WELCOME TO MY PRESENTATION

ON

NUCLEUS & ENDOPLASMIC RETICULUM

Submitted ToDr. Sayda Rehana

Assistant Professor

Biotechnology & Genetic Engineering

Khulna University

Khulna

Submitted ByMd. Moin Uddin Talukder

Student Id:130703

1st YEAR, 2nd TERM

Biotechnology & Genetic Engineering

Khulna University,

Khulna

Course Title: Cytology

Course No: BGE-1203

DATE OF SUBMISSION: June 23,2014

DISCOVERY OF NUCLEUS

• It was discovered by A.V Leeuwenhoek for the first time.

• Franz Bauer also described it in 1804.

• In 1831 Scottish Botanist Robert Brown explained it in more detail in a talk at the Linnean Society of London.

Oldest known depiction of cells and their nuclei by Antonie van Leeuwenhoek, 1719.

DEFINITION OF NUCLEUS

• The nucleus (pl. nuclei; from Latin nucleus or nucleus, meaning kernel) is a membrane-enclosed organelle found in eukaryotic cells (plant, animal, fungal, and Protista).

• It is the control center of the cell.

• The nucleus is a large organelle and contains most of a cell’s genetic material.

MAIN CHARACTERISTICS• Membrane-enclosed

organelle found in eukaryotic cell.

• Generally found in the central region of the cell (in animal cell).

• It appears as a dense, roughly spherical organelle.

• Largest & most easily seen organelle.

SIZE & SHAPE• It is a spherical organelle.

• It is approximately 3-10 μm in diameter

• Usually only one nucleus is present in each cell but certain cells maybe binucleate (e.g., some liver cells) or multinucleate (e.g., skeletal muscle cells).

ULTRASTRUCTURE OF NUCLEUS

STRUCTURE• Nuclear Envelope

• Nuclear Pores and complex

• Nuclear lamina

• Chromosomes & Chromatin

• Nucleolus

• Nucleoplasm

• Subnuclear bodies

Average diameter of nucleus is 6um, which occupies around 10% of cell volume. Basic components of nucleus are:

NUCLEAR ENVELOPE

• Also known as perinuclear envelope, nuclear membrane or karyotheca.

• Encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm.

• It is a lipid bilayer.

• Consists two cellular membranes, an inner & outer membrane, arranged parallel to one another and separated by 10-50(nm) of space.

NUCLEAR PORES

• Nuclear pores are aqueous channels through the nuclear envelope.

• Composed of multiple proteins called nucleoporins.

• Have molecular weight of 125 million Daltons.

• Nucleus of a cell has 3000 - 4000 pores.

• Pores are formed by fusion of outer and inner nuclear membranes.

• NPC permits passive movement across the nuclear envelope via 9-11nm channels by simple diffusion.

• Allows free passage of water soluble molecules

• Most proteins, ribosomal subunits and RNA are transported via transport factors called KARYOPHERINS.

NUCLEAR PORE

NUCLEAR LAMINA

• Network of intermediate filaments ,Composed primarily of lamins A, B1, B2 and C.

• Helps in organizing the nuclear envelope and perinuclear chromatin ,Also plays a role in DNA elongation phase.

• Essential during mitotic events where, Phosphorylation of lamins leads to disassembly, and dephosphorylation results in reassembly of the nuclear envelope.

• Apoptosis a highly regulated process in which nuclear lamina is disassembled following proteolytic activity of capase protein.

0UTER MEMBRANE • 6 nm thick.

• Faces cytoplasm and is continuous at certain sites with the RER.

• A loosely arranged mesh of intermediate filaments (vimentin).

• Ribosomes stud the cytoplasmic surface of the outer nuclear membrane.

• Ribosomes synthesize proteins that enter the perinuclear cisterna (space between two membranes 20-40nm wide).

INNER MEMBRANE • Faces the nuclear material.

• Primary site for location of inner nuclear membrane proteins IMP.

• Inner membrane proteins – LAP2, SUN1, EMERIN, MAN1, LBR (used during formation of NE during mitosis as well as some role in transcriptional activity).

