Lec.1Lec.1Date:11/12/2011 Dr: Date:11/12/2011 Dr: Buthaina Al-SabawiButhaina Al-Sabawi

Cell BiologyCell Biologycellscells

A cell is the basic unit of structure and function in a living thing.  All living things are made up of cells and share a common genetic code, store genetic information in nucleic acids (usually DNA), transfer genetic information from DNA to RNA to protein. Most cells carry out all the activities needed to stay alive. The aqueous phase of cell contains a wide variety of solutes, including inorganic ions, building block major organic constituents, intermediates in metabolic pathways (carbohydrates, and lipid energy stores, and high concentrations of proteins and RNA) in addition, eukaryotic cells have a dense network of cytoskeletal fibers.

One of the most interesting features of cytoplasm is its ability to change from a liquid (or sol) state to semisolid (or gel) state.The cytoplasm is composed of cytosol, organelles and inclusions.

Cellular OrganellesEukaryotic cells involved membrane-bound compartments specialized to provide energy; to synthesize lipids, carbohydrates, proteins, and nucleic acids and to degrade cellular constituents. These

subcellular compartments, called organelles.,

organelles vary in abundance and size in different cell types, even within multicellular organisms, in which each tissue and organ has specialized functions. A semipermeable membrane surrounds each organelles

Endoplasmic reticulumEndoplasmic reticulumStructure:Structure: One of the key distinguishing featues of eukaryotic cells One of the key distinguishing featues of eukaryotic cells

is the presence of the endoplasmic reticulum(ER), the is the presence of the endoplasmic reticulum(ER), the largest of numerous membrane compartments. It provides largest of numerous membrane compartments. It provides both an expanded membrane surface (up to 30 times that both an expanded membrane surface (up to 30 times that of the plasma membrane) for carry out vital cellular of the plasma membrane) for carry out vital cellular functions, including protein and lipid biosynthesis.functions, including protein and lipid biosynthesis.

The largest of the internal membranes is called the The largest of the internal membranes is called the endoplasmic reticulum (ER). Endoplasmic means "endoplasmic reticulum (ER). Endoplasmic means "within within the cytoplasmthe cytoplasm" , and reticulum is Latin for "" , and reticulum is Latin for "a little neta little net". ". Like the plasma membrane, the ER is composed of a lipid Like the plasma membrane, the ER is composed of a lipid bilayer embedded with proteins. It weaves in sheets bilayer embedded with proteins. It weaves in sheets through the interior of the cell, through the interior of the cell,

Creating a series of channels its folds. The Creating a series of channels its folds. The endoplasmic reticulum (ER) is an organelle found in endoplasmic reticulum (ER) is an organelle found in all eukaryotic cells is an interconnected network of all eukaryotic cells is an interconnected network of tubules, vesicles and an extensive membrane network tubules, vesicles and an extensive membrane network of cisternae (sac-like structure)held together by of cisternae (sac-like structure)held together by cytoskeleton. The endoplasmic reticulum is part of cytoskeleton. The endoplasmic reticulum is part of the endomembrane system. The phospholipid the endomembrane system. The phospholipid membrane encloses a space, the cisternal space (or membrane encloses a space, the cisternal space (or lumen),from the cytosol. The functions of the lumen),from the cytosol. The functions of the endoplasmic reticulum vary greatly depending on the endoplasmic reticulum vary greatly depending on the exact type of endoplasmic reticulum and the type of exact type of endoplasmic reticulum and the type of cell in which it resides.cell in which it resides.

FunctionFunction:: The membrane surface of the performs several The membrane surface of the performs several

functions for cells, fore most is the production functions for cells, fore most is the production of the proteins and lipids that will make up the of the proteins and lipids that will make up the membranes of the other organelles, including membranes of the other organelles, including the Golgi apparatus, nucleus, endosomes, the Golgi apparatus, nucleus, endosomes, lysosomes and plasma membrane, as well as lysosomes and plasma membrane, as well as nearly all proteins that will be secreted from nearly all proteins that will be secreted from the cell. Another key function of the ER the cell. Another key function of the ER membrane is to form the nuclear envelope, membrane is to form the nuclear envelope, which encloses the nucleuswhich encloses the nucleus..

