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P & A Notes Chap. 3

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P & A Notes Chapter 3

February 07, 2011

The Cell 

The Cell...
-Unit of structure and function of your body.
-Vary in shape and size to fit their function.
Ex.- cells of the mouth are flat and tightly packed.
(protect underlying cells)
- cells of trachea- columnar with cilia to sweep out
unwanted particles.
- Cuboidal cells of kidney tubials.
- Slender rod-like muscle cells.

Cell: two major parts-
- Cell nucleus, which is enclosed by a nuclear membrane.
- Cytoplasm, fluid that surrounds the nucleus. It is enclosed by the plasma or cell membrane.

Plasma membrane-
-the outer most boundary of the cell
-is made up of lipids and protein
-has pores allowing some material to pass through and excluding others (selectively permeable). Water and small molecules can fit through the pores.
Molecules soluble in lipids can just dissolve through the membrane. (it contains lipids)
Nucleus- largest structure in the cell.
The nuclear membrane is continuous with the plasma membrane
-this membrane is also semi permeable.
-it is filled with fluid called neucloplasm
-has a nucleolus- composed of RNA and protein.

Functions-
1.) Ribosomes form in the nucleolus. They then
migrate through nuclear wall and enter the
cytoplasm.
2.) Chromatin also present in the nucleus contain
protein and DNA.
Chromatin condenses into chromosomes when
the cell is dividing.
DNA is the genetic or hereditary material.
Transmission of its genetic information during
division is a function of the cell.
DNA also controls metabolism of the cell. All
the chemical reactions in a cell are regulated by
enzymes produced in the nucleus.
3.) The nucleus synthesizes ribosomal RNA
Cytoplasm- everything between the nuclear membrane & the cell membrane.
-Under a light microscope it appears as a clear liquid.
-Under the electron microscope you could see many organelles.
-Where food is received, processed and used.
-It is the site of metabolic reactions and each organelle plays a role.

Organelles:
1.)Endoplasmic reticulum: is a network of canals that is
connected to both the nuclear and cell membranes
-functions in transport of molecules to other parts of
the cell. (intercellular transportation)
-also functions in synthesis of lipid molecules.
-it often contains ribosomes that attach to its outside
wall. Its then called rough E.R.
2.)Ribosomes: are attached to E.R. and free in the
cytoplasm.
-they contain protein and RNA molecules. Function in
the synthesis of protein molecules.
3.)Golgi apparatus: is located close to the nucleus. Its
membrane is continuous with E.R.
-it packages secretions which are moved to the
outside
-Is thought to manufacture lysosomal membranes.
-possible production of large carbohydrates that
combine with proteins to form glycoproteins.
4.) Lysosomes: (suicide sac) Contain digestive
enzymes that function in intracellular digestion. When
WBC’s engulf bacteria it is the lysosome that digests
it.
-when the cell dies the lysosome enzymes digest the
rest of the cell.
5.) Mitochondria: “Power house of the cell”
-play major role in cellular respiration
-inner membrane contains many folds called cristae.
On these cristae are enzymes that control the
chemical reactions by which energy is released from
glucose and other molecules. This energy is
converted to ATP before it is used by the cell.
6.) Centrosomes: Located close to the nucleus. They
contain microtubules which operate as a spindal in
mitosis.
7.) Vacuoles: Is actually a portion of the cell membrane
which has pinched itself off. As a result some of the
liquid that was on the outside is now on the inside.
8.) Microtubules: hollow rods, contain a substance called
tubulin.
- found in cilia... and in flagella
- Also found in the cytoplasm and seem to function in
support.

*Cells must be able to get food in and get wastes out.
Diffusion- movement of ions or molecules from an area of high concentration to an area of low concentration. It will do this until equilibrium is reached.

Passive diffusion- diffusion of substances through a membrane until equilibrium is reached on both sides.
-Oxygen molecules enter the cell. It is more concentrated on the outside.
-CO2 leaves the cell (O2 and CO2 are soluble in lipids)

Facilitated transport-
Substances not coluble in lipids like glucose, must be carried by a special carrier molecule.
In facilitated transport the carrier brings molecules across the membrane until equilibrium is met.
High--> low. Once equilibrium is met molecules will go both ways.

Active transport
Moves material against the concentration gradient. (From an area of low to an area of high concentration)
-Once again you ave a carrier molecule. Active transport requires energy to move substances against this gradient.
-the carrier is a protein molecule found within the cells membrane.... the molecule combines with the carrier at the cells surface. They move across the membrane, the molecule is released and the carrier returns for another load.

Osmosis- special type of diffusion where water molecules diffuse from a region of high concentration to a region of low concentration to a region of low through a selectively permeable membrane.
-the more dissolved material there is in the H2O the higher the osmotic pressure.
*H2O goes from low O.P. to high O.P.

Types of solutions

Hypertonic Solution- the solution has more dissolved material than the cell.
-the cell will lose H20 and shrink
-the O.P. is higher outside the cell

Hypotonic Solution- the solution has less dissolved material than the cell.,
-the cell will gain H2O and swell.
-the O.P. is lower outside the cell

Isotonic Solution-
-O.P. is the same outside and inside the cell.
-H2O goes in and out at same rate

Filtration- body tissue fluid is formed when H20 and dissolved material are forced out through the thin walls of the capillaries, while the larger particles are filtered back.

Pinocytosis- cell drinking
Phagocytosis- cell eating

Cell division;
Meiosis- the production of the gametes. (reproduction) will cover in later chapter
Mitosis- allows for growth and repair.
-is a continuous life process.
-produces regular body cells.
-mitosis involves only the division of the nuclear parts and consists of 5 steps
1.) Interphase- period between divisions. This is when
the DNS (chromosomes) are duplicated. In man each
cell contains 23 pair of chromosomes.
2.)Prophase- chromatin condense into chromosomes
-centrioles migrate to opposite poles, they form
asters, and then the spindal.
-at the end the nucleolus breaks down and so does
the nuclear membrane.
3.) Metaphase- the chromosomes line up on the
equatorial plate.
-microtubials attach to the sister chromatids at there
centromere.
4.) Anaphase- the sister chromatids split and migrate to
different poles.
-46 chromosomes go to both poles
5.) Telophase- (reverse of prophase)
-nuclear membrane reforms
-chromosomes unwind to form chromatin
-spindal disappears
-cell membrane begins pinching in. (Cytokinesis)

Cytokinesis- division of cytoplasm.
-begins during telophase
-cell membrane pinches in between the two daughter nuclei
-each new cell gets about 1/2 of the organelles
-each daughter cell has the same number and kind of chromosomes as the mother cell did.

Cellular differentiation
Meiosis --> sperm and egg --> fertilization
zygote --> division by mitosis --> (Cellular differentiation) RBC, nerve cells, muscle, bone....

 

 

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