CELLS

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CELLS

• All organisms are made up of cells
• The cell is the unit of structure and function of
  all living things
• Life arises from the interaction of all cellular
  components.

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You must check this web site

• www.cellsalive.com

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There is correlation between the structure of
cells and their function

• Ex The shapes of muscles cells, sperm cells, red
  blood cells,, nerve cells are appropriate for
  their function.
• Example the flat tile like epithelial cells of
  the skin fit closely together making a barrier to
  bacterial entrance, water loss etc.
• Another way to say this is that
• shape reflects function

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• How small are cells?
• Most cells are microscopic
• Cells vary in size and shape

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History

• Robert Hook (1665) named cells after observing
  tiny compartments in cork .
• Anton VanLeeuwenhoek (1600s) improved the
  primitive microscopes and observed one celled
  organisms, even bacteria. He documented his
  findings with letters and diagrams to the Royal
  Society (of Science) in London.
• Robert Brown (1600s)discovered the nucleus
• Electron microscope was developed in the late
  1930s and allows scientist to see up to 0.5
  nanometers. About 1000 times larger than regular
  microscopes.
•  

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How are cells studied?

• Microscopes and Biochemistry
• The light microscope (LM) magnify cells up to
  1000 times
• Enables us to see the overall shape and structure
  of a cell

Figure 4.1A
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• The electron microscope
• Allows greater magnification and reveals cellular
  details

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The cell theory (mid-1800s)

• Mathew Schleiden and Theodor Schwann examined
  plant and animal tissues and came to the
  conclusion that they both consist of cells
• Rudolph Virchow came to the conclusion that
  young cells come from the division of other cells
•  1.    All organisms are made up of cells
• 2.    Cells are the units of structure and
  function of all living things, that is cells have
  all the properties of life.
• 3.    All cells come from pre-existing cells
•  

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• Prokaryotic cells are structurally simpler than
• eukar yotic cells
• There are two kinds of cells
• Prokaryotic- No nucleus- Bacteria and Archeae
• Eukaryotic- have nucleus- plants, animals and
  fungi

Figure 4.3A
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• TYPE OF CELLS Prokaryotic and Eukaryotic
• Prokaryotic cells are small, relatively simple
  cells
• That do not have a membrane-bound nucleus

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• Eukaryotic cells have a nucleus and are
• par titioned into functional compar tments.
• All other forms of life( plants and animals) are
  composed of complex eukaryotic cells
• Membranes form compartments inside eukaryotic
  cells to facilitate metabolic activities

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• A small cell has a greater ratio of sur face area
  to volume
• Than a large cell of the same shape

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• A typical animal cell
• Contains a variety of membranous organelles

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THE CYTOSKELETON AND RELATED STRUCTURES

• The cells internal skeleton helps organize its
  structure and activities
• A network of protein fibers
• Make up the cytoskeleton.

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Functions of the cytoskeleton

• Tubules and filaments are made up of protein
  fibers
• Microfilaments of actin
• Enable cells to change shape and move
• Intermediate filaments
• Reinforce the cell and anchor organelles
• Microtubules give the cell rigidity
• provide anchors for organelles and act as tracks
  for organelle movement

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• Over view Many cell organelles are connected
  through the endomembrane system

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• All cells on earth are enclosed in membranes that
  maintain internal conditions different from the
  surroundings, have DNA as their genetic material
  and can convert forms of energy from one to
  another.
• Membranes form the boundaries of many eukar
  yotic cells
• Compartmentalizing the interior of the cell and
  facilitating a variety of metabolic activities

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• The nucleus is the cellular control center
• Containing the cells DNA, which directs cellular
  activities

Figure 4.5
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ORGANELLES OF THE ENDOMEMBRANE SYSTEM

• The nucleus is the cells genetic control center
• The largest organelle is usually the nucleus
• Which is separated from the cytoplasm by the
  nuclear envelope

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Inside the nucleus

• Chromatin fibers made up of DNA
• These thin fibers coil up during cell
  division becoming thicker and visible. They are
  called now a chromosome
• Nucleolus makes ribosomes

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• Ribosomes on the sur face of the rough ER
• Produce proteins that are secreted, inser ted
  into membranes, or transpor ted in vesicles to
  other organelles

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• The endomembrane system is a collection of
  membranous organelles
• That manufactures and distributes cell products\
• Smooth endoplasmic reticulum has a variety of
  functions
• Smooth endoplasmic reticulum, or smooth ER
• Synthesizes lipids
• Processes toxins and drugs in liver cells
• Stores and releases calcium ions in muscle cells

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• A typical animal cell
• Contains a variety of membranous organelles

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• The Golgi apparatus finishes, sorts, and ships
  cell products
• Stacks of membranous sacs receive and modify ER
  products
• Then ship them to other organelles or the cell
  sur face

Figure 4.9
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• The endomembrane system
• The various organelles of the endomembrane system
  
• Are interconnected structurally and functionally

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• Mitochondria gets chemical energy from food
• Mitochondria carry out cellular respiration
• It uses the chemical energy in food to make ATP
  for cellular work

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• Lysosomes are digestive compar tments within a
  cell
• Lysosomes are sacs of enzymes that function in
  digestion within a cell

Food
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• Lysosomes in white blood cells
• Destroy bacteria that have been ingested
• lysosomes also help to digest worn out , damaged
  cell parts, recycle materials within the cell and
  fuse with food vacuoles to digest nutrients.

