Biology F212 - Biological Molecules

As biology flashcards of ocr f212

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Water 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


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Amino Acid

Proteins are made of 20 different amino acids.

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


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Peptide bonds

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.


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Protein structure

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

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Types of protein

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

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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


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Soluble in water

Produced when 2 monosaccharides join by glycosidic bond


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


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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


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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


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

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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

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Lipids - Triglycerides


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

Ester bond: condensation reaction between carboxyl group and hydroxyl group


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Lipids - Phospholipids


2 fatty acids and a phosphate group joined to glycerol

Phosphate group - hydrophilic; fatty acids - hydrophobic

Important property of membrane structure


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Lipids - 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

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Chemical tests

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

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Chloe Thorn

nice overview :)

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