Cell Membrane, Cell Transport

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Cell Membrane, Cell Transport Cell Division
Chapter 7 Membrane Structure and
Function Chapter 12 The Cell Cycle
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Plasma Membrane
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Plasma Membrane Structure

• Boundary that separates the living cell from its
  surroundings
• Phospholipids are the most abundant lipid
• Arranged in a bilayer
• hydrophobic region (tails)
• hydrophilic region (heads)
• Exhibits , allowing some substances to
  cross it more easily than others
• The states that a membrane is a fluid
  structure with a mosaic of various proteins
  embedded in it

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Phospholipid Structure
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Selective Permeability

• A cell must exchange materials with its
  surroundings, a process controlled by the plasma
  membrane
• Regulates what enters and leaves the cell
• Hydrophobic (nonpolar) molecules, such as
  hydrocarbons, can dissolve in the lipid bilayer
  and pass through the membrane rapidly
• Polar molecules, such as sugars,
• Maintains inside the cell
• Allows for of cells in same organism

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Fluid Mosaic Model

• Phospholipid molecules can
• Makes the membrane act like a
• Fluid Mosaic Model Animation

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Membrane Cholesterol

• Cholesterol is a
• Adds to plasma membrane
• Helps keep fatty acid tails of phospholipids
  separated

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Membrane Proteins

• Different proteins are embedded in the fluid
  matrix of the lipid bilayer
• They determine most of the
• Spread throughout the membrane like raisins in
  raisin bread
• Allow membrane to with its environment

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Membrane proteins

• are bound to the surface of the membrane
• penetrate the hydrophobic core
• Integral proteins that span the membrane are
  called
• The hydrophobic regions of an integral protein
  consist of one or more stretches of nonpolar
  amino acids, often coiled into

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Membrane proteins

• Six major functions of membrane proteins
• Signal transduction
• Intercellular joining
• Attachment to the cytoskeleton and extracellular
  matrix (ECM)
• Includes a carbohydrate chain

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Carbohydrate chains

• Carbohydrates on the external side of the plasma
  membrane vary among species, individuals, and
  even cell types in an individual
• Attached to phospholipids ( ) or proteins (
  )
• These a cell
• Individual (Mr. Fusco cell)
• Species (Human cell)
• Type (kidney cell)
• Cells recognize each other by binding to surface
  molecules, often carbohydrate chains, on the
  plasma membrane

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LABEL THESE PARTS Cholesterol Glycolipid Phosphol
ipid Glycoprotein Integral protein Carbohydrate
chain Peripheral protein Inside/Outside of cell
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Cell Transport

• Because of the numerous amount of activities
  associated with the cell, substances must
  constantly move in and out of the cell
• There are 2 types of cell transport

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Passive versus Active

• Passive
• the concentration gradient ( )
• From random molecular motion

• Active
• the concentration gradient ( )

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Concentration Gradient

• From High ? Low
• NO energy needed
• From Low ? High
• Energy Needed

• Substances diffuse down their concentration
  gradient easily
• No work must be done to move substances
  the concentration gradient
• Work is required to move substances
  the concentration gradient

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Transport Types

• Passive
• Diffusion
• Osmosis
• Facilitated Diffusion

• Active
• Protein pumps
• Endocytosis
• Exocytosis

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Diffusion

• Diffusion is the tendency for molecules to
  into the available space
• Although each molecule moves randomly, diffusion
  of a population of molecules may exhibit a net
  movement in one direction
• the concentration gradient
• HIGH ? LOW
• require energy
• Results in (as many molecules cross
  one way as cross in the other direction)
• Diffusion Animation

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Osmosis

• Osmosis is the across a selectively
  permeable membrane
• Water diffuses across a membrane from the region
  of lower solute concentration to the region of
  higher solute concentration

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Simple Rule for Osmosis

• Salt is a
• When it is concentrated inside or outside the
  cell, it will draw the water in its direction

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Tonicity

• is the ability of a solution to cause a cell
  to gain or lose water
• Three types of solutions
• solution
• solution
• solution
• Hypertonic or hypotonic environments create
  osmotic problems for organisms
• , the control of water balance, is a
  necessary adaptation for life in such environments

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Isotonic Solutions

• water and solute (salt) concentrations
  inside and outside the cell
• Dynamic Equilibrium
• Water in water out
• Cells keep normal shape
• Solute concentration is the same as that inside
  the cell
• across the plasma membrane

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Hypotonic Solutions

• solute (salt) concentration outside than
  inside
• Since salt sucks, water will move into the cell
• Solute concentration is less than that inside the
  cell
• (swells) and may burst

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Plant Cells in Hypotonic Solution

• is the pressure inside plant cells
• Cell walls help maintain water balance
• A plant cell in a hypotonic solution swells until
  the wall opposes uptake
• Cell is now
• If a plant cell and its surroundings are
  isotonic, there is no net movement of water into
  the cell
• Cell becomes , and the plant may wilt

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Hypertonic Solutions

• solute (salt) concentration outside than
  inside
• Water sucked out of the cell
• Solute concentration is greater than that inside
  the cell

