Section 4 -Genetic information, variation and relationships between organisms

gene

a section a DNA which contains a section of code to code for a specific polypeptide chain or RNA strand

the genetic code

* only 20 commonly coded for amino acids
* pair of bases means 16 amino acids can be coded for
* 3 bases are required so there are 64 possible amino acids that can be coded for

features of genetic code

* degenerate as most of the proteins require more than one amino acid
* non overlapping code as bases are read 123 456 not 123234345456
* 3 bases that code for methionine are the start bases this can be removed afterwards if not required in the final polypeptide
* there is an end mark of three triplets
* universal as most of organisms have the same bases coding for the same amino acids
* indirect link for evolution

chromosomes strucutre

* DNA coils are tightly wrapped around histone proteins which provide strength for the chromosomes
* DNA histone coils are coiled and then folded to pack together.
* one strand of the chromosomes is called a chromatid
* chromosomes are only visible during the stages of mitosis

structure of RNA

* one ribose sugar (pentose)
* 4 bases (ACGU)
* phosphate group
* \

mRNA

transfers the code from DNA out of the nucleus through the nuclear pores and into the cytoplasm to associate with the ribosomes to transfer the DNA.

messenger RNA

* long single strand of DNA
* base sequence is determined by a section of DNA’s bases.
* leaves nucleus through nuclear pores and goes into the cytoplasm
* associates with ribosomes
* template for protein synthesis
* structure suits function as it has codons

transfer RNA

* small molecule with 80 nucleotides
* single strand folded into a clover shape with one end extending further which is where the amino acid is attached
* the other end has the triplet code and is called the anticodon

protein synthesis - transcription

1. DNA helicase breaks the hydrogen bonds between a section of DNA
2. free floating nucleotides join to the sense strand (strand to be coded for )
3. the RNA polymerase moves along the nucleotides and joins them together with phosphodiester bonds
4. the mRNA stops forming once the stop codon has been reached. behind the dna helicase, the strands reform meaning only 12 bases are exposed at a time
5. the pre-mRNA is now ready for splicing

protein synthesis - splicing

1. pre-mRNA has exons and introns involved
2. introns are non coding whereas the exons actually do code for the protein. this means that with introns, the code for the protein will become disrupted.
3. splicing removes the introns so that the exons in the mRNA can now move out the nucleus and into the cytoplasm

protein synthesis - translation

1. the mRNA strand attaches to a ribosome at the start codon
2. free tRNA bases will read the codons and attach with complimentary anticodons. he next codon of mRNA is read and the complimentary tRNA attaches again.
3. the amino acids which are attached to the tRNA molecules join with the help of an enzyme and ATP to form a peptide bond
4. this continues until the stop codon is reached. this does not have a complimentary tRNA molecule so the ribosome detaches and the new polypeptide strand goes to the Golgi apparatus for folding and modification.