Lecture 21: protein synthesis Flashcards
DNA
-can replicate
transcription
info coded in the sequence of nucleotide bases in DNA is passed to a sequence of nucleotide bases in RNA
translation
information in RNA is passed to polypeptides but never in the reverse (polypeptides to Nucleic acids)
muscle cells and nerve cells in one species of animal owe their differences in phenotype to
different proteins being synthesized; differential gene expression
we know that the “one gene codes for one protein” hypothesis is not entirely accurate because
- many genes code oft RNAs that are not translated into proteins
- a single gene may code for a single polypeptide Chaim, and many proteins are made up of more than one polypeptide chain
- many genes code for immature mRNAs that are processed into different mRNAs
four steps of eukaryotic protein synthesis
- transcription (nucleus)
- RNA processing (nucleus)
- translation (cytoplasm)
- protein modification (secondary, tertiary, quaternary modification)
Steps of protein synthesis
- transcription of DNA into all types of RNA
- modifications of the RNAs
- translation of mRNA sequences into amino acid sequences (polypeptides)
- folding and twisting of polypeptide into protein
transcription
formation of any RNA sequence from a specific DNA sequence
a particular triplet of bases in the template strand of DNA is AGT. The corresponding codon of the mRNA transcribed is
UCA
steps of transcription
- initiation: formation of transcription initiation complex
- elongation: synthesis of RNA
- termination: liberation of RNA from transcription unit
Structure of the eukaryotic gene
- control elements: promoter, TATA box, enhancers, silencers, terminators
- introns: region of DNA that are transcribed but not translated
- exons: regions of DNA that are translated and transcribed
exons
often code for protein domains
promoter
sequence of DNA that regulates transcription
- regulatory protein binding regions
- transcription factor binding site
- RNA polymerase binding site
- start point: transcription initiation site
- made in cytoplasm then enters nucleus
transcription factors
proteins that help direct and regulate gene expression
required tools for transcriptions
- promoters
- nucleoside triphosphate (ATP, GTP, CTP, UTP)
- RNA polymerases
transcription initiation complex (TIC)
suite of proteins and DNA that allow transcription to proceed
which of the following is not required for eukaryotic transcription
DNA polymerase
Protein synthesis in eukaryotes is a
four step process:
- transcription
- mRNA processing
- translation
- protein maturation
RNA polymerase differ in that
RNA polymerase must initiate RNA and DNA synthesis
translation
decoding of one chemical language (sequence of codons) to another (sequence of Amino acids)
genetic code is
- specific
- redundant
- universal
codons
may code for the same amino acid as another codon
initiation complex of translation
- start codon
- initiator (met)
- tRNA
- small subunit
- large subunit
tRNA
- carries the AA to the growing peptide strand
- mediates between mRNA and the polypeptide
- specificity of tRNA-amino acid covalent bond (at 3’ end) due to aminoacyl-tRNA synthetase
Using RNA as a template for protein synthesis instead of translating protein directly from the DNA is advantageous for the cell because
- RNA acts as an expendable copy of the genetic material, allowing the DNA to serve as a permanent, pristine repository of the genetic material
- many mRNA molecules can be transcribed from a single gene, increasing the potential rate of gene expression
RNA processing
modification of pre-mRNA transcript to mature mRNA transcript
mature mRNA
- 5’ Cap-protects transcript from enzymes, ribosomal attachment site
- 5’ UTR: untranslated regulatory region
- start codon: initiation of translation
- stop codon: termination of translation
- 3’ UTR: untranslated regulatory region
- Poly-A tail: protects transcript, controls amount of translation of transcript
RNA editing
removal of introns, alternative inclusions of exons allows for diverse proteins from one DNA transcription unit
spliceosome
excises introns, unites exons in mature mRNA
-newly transcribed pre-mRNA is bound by snRNPs-small nuclear ribonucleoprotein particles that recognize short sequences between exons and introns
translation
mRNA sequence is used to create an amino acid sequence of a polypeptide
elongation
codon recognition
peptide bond formation
translocation
peptide bond formation
catalyzed by the ribozymal activity of the large subunit of the ribosome
termination of translation
occurs when the ribosome encounters a STOP codon
a eukaryotic protein is 300 amino acids long. which of the following could be the minimum number of the nucleotides in the DNA template strand that codes for the amino acid protein
903
a eukaryotic protein is 300 amino acids long. which of the following could be the maximum number of nucleotides in the DNA template strand that codes for the amino acids in this protein?
cannot tell from the info given (don’t know # of introns)
