Cell Structure

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Cell Structure Function
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Eukaryotic Cells an introductory video
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Living Things Cells

• The cell is the basic unit of structure
  function of all living things.
• The cell is the smallest unit of life that can
  still carry on all life processes.
• Both unicellular (one celled) and multicellular
  (many celled) organisms are composed of cells

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History

• Before the 17th century, no one knew cells
  existed
• In the early 17th century microscopes were
  invented cells were seen for the 1st time

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• Anton Von Leeuwenhoek, a Dutchman, made the 1st
  hand-held microscope viewed microscopic
  organisms in water bacteria from his teeth

• In 1665, an English scientist named Robert Hooke
  made an improved microscope and viewed thin
  slices of cork viewing plant cell walls
• Hooke named what he saw "cells"

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• In 1831, Scottish botanist Robert Brown used the
  word nucleus to describe the dark, central
  globule. 
• (The word nucleus is Latin for little nut.)

• In the 1830s, Matthias Schleiden (German
  botanist studying plants) Theodore Schwann
  (German zoologist studying animals) stated that
  all living things were made of cells

• In 1855, German scientist Rudolf Virchow stated
  that cells only arise from pre-existing cells

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The Cell Theory

• The combined work of Schleiden, Schwann,
  Virchow is known as The Cell Theory
• 1) All living things are made of one or more
  cells
• 2) Cells are the basic unit of structure
  function
• in organisms
• 3) Cells come only from the
  reproduction of
• existing cells

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Cell Diversity

• Not all cells are alike
• Cells differ in size, shape, and function

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Cell Size

• Most cells measured in micrometers (10-6)
• The female egg cell is the largest cell in the
  body can be seen without a microscope (ostrich
  egg is the largest known cell)
• A group of bacteria called mycoplasmas are the
  smallest known cells
• Nerve cells, although microscopically thin, can
  be very long (some up to 6 feet in giraffes)

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Cell Size Analysis
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Why are cells small ?
Surface Area Volume SAVol
Ratio (L x H x 6) (L x H x W)
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1 x 1 x 6 6 1 x 1 x 1 1 61 (6)
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2 x 2 x 6 24 2 x 2 x 2 8 248 or 31 (3)
4
4 x 4 x 6 96 4 x 4 x 4 64 9664 or 32
(1.5)
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Assume Oxygen is the substance moving across
through the membrane
Large Cell
What of each cell would not receive oxygen ?
Small Cell
About 5 This cell should survive
About 80 This cell probably will not survive
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Cells are small because

• Cells need surface area in order to exchange
  materials across their membrane
• Cell are limited by the surface area to volume
  ratio
• Smaller cells have a much higher ratio
• As cells grow, the amount of surface area becomes
  too small to allow materials to enter leave the
  cell quickly enough

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Cell Shape/Function

• Cells come in a variety of shapes, the shape
  helps determine the function of the cell
• Remember Function dictates shape !

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Blood Cells
Blood Cells are round travel through small
vessels (sickle cell anemia problem)
SICKLE CELL
NORMAL ROUND
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Nerve Cells
Nerve Cells are long and thin transmit nerve
impulses across long distances
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Skin Cells
Skin Cells are squared provide a wall-like
barrier when linked together
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Muscle Cells
Muscle Cells are tapered provide for
contraction allowing movement
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Cell Organelles

• A Cell Component that PERFORMS SPECIFIC FUNCTIONS
  FOR THE CELL.
• Little Organs
• Just as the organs of a multicellular organism
  carry out the organisms life functions, the
  organelles of a cell maintain the life of the
  cell.

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CELL MEMBRANE /PLASMA MEMBRANE

• Entire cell is Surrounded by A THIN MEMBRANE
• The Cell Membrane is a complex barrier separating
  the cell from it's external environment.
• This "Selectively Permeable" Membrane regulates
  what passes into and out of the cell.

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• Cell membranes are made mostly of phospholipid
  molecules.
• The phospholipids are arranged into two layers
  called a lipid bilayer. 
• The hydrophilic phosphate heads face the watery
  fluids inside and outside the cell.
• The hydrophobic lipid tails are sandwiched
  inside the bilayer.
• In addition, other structures, like proteins are
  embedded into the lipid bilayer and serve various
  functions.

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Phospholipid Bilayer
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The Fluid Mosaic Model of cell membranes

• Membranes are fluid and have the consistency of
  vegetable oil.
• The lipids and proteins of the cell membrane are
  always in motion.
• Phospholipids are able to drift across the
  membrane, changing places with their neighbor.
• Proteins in and on the membrane form patterns, or
  MOSAICS. 

