CELL AND ITS ORGENELLSDR. ASHISH PATEL

Assistant professorDept. AGB, Veterinary College,

AAU, Anand

Cell Cell is the structural and functional unit of living

organism There are two main groups of cells. and eukaryotic

cells.Prokaryotic cell Eukaryotic cell• Cells that have membrane-

bound nucleus• Cells also contain internal

membrane-bound structures called organelles, such as mitochondrion or chloroplast

• The genetic information is on a chromosome which are found in nucleus

• Prokaryotic cells shapes: irregular e.g. Animals, Plants, Fung, Algae, Protozoa

• Cells that lack a membrane-bound nucleus

• The genetic information is in a circular loop called a plasmid.

• Prokaryotic cells shapes: rod shaped, spherical, and spiral.

• Replication by binary fission.

• E.g. Bacteria

Prokaryotic cell Eukaryotic cell

Animal Cell

Plant Cell

Animal cells are typical of the eukaryotic cell, enclosed by a plasma membrane and present in different shapes and containing a membrane-bound nucleus and cell organelles.

Cell contents are called the protoplasm. Most cells, both animals and plants, range in size between

1 and 100 micrometers and are thus visible only with the aid of a microscope.

In 1665, Robert hook discovered “Cell”. In 1839 Theodor Schwann formulated the Cell Theory

which set the concept that “the elementary parts of all tissues are formed of cells through much diversified in manner”.

Animal cell is distinct from other eukaryotes especially plant cells by lack of cell walls and chloroplasts, and have smaller vacuoles.

Animal CellCell Organelles Various membrane bound structures found within a cell are

knowCell Membrane (Plasma membrane/Plasmalemma/ phospho-

lipid bilayer) Cell membrane is of double layer of phospholipids. It physically separates the intracellular components from

the extra cellular environment and also serves as a protection layer for the interior of the cell.

The phosopholipids are "hydrophobic" (water fearing), so the cell membrane acts as a protective barrier to the uncontrolled flow of water.

The cell membrane is selectively permeable, which allowing some substances to pass into the cell and blocking others.

The membrane contains numerous proteins which include receptors for odours, tastes and hormones, as well as pores responsible for the controlled entry and exit of ions like sodium (Na+) potassium (K+), calcium (Ca++) and chloride (Cl-).

Cytoplasm Cytoplasm is a collective term for the cytosol plus the

organelles suspended within that cytosol. The cytoplasm has three major elements as follows,

• Cytosol • Organelles and • Inclusions

Cytosol The cytosol is the gel like fluid within which all the

other cell organelles reside. It is the internal fluid of the cell.

Most of the cellular metabolism occurs within it. Proteins in cytosol control cell metabolism

including signal transduction pathways, glycolysis, intracellular receptors and transcription factors.

Centrosome It also called the "microtubule organizing center (MTOC)". It is a small body located near the nucleus where

microtubules are produced. The centrosome is duplicated during cell division resulting

in two centrosomes, each with its own pair of centrioles. Centriole Centrioles are barrel shaped self-replicating organelles

found in most animal eukaryotic cells (absent in plants and fungi).

Centriole is made up of ring of nine bundles of microtubules and each bundle is composed of three microtubules (protein of the cytoskeleton).

Centrioles are involved in the organization of the mitotic spindle.

Golgi Apparatus It also called as Golgi body or Golgi complex or

Dictyosome. It is an organelle composed of membrane-bound stacks

known as cisternae. The Golgi body processes and packages the

macromolecules such as proteins and carbohydrates synthesized by the cell into membrane bound vesicles for cell secretion (exocytosis) or for use within the cell.

The enzymatic or hormonal contents of lysosomes, peroxisomes and secretory vesicles are packaged in membrane-bound vesicles at the periphery of the Golgi apparatus.

Endoplsmic Reticulum The cytoplasm contains an extensive network of membrane enclosed

spaces; these spaces along with the membrane enclosing them are known as Endoplasmic Reticulum (ER).

The main functions of ER are (1) It provide structural base for synthesis of proteins (Rough ER),

hormones (Smooth ER), lipids, phospholipids (both rough ER and smooth ER)

(2) It provides channel for the transport of materials synthesized in association with ER to various parts of cell.

ER grouped in to two categories.

Smooth Endoplsmic Reticulum

The smooth endoplasmic reticulum is named because its outer and inner surfaces are appears smooth and regular.

In those cells where only smooth ER found, where there are little or no any protein synthesis occurs.