There are two distinct types of ER that perform different There are two distinct types of ER that perform different functions within the cell. ER is responsible for several functions within the cell. ER is responsible for several specialized functions: Protein translation, folding, and specialized functions: Protein translation, folding, and transport transport of of proteins to be used in the cell membrane proteins to be used in the cell membrane (e.g., transmembrane receptores and other integral (e.g., transmembrane receptores and other integral membrane proteins), or to be secreted (exocytosis) from membrane proteins), or to be secreted (exocytosis) from the cell (e.g., digestivethe cell (e.g., digestive enzymes); sequestration of enzymes); sequestration of calcium; and production and storage of glycogen, calcium; and production and storage of glycogen, steroids, and other macromoleculessteroids, and other macromolecules..The rough ER, which is covered by proteinThe rough ER, which is covered by protein- - manufacturing ribosomes on its outermanufacturing ribosomes on its outer surface function is surface function is protein processing. The smooth ER is not associated protein processing. The smooth ER is not associated with ribosomes and is involved in lipid rather than with ribosomes and is involved in lipid rather than protein, metabolismprotein, metabolism..

Rough endoplasmic reticulumRough endoplasmic reticulum

The membrane of the rough endoplasmic reticulum is continuous with the outer layer of the nuclear envelope . Although there is no continuous membrane between the rough ER and the Golgi apparatus, membrane bound vesicles shuttle proteins between these two compartments The rough endoplasmic reticulum works in concert with the Golgi complex to target new p[roteins to their proper destinations.

Smooth endoplasmic Smooth endoplasmic reticulumreticulumThe smooth endoplasmic reticulum has functions in

several metabolic processes, including synthesis of lipids, metabolism of carbohydrates and calcium concentration, drug detoxification, Glycosylation and attachment of receptors on cell membrane proteins. It is connected to the nuclear envelope. Smooth endoplasmic reticulum is found in a variety of cell types (both animal and plant) and it serves different functions in each. The Smooth ER also contains the enzyme Glucose-6- phosphatase which converts glucose -6- phosphate to Glucose, a step in gluconeogenesis.

Sarcoplasmic reticulum The sarcoplasmic reticulum is a specialized

type of smooth ER found in smooth and striated muscle.

The fundamental difference is indicative of their functions, the smooth ER is built to synthesize molecules and the sacroplasmic reticulum is built to contraction. store and pump calcium ions. This has the effect of triggering muscle

Golgi apparatusGolgi apparatus At various locations within the endomembrane

system, flattened stacks of membrane called Golgi bodies. They are specially abundant in glandular cells, which manufacture and secrete substances.

The Golgi apparatus functions in the collection, packaging, and distribution of molecules synthesized at one place in the cell and utilized at another location in the cell.

Proteins and lipids manufactured on the rough and smooth ER membrane are transported into the Golgi apparatus and modified as they pass through it. The most common alteration is the addition or modification of short sugar chains, forming a glycoprotein when sugars are complexed to a protein and a glycolipid when sugars are bound to a lipid. The Golgi apparatus The Golgi apparatus (also called the Golgi(also called the Golgi complex complex, , oror dictyosomedictyosome) is an ) is an organelle found in typical eukaryotic cells. The Golgi organelle found in typical eukaryotic cells. The Golgi apparatus forms a part of the endomembrane system apparatus forms a part of the endomembrane system present in eukaryotic cells. present in eukaryotic cells.

StructureStructure The Golgi is composed of membrane-bound sacs known The Golgi is composed of membrane-bound sacs known

as cisternae,. Between five and eight are usually as cisternae,. Between five and eight are usually present, however as many as sixty have been observed. present, however as many as sixty have been observed. Surrounding the main cisternae are a number of Surrounding the main cisternae are a number of spherical vesicles which have budded off from the spherical vesicles which have budded off from the cisternae. Vesicles from the endoplasmic reticulum cisternae. Vesicles from the endoplasmic reticulum fuse with the fuse with the cis-Golgi networkcis-Golgi network and subsequently and subsequently progress through the stack to the progress through the stack to the trans-trans- GolgiGolgi network,network, where they are packaged and sent to the required where they are packaged and sent to the required destination. Each region contains different enzymes destination. Each region contains different enzymes which selectively modify the contents depending on which selectively modify the contents depending on where they are destined to residewhere they are destined to reside..

FunctionFunction::The Golgi apparatus performs three primary functions The Golgi apparatus performs three primary functions within the secretory membrane systemwithin the secretory membrane system..

First:First: It acts as carbohydrate factor in which It acts as carbohydrate factor in which glycoproteins, polysaccharides(in plants) and glycoproteins, polysaccharides(in plants) and proteoglycans received from the ER are further proteoglycans received from the ER are further processedprocessed..

