Biomolecules Flashcards
What’s the difference between an aldo group and keto group?
Aldo: C=O at beginning of C skeleton
Keto: C=O within C skeleton
What’s the difference between alpha and beta glucose?
α-glucose: -OH grp attached to C1 below plane of the ring
β-glucose: -OH grp attached to C1 above plane of the ring
Describe the structure and properties of glucose.
- Small size + many polar hydroxyl grps (-OH) which forms H bonds w water⇒ readily soluble in water (easily transported)
- Linear forms has a free carbonyl grp (C=O) ⇒all reducing sugars
- Pentose and hexose exists as rings⇒ rings are stable building blocks for larger mlcs (not impt pt)
- Ring struc exhibit α & β isomerism⇒ ↑ diversity of
monosaccharides, building blocks for diff mlcs
Describe how maltose –> glucose + glucose
- maltose–> 2 α glucose
- maltase
- α(1-4) glycosidic bond
- hydrolysis
- H2O
Describe the procedure for the Benedict’s test.
Equal vol of sample + benedict’s solution
Shake
Boiling water bath for 3-4 min
Describe the procedure for the test for non-reducing sugars.
- -ve benedict’s test
- Boil equal vol of test soln + dilute HCl for abt 1 min→ hydrolyses disaccharide to monosaccharide
- Cool contents of tube
- Neutralise acidic content w sodium bicarbonate soln
- Carry out Benedict’s test for reducing sugar
Compare the structure and function of starch (amylose, amylopectin), glycogen and cellulose: monomers + no. of units
- (all) Large mlc–> insoluble, won’t affect wp of cell
- starch and glycogen made up of a-glucose, while cellulose is made up of b-glucose
- starch and and glycogen is made up of thousands of glucose mlcs–> large energy store–> hydrolysed ultimately to glucose for aerobic respiration for ATP
Compare the structure and function of starch (amylose, amylopectin), glycogen and cellulose: bond
α(1-4) glycosidic bonds: allow α-glucose monomers to be packed into a helical coil within a branch
(amylopectin & glycogen) α(1-6) glycosidic bonds: links the α-glucose monomer at branch points→ branched helical structure
Bonds are all between α-glucose
- Enzymes that hydrolyse these bonds commonly available. Glucose readily released for respiration
- helical–> compact molecule, more glucose units packed per unit volume
Cellulose has 𝛽(1-4) glycosidic bonds between 𝛽-glucose–> Cellulase found in v few organisms → cellulose X hydrolysed and used as a respiratory substrate
Compare the structure and function of starch (amylose, amylopectin), glycogen and cellulose: monomer orientation & shape
All with same orientation.
Helical coil: α(1-4) glycosidic bonds, each residue bent in one direction w respect to the previous residue
- Intramolecular bonding by OH grps & OH grps project into core of helix formation→ relatively fewer OH groups available H bonding with water, insoluble in water & will not affect wp
- compact mlc, pack many glucose units per unit volume for storage
Alternate 𝛽-glucose monomers rotated 180° wrt each other→ forms long, linear, unbranched mlc w OH grps projecting out in both directions, which can form intermolecular H bond w OH grps of other adjacent cellulose mlcs lying // to it→ form microfibrils with high tensile strength
Only sf of microfibril exposed to water + most OH grps involved in interchain H bonding w other OH grps→ relatively fewer OH grps available for H bonding w water + large molecule
- insoluble
Compare the structure and function of starch (amylose, amylopectin), glycogen and cellulose: branching
amylose: unbranched
amylopectin: branched
glycogen: extensively branched
- compact
- more branch ends to allow multiple hydrolytic enzymes to work on at the same time→ more glucose mlcs released rapidly at the same time→ ↑ ATP generation by respiration per unit time
cellulose: unbranched
Why is cellulose synthesised in the cell sf membrane?
- Cellulose is a macromolecule (too large) + insoluble in hydrophobic core of p.lipid bilayer→ can’t pass through cell sf membrane if it needs to be transported to the cell exterior
- Cellulose is a macromolecule found outside the cell as part of the cell wall→ easier to just deposit it there (closer proximity)
Mesh work of criss-crossing microfibrils form cellulose cell wall. What properties of the cell wall does this result in?
Porous struc: gaps between microfibrils→ freely permeable to water and solutes; allows free movement of substances in and out of the cell
Strong & rigid substance: meshwork distributes stresses in all directions→ enclose plant cells, protecting them from physical damage and bursting due to osmotic stress
What’s the difference between saturated and unsaturated fatty acids?
- saturated: only C-C single bonds & C-H bonds; linear chain
- unsaturated: 1 or more C=C cis double bonds → kink in HC chain
Describe the formation of an ester bond.
- between -OH and -COOH
- condensation rxn, one water mlc is removed for each fatty acid joined to the glycerol
Describe the structure and property of triglycerides.
Structure: 3 long, non-polar, hydrophobic HC chains/ fatty acid tails joined to a glycerol backbone via ester linkages
Property: non-polar
Describe the role of triglycerides in living organisms
- Suitable for energy storage
- Cannot form H bonds w water→ insoluble, does not affect wp & won’t be easily transported out of the cell
- For an equivalent mass of carbs, triglycerides release x2 as much energy→ compact energy store
> Less oxidised than carb→ yield more energy upon oxidation
> Higher proportion of C and H atoms & C-H bonds, which releases energy in the form of ATP during oxidation→ undergo more oxidation events (need more O2 per gram of for oxidation) - Highly reduced, produce more metabolic water per unit mass (compared to carbs) when oxidised during respiration
- Protective layer around delicate internal organs; act as shock absorber, protect from mechanical damage
- Thermal insulation by fat beneath layer of skin, for mammals in cooler climates
- Less dense than water→ Improve buoyancy in marine mammals
- Reservoir for storage of fat soluble vitamins eg A, D
Describe the structure of phospholipids.
glycerol backbone + 2 long, non-polar, hydrophobic HC tails via ester linkages + 1 -vely charged phosphate grp via phosphoester linkage. Additional small mlcs, e.g. nitrogen containing choline, may be present
Describe the ethanol emulsion test for solid and liquid samples.