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2. CYTOPLASM

• Everything between the cell membrane and the
  nucleus is the cells CYTOPLASM.
• Cytoplasm consists of two main components 
  CYTOSOL and ORGANELLES.
• CYTOSOL is a colloid mixture that consists mostly
  of water, along with proteins, carbohydrates,
  salts, minerals and other organic molecules.
• Cytoplasm is always in constant motion
  Cytoplasmic Streaming or Brownian Motion

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3. ENDOPLASMIC RETICULUM (ER)

• The ER is an extensive network of membranes
  connects different parts of the cell and usually
  connects the nuclear envelope to the cell
  membrane.
• The ER functions primarily as an intracellular
  highway, a path along which molecules move from
  one part of the cell to another.

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Rough vs. Smooth ER

• Rough ER is studded with ribosomes and processes
  proteins to be exported from the cell.
• Smooth ER is NOT covered with ribosomes and
  processes lipids and carbohydrates. The Smooth ER
  is involved in the synthesis of steroids in gland
  cells, the regulation of calcium levels in muscle
  cells, and the breakdown of toxic substances by
  liver cells.

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4. RIBOSOMES

• Ribosomes are the site of protein synthesis in a
  cell.
• They are the most numerous organelles in almost
  all cells.
• Some are free in the cytoplasm others line the
  membranes of rough endoplasmic reticulum.

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5. GOLGI APPARATUS

• The Golgi Apparatus is a system of membranes made
  of flattened sac-like structures and is involved
  in the processing, packaging and secreting of
  materials in the cell.
• Vesicles (packages of chemicals) bud off at the
  edges.

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6. MITOCHONDRIA

• Mitochondria are found scattered throughout the
  cytoplasm, and are relatively large, bean-shaped
  organelles
• The powerhouse" of the cell Site of cellular
  respiration and the production of ATP. ATP is the
  molecule that most cells use as their main energy
  currency.

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• Mitochondria is surrounded by two membranes
• The inner membrane has many folds, known as
  cristae. The cristae greatly increases the
  surface area of the inner membrane, providing
  more space for the chemical reactions to occur
  (more ATP).
• Mitochondria have their own DNA, and new
  mitochondria arise only when existing ones grow
  and divide.

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7. LYSOSOMES

• Lysosomes are small spherical organelles that
  enclose digestive enzymes within a single
  membrane.
• Lysosomes are the site of food digestion in the
  cell
• Lysosomes are formed from pieces of the golgi
  that break off.
• Common in animal, fungi, and protist cells, but
  rare in plant cells

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8. Nucleus

• The nucleus is often the most prominent structure
  within a eukaryotic cell
• The nucleus is the control center of the cell.
• The nucleus is surrounded by a double layer
  membrane called the nuclear envelope (has nuclear
  pores)

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• The nucleus contains DNA, the hereditary material
  of the cell.
• The DNA is in the form of a long strand called
  chromatin (cell not dividing)
• During cell division, chromatin strands coil and
  condense into thick structures called chromosomes

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9. Nucleolus

• Most nuclei contain at least one nucleolus
  (plural nucleoli)
• The nucleolus produces (synthesizes) ribosomes.

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10. Cytoskeleton

• In animal cells, an internal framework called the
  cytoskeleton maintains the three-dimensional
  shape of the cell, participates in the movement
  of organelles within the cytosol, and helps the
  cell move.
• Composed of microfilaments and microtubules.

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Microfilaments

• Microfilaments are NOT HOLLOW and have a
  structure that resembles ROPE
• Microfilaments can CONTRACT, causing movement.

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Microtubules

• Microtubules are HOLLOW TUBES like plumbing
  pipes. They are the largest strands of the
  cytoskeleton

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Microtubules have three functions

• A. Maintain shape of cell and hold organelles in
  place.
• B. To serve as tracks for organelles and
  molecules to move along within the cell.
• C. When the cell is about to divide, two short
  cylinders of microtubules at right angles known
  as centrioles create bundles of microtubules
  known as SPINDLE FIBERS.

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11. Cilia

• Short, hair-like projections.
• Often numerous

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12. Flagella

• Long, whiplike projections
• Often singular, but not always

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Cilia Flagella

• Unicellular organisms such as
• Paramecium and Euglena use Cilia
• and Flagella to move through water.
• Sperm use flagella to swim to the egg.
• In Humans, beating Cilia line parts of the
  respiratory system, moving dust particles and
  bacteria away from the lungs.

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Types of Cells

• Prokaryotic
• Have NO membrane bound nucleus
• Have FEW membrane bound organelles
• All bacteria are prokaryotic

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• Eukaryotic
• Have a membrane bound nucleus
• Have many organelles
• All protists, fungi, plants and animal cells

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Plant Cells vs. Animal Cells

• Plant Cells
• Have a cell wall made of cellulose
• Typically have one central vacuole (food water
  storage)
• Contain plastids
• Chloroplasts sites of photosynthesis
• Contains chlorophyll (green)
• Typically square-like in shape

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• Animal Cells
• No cell wall
• Many small vacuoles (food storage)
• No chloroplasts
• Typically round

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Inside a Plant Cell
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