Cell Structure: Nucleus & Plasma Membrane PDF

Cell Ultrastructure : Nucleus & Plasma Membrane Class: Foundation Year Course: Fundamentals of Human Biology Code: FUNBIO 4 Lecturer: Adrian Dervan PhD nd Learning outcomes At the end of this lecture, the learner will be able to Describe the fluid mosaic model structur...

Cell Ultrastructure : Nucleus & Plasma Membrane Class: Foundation Year Course: Fundamentals of Human Biology Code: FUNBIO 4 Lecturer: Adrian Dervan PhD nd Learning outcomes At the end of this lecture, the learner will be able to Describe the fluid mosaic model structure of the plasma membrane. Discuss the difference between integral and peripheral membrane proteins Explain how these membrane proteins function in semipermeable membranes Describe the structure of the nucleus including nuclear envelope, pores and karyoplasm. Differentiate between euchromatic and heterochromatic nuclei Explain how each organism has a characteristic number of chromosomes. Cell membranes – plasma & nuclear membrane Animal cell Animal and plant cells are eukaryotic. These cells contain a nucleus and other structures (called organelles), each enclosed within a membrane These organelles are needed for the cell to function The organelles include the nucleus, plasma membrane, lysosomes, mitochondria, etc Plasma Membrane Under the EM it appears as a three-layered structure between 7.5 – 10 nm in diameter All living cells have plasma membrane Youtube video explaining EM https://www.youtube.com/watch?v=fToTFjwUc5M Biology Fig. 4-10 Plasma Membrane structure The lipid bilayer is the universal basis of cell membrane structure It is composed of two lipid layers largely phospholipids Amphipathic molecules Hydrophobic tails facing inwards Hydrophilic heads These molecules have the ability to Biology form a bilayer due to Fig. 5-1 their chemical Cell Membrane: Fluid Mosaic Model Proposed by Singer & Nicolson (1972) Biological membranes can be considered as a two-dimensional liquid: Consists of phospholipid molecules With embedded or associated proteins & lipids Many cells surrounded by cell coat or glycocalyx Position of many of the proteins is Formed by polysaccharide side chains of proteins and constantly changing lipids Protects the cell and may help keep other cells as a distance Cell Membrane Biology Fig. 5-4 Plasma Membrane - Structure The outer face has more saturated fatty acids E.g. Higher amount of cholesterol This makes it more solid or viscous The inner face has more unsaturated fatty acids This makes it more fluid than the outer layer Biology Fig. 5-2 Membrane Proteins Two classes: 1. Integral membrane proteins A. Transmembrane proteins B. Integral monotopic membrane proteins 2. Peripheral proteins Integral Membrane Proteins Permanently attached to the p membrane Cannot be removed easily Biology Fig. 5-6 Peripheral Proteins Attached to integral membrane proteins Associated with peripheral regions of the lipid bilayer. Temporary interactions with biological membranes Molecule associates then dissociates to the cytoplasm. Biology Fig. 5-6 Plasma Membrane - Function All membranes act as semi-permeable membranes Small uncharged lipid-soluble molecules readily cross or pass through the membrane Given enough time virtually any molecule will diffuse across a lipid bilayer The rates at which water and charged inorganic ions move across membranes can only be explained by the existence of carriers or special channels through the bilayer Integral Transmembrane Proteins Integral Transmembrane proteins Spans entire plasma membrane Usually folded as a-helix Can be b-barrel Can act as Anchors (a and g) Transporters or ion Channels, (b and c) Biology enzymes, (d and e) Fig. 5-9 Receptors (f) Integral Transmembrane Proteins Biology Fig. 5-9 The Nucleus Eukaryotes (containing a nucleus) All cells in the human body, except… Specialised exceptions Mammalian red blood cells Platelets “Cells without nuclei have limited futures”  Prokaryote Eukaryote s s Animals & Plants (Bacteria & Archea) - Do not have a nucleus - Have a nucleus - DNA sits in the cytoplasm - DNA sits in the nucleus The Nucleus Functions 1. control of genetic information in the cell 2. control of heredity characteristics 3. control of the protein and enzyme synthesis. 4. control of cell division and cell growth. 