BIOL2161 Lecture Notes - Lecture 7: Sedimentation Coefficient, World Federation Of Trade Unions, Cycloheximide
BIOL6: Genes: Replication and Expression
Block 2: Gene structure & regulation in prokaryotes
The genetic code cont.
ELONGATION
• In ribosome, there are three sites
o A: aminoacyl-tRNA
o P: peptidyl tRNA
o E: exit
• mRNA bound to 70s ribosome, P is occupied with tRNA (charged)
• Another complementary tRNA enters, charged tRNA is complexed to an elongation factor (Tu)
combined with GTP
• Occupies A site (tRNA only comes into P site at initiation, all others at A)
• GTP is hydrolysed reuslting in a confirmational change, EF-Tu and GDP + Pi are released
• GDP AND EF-Tu are released and recycled back to another tRNA (via EF-Ts)
• One amino acid gets linked to another from adjacent tRNAs, forming a dipeptide
o Enzyme that catalyses it is the ribosome large subunit (ribozyme, RNA molecule acting as
an enzyme)
• GTP, EF-G leads to translocation of ribosome along mRNA (moves along a codon)
• Loaded tRNA sits in P site, empty tRNA exits via E site, A site is unoccupied
Peptide Bond Formation
• Proteins grow from the N (amino) terminus to the C (carboxyl) terminus
• mRNAs are translated 5' to 3'
• Peptide bond formation is catalysed by the rRNA of the large subunit and not the protein
o Ribozyme e.g. peptidyl transferase
• Elongation cycle mechanism is the target for most antibiotics
o Tetracycline can fit into A site, occupy it and inhibits bacterial translation
o Amphenical interferes transfer of amino acids
o Streptomycin prevents step 2
o Cycloheximide prevents movement along chain
TERMINATION
• Release factors 1,2,3
o 1 and 2 can be used dependent on the stop codon (no corresponding tRNA)
o 3 brings in GTP, hydrolysed GTP leads to structural cha
o Ribosome is disassembled
Density Centrifugation
• Sedimentation coefficient
• All particles have different buoyancy/weight
• Separation by spinning
1. Low speed -> large sediment at bottom, pour off light
2. High speed-> small sediment at bottom, pour off
• Can also do a gradient
o High sugar at bottom, more liquid on top
o Lysosomes are lighter than mitochondria, lighter than peroxisomes
• Svedberg Unit (S) -> measures particle size based on rate of travel in a tube subjected to high
g-forces
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Document Summary
Block 2: gene structure & regulation in prokaryotes. Loaded trna sits in p site, empty trna exits via e site, a site is unoccupied. Termination: release factors 1,2,3, 1 and 2 can be used dependent on the stop codon (no corresponding trna, 3 brings in gtp, hydrolysed gtp leads to structural cha, ribosome is disassembled. Svedberg unit (s) -> measures particle size based on rate of travel in a tube subjected to high g-forces: not directly additive, dependent on particle"s mass, shape, density. Gtp vs atp: different reactions use gt/atp, normal currency of cell is atp, hard for cell to distinguish whether atp should be used for motility/protein synthesis, essential mechanisms gtp is used, atp is for normal, theory not fact. Immensely diverse: different sources of energy need to be processed differently. Bacteria: genes are turned on and off in response to environmental changes, most of the mechanisms are dedicated to food.
