Lecture 10 Flashcards
translation
polymerization of amino acids into polypeptide chains
what does translation require?
-amino acids
-mRNA
ribosomes
-tRNA
transfer RNAs
- adapt genetic information present as specific triplet codons in mRNA to corresponding amino acids
- tRNA anticodons complements mRNA
- carry corresponding amino acids
ribsosomes
- have an essential role in expression of genetic information
- consists of ribosomal proteins and ribomsomal RNAs
- consists of large and small subunits
size of ribsosomes
- 70S in prokaryotes
- 80S in eukaryotes
tRNAs
- small in size and very stable
- 75-90 nucleotides
- transcribed from DNA tRNA genes
- contain posttranscriptionally modified bases
- have a cloverleaf structure
aminoacylation
- tRNA charging
- before translation can proceed, tRNA molecules must be chemically linked to respective amino acids
aminoacyl tRNA synthetase
enzyme that catalyzes aminoacylation
- 20 different kinds for each amino acid
- highly specific and only recognize for its respective amino acid
what are the three steps of mRNA translation?
initiation, elongation, and termination
what does initiation require?
- small and large ribosomal subunits
- mRNA molecule
- GTP
- charged initiator tRNA
- Mg2+
- initiation factors
what are the initiation factors?
- IF1 = blocks A-site
- IF2 = GTPase
- IF3 = inhibits small subunit binding
Shine-Dalgarno sequence
-precedes AUG start codon in bacteria and base-pairs with region on 16S rRNA of 30S small subunit, facilitating initiation
initiation complex
-small ribosomal subunit and initiation factors
termination
signaled by stop codons at the A site
-codons do not specify for an amino acid
FTP-dependent release factors
stimulates hydrolysis of polypeptide from peptidyl tRNA released from translation complex
translation in eukaryotes
- ribosomes are larger and longer lived than bacteria
- transcription occurs in the nucleus
- translation occurs in the cytoplasm
what proceeds the start codon in eukaryotes?
-eukaryotes mRNAs contain purine three bases upstream from AUG initiator codon
Kozak sequence
increases efficiency of translation by interacting with initiator tRNA
what is different with translation in eukaryotes?
requires more factors for initiation, elongation, and termination
-ribosomes are not free floating and are associated with the endoplasmic reticulum
polypeptides
precursors to proteins
proteins
polypeptides folded up into a 3-dimensional conformation
-most abundant macromolecules in the cell
what do amino acids contain?
- carboxyl group
- amino group
- R group on the central carbon
what determines the type of amino acid?
- the R group (side chain)
- it is either nonpolar, polar, and positively or negatively charged
primary protein structure
sequence of amino acids
