Cell structure and function

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Chapter 7

• Cell structure and function

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Cell Discovery

• First used in mid 1600s.
• Robert Hooke-first observed cell.
• He looked at a cork cell.
• Named it after tiny rooms in monastery
• Anton van Leeuwenhoek-observed first living cell.

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Cell Theory

• Based on work of Schleiden, Schwann, and Virchow.
• Three parts
• All living things made of cells.
• Cell is basic unit of structure and function in
  living things.
• Cells come only from existing cells.

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Studying the cell-Electron microscopes
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Electron microscopes cont.

• Resolution-ability to focus or produce a clear
  image decreases as magnification increases.
• Light microscope magnification limit is 2000X.
  Light rays become too scattered to focus.
• Electrons wavelengths shorter.
• Types of electron microscopes
• A. Transmission-looks at internal cell
  structures.

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• Objects must be sliced very thin for electrons to
  pass through.

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• Scanning electron microscopes-look at outside
  surface. Object coated with thin layer of gold
  first.
• Specimen must be in a vacuum in both types.
  Specimen therefore is nonliving.

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Scanning probe microscope.

• Probe moves over surface and picks up electrons
  emitted from sample.
• Can be used in open air.
• Specimen can be living.
• Invented in 1990s

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Cell categories

• Cell size and shape vary from one type to next.
• Cells usually measure in micrometers. (1/1000th
  of a millimeter)
• Two characteristics of all cells 1) cell
  membrane 2) at some point contain DNA
• If DNA is surrounded by a membrane or not sets up
  two general categories.

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Prokaryote

• pro means before karyon means kernel
  (nucleus).
• Genetic material not contained within a
  nucleus/membrane.
• No membrane bound organelles
• Less complex
• Carry out all life processes.
• Ex. bacteria

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Eukaryote

• eu means true.
• Cells have a nucleus/DNA is contained within a
  membrane. Also have membrane bound organelles.
• May be single celled or multi-celled.
• Include all other cell types besides bacteria.

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Cell (plasma) membrane
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Structure of cell membrane

• Made of phospholipid bilayer.
• Hydrophilic portion faces outside environment and
  inside toward cytoplasm. What does this say
  about each?
• Hydrophobic parts inward. Why?
• Proteins found scattered in bilayer
• Carbohydrates attached to proteins

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Function of cell membrane

• Regulates what enters and leaves.
• Flexible
• Found as outer boundary of all cells.

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Cytoplasm

• Made mainly of water
• Proteins suspended in water.
• Region between nucleus and cell membrane.
• Distributes materials to organelles.

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Organelles

• Small structures found in cytoplasm
• All membrane bound except ribosomes.
• Found in eukaryotic cells only (exception-prokaryo
  tic cells have ribosomes)
• Each has specific function

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Mitochondria

• Convert chemical energy (food) into energy form
  usable by cells.
• Unique structure- two membranes.
• Outer membrane smooth
• Inner membrane folded called cristae

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• Contain their own DNA not bound by membrane.
• Thought to have been a prokaryotic, one celled
  organism at one time.
• Taken in by a bigger cell. Why?
• Symbiosis-two organisms that live together and
  benefit each other.

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• Bigger cell got way to get more energy out of
  food.
• Smaller cell (now the mitochondria) got
  protection
• Endosymbiotic hypothesis-explains the history of
  mitochondria.
• Humans inherit mitochondria only in egg cells.

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Ribosomes
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Ribosomes

• Function
• Assemble proteins instructions in DNA in
  nucleus.
• Description
• Small, made of RNA and protein
• Found throughout cytoplasm but also found
  attached to ER.
• Proteins that stay in cell made by free
  ribosomes
• All cells have ribosomes

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Endoplasmic reticulum (ER)

• Two types
• Rough
• Smooth
• Overall description
• Internal membrane system

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Rough ER

• Function
• Synthesis of proteins chemically modifies them.
• Proteins from here will be exported out of cell.
• Description has ribosomes attached

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Smooth ER

• Function
• Assembles lipid portion of cell membrane.
• Detoxifies chemicals. Ex. Liver
• Description No ribosomes on surface.

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Golgi Apparatus

• Function modify, sort, and package proteins to
  be shipped out of cell.
• Description series of membrane sacs contain
  enzymes.
• Modifies proteins from RER.

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Lysosomes

• Function Helps get rid of worn out cells,
  bacteria, etc.
• Description Contains digestive enzymes
• Membrane bound sac.
• Ex. Fingers and toes
• Tay-Sachs disease

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Cytoskeleton
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Cytoskeleton

• Function physical support to cell involved in
  movement
• Description made of protein fibers.
• Two types of fibers
• 1. microfilaments-made of actin threadlike can
  assemble and disassemble as needed.

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• 2. Microtubules-hollow made of tubulin
  important to cell division-make up structures
  that move chromosomes.
• Also make up centrioles-structure found in animal
  cells only help in cell division.

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Cilia and flagella

• Function produce movement
• Description
• 1. cilia-shorter found in large numbers
• 2. flagella-longer whiplike tail not as many
  present as cilia.
• Both are made of microtubules. Both extend out
  from surface of cell.

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Nucleus

• Function control cell activity
• Description membrane enclosed area contains
  genetic information

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Nuclear envelope (membrane)

• Function control movement in and out
• Description made of lipid bilayer
• Has openings known as nuclear pores.

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Nucleolus

• Function makes ribosomes
• Description dense area of organic material in
  center of nucleus.

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Chromatin/chromosomes

• Function contains information about proteins to
  be made.
• Description made of DNA
• Chromatin-thin threadlike non dividing cell.
• Chromosomes Condensed chromatin cell is
  dividing.

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Vacuole

• Function storage
• Description membrane bound space
• Large vacuole in plant cells.
• Contractile vacuole-one-celled organism gets rid
  of excess water.

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Chloroplasts

• Function capture energy from sun
• Location of photosynthesis
• Description 2 membranes contains DNA
• Contain chlorophyll

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Other plastids

• Chromoplasts chroma means color.
• Membrane bound structure that contains pigment
  other than chlorophyll

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Leucoplasts

• leuco means without color
• Leucoplasts store
• starch in plants