T2 modules 3+4 Flashcards
name the key components of translation
- mRNA
- initiation, elongation and release factors
- aminoacyl tRNA synthase
- tRNA
- Ribosome
structure and function of tRNA
function
- mRNA -> polypeptide
- transfer amino acids from cytoplasm to growing chain @ ribosome
structure (not all the same!)
- single rRNA (70-90 nucleotides long)
- in all tRNA: complementary bases HB together (4 double helical segments, 3 loops)
- folds into L shape (bottom has ANTICODON that attaches to codons, written 3’-5’)
- 3’ end = CCA sequence (A is attachment point during tRNA activation)
tRNA activation process
AMINOACYL tRNA SYNTHASE activates tRNA
- pairs amino acid with tRNA @ amino acid attachment site
- also recognizes anticodon @ active site
- 20 different enzymes (same as # of amino acids)
- catalyze covalent attachment of tRNA+AA
- released tRNA called AMINOACYL tRNA
- 45 total aminoacyl tRNA sybthases because of the ‘wobble’
what is the ‘wobble’
flexibility in 3rd nucleotide base pairing in tRNA
- tRNA molecules may be able to bind to more than 1 codon
- this is why there are 64 codons and only 45 aminoacyl tRNA
- contributes to redundancy in genetic code
process of translation in eukaryotes
INITATION
- translation initiation complex starts at 5’ end, recruits small ribosomal subunit, scans until start codon
- other initiation factors bind to charged aminoacyl tRNA with MET, joins the initiation complex
- when AUG hit, large ribosomal subunit attaches
- once ribosome assembles, IFs released
ELONGATION
- ribosome has A, P and E site
- chain assembled amino end to carboxyl end of AA
- Met attaches in P site, charged tRNA enter A site via GDP bound elongation factors. When correct codon match made, GDP hydrolyzed released.
- peptide bond made between AAs
- another GDP-bound EF attaches to ribosome to move unit along mRNA
- uncharged tRNA ejected from E site
STOP
- stop codon reached
- GT-bound release factors bind to A site
- catalyze disassociation of translation complex, including ribosomal subunits and any remaining tRNA
1 gene 1 enzyme hypothesis
Beatle + Tatem bread mould experiment (Neurospora crassa)
- connected genes and proteins
- mould grew well on surfaces with minimal medium (nutrients) because they must have some enzymes that can break down minimal substances into what’s needed for growth
- grow well on low argenine because they can synthesize its own through a series of steps and enzymes
Cerb + Horawitz
- further tested hypothesis
- radiation treated neurospora samples grown on different mediums
- on supplemented (argenine, orthine, citrulline) they grew
- on unsupplemented, no growth.
- radiation produced mutations in the genes that encode for the necessary enzymes (1, 2 and 3) for the production of arginine
exceptions to the 1 gene 1 enzyme hypothesis
- human genome project: a single gene can produce more than just one protein
- post-translational modifications also contribute to proteome diversity
genomic to proteomic complexity
Genome: 25 000 genes
Transcriptome: 100 000 transcipts
Proteome: 1 000 000 proteins
blood glucose level response
regulated at transciptional and translational levels
1) stimulus: increased blood glucose post-meal
2) sensor: pancreas (beta isolate cells)
3) effector: insulin released (body cells take up glucose, liver cells take up glucose and turn to glycogen)
4) response: decreased blood glucose
insulin structure
pre-pro insulin
- 110 AA in length
- includes N-terminal sequence that is used to attach to ER via signal recognition particles. this creates…
pro-insulin
- A chain 21 AA
- B chain 30 AA
in ER
- chaperone assisted folding
- 3 disulphide bonds
in GA
- c stand cleavage
- leaves N terminal B stand and C terminal A strand to bind to receptor cells
types of post translational modifications
covalent attachment of other molecules
- phosphorylation (via KINASE enzymes)
- methylation
- acetylation
cleavage
folding
disulphide bridges
degradation of entire proteins
process of insulin effect
IDEA: extracellular trigger, intracellular signal amplification
- signal releases insulin effector molecules
- bind to RECEPTOR KINASES on target tissues
- attachment triggers DIMERIZATION (where 2 receptors bind together)
- cytoplasmic receptor domains act as KINASES, phosphorylating each other and binding important signalling proteins
- these signals activate GLUCOSE TRANSPORT PRs to allow glucose into cell
- signals can be amplified via TRANSDUCERS
- signals can be inhibited via inhibitors and double negative feedback loops (inhibitors inhibited)
alternative splicing and insulin receptor example
different proteomic expression from same gene via alternative methods of splicing. This creates different ISOFORMS
for example: insulin receptor gene
- 22 exons
- skeletal muscle: exon 11 removed (high insulin affinity)
- liver cells: exon 11 stays (low insulin affinity)
result: because of alternative splicing, muscle cells have higher insulin affinity and can take up more glucose
name possible problems in insulin pathway
no glucose uptake = hyperglycaemia, diabetes
- insulin pr miscoding
- insulin receptor miscoding
- glucose transport protein