• Outer and inner membranes are fused at the nuclear pore complex sites.

• Inner Membrane is supported underneath by Nuclear lamina.

NUCLEOLUS • Nucleolus is the discrete densely stained structure found in nucleus

• It is a nuclear inclusion that is not surrounded by a membrane

• Present in cells that are actively synthesizing proteins

• Its size depends on metabolic activity of cell

• Average size .5-5um in dia

• It is generally detectable when the cell is in interphase

• Synthesis of rRNA and its assembly into ribosome precursors- main function

• More than one nucleolus can be present in the nucleus.

CHROMOSOMES & CHROMATIN

• It is an organized structure of DNA

• Containing genetic information of cell, regulatory elements and other nucleotide sequences

• Chromatin is a complex of DNA and histone protein, which packages chromosomes also known as nucleosomes

• The structure of chromosomes and chromatin varies throughout the cell cycle

• Interphase chromatin consists of euchromatin and heterochromatin (chromosomes are not visible during this phase)

• Euchromatin – contains active form of DNA.

• Heterochromatin - contains inactive form.

• Metaphase chromatin- the chromatin becomes more and more condensed and compact, making the chromosome visible with a classic four arm structure, having a pair of sister chromatids attached at centromere.

• Humans have 23 pairs of chromosomes- 22 are autosomes & 2 sex chromosomes.

NUCLEOPLASM

• Nucleoplasm is the protoplasm within the nuclear envelope

• It consists of a nuclear matrix and various types of particles

• Highly viscous liquid which scaffolds chromosomes, nucleolus and various granules like heterochromatin, perichromatin granules

• Many substances like nucleotides and certain enzymes are also dissolved in it.

NUCLEOPLASM

SUBNUCLEAR BODIES

• Nucleus contains a number of non-membrane delineated bodies which are present in the nucleoplasm

Subnuclear structures namely

• Cajal bodies

• PIKA bodies

• PML bodies

• Paraspeckles

• Speckles

FUNCTIONS OF NUCLEUS

• It stores the cell's hereditary material, or DNA.

• Site of DNA replication

• Site of DNA transcription to mRNA

• Ribosomal formation

• Nucleolus: RNA & protein required for ribosomal synthesis

• It coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division) by regulating gene expression.

CHEMICAL COMPOSITION

• Basic proteins ( Protamines and Histones ): They are simple basic proteins, having low molecular weight.

• Acid proteins ( Non-Histones ): Nuclear phosphoproteins are important non-histone proteins found mainly in diffuse chromatin or active chromatin or euchromatin.

• Nuclear enzymes: The enzymes of nucleoside metabolism namely adenosine diaminase, nucleoside phosphorylase, guanase etc are present.

• Nucleic acids: The nucleic acids, DNA and RNA form most part of the nucleus. Both are made of fundamental repeating units called nucleotides.

• Lipids: They occur mainly as lipoproteins or phospholipids.

• Inorganic and other compounds: The nucleus has a greater concentration of ash than the cytoplasm. The ash is mainly composed of phosphorous, potassium, sodium and particularly calcium and magnesium.

Conclusively cell nucleus is the storehouse of everything what a cell shall do in future, since it handles the gene expression and overall metabolism of cellthus called “DIRECTOR OF CELL”.

WHO DISCOVERED THE ER?

• The endoplasmic reticulum were first seen in 1945 by Keith R. Porter, Albert Claude, Brody Meskers and Ernest F. Fullam.

• Used the newly developed electron microscope to explore the interior of cells in 1945 observed the presence of a “lace-work structure.”

• 1952- ER term used by Porter and Kallman in their published article.

DEFINITION OF ENDOPLASMIC RETICULUM• The endoplasmic reticulum

(ER) is a type of organelle in the cells of eukaryotic organisms.

• It forms an interconnected network of flattened, membrane-enclosed sacs or tubes known as cisternae.

HOW DOES THE ER LOOKS LIKE?

