Cellular Transport And the Cell Cycle

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Cellular Transport And the Cell Cycle
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Diffusion

• At all temperatures above absolute zero, the
  individual atoms that constitute any substance
  are always in movement. Indeed, the amount of
  this movement is what constitutes temperature
  itself.
• Simply put, diffusion is the movement of
  particles from a region of high concentration to
  an area of lower concentration

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Diffusion Cont.

• Particles of a substance will move from a region
  of high concentration to a region of lower
  concentration.
• The difference in concentration of atoms is know
  as a concentration gradient

• As particles move in a given area, an equilibrium
  is reached where the space between the particles
  becomes fairly uniform.
• This equal distribution of atoms is called
  dynamic equilibrium

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Diffusion Cont.

• Follow link to animation of diffusion
• The Diffusion Applet
• Follow link to tutorial of diffusion and osmosis
• Diffusion and osmosis tutorial

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What is Osmosis?

• Osmosis Diffusion of water across a selectively
  permeable membrane
• The plasma membrane does not limit the diffusion
  of water
• In a cell, water always tries to reach an equal
  concentration on both sides of the membrane
• Regulation of water flow through the membrane is
  important in maintaining homeostasis

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What Controls Osmosis?

• Concentration gradient - Unequal distribution of
  particles

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Cells in an Isotonic Solution

• Isotonic Solution when the concentration of
  dissolved substances in the solution is the same
  as the concentration of dissolved substances
  inside of the cell
• Equal movement of water into and out of the cell,
  cell stays the same size

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Cells in a hypotonic solution

• Hypotonic solution when the concentration of
  dissolved substances is lower in the solution
  outside the cell than the concentration inside
  the cell
• Water is pulled into the cell, the cell swells
  and the internal pressure increases

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Cells in a hypertonic solution

• Hypertonic Solution where the concentration of
  dissolved substances outside the cell is higher
  than the concentration inside the cell.
• Water moves out of the cell, the cell shrinks,
  and internal pressure decreases

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Passive Transport

• Transport (diffusion) of particles across the
  membrane without the use of energy by the cell
• Particles move from a region of high
  concentration to a region of low concentration
  across the concentration gradient

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Passive transport by proteins
Facilitated Diffusion - Transport of materials
across the plasma membrane with the aid of
transport proteins

• Common method for moving sugars and amino acids
  across membranes
• Driven by a concentration gradient (substances on
  both sides of the membrane are trying to reach
  equal concentration)

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Active Transport

• Cells can move particles from a region of low
  concentration to a region of high concentration,
  but it takes !
• Active Transport movement of materials through
  a membrane against the concentration gradient

energy
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Active Transport Cont.

• Proteins in the cell membrane (Carrier proteins)
  bind with particles of the substance. When the
  right molecule binds to the right carrier
  protein, chemical energy allows the carrier
  protein to change shape so that the particle can
  be moved to the other side of the membrane

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Transport of Large Particles

• Some cells can take in large molecules, groups of
  molecules, or even whole cells
• Endocytosis process by which a cell engulfs a
  material and forms a vacuole inside of the cell
• Exocytosis expulsion or secretion of materials
  from the cell
• Used to get rid of waste, secrete hormones
• Both endocytosis and exocytosis require cellular
  energy (Active transport)

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Endocytosis
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Exocytosis
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Cell Growth
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Cells come in different sizes

• Red blood Cells 8 µm
• Some nerve cells can be up to 1mm in length
• The yolk of an Ostrich egg measures 8cm
• Most living cells are between 2 and 200 µm
• Given the wide range of cell sizes, why cant
  most organisms be just one giant cell?

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What limits cell size?

• Diffusion
• Diffusion is fast and efficient over short
  distances but slow and inefficient over larger
  distances
• a mitochondrion at the center of a hypothetical
  cell with a diameter of 20 cm would have to wait
  months before receiving molecules entering the
  cell

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What limits cell size? cont.

• DNA
• The nucleus contains blueprints for the cells
  proteins (proteins are used throughout the cell
  by the organelles)
• There is a limit as to how quickly the DNA
  (blueprints) can be copied
• The cell cant survive unless there is enough DNA
  to support the protein needs of the cell
• Some large single celled organisms have developed
  more than 1 nucleus

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What limits cell size? Cont.

