Cell Biology

• The core promoter is just ‘upstream’ of the transcriptional start site and is where RNA pol II binds prior to initiatingtranscription.• RNA pol II requires the help of general transcription factors (GTFs) to recognize the part of the promoter and form a pre-initiation complex (PIC)• A critical portion of the eukaryotic promoter lies 24-32 bases upstream from the initiation site, and contains the TATA box.8Core promoter
• Cells are the smallest unit of life, defined as a self-contained membrane-bound unit which carries out the functions of life, is organized, autonomous, and internally regulated.
• Living cells have all inherited their genetic instructions from this same ancestral cell.
• Genome sequence comparisons produce a family tree of life that contains three major divisions: the living world was classified on the basis of outward appearances.
• Anton van Leeuwenhoek was the first to describe living cells in pond water and also the first to describe bacteria (prokaryote) cells.
• Organisms that have inherited their genetic instructions from a common ancestor share the same DNA sequence.
• Theodor Schwann observed that animal life is made of cells too! and proposed the first two tenets of Cell Theory.
• The bacterium Escherichia coli lacks a defined nucleus, lacks membrane enclosed organelles, and its genome is 4.6 million base pairs in size.
• Robert Hooke first observed chambers in cork, which he called ‘cells’ because they reminded him of the cells monks lived in.
• Proteins provide the catalytic activity needed to synthesize DNA, RNA, and themselves.
• The discovery of cells was facilitated by the development of microscopes.
• These feedback loops create the self-replicating system that endows living cells with their ability to reproduce.
• Prokaryotes, which include both bacteria and archaea, are single-celled organisms that are 1-10 μm in size, their DNA lies free in the cytoplasm, and it is not associated with DNA-condensing proteins.
• Black arrows represent the biochemical processes by which new DNA, RNA, and proteins are manufactured in cells.
• Matthias Schleiden observed that all plant tissues he looked at were made of cells, and that plant embryos come from one single cell.
• Rudolf Virchow observed a lot of cells, and most importantly cells dividing, and proposed the third tenet of Cell Theory.
• All living cells appear to have evolved from a common ancestral cell.
• Mitochondria generate usable energy from food molecules, chloroplasts capture energy from sunlight, internal membranes create intracellular compartments with different functions, and the ER is a major site of protein synthesis and transport.
• Some antibiotics target features that are unique to bacterial cells and absent from our own cells.
• Although many archaea resemble bacteria in their outward appearance, DNA sequencing reveals that the genomes of archaea are much more closely related to those of eukaryotes.
• The nucleus is the information store of the cell, enclosed within two concentric membranes that form the nuclear envelope.
• Genome sequencing has revealed that archaea and bacteria, which are both prokaryotes, differ as much from each other as either does from the eukaryotes.
• The Golgi apparatus transports, sorts, and modifies both proteins and lipids, and the cytosol is a concentrated aqueous gel of large and small molecules.
• Eukaryotic cells divide by mitosis/meiosis, prokaryotes divide by binary fission, eukaryotic cells have more complex cytoskeletons and motility machinery than prokaryotes, and the ER is a major site of protein synthesis and transport.
• Eukaryotic cells have a membrane-bound nucleus, more DNA than prokaryotes, are typically 10-100 um in diameter, and have organelles such as mitochondria, endoplasmic reticulum, Golgi, etc.
• Prokaryotes, eukaryotes, and archaea are different cell types that are distinct from each other.
• Phormidium laminosum is a prokaryote with intracellular membranes where photosynthesis occurs.
• Bacteria are the most diverse collection of organisms on earth, with some being aerobic, some strictly anaerobic, and some that can live entirely on inorganic substances.
• Coli has an outer membrane and an inner membrane and a thin cell wall in between.
• The nucleoid (nucleus like) of Coli contains DNA but is not enclosed in a membrane.
• Archaea are identified only by DNA sequencing of environmental samples, lack a nucleus and membrane-enclosed organelles, and can live on skin, in soil, or in seawater, but also thrive in environments that are too hostile for most other cells.
• Anabaena cylindrica forms long, multicellular chains and specialized cells can fix nitrogen, fix CO2, and form resistant spores.
• The preinitiation complex assembly starts with the binding of the TATA-binding protein (TBP) to the promoter.
• TBP is a subunit of the TFIID and when it binds to the promoter causes a conformation change in DNA.
• Binding of TFIID sets the stage for the assembly of the complete PIC.
• The three GTFs bound to the promoter allows the binding of RNA polymerase II with its TFIIF.
• The spacing of the TATA box and the other GTS means that RNApol II is positioned right at the transcriptional start site.
• As long as TFIID remains bound to the promoter, additional RNA polymerases may be able to attach for additional rounds of transcription.
• Multiple mRNAs can be made from a gene at once.
• From each of these mRNAs, multiple proteins can be translated.