Cell Structure and Function 1 Cellular & Molecular Biology F2024 PDF

Cellular & Molecular Biology MD105 Dr C. Michaeloudes Cell structure and function 1 Dr C. Michaeloudes Cellular & Molecular Biology MD105  Lecture Objectives To understand: What is a cell and its basic functions The main chemical components of cells...

Cellular & Molecular Biology MD105 Dr C. Michaeloudes Cell structure and function 1 Dr C. Michaeloudes Cellular & Molecular Biology MD105  Lecture Objectives To understand: What is a cell and its basic functions The main chemical components of cells That cells are very diverse in terms of their morphology and function The basic differences between prokaryotic and eukaryotic cells What is a cell?  Cells are the fundamental units of life Sea urchin Mouse Seaweed Living organisms are incredibly diverse! What do they have in common? What distinguishes living from non-living matter? All living things are made of CELLS  What is a cell? A cell is the smallest unit capable of performing life functions Cells are small, membrane-enclosed units filled with a concentrated aqueous solution containing numerous chemicals Cells have the ability to generate copies of themselves by growing and then dividing in two Growth Division The main functions of a cell  Cells have 3 main jobs…. 1. To generate energy Energy is required to power all the activities of the cell Cells obtain energy from their environment o Animal cells – energy in chemical bonds in food molecules they eat o Plants – energy from sunlight 2. Synthesize proteins Proteins perform all the functions in a cell o Cell structure (skeleton), enzymes (reaction catalysts), signaling molecules and receptors (communication) 3. Make more cells Make copies of themselves by dividing Required for growth and damage repair  Cells generate energy by breaking down nutrients Mitochondrion Glucose ENERGY Fatty acids Cells break down nutrients (glucose/fatty acids) we obtain from food using oxygen to produce chemical energy in the form of adenosine triphosphate (ATP) This process occurs in structures called mitochondria The instructions for all the cell’s functions are stored in the DNA The instructions for all the cell’s functions are stored in the DNA Cells need to store their hereditary information (like computers store information on hard drive or cloud) The instructions for all the cell’s functions are stored in the DNA Deoxyribonucleic acid (DNA) o Long polymer chain made of 4 types of monomers - nucleotides Nucleotides contain 4 different nitrogenous bases o Adenine (A), Guanine (G), Thymine (T), Cytosine (C) Joined together in a linear sequence that encodes the genetic information The DNA code provides the instructions for making proteins The DNA sequence guides the synthesis of mRNA molecules - TRANSCRIPTION mRNA sequence guides the synthesis of protein molecules – TRANSLATION Cells make identical copies of themselves Cells make make copies of themselves that are genetically identical (have exactly the same DNA) To do this, cells duplicate their DNA and then divide in two Daughter cells are able to divide further producing more cells  Cells can accurately duplicate their DNA Template strand New strand New strand Parent DNA double helix Template strand Cells make accurate copies of their DNA - DNA replication The two strands of the DNA helix are pulled apart and used as templates for synthesis of complementary strands The chemical composition of cells  Chemical constituents of cells Although cells show diversity in their morphology and function, they are composed of the same chemicals, which are involved in the same types of chemical reactions Cells are composed of 6 main substances: 1. Water 2. Ions 3. Amino acids 4. Sugars Small organic molecules 5. Fatty acids 6. Nucleotides  Water Hydrogen bond Hydrogen bond Most cells, apart from fat cells, contain 70-85% water Water molecule is polar = it has uneven distribution of electrons ▪ one side of the molecule is slightly more positive or negative than the other side Water molecules are held together by hydrogen bonds ▪ Electrostatic attractions between H in one molecule and O in another Molecules that are also polar can be dissolved in water by forming hydrogen bonds Water is the medium for most of the reactions in the cell  Hydrophilic molecules δ- δ+ δ- δ+ - + Hydroxyl group Carbonyl group Carboxyl group Amino group Hydrophilic = molecules that easily dissolve in water -“Water- loving” Polar or charged (negative/positive) molecules They can form hydrogen bonds with water  Hydrophobic molecules Hydrocarbon chain Ring structures Hydrophobic = molecules that do not dissolve in water – “Water- fearing” ▪ Do not form hydrogen bonds with water Non-polar/uncharged side chains Non-polar = hydrocarbon chains and ring structures  Ions Ca2+ Calcium ions Na+ Sodium ions Mg2+ Magnesium ions PO43- Phosphate ions Atoms carrying an electrical charge, either negative (anions) or positive (cations) Provide inorganic chemicals (e.g potassium, calcium) for chemical reactions Required for key cellular control mechanisms ▪ Transmission of electrical signals in nerves and muscles Glucose Sugars Simplest forms are monosaccharides made up of carbon hydrogen and oxygen – (CH20)n, where n=3,4,5 or 6 ▪ Also called carbohydrates Monosaccharides can be linked together by glycosidic bonds to form larger carbohydrates ▪ Disaccharides - 2 monosaccharides ▪ Polysaccharides – up to thousands of monosaccharides  Sugars Glucose Glucose is a very important energy source for cells ▪ Broken down into smaller molecules through a series of metabolic reactions to release energy in the form of ATP Glycogen Glucose is stored in cells in the form of the polysaccharide glycogen ▪ Cell’s energy store ▪ Primarily in liver and skeletal muscle  Fatty acids Organic molecules that contain two distinct regions: 1. Long hydrocarbon chain (carbons and