• Surface area to volume ratio
• As cell size increases, its volume increases
  faster than its surface area
• If cell size doubles, the cell would require
  eight times more nutrients and would have eight
  times more waste to excrete. The surface area
  would increase only by a factor of four. The
  plasma membrane would not have enough surface
  area for nutrients, waste and oxygen to diffuse
  through

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Surface area to volume ratio
Surface area 6mm2 Volume 1mm2
Surface area 24mm2 Volume 8mm2
Surface area ?? Volume ??
Refer to PS lab 8.1 pg 209
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Cell Reproduction
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Cell Reproduction

• The cell theory states all cells come from
  preexisting cells
• We know that all organisms grow and change
• Throughout our lives, worn-out tissues are
  repaired or replace by new cells
• All of this occurs through Cell Division
• The process by which new cells are produced from
  one cell
• Results in two cells that are identical to the
  parent cell

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What are Chromosomes?

• Chromosomes dark staining structures that
  contain genetic material (DNA)
• Made up of DNA and protein
• Chromatin long strands of DNA wrapped around
  protein (resembles a tangled plate of spaghetti)
• Before a cell can divide,
• the long strands of chromatin
• must be organized into a
• chromosome

http//www.sirinet.net/jgjohnso/modchromosome.jpg
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Chromosomes
http//www.uic.edu/classes/bios/bios100/labs/realc
hromo.jpeg
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http//lhs.lps.org/staff/sputnam/Biology/U3Cell/ch
romosome_1.png
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The Cell Cycle

• The sequence of growth and division of a cell
• 2 phases
• Growth
• Division

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The Growth Phase Interphase

• The majority of a cells life is spent growing
  and making more DNA, this period is called
  Interphase
• During interphase, cell grows in size and the
  chromosomes are duplicated
• G1 phase - rapid growth
• S phase DNA synthesis and replication
• G2 phase Centrioles replicate and cell prepares
  for division

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The Division PhaseMitosis

• Cells undergo mitosis as they approach the
  maximum cell size at which the nucleus can
  provide blue-prints for proteins and the plasma
  membrane can efficiently transport nutrients and
  waste into and out of the cell
• 4 phases of Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase

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The Cell Cycle
http//lhs.lps.org/staff/sputnam/Biology/U3Cell/ce
llcycle_1.png
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Mitosis Prophase

• 1st stage of mitosis (longest stage)
• Chromatin coils up into visible chromosomes
• Each duplicated chromosome is made of 2 sister
  chromatids held together by a centromere
• The nucleus begins to disappear
• Centrioles migrate to opposite ends of cell
• Spindle fibers become visible

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Mitosis Metaphase

• 2nd stage of mitosis (short stage)
• Chromosomes become attached to the spindle fibers
  by their centromeres
• Chromosomes line up on the midline

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Mitosis Anaphase

• 3rd stage of mitosis
• Sister chromatids are pulled apart
• the spindle fibers attached to the centromere and
  the centriole begin to shorten pulling the
  chromatids from each other

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Mitosis Telophase

• 4th stage of mitosis
• Chromatids reach the opposite poles of the cell
• Chromosomes unwind, spindle begins to break down,
  nucleolus reappears and nuclear envelop forms
  around each set of new chromosomes

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Mitosis
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hnso2Freprod.htmlsize35.1kBnamemodchromosome.
jpgpchromosomestructuretypejpegno85tt573
eiUTF-8
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• Mitosis animation

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Division of Cytoplasm

• Cytokinesis division of cytoplasm between the
  two newly formed cells
• Different for plant and animal cells

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Results of Mitosis
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So whats the point?

• Mitosis guarantees that the two new cells that
  are produced are genetically identical. The two
  new daughter cells will carry out the same
  cellular processes and functions as those of the
  parent cell and will grow and divide just as the
  parent cell did.

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Growth and Development in Multicellular Organisms

• Cells
• Tissues
• Organs
• Organ systems
• Organism
• No matter how complex the organism, the cell is
  still the basic unit of organization