The Nature of a Cell A cell is a compartment containing a variety of controlled chemical reactions. All organisms are made of cells. Intracellular Aqueous Environment Extracellular Aqueous Environment Cell Boundary Insoluble and Semi-permeable
The Tasks of a Cells Take in small molecules Produce useful products for export Make specific biomacromolecules Control and regulate chemical reactions Produce energy to drive chemical reactions Receive and respond to chemical signals Remove waste products Grow, reproduce and pass on genetic information to the next generation of cells. The Nature of a Cell
The Needs of a Cell Chemical processes involve the interaction of atoms and molecules Atoms and molecules need to move into, and around, the cell in order to reach their specific site of activity. Atoms and molecules must be present in adequate concentrations if chemical reactions are going to occur at the right rate. Cell structure must * facilitate these movements * and maintain adequate concentrations so that reactions can occur and the cell can function. The Nature of a Cell
Size and Shape Matters The surface area of a cell must provide enough exposure to the extracellular environment to allow sufficient movement of the molecules and atoms necessary for its function. l = 10, w = 10, h = 10 l = 100, w = 10, h = 1 l = 1 w = 1, h = 1 Surface Area = 600 Surface Area = 2200 Surface Area = 6 Volume = 1000 Volume = 1000 Volume = 1 SA:V = 0.6 SA:V = 2.2 SA:V = 6 Think about: Think about: Think about: the size of eukaryotic cells the shape of ER the size of a prokaryotic cell
Size matters Size and shape will have an effect on function as the cell strives to control and regulate complex chemical reactions. The Nature of a Cell
Prokaryotic vs Eukaryotic Cells My volume is small enough to meet the needs of my molecules I need lots of internal membranes and compartments to meet the needs of molecules Eubacteria and Archaebacteria lacks internal compartments. These cells are less than 2μm in diameter Animal, plants and fungi have cells from 10μm+ in diameter. They meet their needs by being full of compartment (organelles) that do specific tasks. The Nature of a Cell
Prokaryotic Cells The Nature of a Cell
Eukaryotic Cells (Plant) The Nature of a Cell
Eukaryotic Cells (Animal) The Nature of a Cell
Molecular Biology Molecules are groups of non-metal atoms covalently bonded together. Molecules have a polarity that is determined by their overall charge. What is important about these relationships is that Nonpolar molecules * have no overall charge * are hydrophobic Polar Molecules * have regions of positive and negative charge * are hydrophilic Molecular Biology: Bonding Polarity
Non-Polar Molecules: Hydrogen Gas Nonmetal atoms form covalent bonds by sharing electrons. The electrostatic forces of attraction between the positive nucleus and the negative electrons hold this arrangement together. The electron attracting power of each atom (electronegativity) determines how equally the electrons are shared. These hydrogen atoms have the same electronegativity- the electron pair will be shared equally, leaving the molecule nonpolar and hydrophobic. Molecular Biology: Bonding Polarity
Polar Molecules: Water Because of the unequal sharing of electrons, water is a polar molecule. As an oxygen atom I have very high electronegativity so I can hold the electrons closer and become slightly negative! We hydrogen atoms cannot compete with oxygen's pulling power for electrons. As a result we are always slightly postive. Molecular Biology: Bonding Polarity
Intermolecular Attraction The slight opposite charges on different regions of a water molecule lead to a weak bonding between the molecules. This is called dipole-dipole bonding; or more specifically in this case hydrogen bonding. Thus, there is a weak attraction between polar molecules. Molecular Biology: Intermolecular Attraction
Biomolecules: The Main Elements C H S The main elements that make up biomolecules. All are nonmetals and all are able to bond together by sharing outer shell electrons. O Sometimes the sharing is uneven. P N Molecular Biology: Basics of Biomolecules
Biomolecules: Why Carbon? C Forms strong, stable covalent bonds with other carbon atoms and nonmetal atoms. Each carbon atom can form up to 4 single covalent bonds. They can also form double and triple bonds. C Can create chains, and other structures, by bonding to other carbon atoms. Other groups of atoms can be attached to these structres to create different compounds. C Molecular Biology: Basics of Biomolecules
Biomolecules: Hydrocarbons Hydrocarbons form the backbone of many organic molecules. Formed by bonding between hydrogen and carbon atoms these molecules can exist as branched or unbranched chains, or as ring (cyclic) structures. In this form hydrocarbons are nonpolar and hydrophobic. Molecular Biology: Basics of Biomolecules
Hydrophilic & Hydrophobic Don't Mix! Oil and Water do not mix. Stay away from us! Like oil, ethane (shown) is hydrophobic because it is made up of non-polar hydrocarbon molecules. We won't mix with you! Water is polar. Water molecules will mix with other polar molecules that have a charge (because they will be hydrophilic) I'll mix with you! We can make hydrogen bonds together! Molecular Biology: Basics of Biomolecules