Figure 4.10B
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Lysosomes in white blood cells destroy bacteria
and lysosomes also can digest other parts of the
cell

• Abnormal lysosomes can cause fatal diseases
• Lysosomal storage diseases. These are rare.
• Inter fere with various cellular functions
• Ex Tay- Sachs, does not break down lipids in
  nerve cell membranes. Lipids accumulate
• Pompes disease, lysosomes cannot digest glycogen
  and it accumulates in muscle and liver cells

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Peroxisomes

• Specialized vesicles that contains enzymes
  (catalase) that digest hydrogen peroxide H2O2
• Our cells produce hydrogen peroxide during
  metabolism and the enzymes in peroxisomes break
  it down into water and oxygen gas which are
  harmless to the cell.

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Plant Cells

• Three organelles animals do not have
• Chloroplasts
• Cell wall
• Central vacuole

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• A typical plant cell has some structures that an
  animal cell lacks
• Such as chloroplasts and a rigid cell wall

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ENERGY-CONVERTING ORGANELLES

• Chloroplasts conver t solar energy to chemical
  energy. This is where PHOTOSYNTHESIS takes place
• Chloroplasts, found in plants and some protists
• Conver t solar energy to chemical energy in
  sugars

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• Vacuoles function in the general maintenance of
  the cell
• Plant cells contain a large central vacuole,
• Which has lysosomal and storage functions

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Central vacuoles in plants

• Also help increase the size of cells by absorbing
  water
• Are mostly water, minerals and nutrients
• Store color pigments (that attract insects)
• Store waste products and poisons

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• Some protists have contractile vacuoles
• That pump out excess water

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Organelles

• NAME LOCATION
  
  FUNCTION
• Cytoskeleton cytoplasm
  Maintains cell shape
• 
  facilitates
  movement and move
• 
  materials within
  the cell
• Cytosol cytoplasm
  Protein rich fluid in which
• 
  organelles and
  cytoskeleton
• 
  are immersed
• Nucleus Inside nuclear envelope
  Site of most of cells DNA
• 
  
  and nucleolus
• Nucleolus Inside the nucleus
  Synthesis of ribosomal RNA

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ORGANELLES

• NAME
  LOCATION
  FUNCTION
• Rough Endoplasmic Reticulum cytoplasm
  Protein synthesis,Cell metabolism,
• Smooth Endoplasmic Reticulum cytoplasm
  Lipid synthesis, storage of calcium,
• 
  
  Detoxification of toxic substances
• Ribosomes Rough ER and
  Protein synthesis
• 
  free in the cytoplasm
• Vesicles move
  through cytoplasm Transport
• Golgi Bodies cytoplasm
  Processing, sorting,
• 
  
  shipping of proteins and lipids
• Mitochondria cytoplasm
  Gets energy from food
  (makes ATP
• 
  
  during aerobic respiration)
•  

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ORGANELLES

• NAME
  LOCATION
  FUNCTION
• Lysosomes
  cytoplasm Digestion and breaking down
  of materials
• (only in animal cells)
  ( including the cells
  own)
• Peroxisomes cytoplasm
  Sacs of enzymes that break down substances
  
• 
  (alcohol,
  amino acids) into hydrogen peroxide
• 
  and then the
  hydrogen peroxide into water
• 
  and oxygen.
• Plasma Membrane all around the cell
  Controls substances and signals that go in
• 
  and
  out of cells. Maintains shape and
• 
  
  volume
• Cell wall ( plant cells) cytoplasm
  Keeps water inside and limits water
• 
  uptake,
  protects from outside influences,
• 
  maintains
  shape.

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ORGANELLES

• NAME
  LOCATION FUNCTION
• Central vacuoles center of plant
  cell water maintenance, stores waste
• (plant cells only)
• Plastids cytoplasm
  plastids provide nutrients
  and
• (plant cells only)
  
  pigmentation
• Chloroplast many
  throughout carry out photosynthesis
• (plant cells only)
  the cytoplasm contain
  chlorophyll

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CELL JUNCTIONS

• What are junctions? Protein or cytoplasmic
  bridges that serve as physical links between
  cells.
• The junctions between cells help integrate cells
  into tissues and higher levels of functioning.
  Junctions make cells living units greater than
  each individual part.
• Junctions serve to send and receive signals and
  materials and to cement itself to other cells and
  junctions coordinate cell activities.

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Plant cells

• Plants are covered by cell walls composed of
  cellulose fibers.
• Cell walls have plasmodesmata, these are channels
  that pass through adjoining cell walls connecting
  plant cell to plant cell.