hydrogens), which is hydrophobic (does not dissolve in water) 2. A carboxyl group (-COOH), which is hydrophilic and chemically reactive Fatty acids can be broken down in the mitochondria to produce energy Almost all fatty acids use their carboxyl group to link to other molecules forming more complex lipid molecules  Lipids Organic complex molecules that are insoluble in water but soluble in non-polar organic solvents Contain long hydrocarbon chains or multiple rings Important types of lipids are : ▪ Phospholipids and cholesterol, which constitute 2% of the cell’s mass Formation of the cell membrane and intracellular membranes around organelles ▪ Triglycerides (neutral fats) The body’s main store of energy-rich nutrients that can be used wherever energy is needed Stored in the cytoplasm as lipid droplets Phospholipids and cholesterol Phospholipids Cholesterol 2 fatty acids Main constituents of cell membranes  Triglycerides Glycerol Fatty acids Triglycerides made of glycerol and three fatty acids Fatty acids can be used as sources of energy in the cell Triglycerides act as energy stores for the cell  Amino acids Amino Carboxyl group group Side chain Small organic molecules, which possess a carboxyl group (- COOH) and an amino group (-NH2) attached to a central α- carbon The α-carbon carries a specific side chain that distinguishes one amino acid from the other  Proteins Polypeptide chain Cells make polymers of amino acids by joining amino acids together in a long chain by forming peptide bonds ▪ polypeptide chain Polypeptide chain folded into a 3D Protein structure – proteins Perform most of the cell’s functions – workhorses of the cell ▪ 10-20% of cell’s mass Two types of proteins: 1. Structural proteins 2. Functional proteins  Structural proteins Long chains of proteins – filaments ▪ Actin, intermediate, microtubules Form the cytoskeleton that holds the cell together and allow the cell to move Also found outside the cell, in connective tissue, tendons and ligaments  Functional proteins Functional proteins are mainly enzymes – catalysts for specific reactions in the cell ▪ Speed up the rate of reaction Bind to specific molecules called ligands and convert them into chemically modified products ▪ This happens again and again without the enzyme changing  Nucleotides Nitrogen- containing base 5 4 1 3 2 Phosphate groups Five-carbon sugar Nucleotides consist of a 5-carbon sugar linked to a nitrogen- containing base, and one or more phosphate groups Sugar is either ribose or deoxyribose 5 different bases: adenine, thymine, uracil, cytosine, guanine Nucleotides are building blocks of nucleic acids Nucleic acids are linked by phosphodiester bonds forming long polymers called nucleic acids ▪ DNA (deoxyribose as sugar) and RNA (ribose as sugar) ▪ Storage and retrieval of biological information  Adenosine triphosphate is a carrier of energy Adenosine triphosphate (ATP) is a molecule that carries energy needed for cellular processes ▪ i.e muscle cell contraction, nerve firing ATP captures the chemical energy released from the breakdown of glucose and fatty acids ▪ Stored in the high-energy phosphate bonds Cleavage (breakage) of phosphate bonds releases large amounts of energy which can be used by the cell Small organic molecules are the building blocks of macromolecules The diversity of cells  The tree of life Three major divisions of the living world Genome analyses suggest that the first eukaryotic cell emerged after an archaeal cell engulfed a bacterium  Prokaryotic and eukaryotic cells Cells can be distinguished into prokaryotic and eukaryotic based on their morphology under a microscope Prokaryotic cells (no nucleus) Eukaryotic cells (with nucleus) Pro (before) – karyon (kernel/nucleus) Eu (good) – karyon (kernel/nucleus)  Prokaryotic cell structure Small size (0.2-2 μm) Spherical, rod-like or cork-screw shape No membrane-enclosed organelles Cell wall – tough protective coat Plasma membrane enclosing cytoplasm No nuclear compartment to house DNA – DNA found in a Unicellular organisms compartment called nucleoid ▪ Bacteria Circular DNA ▪ Archaea Divide very quickly (every 20mins)  Prokaryotic cells Live as individual cells or as loosely organized communities Survive in a large variety of ecological niches (i.e human body, ocean floor, volcanic mud) They can utilize a wide range of energy sources to survive Organic molecules (sugars, amino acids, hydrocarbons, methane) Inorganic molecules (CO2, Fe2+) Light Bacteria Archaea  Bacteria Bacteria are traditionally classified by shape (spherical, rod- shaped, spiral) Also, classified as Gram-positive or negative Gram-positive - single cell membrane and a thick cell wall/retain the Gram dye Gram-negative – two cell membrane with a thin cell membrane between them/do not retain Gram dye  Bacteria They have been around for 3.5 billion years The human body contains approximately 1014 microbes (bacteria, fungi, protozoa), primarily in the gut, mouth, skin and vagina – human flora 10X more bacterial cells than human cells in the human body Large numbers of harmless or beneficial bacteria – commensal bacteria Some bacteria cause disease – pathogenic bacteria Commensal bacteria can become pathogenic through transfer of specific genes (virulence genes) from one cell to the other  Eukaryotic cell structure Larger size (10-100μm) Contain membrane-enclosed organelles No cell wall – only cell membrane DNA enclosed in nucleus Multicellular organisms Linear DNA – multiple ▪ Animal cells strands ▪ Plant cells ▪ Fungi Cell sizes Electron microscope Electron or light microscope Light microscope 1 nm = 1x10-9 m 1 μm = 1x10-6m  Human cell diversity 30 trillion cells in the human body >200 types of cells with different morphologies and functions Different cell types have different life spans White blood cells Red blood cells Neurons Approx. 13 days Approx. 120 days Survive for a lifetime