• Rough ER appears as lumpy sheets of folded membranes; the lumps are the ribosomes. They are not permanently attached, adhering only when there is protein manufacturing work to be done.

• Smooth ER which isn't coated with ribosomes looks like smooth tubes.

ULTRASTRUCTURE

MAIN CHARACTERISTICS

• These are membrane bound channels, seen in the form of a network of delicate strands and vesicles in the cytoplasm.

• These are single membrane cell organelles.

• These form an interconnected network of tubules, vesicles and cisternae with in cells.

• ER are considered as one of the components of cytoskeleton along with microtubules, microfilaments and intermediate filaments.

• There are two basic morphological types of ER namely RER and SER.

• The ER membrane is thinner (50 Ǻ) than that of plasma membrane (80-100Ǻ thick).

LOCATION • Present in almost all eukaryotic cell.

• These are found to be absent in mature erythrocytes, ova, embryonic cells and prokaryotes.

• The ER often occupies most of the cytoplasm.

AMOUNT • The ER varies in amount from cell to cell. In spermatocytes, it is represented by a few vacuoles only.

• In the cells of adipose tissue, it is quite simple, having the form of a few tubules.

• The cells that are actively synthesizing proteins, such as liver and pancreatic cells and fibroblast, have abundant ER.

• Endoplasmic reticulum forms 30-60 % of the total membrane in a cell.

ORIGIN OF ENDOPLASMIC RETICULUM

• At present manner of origin of the endoplasmic is not definitely known. The most concrete hypothesis is that the ER is “budded” off from the nuclear envelope (Wischnitzer, 1974).

• The ER appears to arise from the outer membrane of the nuclear envelope by out folding , or from the plasma membrane by in folding.

• The smooth ER seem to arise from the rough ER by detachment of ribosomes.

PHYSICAL STRUCTURE

The ER is three dimensional network of intracellular. It is formed of three types of element:

1. Cisternae

2. Tubules

3. Vesicles

CISTERNAE • These are flattened , unbranched, sac-like element.

• They lie in stacks parallel to one another.

• They bear ribosomes on the surface that, therefore, appears rough.

• It contain glycoproteins named ribophorin-I & ribophorin-II that bind the ribosomes.

These are irregular branching element which form a network along with other element.

These are often free of ribosomes.

TUBULES

VESICLES • These are oval and rounded ,vacuole like element.

• These are also free of ribosomes.

• All the element of ER freely communicates with one another, and contain a fluid called endoplasmic matrix, in the ER lumen.

• These matrix is different from cytoplasmic matrix outside the ER

• The ER may pass from one cell to another through the plasmodesmata in the form of desmotubules.

ENDOPLASMIC MATRIX

• The space inside the tubules and vesicles is filled with a watery medium that is different from the fluid in the cytosol outside the ER.

• Their walls are constructed of lipid bilayers membranes that contains large amount of proteins , similar to the cell membrane.

• There are two basic morphological types of ER namely RER and SER.

• The ER membrane is thinner (50 Ǻ) than that of plasma membrane (80-100Ǻ thick)

MOLECULAR STRUCTURE

The membrane of ER are composed of two layers of phospholipid molecules sandwiched by two layers of proteins molecules like other membrane in the cell wall.

TYPESThe endoplasmic reticulum is of two types:

1. Rough endoplasmic reticulum (SER)

2. Smooth endoplasmic reticulum (RER)

ROUGH ENDOPLASMIC RETICULIM (RER)

• The surface of the RER is studded with ribosome, giving it a rough appearance.

• It mainly consists of cisternae.

• The membrane of the RER forms large double membrane sheets

• Which is located near and continuous with the outer layer of the nuclear envelope.

• RER is very important in the synthesis and packaging of proteins e:g, Russell’s bodies of plasma, nissel’s granules of nerve cell

• Binding site of the ribosome on the RER is the translocon.

• The ribosomes bound to the RER at any one time are not a stable part of this organelles structure

• Because ribosomes are constantly being bound and released from the membranes.

• Ribosomes only binds to the RER once a specific protein-nucleic acid complex forms in the cytosol.

