Cell Nucleus Structure & Function PDF

Last edited: 2/10/2023 CELL NUCLEUS STRUCTURE & FUNCTION Cell Nucleus Structure & Function Medical Editors: Sarah Abimhamed OUTLINE I) INTRODUCTION III) HEMIDESMOS...

Last edited: 2/10/2023 CELL NUCLEUS STRUCTURE & FUNCTION Cell Nucleus Structure & Function Medical Editors: Sarah Abimhamed OUTLINE I) INTRODUCTION III) HEMIDESMOSOMES V) SUMMARY (A) DEFINITION (A) COMPONENTS VI) REVIEW QUESTIONS (B) FUNCTIONS (B) FUNCTION CHECK YOUR ANSWERS (C) TYPES (C) PATHOLOGY VII) REFERENCES II) TIGHT JUNCTIONS IV) GAP JUNCTIONS (A) STRUCTURE (A) COMPONENTS (B) FUNCTION (B) FUNCTION (C) LOCATION (D) CLINICAL SIGNIFICANCE I) NUCLEUS STRUCTURE (A) NUCLEAR ENVELOPE (B) NUCLEAR CONTENTS (1) Outer Membrane (1) Chromatin Made up of a phospholipid bilayer, this contains: Contains DNA o Phosphate groups (2) Nucleolus  Fatty acid tails o Cholesterol (2) Inner Membrane This contains: o Phospholipid bilayer  Lamina layer  Made up of proteins called lamins (3) Nuclear Pores Made of integral “transmembrane” proteins which span Figure 2: The nucleus contains a nucleolus and chromatin the entire nuclear envelope. Figure 1: The nuclear envelope contains an outer and an inner membrane, as well as nuclear pores. Cell Nucleus Structure & Function CELL BIOLOGY: Note #12. 1 of 4  II) NUCLEUS FUNCTIONS (A) NUCLEAR ENVELOPE (1) Outer Membrane (3) Nuclear Pores This is continuous with the Rough Endoplasmic Reticulum The main function of these pores is to allow the (RER) import/export of molecules in and out of the nucleus. This It is important that the envelope is in close proximity depends on the size of the molecules. to the RER for DNA transcription and Translation o Small molecules enter the nucleus via a passive DNA in the nucleus gets transcribed into mRNA process. o Then it gets transported to the ribosomes in the rER,  They also allow the movement of large molecules where they undergo Translation. out of the nucleus (e.g., RNA) via an active process  A protein is synthesized in the RER using ATP. It undergoes specific modifications in RER  If these RNA (e.g., tRNA, mRNA, etc.) move out of o Protein exits the RER via exocytosis and the cell, they bind with the ribosomes and help binds to the Golgi apparatus synthesize proteins Some of the proteins (e.g., ribosomal subunits) need to be sent back into the nucleus; as they are large molecules, ATP is needed to import the molecules into the nucleus. o DNA can make rRNA which combines with these ribosomal subunits  The ribosomal subunits and the rRNA will enter the Nucleolus and combine to make true ribosomes  These large proteins are then sent out of the nucleus to bind to the RER. Figure 3: The outer membrane is continuous with the RER. This is important for DNA transcription and Translation. (2) Inner Membrane This contains the lamina layer The lamin proteins have many different functions: o DNA replications  DNA Transcription (DNA → RNA) o Organize and condense the DNA Figure 5: Nuclear pores function mainly in importing and exporting molecules through the nucleus. Figure 4: The inner membrane contains the lamina layer, which has functions in DNA replication, transcription, and organization. 2 of 4 CELL BIOLOGY: Note #12. Cell Nucleus Structure & Function  (B) NUCLEAR CONTENTS (1) Chromatin (2) Nucleolus Consists of 2 components: It is the site of rRNA and ribosomal synthesis. o DNA From the DNA, RNA molecules are produced: o Histone Proteins o tRNA and mRNA: go out of the nucleus via the nuclear pores (i) DNA  They interact with a ribosome (either free in the It is a negatively-charged double-helical molecule cytosol or bound to the rER) mRNA binds with the ribosome (a) DNA Replication tRNA carries an amino acid (anti-codon) This process is mediated by DNA polymerases, which o rRNA is incorporated within ribosomal subunits inside replicate the genome in DNA during mitosis. the Nucleolus, making up ribosomes.  