Biology

• Biological molecules

  • Carbohydrates
  • Proteins
  • Lipids
• Carbohydrates


  • Contains hydrogen, carbon, and oxygen
  • General formula is C[x](H2O)y
  • Has three main groups – Monosaccharides, disaccharides, polysaccharides
• Monosaccharides


  • Triose – 3 carbons
  • Pentose – 5 carbons (ribose in DNA)
  • Hexose – 6 carbons (galactose, glucose, fructose)
• Determination of monosaccharides


  1. Does it have 5 carbons? Ribose

  2. Is it pentagon shape? Fructose

  3. Are -OH groups of C(1) and C(4) both above? Beta-galactose

  4. Are -OH groups of C(1) and C(4) both below? Alpha-glucose

  5. Are -OH groups of C(1) and C(4) opposite to each other? Beta glucose
• Glycosidic bonds


  Formed between molecules via condensation, broken by hydrolysis reactions
• Disaccharides


  • Maltose (2 alpha-glucose)
  • Lactose (alpha-glucose and beta-galactose)
  • Cellobiose (2 beta-glucose)
  • Sucrose (alpha glucose and beta fructose)
• Disaccharides


  • Maltose has alpha-1,4 glycosidic bond
  • Lactose has beta-1,4 glycosidic bond
  • Cellobiose has beta-1,4 glycosidic bonds, makes up cellulose
  • Sucrose has alpha-1,2 glycosidic bonds, pentagonal shape, non reducing sugar
• Polysaccharides


  • Amylopectin
  • Amylose
  • Glycogen
  • Cellulose
• Amylopectin


  • Composes 70-80% of starch
  • Made of only alpha molecules
  • Has alpha-1,4 glycosidic bonds between molecules
  • Branches off in chains, linked by alpha-1,6 glycosidic bonds
  • Terminal glucose (located at the tip of the branches) can be broke/hydrolyzed easily when required by body
• Amylose


  • Composes 10-30% of starch
  • Made of alpha-glucose molecules
  • Only has alpha-1,4 glycosidic bonds (does not branch)
  • Causes coiling into a helical shape, makes amylose impact, stabilized by hydrogen bonds
• Glycogen


  • In animals/fungi
  • Alpha-glucose monomers
  • Has both alpha-1,4 and 1,6 glycosidic bonds
  • Branches more than amylopectin
  • Insoluble, does not undergo reactions and does not change water potential
  • Compact thus stores a lot of glucose
  • Chemically inactive
• Cellulose


  • Made of beta-glucose molecules
  • Every second molecule is rotated 180 degrees
  • Has beta-1,4 glycosidic bonds
  • Very strong macromolecule, no branching
• Plant cell walls


  • 60-70 cellulose molecules
  • Microfibrils - Fibers layers in cell wall that are cross-linked
  • Fibers have very high tensile strength to withstand osmotic pressures
  • Freely permeable to allow exchange of resources
• All monosaccharides are reducing sugars
• All disaccharides are reducing sugars except for sucrose
• Proteins


  • Made up of amino acids
  • Consists of a central carbon bonded to an amino group (NH2-), a carboxylic group and a variable R group
  • Adjacent amino acids joined together by a covalent dipeptide bond, the C-N link
  • Dipeptide bond formed via condensation reaction, can be broken by hydrolysis
  • Many amino acids linked together is called polypeptide
  • Amino acids in a protein is called amino acid residue
• Protein structure


  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure
• Primary structure


  • The sequence of amino acids in a chain
• Secondary structure


  • The structure of the protein as a result of coiling/folding of chain of amino acids
  • Held together by hydrogen bonds between N-H and C=O
  • Can form alpha helix, a helical shape
  • Can for beta-pleated sheet, a loose sheetlike structure
• Tertiary structure


  • The compact/3-dimensional coiling of amino acid chain
  • Caused by the interactions between the R groups: Disulfide bonds, Ionic bonds, Hydrogen bonds, Hydrophobic interactions
• Quaternary structure


  • The 3-dimensional structure of 2+ polypeptides or a polypeptide and a prosthetic (non-protein) group
• Protein types


  • Fibrous proteins
  • Globular proteins
• Fibrous proteins


  • Form long strands
  • Insoluble/nonpolar
  • Involved in structural functions
• Globular proteins


  • Roughly spherical
  • Soluble/polar
  • Hydrophobic R group interactions cause them to orient toward the center
  • Hydrophilic R groups on outside allowing it to dissolve in water
• Hemoglobin


  • A globular protein
  • Quaternary structure of a polypeptide and a haem group
  • Carries oxygen around the body with iron, binds to oxygen
  • Quaternary structure is made up of four subunits: two alpha and two beta globin's and 4 haem groups
  • One hemoglobin can carry four oxygen MOLECULES and 8 ATOMS
  • Oxygen + hemoglobin = oxyhemoglobin, a bright red color
  • Sickle cell anemia – a disease that occurs when there is amino acid substitution, with hydrophobic R group on outside causing it to be less soluble, different amino acids will have different R group, prevents bond formation, or forms new/different bonds between R groups, causing change in structure of protein
• Collagen