• This special complex forms when a free ribosome begins translating the mRNA of a protein destined for the secretory pathway.

• The first 5-30 amino acid polymerized encode a single peptide, a molecular message that is recognized and bound by a single recognition particle (SRP). The ribosomes that become attached to the endoplasmic reticulum synthesize all trans membrane proteins.

• Most secreted proteins that are stored in the Golgi apparatus, lysosomes, and endosomes.

• Translation pauses and the ribosomes complex binds to the RER translocon

SMOOTH ER

• Smooth ER is an arrangement of tubules, vesicles and sacs.

• The size and structure of the SER varies between the cells.

• The SER can change within a cells lifetime to allow the cell to adapt to changes in its function and requirements.

• There are no ribosome’s attached to the membrane surface.

• The SER is connected to the nuclear envelope.

• The network of the SER allows there to be enough surface area for the action or storage of key enzymes or the products of the enzymes.

• The SER is less stable.

• The SER is characteristic of cells in which synthesis of non-protein substances takes place

ROUGH ER VS SMOOTH ER

ROUGH ER

• Ribosomes on its outer surface.

• Site of synthesis of proteins destined for secretion.

SMOOTH ER

• Not associated with ribosomes.

• Involved in lipid metabolism.

SARCOPLASMIC RETICULUM (SR)

• The sarcoplasmic reticulum (SR) is smooth ER found in smooth and striated muscle.

• The only structural difference between this organelle and the smooth endoplasmic reticulum is the medley of proteins they have, both bound to their membranes and drifting within the confines of their lumens. This fundamental difference is indicative of their functions.

• The endoplasmic reticulum synthesizes molecules, while the sarcoplasmic reticulum stores and pumps calcium ions. The sarcoplasmic reticulum contains large stores of calcium, which it sequesters and then releases when the muscle cell is stimulated.

• It plays a major role in excitation-contraction coupling in muscles cells.

PROTEIN TRANSPORT

• As proteins are formed in the endoplasmic reticulum, they are transported through the tubules toward proteins of the SER that lie nearest to Golgi apparatus.

• At this point, small transport vesicles composed of small envelopes of smooth ER continually break away and diffuse to the deepest layer of Golgi apparatus.

• Inside this vesicles are the synthesized proteins and other product from the ER present.

FUNCTION OF RER • Surface for Ribosomes: The RER provides

space and ribophorins for the attachment of ribosomes to itself.

• Surface for protein synthesis

• Formation of Glycoprotein: Linking of sugars to for glycoprotein starts in the RER and is completed in Golgi complex.

• Synthesis of precursors: The RER produce enzyme precursors for the formation of lysosomes by Golgi Complex.

• Smooth ER formation: The RER gives rise to the smooth ER by loss of ribosomes.

FUNCTION OF SER

• The smooth endoplasmic reticulum lacks ribosomes and functions in lipid metabolism, carbohydrate metabolism, and detoxification and is especially abundant in mammalian liver and gonad cells.

• It also synthesizes phospholipids. Cells which secrete these products, such as those in the testes, ovaries, and skin oil glands have a great deal of smooth endoplasmic reticulum.

• Detoxification-The SER brings about detoxification in the liver , i.e., converts harmful materials(drugs, poisons) into harmless ones for excretion by the cell.

• Formation of organelles- The SER produces Golgi apparatus , lysosomes and vacuoles.

• It also carries out the attachment of receptors on cell membrane proteins and steroid metabolism.

• In muscle cells, it regulates calcium ion concentration

• The smooth endoplasmic reticulum also contains the enzyme glucose-6-phosphatase, which converts glucose-6-phosphate to glucose, a step in gluconeogenesis.

TRANSPORT VESICLES

• They are surrounded by coating protein called COP I, COP II.(Coat Protein complex)

• COP II targets vesicles to the Golgi apparatus.

• Transparent proteins from the RER to Golgi apparatus.

• This process is termed as anterograde transport.

• COP I transports proteins from the cis end of the Golgi complex back to the RER.

• This process is termed as retrograde transport.

THANK YOU