4.1 Cell Structure and Function PDF

Topic 4.1 Cell Structure and Function Introduction to Cells Important scientists, facts and dates  The Cell Theory All living things are made of cells. Cells are the structural and functional unit in living things. All cells come from preexisting cells. The Light microscope...

Topic 4.1 Cell Structure and Function Introduction to Cells Important scientists, facts and dates  The Cell Theory All living things are made of cells. Cells are the structural and functional unit in living things. All cells come from preexisting cells. The Light microscope Up to 1000x magnification Up to 0.2 µm resolution Different types: bright field m., dark field m., fluorescent m., phase contrast microscopes, etc… https://www.youtube.com/watch?v=6vZZeWqbmU8 The Electron microscope Up to 1000000 x magnification Up to 0.2 nm resolution Different types: transmission e.m. and scanning e.m. Light microscope vs. Electron microscope https://www.pinterest.com/pin/52635889370647635/  Prokaryotic and Eukaryotic cells Science Photo Library  Types of Cells Prokaryotic Eukaryotic Eubacteria Archaea Plants Animals Fungi Protista Prokaryotic cells Prokaryotic cells Eukaryotic cells: animal Eukaryotic cells: plants Cell organelles Travel inside a plant cell  All cells have these four structures: Plasma membrane Cytoplasm Ribosomes DNA  The Plasma Membrane The plasma membrane controls what enters and leaves the cell. Since some molecules are allowed to pass through, but others are not, it is said to be semipermeable. The plasma membrane has four components: A phospholipid bilayer Proteins Cholesterol Glycocalyx Source: http://cytochemistry.net/cell-biology/membrane.htm  Cytoplasm The Cytoplasm is the space between the plasma membrane and the nuclear envelope. It an aqueous solution, made of water plus sugars, lipids, proteins, etc.  Ribosomes The ribosomes are organelles without a membrane, spherical and only visible under electron microscope. They are made of proteins, rRNA and water (80%). The ribosomes are made of two subunits, a large heavy unit and a small light one, that are separated in the cytoplasm only joining together when reading the mRNA.  Ribosomes The function of the ribosomes is the synthesis of proteins. DNA The molecule of DNA contains the genetic information to synthesize proteins In prokaryotic cells, the DNA forms only one circular chromosome and is NOT surrounded by a nuclear envelope. The area where the DNA is located is called NUCLEOID. In eukaryotic cells, the DNA is associated with proteins called histones, forming a substance called chromatin, and it is surrounded by a nuclear envelope, forming the NUCLEUS.  The Nucleus The nucleus is the most important organelle in the eukaryotic cells. It has three functions: Contains the cell's genetic material. Synthesis of RNAs (in the nucleolus). Control all the functions of the cell. The Nucleolus It is a spherical darker structure inside the nucleus. It is believed to be made of ribosomal subunits and chromatin fibers. The functions of the nucleolus are: Synthesis of all rRNA Formation of the ribosomal subunits by the joining of rRNA and proteins coming from the cytoplasm. Heterochromatin Nucleolus Euchromatin  The Endoplasmic Reticulum (ER) The ER is a net of tubes and sacs whose membranes are connected forming a continuum and are present in the entire cytoplasm. When they are associated to ribosomes they form the rough ER, and if ribosomes are not present, they form the smooth ER.  Smooth Endoplasmic Reticulum (SER) The SER is a net of tubes not associated to ribosomes.It is especially abundant in muscle cells, in steroid producing cells and in liver cells. The SER main functions are: - Synthesis, storage and transport of most cellular lipids. - Detoxification. Membrane enzymes of the smooth ER deactivate toxins from the exterior and produce soluble substances that can be excreted through the excretory system, lungs, skin, etc.  Rough Endoplasmic Reticulum (RER) The RER presents ribosomes associated to its cytosolic side. It is a net of tubes and mainly large, flat sacs. It is absent in the red blood cells of mammals. The RER main function is the modification, storage and transport of proteins. The proteins synthesized by the ribosomes will be modified inside the RER, and then sent to the Golgi apparatus. Source: http://cytochemistry.net/cell-biology/membrane.htm  Golgi Apparatus Structure: It is made of a group of round flat sacs called cisternae and associated vesicles. It is commonly situated close to the nucleus of all eukaryotic cells except in red blood cells, where it is absent. https://www.youtube.com/watch?v=rvfvRgk0MfA Golgi Apparatus: Main Function Modification, packing, transport, distribution and secretion of molecules synthesized in the RER  The lysosomes Structure: Membrane-bound vesicles with about 50 different digestive hydrolytic enzymes. Function: These enzymes are used to digest (break down) undesired molecules: old organelles, toxins, pathogens…  Centrioles The centrioles are two short cylinders made of microtubules joined together, FOUND ONLY IN ANIMAL CELLS. Their function is to organize the cytoskeleton and develop the microtubules that move the chromosomes during the process of mitosis.  Cilia and Flagella Cilia and flagella are mobile cell membrane extensions containing microtubules. Cilia are short and large in number. Their functions are to move the liquid surrounding the cell (for feeding purposes) and to move the cell in the fluid (locomotion). Flagella are long and scarce (usually one or two). They move in an undulating way. The function of the flagella is to move the cell (bacteria, protozoa and sperm cells). See them move here!  