Lecture 20 Flashcards
translation
transalting bn language of nucleotides to language of aa
tRNA
single stranded RNA folds on itself to clover lead (bc of complementary regions)
attach to an aa at one side and binds a codon at the other end
last codon is CCA, then aa binds to 3’
5’ starts w a G
the codon ON the tRNA that binds TO the mRNA = anti-codon
tRNA bases
CAGU but also other bases
pseudouridine and duhydrouridine (mods done to uracil)
tRNA’s and aa’s
aa bind to 3’ region
aminoacyt-tRNA synthetase attaches an aa to a tRNA
one aminoacet-tRNA synthetase for each aa
charged = w aa, uncharged = w/o
bonding of first 2 bases= normal CGAU
third = more flexible
G = C and U
U = G and A
ACU = U mods.
w flexibility = 1 tRNA can rec more than one codon fro the same aa
done need 61 tRNAs but 30
ribosome structure
workbench for translation
have large and small subunits
each subuntue = many proteins and several RNA molecs.
in cytoplasm
subunits assembled in nucleus and sent to cytoplasm
ribosome binding sites
each has a binding sites for mRNA
and 3 binding sites for tRNAs
A = where charged tRNA ancticodn binds to the mRNA codon
P = where tRNA w the growing polypeptide bond is
E =where uncharged tRNA sits
translation initiation in por
sequence reco in the small subunit of the ribo (bc has comp sequence, so binds w H bonds)
sequence before the start codon called Shine sequence
translation initiation in euk.
no Shine,
we reco the G cap and ribs binds it
the small subunit alr has a initiator tRNA (with Met aa) and an initiation factor, scans the mRNA until finds its comp sequence (AUG)
initiation factor is removed
Large will join
tRNA corresponding to next codon comes and binds.
keeps on going making peptide bonds.
elongation
by making peptide bonds
we have 2 codons, 1 in P site, other in A site
both been reco by tRNA w comp sequence, tRNAs are att to respective aa
peptide bonds formed bn carboxyl grp of aa in P site and amine group of aa in A site
once bond is formed, tRNA in P site is detatched from polpeptide chain
tranalsation termination
stops at STOP codons
stop codons UAA, UAG, AND UGA
don’t correspond to any aa
stop codons bind release factor = hydrolysis of the bond bn polypeptide chain and tRNA in P site
how to inc rate of protein synth
polysomes (polyribosome)
multiple ribosomes that simultenoulsy translate the mRNA
makes several copies of a protein in short amount fo time that mRNA is stable
polypeptides grow longer as each robot moves towards 3’ end (have done the whole mRNA, just finishing)
at 5’ short, just started, since we transalte from 5’ to 3’
protein modification
has ot be matured
phos. = changes conf = maces active, able to ine w other proteins
makes fully functional, helps them survive getting to their location.
adding sugars = glycosylation,
proteolysis (cutting)
end locations of proteins
if assoc w
glycolysis = stay in cytoplasm
krebs = mitochondria
Calvin = chloropast
if DNA poly = go nucleus
to be secreted = ribs gets att tot ER while in synth, proteins go into ER, matured, to Golgi, out
if lysosomal = bind to ER, through Golgi to lysozyme.s
how to know where to go?
protein finds its way because of its signal sequence
to go through ER = end part has short sequence telling cell to take to ER
a lot of hydrophobic aa
w/o signal sequence = stay in cytoplasm
protein entering mitochondria
Has sequence, recognized by receptor in outer mb of mitochondria wihich is connected to a channel, hands over the proteins to chanel,takes proteins (the signal part), brings into the intermb space, the proteins move and once encounter another translocater of the inner mb, is pulled further in the mito into the matrix
same for chloroplast
proteins for nucleus
has to pass the nucleur pores
Lined with several layers of proteins in the shape of a ring.
Part of protein reach out towards cytoplasm or w in the nucleus
A receptr has to recognizes it, is reco, int w the tails of the proteins that are part of the pore
W these extensions, are guided twds pore
inside pore = meshwork
leaves
guided out w extensions of the other side of the poe
proteins entering ER during synth
while still synth, the signal sequence telling it to go to ER is translated
ribo is brought to ER binds to receptor in ER, hands over the protein to Chanel, brings protein inside the ER,
protein starts getting pushed into the ER through translator
transmit proteins staying in ER mb
same process,
protein gets pushed into ER through translator
but protein has hydrophobic region, when that region reaches bilayer = transfer stops,
h phobic likes h phonic
we get a protein that crosses the mb once = trans mb protein
multipass = er signal is not at end terminal but more interiorly
now, has more start/stop regions so can cross many times
soluble proteins cross ER mb and enter lumen
if soluble entirely cross the mb and enter the ER
w/o stop transfer
