THE CELL

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THE CELL
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Random Cell Facts

• The average human being is composed of around 100
  Trillion individual cells!!!
• It would take as many as 50 cells to cover the
  area of a dot on the letter i
• The longest cells in the human body are the motor
  neurons. They can be up to 4.5 feet long and run
  from the lower spinal cord to the big toe.

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Abiogenesis vs. Biogenesis

• Early scientists thought that some living things
  could arise from nonliving things eg. Frogs could
  come from mud, flies from rotting meat, plants
  from the dried out mud of ponds, etc.
• We call this process abiogenesis (also called
  spontaneous generation). They did not know about
  microscopic life such as bacteria. They did not
  yet know how many organisms reproduced.
• Biogenesis - the theory that states that only
  living things can give rise to other living
  things.
• This is the theory we accept today as true.

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Abiogenesis / Biogenesis Debate

• Many scientists, over time, contributed to the
  debate. Some were
• - Aristotle (334BC)
• - Francesco Redi (1660)
• - John Needham (1748)
• - Lazzaro Spallazani (1800)
• - Louis Pasteur (1861)
• - Robert Brown (1831)
• - Matthias Jakob Schleiden (1839)
• - Theodor Schwann (1839)
• - Braaun (1845)
• - Rudolf Virchow (1858)
• Timeline Presentation Activity

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The Invention of the Microscope

• The Invention of the Microscope, thanks to the
  contributions of Hooke and Leeuwenhoek, permitted
  scientists to discover the existence of cells.
• Hooke - (1665) published a book full of drawings
  of tree bark (cork) observed under a microscope.
  He uses the word cells to describe what he
  sees.
• Leeuwenhoek- (1673) read Hookes book and begins
  to design his own microscopes. Starting in 1673,
  he writes long letters to other scientists
  describing the microscopic life he was studying.
  He becomes an expert microscope maker, better
  than anyone of his time. His microscopes were the
  best you could buy. Hooke confirms what
  Leeuwenhoek was seeing.

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Cell Theory

• Cells have been observed since the 1600s when
  Robert Hooke made his first observations of cells
  in cork using one of the first microscopes.
• A cell theory was developed in the 1800s from
  the work of many scientists. Schleiden, Schwann,
  and Virchow were the major scientists involved.
• The cell theory states
• - All living things are composed of cells.
• - Cells are the basic units of structure and
  function in living things.
• New cells are produced from existing cells. (No
  spontaneous generation).

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The Microscope

• Biologists still use microscopes today to explore
  the cell. Our understanding of cells and their
  functions has increased dramatically due to
  improvements in microscopy.
• Researchers can use fluorescent labels and light
  microscopy to follow molecules moving through the
  cell.
• Confocal light microscopy, which scans cells with
  a laser beam, makes it possible to build 3D
  images of cells and their parts.
• High-resolution video technology makes it easy to
  produce movies of cells as they grow, divide, and
  develop.
• Electron microscopes are capable of revealing
  details as much as 1000 times smaller than those
  visible in light microscopes. Why?
• Scanning probe microscopes allow scientists to
  observe single atoms, DNA and protein molecules
  as well as a number of important biological
  structures.

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Cell Structures

• Every organism must be either a prokaryote or a
  eukaryote.
• Prokaryotic cells lack internal compartments and
  membrane-bound organelles, and these organisms
  are all unicellular. Bacteria and other simple
  cells of the kingdoms Archaebacteria and
  Eubacteria are the only prokaryotes.
• Eukaryotic cells may be single-celled or
  multicellular and include all protists, fungi,
  plants, and animals. Eukaryotes have a good or
  real nucleus as well as other structures.
  Eukaryotic cells are divided into compartments by
  membranes. These different compartments have
  specific functions and are called organelles.
  Each type of organelle has its own unique
  function.

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Cell (Plasma Membrane)

• The cell membrane is the only thing between a
  cell and its environment.
• It has a crucial role to play in the life of a
  cell it must control what enters and leaves the
  cell. The cell membrane must allow a sufficient
  number of food molecules in and must also allow
  for the prompt removal of waste products.
• It is made of a double layer of phospholipid
  molecules called the phospholipid bilayer.
• Because the membrane is too small to be seen
  clearly with a microscope, scientists have
  developed a model to explain what they think it
  looks like. This is called the fluid mosaic
  model.

