CELLS AND CELL RESEARCH Prokaryotes Eukaryotes genetic material not membrane-enclosed genetic material in nucleus (enclosed) DNA not associated with histone proteins DNA packed , tightly folded around h .p.s. 0.6x10' to 5x106 DNA base pairs 1.5 ×10+ to 5×109 DNA base pairs no other membrane-bound organelles E.R., Golgi, lysosomes etc. typical cell diameter = 1 um (micrometer) typical cell diameter ~ 10-100um asexual reproduction - binary fission mitosis / meiosis, sexual / asexual Lecture 1 . macromolecules can form from simple monomer units spontaneously under prebiotic conditions. (polymerise) . the same molecular mechanisms are found in prokaryotes & eukaryotes 1 processes of DNA replication , transcription of DNA into intermediate molecule RNA , & protein production Genes: functional units of inheritance - segments of DNA that encode RNA / proteins Transcription: process by which nucleotide gene sequence is copied into RNA > intermediate molecule Translation: nucleotide sequence of RNA is used to specify the order of amino acids in protein Self- replication of RNA : > RNA can both serve as its own template and catalyse its own replication - independent > theory : enclosure of self - replicating RNA in a phospholipid membrane gave rise to the first cell Archaea found in ocean & extreme environments ( thermophiles , halophiles, acidophiles etc ) cell walls lack peptidoglycan Prokaryotic cells 4 spherical rod - shaped spiral Bacteria wide range of environments ( soil , water , other Organisms ) cell walls usually present and contain peptidoglycan Cyanobacteria : largest / most complex prokaryotes - bacteria in which photosynthesis evolved
Escherichia coli (E. coli) . most commonly studied prokaryotic cells . rod- shaped (bacillus) · rigid cell wall : polysaccharide & peptides, maintains shape & provides some protection against environmental stress, porous- allows for transport · plasma membrane: phospholipid bilayer & associated proteins · DNA: 1 circular chromosome in nucleoid (not membrane-enclosed) . Ribosomes: sites of protein synthesis, ~30,000 in cytoplasm Eukaryotic cells rigidity & structure > more complex than prokaryotic : nucleus, cytoplasmic organelles, & cytoskeleton > nucleus : largest organelle, contains linear DNA, site of DNA replication & RNA synthesis > mitochondria: sites of oxidative phosphorylation, generate ATP > Chloroplasts: sites of photosynthesis, only found in plants & some algae transcription > lysosomes & peroxisomes (in animal cells) : provide specialised metabolic compartments for digestion of macromolecules (1), various oxidative reactions (p) > vacuoles ( in plant cells) digestion of macromolecules, storage of waste products & nutrients > endoplasmic reticulum (ER): membrane network extending from nuclear envelope, protein processing & transport, lipid synthesis > golgi apparatus: recieves proteins from ER, protein processing & sorting, lipid synthesis in plants , cell wall polysaccharide synthesis > cytoskeleton: network of protein filaments extending throughout cytoplasm provides structural framework determines cell shape & organisation involved in movement of whole cells , organelles , & chromosomes during cell division Endosymbiotic Theory L> Eukaryotic cells may have arisen from a fusion of genomes from bacteria . archaea mitochondria & chloroplasts : similar in size to