Rough ER is particularly abundant in cells that specialized to produce secreted proteins.

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The pancreatic acinar cells synthesize digestive enzyme such as chymotrypsin, because the cytosol filled with rER.

The plasma cells produce antibodies also caused by abundant rER in the cytosol.

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Smooth ER are abundant in hepatocyte. Enzyme in sER of the liver modify or detoxify chemicals.

High doses of pesticides or carcinogens result in a large proliferation of sER in the liver.

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Smooth ER also forms transport vesicles, in which large molecules are transported.

The secretory proteins are found in the lumen of rER will be transfered to the Golgi vesicles.

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Ribosome.

Small particles composed of RNA and proteins.

Composed of 2 subunits, a large subunit and a small subunit.

Perform a very important function, they carry out the protein synthesis.

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Several ribosom synthesizing the same protein are called polysome.

Polysome can lie freely in the cytosol or attached to ER.

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Cells that produce proteins for secretion, contain a ten million ribosomes.

The ribosomal RNA is produced in the nucleolus and the subunits of ribosomes are assembled.

The subunits of ribosoms pass through the nuclear envelope at nuclear pore.

Some remains free within cytoplasm and some attached to ER.

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Most proteins in mitochondria and all of the protein in the other organelles, membrane etc. are encode by nuclear DNA and are synthesized on ribosome in the cytosol.

The membrane attached and membrane unattached ribosomes synthesized different protein.

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On membrane attached, the protein synthesized are those that enter the secretory pathway during synthesized

This include secretory protein, lysosomal enzymes, and proteins in the lumen of ER, Golgi vesicles, secretory vesicles and plasma membrane

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Golgi Apparatus

Discovered by Camillo Golgi → named Golgi apparatus.

Consists of a stack of 3 – 20 curved saccules.

The inner face is directed toward the ER and the outer face toward the plasma membrane.

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Vesicles can frequently be seen at the edges of the saccules.

Protein or lipid filled vesicles that bud from the sER are received at the inner face or cis face.

Golgi Apparatus contains enzymes that alter the carbohydrate chains of glyco- proteins from rER.

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The monomer carbohydrates could be modified or phosphate might be added

The products in vesicles depart the Golgi apparatus at the outer face or trans face.

The vesicles move to the other organelles such as lisosome.

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Some vesicles proceed to plasma membrane and discharge their contents as secretion.

The secretion is termed exocytosis.

Some of secretory proteins are secreted continuously.

Collagen secretion by fibroblast and serum protein by hepatocytes are continuous secretion.

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Continuous secretion also termed as constitutive secretion.

In certain cells the secretion is not conti- nuous but stored inside the vesicles,

The secretory vesicles.

The stimulus for exocytosis triggered the secretory vesicles to release the secretion.

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The secretion is termed as regulated secretion.

Examples of this: exocrine cells of pancreas which secrete precursor of digestive enzyme, hormone secreting endocrine cells synthesize insulin and other hormones and store them in the vesicle secretory.

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Maturation of secretory protein: from ER → cis Golgi reticulum: modification on carbo- hydrate chains.

From Golgi face, trough Golgi vesicles migrate to further modification to medial Golgi → trans Golgi reticulum.

The proteins are shuttled between Golgi vesicles by small transport vesicle.

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Some proteins are stored in secretory vesicle awaiting a signal for secretion.

Proteins are also sorted in the trans Golgi vesicle to lysosome.

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Lysosome

Vesicles produced by Golgi apparatus.

Contains hydrolytic digestive enzymes.

Molecules are brought into cell → fuse with lysosome → digested by enzyme → simple subunits → cytoplasm.

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Bacteria are engulfed by white blood cell → fuse with lysosome → digested.

Autodigestion:parts of the cells are digested by its own enzymes → rejuvenation, during development, apoptosis or programmed cell death.

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A metabolic disorder: a missing or inactive lysosomal enzymes → macromolecules cannot be broken down → full of lysosome → die.

The lysosomal enzymes are precursors: proenzyme → maturation → enzymatically active polypeptide.

Maturation occurs in the acidic endosome or lysosome..

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lysosomal enzyme inserted into the ER lumen, receive olygosaccharide. from ER move to cis Golgi

In the cis Golgi the olygosaccharide become phosphorilated → mannose 6 phosphate

In order the lysosomal enzyme diverted to lysosome it must bind to receptor M6P

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PEROXISOME

Microbodies are small vesicle bounded by membrane contain specific enzymes.

Peroxisomes are microbodies that contain enzymes for oxidizing small organic molecules with the formation of hydrogen peroxide (H2O2).

Peroxisomes are present in all eukaryotic cells.

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The size and enzyme composition vary considerably, but peroxisomes are always contain catalase or peroxidase

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Microbodies are produced by ER. Their proteins are encoded by nuclear genes.

Peroxisomes lead to progressive enlargement and divided into new ones.

Peroxisomes membrane are also synthe sized on free ribosomes.

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Receptor and transport proteins in the peroxisome membrane are also required.Mutation → defective peroxisome assembly.Zellweger syndrome → the transport of all proteins in the peroxisome matrix is impaired.The cells contain empty peroxisomeThe mutation → defect in the receptor or transport protein.The patients has defective in the oxidation of the very long chains fatty acids.

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Mitochondria

Most eukaryotic cells, plants and animals contain mitochondria.

Mitochondria → formation of ATP (adenosine triphosphate).

The size and the shape is variable usually 0.5-1.0 um in diameter and 2-5 um in length.

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Mitochondria as the nucleus is bounded by two different membrane, the inner and the outer membrane.

The outer membrane contains the protein porin, → form transmembrane channels → freely permeable to small molecules, particularly to protons.

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The inner membrane contains cardiolipin, the lipid concentrated → reduce the permeability to protons → permeability barrier between cytosol and matrix.

The inner membrane invaginates → cristae → provide a much greater surface area.

The cristae project into the matrix, the inner space filled with semifluid medium contains enzymes.

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The enzymes break down carbohydrates and lipids products → ATP production.

The matrix also contains DNA and ribosome → synthesize its own protein.

Metabolism of pyruvate and fatty acids.

In the cytosol, glucose by glycolysis is converted to pyruvate and lipids are hydrolyzed to fatty acids and glycerol.

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Pyruvate and fatty acids transported into matrix → oxidized to acetyl CoA

The final stage of the oxidation is the citric acid cycle or Krebs cycle → NADH and FADH2

The free energy released during oxidation of NADH and FADH2 → ATP from ADP.

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The inner membrane and the matrix are the sites of the synthesis of ATP from ADP and P.

The processes are very complicated.

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