Unit One‎ > ‎

Protein Synthesis and DNA

Structure of DNA
Chromosomes are thread like structures located within the nucleus, they all contain deoxyribonucleic acid (DNA).
DNA consists of two strand
s composed of repeating molecules called nucleotides, these are composed of a phosphate, a deoxyribose sugar and a base (either Adenine, Thymine, Cytosine or Gu
) A strong chemical bond forms between the phosphate of one nucleotide to the sugar of another, forming a strong strand. The two seperate strands are joined together through weak hydrogen bonds, this allows theme to be split apart during transcription of R
The DNA strand is joined together in a specific order, it is joined together by corresponding bases - Adenine with Thymine and Guanine with Cytosine, giving it a unique sequence everytime.

Untitled drawing

DNA itself is two strands, forming a double helix, this is similair to a spiral ladder.
There is a second type of Nucleic acid - Ribinucleic acid (RNA), this also consists of nucleotides and resembles the structure of DNA. The excpetions and differences between RNA and DNA is that RNA only conatins one strand, the complementary base of Adenine is Uracil and not Thymine, also the sugar in the nucleotide is ribose and not deoxyribose. 
As we know from the Enzymes page, enzymes are made up of protein and are specific to their substrate. Therefore, the shape and the function of the enzyme depends on the sequence of bases in the DNA, therefore it also controls the organisms inherited characteristics.
Genetic Code
The information present in DNA makes up the genteic code, this is the body's own language. DNA may only posses four different bases yet proteins conatin about twenty different types of amino acids. This is made possible by the use of codons, codons are made up of 3 seperate bases which code for one amino acid, this gives 64 triplets of bases, allowing 64 amino acids.
Protein Synthesis
DNA is unable to leave the nucleus, therefore it needs a go between molecule, this is called messengerRNA (mRNA), this is transcribed from a single strand of DNA from the free nucleotides present.

Here's a little video to mix it up a bit:

DNA Transcription

The second type of RNA is TransferRNA (tRNA), tRNA also contains triplets, although these are called the anticodons, these once again correspond to a specific amino acid. This is found in the cell's cytoplasm, the tRNA molecule pics up the correct Amino Acid and takes it to a ribosome where the chain of amino acids is formed.
Ribosomes attach to one end of the mRNA molecule that is about to be translated, inside this ribosome their are sites that tRNA is able to attach to. This allows the tRNA molecule to form weak hydrogen bonds with the complementary codon of the mRNA, the process repeats and strong peptide bonds are formed to join the amino acids together the polypeptide chain then is able to become part of a protein.    

The Endoplasmic Reticulum (ER)

There is two types of ER, these are the Rough ER and the Smooth ER

  • Rough ER - This is a system that is composed of many flattened sacs and tubules, covered in ribosomes on both the outside and the inside. The Rough ER is continuous with the nuclear membrane, its main purpose is to provide a large surface area in which chemical reactions can occur. It also acts as a pathway for the transport of materials. It then passes proteins onto the Golgi Body.
  • Smooth ER - This is very similar to the Rough ER except from it lacks the ribosomes. It's main purpose is to produce steroid hormones 
The Golgi Body (or Golgi Apparatus) 

This is where proteins are processed and packaged (they become specific). It is here where such proteins are made into mucus, hormones or digestive enzymes, they are then pinched of in vesicles and excreted out of the cell.

The Golgi Body is also a source of small vesicles called lysosomes,  they come about by the same means as vesicles but they contain digestive enzymes that are able to break down substances. Lysosomes play a key role in Phagocytosis.
Subpages (1): Vesicles