Reactive Groups Sometimes a hydrogen is substituted for a different group of atoms and the molecule acquires a new chemical character. These groups are called functional groups and confer polarity on the molecule. H Main functional groups in Biology H C H H Methane OH COOH NH2 HS Methanol With an OH group substituted in the molecule is now functions as an alcohol. Molecular Biology: Basics of Biomolecules
Biomacromolecules Cells import water, mineral ions, and a host of small organic molecules like simple sugars, fatty acids and amino acids. Many other small organic molecules are made and altered in different chemical reactions in the cell. Small molecules also store and distribute energy for cellular processes and other, such as hormones, act as signals in directing the activities of the cell. Cells can only acquire biomacromolecules by making them. They are made in a condensation reaction. Breaking down these biomacromolecules occurs in a reverse process called hydrolysis. Molecular Biology: Biomacromolecules
Condensation Reactions I donate my OH group H O monomer O-H I donate a hydrogen from my OH group H O When functional groups react together a new chemical bond is formed that links the subunits. Polymer (has repeating subunits) monomer H20 monomer monomer O-H We are removed from the reactants as a water molecule monomer If a water molecule is lost, a condensation reaction is sometimes called a dehydration reaction. Biomacromolecules: Synthesis
Condensation & Hydrolysis Reactions Just as condensation reactions allow cells to build biomacromolecules by removing water......by adding water, cells are able to break down biomolecules in a process called hydrolysis. Biomacromolecules: Synthesis and Breakdown
Biomacromolecules Biomacromolecules are very large molecules that play an essential role in the structure and function of cells. Biomacromolecule Sub-units Bond Formed by Condensation Cellular Functions Lipids Lipids are not polymers Fatty Acids & Glycerol Ester linkage Energy storage, phospholipids, signalling molecules Complex carbohydrates Polysaccharides Simple sugar monomers Monosaccharides Glycosidic linkage Energy storage, structral components (eg. cellulose) Nucleic Acids Polynucleotides Nucleotide monomers Phosphodiester linkage Genetic material Proteins Polypeptides Amino Acid monomers Peptide linkage Diverse roles; control and regulation, transport, receptors, structural components Biomacromolecules: Features
Lipids Lipids do not form polymers Lipids are usually hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bonds The most biologically important lipids are fats, phospholipids, and steroids Lipids are constructed from two types of smaller molecules: glycerol and fatty acids Biomacromolecules: Lipids
Triglycerides Ester linkage A triglyceride is formed with the bonding of 3 fatty acids to a glycerol molecule. Lipids: Glycerol & Fatty Acids
Saturated and Unsaturated Fats Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats Fatty acids vary in length (no. of carbons) and in the number and locations of double bonds Saturated fatty acids have no double bonds- the maximum number of hydrogen atoms possible is attached Unsaturated fatty acids have one or more double bonds The major function of fats is energy storage Lipids: Saturated and Unsaturated Fats
Saturated Fats Fats made from saturated fatty acids are called saturated fats Most animal fats are saturated Saturated fats are solid at room temperature A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits Lipids: Saturated Fats
Unsaturated Fats Fats made from unsaturated fatty acids are called unsaturated fats Plant fats and fish fats are usually unsaturated Plant fats and fish fats are liquid at room temperature and are called oils Lipids: Unsaturated Fats
Phospholipids In a phospholipid, two fatty acids and a phosphate group are attached to glycerol The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head Lipids: Phospholipids
Phospholipid Bilayer When phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior The structure of phospholipids results in a bilayer arrangement found in cell membranes Phospholipids are the major component of all cell membranes Lipids: Phospholipids
Steroids Steroids are lipids with a carbon skeleton of four fused rings. They include cholesterol, estrogen and testosterone. Because they are non-polar and hydrophobic, steroids are soluble in fats and pass easily across the phospholipid bilayer. Cholesterol is a component in animal cell membranes Lipids: Steroids
The Plasma Membrane Why are they important? Membranes define the cell boundary and provide a permeability barrier. Membranes have sites for specific functions Membranes regulate the transport of solutes Membranes detect electrical and chemical signals Membranes assist in cell to cell communication The Plasma Membrane: Fluid Mosaic Model
The Bilayer Boundary (1) Size Permeable to small molecules such as oxygen, carbon dioxide, ethanol, water. Rate of exchange may be decreased depending on polarity. (2) Degree of Polarity Permeable to hydrophobic molecules such as steroids. (3) Charged Atoms Not permeable to large hydrophilic polar molecules (such as glucose) or charged groups of atoms and metallic ions. The Plasma Membrane
