Cells: The Living Unit

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Cells The Living Unit
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Cells general

• 4 aspects of cell theory
• A cell is the basic structural functional unit
  of life
• Cell properties directly relate to the properties
  of life
• The activity of an organism depends on the
  activities of individual and collective cells
• Principle of complementarity
• Activities of cells are dictated by specific
  structures of cells
• Continuity (the smooth working) of life is based
  on a cellular level
• Cells come from pre-existing cells

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Cells general cont.

• Characteristics of cells
• Cells vary greatly in their size, shape, and
  function
• All cells are composed primarily of carbon,
  hydrogen, nitrogen, and oxygen (CHON)
• All cells have the same basic parts some common
  functions
• All general cells contain a plasma membrane,
  cytoplasm, and nucleus

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Cell diversity
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Plasma membrane structure

• Plasma membrane
• Defines the extent of the cell
• Separates bodies major fluid components
• Intracellular fluid within cells
• Extracellular fluid outside cells
• The plasma membrane is composed of a double layer
  of phosopholipids embedded with smaller amounts
  of cholesterol and glycolipids and proteins

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Plasma membrane structure cont.

• Fluid mosaic model
• Membrane structure composed of a double layer
  (bilayer) of lipid molecules with protein
  molecules dispersed in it.
• Proteins which float within the bilayer form an
  ever changing mosaic pattern
• Composed of
• Double layer of phospholipids (lying tail to tail
  with their polar heads exposed to the water
  inside and outside the cell) embedded with
  cholesterol, proteins, and glycolipids

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Plasma membrane structure cont.

• Surfaces of the plasma membrane
• Outside surfaces of the cell contain more lipids
• Contains glycolipids (sugar lipid)
• Helps to make the outer surface more polar
• Inside contains integral proteins, phospholipids,
  cytoskeleton
• Phospholipids
• Modified lipid containing phosphorus
• 2 components
• Hydrophilic
• Polar head
• Has a charge
• Water loving
• Hydrophobic
• Nonpolar tail
• Does not have a charge
• Water hating

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P.M.
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Plasma membrane structure cont.

• Plasma membrane proteins
• Integral proteins are firmly inserted into the
  plasma membrane
• Have both hydrophobic and hydrophilic regions
• Some protrude from only one side of the plasma
  membrane
• Usually involved in receptors for hormones or
  chemical messengers or act as chemical relay
  messengers
• Transmembrane proteins span the entire plasma
  membrane
• Mainly involved in transport
• Channel proteins
• Have a pore in which water soluble molecules pass
  
• Carrier proteins
• Bind to substances to move them through the
  membrane

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P.M
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Plasma membrane structure cont.

• Peripheral proteins are not embedded in the
  plasma membrane, but attach to integral proteins
  or to phospholipids
• Can be removed w/o disturbing the plasma membrane
  
• Contain filaments that helps support the membrane
  on the cytoplasmic side
• Some involved in changing the cells shape (during
  division)
• The glycocalyx is the fuzzy, sticky,
  carbohydrate-rich area surrounding the cell
• sugar covering
• Provides a highly specific biological markers
• Recognize self from non-self

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P.M.
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Specialization of the plasma membrane

• Microvilli
• shaggy hairs
• Fingerlike extensions of the plasma membrane that
  increase the surface area of the cell
• Most often found in cells with an absorptive
  function
• Kidneys and intestines
• Contains actin
• Contractile protein that helps stiffen the
  microvilli to keep them erect

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Specialization of the plasma membrane cont.

• Membrane junctions
• Many cells are close together and in tight
  communities
• Glycoproteins act as the cells adhesive
• Wavy contours of cells edges allow cells to stick
  together in a tongue and grove fashion
• Special membrane junctions are formed
• Tight Junctions
• Desmosomes
• Gap Junctions

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Specialization of the plasma membrane cont.

• Tight junctions
• Integral proteins on adjacent cells fuse together
  to form impermeable junctions
• Prevents molecules from passing through the
  extracellular space between cells

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Specialization of the plasma membrane cont.

