Chapter 14 Flashcards
Translation
Biological polymerization of amino acids into polypeptide chains
Translation requires
Amino acids
mRNA
Ribosomes
tRNA
Transfer RNAs (tRNA) Adaptor molecule
Adapt genetic information present as specific triplet codons in mRNA to corresponding amino acids.
Carry corresponding amino acids
Ribosomes
Have an essential role in expression of genetic information.
Consist of proteins & rRNAs
Has large and small subunits
Prokaryote ribosomes are __s
70s
Eukaryote ribosomes are __s
80s
rDNA
Moderately repetitive DNA fraction present in clusters at various chromosomal sites
Each rDNA cluster contains
Tandem repeats separated by no coding spacer DNA
tRNAs
Small, stable, transcribed from DNA
75-90 nucleotides
Contains posttranscriptionally modified bases
Anticodon
tRNA has an anticodon that Complementarily base pairs with codon in mRNA
Aminoacylation
tRNA charging:
Before translation can proceed, tRNA molecules must be chemically linked to respective amino acids
Aminoacyl tRNA synthetase
Enzyme that catalyzes aminoacylation
Highly specific
20 different synthetases
Step 1 of translation
Initiation
Initiation requires
GTP Mg2+ Initiation factors mRNA molecule Small and large ribosomal subunits mRNA molecule
Step 2 of translation
Elongation
Elongation
Both ribosomal Subunits assembled with mRNA
Forms P site and A site
Step 3 of translation
Termination
Termination
Signaled by stop codons in A site.
Codons do not specify any amino acid
Stop codons
UAG
UAA
UGA
GTP dependent release factors
Stimulate hydrolysis of polypeptide from peptidyl tRNA
Polyribosomes
mRNAs with several ribosomes translating at once
Translation in eukaryotes
Ribosomes are larger and longer lived than bacteria
Where do transcription and translation occur?
Transcription: nucleus
Translation: cytoplasm
Kozak sequence
Is considered to increase efficiency of translation by interacting with initiator tRNA
