cells.doc

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    Found only in Plant cells

    Cellulose cell wall- provides cell wit itscharacteristic shape. Strong and elastic.Cells are held together by the sticky middleamella.Large molecules enter the cell troughplasmodesmata- cytosol filled channels.Plant cells contain large vacuoles surrounded by the tonoplast membrane.Chloroplasts are surrounded by a doublemembrane containing grana  –membranebound structures enclosing a fluid filled

    cavity. This is where chlorophyll  iscontained and the light stage ofphotosynthesis takes place. The lamellae spread the grana out for maimum lightabsorption. The Calvin cycle takes place inhe surrounding stroma.

    Found only in Animal cells

    ! pair of centrioles can be found close to

    he nucleus in the centre of the "T#Cmicrotubule organising centre%& they controlhe spindle.The MTOC also control the cytoskeleton- aramework of protein fibres that control acells shape and movement.Microvilli are supported by the cytoskeletonand greatly increase the surface area of thecell.

    Eukaryotic Cells

    Contain a true nucleus i.e. The '(! iscontained in a double nuclear membraneThey have numerous cell organelles madefrom membranes

      )ave an extracellular matrix surrounding the plasmamembrane.'(! is surrounded by a nuclear envelope& the outer layer ofwhich is part of the endoplasmic reticulum.(uclear envelope is punctured with small pores that allowthe transport of m*(!. !t each pore the outer and innermembranes are fused together and the pore is encircled withtransport proteins.'(! is associated with + histone proteins& which combine to

    make nucleosomes.ucleolus is the area of the nucleus that stains more darkly.,t is made up of chromosomes that always associatetogether and are in control of ribosomal *(! synthesis. ! polysome is the name given to many ribosomes attachedonto an m*(! molecule.n/ymes embedded in the rough endoplasmic reticulum modify the protein by adding short sugar chains- creatingglyco proteinsSometimes tips of the * are 0budded1 off& and becometransport vesicles which migrate and merge wit the plasma

    membrane or organelles to Some vesicles containingglycoproeinsmerge with the flattened sacs of the golgi !ody.The smooth  endoplasmic reticulum  has a different rolewithin the cell. Lipids such as fatty acids& phospholipids andsteroids are synthesi/ed here."ysosomes  separate en/ymes from the cytoplasm by amem!rane envelope& creating optimum conditions. Theyoften merge with vacuoles containing obsolete organelles ormicroorganisms and digest themThe micro !ody is also a membrane envelope surrounding

    a number of en/ymes& which oidise fatty acids and toicsubstances. !ll the membrane bound structures are part of theendomem!rane system.The mitochondrion  is the site of aerobic respiration. ,t issurrounded by a double membrane& enclosing the matri- thesite of the 2rebs cycle and the cristae#  where !TP issynthesised by the cytochrome system.

    Prokaryotic Cells'(! not enclosed within a nuclear envelope."ost of the '(! is contained within a single circular molecule known as a nucleoid.#ften there are small rings of '(! known as plasmids& which allow genetic information to bepassed between cells.,t has a cytosol- a cytoplasm with no organelles.$i!osomes are still present& smaller than in eukaryotes."ovement is achieved using a %lagellum & in an anti clockwise rotation. Cells can reach up to 34 their own length per second"any have pilli to stick to surfaces& sometimes to swap plasmids.The plasma mem!rane is t only membrane structure found in prokaryotes.

    5acteria cells have a cell wall made from peptidoglycan& providing a strong and rigid coating."any have a capsule& a slimy layer of mucus type substance& which helps bacteria to stick& andhelps to protect against en/yme and phagocyte attack."ost bacteria cells are approimately the same si/e as mitochondrion in eukaryotes '.( ) * um.

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