Biology F212 - Biological Molecules

Hydrogen bonding between δ+ Hydrogen and δ- oxygen atoms

Solvent: Ions and polar molecules. Water molecules are attracted to charged parts of molecules separating them for the rest, forming a solution eg ions for fish

Liquid: Transports ions, minerals, blood cells (plasma)

Cohesion: Water molecules stick together by hydrogen bonds - surface tension created. Pond skaters/ xylem vessels

Freezing: Water cools, density increases so sinks. Below 4˚C water becomes less dense and rises. Hydrogen bonds separate, form a semi-crystalline network that insulates water below so aquatic life survive

Thermal properties: Temp increases, molecules gain KE, hydrogen bonds break. so water requires alot of energy when changing state. This cools down the body while sweating

 

Proteins are made of 20 different amino acids.

Amine group, hydrogen atom, carboxylic acid group, R-group.

Peptide bonds join amino acids. Bonds formed by condensation and broken by hydrolysis reactions.

A dipeptide is formed when 2 amino acids join. Polypeptide is when multiple amino acids join in a chain.

Primary structure is the sequence of amino acids on a polypeptide. Determined by DNA base sequence

Secondary structure is the folding of the polypeptide chain. Hydrogen bonds form between C=O and N-H. In α-helix or β-pleated sheet

Tertiary structure is the secondary structure coiled into a complex 3d shape. Stabilised by hydrogen, disulphide, ionic, hydrophilic/phobic bonds.

Quaternary structure multiple tertiary structures together

Haemoglobin: Globular protein;

4 polypeptide chains + 4 heam groups;

Heam group – prosthetic group binds to an O₂ molecule;

Soluble die to hydrophilic R-groups outside the structure – dissolves in blood plasma

Collagen: Fibrous;

Triple helix structure;

Links between helices lined up and held by hydrogen bonds and covalent cross links;

Molecule ends staggered for tensile strength – tendons, skin, basement membrane

Soluble in water

Hexose sugars have formula c6h12o6

Can be ring or chain

Alpha glucose: oh group on c1 can form above/below the plane of the molecule. Above=beta-glucose below=alpha-glucose

Soluble in water

Produced when 2 monosaccharides join by glycosidic bond

Maltose

Formed by a condensation reaction: 2 α-glucose molecules join, removing water molecule from oh groups of c1 and c4

Split by a hydrolysis reaction: water is added to the 1-4 glycosidic bond, forming 2 α-glucose molecules. Requires enzyme maltose

Many monosaccharides joined together

Amylose - plants

Many α-glucose molecules joined by 1-4 glycosidic bonds

Amylose + amylopectin=starch

Amylose chains coil up and are bonded with amylopectin branches to make water-insoluble storage molecules

Amylose (starch)

Long chain of α-glucose molecules attached to Amylopectin branches

Coils to make a storage molecule. more energy stored in a smaller area so more molecules stored

Cellulose

Chain of β-glucose molecules linked at 180˚ to each other, forming a long straight molecule

60-70 cellulose molecules cross-linked by H bonds - form microfibrils which are grouped into fibres

Cell wall: cellulose is strong so withstands osmosis

Gycogen

found in animals instead of strach

α(1→4) glycosidic bonds linked, with α(1→6)-linked branches

branched, compact structure forms dense granules

found in the liver

stores alot of energy as the moecules are very dense

Triglycerides

3 fatty acid chains joined to a glycerol molecule via ester bonds

Ester bond: condensation reaction between carboxyl group and hydroxyl group

Phospholipids

2 fatty acids and a phosphate group joined to glycerol

Phosphate group - hydrophilic; fatty acids - hydrophobic

Important property of membrane structure

Cholesterol

Has a hydrophilic and hydrophobic region

Fits between phospholipids in cell membranes

Prevents membrane becoming too fluid and leakage of ions across the membrane

Makes steroid hormones

Derivative of bile acids - important for digestion

Protein: Add to biuret reagent. Lilac solution forms

reducing sugar: Add to Benedicts and heat (100deg.) Brick-red precipitate forms

non-reducing sugar: Add dilute HCl. shake and heat (100deg.). Cool and add dilute NaOH, mix. Add Benadicts and heat. Brick-red precipitate forms

starch: Add iodone solution. Blue-black colour forms

lipids: Add to ethanol and shake to dissolve. Ad cold water, emulsion forms on surface