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The CellThe Cell

“building block of life”

The Cell1. 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.

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;

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.

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.

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

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.

the structure of a cell membrane

It is mainly composed ofa lipid bilayer of phospholipidmolecules but with a large numbersof protein molecules protrudingthe 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.

the chemical composition of a cell membrane

PROTEINS (55%)a.Integral Proteinsb.Peripheral Proteins

CARBOHYDRATES (3%)a.Proteoglycansb.Glycocaylx

PHOSPOLIPIDS (25%)-consist of phosphate heads (hydrophilic) and two

fatty acid tails (hydrophobic) CHOLESTEROL (13%) Other LIPIDS (4%) Glycolipids

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 bidirectionally2. 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

1. PASSIVE TRANSPORT (diffusion)

a. Simple diffusion b. Facilitated diffusion

2. ACTIVE TRANSPORT

Cross membrane transport of small molecules

Cross membrane transport of large molecules1. ENDOCYTOSIS

a. Pinocytosis b. Phagocytosis

2. EXOCYTOSIS

the various ways by which substances pass across the cell membrane

-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)

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

Common features of Facilitated diffusion & Active transport

1. Both involve carrier protein2. Specify for ions, sugars & amino acids3. 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 unidirectional2. 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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