Cell Presentation -Angitha

8/6/2019 Cell Presentation -Angitha

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by

ANGITHA

CLASS XI


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CELLy The cell is the functional basic unit of life.

y It was discovered byRobert Hooke and is the

functional unit of all known living organisms.y It is the smallest unit of life that is classified as a living

thing, and is often called the building block of life.[1


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PROKAYOTIC CELL


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PROKARYOTIC CELLy The prokaryote cell is simpler, and therefore smaller,

than a eukaryote cell, lacking a nucleus and most of

the other organelles of eukaryotes.y There are two kinds of prokaryotes: bacteria and

archaea; these share a similar structure.

y Nuclear material of prokaryotic cell consist of a single

chromosome which is in direct contact withcytoplasm.

y the undefined nuclear region in the cytoplasm iscalled nucleoid.


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PROKARYOTIC CELL(cont.) A prokaryotic cell has three architectural regions:y On the outside, flagella and pili project from the cell's

surface. These are structures (not present in all

prokaryotes) made of proteins that facilitate movementand communication between cells;y Enclosing the cell is the cell envelope .The envelope gives

rigidity to the cell and separates the interior of the cell fromits environment, serving as a protective filter.

y

Inside the cell is the cytoplasmic region that contains thecell genome (DNA) and ribosomes and various sorts ofinclusions. Aprokaryotic chromosome is usually a circularmolecule (an exception is that of the bacterium Borreliaburgdorferi, which causes Lyme disease).


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RIBOSOMESy Prokaryotic ribosomes are around 20 nm (200 ngstrms) in

diameter and are composed of 65% ribosomal RNAand 35%ribosomal proteins (known as a ribonucleoprotein or RNP).

y Eukaryotic ribosomes are between 25 and 30 nm (250-300ngstrms) in diameter and the ratio of rRNA to protein is closeto 1.

y Ribosomes translate messenger RNA (mRNA) and buildpolypeptide chains (e.g., proteins) using amino acids delivered

bytransfer RNA (tRNA). Their active sites are made of RNA, soribosomes are now classified as "ribozymes".[2]

y Ribosomes build proteins from the genetic instructions heldwithin messenger RNA.


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INCLUSION BODIESy They are nuclear or cytoplasmic aggregates of

stainable substances, usually proteins.

y They typically represent sites of viral multiplication ina bacterium or a eukaryotic cell and usually consist of

viral capsid proteins.

y Inclusion bodies can also be hallmarks of genetic

diseases, as in the case of Neuronal Inclusion bodies indisorders like Frontotemporal dementia andParkinson's disease.[1]


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EUKARYOTIC CELL


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Eukaryotic celly Aeukaryote is an organismwhose cells contain complex

structures enclosed within membranes.y The defining membrane-bound structure that sets

eukaryotic cells apart from prokaryotic cells is the nucleus,or nuclear envelope, within which the genetic material is

carried.y The presence of a nucleus gives eukaryotes their name,

which comes from the Greek (eu, "good") and (karyon, "nut" or "kernel").

y Most eukaryotic cells also contain other membrane-boundorganelles such as mitochondria, chloroplasts and theGolgi apparatus.

y All species of large complex organisms are eukaryotes,including animals, plants and fungi, although most speciesof eukaryotic protists are microorganisms.


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CELL MEMBRANEy It is composed of lipids that are arranged in a bilayer.

y Lipids are arranged within the membrane with the

polar head towards the outer sides and thehydrophobic tail towards the inner part.

y The lipid component of the membranes mainlyconsists of phosphoglycerides.cell membrane also

possess proein and carbohydrate.y In human beings.the membrane of the erythrocyte has

approximately 52%protein and 40%lipids.


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MEMBRANE PROTEINSy Depending on the ease of extraction, membrane

proteins membrane proteins can be classified as

integral or peripheral.y Peripheral proteins lie on the surface of membrane

while the integral proteins are partially or totallyburied in the membrane.