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Cells in Hypertonic Solutions

• Animal Cells
• Plant Cells
• Turgor pressure drops
• In a hypertonic environment, plant cells lose
  water
• Eventually, the membrane pulls away from the
  wall, a usually lethal effect called

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Facilitated Diffusion

• Some molecules are so small that they pass
  through the membrane with little resistance
• Oxygen Carbon Dioxide
• Lipid molecules (even though very large) also
  pass easily
• In speed the passive movement of
  molecules across the plasma membrane
• (transmembrane) provide corridors that
  allow a specific molecule or ion to cross the
  membrane
• , for facilitated diffusion of water
• that open or close in response to a
  stimulus (gated channels)

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Active Transport

• Moves substances their concentration
  gradient (Low ? High)
• Requires energy in the form of
• Active transport is performed by specific
  proteins embedded in the membranes

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Protein Pumps

• Protein 'pump' requires energy (ATP) to function
• Allows cells to maintain concentration gradients
  that differ from their surroundings
• The is one type of active transport
  system
• Exchanges in animal cells
• Transported molecules enter the in the
  membrane
• The energy causes a shape change in the protein
  that allows it to move the molecule to the other
  side of the membrane

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Endocytosis

• Ability of a cell to
• Ex. large molecules, groups of molecules, or
  whole cells
• Requires Energy
• Cell takes in macromolecules by forming vesicles
  from the plasma membrane
• There are three types of endocytosis
• Phagocytosis ( )
• Pinocytosis ( )
• Receptor-mediated endocytosis

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Types of Endocytosis

• In a cell engulfs a particle in a vacuole
• The vacuole fuses with a lysosome to digest the
  particle
• In , molecules are taken up when
  extracellular fluid is gulped into tiny
  vesicles
• In , binding of ligands to receptors
  triggers vesicle formation
• A is any molecule that binds specifically to
  a receptor site of another molecule

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Phagocytosis
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Pinocytosis
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Receptor-Mediated Endocytosis
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Exocytosis

• Opposite of endocytosis
• To expel wastes or secrete hormones
• Requires energy
• Transport vesicles
• Many secretory cells use exocytosis to
• Endocytosis and Exocytosis Animation

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Cell Division

• Life is based on the ability of cells to
  
• Rudolf Virchow (German physician) stated omnis
  cellula e cellula meaning
• cell division one cell divides into two cells

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Why Cells Divide

• Unicellular organisms
• cell division asexual reproduction (new
  organism)
• Multicellular organisms
• (single cell to trillions)
• Cell division is an integral part of the cell
  cycle, the life of a cell from formation to its
  own division

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Cell Cycle - Eukaryotes

• Defined nucleus houses DNA as chromosomes, a
  condensed form of chromatin
• Most cell division results in daughter cells with
  identical genetic information (DNA)
• A special type of division produces nonidentical
  daughter cells (gametes, or sperm and egg cells)
• Goal
• Chromosomes are from 1 parent cell
  (before division) to each daughter cell (after
  division)
• Includes

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Cell Cycle - Eukaryotes
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Cell Cycle

• Interphase ( ) can be
  divided into 3 subphases
• (first gap)
• (synthesis)
• (second gap)
• The cell grows during all three phases
• Makes proteins
• Copies organelles
• Chromosomes are duplicated only during the S
  phase
• Mitosis is the division of the
• Cytokinesis is the division of the

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Eukaryotic Chromosomes

• Chromatin
• Long strands of DNA wrapped around proteins
• In preparation for cell division, DNA is
  replicated and condenses to form chromosomes
• Each duplicated chromosome has two , which
  separate during cell division
• The is the narrow waist of the
  duplicated chromosome, where the two chromatids
  are most closely attached
• Chromosomes must be copied before a cell divides
• Each new cell must have a complete set
• Contain thousands of genes
• Vital for organisms to properly function

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Human Example

• 23 pairs of chromosomes
• 1 originally from mom, 1 from dad
• Every time our body cells ( )
  reproduce
• Each NEW cell must also end up with 23 pairs of
  chromosomes

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Chromosome Duplication

• One chromosome
• 2 sister chromatids
• Exact copies
• Attached by a centromere
• Cell division separates sister chromatids
• Each new cell gets one copy of each chromosome

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Mitotic Phase

• Mitosis is conventionally divided into five
  phases
• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis is well underway by late telophase
• Some texts do not recognize this as a separate
  phase

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Mitosis
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ProphasePro before

• Chromosomes
• Nucleolus and nuclear envelope
• Microtubules that controls chromosome movement
  during mitosis
• Includes the centrosomes, the spindle
  microtubules, and the asters
• An aster is a radial array of short microtubules
• During prophase, assembly of spindle microtubules
  begins in the centrosome, the microtubule
  organizing center

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Prophase
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Prometaphase

• Nuclear envelope completely gone
• Microtubules
• Some spindle microtubules attach to the of
  chromosomes and begin to move the chromosomes
• Kinetochores are specialized protein structures
  at the centromere

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Prometaphase
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MetaphaseMeta with (middle)

