Cell Biology Lecture: Cell Size, Type and Cycle - PDF

ANHB1101 Cell Biology Lecture 1 – cell size, type and cycle Archa Fox [email protected]  learning objectives Appreciate the diversity of cellular shapes and functions and how this arises Appreciate the importance of scale and measurement in understanding cells Un...

ANHB1101 Cell Biology Lecture 1 – cell size, type and cycle Archa Fox [email protected]  learning objectives Appreciate the diversity of cellular shapes and functions and how this arises Appreciate the importance of scale and measurement in understanding cells Understand different types of microscopes, their limitations and limitations of 2D images for 3D reality Understand the basics of the cell cycle and mitosis Length scales in human biology  The Cell Structural and functional unit of living organisms All human cells originate from a single fertilized egg Development involves cell replication & specialization  Tissues… made of cells Four main types of tissues in humans: 1. Epithelium 2. Muscle 3. connective tissue 4. nervous tissue Epithelial cells make up the epithelium. The cells come from the surfaces of your body, like skin, digestive tract and organs CellDiversity diversity –ofshape cell shapes How is cell diversity determined? Genes Proteins Determine cell structure and function Each cell expresses only a subset of its genes How many cell types are there in a human? Textbook tells you: 200 cell types, but new cell types are being discovered, and new cellular states analysed www.humancellatlas.org Mission: To create comprehensive reference maps of all human cells—the fundamental units of life—as a basis for both understanding human health and diagnosing, monitoring, and treating disease. Nature volume 581, pages303–309(2020) Discovery of new cell type in the lung The "pulmonary ionocyte” similar to salt-balancing ionocytes in fish gills or frog skin. Make up 1% of airway epithelial cells Main source of CFTR expression (the gene involved in cystic fibrosis)  Size matters! How big or small are cells? How big or small are cell components? 5-20 µm µ = micro = 10-6 = 1 / 1,000,000 µm = micrometre = 1/1,000,000 of a metre (i.e. 10-6 metre) = 1/1000 of a millimetre (i.e. 10-3 millimetre)  Measurements to know: 1 millimetre = 1/1000 of a metre (1 mm = 10-3 m) 1 micrometre = 1/1000 of a mm 100 µm (1 µm = 10-6 m) 1 nanometre = 1/1000 of a µm (1 nm = 10-9 m)  Useful sizes to remember Cell sizes range from 5 to 100 µm Average cell nucleus is around 5 µm in diameter A useful cellular ‘ruler’: a red blood cell is about 8 µm in diameter 8µm Viewing Cells: Resolving Power The Human Eye (down to 0.2 mm) Light microscope (down to 0.2 µm) Super- resolution microscopy: down to Electron microscope 20nm (down to 0.2 nm)  electron microscopes Transmission electron microscope Electrons pass through sample Suited to resolving cell organelles and cell contacts 5µm Scanning electron microscope Electrons bounce off the sample Suited to resolving surface morphology of cells and structures 5µm  Viewing Cells: 3D to 2D A 2-dimensional view We need to use this view to (i.e. a very thin slice) is construct what we normally a 3-dimensional view see via a light microscope in our mind’s eye  Viewing Cells: 3D to 2D 5µm 10 µm Scanning EM Light microscope view of a neuron view of a neuron (appears ‘3D’) (appears ‘2D’) Viewing Cells – case study ‘microvilli’ 5µm 0.1µm 0.5µm Light microscopy Electron microscopy (down to 0.2 µ m) (down to 0.2 nm)  Cell division in the body Mitosis is needed for growth and repair 500 µm 100 µm 30 µm Some cells are just too specialised to divide Some cells divide very rapidly! 100 µm 10 µm The Cell Cycle  Chromosomes In a normal human cell there are 46 chromosomes, also called 23 pairs of chromosomes In a cell in S phase, each chromosome doubles it’s DNA, forming 2 chromatids, joined by a centromere A DIPLOID cell has the full complement of chromosomes, a HAPLOID cell has half Cell Cycle Phases - interphase G1 phase (gap phase 1) G2 phase (gap phase 2) - growth & normal - brief, final preparation cellular activity - for cell division - 3-4 hours S phase (synthetic phase) - DNA replication - 6-8 hours Cell Cycle Phases - Mitosis Prophase - chromosomes condense and become visible - nuclear membrane disappears - mitotic spindle starts to form from centrioles Prophase to metaphase Gao et al 2019. Science 363:eaau8302. https://doi.org/10.1126/science.aau8302 Cell Cycle Phases - Mitosis Metaphase - chromosomes line up on equator - the spindle is fully formed Cell Cycle Phases - Mitosis Anaphase - chromosomes split at centromere Anaphase in living cells Gao et al 2019. Science 363:eaau8302. https://doi.org/10.1126/science.aau8302 Cell Cycle Phases - Mitosis Telophase - decondensation of chromatin - reformation of nuclear envelope - cytokinesis Case study: paraspeckles in the cell Cycle For a bit of fun, watch: https://www.youtube.com/watch?v=pOsAbTi9tHw