PL1003 Lecture 3.1 - Eukaryotic Cells PDF

The Eukaryotic Cell Dr. Gemma Barron [email protected] Mediran, CC BY-SA 3.0 , via Wikimedia Commons Today’s Learning Outcomes At the end of today’s class, you should be able to: Identify and describe the main struc...

The Eukaryotic Cell Dr. Gemma Barron [email protected] Mediran, CC BY-SA 3.0 , via Wikimedia Commons Today’s Learning Outcomes At the end of today’s class, you should be able to: Identify and describe the main structures of membrane-bound and non-membrane-bound organelles found within typical eukaryotic cells: Nucleus, nucleolus, plasma membrane, cytosol, lysosome, proteasome, ribosome, peroxisome, mitochondrion, Golgi, endoplasmic reticulum, cytoskeleton Explain their function Why is this relevant…. Understanding how to target specific properties of one cell type over another. Targeting of drugs to specific organelles (increased efficacy, reduced side effects). Targeting functions of parasite organelles to combat infection, while sparing host cells. General features of eukaryotic cells Many of the structures and organelles we will look at are shared between multiple cell types. Adaptations to ‘survive in By CNX OpenStax (modified by expii) diverse physiological capacities’. CC BY 4.0, via Wikimedia Commons Changes to cellular machinery. Differences allow processes to be Toxoplasma gondii Copyright Graham Colm at English Wikipedia ‘singled out’ and targeted (licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license). pharmacologically. Plasma membrane (1) Defines the cell surface Impermeable to large molecules Selectively permeable to small molecules Allows there to be differences between the internal (cytosol) and external environments (extracellular fluid) Mediran, CC BY-SA 3.0 , via Wikimed Commons Plasma membrane (2) Maintains ’biochemical constraints’ necessary for biological activity Glycolysis Maintains concentration gradients of ions across the cell membrane firing of nerve cells contractions of muscle cells release of secretory products (e.g. insulin) Plasma membrane (3) Made up of phospholipids, proteins, and cholesterol. By OpenStax, licensed under CC BY 4.0, via Wikimedia Commons Phospholipids are amphipathic: charged, hydrophilic (polar) head hydrophobic (non-polar) fatty acid tails Form Lipid bilayer 'Fluid mosaic’ model: rotation Source https://cnx.org/contents/[email protected]:fEI3C8Ot@10/Preface. and lateral movement of This file is licensed under the Creative Commons Attribution 4.0 International license. phospholipids and proteins in Plasma membrane (4) ‘Studded’ with proteins (e.g., ion channels, receptors, transporters etc.) Allows cell to receive signals and transport molecules into and out of the cell. “External Reactions and the Internal Reactions of Receptors” by Laozhengzz. License: Public Domain A Quick Recap (1) Proteins carry out cellular functions. They are the result of gene expression and are made outside the nucleus in ribosomes. mRNA The information for making proteins is encoded in DNA. The DNA must be protected and remains in the nucleus. Khan Academy Stages of Translation. Licensed under a CC BY-NC-SA 4.0 license A Quick Recap (2) When a gene is “expressed,” a disposable mRNA copy of the DNA is created (TRANSCRIPTION) The mRNA is exported to the mRNA cytoplasm where it associates with ribosomes The mRNA code is used to assemble a protein (TRANSLATION) Khan Academy Stages of Translation. Licensed under a In Eukaryotic cells, transcription CC BY-NC-SA 4.0 license and translation are separated Nucleus Keeps the chromosomal DNA safe Consists of two lipid bilayers Pores which allow communication with the cytoplasm Pores allow molecules to move in and out of the nucleus This is highly regulated – larger molecules which need to move across the nuclear membrane possess a nuclear localisation sequence NUCLEAR IMPORT AND EXPORT  What sort of things need to move across the nuclear Nucleotides, ions…. (needed for transcription) membrane? Proteins with a nuclear localization signal e.g. histones, DNA/RNA polymerases transcription factors mRNA and ribosomal subunits from the nucleus to the cytoplasm  Fruleux and Hawkins. DOI: 10.1088/0953-8984/28/36/363002 allows for License CC BY 3.0 translation  The nuclear pore Diameter of pore in resting state = 9nm Interaction of pore with nuclear localization sequence results in 1. Nuclear Envelope 2. Outer Ring conformational change 3. Spokes  dilation of pore 4. Basket 5. Filaments. Artwork created for Wikipedia by Mike Jones. This file is licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license  Nucleolus Located inside the nucleus (no membrane) Condensed chromatin containing genes encoding ribosomal RNA (rRNA) Transcription and processing of rRNAs Assembly of ribosomal subunits (ribosomal protein + rRNA) Ribosomal subunits are exported to cytoplasm Ribosome The site of protein translation It converts the mRNA ‘code’ into an amino acid sequence tRNA is an adapter molecule that allows selection of the correct amino acid ‘Free’ ribosomes and those associated with the endoplasmic reticulum Ribosome Secretory proteins and membrane proteins are translated by ribosomes attached to the ER (”rough” ER) As these proteins are made, they end up in the ER membrane, or the ER lumen. The proteins are then transported in vesicles, via the golgi. Endoplasmic reticulum network of tubules and vesicles The membranes of the ER are continuous with the nuclear membrane. Rough ER (3): Associated with ribosomes protein synthesis  secreted or transmembrane proteins. Post-translational modification Endoplasmic reticulum Smooth (4): Lipid and steroid synthesis Carbohydrate metabolism Calcium storage and release Particularly well-developed in contractile cells Sarcoplasmic reticulum Golgi Part of the endomembranous system Physically separate ‘Advanced’ post-translational modification Communicates via vesicles ‘Bud’ and ‘fuse’ This budding process also produces vesicular structures Vesicular structures Lysosomes (bud from golgi) Contain hydrolytic enzymes – general destruction More about lysosomes in the immune system lectures Peroxisomes (bud from ER) Lots of functions, including b-oxidation of fatty acids (important in breakdown and secretion  fatty acid levels in blood can be controlled by the activity of peroxisomes in the liver in some species) Takes part in synthesis of cholesterol, bile acids We will return to this – steroid hormones and transcription factors  Ubiquitinated protein Proteasome Large protein complex Not bound by a membrane proteasome Cytoplasm and nucleus Targeted degradation of proteins Misfolded Too much Degraded protein To modify cell signalling pathways These are first labelled by adding a ubiquitin tag. The proteasome can now recognise the protein for degradation. Immunoproteasome – specialised proteasome involved in antigen presentation Mitochondria ATP - Energy currency of cell Generated by glycolysis, Krebs cycle, but mostly by mitochondrion Important in muscle contraction Cytoskeleton Protein scaffold that supports the cell Very dynamic Shape changes and movement of vesicles Cell cycle Assembly/disassembly of protein polymers Summary These features are shared by almost all eukaryotic cells. You need to be able to identify and describe the main structures within typical eukaryotic cells. You also need to explain their function in basic terms. Ideas for further reading and discussion will be uploaded to the PL1003 Moodle page.