Introduction to the Cell - PDF

An Introduction to Cells - definitions A cell is surrounded by a watery medium known as the extracellular fluid = interstitial fluid = thin layer of fluid that bathes the external surface of a cell. Cytosol - intracellular fluid = surrounds the organelles Plasma membrane separates cytoplasm...

An Introduction to Cells - definitions A cell is surrounded by a watery medium known as the extracellular fluid = interstitial fluid = thin layer of fluid that bathes the external surface of a cell. Cytosol - intracellular fluid = surrounds the organelles Plasma membrane separates cytoplasm from the extracellular fluid/interstitial fluid Cytoplasm = Cytosol plus organelles inside a cell. Cyto = cell The Anatomy of a Model Cell Plasma Membrane Functions of the Plasma Membrane 1) Physical isolation 2) Regulates exchange with environment Ions and nutrients enter Wastes eliminated and cellular products released 3) Monitors the environment Extracellular fluid composition Chemical signals 4) Structural support Anchors cells and tissues The Cytoskeleton The Cytoskeleton = network of protein filaments Microfilaments = thin filaments composed of the protein actin Provide additional mechanical strength Pair with thick filaments of myosin for muscle movement Intermediate filaments = mid-sized between microfilaments and thick filaments = durable = composed of the protein collagen Strengthen cell and maintain shape; Stabilize organelles and cell position The Cytoskeleton cont… Microtubules = large, hollow tubes of tubulin protein Strengthen cell and anchor organelles Change cell shape Move vesicles within cell Centrioles, Cilia, and Flagella = also made of microtubules Microvilli, Centrioles, and Cilia Microvilli = Increase surface area for absorption = small intestine = help to absorb nutrients = contain protein actin = microfilaments Centrioles = form spindle apparatus during cell division. Are bundles of microtubules. Cilia = Small hair-like extensions that beat rhythmically back and forth. Formed from microtubules. Cilia move fluids across the cell surface. Important in trachea to remove debris, pathogens. Flagellum: tail-like projection (microtubules) that protrudes from the cell body and functions in locomotion. Flu virus among cilia. Graphic by NatGeo Ribosomes and Proteasomes Ribosomes = Build polypeptides during protein synthesis Two types Free ribosomes in cytoplasm Fixed ribosomes attached to Endoplasmic reticulum Proteasomes = continuously destroy unneeded, damaged, or faulty proteins, found in the cytosol and the nucleus = contain enzymes = proteases Endoplasmic reticulum (ER) Smooth endoplasmic reticulum (SER) = No ribosomes attached Is involved in the production of lipids, carbohydrate metabolism, and detoxification of drugs. Lots in liver Rough endoplasmic reticulum (RER) = Surface covered with ribosomes active in protein and glycoprotein synthesis Golgi apparatus Golgi = packages macromolecules (proteins and lipids) into vesicles after their synthesis and before they make their way to their destination. Vesicles = circular “bags” that contain stuff = can hormones, wastes Types of vesicles: Secretory vesicles - modify and package products for exocytosis Membrane renewal vesicles - add or remove membrane components Lysosomes - Powerful enzyme-containing vesicles = carry enzymes to cytosol. lyso- = dissolve, soma = body Golgi apparatus More about lysosomes Clean up inside cells Break down large molecules Attack bacteria = part of immune system Recycle damaged organelles Eject wastes by exocytosis Autolysis = cell death when cell stops functioning properly Auto- = self, lysis = break Self-destruction of damaged cells by lysosomes Apoptosis = programmed cell destruction Autolysis versus Apoptosis Autolysis Apoptosis Destruction of a cell via lysosomes Programmed cell death involving an ordered sequence of events It is unintentional It is intentional = planned Does not happen in healthy tissues Happens in healthy tissues and cells and cells Not a controlled process A controlled process Occurs in response to injury or Occurs in all tissues; Plays a key role infection in the development of the organism; important for the normal process of cell ageing Peroxisomes Peroxisomes = use oxygen to catalytically detoxify and break down fatty acids. Detoxify toxic substances such as alcohol. Why are peroxisomes important? Adrenoleukodystrophy (ALD) is a rare genetic condition that causes the buildup of very long chain fatty acids (VLCFAs) in the brain. When VLCFAs accumulate, they destroy the protective myelin sheath around nerve cells, responsible for brain function. Mitochondria and ATP Mitochondrion takes chemical energy from food (glucose): produces energy molecule ATP Aerobic metabolism (cellular respiration) Mitochondria use oxygen to break down food and produce ATP glucose + oxygen + ADP → carbon dioxide + water + ATP Glycolysis: glucose to pyruvic acid = in cytosol = anaerobic = don’t need O2 here Krebs cycle or Tricarboxylic acid cycle (TCA cycle): in mitochondrial matrix = CO2 is produced here Electron transport chain: inner mitochondrial membrane Summary: Glycolysis, Krebs cycle, and the ETC Glycolysis = anaerobic = no O2 needed = in cytosol Converts glucose to pyruvate (pyruvic acid) Net gain of 2 ATP, 2 NADH and 2 H+ If no O2 available will convert the pyruvate to lactic acid with net yield of 2 ATP If O2 is available will proceed to Krebs cycle The Krebs cycle = Function: To remove hydrogen atoms from organic molecules and transfer them to coenzymes CO2 is a waste product = this is why you must exhale Products: 4 CO2, 2 ATP, 6 NADH + 6 H+, 2 FADH2. Oxidative Phosphorylation and the Electron transport chain (ETC) = aerobic = use/need O2 Is the generation