Simple Diffusion Simple diffusion is a passive process in which solutes move down a concentration gradient. Here the ink is spreading by moving to areas of lower ink solute concentration. Eventually all the water will be evenly coloured. Animation: Simple Diffusion The Plasma Membrane: Transmembrane Migration
Passive Facilitated Diffusion Membrane proteins can assist the diffusion process Polar, charged ions may cross the membrane through channel proteins. Larger polar molecules may cross via carrier proteins. Transmembrane Migration: Passive Facilitated Diffusion
Active Transport Some membrane proteins can help a cell to push solutes against the concentration gradient. These are often called pumps and require energy from ATP. A sodium-potassium pump is shown here. Transmembrane Migration: Active Transport
Active Transport Why should active transport be necessary? Uptake of essential nutrients against the concentration gradient Removal of secretory and waste products against the concentration gradient Maintain ion concentrations in a steady, non-equilbrium state. Transmembrane Migration: Active Transport
Osmosis Is a special case of passive diffusion involving the migration of water molecules down a concentration gradient. Transmembrane Migration: Osmosis
Hypertonic and Hypotonic Solutions Transmembrane Migration: Osmosis
Hypertonic and Hypotonic Solutions Identify the cell types shown the process occurring the solution type in which the cells have been placed. Transmembrane Migration: Osmosis
Exocytosis & The Secretory Pathway During exocytosis a small membrane bound vesicle will fuse with the cell membrane and expel it contents into the extracellular space. This is a form of bulk transport and is especially important for the secretion of biomacromolecules such as hormones, antibody, neurotransmitters, mucous, growth regulators and even toxins. Transmembrane Migration: Bulk Transport
Endoplasmic Reticulm ER is a series of folded membranes and tubules that extend out continuously from the nucleus Rough ER is studded with ribosomes. Cytosolic ribosomes will bind to the ER once it begins to synthesize a protein destined for the secretory pathway The rough ER will then send these products the Golgi body in small vesicles. Exocytosis & The Secretory Pathway: Endoplasmic Reticulum
Endoplasmic Reticulm Smooth ER is free of ribosomes Smooth ER is the site of lipid and steroid synthesis (inc. phospholipids and cholesterol) synthesis and metabolism of some carbohydrates drug and poison detoxification regulation of calcium concentration Exocytosis & The Secretory Pathway: Endoplasmic Reticulum
Golgi Body The Golgi body is a series of flat membrane compartments resembling tubes Proteins and lipids manufactured on the ER may be chemically modified (often by adding carbohydrate groups to form glycoproteins and glycolipids) These biomacromolecules are packaged into transport vesicles bound for the surface. Exocytosis & The Secretory Pathway: Golgi Body
Secretory Pathway: Overview From p61 Nelson Biology Exocytosis & The Secretory Pathway
Endocytosis During endocytosis, the plasma membrane sinks inward and engulfs the extracellular space. It encloses the material within to form an endocytic vesicles which transport the contents within the cytoplasm. If solids are engulfed it is phagocytosis If liquid is engulfed it is pinocytosis Phagocytosis Pinocytosis Endocytosis: Bulk Transport
Lysosomes Solids that are engulfed are digested by in vesicular structures called lysosomes. Lysosomes fuse with the membranes of old organelles or the membranes created by phagocytosis and endocytosis. They empty their enzymes into the space and breakdown the molecules. Lysosomes recycle cellular materials and offer protection. Endocytosis: Lysosomes
Additional Membrane Proteins The Plasma Membrane: Membrane Proteins
Additional Membrane Proteins Receptor proteins are important for cell signalling. Recognition proteins allow cells to identify each other and interactidentifying the cell as self. Adhesion proteins provide binding potential between the cells of multicellular organisms The Plasma Membrane: Membrane Proteins
The Plasma Membrane Lipids provide fluidity to the cell membrane. Proteins and cholesterol molecules are embedded in the membrane creating a mosaic. This is the fluid mosaic model of the plasma membrane. The Plasma Membrane: Fluid Mosaic Model
The Cell Cytoskeleton What were those funny worm things?! Eukaryotes have a network of protein fibres in the cytosol. Microtubules: Movement of chromosomes, organelles, cilia, flagella Intermediate Filaments: Adds tensile strength to maintain tissue shape and attachment of cells to each other. Microfilaments: Muscle contraction, maintenance of cell shape, cellular movements. When a white blood cell squeezes between the cell junction of a blood vessel it is the cytoskeleton that provides flexibility and returns the cell to its original shape. The Cell Cytoskeleton
The Extracellular Matrix The extracellular matrix (ECM) determines the shape and mechanical properties of tissues and organs. Bone and cartilage are largely composed of ECM material. The Extracellular Matrix