2.2 Biological molecules Flashcards
Elements in carbohydrates, lipids, proteins and nucleic acids
CHO and OH – carbohydrates, lipids, + NS for proteins, + NP for nucleic acids
Role of lipids
thermal insulation, energy store, protection, component of cell membranes/phospholipid bilayer, steroid hormones, buoyancy, waterproofing, source of water from respiration, electrical insulation as forms myelin sheath around neurones, aid production of vitamins
Role of cholestrol and why RBCs have more
regulates fluidity of phospholipid bilayer/supports structure of membranes, converted in steroid, waterproofing the skin, making vitamin D, making bile
* RBCs have more cholesterol because they are free in the blood / not supported by other cells, so cholesterol helps to maintain shape
Role of mRNA
carries the copy of the gene
Role of glucose
respiratory substrate / used in respiration, source of energy, formation of ATP
Why glycogen is a good storage molecule
- Insoluble so it doesn’t change the water potential of a cell
- Can be broken down / hydrolysed quickly: lots of branches for enzymes to attach
- Compact = high energy content for mass / energy dense
Ways glucose molecule is well suited to its function
- Soluble so can be easily transported around organism
- Small so can be transported / diffused across cell membranes
- Easily / quickly respired / broken down to release energy / produce ATP
- Molecules can join to produce di / polysaccharides
Ways starch suited for its function
- Helical so compact
- Insoluble so doesn’t affect water potential
- Large molecule so doesn’t leave cell
Cellulose and chitin structure
- Cellulose: long straight chains is linked together by many H- bonds to form fibrils provide strength
- Chitin: glycosidic bonds between glucose monomers formed by condensation, produces water. Long straight chains with H bonding. Alternative monomers are flipped - like cellulose
Saccharides and the polysaccharides they form
- Alpha glucose (x2) = maltose
- Alpha glucose + beta fructose = sucrose
- Glucose + galactose = lactose
- Amylose: alpha glucose 1,4 and amylopectin: alpha glucose 1,4 and 1,6 every 25 glucose subunits. Forms starch (plants), glycogen (in animals and fungi)
Condensation to form glycosidic bonds
Protein structure
- Peptide bond: between H from the amine group and OH from the carboxyl group, condensation reaction so water is lost / produced –> covalent bond, opposite = hydrolysis (catalysed by peptidyl transferase)
- Primary: sequence of amino acids joined by peptide bonds
- Secondary: H bonds between NH group and C=O group of 2 amino acids –> α helix / β-pleated sheets
- Tertiary: secondary structure undergoes further coiling / folding, 3D shapes
- R groups attract/repel, disulfide bonds between cysteine atoms, H bonds, ionic bonds between oppositely charged R groups, hydrophilic / hydrophobic interactions
- Quaternary: arrangement of 2(+) polypeptide chains in a protein
Simple vs conjugated protein
- Contains non-protein groups, has prosthetic group which is attached by covalent bonds / ionic interactions / H-bonds
- Prosthetic group is required for the protein to be functional
Structure of a collagen (+keratin/elastin) molecule
- Peptide bonds between amino acids to form 3 polypeptide chains that are coiled into a left-handed helix. Every 3rd amino acid is glycine (small R group) allowing the closeness of polypeptide chains. H bonds between polypeptide chains to form fibrils
- Adjacent molecules are joined by crosslinks, crosslinks / end of molecules is staggered = high mechanical strength
- Few hydrophilic R groups on the outside
- Properties: strong, has structural role, forms parts of cartilage / connective tissue
- Found in ligaments: strong, not elastic, insoluble, unreactive, and flexible
Haemoglobin structure
- Spherical - globular protein
- Hydrophilic R groups on outside, forms H-bonds with water, soluble
- Contains prosthetic group: haem / Fe2+ which allows oxygen to be carried. Polypeptide chains within haemoglobin have 3o structure. 2 alpha and 2 beta subunits – 1 haem group per polypeptide / 4 per molecule
Haemoglobin and collagen structure (similarities and differences)
- Similarities: amino acid chain, peptide bonds, helical, 4o structure: 1+ polypeptide, H-bonds…
- Differences: haemoglobin is globular, hydrophilic R groups on outside, 2 alpha and 2 beta chains, alpha helix (?)
Fibrous proteins - keratin: structure and properties
- In hair, skin, and nails – contains lots of cysteine so forms strong disulfide bridges (more in nails so less flexible)
- Properties: strong, inflexible, insoluble, mechanical protection, impermeable barrier to infection, waterproof
Fibrous proteins - actin/myosin: function
in muscle for contraction / mechanical movement + found in microtubules in cilia / flagella / spindle / cytoskeleton
Fibrous proteins - fibrin: role
involved in formation of blood clots
Fibrous proteins - elastin: structure and properties
- Found in walls of blood vessels and alveoli in lungs
- Quaternary structure: made of many soluble, stretchy tropoelastin molecules –> v. large, insoluble, and stable cross-linked structure
- Oroperties: strong and elastic / flexible (can stretch and recoil w/o breaking)
Globular proteins - properties
specific / complementary to another molecule, pH / temp sensitive
Globular proteins - enzyme example
pepsin: 1 polypeptide chain folded into tertiary structure with many acidic R groups, soluble (hydrophilic R groups on outside), specific 3D shape to form AS
Globular proteins - hormone example
insulin: hormone = globular protein with chain a and b, soluble, specific shape to bind to specific receptors on muscle, fat and liver cells to increase glucose uptake, hormone to lower blood glucose conc
Alpha and beta glucose structure
Chemical test for reducing sugars
- Add Benedict’s reagent and heat. Forms precipitate – colour changes from blue to red
- Estimate the concentration: use different colours and compare with standard solutions OR filter, centrifuge and weigh precipitate and greater mass = more sugar present