• Membrane junctions cont. -
• Desmosomes
• Anchoring junctions
• Scattered like rivets to prevent the cells
  separation
• Held together by linker proteins that extend from
  the plaque on the cytoplasmic face
• Linker proteins span from one cell to the other
  attach themselves to the other cells plaque
• Reduces the chances of ripping the cell when
  tension is applied

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Desmosomes
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Specialization of the plasma membrane cont.

• Membrane junctions cont.
• Gap junctions
• Communication junction
• Allows chemical substances to pass between
  adjacent cells
• Connected by connexons hollow tubules that
  allow the cells to communicate because their
  cytoplasm's are so close
• Allows small molecules to pass between two cells
• In electrically charged tissues

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Gap junctions
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P.M. Functions general

• Cells are bathed in interstitial fluid
• Contains important substances cells need to
  survive
• Cells extract nutrients to remain healthy
• Where the cells eject their waste
• The plasma membrane is a selectively permeable
  barrier, regulating how substances pass into and
  out of the cell
• Allows some substances to pass while excluding
  others

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P.M. Functions cont.

• Solute
• Substance being dissolved within a solution
• Ex. Sugar, salt, calcium, etc.
• Solvent
• Substance in which solutes are dissolved
• vat in which substances are dissolved
• Typically water
• Concentration gradient
• The difference in solute concentration inside and
  outside the cell

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Passive processes

• Passive processes
• Does not require energy (ATP)
• Move substances down (or with) a concentration
  gradient
• Substances move from areas of higher
  concentration to areas of lower concentration
• Types
• Diffusion
• Simple diffusion
• Facilitated diffusion
• Osmosis
• Filtration

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Passive processes

• Diffusion
• The tendency of molecules/ions to scatter evenly
  throughout the environment
• Substances move directly through the plasma
  membrane if its
• Lipid soluble
• Small enough to pass through membrane channels
• Assisted by carrier proteins
• Goal of diffusion to reach equilibrium where
  molecules are moving equally in all directions
  there is no net movement molecules are balanced
  on each side

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Passive processes cont.

• Diffusion cont
• Move from areas of higher concentration to areas
  of lower concentration move down the
  concentration gradient
• Molecules move very quickly erratically
• Bounce off each other
• They dont like to be close they naturally move
  to areas where numbers are lower (move from high
  to low)
• The greater the concentration difference the
  faster the diffusion process
• Movement occurs due to the kinetic energy of the
  molecules
• The smaller the molecule the faster the diffusion
• Warmer the temp the faster the diffusion

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Diffusion
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Passive processes cont.

• Diffusion cont.
• Simple diffusion
• Unassisted diffusion of lipid-soluble or very
  small particles
• Substances that are nonpolar
• Oxygen, carbon dioxide, alcohol, fat-soluble vit
• Down the concentration gradient
• Facilitated diffusion -
• Substances are moved through the plasma membrane
  by binding to protein carriers or by membrane
  channels
• Transport proteins change shape to allow
  substances (glucose simple sugars) through
• Transported down the concentration gradient

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Passive processes
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Passive processes cont.

• Osmosis
• Diffusion of water
• Water is polar, but it is a small molecule that
  can slip through the plasma membrane as the
  membrane changes shape
• Occurs until solute concentrations are balanced
• Movement occurs due to solute concentrations
• Water moves when solute concentrations differ
• Requires less energy to move water than a solute
• Osmolarity the total number of all solute
  particles w/in a solution
• Osmotic pressure the cells ability to resist
  further (net) water movement when solute
  concentrations are equal

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Osmosis
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Passive processes cont

• Osmosis cont.
• Tonicity
• A solutions ability to change the tone or shape
  of cells by altering their internal water volume
• The number of nonpenetrating solutes
• Isotonic
• Solutions with the same concentration of
  nonpenetrating solutes on either side of the cell
  or the total solute concentration
• Solutes are equal inside and outside the cell
• Cells keep their normal shape because there is
  no net movement of water
• Body fluids isotonic

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Passive process cont.