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• The phospholipid bilayer is composed of two rows
  or layers of phospholipid molecules. The
  hydrophilic (water-loving) heads of the
  phospholipids are found on the outside and inside
  of the membrane facing the watery environment.
  The hydrophobic fatty acid tails from each layer
  face one another in the middle of the membrane.
• The protein molecules embedded in the membrane
  are called integral proteins. They have several
  functions. Some serve as special carriers or
  transport channels for molecules that are either
  too large or too hydrophilic to pass through the
  bilayer. Other membrane proteins (glycoproteins)
  have sugar chains attached to them. These act as
  attachment sites for molecules that need to enter
  and carry a message to the cell. (Immune
  System).
• Cholesterol molecules are found within the
  membrane and function in keeping the membrane
  fluid.

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The Fluid mosaic model
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Cell Wall

• Cell walls are not found in animal cells, but
  they are found in bacteria, some protists, fungi,
  and plant cells.
• Plant cell walls are mainly made of the
  polysaccharide cellulose. Cell walls are much
  stronger and thicker than cell membranes, and in
  plants provide structural support to the cell.
  This structure allows trees to grow tall and wood
  to be as strong as it is.
• Penicillin works by preventing the formation of
  bacterial cell walls leading to death of the
  bacteria.

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Nucleus

• The nucleus is the genetic control centre of the
  cell. It is usually spherical in shape and is
  often the most easily seen structure when cells
  are viewed through a light microscope.
• The nucleus houses the cells DNA. In eukaryotes,
  the DNA is combined with proteins into a fine,
  thread-like structure called chromatin.
• The nucleus is separated from the rest of the
  cell by the nuclear envelope, a double membrane
  with many nucleospores to allow materials to pass
  in and out of the nucleus.
• The nucleolus is also found in the nucleus and it
  is composed of DNA, granules, and fibres, and it
  is the location where ribosomes are made.

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Cytoplasm

• In eukaryotic cells this includes the interior of
  the cell between the nuclear envelope and the
  cell membrane.
• One half of the space in the cytoplasm is taken
  up by other organelles. The other half of the
  cytoplasm is the liquid portion known as the
  cytosol.
• The cytosol contains a concentrated mix of ions
  and molecules such as enzymes, amino acids, ATP,
  and carbohydrates.

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Cytoplasmic Organelles

• Structures that perform specialized functions in
  the cell are called organelles.
• Vacuoles and Vessicles are both containers, bags
  made of membrane, filled with water and dissolved
  molecules.
• Vacuoles are found mainly in plant cells and are
  used for storage of starch molecules or water and
  to give support to the cell.
• Vessicles are used for transporting materials
  throughout the cell and keep the different parts
  of the cell in contact.

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• Ribosomes are dense-looking dark granules located
  on the surface of parts of the endoplasmic
  reticulum and floating within the cytoplasm.
  They are made of a combination of RNA and
  protein, and are the sites where amino acids are
  assembled into proteins. (protein synthesis).
• The Endoplasmic Reticulum is a series of
  interconnected small tubes (tubules) made of
  membranes that branch out from the nuclear
  envelope. Part of the ER has ribosomes attached
  to it giving it a rough looking appearance
  therefore, this portion is known as the rough
  endoplasmic reticulum. This is where protein
  synthesis takes place, particularly for proteins
  for use outside of the cell. Additional
  membranes are also manufactured here for use by
  other organelles. The smooth endoplasmic
  reticulum lacks ribosomes and functions in making
  lipids including phospholipids and steroids.
  It also serves as storage for calcium ions.

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• The Golgi Complex (Apparatus) is named after the
  Italian scientist who discovered them. Golgi
  complexes are numerous and important to the
  operation of the cell. They consist of flattened
  stacks of membrane, whose function is to receive,
  modify and transport proteins produced by the
  endoplasmic reticulum. If the protein is to be
  used outside of the cell, the golgi packages it
  into a membrane-bound vesicle and sends it to the
  cell membrane for export.
• Lysosomes are produced by the Golgi and E.R. They
  are membrane-bound sacs that make compartments in
  the cell to allow digestion. They contain
  hydrolytic enzymes and have a variety of roles.
  Lysosomes may be used to digest food, while
  certain types of human white blood cells use them
  to destroy invading bacteria. They are also used
  to break down damaged organelles within a cell.
  Ex. Brain cells survive from birth to death and
  have organelles less than one month old.

