1 Cells & Organelles

4 phases of cells

* abiotic (nonliving) synthesis of simple organic compounds (i.e., amino acids and nitrogenous bases)


* abiotic polymerization of these monomers into macromolecules (i.e., proteins or nucleic acids)


* emergence of a macromolecule capable of both storing genetic information and replication


* encapsulation of this first “living” molecule within a simple membrane to form the first primitive cell

RNA

* Required energy to synthesize the simplest organic molecules (e.g., amino acids, nucleic acid bases, and monosaccharides).
* RNA – key component of abiotic systems prior to DNA
* Deoxyribonucleotide monomers are the building blocks of DNA are derived enzymatically from corresponding ribonucleotides ó monomer subunits of RNA are precursors of DNA monomer subunits.
* RNA generated and replicated in the absence of enzymes: ribonucleotides, the building blocks of RNA polymers, can form abiotically and that in some cases RNA polymers can form (not nearly as efficient as in cells).
* Replication of RNA: some RNAs can fold into shapes that resemble protein enzymes, allowing them to catalyze chemical reactions = catalytic RNAs became – ribozymes.
* Ribozymes – catalyze an array of different reactions, (i.e., synthesis of short pieces of RNA by complementary base pairing when supplied with nucleotide building blocks)
* In the ribosome, the site of protein synthesis in all known organisms, it is the ribosomal RNA, not ribosomal proteins, that catalyzes peptide bond formation between amino acids to produce proteins.

Liposomes

* Hollow membrane-bound vesicles of varying sizes that form spontaneously when lipids are mixed with water
* Abiotically produced vesicles can “reproduce” by splitting on their own.
* They can increase in size under appropriate conditions.
* Primordial lipids may have similarly formed in aqueous environments in the early Earth, trapping nearby RNAs and in the process forming the first “protocells.”

Limitation of cell size

* requirement for an adequate surface area/volume ratio
* rates at which molecules diffuse
* need to maintain adequate local concentrations of the specific substances and enzymes involved in important cellular processes

Rough ER

studded with ribosomes on the side of the membrane that faces the cytosol

Rough ER

synthesize polypeptides → either accumulate within the membrane OR transported to ER lumen