Cells: the building blocks of life!!!

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Cells the building blocks of life!!!
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What is a cell?

• A cell is the basic structural and functional
  unit of a living organism
• What kind of cells can you think of ?

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Cells An Overview Generalized

• There are trillions of cells in the human body
• Of those trillions, there are over 200 different
  kinds that vary in size, shape and function

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Cells vary in size and shape
1 micrometer (1µm) 1 x10-6 m)
Red Blood Cell (RBC) 7.5 µm
Smooth Muscle Cell 20-500 µm long
Human Egg Cell (Ovum) 140 µm
Nerve Cell Can be many cm in length
White Blood Cell 10-12 µm
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Despite all their differences.ALMOST all human
cells have 3 common components

• Plasma membrane the outer layer of the cell
• Cytoplasm fluid inside the cells. Contains
  organelles
• Nucleus the control center of the cell
• RBCs do not have a nucleus!!!!

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The Plasma MembraneWhat is it?

• The outer layer of the cell. Think of it as the
  traffic controller for the cell
• It is a semi-permeable membrane that is selective
  about what can enter or leave the cellthe
  bouncer
• Separates the bodys 2 main fluid compartments
• Intracellular fluid fluid inside the cell
• Extracellular fluid- fluid outside and in between
  the cells

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The Plasma Membrane Structure

• Phospholipids 75
• Glycolipids 5
• Cholesterol 20
• Double layer membrane composed primarily of
  phospholipids

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Phospholipids

• The polar heads are attracted to water so they
  lie on the inner and outer surface of the
  membrane
• remember intracellular fluid and extracellular
  fluid water
• The nonpolar tails avoid the fluid and line up in
  the center of the membrane

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Glycolipids

• Lipid with an attached sugar group
• Found only in the outer surface of the plasma
  membrane
• Combine with other glycolipids to make glycocalyx
  (sugar coating)

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Glycocalyx

• The fuzzy, sticky carbohydrate-rich area
  surrounding the cell
• Every cell has a different pattern of sugars in
  its glycocalyx therefore, the glycocalyx
  provides a very specific biological marker for
  cell recognition
• Essentially I.D. tags for the cell to cell
  recognition

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CholesterolIts not the devil!

• Wedges between the phospholipid tails
• Stabilize the membrane

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Membrane Proteins
Integral Proteins Peripheral Proteins
Most are transmembrane (span the entire width of the membrane and protrude on both sides) Most are involved in transport as channels or carriers Not embedded in the membrane. Attached loosely to integral proteins or phospholipids May act as enzymes, and others help to bring about changes in cell shape during cell division
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What 3 factors bind cells together?

1. Glycoproteins in the glycocalyx act as an
   adhesive
2. Wavy contours of membranes fit together in a
   tongue and groove fashion
3. Special membrane junctions are formed

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Special Membrane Junctions

• Tight Junction
• impermeable junction helps prevent molecules
  from passing through the extracellular space
  between adjacent cells

• Desmosome
• anchoring junctions scattered like rivets
  along the sides of adjacent cells that prevent
  separation
• Button like plaque on cytoplasmic side held
  together by thin linker proteins (cadherins) on
  the cellular side
• Thicker protein filaments lock together with
  the plaque on the opposite side to anchor them
  together
• Strong yet flexible junctions

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Special Membrane Junctions

• Gap Junctions
• Allows chemical substances to pass between
  adjacent cells
• Connected to other cells by a hollow cylinder
  (connexons)
• Ions, sugars, and other small molecules pass
  through these channels

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Cell Junction Junction Whats Your Function?
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Membrane Transport

• The plasma membrane is a selectively permeable
  membrane that allows nutrients to enter the cell
  while keeping unwanted elements out of the cell
  as well as ridding itself of toxic waste
  products.
• Interstitial Fluid (the cellular super highway)
• Fluid between the cells that contains nutrients
  such as vitamins, sugars and amino acids,
  hormones and neurotransmitters, and waste
  products

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Passive Transport(See Table 3.2 on Page 80)

• Simple Diffusion
• Facilitated Diffusion
• Osmosis
• Filtration

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Active Transport(See Table 3.2 on Page 80)

