Chapter 7. The Cell: Basic Unit of Life

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Chapter 7. The Cell: Basic Unit of Life

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Why do we study cells?

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Cell TheoryAll organisms are made up of cells The cell is the basic living unit of organization for all organisms All cells come from pre-existing cells

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Biological diversity & unityUnderlying the diversity of life is a striking unity DNA is universal genetic language Cells are the basic units of structure & function lowest level of structure capable of performing all activities of life

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Activities of lifeMost everything you think of a whole organism needing to do, must be done at the cellular level… reproduction growth & development energy utilization response to the environment homeostasis

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How do we study cells?Microscopes opened up the world of cells Robert Hooke (1665) the 1st cytologistDrawings by Hookefleacork

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How do we study cells?Microscopes light microscopes electron microscope transmission electron microscopes (TEM) scanning electron microscopes (SEM) Technology advancing science

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Light microscopes0.2µm resolution ~size of a bacterium visible light passes through specimen can be used to study live cells

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Electron microscope1950s 2.0nm resolution 100 times > light microscope reveals organelles but can only be used on dead cells

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Transmission electron microscopesTEM used mainly to study internal structure of cells aims an electron beam through thin section of specimencucumber seed leafrabbit trachea

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Scanning electron microscopesSEM studying surface structures sample surface covered with thin film of gold beam excites electrons on surface great depth of field = an image that seems 3-Drabbit trachea

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SEM imagesgrasshopper

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SEM imagesspider head

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Isolating organellesCell fractionation separate organelles from cell variable density of organelles ultracentrifugeWhat organelle would be heaviest? What organelle would be lightest?

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Ultracentrifuge spins up to 130,000 rpm forces > 1 million X gravity (1,000,000g) Why is it in a BIG thick lead-lined housing?

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Microcentrifuge Biotechnology research study cells at protein & genetic level

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Tour of the Cell

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Cell characteristicsAll cells: surrounded by a plasma membrane have cytosol semi-fluid substance within the membrane cytoplasm = cytosol + organelles contain chromosomes which have genes in the form of DNA have ribosomes tiny “organelles” that make proteins using instructions contained in genes

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Types of cellsProkaryotic cell DNA in nucleoid region, without a membrane separating it from rest of cellEukaryotic cell chromosomes in nucleus, membrane-enclosed organelleProkaryotic vs. eukaryotic cells Location of chromosomes

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Cell typesProkaryote Eukaryoteinternal membranes“Let’s go to the video tape!” (play movie here)

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The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.“Let’s go to the video tape!” (play movie here)

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Eukaryotic cellsEukaryotic cells are more complex than prokaryotic cells within cytoplasm is a variety of membrane-bounded organelles specialized structures in form & function Eukaryotic cells are generally bigger than prokaryotic cells

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“Let’s go to the video tape!” (play movie here)

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Limits to cell sizeLower limit smallest bacteria, mycoplasmas 0.1 to 1.0 micron (µm = micrometer) most bacteria 1-10 microns Upper limit eukaryotic cells 10-100 microns micron = micrometer = 1/1,000,000 meter diameter of human hair = ~20 microns

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What limits cell size?Surface to volume ratio as cell gets bigger its volume increases faster than its surface area smaller objects have greater ratio of surface area to volumeWhy is a huge single-cell creature not possible?What cell organelle governs this?6:1~1:16:1s:v

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Last Updated: 8th March 2018

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