DNA in Prokaryotes and Eukaryotes
DNA in Prokaryotes
NOT ASSOCIATED WITH PROTEINS
DNA in Eukaryotes
ASSOCIATED WITH PROTEINS CALLED HISTONES (DNA with associated proteins make chromosomes)
Mitochrondria of Eukaryotes Chloroplasts has DNA thats short, circular and not associated with protein.
A gene is a base sequence for DNA that codes for;
Amino acid sequence of polypeptides
Locus is a fixed position a DNA molecule is in.
Three DNA bases (a triplet) codes for a specific amino acid. The genetic code is universal (DNa code is the same for all living organisms) Non- overlapping (DNA is read 3 bases at a time) and degenerate (There are more then one triplets that code for a specific amino acid)
Introns and Exons
In Eukaryotes much of the DNA does not code for polypeptides.
The parts that code for polypeptides are called EXONS.
The parts that don't are called INTRONS.
DNA and proteins synthesis
Genome: All the genes in a cell
Proteome: Full range of proteins a cell can produce
Synthesising proteins needs RNA
There are two types involved
mRNA a single stranded polynucleotide consisting of hundreds/thousands of RNA nucleotides complementry to the DNA in the gene.
tRNA a single stranded polynucleotide about 75 polynucleotides long. hydrogen bonds between bases cause it to be a clover shape. It carries specific amino acids to the ribosome. One end there are three exposed bases called the anticodon, which are complementry to the mRNA codons. The other end there are another three exposed bases, but they form a amino acid attachment site.
Transcription is the first stage of protein synthesis. (The production of DNA into mRNA).
1. The section of DNA be transcribed (the gene) unwinds and the hydrogen bonds between bases break.
2. On strand of the DNA is the template.
3. New RNA bases alinged and match with their complementry DNA bases.
4. RNA polymerase joins the RNA nucleotides together to form a molecule of mRNA from DNA.
5. The completed pre-mRNA leaves the molecule via the nuclear pore.
In Eukaryotes pre-RNA is then spliced. (has it's introns removed) To leave only coding Exons.
In prokaryotes Transcription makes mRNA without this process.
Translation is the second stage of protein synthesis
1.Mature mRNA enters the cytoplasm and enters a ribosome.
2. tRNA molecule with complementry anticodons to the first two codons on the mRNA enters the ribosome with their amino acids attached.
3. A peptide bond is formed between the amino acids. ATP is used.
4.tRNA bound to the first codons leaves.
5. Ribosome moves along one codon. A new tRNA enters with complementry anticodons to the 3rd mRNA codon.
6. Peptide bond is formed again using ATP.
7.Ribosome moves along the codons until it reaches a stop codon and releases the amino acid chain.