Smooth ER plays different functions depending on the cell type like lipid and steroid hormone synthesis, breakdown of lipid-soluble toxins in liver cells and control of calcium release in muscle cell contraction.

Rough Endoplasmic Reticulum The surface of the rough ER is found with protein-

manufacturing ribosomes giving it a "rough" appearance.

Proteins synthesized on these ribosomes are collected in the endoplasmic reticulum for transport throughout the cell.

Ribosomes Ribosomes are packets of RNA and protein that are sites

for protein synthesis (that process called as Translation). Messenger RNA from the cell nucleus is moved at the

ribosome where transfer RNA adds individual amino acid molecules to form a protein chain.

Each ribosome comprises of two parts - a large subunit and a small subunit.

Ribosomes are classified as being either "free" (anywhere in the cytoplasm) or "membrane-bound" (endoplasmic reticulum).

Mitochondria Mitochondria also called as “Power House of Cell". Mitochondria are spherical to rod-shaped organelles with

a double membrane.

The inner membrane is infolded many times, forming a series of projections called as cristae. On these cristae the food (sugar) is combined with oxygen to produce ATP - the primary energy source for the cell.

The most prominent role of the mitochondria is production of energy, which stored in the form of glucose by conversion into ATP (adenosine triphosphate) - the primary energy source for the cell.

Lysosome It is also known as cell vesicles/suicide-bags/suicide -

sacs. Lysosomes are organelles that contain digestive enzymes

necessary for intracellular digestion. They are common in animal cells, but rare in plant cells. They digest excess or useless organelles, food particles, and

engulfed viruses or bacteria, which are transferred to the cytoplasm as new cell-building materials.

Peroxisome Peroxisomes are membrane-bound packets of oxidative

enzymes. Peroxisomes break down organic molecules by the

process of oxidation to produce hydrogen peroxide and then quickly into water and oxygen.

They are called peroxisomes because they all produce hydrogen peroxide.

Secretory vesicle It is a membrane bounded vesicle derived from the golgi

apparatus and cell secretions viz. hormones, neurotransmitters are packaged in secretory vesicles at the Golgi apparatus.

The secretory vesicles are then transported to the cell surface for release.

Vacuoles A vacuole is a membrane-bound sac that plays roles in

intracellular digestion and the release of cellular waste products.

Vacuoles are generally small in animal cell but large in plant cells.

Cytoskeleton Cytoskeleton is a network of protein filaments and motor

proteins in the cytoplasm that give shape to a cell, hold and move organelles, and typically involved in cell movement.

The cytoskeleton maintains the cell shape. Nucleus (Controlling center of the cell) Generally there is a single nucleus per cell that is spherical or

oval in shape. The nucleus is the largest cellular organelle that includes the

nucleolus. It is enclosed by a nuclear envelope, a double membrane and

communicates with the surrounding cytosol via numerous nuclear pores.

The viscous liquid within the nucleus is called nucleoplasm. Nucleus contains most of the cell's genetic material, double

helix DNA molecules held in complex manner with proteins, (histones protein) to form chromosomes.

Nucleus has DNA within it. The DNA is similar in every cell of the body, but depending on the specific cell type, some genes may be turned on or off – that is why a liver cell is different from a muscle cell and a muscle cell is different from a fat cell.

The main function of the nucleus is the coordination of the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division).

A nucleus consists of three main parts, viz., nuclear membrane, nucleolus and chromation

Nuclear Membrane (perinuclear envelope /nucleolemma / karyotheca)

It is a double membrane surrounds the nucleus and separates the contents of the nucleus (DNA in particular) from the cytosol (cytoplasm).

Nuclear Pores They are formed at sites where the inner and outer

membranes of the nuclear envelope are joined. Nucleolus The nucleolus is a membraneless organelle found in the

nucleus. The main function of the nucleolus is the biogenesis and

assembly of ribosome components. Some cells have more than one nucleolus, but some cell do

not have any. Nucleolus is a spherical body found in the nucleus. It

disappears during prophase of mitosis and meiosis and reappears during telophase.

Nucleolus consists of three parts, viz., granules, fibrils and matrix. Granular region contains proteins and RNA. The matrix contains scattered granules and fibrils.

Functions of Nucleolus: Formation of ribosomes Synthesis of RNA.Chromatin: Chromatin refers to partly clumped and tangled mass of

nuclear chromosomes. The chromatin fibre contains about 55 per cent proteins,

40 per cent DNA and 4‑5 per cent RNA. Chromatin is a basic unit of chromosomes, contains

genes and thus plays an important role in the inheritance of characters from the parents to their offspring.

We studied which structures of an animal cell ?

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