Organelles: Ribosomes, ER, Golgi Apparatus, Mitochondria | PDF

Major Organelles: Ribosomes, Endoplasmic Reticulum, Golgi Apparatus, and Mitochondria Alberts MBotC Chapters 12, 13, 14  The Big Picture Mitochondria are the major energy production organelles, and are responsible for oxidative metabolism of...

Major Organelles: Ribosomes, Endoplasmic Reticulum, Golgi Apparatus, and Mitochondria Alberts MBotC Chapters 12, 13, 14  The Big Picture Mitochondria are the major energy production organelles, and are responsible for oxidative metabolism of carbohydrates, lipids, and amino acids Ribosomes are the protein-synthesizing organelles in all cells Endoplasmic reticulum is a complex membranous organelle that is responsible for modification and maturation of integral membrane and secreted proteins, and for lipid synthesis Golgi apparatus is a sorting center for proteins and membranes, and is also involved in the modification of proteins  Which of the following is evidence for the endosymbiont theory? ? A. The catalytic component of ribosomes is rRNA ? B. The mitochondrion contains ribosomes C. Ribosomes are assembled in the nucleus and then exported to the cytoplasm D. All of the above ? ?  Mitochondria Mitochondria are the site of oxidative metabolism of carbohydrates, amino acids, and lipids They generate most of the cell’s ATP: “powerhouses” of the cell Double membrane structure: – Outer membrane: contains many porins (channel proteins) – Inner membrane: rich in the special lipid cardiolipin; folded into cristae; site of the electron transport chain – Intermembrane space: contains cytochrome c and several factors that regulate programmed cell death – Matrix: site of oxidative metabolism; also contains mtDNA, ribosomes, and other components for expression of mitochondrial genome Figure 14-8 (part 1 of 2) Molecular Biology of the Cell (© Garland Science 2008) Figure 14-8 (part 2 of 2) Molecular Biology of the Cell (© Garland Science 2008) Figure 14-10 Molecular Biology of the Cell (© Garland Science 2008)  Mitochondrial DNA and the Search for “Eve” Mitochondrial genome consists of multiple copies of a small (~16 kb; 37 genes) circular DNA Unlike the nuclear genome, the mitochondrial genome is inherited only from the mother Using mtDNA from people around the world, researchers built an evolutionary tree based on the human maternal lineage Result: convergence on a single woman in Africa 140- 200,000 years ago, who is the ancestor of all current living humans (popularly called “mitochondrial Eve”) From Cann, R.L., Stoneking, M., and Wilson, A.C., Nature 325, 31-36 (1987)  Some Questions About Mitochondrial “Eve” Does the finding of a single common female ancestor imply that no other women from her time have current descendants? What is the principle behind using DNA sequences to map evolutionary history? If mtDNA allows us to trace back the female lineage, is there a way to trace the male lineage? Does this finding prove (or even just support) the truth of the biblical Eve story?  Ribosomes Ribosomes are the protein-synthesizing organelles in all cells Found in the cytoplasm and within mitochondria (and chloroplasts); not enclosed by membrane Large complexes of protein plus RNA (hence name): over 80 proteins in eukaryotes (55 in prokaryotes), and 4 different RNA molecules (3 in prokaryotes) Composed of large and small subunits, which only assemble when protein synthesis initiates Often associated with endoplasmic reticulum (more on this later). Figure 6-63 Molecular Biology of the Cell (© Garland Science 2008) Figure 6-62 Molecular Biology of the Cell (© Garland Science 2008)  Endoplasmic Reticulum The endoplasmic reticulum (ER) is a complex membranous organelle that extends throughout the cytoplasm Constitutes ~50% of membrane in typical eukaryotic cell Continuous with nuclear membranes – ER lumen merges with nuclear intermembrane space Divided into “rough” ER and “smooth” ER – Rough ER is associated with many ribosomes, giving it a rough appearance in microscope images – Smooth ER lacks attached ribosomes doplasmic reticulum in a mammalian cell (antibody stain for ER-resident protein) Figure 12-34a Molecular Biology of the Cell (© Garland Science 2008) Figure 12-36a Molecular Biology of the Cell (© Garland Science 2008) Figure 12-36b Molecular Biology of the Cell (© Garland Science 2008) Figure 12-36c Molecular Biology of the Cell (© Garland Science 2008)  Endoplasmic Reticulum ER serves many functions in cells: Major storage site for calcium ions (Ca++), which is important for cellular signaling Smooth ER is the site of lipid synthesis, including sterols, and detoxification of lipid-soluble compounds Rough ER is the site of synthesis of transmembrane and secreted proteins (plus proteins found in lumens of organelles along the secretory pathway) Figure 12-57 Molecular Biology of the Cell (© Garland Science 2008) Figure 12-58 Molecular Biology of the Cell (© Garland Science 2008) Figure 12-38 Molecular Biology of the Cell (© Garland Science 2008)  Endoplasmic Reticulum Most rough ER-synthesized proteins are modified by adding a common oligosaccharide Attachment site is the –NH2 group of an asparagine, so it is called N-linked glycosylation N-linked glycosylation helps during protein folding in ER, and then can be modified later in the Golgi apparatus to provide additional functions Figure 12-50 Molecular Biology of the Cell (© Garland Science 2008) Figure 12-51 Molecular Biology of the Cell (© Garland Science 2008) Figure 12-53 Molecular Biology of the Cell (© Garland Science 2008)  Golgi Apparatus Golgi apparatus is the central sorting station for proteins and membranes along the secretory pathway It consists of a series of flattened discs called cisternae arranged in a stack The stack has two distinct faces: the cis face is closest to the ER and receives vesicles containing ER-synthesized proteins The trans face is furthest from ER and represents the exit from the Golgi apparatus Figure 13-25a Molecular Biology of the Cell (© Garland Science 2008) Figure 13-25b Molecular Biology of the Cell (© Garland Science 2008) Figure 13-27 Molecular Biology of the Cell (© Garland Science 2008)  Golgi Apparatus In addition to its sorting functions (which we will come back to in a later lecture), the Golgi is the synthesis site for most cellular carbohydrates N-linked oligosaccharides are trimmed and further processed by addition of other sugars to generate a wide range of complex oligosaccharides and high mannose oligosaccharides Some proteins also get carbohydrates added to the hydroxyl group of serine or threonine: O-linked glycosylation Other protein modifications can also occur in the Golgi Figure 13-28 Molecular Biology of the Cell (© Garland Science 2008) Figure 13-31 Molecular Biology of the Cell (© Garland Science 2008)  Why do you think N-linked glycosylation uses a pre-formed common carbohydrate that is later modified for each protein? ? A. It takes less energy to assemble the carbohydrate first and then ? modify it, instead of building each unique carbohydrate from scratch B. The process simplifies regulation, since most of the assembly steps and the sequence of the attachment site will be the same for all proteins C. The common carbohydrate has one function in the ER, and ? then new functions can be added by modifying the carbohydrate on individual proteins later ? Figure 13-32 Molecular Biology of the Cell (© Garland Science 2008)  The Big Picture Ribosomes are the protein-synthesizing organelles in all cells Endoplasmic reticulum is a complex membranous organelle that is responsible for modification and maturation of integral membrane and secreted proteins, and for lipid synthesis Golgi apparatus is a sorting center for proteins and membranes, and is also involved in the modification of proteins Mitochondria are the major energy production organelles, and are responsible for oxidative metabolism of carbohydrates, lipids, and amino acids