CELLS AND THEIR FUNCTIONS

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CHAPTER 3

• CELLS AND THEIR FUNCTIONS

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CHAPTER 3

• CELLS THE BASIC UNIT OF LIFE
• It is possible for a single cell to live
  independently of other cells. (ex. Protozoa and
  bacteria)
• Human cells must work together function
  interdependently
• There are 200 different kinds of human cells with
  200 different functions

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CELLS

• All the activities of the human body, which is
  composed of millions of cells, result from the
  activities of individual cells
• Cells produce all the materials manufactured
  within the body
• Most human cells can only be seen with a
  microscope. Exception is the human ovum which
  can be seen with the naked eye. It is about 1mm
  in diameter. Nerve cell is microscopic, but 2
  feet long.

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THE CELL
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STRUCTURE OF THE CELL

• Plasma membrane also called the cell membrane
  is the outer limit/wall of the cell
• Regulates what enters and leaves the cell
• Present in the cell wall are specialized
  proteins
• 1. pores or channels to permit passage of
  materials
• 2. enzymes that help substances enter the cell
  
• 3. antigens are markers that identify the
  cells of an individual as self
• 4. receptor sites for hormones
• It is selectively permeable it allows certain
  substances to pass into the cells, while others
  are not allowed

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STRUCTURE OF THE CELL

• NUCLEUSthe largest organelle that is often
  called the control center of the cell, contains
  46 chromosomes or the genetic material which
  governs all the activities of the cell, including
  protein manufacturing and cell reproduction. The
  nucleus is surrounded by the nuclear membrane.
  
• Within the nucleus is a smaller globule called
  the nucleolus, which means little nucleus, made
  up of DNA, RNA, protein.

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STRUCTURE OF THE CELL

• CYTOPLASMa watery substance that fills the cell
  and holds the cell contents.
• This is a suspension of nutrients, minerals,
  enzymes, and other specialized materials in
  water.
• ORGANELLES- (little organs)-different organs to
  carry out special functions or tasks that are
  present within the cytoplasm

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ORGANELLES

• RibosomesWhere protein is formed
• Endoplasmic reticulum (ER)synthesis of lipids
  a passageway for transport of materials within
  the cell.
• Mitochondriathreadlike structures within the
  cytoplasm that provide most of the bodys
  adenosine triphosphate (ATP)the enzyme that
  fuels many cellular activities. These are the
  power plants of the cell.

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STRUCTURE OF THE CELL

• Golgi apparatus, synthesis of carbohydrates
  packaging of materials for secretion from the
  cell.
• Lysosomes, contain digestive enzymes to digest
  materials that enter the cell or damaged tissue
• Centrioles, rod-shaped bodies near the nucleus
  that function in cell division.

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STRUCTURE OF THE CELL

• CILIA-small, hair-like projections which wave to
  create movement around the cell. (ex, cells that
  line the passageways of the respiratory and
  reproductive tracts.
• FLAGELLUM-long whip-like structure used for
  locomotion(ex. Sperm cell)
• MICROVILLI-increase a cells surface area for
  absorption

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Cellular Transport Mechanisms

• The processes by which cells move materials in
  and out of the cell.
• Not only do molecules pass in, waste products
  pass out of the cell in the opposite direction,
  enabling the cell to perform the function of
  elimination.

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DIFFUSION

• Movement of molecules from an area of greater
  concentration to an area of lesser concentration.
• In the body there is a high concentration of 02
  in the alveoli (air sacs of lung) a low
  concentration of 02 in the blood in the
  surrounding capillaries. Once the 02 gets into
  the blood it is circulated back to the heart
  then to the body
• See fig 3-3A

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OSMOSIS

• The diffusion of water through a selectively
  permeable membrane or barrier from an area where
  there is more water to an area where there is
  less water.
• Another way to say it is that water will
  naturally tend to move to an area where there is
  more dissolved material such as salt or sugar
• Fig 3-3B
• In the body the cells lining the small
  intestine absorb water from digested food by
  osmosis

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FACILITATED DIFFUSION

• When molecules move from an area of greater
  concentration to an area of lesser concentration
  with help.
• In the body in order for glucose to enter the
  cell to be used as energy it requires carrier
  enzymes or transporters which are part of the
  cell membrane
• Fig 3-3C

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ACTIVE TRANSPORT

• Movement of molecules from an area of lesser
  concentration to an area of greater concentration
  with help of ATP
• Opposite of diffusion!
• In the body absorption of amino acids
  glucose from food by the cells of the small
  intestine
• In the body sodium pump of the nerve muscle
  cells
• Fig 3-3D

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FILTRATION

• Passage of water containing dissolved materials
  through a membrane as a result of a mechanical
  (pushing) force on one side from an area of
  higher pressure to an area of lower pressure
• In the body the formation of urine in the
  kidney
• Another is the movement of materials out of the
  capillaries into the surrounding tissue spaces
  under the force of blood pressure
• Fig 3-3E

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Movement that does not require cellular energy

• Osmosis, diffusion, and filtration are described
  as PASSIVE because they do not require cellular
  energy or ATP.
• They depend on the natural energy of the
  molecules for movement.

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Movement that does require cellular energy

• ACTIVE TRANSPORT Molecules move into or out of
  a cell in a direction opposite to the way they
  would normally flow by diffusion they move
  from an area where they are in lower
  concentration to an area where they are in higher
  concentration.
• This movement, is against the natural flow,
  requires energy in the form of ATP like a fish
  swimming upstream
• FACILITATED DIFFUSION also requires help, but not
  of ATP. Uses carrier enzymes.

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Movement that does require cellular energy

• PHAGOCYTOSIS is the engulfing (or eating) of
  relatively large particles by a moving cell
• In the body white blood cells engulf bacteria
• Fig 3-3F
• PINOCYTOSIS a stationary cell engulfs something
  also known as cell drinking
• In the body cells of the kidney tubules
  reabsorb small proteins
• Fig 3-3G

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DNA

• Found in the chromosomes in the nucleus of the
  cell
• It is a double helix, like a spiral ladder with
  complementary base pairing A-T G-C
• The sequence of bases in the DNA is the genetic
  code for our proteins
• Each organism has its own genetic code that sets
  it apart from each other

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RNA

• Responsible for protein synthesis which takes
  place in the ribosomes in the cytoplasm
• Messenger RNA or mRNA is the intermediary between
  the DNA in the nucleus the ribosomes in the
  cytoplasm
• The transfer RNA or tRNA found in the cytoplasm
  picks up the amino acids from foods puts them
  into their proper place on the mRNA molecule

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Genetic Code

• DNA to RNA to Proteins hereditary
  characteristics
• A genetic disease is a mistake in the DNA, which
  is copied by the mRNA results in a
  malfunctioning protein

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CELL DIVISION

• Mitosis
• one cell with the diploid number or
  usual/normal number of chromosomes for that
  organism (46 in humans) divides once to form 2
  cells, each containing the same diploid number
• See figure 3-5 table 3-4 for cell division

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Mitosis in the Body

• Constantly Ongoing
• Epidermis of the skin
• Stomach lining
• Red blood cell production in the bone marrow

• Limited or No Mitosis
• Nerve cells of the spinal cord
• Cardiac muscle cells

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Meiosis/Reduction division

• Results in formation of gametes, which are egg
  and sperm cells
• One cell with the diploid number/ usual number of
  chromosomes divides twice to form four cells with
  the haploid number or half the usual number of
  chromosomes which is 23 for humans

• Females formation of egg cells called oogenesis
  
• Males Formation of sperm cells called
  spermatogenesis
• Fertilization of an egg by a sperm restores the
  diploid number of chromosomes