These ribosomes either become free or are bound (b) Transcription to the rER) Also mediated by DNA polymerases, transcription is the process of copying the DNA sequence into an RNA molecule. Different types of RNA, such as rRNA, tRNA, and mRNA are produced. o All types of RNA are involved in the process of reading mRNA in order to produce proteins, which are important for the function and structure of cells. (ii) Histone Proteins They are positively-charged proteins, and they function as an 8-protein complex, also known as a histone octamer. o They interact with the negatively-charged DNA. (a) DNA Packaging Since the DNA strand is about 2 meters long, it needs to be condensed to fit into the nucleus. The DNA wraps around complexes of histone proteins twice, which makes up a nucleosome. o This process is important, especially during mitosis, Figure 7: The Nucleolus is the site of rRNA and ribosomal where DNA is compacted into a chromosome. synthesis. (b) Gene Expression Regulation In methylation of histone protein (adding a -CH3 group), the DNA around is condensed and is called Heterochromatin. This makes it hard to read the gene, in other words, inhibiting transcription. In the acetylation of histone protein (adding a -COO- CH3), the DNA is allowed to loosen up, becoming Euchromatin. This makes it easy to read the gene and allows the process of transcription. Figure 6: Chromatin is made out of DNA and Histone Proteins. Cell Nucleus Structure & Function CELL BIOLOGY: Note #12. 3 of 4  III) REVIEW QUESTIONS IV) REFERENCES 1) In which part of the nucleus is lamin proteins found? Le T, Bhushan V, Sochat M, Chavda Y, Zureick A. First Aid for the USMLE Step 1 2018. New York, NY: McGraw-Hill Medical; 2017 a) The outer membrane of the nuclear envelope b) The inner membrane of the nuclear envelope Marieb EN, Hoehn K. Anatomy & Physiology. Hoboken, NJ: Pearson; c) Nucleolus 2020. d) Chromatin Boron WF, Boulpaep EL. Medical Physiology.; 2017. 2) Which of the following statements are true about the Urry LA, Cain ML, Wasserman SA, Minorsky PV, Orr RB, Campbell NA. import/export of molecules in/out of the nuclear Campbell Biology. New York, NY: Pearson; 2020 pore? a) Small molecules enter the nucleus via an active Hahn S. (2014). Ellis Englesberg and the discovery of positive control process in gene regulation. Genetics, 198(2), 455–460. https://doi.org/10.1534/genetics.114.167361 b) Large molecules exit the nucleus via a passive process Nelson, D. L., & Cox, M. M. (2017). Lehninger principles of c) Small molecules enter the nucleus via a passive biochemistry (7th ed.). W.H. Freeman. process Reed, U. C., & Zanoteli, E. (2018). Therapeutic advances in 5q-linked d) Molecules like ribosomes can exit the cell without spinal muscular atrophy. Arquivos de neuro-psiquiatria, 76(4), 265–272. requiring ATP https://doi.org/10.1590/0004-282x20180011 3) Which of the following is continuous with the RER? Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. a) The outer membrane of the nuclear envelope (2015). Molecular biology of the cell. New York: Garland Science. b) The inner membrane of the nuclear envelope c) Nucleolus Two Mechanistic Models for Nucleophilic Substitution. (2021, June 23). Retrieved August 12, 2021, from d) Chromatin https://chem.libretexts.org/@go/page/106337 4) What does methylation of histone proteins do to the DNA? a) Condensed form – Euchromatin b) Condensed form - Heterochromatin c) Loose form - Euchromatin d) Loose form – Heterochromatin 5) What is the site of ribosomal synthesis? a) Nucleolus b) Cytosol c) Rough Endoplasmic Reticulum d) Extracellular space 6) What type of RNA is incorporated into ribosomal subunits? a) tRNA b) rRNA c) mRNA d) None of the above 4 of 4 CELL BIOLOGY: Note #12. Cell Nucleus Structure & Function