Cell Bio Exam 4

• Nucleus


  Double lipid bilayer, meaning it contains four monolayers, with the outer bilayer facing the cytoplasm and the inner bilayer facing the nucleoplasm
• Cytoplasm


  Contains proteins, lipids, carbohydrates, and organic/inorganic molecules
• Nucleoplasm


  Denser and has granules, mainly ribonucleoproteins (RNPs) and is in a gel-like state
• Nuclear pores


  Regions in the nucleus that act as doors, allowing large molecules to move rapidly and quickly without having to go through a transport phenomenon. Their function is to regulate the traffic of molecules into and out of the nucleus
• Nuclear pore complexes


  A series of proteins that surround the nuclear pores and act as gatekeepers, regulating the passage of specific molecules into and out of the nucleus
• Nucleolus


  A sub-organelle of the nucleus that is made up of the fibrillar region and granular region
• Nuclear laminas


  A series of proteins called Lamins that form a mesh-like network lining the inner surface of the nuclear envelope. Its function is to provide mechanical support and maintain the shape of the nucleus
• Ribosomes


  A couple of ribosomes are attached to the outermost monolayer facing the cytoplasm. Ribosomes can move from the rough endoplasmic reticulum (ER) into the smooth ER and into the nucleus
• Perinuclear space


  The space between the outer and inner layers of the nuclear envelope. Its length is 20-40nm
• Heterochromatin


  A visible component of the nucleus with a light or electron microscope. It is part of the chromatin that is tightly packed, and its function is to regulate gene expression. It often forms a network of fibers extending to the lamaina and to the nucleus
• Outer monolayer of nuclear envelope

  Contains proteins and other compounds that interact with the cytoplasm
• Inner monolayer of nuclear envelope

  Designed to interact with molecules in the nucleoplasm
• The nuclear pore complex is 80nm in diameter with the closing part is 9nm in diameter, and an average nucleus has about 3000-4000 nucleur pores complex distributed evenly across the surface
• Proteins on the bilayer facing the nucleoplasm

  Fibrous proteins that extend vertically into the nucleoplasm, some exist in crosslink and go horizontally as well
• Lamina and Lamins


  Very strongly positively charged, even more positive than the histochromatins, and they bind and organize chromatin. The lamina keeps chromatin out of the pore. The lamina gives the nucleus its ovular shape. The lamina holds all of the stuff in the pore complexes in place. 50-80nm in length
• Primary function of the nucleus

  Regulation of transcription
• Liver cells and stomach cells are different due to differential gene expression, which is due to the regulation of transcriptional activity in the nucleus
• Regulation of transcription


  Can occur at numerous levels, including post-transcriptional mechanisms, transport, translation, post-translational mechanisms, and transport again
• Best location for regulation in terms of the economy of the cell

  Transcription, because it saves energy
• Lac-operon


  An example of single gene regulation in a prokaryote, allowing the gene to be transcribed in response to environmental signals, such as lactose
• Negative gene regulation


  When something must be moved in order to transcribe a gene, such as removing a repressor from a promoter
• Positive gene regulation


  Activation of a gene through the addition of a transcription factor
• Master gene regulatory proteins

  Can turn on a suite of genes, allowing for the differentiation of cells. They can work by binding to enhancer regions and opening up one or multiple genes, or by acting as receptor proteins
• Environmental signals in single gene regulation

  Play a role by triggering the transcription of genes in response to changes in the environment
• Differential gene expression leads to differences between cell types by regulating which genes are expressed in each type of cell
• ATP


  The energy currency of the cell, allowing for the performance of essential cellular functions
• Post-transcriptional mechanisms


  Play a role in gene regulation by controlling the processing and stability of mRNA transcripts
• Transport in gene regulation

  Can play a role by regulating the movement of proteins and other molecules within the cell
• Testosterone receptor protein in humans


  Significant because it controls the development of male characteristics and influences the expression of multiple genes
• Ribosomes can be attached to the membrane of the nucleus envelope
• Components of the nucleus

  • DNA
  • Nucleosomes
  • Histones
  • RNA
• Gene regulation


  The process of controlling the expression of genes to produce specific proteins
• Transcription


  The process by which DNA is converted into RNA
• Lac operon


  An example of gene regulation through the regulation of transcription, and it is an example of the environment providing an outside influence
• Negative gene regulation


  Reduces or inhibits gene expression
• Positive gene regulation


  Enhances gene expression
• Master gene regulation proteins


  Proteins that control the expression of many different genes
• Selective decondensation


  The process by which chromatin is decondensed to regulate transcription
• Components of chromatin


  • DNA
  • Nucleosome histones
• Effect of phosphates on histones

  Phosphates make the histones negative, which reduces the binding of DNA to histones, leading to decondensation of chromatin