Protein Synthesis QUIZ Flashcards
Why does the cell need to make RNA?
- DNA too important to leave nucleus
- RNA needed to bring genetic information outside the nucleus to the ribosomes
- needed for protein synthesis
Describe the structure of RNA.
- ribose sugar
- uracil pairs
- single stranded
- travel from nucleus –> cytoplasm
What are the 3 different types of RNA is involved in protein synthesis?
1) messenger RNA (mRNA)
2) transfer RNA (tRNA)
3) ribosomal RNA (rRNA)
What are the 2 steps in PROTEIN SYNTHESIS?
1) Transcription - Copying information in DNA into messenger RNA
2) Translation - Ribosomes use mRNA to synthesize a protein made of amino acids
What are the 3 stages of TRANSCRIPTION?
1) INITIATION
- RNA polymerase binds to the DNA at the promoter (TATAS)
2) ELONGATION
- Uses DNA as template, binds mRNA using paired nitrogenous bases
3) TERMINATION
- leaves nucleus
What are the 3 stages of TRANSLATION?
1) INITIATION
- Ribosome binds to mRNA
2) ELONGATION
- ribosomes read mRNA in sets of 3 (codons), each codon translates to different amino acid
3) TERMINATION
- polypeptide chain created and released
Describe the INITIATION stage of TRANSCRIPTION
- RNA polymerase binds to promoter region
- Promoter region = lots of A’s and T’s
- RNA polymerase spends less energy opening up the double helix
Describe ELONGATION stage of TRANSCRIPTION
- RNA polymerase begins building mRNA in 5’ to 3’ without primer
- Promoter region NOT transcribed
In DNA:
- TEMPLATE STRAND - (3’ to 5’) is used
- CODING STRAND (5’ to 3’) is not used
Describe TERMINATION stage in TRANSCRIPTION
- RNA Polymerase recognizes end of gene –> terminator sequence
- newly synthesized mRNA dissociates from DNA template strand –> PRIMARY TRANSCRIPT
- RNA polymerase can bind to another promoter region and transcribe another gene
What is POST TRANSCRIPTIONAL MODIFICATION?
- 5’ Cap –> added to 5’ end of primary transcript, protect mRNA from digestion by enzymes (nucleases + phosphatases), initiates translation
- Poly-A-Tail –> added to 3’ end of primary transcript by POLY-A-POLYMERASE to protect from degradation
- Introns –> noncoding regions are cut out by SPLICEOSOMES, if not cut out protein does not fold properly
- Exons –> coding regions, joined together by SPLICEOSOMES
- mRNA transcript = mRNA after capping and tailing
What is GENETIC CODE?
- proteins made of 20 different amino acids
- 3 nucleotides (codon) used to code each amino acid
- AUG start codon
- 3 stop codons
- 64 codons in genetic code
What is Transfer RNA (tRNA)?
- ribosome alone can’t synthesize the polypeptide chain
- correct amino acid must be delivered to polypeptide building site by tRNA
What is an ANTICODON?
- end of lobe of tRNA
- 3 bases that recognize and compliment the codon of mRNA
- 3’ to 5’ direction
- 3’ end of strand is attachment site for corresponding amino acid
Describe RIBOSOMES
- site of protein synthesis
- contains a cluster of different kinds of proteins and rRNA (linear strands of RNA)
- binding sites for mRNA transcript and amino acid (tRNA molecules)
What are the 3 binding sites for tRNA molecules?
1) P (peptide) site: holds one amino acid-tRNA and growing chain of amino acids
2) A (acceptor) site: holds tRNA bringing next amino acid to be added to the chain
3) E (exit) site: releases the tRNA molecules back into cytoplasm
Describe the TERMINATION of TRANSLATION
- translocation of ribosome exposes stop codon in A site
- RELEASE FACTOR - protein binds to exposed A site, makes polypeptide separate from the remaining tRNA molecule
