The Cellular Level of Organization

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The Cellular Level of Organization
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• Antonie van Leewenhoek - first person to see
  cells.
• Robert Hooke coined the term cell and
  illustrated what he saw.

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Cell Theory

1. All organisms are composed of one or more cells
2. Cells are alive, and are the basic living unit of
   organization of all organisms
3. All cells come from other cells

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• Every cell has three main parts
• Plasma (cell) membrane a boundary that
  separates inside of cell from external
  environment.
• A set of genetic instructions In eukaryotes
  this is in the Nucleus in prokaryotes there is
  no membrane, stays in a section of the cell is
  called the nucleoid.
• A cell body - the cytoplasm

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• Cytosol gel like substance not contained in
  organelles
• Cells are measured in micrometers or microns.
• Eukaryotic cells are bigger than prokaryotic
  cells.

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Advantages of being made of cells

• Specialization
• Surface area
• Obtaining nutrients
• Separating chemical processes
• A multicellular organism can survive the loss of
  single cells.

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Cytoplasm refers to cytosol plus organelles and
inclusions. cytosol - contains proteins,
enzymes, nutrients, ions, and other small
molecules organelles -little organs - highly
organized structures with characteristic shapes
that are specialized for specific cellular
activities. inclusions - are temporary
structures in the cytoplasm that contain
secretions and storage products of the cell.
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Nucleus

• Double membrane called the nuclear envelope
• Nucleoplasm
• Chromatin granules unwound DNA
• Nucleoli puts RNA and protein together to make
  ribosomes
• Nucleus is essential for cell survival

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Ribosomes made of ribosomal RNA and protein,
these are the work benches where proteins are
put together. Made up of two subunits that come
together when needed. Found free in cells Also in
association with endoplasmic reticulum
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Endoplasmic reticulum (ER)
Can be rough or smooth Smooth ER is the site of
fatty acid, phospholipid and steroid synthesis.
In certain cells also detoxifies chemicals, such
as alcohol and pesticides.
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• Rough ER has ribosomes, makes proteins for export
  outside the cell.
• May add sugars to proteins and make
  glycoproteins.

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Gogli complex (apparatus, body)
Made of flattened sacs Process, sort and deliver
proteins and lipids to the plasma membrane and
forms vesicles and lysosomes. The carbohydrates
of the glycoproteins may be modified to act as
shipping labels The UPS of the cell
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Lysosomes
The cells stomach vesicles that contain
digestive enzymes. Fuses with vesicles
containing food or microorganisms. Can be
released outside the cell frustrated
phagocytosis
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Mitochondria
Mitochondrion singular Two membranes inner
membrane folded. Main function is the use of
oxygen to produce ATP cellular (aerobic)
respiration These are the power plants of the
cell. Believed to once be free living organisms
have unique DNA and RNA
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Plastids

• Found in plants and some protista
• Surrounded by a double membrane
• Function photosynthesis chloroplasts
• Contain chlorophyll
• Chromoplasts contain red, orange or yellow
  pigments
• Amyloplasts used to store starches

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Cytoskeleton

• Made of protein tubules
• Gives structure and support
• Also acts as muscle in moving the cell and
  transporting materials within it.
• Musculoskeletal system of the cell.

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Centrosomes and Centrioles
Centrioles are 2 cylinders of tubules arranged at
right angles. Form the microtubules of the
mitotic spindle during cell division, and also
make up a part of cilia and flagella
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Flagella
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Vesicles
Membrane sacs that transport substances within
the cell. Vesicle trafficking
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Vacuoles

• Larger than vesicles
• Found in plant cells
• Can be storage areas
• Can contain enzymes or waste products
• Central vacuole helps plants maintain turgor
  pressure

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Inclusions
Usually contain chemical substances produced by
the cell, these are temporary structures that are
not surrounded by a membrane. Melanin, glycogen,
triglycerides ribosomes
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Plasma Membrane
The plasma membrane does more than just separate
the outside of a cell from the inside it
controls what enters and leaves the cell, and
much of the activity within the cell. Most of the
cell membrane is made of a phospholipid bilayer.
Amphipathic molecule phosphate heads on the
outside and inside, and fatty acid tails in the
middle.
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The membrane is selectively permeable it allows
fat soluble substances to pass through (such as
steroid hormones) and some other small,
uncharged molecules. Cholesterol is a large
molecule, and helps to stabilize the membrane in
animals. Plants use phytosterol.
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Fluid mosaic model - proteins float like
icebergs in a sea of phospholipids. Proteins can
be integral proteins go all the way through the
membrane, or may be peripheral proteins -bound
to the inside or outside membrane.
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Integral Proteins can be channels or
transporters. Peripheral proteins can be
receptors, or can be cell identity markers or
recognition proteins that identify a cell as
self (like UPC codes). These are often
glycoproteins. They may also mark worn out red
blood cells or cells that have been infected with
a virus.
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• All cells have a plasma membrane
• Some cells, such as bacterial, fungal and plant
  cells, also have a cell wall.

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Cell Physiology

• Cell membrane function
• Are selectively permeable
• Lipids
• Size
• Electrical charge
• Presence of channels and transporters

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• Movement of molecules depends on
• 1. Kinetic energy
• Temperature
• 2. Concentration
• gradient more of something in one area than
  another

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Diffusion

• Passive process
• Depends on concentration and kinetic energy
• Does not require energy
• Moves substances from an area of high
  concentration to an area of low concentration
• Down a concentration gradient

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• The most concentrated form of water is
• pure water.
• To make water less concentrated, we dissolve
  substances in it.

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Tonicity

• Concentration of one solution relative to another
• Isotonic equal concentrations
• Hypertonic more concentrated
• Hypotonic less concentrated

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Tonicity relative concentrations of solutions

• Isotonic two solutions contain the same amount
  of substance dissolved in them- equal
  concentrations
• Hypertonic a solution containing a greater
  amount of dissolved substance- more concentrated
• Hypotonic a solution containing a lesser amount
  of dissolved substance less
  concentrated

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Osmosis

• The movement of water across a selectively
  permeable membrane, down a concentration
  gradient.
• Dialysis is the diffusion of a solute across a
  selectively permeable membrane.

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Cell in an isotonic solution
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Cell in a hypertonic solution
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Cell in a hypotonic solution
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Facilitated diffusion

• Passive process
• Substances can move through protein channels
• Substances may be shuttled across by carrier
  proteins
• Substances still move down a concentration
  gradient

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Filtration

• Movement of water and solutes across a membrane
  due to physical pressure
• Gravity
• Hydrostatic pressure (water pressure or blood
  pressure)

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Active Transport

• Depends on the use of energy (ATP)
• Moves substances up a concentration gradient (up
  hill)
• These permease proteins are often called pumps
• Na / K pump

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Vesicular Transport
Exocytosis moves substances outside the
cell Endocytosis takes substances into the
cell Phagocytosis cell eating
Pinocytosis cell drinking Receptor mediated
endocytosis
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Human Immunodeficiency Virus

• Originally developed in apes or monkeys
• Probably transmitted to man in central Africa
  before 1931
• First cases reported 1980s in male homosexuals
• Transmitted by sexual intercourse, sharing
  needles, blood products
• Incidence increasing most rapidly in
• heterosexual females