Biol111 Week 9 Lecture 2 nuclei upload.pdf

BIOL111/BCHM111: Cellular Biology and Biochemistry Lecture 25 The Nucleus  Organelles of the eukaryotic cell Storage and E nucleus maintenance...

BIOL111/BCHM111: Cellular Biology and Biochemistry Lecture 25 The Nucleus  Organelles of the eukaryotic cell Storage and E nucleus maintenance of Plant Cell A endoplasmic reticulum cell shape G plasma membrane Vacuole D cytoskeleton Cell wall Provide rigidity C ribosome F Golgi apparatus B mitochondrion Chloroplasts H peroxisome Photosynthesis Reece et al. (2011) Campbell Biology, 9th ed, Fig. 6.08 Animal Cell A prokaryotic cell Prokaryotes lack a nucleus and membrane bound organelles https://commons.wikimedia.org/w/index.php?curid=44194140 5. How do we study cells?  Light microscopy Important parameters in microscopy: magnification resolution contrast Tricks are often used to increase contrast Cells may be living or dead (fixed) Fluorescence microscopy Can be used to study location of specific molecules/proteins in the cell Resolution of light microscopy is limited by the wavelength of light to ~0.2 mM Electron microscopy Electron microscopy Scanning electron Transmission microscopy electron microscopy (SEM) (TEM)  Scanning electron microscopy Study surfaces of objects by (SEM) measuring the scattered electrons Fibrobla Pollen sts Samples need to be coated with a conductive material Samples are dead Image by Tescan  Transmission electron microscopy Electrons are passed through a (TEM) sample and the transmitted electrons are detected Cells are dead Centriole Bacteriophage Image by Carina Buttner, Laboratory of Dr. Alan Davidson Immunity. 2017 Jun 20; 46(6): 943–956. Intro to Cell Biology: Key Points Cell Biology - the study of cells, their structures and organelles, their physiology and life cycle. Cell theory states that: 1) All organisms are composed of one or more cells. 2) Cells are the smallest living units of living organisms. 3) Cells arise only by division of a previously existing cell. Across life, 3 domains are recognised: 1) Bacteria 2) Archaea 3) Eukaryota Eukaryotes are distinct from prokaryotes as they contain a nucleus, have organelles and can be multicellular. Microscopy is used to study cells and sub-cellular structures  Outline of the Nucleus 1. Organising DNA: the chromosome 2. Structure of the nucleus: nuclear envelope and nuclear pores 3. The nucleolus and ribosomes 4. Functions of the nucleus 5. Bacterial chromosomes 1. Organising DNA Homo sapiens Paris japonica 46 chromosomes 40 chromosomes ~25 000 genes unknown number of genes ~6 billion base pairs ~298 billion base pairs ~2 m of DNA ~90 m of DNA What determines genome size? Organising DNA Hummingbird Brown kiwi Archilochus alexandri Apteryx mantelli 0.9 billion base pairs 1.7 billion base pairs Nature. 1995 377(6548):391. Small genomes for better flyers. Hughes AL, Hughes MK. Le Duc et al Genome Biology 2015 16:147 Organising DNA A human cell contains 46 chromosomes, and about 6 billion base pairs of genetic information. This corresponds to about 2 m of DNA. How does this get packed into each and every cell? Organising DNA Physical basis of chromosomal packing is successive rounds of coiling and looping Supercoiling A supercoiled scarf A supercoiled phone cord Organising DNA Histone proteins are involved in packing of DNA Reece et al. (2011) Campbell Biology, 9th ed, Fig. 16.22  Organising DNA Condensed form exists only during cell division! Histone proteins are involved in packing of DNA Chromatin is about 50% protein 50% DNA Histones proteins are also involved in opening of DNA Chromatin Reece et al. (2011) Campbell Biology, 9th ed, Fig. 16.22 2. Structure of the nucleus By TenOfAllTrades at English Wikipedia - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1583880  