• Chromosomes line up at
• Also called the metaphase plate (midway point
  between the spindles two poles)
• Microtubules attach

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Anaphase Ana upward or back (apart)

• Sister chromatids
• Move along microtubules connected to kinetochore
  towards opposite ends of cell
• Chromatids now chromosomes
• Other microtubules elongate cell

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TelophaseTelos end

• Reverse of prophase
• Begins when chromosomes reach poles
• Chromosomes (less condensed)
• Genetically identical daughter nuclei form at
  opposite ends of the cell

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Cytokinesis

• Division of cellular contents
• Cytoplasm
• Organelles
• In animal cells, cytokinesis occurs by a process
  known as

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Cytokinesis

• In plant cells, a
• Formed from vesicles that pinch off of the Golgi
  body, move along microtubules, and join in the
  middle of the cell

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Some Animations

• Mitosis Animation
• Mitosis and Cytokinesis Animation
• Mitosis Animation 2

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Mitosis Ho-Down

• MITOSIS is a process that helps one cell become
  two
• It happens when a cell dies or makes some brand
  new
• This is how a cut heals and how a baby grows
• It works all oer the body from your head down to
  your toes
• PROPHASE is the first phase where chromosomes
  you'll see
• Then comes METAPHASE where they line up perfectly
• After that is ANAPHASE where they are pulled
  apart
• Finally is TELOPHASE, cells split then go back to
  start

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Cell Cycle Controls

• The sequential events of the cell cycle are
  directed by a distinct , which is similar
  to a clock
• The cell cycle control system is regulated by
  both internal and external controls
• The clock has specific where the cell cycle
  stops until a go-ahead signal is received
• G1, G2, M checkpoints

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Cell Cycle Controls

• G1 checkpoint seems to be
• A go-ahead signal at the G1 checkpoint allows
  cell to complete the S, G2, and M phases and
  divide
• No go-ahead signal and the cell will exit the
  cycle, switching into a
• G2 checkpoint
• Assesses success of
• Triggers start of mitosis
• Mitosis checkpoint
• Assesses accuracy of mitosis
• Occurs during

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Cell Cycle Controls

• Two types of regulatory proteins are involved in
  cell cycle control
• Activity of cyclins and Cdks fluctuates during
  the cell cycle
• MPF (maturation-promoting factor)
• A cyclin-Cdk complex
• Triggers a cells passage past the G2 checkpoint
  into the M phase
• Also called mitosis-promoting factor
• Cell Cycle Control Animation

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Cancer

• Disease of cell cycle
• DNA mutation changes genes that normally control
  growth
• Cancer cells do not respond normally to the
  bodys control mechanisms

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Features of Cancer Cells

• Normal cells divide about 50 times before dying
• Aging, toxins (smoking), mutagens (UV light), DNA
  replication errors
• Instead of sticking to neighbors, cancer cells
  become round, allowing for metastasis (spread)
• Keep growing after touching neighbor

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Tumors

• Cancer cells form
• Masses of abnormal cells within otherwise normal
  tissue
• Abnormal mass of essentially normal cells
• Remain at original site
• Invade surrounding tissues
• Can
• Move to other sites and create a new tumor
  (secondary)
• Cells send out signals for blood vessel
  production
• Gives them food, oxygen, escape route

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Review Questions

1. Identify and describe the parts of the fluid
   mosaic model of the plasma membrane.
2. Describe the various regions of a phospholipid
   molecule as they apply to the arrangement of the
   plasma membrane.
3. Explain the role of cholesterol in the membrane.
4. Describe the 2 main types and 6 various functions
   of membrane proteins.
5. Differentiate between passive and active
   transport.
6. Explain the idea of a concentration gradient,
   along with moving down and against it.
7. Define tonicity and explain hypertonic, isotonic,
   and hypotonic solutions.
8. Define osmoregulation and turgor pressure.
9. Differentiate between diffusion, osmosis, and
   facilitated diffusion, naming the parts of the
   membrane that help these transports.
10. Differentiate between protein pumps, endocytosis,
    and exocytosis, naming that parts of the membrane
    that help these transports.
11. Name and describe 3 types of endocytosis.
12. Explain the importance of cell division.
13. Name the parts of the cell cycle and state the
    events that occur in each stage.
14. Differentiate between chromatin, chromosome, and
    chromatid.

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Review Questions

1. Define somatic cells.
2. Name the 5 steps to the cell cycle.
3. Define cytokinesis and explain how it differs in
   plant and animal cells.
4. Describe the 3 events that occur in prophase.
5. Name 2 events that occur in prometaphase.
6. Name 2 events that occur in metaphase.
7. Name the main event of anaphase.
8. Name 3 events that occur in telophase.
9. Explain how the cell plate forms in plant cell
   cytokinesis.
10. Name the 3 checkpoints of the cell cycle control
    system and explain what occurs in each step.
11. Differentiate between the roles of cyclins and
    cyclin-dependent kinases.
12. Define the importance of MPF.
13. Relate the formation of cancer to the cell cycle.
14. Name 4 major features of cancer cells.
15. Define tumor and differentiate between benign and
    malignant.
16. Define metastasis.