Basic Cell Structure - RVC Lecture Notes PDF

Dr Andrew Hibbert Basic cell structure Biology of Cells – Basic cell structure Aims Describe the basic structures of proteins, nucleic acids, carbohydrates and phospholipids. Outline the differences between eukaryotic and prokaryotic cells. Outline the functions...

Dr Andrew Hibbert Basic cell structure Biology of Cells – Basic cell structure Aims Describe the basic structures of proteins, nucleic acids, carbohydrates and phospholipids. Outline the differences between eukaryotic and prokaryotic cells. Outline the functions of: the plasma membrane; cytoskeleton; nucleus; endoplasmic reticulum; Golgi apparatus; secretory vesicles; endosomes; lysosomes and mitochondria. Identify the above cellular structures as seen using appropriate imaging techniques. A brief outline of microscopy methods Light microscopes use glass lenses to magnify samples up to 1000x The light might be shone through the sample (like looking at a stained glass window) Alternatively, the sample might be glowing To see more detail we can use electron microscopes, where stained lipids or proteins look dark The main molecules found in cells Phospholipids part 1 Phospholipids are a major component of membranes. They contain a hydrophobic (avoids water) part and a hydrophilic (likes water) part. Fatty acid Phosphate Glycerol Choline Fatty acid Hydrophilic Hydrophobic Phospholipids part 2 Inside and outside the cell is mainly water The hydrophilic parts of the phospholipids “want” to be there This leads to the formation of a bilayer (two sheets of phospholipid molecules) Proteins part 1 Proteins are chains of amino acids Proteins contain hundreds of amino acids in long chains These chains fold in on themselves to create complex 3D shapes Proteins part 2 Side group Side group + H2N C COOH H2N C COOH H H Side group Side group O H2N C C N C COOH H H H Phospholipids and proteins Proteins exist in solution, solution in chains, chains in complexes associated associated with one with one another andanother connectand to, connect to the the or pass through, membranes Inside Outside Carbohydrates Made of carbon (carbo-), hydrogen and oxygen (hydrate) Often considered as ring structures Rings found alone, in pairs or in chains CH2OH O Used by cells, for example, to provide energy and to make extracellular OH structures OH OH OH Polynucleotides DNA and RNA are made of chains of nucleotides, which come in four flavours. These chains provide the code to describe how proteins are made. In eukaryotes, DNA is found in the nucleus, RNA in the cytoplasm At the dawn of time, which of these came first? 1. DNA 2. RNA 3. Protein 4. Phospholipids 5. I don’t know All of these are inter-related... DNA replication is catalysed by proteins RNA regulates and catalyses protein formation DNA translation to RNA is catalysed by proteins Proteins catalyse phospholipid formation Phospholipids control the locations of DNA, RNA and proteins The major cellular organelles Plasma membrane The outer boundary of the cell Contains many proteins which serve as pores, pumps, receptors, signalling molecules and more Inside Outside Cytoskeleton part 1 The cytoskeleton controls the shape of the cell, allows it to move and provides tracks which proteins or organelles move along The cytoskeleton is largely made up of two proteins, actin and tubulin Actin forms filaments, tubulin forms microtubules Cytoskeleton part 2 Green – microtubules Orange – actin Red - nucleus Images reproduced with kind permission of Life Technologies Ltd. Cells come in many shapes and sizes Neuron s Glial cells Nathan B P et al. Endocrinology 2004;145:3065-3073 Electron microscopy of mitochondria Mitochondria are the power stations of the cell They produce ATP which powers most cellular processes Electron microscopy shows a smooth outer membrane and a folded inner one Nucleus The nucleus is the structure where DNA is found To visualise it, we typically use stains which bind to DNA Often (but not always) these are a shade of blue Nuclei often stain a form of “blue” H and E (routine coloured staining) DAPI (routine blue fluorescent stain) Making proteins part 1 DNA RNA Protein Transcription Translation In the nucleus In the cytoplasm Making proteins part 2 Proteins destined to “swim around” in the cell are made by ribosomes and released Ribosomes are small complexes of RNA and protein Endoplasmic reticulum part 1 Proteins destined to live in membranes or to be released from the cell follow a more complex path The endoplasmic reticulum is where membrane and secreted proteins are made Most endoplasmic reticulum is “rough”, having ribosomes along its surface Endoplasmic reticulum part 2 Nucleus Endoplasmic reticulum Taken from “The Cell”, Don W Fawcett Leaving the endoplasmic reticulum part 1 This cell has a fluorescent protein trapped in the endoplasmic reticulum. We can watch it as we let it out What do you think will happen? ©HIRSCHBERG et al., 1998. Originally published in JOURNAL OF CELL BIOLOGY. doi:10.1083/jcb.143.6.1485 Leaving the endoplasmic reticulum – what do you expect will happen? 1. Nothing will change 2. The protein will disappear 3. The protein will move to a bright area 4. The protein will move to lots of bright dots 5. The protein will move to the edge of the cell Leaving the endoplasmic reticulum part 2 This cell has a fluorescent protein trapped in the endoplasmic reticulum. We can watch it as we let it out What do you think will happen? ©HIRSCHBERG et al., 1998. Originally published in JOURNAL OF CELL BIOLOGY. doi:10.1083/jcb.143.6.1485 Golgi apparatus All membrane and secreted proteins pass through it It makes sure the proteins are “finished” and begins to sort them By electron microscopy it looks like a stack of flattened loops of membrane Taken from “The Cell”, Don W Fawcett Leaving the Golgi apparatus part 1 This fluorescent protein is trapped in the Golgi apparatus What happens when we release it? What do you think will happen? Patterson et al. Cell. 2008 Jun 13;133(6):1055-67. Copyright © 2008 Elsevier Inc. All rights reserved. Leaving the Golgi apparatus – what do you expect will happen? 1. Nothing will change 2. The protein will disappear 3. The protein will move to another bright area 4. The protein will move to lots of bright dots 5. The protein will move to the edge of the cell Leaving the Golgi apparatus part 2 This fluorescent protein is trapped in the Golgi apparatus What happens when we release it? What do you think will happen? Patterson et al. Cell. 2008 Jun 13;133(6):1055-67. Copyright © 2008 Elsevier Inc. All rights reserved. Other intracellular membranes part 1 Proteins pass through several structures in the cell after the Golgi Those structures are mainly called “vesicles” or “endosomes” They are loops of phospholipid membrane with proteins inside them (and in their membranes) Other intracellular membranes part 2 Vesicles and endosomes look like loops of membrane on under electron microscopy All look like bright spots under fluorescence We distinguish them by knowing what proteins they contain, what is special about their chemistry or how they move After the Golgi apparatus Plasma membrane Secretory vesicles Endosomes Lysosomes Golgi apparatus (destroy protein) Endosomes Endosomes have been stained red or green (with some staining for both) Images reproduced with kind permission of Life Technologies Ltd. Which of these organelles are found in both eukaryotes and prokaryotes? 1. Plasma membrane 2. Cytoskeleton 3. Mitochondria 4. Nucleus 5. Ribosomes 6. Endoplasmic reticulum 7. Golgi apparatus 8. Vesicles Which of these organelles are found in both eukaryotes and prokaryotes? Answers 1. Plasma membrane 2. Cytoskeleton A further general 3. Mitochondria difference: 4. Nucleus Prokaryotes are 5. Ribosomes generally smaller 6. Endoplasmic reticulum than eukaryotes 7. Golgi apparatus 8. Vesicles