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OVERVIEW OF THE CELLULAR BASIS OF LIFE

THE CELL THEORY

CELL TYPES
There are three classes of functional biological units: virus, prokaryotic cells and eukaryotic cells.

CELL COMPARTMENTS

.
PLASMA MEMBRANE

FUNCTIONS OF THE PLASMA MEMBRANE
1.Transport: A protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Some transport proteins hydrolyze ATP as an energy source to actively pump substances across the membrane. The hydrophilic substances avoid contact with the lipid bilayer by passing through transport proteins.
            a.  Each transport protein is specific for the substances it moves.
            b. For example: glucose carried in blood to the human liver enters liver cells rapidly through specific transport proteins in the plasma membrane.
2. Enzymatic Activity: A protein built into the membrane may be an enzyme with its active site exposed to substance in the adjacent solution. In some case, several enzymes in a membrane are ordered as a team that carries out sequential steps of a metabolic pathway.
3. Signal Transduction: A membrane protein may have a binding site with a specific shape that fits the shape of a chemical messenger such as a hormone. The external messenger (signal) may cause a conformational change in the protein that relays the message to the inside of the cell.
4. Linkers: (attachment to the cytoskeleton and extracellular matrix (ECM)). Microfilaments or other elements of the cytoskeleton may be bonded to membrane protein, a function that helps maintain cell shape and fixes the location of certain membrane proteins. Proteins that adhere to the ECM can coordinate extracellular and intracellular changes.
5. Intercellular joining: Membrane proteins of adjacent cells may be hooked together in various kinds of junctions
6. Cell-cell recognition; some glycoprotein (proteins with short chains of sugars) serve as identification tags that are specifically recognized by other cells.

 

PERMEABILITY OF THE MEMBRANE

1. A steady traffic of small molecules and ions move across the plasma membrane in both directions.

            2. The hydrophobic core of the membrane impedes the transport of ions and polar molecules, which are hydrophilic

            3. The selective permeability of a membrane depends on both the discriminating barrier of the lipid bilayer and the specific transport protein built into the membrane.

MODES OF MEMBRANE TRAFFIC

1. A result of thermal motion (intrinsic kinetic energy) is diffusion. Diffusion: The tendency for molecules of any substance to spread out into the available space.

2. The diffusion of a substance across a biological membrane is called passive transport, because the cell does not have to expand energy to make it happen
3. Osmosis: Diffusion of water across a selectively permeable membrane.
a. It’s a special case of passive transport.
                        b. Osmoregulation: the control of water balance
A variety of molecules can be dissolved in water, therefore water is an important molecule for all living organism. It is considered to be the universal solvent.
Solvent: the substance that does not dissolve in a solution
Solute; the substance that dissolves in a solution
Hypertonic: The solution with higher concentration of solutes
                        Hyper = more (solute concentration)
Hypotonic: The solution with lower concentration of solutes
                        Hypo = less (solute concentration)
Isotonic: Solution of equal solute concentration
                        Iso = same
(These are relative terms that are meaningful only in comparative sense)
Examples:
            Tap water is hypertonic to distilled water. However, tap water is hypotonic to seawater.
How living things react to changes in the solute concentration of their environments depends on whether or not they have cell walls.

 

Hypertonic Solution

Isotonic Solution

Hypotonic Solution

 

 

 

 

Animal Cell

 

 

 

Shriveled

 

The cell will loose water to its environment, shrivel, and probably die. This is one reason why an increase in the salinity of lakes can kill the animals there.

Normal

 

Unless it has special adaptations to offset the osmotic uptake or loss of water, an animal cell fares best in an isotonic environment.  No net movement of water across the cell membrane. Water flows in and out of the cell at the same rate. Volume is stable.

Lysed

 

Water will enter the cell faster than it leaves and it will swell and lyse (burst) like an overfilled water balloon.

 

 

 

 

 

Plant Cell

 

 

Plasmolyzed

 

Plant cell, like an animal cell, will loose water to its surrounding and shrink. As the plant cell shrivels, its plasma membrane pulls away from the wall. Usually lethal.

Flaccid

 

If a plant cells and their surrounding are isotonic, there is no tendency for water to enter and the cell becomes flaccid (limp) causing the plant to wilt

Turgid (normal)

Plant cells are turgid (firm) and generally healthiest in a hypotonic environment, where the tendency for continued uptake of water is balanced by the elastic wall pushing back on the cell.

5.  Facilitated diffusion: The spontaneous passage of typically polar molecules and ions, bound to specific carrier proteins, across a biological membrane down its concentration gradients. Facilitated diffusion is a passive transport process.

6.  Active transport: The pumping of solutes against the concentration gradient.

7.  Exocytosis and endocytosis: The transport of large molecules involving vesicles.

COMPONENTS OF CELLS

 

NUCLEUS

  1. The nucleus transmits and expresses genetic information.
  2. Most cells have a single nucleus and without a nucleus the cell could not divide or produce proteins.
  3. The nucleus is surrounded by the nuclear envelop that fairly large nuclear pores.
  4. Chromatin, which is composed of DNA and protein, are housed in the nucleus.  As a cell divides the chromatin condenses into chromosomes.
  5. The parts of the nucleus are the nuclear envelope, nucleoli, and chromatin.

 

CYTOPLASM

  1. The region between the nuclear envelope and the plasma membrane consist of fluid known as the cytosol and cytoplasmic organelles.
  2. The cytoplasm is the major functional area of the cell. These cytoplasmic organelles are:

CYTOPLASMIC ORGANELLES:

ORGANELLE: A SMALL STRUCTURE WITHIN A CELL THAT PERFORMES A SPECIALIZED FUNCTION.

  1. ENCLOSED BY A MEMBRANE.

ANIMAL CELLS

RIBOSOMES:

ENDOPLASMIC RETICULUM:
The ER membrane is a continuation of the outer nuclear membrane and its function is to make macromolecules.
           
TWO TYPES OF ENDOPLASMIC RETICULUM:
            ROUGH ER: CONTAINS RIBOSOMES
            SMOOTH ER: DOES NOT CONTAIN RIBOSOMES. RESPONSIBLE FOR MAKING LIPIDS.

GOLGI APPARATUS:

Lysosomes:

 

Peroxisomes:

Vacuoles:

Secretory Vesicles:

Mitochondria:

Mitochondria contains its own DNA.
Able to reproduce and make more mitochondria.

Centrioles

Centrosomes:

Cytoskeleton:

 

 

 

 

PLANT CELL

Organelles that are found in plant cells, but ARE NOT found in animal cells are:

Organelles that plant and animal cells share in common are:

Cell Wall

Vacuole

Chloroplast:

Centrosomes:

 

Bacterial Cell

Nucleoid:

Ribosomes:

Capsule:

Cell Wall

Plasma Membrane

Bacteria may have the following extentions:

Pili

Flagella