• Osmosis cont.
• Hypertonic
• Solutions with high concentrations of solutes
• Cells loose water trying to equalize the solutes
• Loosing water causes them to shrink or crenate
• Hypotonic
• Solutions that contain fewer solutes
• The solution bathing the cell is more dilute than
  the cell itself
• Cells take on water as it tries to equalize the
  lower number of solutes on the inside of the cell
  
• Cells take on so much water they eventually burst
  or lyse
• Rehydrating sports drinks, cola, and apple
  juice are hypotonic increasing the amount of
  water cells absorb, causing rehydration

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Tonicities
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Passive processes cont.

• Filtration
• A pressure-driven process that forces water and
  solutes through a membrane or capillary wall by
  fluid or hydrostatic pressure
• Passive processes
• Involves a pressure gradient that pushes the
  solute fluid (filtrate) from higher-pressure
  areas to lower-pressure areas
• Not a selective process
• Anything that is small enough will be pushed, by
  pressure, through the plasma membrane

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Active processes

• Cells use energy, ATP, to move substances against
  their concentration gradient
• Active transport
• Uses solute pumps to move substances against
  their concentration gradient
• Energy is needed either directly or indirectly
• Provide movement for substances who cant pass by
  diffusion
• Ions such as Na and K need a protein transport
  (solute pump) to move across the membrane against
  their concentration (moving them uphill)

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Active processes cont.

• Active transport cont.
• Primary active transport
• Energy provided directly by the hydrolysis of ATP
• Causes the transport protein to change shape
  which pumps the bound solute across the membrane
• Sodium potassium pump
• K higher inside the cell
• Na higher outside the cell
• They leak across the plasma membrane along their
  concentration gradient the pump is needed to
  keep K higher inside and Na higher outside

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Active processes cont.

• Active transport cont.
• Secondary active transport
• The driving forces of primary transport can
  indirectly drive the transport of other solutes
• As sodium is transported it drags other solutes
  with it they are cotransported (sugars and
  amino acids)
• Even though solutes are cotransported which is
  passive they would not be able to be
  transported w/o the energy required movement of
  sodium

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Active transport
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Active transport cont.

• Active transport cont
• Vesicular transport
• Means by which large particles (macromolecules)
  fluids are transport across the plasma membrane
• Energized by ATP
• Two types
• Endocytosis
• Exocytosis

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Active transport cont.

• Vesicular transport
• Exocytosis
• out of the cell
• Used to move substances from inside the cell to
  the extracellular environment
• Hormone secretion, neurotransmitting, ejection of
  waste, mucus secretion
• Substance to be secreted is enclosed in a
  membranous sac called a vesicle

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Exocytosis
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Active transport cont.

• Endocytosis
• into the cell
• Move substances into the cell using
  protein-coated vesicles
• Clathrin-coated
• Non-clathrin-coated (Caveolae or coatomer)
• Moved into the cell by extensions of the plasma
  membrane

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Active transport cont.

• Endocytosis cont
• 3 Types of Clathrin-coated vesicles
• Phagocytosis
• Pinocytosis
• Receptor-mediated endocytosis
• Phagocytosis
• cell eating
• Cytoplasmic extensions pseudopods protrude
  from cell and cover/contain large/solid material
• Formed vesicle phagosome
• Fuses with a lysosome to digest the contents

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Active transport cont.

• Endocytosis cont
• Pinocytosis (fluid phase endocytosis)
• Infolding of the plasma membrane
• Contains extracellular fluid w/ dissolved
  molecules
• Allows the cell to sample the contents of the
  extracellular fluid
• Important for cells that absorb nutrients

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Active transport cont.

• Receptor-mediated endocytosis
• Most common method for specific uptake
• Enzymes, insulin, hormones, and iron
• Flu viruses utilize this method to attack our
  cells
• Receptors membrane proteins that only bind with
  certain substances
• Create a vesicle coated pit
• Contents dissolved/utilized within the cell

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Enodcytosis
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Active transport cont.

