Molecules AS

• Potassium is used as a enzyme cofactor in maintaining osmotic equilibrium
• calcium produces calcium pectate which binds adjacent cell walls in plants ensuring they stick together
• Magnesium acts as a prosthetic group in chlorophyll and activates many enzymes
• iron- the prosthetic group in haemoglobin
• Hydrogen carbonate transports co2 and acts as a buffer in blood
• nitrogen makes proteins, and gives ATP and ADP (energy)
• a buffer is a compound which acts in such way as to resist small changes in pH on addition or dilution of moderate amounts of acid alkaline.
• Buffers act to mop up +ve/-ve charged ions that affect pH because cells at tissues can only function at nuetrality
• Proteins contain CARBON, HYDROGEN, OXYGEN, NITROGEN AND SOMETIMES SULPHER.
• proteins are huge molecules fromed from a amino acid chain
• after a amino acid chain is made, proteins take up a specific shape.

  The shape of a protein is closely related to the function it performs
• in the functional group -NH2 and 0COOH, the groups are attached to the same carbon atom.

  The rest of the chain, the R part is very variable
• The R group influences solubility, it may act as a buffer as its involved with bonding that maintains its secondary and tertiary structure
• Whilst amino acids have

  the same basic structure, they are all rather different in character. This is

  because they all carry different R-groups.
• Bringing amino acids together in different combinations produces proteins

  with very different properties. This helps explain how the range of proteins in

  organisms are able to fulfil the very different functions they have)
• Peptide Linkages – two amino acids can react together with the loss of water

  to form a dipeptide.
• a dipeptide is a molecule formed by the condensation of two amino acids
• a condensation reaction is a type of reaction that forms a polypeptide
• after a dipeptide if formed, The amino group of one amino acid reacts with the

  carboxyl group of the other, forming a peptide bond (-CONH-).
• Long strings of

  amino acids linked by peptide bonds are called polypeptides.
• a polypeptide is always a single chain of amino

  acids, whereas a protein may consist of a number of polypeptides joined

  together to give a biologically active molecule.
• The primary structure of a protein is the arrangement of the long chain of

  amino acids in its molecule.
• In the living cell, the sequence of amino

  acids in the polypeptide chain is controlled by the coded instructions stored

  in the DNA of the chromosomes of the nucleus.
• Just changing one amino

  acid in the sequence of a protein may alter its properties completely- cause a mutation, leads to disease and death
• The secondary structure of a protein develops when parts of the

  polypeptide chain take up a particular shape immediately after formation at

  the ribosome.
• IN the secondary structure, The most common shapes are formed either by coiling to

  produce an alpha helix or by folding into beta sheets.
• the alpha and beta sheets in the secondary structure is permanent and held in place by H2 bonds
• beta sheets are arranged in such way to give strength to the structure
• The tertiary structure of a protein is the precise, compact structure that

  arises when the secondary structure is further folded and held in a

  particular complex 3D shape.
• the tertiary structure shape is made permanent by four

  different types of bonding established between different parts of the chains

  R groups.
• Some proteins take up a tertiary structure that is more spherical,

  and are called globular proteins. Most enzymes are globular proteins.
• The tertiary structure of a protein depends on its primary structure, as the

  bonds holding the tertiary structure can only form if the correct amino acids

  are at specific points along a polypeptide chain
• Hydrogen bonds - numerous but relatively weak and easily broken.
• Ionic bonds - formed between amino and carboxyl groups in some amino acid side

  groups. Stronger than hydrogen bonds they are damaged by pH changes.
• Disulfide bonds - covalent bonds between R- groups of sulfur-containing a.a. like

  cysteine. Very strong bonds with an important role in structural (fibrous)

  proteins like collagen.
• The quaternary structure of protein arises when two or more polypeptides

  become held together, forming a complex, biologically active molecule.
• an example of the q-structure is haemoglobin, which consists of four polypeptide chains held around a non-protein haem group.

  A group like this, which is an important,

  permanent, part of a protein molecule but is not made of amino acids, is called a prosthetic group.
• a prosthetic group is a group of amino acids that are not part of the protein chain
• A protein that contains a prosthetic group is called

  a conjugated protein.

  Other examples include glycoproteins, chlorophyll and

  myoglobin.
• Globular proteins – have complex tertiary and sometimes quaternary structures.

  They are relatively unstable and are folded into spherical (globular) shapes

  such as myoglobin, haemoglobin, antibodies, hormones and enzymes.