Microbiology - Prokaryotes and Eukaryotes - Quick Guides

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Study GuideMicrobiology–Prokaryotes and Eukaryotes1.Eukaryotic CellsEukaryotic cellsare generallylarger and more complexthan prokaryotic cells. A key feature thatsets them apart is the presence ofmembrane-bound organelles—specialized structures that carryout specific jobs inside the cell. These organelles act like compartments, keeping different metabolicactivities organized and efficient.Many microorganisms, includingprotozoa, unicellular algae, and fungi, have eukaryotic cells.1.1The Nucleus: The Control CenterEvery eukaryotic cell has a well-definednucleus. It is made mainly ofproteinandDNA(deoxyribonucleic acid).•DNA is arranged intolinear structures called chromosomes.•When chromosomes are not clearly visible, they are referred to aschromatin.•Specific working sections of chromosomes are calledgenes, which carry instructions for cellfunctions.Nuclear Proteins and DivisionDNA is supported by special proteins known ashistones, which help package and organize it.DNA replication in eukaryotic cells occurs duringmitosis.Nuclear Envelope and PoresThe nucleus is surrounded by anuclear envelope, adouble membranesimilar to the cellmembrane.This envelope haspores, allowing communication between the nucleus and the cytoplasm.NucleolusInside the nucleus are one or more dense regions callednucleoli(singular: nucleolus).The nucleolus is rich in RNA and is the site whereribosomes are assembledbefore moving into thecytoplasm.

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Study Guide1.2Cellular Organelles: Specialized Cell StructuresThe fluid inside the cell is called thecytoplasm(orcytosol). Floating within it are many organelles,each with a specific role.Endoplasmic Reticulum (ER)Theendoplasmic reticulumis a network of membranes spread throughout the cytoplasm.•Rough ERhas ribosomes attached and is involved inprotein synthesis.•Smooth ERlacks ribosomes and is involved in other metabolic activities.Eukaryotic ribosomes are80S ribosomes, where amino acids are linked together to form proteins.The spaces inside the ER membranes are calledcisternae.Golgi ApparatusTheGolgi body (Golgi apparatus)consists of flattened, stacked sacs.•Itmodifies, processes, and packages proteins and lipids.•The edges of Golgi sacs often formsecretory vesicles, which carry materials to their finaldestination in or outside the cell.Lysosomes and Peroxisomes•Lysosomesare enzyme-filled sacs derived from the Golgi apparatus.oThey digest food particles and recycle worn-out cell components.•Peroxisomesalso contain enzymes and help break down harmful substances inside the cell.Mitochondria: The PowerhousesMitochondriaare the sites where most cellular energy is released.•Energy is stored asadenosine triphosphate (ATP).•Because of this role, mitochondria are often called the“powerhouses of the cell.”

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Study GuideVacuolesSome protozoa contain a largecontractile vacuole.•It may occupy more than75% of the cell interior.•Its main function is toremove excess waterand prevent the cell from bursting.CytoskeletonThecytoskeletonis a network of protein fibers that gives the cell its shape and internal organization.It includes:•Microtubules•Microfilaments•Intermediate filamentsAll are made of protein subunits and help with movement, transport, and structural support.Flagella and CiliaMany eukaryotic cells haveflagellaorciliafor movement.•Flagellaare long, whip-like structures that propel the cell.•Ciliaare shorter, more numerous, and move in coordinated waves.Both structures have a characteristic9 + 2 arrangement of microfilaments.A well-known example of a ciliated protozoan isParamecium.The Cell WallSome eukaryotes, especiallyfungi and algae, have acell walloutside the cell membrane.•Fungal cell wallscontainchitinand some cellulose.•Algal cell wallscontaincellulose only.Cell walls:•Provide support and protection•Help cells resist mechanical pressure•Arenot selective, unlike cell membranes

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Study GuideThe Cell MembraneThe eukaryotic cell membrane follows thefluid mosaic model, similar to prokaryotic membranes.Functions include:•Regulating movement of substances into and out of the cell•Maintaining the internal environment of the cytoplasmHowever, unlike prokaryotic membranes, it:•Does not contain metabolic enzymes•Does not participate in DNA replication1.3Transport Across the Cell MembraneFor cells to survive, materials must move across the membrane. This happens in several ways:Diffusion•Movement of molecules fromhigh concentration to low concentration•Occurs randomly along aconcentration gradientOsmosis•Diffusion ofwater only•Occurs across asemipermeable membraneFacilitated Diffusion•Uses membrane proteins•Moves substancesdown the concentration gradient•Requiresno energyActive Transport•Moves substances fromlow concentration to high concentration•Goesagainst the concentration gradient•Requiresenergy, usually from ATP

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