Nucleotides and Nucleic acids

Nucleotides and Nucleic acids

Nucleotides are nitrogen containing organic substances wich play a vital role in every espect of an organisms life.Nucleotide molecules occur singly(mononucleotides) or combined in numbers frol two to many thousands(polynucleotides).
Nucleotides are made of three parts:

1. a nuitrogen-containing organic base
2. a five-carbon sugar ( pentose)
3. one or more phosphate groups

ATP is energy to drive reactions.(Adenosine triphosphate or ATP) is a mononucleotide.It is vital because ir the main source of chemical energy. The base is adenine and the sugar is ribose. Attached to the ribose are three phosphate groups.The covalent bond linking the second and third phosphate groups is unstable, and is easily broken by hydrolysis.

When this bond is broken a phosphate group(Pi) is removed, and ATP becomes ADP (adenosibne diphpsphate).Energy is release so it is calle exergonic reaction.This reaction can be reversible because from ADP it can be obtained ATP by resynthesis and the inorganic phosphate by a condensation reaction.(energy for this reaction comes from respiration).

Nucleic acids: DNA

Nucleotides are combined by condensation reactions to form long chains wich are called nucelic acids.DNA plays the key role in inheritance and protein synthesis. The basic structure of DNA seems simple because it is made of only four type of nucleotide.Each DNA nucleotide has a phosphate group, a pentose sugar (deoyribose,and one of four types of base ( all of wich containing nitrogen) adenine, cytosine,guanine or thymine.

DNA FORMS A DOUBLE-HELIX

• The DNA molecule consists of two strands, each of wich is a polynucleotide chain
• Each strand has a helical (spiral) shape, so that DNA has become known as the "double helix"
• The polyunucleotide chains run in opposite directions and are joined by pairs of bases.
• The bases are held together by hydrogen bonds between the hydrogen atoms of a base in one chain and the oxygen and nitrogen atoms of a base in the other chain

Introduction to Proteins

Proteins

Type of proteins

• Enzymes, biological catalysts that control biochemical reactions.
  


• structural proteins, for example collagen that make up tendons.
  


• signal proteins, carry a message around the body, for example insulin.
  


• storage proteins, protein store that form the white of egg.


• defensive proteins, for example, antibodies that fight infections.


• Transport proteins, for example haemoglobin, the carrier of oxygen in blood.

Proteins are polymers formed of amino acids, there are thousands of proteins bu only 20 differents amino acids.

Amino Acids

The amino acids have an amino group(-NH2) and a carboxyl group(-COOH). The amino group is attached by a covalent bond to the central carbon atom called the alpha carbon. In the amino acids the R varies for each different amino acid. The R groups are non-polar and hydrophobic but others are polar and hidrophilic.

Amino Acids as buffers

Amino acids are amphoteric, they have both acidic and basic properties when they dissociate in water. The acidic properties are derived from the carboxyl group, which can donate a proton and being negatively charged in an alkiline solution. The basic properties are derived from the amino group, which can take a proton to be positively charged in an acidic solution. Ions with both, negative and positive charges are called zwitterions. The ability to donate and receive protons allow amino acids to behave as buffers. A buffer solution tends to resist changes in ph. Buffer systems play an essential role in the human body, keeping the ph of blood in tolerable levels.

Peptide bonds

Two amino acids can combine to form a dipeptide by a condensation reaction , this bond is called peptide bond. Further amino acids can combine with the dipeptide to form a polypeptide chain. Proteins consist of one or more polypeptide chains.

Proteins

Proteins

Proteins consist of one or more chains of amino acids folded into a unique three-dimentional shape. The shape is determined by by up to four levels of structure(each level of structure determines the next):

• Primary structure: a proteins primary structure is the sequence of amino acids that make up its polypeptide chains.In order for a protein to carry out its specific function, it must contain the correct amino acids arranges in a precise order.
  
• Secondary structure: Is the coil into an alpha-helix or beta-pleated sheet by hydrogen bonding.
• Tertiary structure: Refers to the overall three-dimensional shape of a polypeptide chain.they are classified into two main groups depending on the basis of their tertiary structure:

Fibrous proteins consist of parallel polypeptide chains cross-linked at intervals of from long fibres or sheets. In globular proteins the polypeptide chains are tightly folded to form a spherical shape. Breaking down the tertiaty structure:denatiration. if the bons holding the proteins chape are broken, a proces called denaturation occurs. the polypeptide chains unravel and lose their specific shape,as a result they lose their specific function.Denaturation is nearly irreversible. It can be cause by:

1. changes in ph
2. salt concentration
3. temperature

• Quaternary structure: the association of polypeptide chains.Many proteins consist of more than one polypeptide chain bonded to each other. It refers to the way these polypeptide chains are arranged.