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• Mitochondria (singular mitochondrion) are found
  in both plant and animal cells. These organelles
  play a vital role in energy-transforming
  activities.
• Mitochondria are composed of an outer membrane,
  an inner membrane organized into folds called
  cristae, and an inner liquid solution known as
  the matrix.
• The mitochondria is the site of cellular
  respiration in eukaryotic cells. This process
  involves extracting energy from food molecules
  such as glucose and using that energy to make
  ATP. In the process CO2 and H2O are produced.

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• Chloroplasts have a double membrane surrounding
  them and also have an internal membrane system
  containing light-capturing molecules of
  chlorophyll. The internal membranes are
  interconnected and frequently form a stack of
  pancake-shaped structures called grana. A thick
  fluid, the stroma, contains enzymes and other
  molecules, occupies the remainder of the space in
  the chloroplast. Chloroplasts are organelles
  that capture the energy from sunlight and convert
  it into chemical energy in a process called
  photosynthesis.

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• Cytoskeleton The cell membrane gives very
  little support to an animal cell. Animal cells
  are able to maintain their shape due to the
  cytoskeleton a supportive network of fine
  protein fibres. These protein fibres, are the
  microfilaments, intermediate filaments, and
  microtubules. Besides offering support to the
  cell, the cytoskeleton helps anchor the
  organelles within the cytoplasm and may play a
  role in relaying messages.

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• Cilia and Flagella are made of fine protein
  fibres that function to provide movement to some
  cells. The most obvious difference between them
  is their length flagella are long cilia are
  short. Also cilia may be very numerous and cover
  the cell while flagella are few in number. Ex.
  Paramecium is covered with tiny cilia, Euglena
  has two whip-like flagella. Human sperm cells
  move due to the presence of a single flagellum.

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Review Questions

• 1. The genetic control centre of the cell is the
  
• a) nucleus b) cytoplasm c) mitochondrion
  d) lysosome
• 2. The structure of the cell between the nucleus
  and cell membrane is called the
• a) mitochondrion b) cytoskeleton c)
  chloroplast d) cytoplasm
• 3. Which of the following organisms have
  prokaryotic cells?
• a) humans b) bacteria c) fungi d)
  plants
• 4. Cells that need a large amount of energy would
  usually contain many
• a) mitochondria b) chloroplasts c)
  vesicles d) Golgi Complexes
• 5. Organisms whose cells do not contain a nucleus
  are called
• a) prokaryotes b) eukaryotes c) plants d)
  fungi
• 6. Which structure is the site of protein
  synthesis?
• a) nucleus b) lysosome c) smooth ER d)
  ribosome
• 7. Where in the cell would you expect to find the
  cytoskeleton?
• a) within the nucleus b) within a
  mitochondrion c) within the cytoplasm
• d) between the cell membrane and the cell wall
• 8. Under a microscope a cell was found to contain
  many mitochondria, chloroplasts, a nucleus, a
  cell wall, cytoplasm, as well as other
  organelles. This cell is most likely a
• a) bacterial cell b) human cell c) plant
  cell d) none of these
• 9. Which of the following structures is not
  involved in cell support or movement?
• a) cytoskeleton b) cell wall c) cilia d)
  lysosome

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• 10. Sketch or trace a typical animal and plant
  cell to show all of the structures and organelles
  they are likely to contain.
• 11. Which structures are found in plant cells but
  not in animal cells?
• 12. Explain the difference between the nucleolus
  and nucleus.
• 13. What are the three points in the Cell Theory?
  
• 14. List some difference between prokaryotic and
  eukaryotic cells.
• 15 What is the difference between cytoplasm and
  cytosol?
• 16. Organelle means "little organ." How are
  organelles similar to organs?
• 17. All large organisms have cells with
  organelles. What advantage do organelles give the
  cell?
• 18. Describe the current model of the cell
  membrane.
• 19. The cell requires instructions in order to
  function correctly where are these instructions
  found?
• 20. Describe the characteristic of mitochondria
  that makes them well suited to their role in the
  cell.
• 21. How are the functions of mitochondria and
  chloroplasts similar?
• 22. By comparing a bee's body mass to its wing
  span, it has been calculated that a bee should
  not be able to fly. Cell biologists have since
  found that the muscles which control the wings of
  the bee have a huge number of mitochondria.
  Explain why this discovery may help explain why
  bees are able to fly.
• 23. What is the function of the ER?
• 24. Describe the function of the Golgi apparatus.
  
• 25. What is the function of the ribosome?
• 26. Cells of the stomach lining have large
  numbers of ribosomes and Golgi. Explain.
• 27. What are the functions of lysosomes?
• 28. Name some types of organisms that have cell
  walls and state what the walls are made of.