PLM

• Molecular components found inside a cell

  • Proteins
  • Carbohydrates
  • Lipids
  • Nucleic Acids
• Water


  Makes up 70% of the intracellular space
• Nucleus


  The most important organelle of a eukaryotic cell, houses DNA and is the site of transcription
• Nuclear envelope


  Separates DNA from protein translation machinery in the cytoplasm
• Mitochondria


  The 'powerhouses' of a cell, carry out oxidative phosphorylation to convert food to ATP
• Plasma membrane


  Semi-permeable, allows selective molecules to pass through
• Small, energy-rich molecules used to store energy

  • ATP
  • NADH
• Metabolic processes used to produce energy in a eukaryotic cell when oxygen is present

  • Glycolysis
  • Citric Acid Cycle
  • Oxidative Phosphorylation
• Enzymes


  Proteins that speed up biochemical reactions by decreasing the activation energy required
• Feedback inhibition


  Process where the metabolic product of one pathway blocks the formation of that specific metabolite at an earlier point in the pathway to prevent a buildup
• DNA structure


  Double helix formed by two strands, with complementary base pairing between nucleotides on the two strands
• During transcription, only one strand of DNA is transcribed into a single-stranded RNA molecule
• Messenger RNA (mRNA)


  The type of RNA molecule that is translated into a protein sequence
• Histones


  Proteins involved in the packaging and condensing of DNA into tightly wound nucleosome structures of a chromosome
• Euchromatin


  The less condensed region of chromatin that contains genes being actively transcribed
• RNA splicing


  The modification that occurs to produce a mature mRNA from a primary RNA transcript containing introns and exons
• Not all genes are expressed at the same time in all cell types
• tRNAs


  Carry individual amino acids, the building blocks of proteins, to match the codons on mRNA
• Secondary protein structure


  Proteins fold into alpha helices and beta sheets
• Cytoskeletal elements


  Provide structure, shape, and movement to cells
• Major classes of cytoskeletal elements in eukaryotic cells

  • Microtubules
  • Actin filaments
  • Intermediate filaments
• Mitochondria and chloroplasts are not part of the endomembrane system
• Protein transport from endoplasmic reticulum (ER)


  Proteins with signal sequence are carried in vesicles, which travel along microtubules to the Golgi apparatus and then to final destinations
• cis-Golgi and trans-Golgi


  The cis-Golgi is closest to the ER and receives vesicles from the ER, while the trans-Golgi sorts proteins and lipids into transport vesicles for final destinations
• Lysosomes


  Organelle containing high levels of hydrolases, responsible for digestion of macromolecules
• Mitochondria


  The 'power plant' or 'power house' of the cell, generate ATP through oxidative phosphorylation
• Mitochondria


  • Surrounded by two membranes, have their own genome
• Electron transport chain


  Creates a gradient of hydrogen (H+ ions or protons) across the inner mitochondrial membrane, which drives ATP synthase to generate ATP
• Most mitochondrial proteins are synthesized from nuclear genes, not the mitochondrial genome
• Classes of cell surface receptors

  • G-protein-coupled receptors (GPCRs)
  • Ion channel receptors
  • Enzyme-linked receptors (e.g. receptor tyrosine kinases - RTKs)
• Second messengers


  Small molecules that initiate and coordinate intracellular signaling pathways, triggered by receptor activation
• Common second messengers and enzymes responsible for their production

  • cAMP - synthesized from ATP by adenylate cyclase
  • Diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3) - produced by phospholipase C
  • Ca2+ - released from intracellular stores
• G proteins


  Proteins that can bind GTP and GDP, functioning as switches - GTP-bound are active, GDP-bound are inactive
• Heterotrimeric G proteins


  G proteins with three different subunits - alpha, beta, and gamma, with the alpha and gamma subunits attached to the plasma membrane
• Second messengers


  Small molecules that initiate and coordinate intracellular signaling pathways
• Common second messengers


  • cAMP - synthesized from ATP by adenylate cyclase
  • diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3)- produced by the phospholipase C
  • Ca2+ - released from intracellular stores
• G proteins


  Proteins that can bind guanosine triphosphate (GTP) and guanosine diphosphate (GDP). They function as switches; GTP-bound G-proteins are active whereas GDP-bound G-proteins are inactive
• Heterotrimeric G proteins


  G proteins with three different subunits, designated as alpha, beta, and gamma. Alpha and gamma subunits attach to the plasma membranes via lipid anchors
• GPCRs


  A large family of surface receptors that associate with heterotrimeric G proteins. They consist of seven transmembrane domains, an external ligand binding site and an intracellular domain that interact with heterotrimeric G proteins
• GPCR and heterotrimeric G protein-mediated signaling


  1. Binding of a signaling molecule (ligand) to GPCRs causes a conformation change in GPCR, leading to heterotrimeric G protein activation, where GTP physically replaces the GDP bound to the alpha subunit

  2. The G protein subunits dissociate into two parts: the GTP-bound alpha subunit and a beta-gamma dimer

  3. The "activated" G protein subunits diffuse laterally and interact with other membrane proteins, leading to the production of any number of second messengers