CELL PHYSIOLOGY

Ribosomes and Protein synthesis:


Role of DNA - In nucleus - carries genetic code for all characteristics of cells.

Role of RNA

Transcription

During replication mRNA is formed inside the nucleus and

migrates to the ribosomes

Translation

At the ribosomes mRNA attaches itself in such a way that the

genetic code is copied, forming tRNA, which serves as a

template to ‘summon’ amino acids.

[Remember the base triplets - each a codon copied by mRNA codes for an amino acid. The triplet on tRNA is termed an anticodon]

Assembly of amino acids

rRNA is also formed inside the nucleus, aggregate with proteins and migrate to the cytoplasm. A small and a large functional unit is formed and at the place where these portions join, mRNA slots in to pass the code to tRNA which ‘summons’ the amino acids in correct sequence. AA’s are linked together in the large rRNA unit as tRNA exits.

tRNA units that have ‘completed’ their function are released and are ‘recycled’. This completes the primary structure.

Shaping of functional protein

As the chain of aa’s is released, bonds begin to form at strategic points. Some proteins consist of more than one chain, thus it is an interplay of intra - and intermolecular forces/bonds that shapes the secondary and tertiary structures of a protein.

Further processing

Any protein with a structure beyond tertiary, will migrate to the Golgi complex where, in the medial cisternae, the protein is modified by conjugation with a prosthetic group.



Further processing

Any protein with a structure beyond tertiary, will migrate to the Golgi complex where, in the medial cisternae, the protein is modified by conjugation with a prosthetic group.


Endocytosis:

endocytosisParticle.jpgendocytosisMolecule.jpg




Exocytosis:

exocytosis.jpg




Phagocytosis:

phagocytosis.jpg



Pinocytosis:

pinocytosis.jpg



Facilitated diffusion:
  • Allows diffusion of large, membrane insoluble compounds such as sugars and amino acids
  • Does not require energy (passive)
  • Highly Selective
  • Substance binds to membrane-spanning transport protein
  • Binding alters protein conformation, exposing the other surface
  • Fully reversible - molecules may enter the cell and leave the cell through the transport protein.
  • Particles move from areas of high concentration to areas of low concentration.
  • Movement rate of particles will saturate
    • Maximum rate limited by number of transporters
    • Once all transporters are operating at 100%, an increase in concentration will not increase rate




Entry of Lipid soluble substances:: Enlarged lipid layer - easy for fat soluble substances to enter cells.


Liposomes:
Liposome.jpg


[from Wikipedia]
A liposome is an artificially-prepared vesicle primarily composed of a lipid bilayer. The liposome is a vehicle for administration of nutrients and pharmaceutical drugs. Liposomes can be prepared by disrupting biological membranes.

Liposomes are composed of natural phospholipids, and may also contain mixed lipid chains with surfactant properties (e.g., egg phosphatidylethanolamine). A liposome design may employ surface ligands for attaching to unhealthy tissue.

The major types of liposomes are the multilamellar vesicle (MLV), the small unilamellar vesicle (SUV), and the large unilamellar vesicle (LUV).

Liposomes should not be confused with micelles and reverse micelles composed of monolayers. [From Wikipedia


Entry of Lipid soluble substances: Enlarged lipid layer - easy for fat soluble substances to

enter cells.