Solution: 2cm3 ethanol + 2 drops sample–> mix & stand for 2 min–> decant ethanol into 2cm3 water
Solid: 2cm3 ethanol + grounded sample–> mix well to dissolve any lipids if its present. Stand for 2 min–> Decant ethanol into 2cm3 of water
Describe the structure of amino acids.
α-carbon atom bonded to 4 groups→ H atom, amino group (NH2), carboxyl group (COOH), variable R group
Describe properties of amino acids
- Classified according to their R groups as hydrophobic/non-polar or hydrophilic
- Exist as zwitterions: carry both +ve and -ve charges
- NH2 receives H+ → +vely charged NH3+
- COOH dissociates, releasing H+ → -vely charged -COO– - Act as buffers, due to being amphoteric: can donate or accept H+ to act as acid or base
- Basic: NH3+ loses H+, which neutralises OH– to form H2O
- Acidic: COO– accept H+ & becomes COOH
- OH- and H+ removed from solution→ minimise changes in pH of surrounding when a small amt of acid or alkali is added; buffer
Describe the formation of a peptide bond
condensation, remove water mlc
between aa
Define: primary structure
no. and sequence of amino acids in a single polypeptide chain
What bonds maintain primary struc?
peptide bonds between successive aa
Define: secondary structure
regular coiling or pleating of a single polypeptide chain
What bonds maintain secondary structure?
H bonds between C=O and N-H groups of polypeptide backbone
Compare structure of a-helix and b-pleated sheet.
Coiled/Spiral shape vs flat-sheet like structure
H bonds formed between C=O group of one aa residue and N-H group of another aa residue:
four aa away VS between adj segments lying side by side of a single polypeptide chain
Coil occurs only in a single direction vs aa in one segment run in same direction or opposite direction relative to another segment
Define tertiary structure
further extensive folding & bending of a single polypeptide chain, usually forming a compact, globular molecule, giving rise to specific conformation of protein
Define quarternary structure
association of 2 or more polypeptide chains/subunits into 1 functional protein molecule
Describe the 4 interactions that hold tertiary/quaternary structure tgt
H bonds between polar R groups w OH, C=O or N-H
ionic bonds: between opp charged R grps of aa
disulfide bonds: between 2 R grps w S (eg cysteine) by oxidation of sulfydryl (-SH) grps
hydrophobic interactions: between non-polar, hydrophobic R grps
Compare fibrous and globular proteins.
Shape: polypeptides folding/forming long, straight fibres vs roughly spherical shape
Solubility: insoluble (large, extensive H bonds alrdy between aa) vs soluble (hydrophilic R grps/aa on exterior of proteins, form H bond w water)
Variation:
- less/more variety of aa used to construct protein–> has/dh regular structure w regular repetitive aa seq
- length of polypeptide and seq of aa varies/identical between 2 samples of the same protein–> protein still functional/else it won’t be functional
Function: structural vs metabolic role
Describe the structure and function of haemoglobin.
- Globular in shape
- quarternary struc w 4 subunits: 2 a-globin and 2 b-globin subunits. each subunit has a haem group w Fe2+ that binds reversibly with O2 ==> 1 Hb mlc carries up to 4 O2 at the same time
- weak intermlc interactions between R grps of subunits that are easily broken==> Allows movement of subunits wrt each other, change in position that influences affinity for O2→ allow cooperative binding of O2: binding of 1 O2 to 1 subunit→ conformation change in remaining 3 subunits so their affinity for O2 ↑
- Each subunit arranged such that aa with hydrophilic R groups found on the exterior of the protein; aa with non-polar, hydrophobic R groups buried in interior of protein, away from aq surrounding==> soluble, transported in blood
Describe the structure and function of collagen.
- 3 helical polypeptide chains wound around each other like a rope to form 1 tropocollagen molecule⇒ high tensile strength
- Each chain usually contains a repeating tripeptide seq: glycine-X-Y, where X is usually proline, Y is usually hydroxyproline
- bulky, inflexible proline and hydroxyproline ⇒ rigidity of molecule
- Glycine, smallest aa, every third residue→ fit into restricted space in center of triple helix→ form very tight, compact triple helical structure⇒ high tensile strength - Extensive/numerous H bonds between aa residues of adjacent polypeptide chains ⇒high tensile strength; interaction w water molecules are limited→ insoluble
- Staggered arrangement of collagen mlcs within fibril (longitudinal displacement) ⇒ minimises point of weakness along length of fibrils
- Covalent cross-links between lysine residues at C and N ends of adjacent tropocollagen mlcs to form fibrils ⇒ greatly increase tensile strength
- Many collagen fibrils lie in parallel, bundle to form collagen fibres ⇒ high tensile strength; large, insoluble
Describe the biuret test for proteins
2cm3 test soln + equal vol 5% KOH soln
Shake
Add 2 drops of 1% copper(II) sulphate soln, shaking well after each drop
What is denaturation?
Loss of 3D conf of protein mlc, due to disruption of interactions that maintain secondary or higher lvl of structure –> lose function
