Proteins

protein overview

• contain C,H,O,N,S

• monomers are amino acids

• joined together by condensation reactions

• about 20 amino acids

amino acid structure

• amino group (-NH2)

• carboxyl group (-COOH)

• R group varies between amino acids (gives amino acids unique properties)

formation of proteins

• amino group of one protein joins with carboxyl group of another

• join in a condensation reaction to form a peptide bond

• polypeptide forms protein when folding or coiling or associating with other polypeptide chains

• to create 3D structures, bonds are made between amino acids in a chain

• include R group atoms, hydrogen bonds, disulfide bonds, and ionic bonds

hydrogen bonds in proteins

• formed between slightly positive hydrogen atoms in amino groups

• and slightly negative oxygen atoms in carboxyl groups

• hydrogen bonds hold amino acids and protein firmly

• important in folding and coiling of polypeptide chain

• bonds break easily if temp or pH change

Disulfide bonds

• happens when two cysteine bonds are close together

• oxidation reaction happens between the two sulfur-containing groups

• disulphide bond is formed

• stronger than hydrogen bonds but happens less often

• helps hold folded polypeptide chains in place

Ionic bonds

• happens between steongly positive and strongtly negative amino acid chains

• forms strong bonds that are rarer than other structural bonds

Protein structures

• primary structure

• secondary structure

• teritiary structure

• quartenary structure

Primary structure

chain of amino acids held together by peptide bonds

secondary structure

• structure made of folded amino acid chain, made up of peptide bonds as well as hydrogen bonds

• has two structural variations: a-helix shape and b-pleated sheet

tertiary structure

• secondary sturcture coil into a unique three dimensional shape

• made up of hydrogen and ionic bonds, disulohide bridges, and hydrophillic and hydrophobic interactions between polar and non-polar R groups

quarternary structure

• two or more polypeptide chains join together

• made up of the same bonds that make up a tertiary structure

• can include prosthetic groups (non protein groups)

fibrous proteins

• have no tertiary structure

• made up of parallel secondary structures with occasional cross-linkages to form fibres

• appear in connective tissue and as keratin and collagen

collagen

• quaternary structure has three polypeptide chains that are made up of up to 1000 amino acids

• primary structures is repeating glyceine molecules with two other amino acids

• arranged in a triple helix help by many hydrogen bonds

• this makes it very storng

globular proteins

• fold into spherical (globular) shapes

• Hydrophilic R groups are on the outside of globular protein

• Hydrophobic R groups are found on the inside of globular protein

• Have ionic properites

• Form a colloid in water that does not settle and is hard to separate

• Used to suspend molecules in position in cytoplasm

• Important for immunity as WBC are globular cells

• Some hormones and enzymes are globular cells

Haemoglobin

• large molecule made up of 574 amino acid chains arranged in four polypeptide chains that surround a haem group that contains iron

• iron in haem group allows it to bind and release oxygen molecules