Lecture 1 - Introduction to Cells PDF

Preview

Summary

Download Lecture 1 - Introduction to Cells PDF

Description

Lecture 1: Introduction to Cells Sunday, 28 July 2019

11:25 pm

Cell Theory: 1. Cell is the basic unit of life 2. All Cells come from pre-existing cells 3. All organisms are made up of one or more cells Prokaryotic cell • Capsule • Cytoplasm • Ribosomes • Nucleoid • Cell membrane • Flagellum • Cell wall - Peptidoglycan - Outer membrane (absent in some bacteria) • Prokaryotes live in communities: biofilms - Individuals living closely together but NOT multicellular Nucleoid • Chromosomal DNA • Circular, double-stranded piece of DNA • Not surrounded by a nuclear membrane Plasmid • Independent DNA molecule • Small circular, independent double-stranded DNA molecule. • Plasmids can frequently be transmitted from one bacterium to another. Cytoplasm • Gel-like matric composed of water, enzymes, nutrients, wastes Plasma membrane • Also called cell membrane • Permeability barrier Bacterial cell wall • Composed of peptidoglycan- polymer of amino sugars that is linked at regular intervals to short peptides Capsule • Layer composed mainly polysaccharide • Encloses the cell wall in SOME bacterial cells Fimbriae • Are shorter

• They help cells adhere to surfaces such as animal cells (attachment pili) Pili • Hair-like structures help bacteria adhere to other cells during bacterial conjugation • Allows transfer of DNA Flagella • Made of a protein called flagellin • Used for locomotion Eukaryotic cells • Organism contains genetic information within a cellular compartment called a nucleus Fluid mosaic model of the structure of the Plasma Membrane • Double layer of phospholipids with cholesterol, proteins and carbohydrates • Not a static sheet of molecules • Selectively permeable boundary between the cell and the environment • Site of attachment of cytoskeleton structures Cytoplasm = cytosol + organelles Function of cytosol - Chemical reactions - Storage The Nucleus: information central • Store genetic code; deoxyribonucleic acid (DNA) - DNA associated with proteins --> chromatin (euchromatin or heterochromatin conformations) --> condenses prior to cell division --> chromosomes ER: Biosynthetic factory • Interconnected system of membrane-enclosed compartments • Two distinct regions of ER: - Rough ER § Ribosomes attached § Protein synthesis --> chemically modified to alter function/tagged --> vesicles - Smooth ER § Lacks ribosomes § Synthesis lipids and steroids § Ca2+ storage --> triggers cell responses § Chemical modification --> detoxification of foreign substances § Site for glycogen degradation Ribosomes: protein factories • Composed of ribosomal RNA (ribonucleic acid) and proteins Golgi Apparatus

Golgi Apparatus • Receives protein-containing vesicles from RER • Modifies, concentrates, packages and sort proteins • Attaches carbohydrates to proteins and modifies other carbohydrates attached to protein • Synthesis of some polysaccharides for the plant cell wall • Cisternae (singular= cisterna) Lysosomes • Digestive sac for proteins, fats and carbohydrates • Transports undigested materials to cell membrane for removal • Plant cells have vacuole-like lysosomes, contains many digestive enzymes Vacuoles • Membrane-bound structures with various functions depending on the cell type • There are different types of vacuoles: - Food vacuoles § Are formed by phagocytosis - Contractile vacuoles § Found in many freshwater protists § Pump excess water out of cells - Central vacuoles § Found in many mature plant cells § Hold organic compounds and water Plant vacuole • Structure • Reproduction • Digestion • Storage Mitochondria • Powerhouse of the cell • Generates adenosine triphosphate (ATP) • Has inner and outer membrane • Cristae Chloroplasts • Chlorophyll- sites of photosynthesis - Sunlight --> ATP and NADPH • Thylakoids arranged in stacks • Stack= granum (plural grana) • 1x granum= roughly 10-20 thylakoids • Chloroplast contains ribosomes and DNA Cytoskeleton

• • • • • •

Flexible, dynamic, lattice of fibrous proteins also called filaments Mechanical support and structure Intracellular transport of materials Suspension of organelles Contraction Cell motility

Extracellular component and connections between cells • Protection, support and interacting with other cells • Extracellular structures include: - Cell walls of plants, fungi, some protists - Extracellular matric surrounding animal cells - Cell junctions Cell walls • In bacteria this is peptidoglycan • Present surround the cells of plants, fungi and some protists • The carbohydrates present in the cell wall vary depending on the cell type: - Plant and protist cell walls- Cellulose - Fungal cell wells- chitin Cell wall of plants • Protects the plant cell • Maintains its shape • Prevents excessive uptake of water • Cellulose fibres embedded in other polysaccharides and protein

•

Cellulose fibres embedded in other polysaccharides and protein Middle lamella- hold cell walls of adjacent cells together

Extracellular structures • Holds cells together in tissues • Contributes to properties of bone, cartilage, skin etc. • Filters materials passing between different tissues • Orients cell movements in development and tissue repair • Plays a crucial role in chemical signalling Gap junctions • Communicating junctions in animal cells • Provide cytoplasmic channels between adjacent cells • Allow for transport of ions, water and other substances • Connexon- set of six membrane proteins form a pore

Tight junctions • Create a watertight seal between two adjacent animal cells • Family of proteins- claudins • Prevent leakage of extracellular fluid

Desmosomes • Anchoring junctions- fasten cells together into strong sheets • Cadherins - Specialised adhesion proteins on the membranes of both cells - Attach to the cytoplasmic plaque - Connects to the intermediate filaments...