lecture 2 part 2 Flashcards
(17 cards)
alternative splicing
-forms different mRNA sequences from same gene
-creates proteins with different amino acid sequences
translation
-mRNA -> protein
-mRNa leaves nucleus and binds to ribosomal subunits of cytoplasm
-mRNA will bind to ribosome which has enxymes needed for translation into proteins (enzymes join amino acids via peptide bond formation)
types of rna involved in protein synth
-rRNA (ribosomal)
-tRNA (transfer)= delivers specific amino acids, tRNA antucodon binds to a complementary mRNA codon
ribosome
-70-80 different proteins with rRNA
-rRNA transcription happens in the nucleolus (genes transcribed from DNA)
-ribosomal proteins synth in cytoplasm
rRNA synth
-in cytoplasm
-proteins move back to nucleolus where they combine with new rRNA to form 2 ribosomal subunits (one large one small)
-subunits are transported to cytoplasm where they combine to form a functional ribosome during protein translation
tRNA
-smallest rna
-single chain of trna looks on itself (looks like clover leaf)
-synth in nucleus then move to cytoplasm
-combines with specific a.a. and a codon on mrna that is specific for that a.a.
-trna is the link btwn a.a. and mrna codon
-covalently linked specific a.a. by aminoacyltrna synthetase
-3 nucleotide sequence at 1 end of trna look (anticodon) base-pairs with complementary codon in mrna
3 stages of protein assembly
-initiation
-elongation
-termination
initiation
-tnra with a.a. methionine binds to small ribosomal subunit
-initiation factors (proteins) establish initiation complex
-large subunit then binds enclosing mrna btwn 2 subunits
-this is the slowest protein assembly step
initiation complex
-positions methionine trna opposite mrna codon that signals start site at which assembly is to begin
elongation
-protein chain elongates bc of the addition of a.a.
-ribosome has 3 trna binding sites
-peptide bond is formed btwn protein chain and new a.a.
-tnra at p site it moved to e site and released from ribosome and tnra at a site is now linked to peptide chain and then stransfered to site 1
-ribosome moves down 1 codon along mrna making room for binding of next a.a. (trna molecule)
tnra binding sites on ribosome
-1) (P) holds trna linked to portion of protein chain that has been assembled up to this point
-2) (A) holds tRNA containing next a.a. to be added to chain
-3) (E) releases tnra into cytoplasm
termination
-ribosome reaches a termination sequence in mrna (stop codon) specifying end of protein
-link btwn polypeptide chain and last rna is broken, and completed protein is released from ribosome
post translation modification
-polypeptide chain undergoes moficiation once its assembled
-a.a. methionine is cleaved from end of proteins
-specific peptide bonds within polypeptide chain can be broken, producing smaller peptides, each may perform a different function
regulation of protein synth
-small perent of genes are actually transcribed to mrna and translated into protein
-transcription of genes is regulated and can be turn on and off depending on signals that the cell receives
-rna polymerase MUST bind to promoter region of gene and be in activated configuration for a gene to be transribed
protein synth regulation
-transcription factors regulate transcription (gene switches)
-transcription factors with accessory proteins from a preinitiation complex at promoter which separated DNA strands and activated RNA polymerase and moves it along the strand
-if the factor binds far from promoter region the DNA containing bound transcription factor forms a loop that brings transcription factor into contact with promoter region
gene B transcription is controlled by?
binding of an activates transcription factor directly to promoter region
points where the rate of protein synth can be regulated
-gene transcriptions into mRNA
-initiation of protein assembly on a ribosome
-mRNA degradation in cytoplasm
