S1L5 - Notes PDF

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Genetics is a powerful tool to reveal cellular mechanisms  Yeast genes that control cell division are evolutionarily conserved  When a mechanism is discovered in yeast, it will likely apply to human cells Comparison of the three domains of life (bacteria, archaea, eukarya)  Nuclear envelope: only present in eukarya  Membrane enclosed organelles: absent (few) in bacteria and archaea, present in eukarya  Peptidoglycan in cell wall: present in bacteria  Membrane lipids: bacteria and eukarya have unbranched hydrocarbons, archaea has some branched  RNA polymerase: one kind in bacteria, several in archaea and eukarya  Initiator amino acid for protein synthesis: Formylmethionine for bacteria, methionine for archaea and eukarya Types of Bacteria  Gram positive bacteria o Thick cell wall made of peptidoglycan o Often have flagella (true for gram-negative) o Cytoplasm rich in ribosomes  Gram negative bacteria o Two membranes: outer with polysaccharide coat, space in between consisting of peptidoglycan layer, inner membrane o Outer layer is bilayer, has pores that allow molecules to penetrate through Archael species Halobacterium harvest light to generate ATP Cell structure and Function Membrane bilayer with proteins spanning from cytoplasm to cell surface  Interior of bilayer is very hydrophobic Membrane compartments separate unique functions in cells  Major functions such as RNA synthesis, respiration in mitochondira, and protein degradation in lysosome physically segregated from cytoplasm  Single or double bilayer membranes capture and enclose specific sets of proteins that define an organelle’s functions  Each organelle membrane boundary has specialized proteins that govern the selective uptake or export of proteins or nucleic acids  Some compartments form a boundary by phase separation not involving a membrane boundary Nuclear pores mediate traffic of proteins and RNA into and out of nucleus

Nuclear pores are size and protein/particle selective  Size of molecules determines whether they enter by free diffusion or active transport Endoplasmic Reticulum  A vast network within the cell that organizes lipid, secretory and cell surface membrane protein synthesis Ribosomes tethered on the cytoplasmic surface of the ER synthesize proteins for secretion and membrane insertion Secretory proteins are synthesized with a signal that directs the ribosome to a channel in the ER membrane Secretory and membrane proteins transit in vesicles from the ER through the golgi apparatus into granules that fuse at the cell surface...