5. storage of DNA, RNA and Transmission electron microscope image of a human ribosome. cell 6. regulation of the transcription of the mRNA to protein. The Nucleus One nucleus per cell Rounded body in the cell cytoplasm The nucleus is composed of: Nuclear envelope Chromatin Nucleolus Nuclear Pores Nucleoplasm Nuclear Envelope Perinuclear space Structure Nucleus is enclosed in a double-layered nuclear envelope Isolates nuclear material from the cytoplasm A perinuclear space (20- 40nm wide) is found between the two membranes Nuclear Envelope Outer membrane is continuous with the endoplasmic reticulum in the cytoplasm Perinuclear space  Nuclear Lamina A nuclear lamina is found adjacent to the inner face Perinuclear space Provides structural support internally Consists of a fine network of protein filaments Intermediate filaments Lamins Genetic mutations cause progeria syndrome Emery-Dreifuss muscular dystrophy (EDMD) Function: Provide support to nuclear envelope Aid in positioning of nuclear pores  Nuclear Pore There may be thousands of pores occupying 10 - 30% of the surface Biology Fig. 4-11 Nuclear Pore Structure : Ring-like arrangement called a pore complex Octagonal structure over 50nm diameter 1nm = 1.0 × 10-9 meters  3. Nuclear Pore - Pore complex Channel protein Cytoplasmic subunit Cytoplasmic face face eight subunits surround a central zone which contains a channel about 9nm in diameter Central zone Nuclear face Nuclear Pore - Pore complex Function: Allows the transport of water- soluble molecules across the nuclear envelope Molecules which can pass though include: RNA Ribosomes Proteins Carbohydrates Signal molecules Lipids Nuclear face Nucleoplas m The cytoplasm in the nucleus is called the nucleoplasm highly viscous liquid that surrounds the chromosomes (Chromatin!) and nucleoli Many substances such as nucleotides and enzymes are dissolved in the nucleoplasm. Glossary Nucleoside – Purine or Pyrimidine base linked to either a ribose or deoxyribose sugar (no phosphate group) Nucleotide – a series of nucleosides joined together by a phosphate group by ester linkage to the sugar. DNA and RNA are polymers of nucleotides ATP – Adenosine triphosphate (Nucleoside triphosphate) Nucleoplas m A network of fibers known as the nuclear matrix Nucleus can also be found in the nucleoplasm. Similar to cell cytoskeleton Precise composition and arrangement in the Nuclear nucleus not known matrix Chromatin Fibers When the cell is not dividing (Interphase) the nucleoplasm contains a collection of threads and fibres which can be seen with the electron microscope Called chromatin fibres The finest chromatin are fibrils about 2nm in diameter This is about the dimension of a DNA molecule Chroma tin Euchromatin Heterochromatin Lightly packed form of chromatin DNA transcribed from Euchromatin Heterochromatin Tightly packed form of DNA Usually located at the periphery of the nucleus The DNA in heterochromatin is not transcribed The functions of heterochromatin are attributed to the dense packing of the DNA: Gene regulation Protection of the integrity of chromosomes Euchromatin The structure of Chromatin Metaphase of cell division chromatid centromere Each chromatid is a mirror image of its sister  Chromatin Packing Chromatin undergoes Histone several levels of coiling to octomer form a chromosome Basic unit: called a Nucleosome Consists of the DNA double helix coiled around a protein unit called a histone These nucleosomes repeat themselves the length of the chromatin Number of chromosomes in species Species Diploid - 2N Haploid - N Mosquito - Aedes 6 3 Fruit fly - Drosophila 8 4 Pike - Esox 18 9 Frog - Rana pipiens 26 13 Alligator - A. mississipiensis 32 16 Rat - Rattus spp. 42 21 Human - Homo sapiens 46 23 Chimpanzee - Pan 48 24 troglodytes Goat - Capra spp. 60 30 Duck - Anas spp. 80 40 Atlas blue Ciliated protozoa 448-452 (Oxytricha trifallax) c/comes 16,000 c/somes Human chromosomes Human Karyotype 22 pairs of autosomes + 2 sex chromosomes Trisomy 21 causes Down’s syndrome  Nucleolus Nucleolus (pleural nucleoli) One to four per cell nucleus Dense basophilic material in nucleoplasm Disappear during cell division Re-appear post-division Re-appearance organized by particular chromosomes which have an area called nucleolar organiser region Nucleolus organiser regions (NORs) are chromosomal regions crucial for the Basophilic – ?? Compounds or structures that stain formation of the nucleolus strongly with basic (not acidic!) dyes Nucleolus: function Associated with specific regions of several chromosomes which transcribe ribosomal RNA (rRNA) rRNA found in other cytoplasmic organelles called ribosomes Ribosomes are closely connected with protein synthesis Ribosomes contain roughly equal amounts of RNA and proteins Within the nucleolus chromosomal DNA transcribes rRNA which then associates with proteins to form ribosomal particles The size of the nucleolus is a reflection of the activity of the cell so it may be quite small or occupy up to 25% of Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T NAME SURNAME E M A I L : A D R I A N D E R VA N @ R C S I. C O M