The cell

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The cell
Figure 3.1
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The Plasmalemma
Figure 3.2
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Membrane Proteins

• In addition to the phospholipids, other molecules
  are present in the plasma membrane.
• Important in achieving selective permeability.
• Important in adhesion and communication.

Figure 3.3a
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Selective Permeability

• Movement across membrane is highly selective.
• Some substance have access, others do not.

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• Diffusion
• Movement of substances from a region of high
  concentration to region of low conc.
• Conc of substances even out.
• Factors
• Temperature
• Size
• Distance
• Concentration (amount)
• Medium

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• Osmosis
• Osmosis movement of water across a semipermeable
  membrane by diffusion

Figure 3.5
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Bulk Flow

• Hydrostatic (Blood) pressure moves H2O.
• If membrane is permeable, solutes move with it
• Ex. Formation of interstitial fluid
• Urine formation

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Which Substances Can Cross Membrane?

• Several factors determine whether a molecule can
  cross the cell membrane
• Molecular size.
• Solubility in lipids (remember, the membrane is
  phospholipid). CO2, O2, alcohol, H2O
• The presence of specific channels or carriers for
  that molecule.

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Facilitated Diffusion

• Diffusion of molecules that require a carrier to
  cross the membrane.

Figure 3.7
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Passive vs. Active Processes

• Passive require no energy (ATP.
• Diffusion, osmosis, facilitated diffusion.
• Active uses energy to transport substances.
• Active transport, endocytosis.

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Active Transport Molecular Pumps

• Molecular pumps are integral proteins use ATP to
  move substances across membrane.

Figure 3.8
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Endocytosis

• Used to move large molecules into cells.
• Three types
• Phagocytosis
• Pinocytosis
• Receptor mediated endocytosis

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Phagocytosis

• Cell eating.
• Cells engulf large molecules and particles.
• Pseudopodia surround particle.
• Particle ends up in a vesicle in the cell.
• Only some cells.
• macrophages and WBC

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Phagocytosis
Figure 3.9a-c
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Phagocytosis
Figure 3.9d-f
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Pinocytosis

• cell drinking.
• Bring droplets of substances into cells.
• No pseudopodia used but otherwise similar to
  phagocytosis.
• All cells have this ability.
• Receptor-Mediated Endocytosis
• Similar to endocytosis except that cell have a
  receptor on surface that specifically binds the
  molecule being transported.

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The Nucleus

• Most cells have only one, some have many, mature
  red blood cells have none.
• Surrounded by a nuclear membrane
• Contains DNA
• Contains another organelle, the nucleolus.
• Found within the nucleus.
• Composed mainly of RNA.
• Ribosomes are produced here.

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Ribosomes

• An organelle found in the cytoplasm but produced
  in the nucleolus.
• Most cells have large numbers of ribosomes.
• Composed of two subunits of RNA.
• Site of protein synthesis.
• May be free or bound.
• In cytoplasm or attached to endoplasmic
  reticulum.

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Endoplasmic Reticulum

• Channels of phospholipid bilayer that extend
  throughout the cell.
• Site where the cell does much of its work.
• Also useful for transport within the cell.
• May be agranular (smooth) or granular (rough)
  endoplasmic reticulum.
• Agranular The site of much lipid and
  carbohydrate synthesis, and many degradative
  reactions.
• Granular The site of synthesis of proteins for
  export from the cell, or membrane insertion.

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The Pathway of Protein Synthesis
Figure 3.10
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Lysosomes

• Vesicles within the cytoplasm which contain
  hydrolytic enzymes.
• Used to digest materials following phagocytosis,
  pinocytosis or autophagy.
• Autophagy (self-eating) is how cells dispose of
  worn-out organelles.

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Mitochondria

• Major site of ATP production.
• ATP is the cells main fuel.
• Mitochondria contain their own DNA.
• Encodes some of the enzymes needed by the
  mitochondria.

Figure 3.11
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ATP Synthesis
Figure 3.12
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The Cytoskeleton

• Gives your cell structure just as your skeleton
  supports your body.
• Has three major components
• Microfilaments
• Intermediate Filaments
• Microtubules

Figure 3.13
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Centrioles

• Organelles important in nuclear division.
• Composed of tubulin, just like microtubules.

Cytoplasmic Inclusions

• Not organelles, but substances stored within
  cells.
• Examples include
• Lipids (Fats)
• Glucose

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Cell Division

• How cells reproduce.
• Two linked events nuclear division and
  cytoplasmic division.
• In somatic cells (non-germ cells), nuclear
  division is mitosis.
• Germ cells (sperm or ova) divide by meiosis.
• Division of the cytoplasm is cytokinesis.

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Mitosis

• Can be divided into five stages
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase

Figure 3.16
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Mitosis

• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase

Figure 3.16
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Mitosis

• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase

Figure 3.16
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Differentiation

• The process whereby cells gain specialized
  structures and functions.
• Primitive (embryonic and stem) cells become the
  specialized cells found functioning in your
  organs.