Protein Synthesis

• The base Pairings in DNA are adenine (A) with thymine (T) and guanine (G) and cytosine (C).
• The RNA bases are Adenine (A) with Uracil (U) and Guanine (G) with Cytosine (C) (It can also be Thymine (T) with Adenine (A))
• There are three types of RNA: mRNA (messenger), tRNA (transfer) and rRNA (Ribosomal).
• RNA nucleotide has a structure of a phosphate group, a nitrogenous group and a ribose sugar (Pentose sugar)
• DNA nucleotide has a structure of one phosphate group, a nitrogenous base and a Deoxyribose sugar (Pentose sugar)
• DNA has two strands and has many millions of nucleotides in a chain
• mRNA is single stranded and has several hundreds of thousands of nucleotides in a chain
• tRNA is single stranded and has about 75 nucleotides in a chain
• mRNA is a copy of a single gene of the DNA template strand
• tRNA has a sugar phosphate backbone
• tRNA has a cloverleaf structure and has regions where it is double stranded and regions where it is single stranded.It also has an amino acid attachment site and an anticodon.
• Protein synthesis involves two processes transcription and translation
• Transcription is the copying of the base sequence of a gene in DNA onto the base sequence of a molecule of mRNA
• Translation is the conversion of the base sequence of mRNA into the amino acid sequence of a polypeptide chain.
• Transcription occurs in the nucleus of eukaryotic cells.
• The base sequence of a gene in DNA contains both introns and exon.
• Introns are non-coding intervening sequences within genes on DNA
• Exons are coding sequences of DNA
• The molecule formed during transcription is called pre-RNA
• Post-transcription mRNA has all of the intron sequences removed and the exons are all joined together
• The Enzyme DNA Helicase attaches to and unwinds the DNA double helix during transcription.
• transcription is when DNA is split in half one strand is used as the template
• Splicing is the separation of exons and introns
• Translation occurs in the cytoplasm (or anywhere there are ribosomes).
• Messenger RNA (mRNA) leaves the nucleus via the nuclear pores in the nuclear membrane and attaches to a ribisome.
• In Translation tRNA carrying a specific amino acid binds to the first codon on mRNA via base paring with its anticodon.
• Enzymes join amino acids together forming peptide bonds (this requires ATP) and then it moves on to the next codon (triple base)
• Many ribosomes can translate a molecule of mENA at the same time (so many polynucleotides can be synthesised at once)
• Protein synthesis requires energy / ATP
• A gene mutation is a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
• The DNA base sequence determines the sequence of amino acids that make up a protein.
• There are three ways in which mutations occur: substitution, deletion or insertion
• Insertion of nucleotides is when a nucleotide with a new base is randomly inserted into DNA (and is known as an insertion mutation)
• Deletion of nucleotides is when a nucleotide and therefore its base is randomly deleted from the DNA sequence.
• Substitution of nucleotides is when a base of a nucleotide is randomly swapped for a different base (unlike deletion and insertion substitution only change the amino acid for the triplet base/codon)
• Missense mutations is when the mutation alters a single amino acid in the polypeptide chain (EG: sickle cell anemia)
• Nonsense mutations is when the mutation creates a premature stop codon (signalling for the cell to stop translation of the mRNA molecule into an amino acid sequence)
• Mutations occur spontaneously during DNA replication and are random events that cause permanent changes to the DNA.
• Mutations in gametes can often prove fatal
• Mutations can also change the chromosome number