  • A fibrous protein
  • Strong and flexible protein found in vertebrate connective tissue
  • Insoluble due to lengths and nonpolar R groups
  • High tensile strength due to: Polypeptide chains held tightly together in collagen molecule due to small size of glycine and hydrogen bonds between chains, Covalent bonds present holding between R groups of collagen molecules in fibril, Staggered ends of helices in fibril prevents conjoined weak points, Collagen fibers arranged so that they are in line with the force they withstand
  • Polypeptide chain is made of roughly 1000 amino acids, every 3rd amino acid is glycine so that the 3 helix chains are held closer together due to smaller size of glycine
  • Collagen molecule is the triple helix of polypeptides held together by hydrogen bonds
  • Collagen fibril is the collagen molecules arranged parallel to each other by covalent bonds
  • Collagen fiber is the arrangement of collagen fibrils in bundles, molecules are arranged in a scattered arrangement to prevent weak points
• Lipids


  • Fatty acids
  • Alcohols
  • Triglycerides
  • Phospholipids
• Fatty acids


  • Hydrocarbons with a carboxyl group
  • Usually around 15-17 carbons long
  • Can be saturated or unsaturated
  • Saturated are animal fats
  • Unsaturated are plant fats
  • Monounsaturated is when there is one C=C double bond
  • Polyunsaturated is when there are multiple C=C double bonds
  • Double bond in carbons causes hydrocarbon tail to twist, bending it at an angle
• Alcohols


  • Contains hydroxyl group(s)
  • Glycerol: 3 carbons linked to 3 hydroxyl groups
• Ester linkage


  Forms between hydroxyl and carboxyl groups, esterification is a form of condensation reaction
• Triglycerides


  • Formed by esterification, releases 3 water molecules
  • Made up of a glycerol and 3 fatty acids
  • Can have saturated or unsaturated fatty acids
  • Hydrophobic/insoluble due to long fatty acid tail
  • Soluble in organic solvents like ethanol
  • Roles: Energy storage, Metabolic water, Buoyancy, Insulation, Waterproofing, Cushioning
• Phospholipids


  • Contains two fatty acid tails, glycerol, phosphate group and a variable R group
  • It is amphipathic – has both hydrophobic and hydrophilic regions
  • Phospholipids orient themselves so that their nonpolar tails orient inwards away from watery environment, phosphate heads face outwards towards watery environment
  • The less saturated fatty acids mean less fluidity and more viscosity due to the larger gaps between each molecule that occurs when the fatty acid tilts due to double bond
  • In a cell membrane: Weak hydrophobic interactions between tails holds the bilayer together, and allows movement and fluidity, Allows compartmentalization of cell interiors from tissue, membrane bound organelles, Hydrophilic heads allow exchange of water-soluble substances and contact with tissue and fluids, Hydrophobic tails prevent free permeability of water-soluble substances across membrane, selective permeability
• Fluid mosaic membrane

  • Phospholipids are able to move around in their monolayer, bilayer can break and reform
  • Proteins in bilayer are scattered randomly similar to a mosaic
• Role of cell surface membrane

  • Acts as boundary between cytoplasm and outside environment
  • Acts as selective barrier
  • Cell to cell recognition
  • Cell signaling
  • Enzyme compartmentalization
  • Attachment for cytoskeleton
• Components of cell surface membrane

  • Phospholipids
  • Cholesterol
  • Glycoproteins/lipids
  • Proteins
• Phospholipids

  • Amphipathic molecules forms bilayers
  • Can often diffuse/move freely within their monolayer
  • Can be modified to form glycolipids by addition of carbohydrates
• Cholesterol

  • A lipid molecule
  • Hydrophilic head and hydrophobic tail
  • Fits between phospholipid, oriented in same direction
  • At low temperatures, prevents tight/rigid packing of phospholipids
  • At high temperatures, binds to phospholipids to prevent them moving apart due to their kinetic energy
• Glycolipids/glycoproteins

  • Glycolipids are lipids with a short chain oligosaccharide chain
  • Glycoprotein are proteins with a short oligosaccharide chain
  • Carbohydrate chains project into extracellular fluid away from cell
  • Can function as receptors, antigens/cell markers
  • Carbohydrate chains can fork hydrogen bonds with molecules in extracellular fluid
• Proteins

  • Globular proteins in/across/on cell membrane
  • Has many roles such as enzymes, receptors, antigens, carrier proteins, channel proteins, adhesion proteins
  • Intrinsic = embedded in cell membrane (integral)
  • Extrinsic = inner/outer surface of cell membrane (peripheral)
  • Transmembrane = span entire layer of membrane
  • Arrangement of proteins in cell membrane is determined by their hydrophobic/hydrophilic regions
  • Transport proteins can form hydrophilic channels for ions and polar molecules
  • Proteins can either float within bilayer or be immobile and fixed to another structure
• Membrane fluidity

  • Less fluid: Fatty acid tails of phospholipids are saturated, fewer cholesterol (at lower temperatures), longer fatty acid tail
  • More fluid: Fatty acid tails are unsaturated, more cholesterol (at higher temperatures), higher temperature, shorter fatty acid tails