• Solute Pumping
• Vesicular Transport
• Exocytosis
• Phagocytosis (Endocytosis)
• Bulk-phase Endocytosis
• Receptor-mediated Endocytosis

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Diffusion

• The tendency of molecules or ions to scatter
  evenly throughout the environment
• Molecules move from areas of higher concentration
  to lower concentration

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Simple Diffusion

• Substances that are nonpolar and lipid soluble
  (oxygen, carbon dioxide, fat-soluble vitamins,
  and alcohol) diffuse directly through the lipid
  bilayer
• However, polar and charged particles can
  selectively pass through channel protein pores if
  they are small enough
• Diffusion Model

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Facilitated Diffusion
Certain molecules (glucose and other simple
sugars) are too polar to dissolve in the lipid
bilayer and too large to pass through membrane
channels so they must be helped across Transport
proteins in the plasma membrane allow entrance to
the cell bypassing the non polar portion of the
cell by engulfing then releasing the molecule
into the cell Facilitated Diffusion Model
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Osmosis

• The diffusion of a solvent, such as water through
  a selectively permeable membrane
• Occurs whenever the water concentration differs
  on the two sides of the membrane
• Even though water is highly polar, it passes
  easily through the lipid bilayer
• Osmosis Model

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Tonicity

• Osmotic imbalances cause cells to shrink or swell
  until the solute concentration on both sides of
  the plasma membrane is the same, or the membrane
  is stretched to its breaking point
• Tonicity is the ability of a solution to change
  the tone or shape of cells by altering their
  internal water volume

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Tonicity

• Isotonic
• solutions with the same concentration of solutes
  as cells
• Cells retain normal shape and have no loss or
  gain of water
• Hypertonic
• Solutions with higher concentration of solutes
  than the cell
• Cells in a hypertonic solutions lose water and
  shrink (crenate)
• Hypotonic
• Solutions with a lower concentration of solutes
  than the cell
• Cells in a hypotonic solution gain water and
  swell and sometimes burst (lyse)

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Active Transport

• Similar to facilitated diffusion in that it needs
  carrier proteins that combine with the
  transported substances.
• Solute pumps move solutes uphill against their
  concentration gradients

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Vesicular Transport

• The transport of large particles and
  macromolecules across the plasma membrane
• The substance or cell product to be released is
  1st enclosed in a membranous sac called a vesicle
• 2 types of vesicular transport
• Exocytosis - movement of substances from the cell
  interior to the extracellular space
• Endocytosis movement of substances from the
  extracellular space into the cell

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Exocytosis

• Moves materials out of the cell
• Material is carried in a membranous vesicle
• Vesicle migrates to plasma membrane
• Vesicle combines with plasma membrane
• Material is emptied to the outside

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Exocytosis
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Endocytosis

• Extracellular substances are engulfed by being
  enclosed in a membranous vesicle
• Types of endocytosis
• Phagocytosiscell eating?
• Pinocytosiscell drinking?
• Receptor mediated
• Exocytosis/Endocytosis Model

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The Cytoplasm

• The stuff between the plasma membrane and the
  nucleus
• Forms the foundation of the cell and contains the
  organelles Little organs

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The Organelles

• The machinery of the cell
• Each organelle little organ has a specific job
  in the cell to maintain the life of the cell

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Mitochondria

• The power plants of a cell providing most of
  its ATP supply
• Carbohydrate, lipid and protein molecules are
  broken down here and the energy is used to form
  molecules of ATP
• Complex organelles that contain their own DNA,
  RNA, and ribosomes and are able to reproduce
  themselves

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Ribosomes

• Made of protein and RNA, these are the site of
  protein synthesis (production)
• Some are free floating in the cytoplam and others
  are attached to membranes forming Rough ER

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Rough ER

• Ribbons of membrane studded with ribosomes, which
  make all the proteins secreted from the cells
• Manufactures the integral proteins and
  phospholipids that form the plasma membrane
  considered a membrane factory
• Once made, proteins are enclosed in vesicles for
  transport to the Golgi Aparatus where they are
  further processed