• Non-clathrin-coated vesicles
• Caveolae inpocketings of plasma membrane
• Caveolin proteins
• Capture specific molecules (folate, tetanus
  toxin)
• Close association with lipid rafts, important for
  cell signaling
• Coatomer (COP1 and COP2) proteins
• Vesicular trafficking

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Membrane potentials

• A membrane potential is a voltage across the cell
  membrane that occurs due to a separation of
  oppositely charged particles.
• In a resting stage a cell exhibits a resting
  membrane potential the cell is polarized the
  inside of the cell is more negative than the
  outside
• Charge only exists at the membrane
• Charges within in the cell are neutral
• Determined by
• Concentration gradient of potassium (K) and
  sodium (Na)
• More K within cells
• More Na in the extracellular fluid
• K diffuses out of the cell cells is
  impermeable to Na
• Now more positive charges are outside the cell
  giving it its negative charge

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Cellular environmental interactions

• Membrane receptors
• Diverse groups of integral proteins and
  glycoproteins that serve as binding sites
• Function in
• Contact signaling
• Touching of cells
• Method for recognizing other cells
• Bacteria and viruses utilize this method
• Electrical signaling
• Responding to the changes in voltage
• Neural and muscle tissue
• Chemical signaling
• Job of most membrane receptors
• Nervous endocrine systems

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Developmental aspects of cells

• Aging
• Due to wear-and-tear
• Accumulation of free radicals
• May be a result of autoimmune responses
  progressive weakening of the immune system
• Apoptosis
• Programmed cell death
• Cell suicide
• Cancer cells fail to go through apoptosis
• Strokes heart attacks increase the rate of
  apoptosis

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• The rest of the material is not necessary for the
  test.

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Components of the cell

• The cytoplasm is the cellular material between
  the cell membrane and the nucleus, and is the
  site of most cellular activity.
• Major elements of the cytoplasm
• Cytosol
• Fluid in which the other cytoplasmic elements are
  suspended
• Largely water w/ salts, proteins, sugars other
  solutes
• Cytoplasmic organelles
• Major components/workings of the cell
• Cytoplasmic inclusions
• Not a functional unit
• Chemical substances
• Ex lipid droplet in a fat cell

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Components of the cell

• Organelles
• Mitochondria
• Sausage-shaped organelle
• Powerhouse of the cell
• Produce ATP
• The more mitochondria the more energy a
  particular cell needs
• Large quantities in liver and muscle cells
• Ribosome
• Consist of proteins ribosomal RNA
• Site of protein synthesis

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Components of the cell cont.

• Endoplasmic reticulum
• Continuous with the nuclear membrane
• network within the cell
• Two types
• Rough endoplasmic reticulum
• Contains ribosomes making it appear rough
• Manufactures all proteins secreted from the cell
• Produces components of the membranes
• Liver secretory cells
• Smooth endoplasmic reticulum
• Continuation of the RER
• Lipid cholesterol synthesis
• Synthesis of steroid-based hormones (sex
  hormones)
• Absorbtion, synthesis transort of fats
• Detoxification of drugs
• Breakdown of glycogen to form free glucose

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Components cont.

• Golgi apparatus
• Moves directs cellular proteins
• Modifies, concentrates, packages proteins
• Proteins bud off in vesicles from the ER bind
  with the golgi in order to be modified
• Golgi vessicles are created allowing proteins to
  be transferred to the plasma membrane in order to
  be excreted into the extracellular space
• Lysosomes
• Involved in digestion phagocytosis (bacteria,
  viruses, toxins)
• Degrading nonfunctional/worn-out organelles
• Break down nonuseful tissues

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Components cont.

• Peroxisomes
• Digestion of alcohol
• Cytoskeleton
• Cells skeleton
• Supports cell structure generates cell
  movements
• Centrosomes centrioles
• Organizes mircrotubules
• Arranged at right angles to each other
• Organize mitotic spindles
• Form base of cilia and flagella
• Cellular extensions
• Cilia
• Occur in large numbers
• Move together in order to move substances
• Propels other substances
• Flagella
• Single
• Whip like motion
• Sperm

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Nucleus

• Control center of the cell
• Nuclear envelope
• Binds the nucleus
• Double layer membrane
• Continuous with rough ER
• Nuclear pores
• Regulates entry and exit of large particles
• Nucleoli
• Site of ribosome production
• Contain DNA
• Chromatin
• DNA (genetic materials) histone proteins
• Nucleosomes
• Eight histone proteins DNA molecule
• Chromosomes
• Condensed chromatin
• Utilized when cells are going to divide