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FLUIDMOSAICMODEL


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FLUIDMOSAIC MODELy It was proposed by Singer and Nicolson(1972).

yAccording to this,the quasi-fluid nature of lipid

enables lateral movement of proteins within theoverall bilayer.

y This ability to move within the membrane is measuredas its fluidity.


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FUNCTIONSOFPLASMA

MEMBRANEy It transports molecules across it.

y The membrane is selectivelypermeable to somemolecules present on either side of it.

y Many molecules can move briefly across the membranewithout any requirement of energy and this is calledpassive transport.

y Water may also move across the membrane from higher to

lower concentration and this is called osmosis.y A few ions or molecules are transported across the

membrane against their concentration gradient,this iscalled active transport.


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CELL WALLyA non living rigid structure forming an outer covering

for the plasma membrane of fungi and plants is known

as cell wall.y It protecs the cell from mechanical damage and

infection.

y It also helps in cell to cell interaction and provides

barrier to undesirable macromolecules.y It consists of cellulose,hemicellulose,pectins and

proteins.


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ENDO-MEMBRANE SYSTEMy Many of the membranous organelles are considered

together as an endomembrane syste,because their

functions are coordinated.y This system includes endoplasmic reiculum(ER),golgi

complex ,lysosomes.and vacuoles.


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ENDOPLASMIC RETICLUMy It is the network or reticulum of tiny tubular sructures

scatteredin the cytoplasm.

y

It divides the intracellular space into luminal and extraluminal compartments.

y The endoplasmic reticulum bearing ribosomes ontheir surface is called rough ER.

y In the absence f ribosomes,they appear smooth andare called smooth ER.

y RER helps in protein synthesis and secretion whereasSER helps in lipid and steroidal hormones.


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GOLGIAPPARTUSy They consists of many flat, disc shaped sacs or

cisternae which are sacked parallel to each other.

y

The Golgi cisternae are concentrically arranged nearthe nucleus with distinct convex cis or the forming faceand the concave trans or the maturing face.

y They perform the function of packaging materials, to

be delivered either to the intra cellular targets orsecreted outside the cell.

y It is an important site of formaion of glcoproteins andglycolipids.


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MITOCHONDRIAy Mitochondria are sometimes described as "cellular power plants"

because they generate most of the cell's supply ofadenosinetriphosphate (ATP), used as a source ofchemical energy.[2]

y In addition to supplying cellular energy, mitochondria areinvolved in a range of other processes, such as signaling, cellulardifferentiation, cell death, as well as the control of the cell cycleand cell growth.[3]

y These compartments or regions include the outer membrane,the intermembrane space, the inner membrane, and the cristaeand matrix.

y Mitochondrial proteins vary depending on the tissue and thespecies. In humans, 615 distinct types of proteins have beenidentified from cardiac mitochondria.

y Although most of a cell's DNA is contained in the cell nucleus,the mitochondrion has its own independent genome.


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PLASTIDSy Plastids are major organelles found in the cells of

plants and algae.

yPlastids are the site of manufacture and storage ofimportant chemical compounds used by the cell.

y Plastids often contain pigments used inphotosynthesis, and the types of pigments present can

change or determine the cell's color.


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NUCLEUSy It is a membrane enclosed organelle found in eukaryotic cells.y It contains most of the cell's genetic material, organized as

multiple long linear DNAmolecules in complex with a largevariety ofproteins, such as histones, to form chromosomes.

y The geneswithin these chromosomes are the cell's nucleargenome. The function of the nucleus is to maintain the integrityof these genes and to control the activities of the cell byregulating gene expression the nucleus is therefore thecontrol center of the cell.

y

Since the nuclear membrane is impermeable to most molecules,nuclear pores are required to allow movement of moleculesacross the envelope. These pores cross both of the membranes,providing a channel that allows free movement of smallmolecules and ions.


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Cell Presentation -Angitha