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Animal cellsJunctions

• There are different kinds of intracellular
  junctions between animal cells, integrating each
  cell into a greater unit.
• Tight junctions
• Desmosomes or Anchoring juctions
• Gap or Communication junctions

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Tight junctions

• They fuse cell to cell to prevent leakage. Ex
  cells of the lining of the intestines keeping the
  fluid inside. All cells of most tissues are
  joined this way. The skin and the lining of
  internal cavities (epithelial).

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Gap or Communication junctions

• Link the cytoplasm of neighboring cells. They are
  open channels that allow a flow of materials and
  signals between cells.
• Very common in embryos and in heart tissue to
  allow for the passage of ions to cause contraction

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Desmosomes or Anchoring juctions

• Joins cells in tissues of the skin, heart and
  other organs such as the bladder subject to
  stretching.

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• Tight junctions can bind cells together into
  leakproof sheets
• Anchoring junctions link animal cells into strong
  tissues
• Gap junctions allow substances to flow from cell
  to cell

Figure 4.18B
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Cilia and flagella

• move when microtubules bend
• Eukaryotic cilia and flagella are locomotor
  appendages that protrude from some cells

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Clusters of microtubules Drive the whipping
action of these organelles

• .

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PLASMA MEMBRANE

• Function
• The cells gate keeper. Very important.
• It controls what goes in and out of a cell.
• Keeps equilibrium between the inside of cells
  and the outside and promotes homeostasis.
• Web site to check
• http//www.wisc-online.com/objects/index_tj.asp?ob
  jidAP1101

• Function
• The cells gate keeper. Very important.
• It controls what goes in and out of a cell.
• Keeps equilibrium between the inside of cells
  and the outside and promotes homeostasis.
• Web site to check
• http//www.wisc-online.com/objects/index_tj.asp?ob
  jidAP1101

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Membranes

• http//www.wiley.com/legacy/college/boyer/04700037
  90/animations/membrane_transport/membrane_transpor
  t.htm

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The plasma membrane of the cell is selectively
permeableControlling the flow of substances into
or out of the cell
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PLASMA MEMBRANE

•  STRUCTURE
• It is a LIPID BILAYER. Its main component is a
  PHOSPHOLIPID molecule.
• A phospholipid is made up of a hydrophilic head
  (water loving) and two hydrophobic fatty acid
  tails (dislike water). These are arranged in two
  layers with the fatty acids tails sandwiched
  between the hydrophilic heads.
• The membrane is fluid, it moves about, tails
  twist and wave
• Embedded in the phospholipid bilayer are the
  surface proteins.
• The membrane is a mosaic of different proteins
  embedded in the fluid matrix of the lipid
  bilayer.

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What makes up the plasma membrane?

• Phospholipids are the main structural components
  of membranes
• Membrane phospholipids form a bilayer
• Have a hydrophilic head and two hydrophobic
  tails

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Phospholipids form a two-layer sheetCalled a
phospholipid bilayer, with the heads facing
outward and the tails facing inward
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How does it work?

• Membrane is selectively permeable or
  semi-permeable. Small molecules that are
  electrically neutral diffuse easily in and out
  such as O2, CO2, and alcohols.
• The non-polar phospholipid tails of the bilayer
  repel charged molecules but allow lipid soluble
  molecules to pass easily.
• Sugars need to be transported through a channel
  as well as charged ions such as H, Na, K, Cl

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• Large molecules (like proteins) cannot diffuse
  through and must enter the cell by other
  mechanisms such as active transport. Active
  transport uses energy (ATP) to push the
  molecules in and out.
• Serious diseases associated with cell membrane
  defects
• Multiple Sclerosis, there is a myelin cover on
  axons of nerve cells. Because it is defective
  muscle control is lost
• Cystic Fibrosis, The channels for chloride to
  pass through the membrane do not work. Chloride
  ion are not able to leave the cell. Results in
  thick mucus in respiratory track and other ducts
  in the body.

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Proteins found in the plasma membrane

• Integral penetrate the hydrophobic core of the
  lipid bilayer
• Peripheral are loosely bound to the surface of
  the membrane
• Transport proteins
• Receptor proteins
• Recognition proteins
• Adhesion proteins

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Proteins found in the plasma membrane

• Transport proteins
• These are open on both sides making a
  channel, a passage. Water soluble substances pass
  through it. It is very specific for the substance
  that it moves.
• Receptor proteins
• Grab or bind substances to pass them
  through. Have a binding site with a specific
  shape that fits the shape of another molecule. It
  can bind a chemical messenger such as a hormone
  which then causes a change in the shape of the
  protein that relays the message to the inside of
  the cell.
• Recognition proteins
• These are glycoproteins. Have a short chain
  of sugars attached to it.
• Are like fingerprints. Serve as identification
  tags that are recognized by other cells. Your
  cells recognize your own
• Adhesion proteins
• Like glue, make cells stick together.

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The membrane is a fluid mosaic of phospholipids
with proteins and other molecules embedded in a
phospholipid bilayer
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Membrane proteins also function in
transportMoving substances across the membrane
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Other membrane proteinsFunction as receptors for
chemical messages from other cells
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Many membrane proteins Function as enzymes