Translation - Protein Synthesis PDF

TRANSLATION Structure of nucleic acids DNA replication Transcription Translation, synthesis of proteins https://www.youtube.co m/watch?v=kmrUzDYA mEI https://www.youtube.com/watch?v =gG7uCskUOrA https://www.youtube.com/watch?v =8nQH0GqFn6k https://www.youtube.com/watch?v =TfYf_rPWUdY...

TRANSLATION Structure of nucleic acids DNA replication Transcription Translation, synthesis of proteins https://www.youtube.co m/watch?v=kmrUzDYA mEI https://www.youtube.com/watch?v =gG7uCskUOrA https://www.youtube.com/watch?v =8nQH0GqFn6k https://www.youtube.com/watch?v =TfYf_rPWUdY https://www.youtube.com/watch?v =2BwWavExcFI  The genetic code = how proteins containing 20 different amino acids are coded by an mRNA sequence containing only 4 different nucleotides Codon = a sequence of 3 nucleotides encoding an a.a. 64 possible combinations Reading frames “Thecatandtherataresad The cat and the rat are sad T hec ata ndt her ata res ad Th eca tan dth ……….. Substitution  Characteristics of the genetic code Specificity Each codon specifies only one a.a. e.g. UCG encodes Serine Universality (almost) All species Degeneracy/Redundancy Multiple codons for most a.a.s These generally differ in the 3rd position e.g. UCU, UCC, UCA and UCG encode Ser Non Overlapping Commaless Non-overlapping Consequences of point mutations  Consequences of other mutations Trinucleotide repeat expansion Sequence of 3 bases is amplified Within coding region – Extra copies of an a.a. e.g. (CAG)n in huntingtin protein  extra Gln  neurodegenerative disorder Huntington disease In non-coding region – Decrease in amount of protein produced e.g. fragile X syndrome, myotonic dystrophy  Huntington disease Triplet expansion diseases UTR UTR > 20 diseases known A polyglutamine disease Fragile-X syndrome , the most common Additional glutamine residues change 2o cause of intellectual disability in males, structure –leads to accumulation of the expansion results in gene silencing protein aggregrates through DNA hypermethylation  Frame shift mutations Frame-shift mutations as a result of addition or deletion of a base - Can alter the reading frame of mRNA Can result in a protein product with very different a.a. sequence OR a truncated protein (e.g. stop codon) Cystic fibrosis deletion of 3 nts  DF508 i.e. loss of Phe at 508th position in cystic fibrosis transmembrane conductance regulator (CFTR) protein CFTR protein is destroyed Remember: over 1000 mutations have been identified for CF – this is the most common in western Europe and in Ireland  Protein synthesis https://www.youtube.com/watch?v=kmrUzDYAmEI requires Amino acids tRNA Aminoacyl-tRNA synthetases mRNA Ribosomes Protein factors ATP and GTP tRNA Amino acid attachment site 3’ CCA Anticodon Base-pairs with complementary codon on mRNA  Anticodon sequence determines which a.a. binds to that tRNA e.g. tRNAPhe anticodon GAA binds to codon UUC encodes Phe Aminoacyl-tRNA synthetase Catalyses addition of a.a. to specific tRNA = ‘activation of a.a.s’ Eukaryotic ribosome = Site of protein synthesis Made of rRNA and ribosomal proteins Have binding sites for tRNAs carrying a.a.s Found free in cytoplasm or attached to endoplasmic reticulum (rough ER) Formation of a peptide bond peptidyl transferase https://www.youtube.com/watch?v=G8RYhV569xg https://www.youtube.com/watch?v=-K8Y0ATkkAI https://www.youtube.com/watch?v=gG7uCskUOrA https://www.youtube.com/watch?v=8nQH0GqFn6k  Steps in protein Translation 1. Initiation 2. Elongation 3. Termination Initiation: involves the assembly of the components of the translation system before peptide bond formation occurs. 1. 2 ribosomal subunits 2. The mRNA to be translated The aminoacyl-tRNA specified by the first codon in the message 3. GTP 4. Initiation factors (eIF) Elongation: Addition of the aas to the carboxyl end of the growing chain Termination: occurs when one of the 3 termination codons moves into the A site. Eukaryotes have a single release factor, eRF, which recognizes all 3 termination codons  Posttranslational modification of polypeptide chains 1. Trimming 2. Covalent alterations a) Phosphorylation (result can be + or -) b) Glycosylation (membrane/secreted ) c) Hydroxylation d) Biotin is covalently bound to  -amino groups of lysine residues of biotin- dependent enzymes that catalyze carboxylation rxns e.g. pyruvate carboxylase e) Attachment of farnesyl groups, can help anchor proteins in membranes. f) Many proteins are acetylated  Energy requirements 4 high energy bonds are broken per a.a. added i.e. – a.a. + tRNA  aminoacyl-tRNA uses 2 bonds in one ATP – Aminoacyl-tRNA binding to ribosome uses 1 GTP per a.a. – Ribosome translocates along mRNA uses 1 GTP per a.a.  Medical relevance Antibiotics (Streptomycin, tetracyclines, puromycin, chloramphenicol, clindomycin and erythromycin) Bind to various parts of translational machinery in prokaryotes Diphtheria toxin Interferes with eukaryotic translation https://www.youtube.com/watch?v=TfYf_rP WUdY 3:03 https://www.youtube.com/watch?v=yKW4 F0Nu-UY 8 mins The inner life of the cell Narrated version https://www.youtube.com/watch?v=QplXd 76lAYQ