Vacuoles They are simple membrane-bound sacs in the cytoplasm. They are scarce and small in animal cells. The functions of the vacuoles in plant cells are: Structural support: vacuoles maintain the plant cells turgid. Storage of: - Water - Reserve biomolecules such as sugars and proteins. - Waste products - Pigments (produce the colors in petals) - Toxins that are dangerous for the cell if stored in the cytoplasm.  The mitochondria The function of the mitochondria is to provide the cell with energy through aerobic cell respiration, a sequence of chemical reactions that break down glucose to release energy from it.  Chloroplasts The chloroplasts are green organelles that contain the pigment chlorophyll, present in photosynthetic plant cells. Their main function is to do photosynthesis. Thylakoid Thylakoid membrane lumen The Plasma Membrane Structure: The fluid mosaic model (Singer and Nicolson, 1972) Components Components of the Plasma Membrane and their functions.  Components of the Plasma Membrane and their functions. The Phospholipid Bilayer The phospholipid bilayer is made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The lipid bilayer is selectively permeable, or semipermeable: permeable to water, CO2 and small uncharged molecules, but impermeable to most water-soluble (hydrophilic) molecules, big molecules (such as glucose), and particularly impermeable to ions (Na+, Cl-,Ca2+, etc).  Components of the Plasma Membrane and their functions. Membrane proteins: Structure Phospholipid bilayers are embedded with proteins, which may be either permanently or temporarily attached to the membrane Integral proteins are permanently attached to the membrane and are typically transmembrane (they span across the bilayer) Peripheral proteins are temporarily attached by non-covalent interactions and associate with one surface of the membrane Components of the Plasma Membrane and their functions. Glycocalyx: Structure The glycocalyx is a coating that covers the outside of many eukaryotic cells and prokaryotic cells, particularly bacteria. It is made of glycoproteins and glycolipids. In eukaryotic cells the glycocalyx can be a factor used for the recognition of the cell. On bacterial cells, the glycocalyx provides a protective coat from host factors. The carbohydrate part always remains on the outer part of the plasma membrane. Transport across the Plasma Membrane Every living cell exists in a liquid environment. The cell membrane regulates movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side. There are two main kinds of transport across the plasma membrane: Passive transport: does not require the use of energy to move substances across the membrane. Two kinds: Diffusion (Simple and Facilitated) and Osmosis Active transport: requires the use of energy to move substances across the membrane. Passive transport Occurs when there is a difference in the concentration of one particular substance on each side of the membrane. This difference is called GRADIENT. The side with the higher concentration is called Hypertonic. The side with the lower concentration is called Hypotonic.If both sides have the same concentration, they are called Isotonic, and there is an EQUILIBRIUM. NOTE: the labels are referring to the solution outside the cell (colored in blue) Particles in a solution tend to move from an area where they are more concentrated to an area where they are less concentrated. In other words, they move along, or down, the concentration gradient. This process is called diffusion. https://www.youtube.com/watch?v=cs8ud7Eh7ko Passive transport: Diffusion There are two kinds of diffusion: Simple diffusion Facilitated diffusion Simple Diffusion Occurs when the molecules do not require any help from other molecules to move across the membrane. They just move through the phospholipid bilayer. Examples: Oxygen, Carbon dioxide. https://www.youtube.com/watch?v=dPKvHrD1eS4&t=16s Facilitated Diffusion Occurs when the molecules require help from proteins (carriers) to move across the membrane. The molecules bind to the protein carriers, which change their shape to help the molecule go through the membrane. Examples: Glucose, Na+, K+. https://www.youtube.com/watch?v=IX-kLh34KcQ Osmosis Occurs when water moves passively (without using any energy) across a semipermeable membrane, from the hypotonic side to the hypertonic side, until equilibrium is reached. https://www.youtube.com/watch?v=-g-VJymtAf4 Active transport Occurs when the molecules move against the concentration gradient. There are two kinds of active transport: Through a protein pump that requires the use of energy as ATP, Bulk transport: endocytosis or exocytosis. Active transport: Pumps Pumps are integral proteins that transfer substances in and out of the cell with the help of ATP. Example: Sodium-Potassium pump. http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pu mp_works.html https://www.youtube.com/watch?v=xweYA-IJTqs https://www.youtube.com/watch?v=_bPFKDdWlCg The Sodium-Potassium Pump Bulk transport: Endocytosis and Exocytosis Processes to move large molecules, vesicles, cells, etc, from the outside to the inside of the cell (endocytosis) or from the inside to the outside of the cell (exocytosis) Endocytosis During endocytosis, the plasma membrane invaginates surrounding the particle in a vesicle, that finally pinches off inside the cell. There are two kinds of endocytosis: Phagocytosis: solid particles Pinocytosis: liquid material Exocytosis In exocytosis, materials are transported from the inside to the outside of the cell. The materials are enclosed in vesicles that fuse with the plasma membrane, releasing the contents outside of the cell. Summary of membrane transport processes: https://www.youtube.com/watch?v=BGeSDI03aaw