Second:Second: The Golgi apparatus functions as a protein- The Golgi apparatus functions as a protein-sorting station for the delivery of proteins to many sorting station for the delivery of proteins to many different destinations within the cell.this includes different destinations within the cell.this includes transport to the plasma membrane, secretion to the transport to the plasma membrane, secretion to the cell exterior, sorting to the endosomel /lysosomal cell exterior, sorting to the endosomel /lysosomal systems, or retrieval back to ERsystems, or retrieval back to ER..

hird:hird: The Golgi apparatus serves as the site where The Golgi apparatus serves as the site where sphingomyelin and glycosphingolipids are sphingomyelin and glycosphingolipids are synthesized within the cell. These lipids are capable synthesized within the cell. These lipids are capable of packing tightly in the membrane, which causes the of packing tightly in the membrane, which causes the bilayer to thicken and be less permeable to water-bilayer to thicken and be less permeable to water-soluble moleculessoluble molecules..

MitochondriaMitochondriaMitochondria are spherical or filamentous Mitochondria are spherical or filamentous organelles. Their distribution in cells varies. They organelles. Their distribution in cells varies. They tend to accumulate in parts of cytoplasm where tend to accumulate in parts of cytoplasm where metabolic activity is more intense, such as the metabolic activity is more intense, such as the apical ends of ciliated cells, in the middle piece of apical ends of ciliated cells, in the middle piece of spermatozoa, or at the base of ion-transferring spermatozoa, or at the base of ion-transferring cellscells..These efficient organelles transform the chemical These efficient organelles transform the chemical energy of the metabolites present in cytoplasm energy of the metabolites present in cytoplasm

into energy that is easily accessible to the cellinto energy that is easily accessible to the cell . .

About 50%of this energy is stored as high-About 50%of this energy is stored as high-energy phosphate bonds in ATP moleculesenergy phosphate bonds in ATP molecules..ATP releases energy when required by the cell to ATP releases energy when required by the cell to perform any type of work, where it be osmotic, perform any type of work, where it be osmotic, mechanical, electrical, or chemicalmechanical, electrical, or chemical..

The compartment located between the two The compartment located between the two membranes is termed the intermembrane membranes is termed the intermembrane space. The other compartment- the intercristaespace. The other compartment- the intercristae ,, or matrix space-is enclosed by the inner or matrix space-is enclosed by the inner membranemembrane..Between the cristae is an amorphous matrix, rich Between the cristae is an amorphous matrix, rich in in proteinprotein and have their own and have their own DNADNA, , this DNA this DNA contains several genes that produce proteins contains several genes that produce proteins essential to the mitochondrions' role in essential to the mitochondrions' role in oxidative metabolism,oxidative metabolism, and RNAand RNA..

Metabolites are degraded within mitochondria Metabolites are degraded within mitochondria by the catalytic activity of the enzymes of the by the catalytic activity of the enzymes of the citric acidcitric acid cyclecycle, and the energy liberated in , and the energy liberated in this process is partially captured through this process is partially captured through oxidative phosphorylation. The end result of oxidative phosphorylation. The end result of these reactions is the production ofthese reactions is the production of CO2, CO2, water, and heatwater, and heat,, as well as the accumulation of as well as the accumulation of energy in the high –energy compound ATPenergy in the high –energy compound ATP..

Mitochondrial deficiency diseasesMitochondrial deficiency diseases Skeletal muscle fibers are very sensitive to Skeletal muscle fibers are very sensitive to

mitochondrial defects, these diseases usually mitochondrial defects, these diseases usually begin with drooping of the upper eyelid and begin with drooping of the upper eyelid and progress to difficulties in swallowing and limb progress to difficulties in swallowing and limb weakness. they are caused by DNA mutations weakness. they are caused by DNA mutations or defects that can occurs in the mitochondria or defects that can occurs in the mitochondria or the cell nucleusor the cell nucleus..

Mitochondrial functionMitochondrial function Although it is well known that the mitochondria Although it is well known that the mitochondria

convert organic materials into cellular energy in the convert organic materials into cellular energy in the form of ATP, mitochondria play an important role in form of ATP, mitochondria play an important role in many metabolic tasks, such asmany metabolic tasks, such as::

Apoptosis (programmed cell deathApoptosis (programmed cell death(( Cellular proliferationCellular proliferation Heme synthesisHeme synthesis Steroid synthesisSteroid synthesisMitochondria also have a key role in cellular responses Mitochondria also have a key role in cellular responses

to toxic stimuli from environmentto toxic stimuli from environment..

Mitochondria in liver cells contain enzymes that Mitochondria in liver cells contain enzymes that allow them to detoxify ammonia, a waste allow them to detoxify ammonia, a waste product of protein metabolism. A mutation in product of protein metabolism. A mutation in the genes regulating any of these functions can the genes regulating any of these functions can result in mitochondrial diseasesresult in mitochondrial diseases..