The Nuclear Envelope NUCLEAR ENVELOPE The nucleus is surrounded by a lipid membrane called the nuclear envelope The nuclear envelope is a double membrane Reece et al. (2011) Campbell Biology, 9th ed, Fig. 5.25  What is a double membrane? A membrane is a lipid bilayer The plasma membrane (cell membrane) is single membrane A double membrane has two lipid bilayers. The nuclear envelope is a double membrane A double membrane modified, Reece et al. (2011) Campbell Biology, 9th ed, Fig. 5.13  Nuclear Pores What needs to pass between the nucleus and the cytoplasm? DNA? RNA? Proteins? Lipids? Reece et al. (2011) Campbell Biology, 9th ed, Fig. 6.09 Nuclear Pores Nuclear pores are large ring-shaped protein complexes Nuclear pores go through both membranes of the nuclear envelope Alberts et al (2008) Molecular Biology of the Cell, 5th ed. Fig. 12.10  Nuclear Pores Nuclear pores complexes are complex: made from > 456 individual proteins Highly conserved during eukaryote evolution. Alberts et al (2008) Molecular Biology of the Cell, 5th ed. Fig. 12.10  3. The Nucleolus A dark staining region of the nucleus that contains very little DNA Cytoplasm Nucleus Nucleolus Cell membrane Reece et al. (2011) Campbell Biology, 9th ed, Fig. 6.9 The nucleolus is where ribosomes are made  The nucleolus is where ribosomes are made Ribosomes are made of protein and RNA Ribosomal proteins and ribosomal RNAs (rRNAs) go to the nucleolus where they are assembled into the two ribosomal subunits The two subunits leave the nucleus through nuclear pores and are put together in the cytoplasm  4. Functions of the nucleus 1. 2.  Functions of the nucleus Where do these processes take place in the cell?  Two Views of Transcription and Translation A biochemist’s view. A cell biologist’s view. Reece et al. (2011) Campbell Biology, 9th ed, Fig. 17.04 Reece et al. (2011) Campbell Biology, 9th ed, Fig. 17.03  Two Views of Transcription and Translation mRNA is processed before export to the cytoplasm Splicing of introns End capping and polyadenylations  7. What about bacteria? Chromosomes usually circular Some species have many chromosomes Plasmids: small independent circles of DNA that can be gained or lost by bacteria and transferred between them No nucleus, but DNA is located in a region called the nucleoid 7. What about bacteria? Nucleoid Reece et al. (2011) Campbell Biology, 11th ed, Fig. 27.9 No nucleus, no histones, but DNA is highly supercoiled in the cell by topoisomerases. https://en.wikipedia.org/wiki/DNA_supercoil#/media/File:Circular_DNA_Supercoiling.png Transcription and translation occur in the same place  Summary of the Nucleus Where ribosomal RNA is Chromosomes processed and ribosomes assembled Surrounded by a double membrane. Transport in and out of nucleus via nuclear pore complexes  Today’s key terminology Chromosome = a single strand of DNA plus associated proteins. Contains a significant fraction of the genetic material of an organism. Histones = proteins that help to organise and pack DNA. Chromatin = the complex of DNA and histone proteins. Chromosomes are made up of chromatin. Nucleus = the big organelle in eukaryotic cells where DNA is stored. Nucleolus = the sub-section of the nucleus where ribosomes are made. Nucleoid = a region within the prokaryotic cytoplasm where the DNA is found. Today’s Key Points DNA is organized into chromosomes. In Eukaryotes, DNA is wrapped around histones and stored in the nucleus. The nucleus is surrounded by a double membrane. Transport in and out of nucleus occurs via nuclear pores. Ribosomal RNA is transcribed and ribosomes made in the nucleolus. The nucleus has a bunch of functions and does not just passively store DNA Bacteria have chromosomes and plasmids, which are supercoiled in the cell. There is no nucleus.