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Golgi Aparatus

• Made of stacked, flattened membranous sacs with
  many tiny vesicles that pinch of for shipping
  proteins.
• Main function is to modify, concentrate and
  package the proteins and lipids made by the rough
  ER. --See figure 3.20 on page 86
• Packages are shipped 1 of 3 ways
• Vesicle is destined for exocytosis
• Vesicle is to become part of the plasma membrane
• Vesicles becomes a lysosomes

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Lysosomes

• Vesicles produced by the Golgi Aparatus that
  contain digestive enzymes
• Function as a cells demolition crewby
• Digesting particles taken in by phagocytosis
  (esp. bacteria, viruses, and toxins)
• Geting rid of worn-out or non-functioning
  organelles
• Performing metabolic functions such as glycogen
  breakdown and release
• Breaking down non-useful tissues such as the
  webbing between the fingers and toes of a
  developing fetus
• Breaking down bone to release Calcium ions into
  the blood

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Peroxisomes

• Membranous sacs containing powerful enzymes
  (oxidases and catalases) which detoxify harmful
  substances and neutralize free radicals
• Especially numerous in the liver and kidney cells
  which are very active in detoxification
• Free Radicals- normal byproducts of cellular
  metabolism that can have harmful effects on cells
  if allowed to accumulate

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Check Your Understanding
What organelle is the major site of ATP
synthesis? What are 3 organelles involved in
protein synthesis and how do they interact? How
does the function of lysosomes compare to that of
peroxisomes?
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The Cytoskeleton

• The cell skeleton it is a network of rods
  running through the cystosol
• Supports cell structure and aids in cell movement
• 3 types of rods from smallest to larges
• Microfilaments
• Intermediate filaments
• microtubules

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Microtubules

• Cylindrical structures made of tubulin proteins
• Support the cell and give it shape
• Involved in intracellular and cellular movement
• Form the centrioles

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Centrioles

• Paired cylindrical bodies each composed of 9
  triplets of microtubules
• Organize a microtubule network during mitosis to
  form the spindle and asters
• Form the bases of cilia and flagella

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Cilia

• Whip-like cellular extensions on the surface of
  certain cells
• Example cells that line the respiratory tract
  have cilia that propel mucus laden with bacteria
  and dust particles upward away from the lungs
• Flagella
• Long tail-like projection formed by centrioles
• Example sperm which have one flagellum used for
  movement
• NOTE Cilia propel other substances across the
  cells surface whereas the flagella propels the
  cell itself

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Microvilli

• Little Shaggy Hairs
• Tiny finger like extensions of the plasma
  membrane
• Increase the plasma membrane surface are
  tremendously

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The Nucleus

• The control center of the cell
• Has 3 regions or structures
• The nuclear envelope
• Nucleoli
• chromatin
• Most cells only have 1 nucleus but some are
  multinucleate having more than 1 nucleus (ex.
  Skeletal muscles)
• All human cells except red blood cells have at
  least 1 nucleus. RBCs are the only anucleate
  cells therefore cannot reproduce and only live
  for 3-4 months in the blood stream

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The Nuclear Envelope

• Surrounds the nucleus in a double layer membrane
  barrier separated by a fluid filled space
• The outer membrane is connected with the rough ER
  of the cytoplasm and studded with ribosomes
  pores

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Nucleoli

• Spherical bodies found within the nucleus
• Produce ribosomal RNA molecules for the creation
  of ribosomes

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Chromatin

• Uncoiled chromosomes consisting of DNA and
  histone protein molecules
• Histone is responsible for packing long DNA
  molecules in a compact, orderly way

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Cell Division

• Cells must reproduce if an organism is to grow
  and repair damaged tissues
• During cell reproduction, a cell divides its
  genes equally and then splits into 2 identical
  cells

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Cell Division

• Cell division involves 2 major events
• Mitosis
• Cytokinesis
• Mitosis- when the chromatin in the nucleus
  combine into chromasomes and are equally divided
  between the 2 forming cells
• Cytokinesis separation of the cytoplasm to
  produce 2 daughter cells. Each daughter cell has
  the same number of chromosomes as the parent cell

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