of ATP within mitochondria Requires coenzymes and oxygen. Need O2 = this is why you inhale = final electron acceptor Results in 2 H2 + O2 → 2 H2O = metabolic water The Nucleus The cell’s control center Nuclear pores = Communication passages Nucleoplasm = Fluid containing ions, enzymes, nucleotides and some RNA Nucleolus = found within the nucleus. The central location for the production of ribosomes. Protein Synthesis The nucleus contains chromosomes → Chromosomes contain DNA → DNA stores genetic instructions for proteins → Proteins determine cell structure and function 1. Transcription = Copies instructions from DNA to mRNA = in nucleus 2. Translation = Ribosome reads code from mRNA = in cytoplasm Assembles amino acids into polypeptide chain 3. Processing = By RER and Golgi apparatus produce protein Summary: Organelles Membrane Transport The plasma (cell) membrane is a barrier, but Nutrients must get in Products and wastes must get out Permeability determines what moves in and out of a cell Lets nothing in or out = impermeable Lets anything pass = freely permeable Restricts movement = selectively permeable Plasma membrane is selectively permeable Selective permeability restricts materials based on Size, Electrical charge, Molecular shape and Lipid solubility = measure on how easily something can cross. Summary: Membrane Transport Membrane transport Passive = no ATP needed Active = need ATP Membrane Transport – Simple diffusion Diffusion Lipid-soluble molecules (alcohol, CO2) = all hydrophobic stuff No specific transporters are needed No energy is needed = no ATP needed Depends on gradients and will seek equilibrium High → low and seek equilibrium Steeper gradient results in higher rates Gradients can be chemical, electrical or both depending on the nature of the molecule Factors affecting diffusion Distance the particle has to move Molecule size - Smaller is faster Temperature - More heat, faster motion Gradient size - The difference between high and low concentrations Electrical forces - Opposites attract, like charges repel = electrochemical gradients Lipid solubility = how easily something can pass Diffusion Membrane Transport – Facilitated diffusion Facilitated diffusion Facilitated diffusion = Materials that pass through transmembrane proteins = Passive = No energy is needed = no ATP needed Hydrophilic molecules = are water–soluble compounds, ions Depends on: size, charge and interaction with channel Depends on gradients but need transmembrane protein Substances are limited by number of channels/transporters Membrane Transport – Facilitated diffusion Membrane Transport – Facilitated diffusion Membrane Transport - Osmosis Osmosis: Movement of water Osmosis is the movement of water across the cell membrane = towards higher solute concentration More solute molecules, lower concentration of water molecules Membrane must be freely permeable to water Osmosis: Movement of water Osmolarity and Tonicity Osmolarity: The measure of total concentration of solute particles in a solution Tonicity: The ability of a solution to cause a cell to shrink or swell Isotonic solution Hypertonic solution Hypotonic solution Membrane Transport – Active Transport Active transport Active transport proteins = against gradients Sodium (Na+), potassium (K+) ATPase/pump (NKA). An enzyme that moves ions via hydrolysis of ATP Why are Na+ and K+ moved against their gradients? Maintains resting potential/charge of cells Moves 3 Na+ out of the cell and 2 K+ into the cell Extracellular fluid Na+ Na+/K+ ATPase 3 Na+ expelled 2K+ gradient 3 Na+ P Cytosol K+ 1 ATP 2 3 4 2 K+ ADP P gradient imported Membrane Transport – Secondary active transport Membrane Transport – Vesicular transport Vesicular Transport or bulk transport Materials move into or out of cell in vesicles = a small spherical sac = move big stuff Endocytosis (endo- = inside) is active transport using ATP = materials move into a cell in a vesicle formed from the plasma membrane. o Pinocytosis = Endosomes “drink” extracellular fluid o Phagocytosis = engulf large objects in phagosomes o Receptor mediated endocytosis = brings in substances such as vitamins, antibiotics, Low density lipoproteins which bring cholesterol to cells – bad cholesterol Exocytosis (exo- = outside) = Granules or droplets are released from the cell = such as proteins, hormones, other chemical messengers Vesicular Transport or bulk transport Summary of Passive Processes Process Energy Example Source Simple Kinetic O2, CO2, Ethanol, NO diffusion energy Facilitated Kinetic Ions, Glucose, Amino acids diffusion energy Osmosis Kinetic H2O energy Summary of Active Processes Process Energy Source Example Primary active transport ATP Na+, K+ ATPase = 3 Na+ out, 2 K+ in against gradient Secondary Active ATP Glucose absorption in the small transport intestine Exocytosis ATP Expel from cell = big stuff like proteins, hormones Phagocytosis ATP Part of immune system Pinocytosis ATP Absorption by intestinal cells Receptor-mediated ATP LDL, antibiotics, vitamins endocytosis Questions reviewing concepts You should answer these questions using simple terms and/or drawing pictures to illustrate what happens. What is the function of lysosomes? What is the net gain of glycolysis? What byproduct during the Krebs cycle can affect pH? Why? Which substances can easily enter cells by simple diffusion? What is the difference between simple diffusion and facilitated diffusion? What is similar? What factors increase the rate of diffusion? What is osmotic pressure? Define isotonic, hypertonic and hypotonic solutions. What are their effects on cells? Why? Draw pictures Define active transport. When do we use active transport? What is vesicular transport? What is the difference between exocytosis and endocytosis?