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2. The Cell
“building block of life”

3. The Cell
1. Describe the typical cell.
2. Describe the structure of a cell membrane/plasma membrane.
3. Give the chemical composition of a cell membrane.
4. Explain the various ways by which substances pass across
the cell membrane.

4. A typical cell
The cell is the structural and functional unit
of all living organisms,
and is sometimes called the "building block
of life;
Some organisms, such as bacteria, are
unicellular (consist of a single cell). Other
organisms, such as humans, are
multicellular. (Humans have an estimated
100 trillion or 1014 cells;

5. A typical cell
 cell size is 10 µm;
 cell mass is 1 nanogram
 two major parts.
† nucleus
† cytoplasm.
The nucleus is separated from the cytoplasm by the nuclear membrane.
The cytoplasm, on the other hand, is separated from the surrounding
fluids by the cell membrane.

6. A typical cell
2 types of cell:
Prokaryotes are not as structurally complex as eukaryotes,
and were thought not to have any compartments enclosed by
lipid membranes. In the past they were often viewed as having little
internal organization, but slowly details are emerging about prokaryotic
internal structures
Eukaryotes are the most structurally complex known cell type, and
by definition are in part organized by smaller interior compartments,
that are themselves enclosed by lipid membranes that resemble the
outermost cell membrane.

7. Organelles
-discrete structure of a cell having specialized functions.
-limited by a membrane
 Plasma membrane
 Ribosomes
 Rough ER
 Smooth ER
 Annulate Lamellae
 Mitochondria
 Golgi apparatus
 Coated Vesicles
 Lysosomes
 Peroxisomes
 Centrioles

8.  also called plasmalemma
 a thin, pliable, very elastic structure only 7.5 to 10 nm thick.
 semipermeable
 composed of a lipid bilayer & associated proteins
 Envelops the cell
aids in maintaining its structural & functional integrity
 Sensory device
recognize other cells & macromolecules
 Exhibits a trilaminar structure called The unit membrane
The structure of a cell membrane/plasma membrane.

9. the structure of a cell membrane
It is mainly composed of
a lipid bilayer of phospholipid
molecules but with a large numbers
of protein molecules protruding
the layer.
LIPID BILAYER is the basic structure of the cell membrane.
It is composed entirely of phaopholipids and cholesterol. Interspersed in
this lipid film are large globular protein molecules. Most of the membrane proteins are
glycoproteins.

10. the chemical composition of a cell membrane
 PROTEINS (55%)
a.Integral Proteins
b.Peripheral Proteins
 CARBOHYDRATES (3%)
a.Proteoglycans
b.Glycocaylx
 PHOSPOLIPIDS (25%)
-consist of phosphate heads (hydrophilic) and two fatty
acid tails (hydrophobic)
 CHOLESTEROL (13%)
 Other LIPIDS (4%)
 Glycolipids

11. TRANSPORT SYSTEM
[Described in a functional sense according to:]
 number of molecules moved
 direction of movement
 whether the movement is toward or away from the equilibrium
1. Uniport system
– moves the molecule bidirectionally
2. Contransport sysyem
- transfer of one solute depends upon the sequential
transfer of another solute that can either be:
a. Symport
b. Antiport
the various ways
by which substances pass across the cell membrane

12. 1. PASSIVE TRANSPORT (diffusion)
a. Simple diffusion b. Facilitated diffusion
2. ACTIVE TRANSPORT
Cross membrane transport of small molecules
Cross membrane transport of large molecules
1. ENDOCYTOSIS
a. Pinocytosis b. Phagocytosis
2. EXOCYTOSIS
the various ways
by which substances pass across the cell membrane

13. -random molecular movement of substance molecule by molecule, either through
intermolecular spaces in the membrane or in combination with a carrier protein.
a. Simple diffusion
 Factors:
 1. Concentration gradient across the membrane
 2. Electrical potential across the membrane
 3. Permeability coefficient of the substance
 4. Hydrostatic pressure gradient across the membrane
 5. Temperature
 6. Pressure of multitude of channels in membrane
 b. Facilitated diffusion
 Factors:
 1. Concentration gradient across the membrane
 2. Amount of carrier protein available
 3. Rapidity of the solute-carrier interaction
 4. rapidity of conformational charge for both loaded and unloaded carrier protein.
1. Passive transport (diffusion)

14. 2. Active transport
-molecules transported away from the thermodynamic equilibrium
Ex. Sodium-Potassium Pump
-the most important transport mechanism in the body which transport sodium out
of cells to the exterior and at the same time pumps potassium ions from the
outside to the inside. This is an example of Active Transport Process.
Functions:
1. Maintain constant cel volume by decreasing the intracellular ion
concentration and increasing the extracellular ion concentration, thus
decreasaing the flow of water into cell.
2. Maintenance of a potential difference across the plasma membrane

15. Common features of Facilitated diffusion & Active transport
1. Both involve carrier protein
2. Specify for ions, sugars & amino acids
3. Resemble substrate-enzyme reaction except that no covalent interactions occurs
>specific binding site for solute
>the carrier protein is saturable
>there is binding constant for the solute & the whole system has a binding constant
>structurally similar competitive inhibitor block transport
Differences:
1. Facilitated diffusion operates bidirectionally
Active transport is usually unidirectional
2. Active transport occurs against electrical on chemical gradient & so requires energy.
Facilitated diffusion occurs down the electrochemical gradients & doesn’t require
energy.

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