Genetics: Protein synthesis Flashcards
Test review
What is the role of RNA in protein synthesis?
RNA carries the DNA code from the nucleus to the ribosome so that (3) DNA nucleotides may code for one amino acid to create proteins.
How do RNA and DNA differ?
RNA:
- Sugar = Ribose
- Contains uracil (A - U)
- Different shapes
- Single stranded
DNA:
- Sugar = Deoxyribose
- Contains thymine (A - T)
- Double helix shape
- Double stranded
What are the 3 types of RNA?
1: Messenger RNA (mRNA)
2: Transfer RNA (tRNA)
3: Ribosomal RNA (rRNA)
What is the function of Messenger RNA? (mRNA)
Carries DNA messages for protein construction from nucleus to ribosome.
What is the function of Transfer RNA? (tRNA)
Attaches to the free amino acids in cytoplasm and carry them to the ribosome.
What is the function of Ribosomal RNA? (rRNA)
Makes up part of ribosomes and it’s believed they are involved in amino acids bonding and formation of protein chains.
What is a Codon?
A 3 nucleotide sequence in an mRNA molecule coding a specific amino acid. 3 bases determined via the triplet of nucleotides on DNA molecules.
What are the 2 protein synthesis methods?
1: Transcription
2: Translation
What are the steps in Transcription?
1: RNA polymerase binds to promoter regions of DNA strand and unzips/unwinds the molecule in the region coding for the protein the cell needs. (No helicase)
2: Free RNA nucleotides bind to either DNA strand forming long single strand chain mRNA, copying the complementary DNA strand.
3: Transcription stops upon mRNA formation reaching DNA strand’s terminator signal.
4: mRNA detaches and DNA strands reform together.
5: After processing, mRNA leaves the nucleus. Done by cutting portions of the mRNA with enzymes. Unused portions are introns.
What are introns?
Nucleotides that don’t code for amino acids.
What are exons?
Nucleotides that do code for amino acids.
What are anticodons?
Sequence of 3 nucleotides on a tRNA molecule that will bind to a codon on a mRNA.
What are initiation codons?
Codons that signal beginning of a protein. Where first tRNA attaches.
What are termination codons?
Codons that signal the end of a protein.
What happens in translation?
1: mRNA travels to ribosomes in the cytoplasm, attaching at initiation codons at the 5’ end. (mRNA is read 5’-3’)
2: tRNA picks up specific amino acid from the cytoplasm, bringing it to the ribosome.
3: tRNA’s anticodon attaches to the mRNA’s corresponding codon.
4: Another tRNA binds the same to the mRNA’s next codon, positioning two amino acids side-by-side. Enzymes and rRNA catalyze peptide bond formation between the acids.
5: Other tRNA is released and picks up other amino acids. The ribosome moves down one codon on the mRNA so other tRNAs may attach.
6: tRNA continues bringing amino acids into position, forming a long protein chain.
7: Process stops upon ribosome reaching mRNA’s termination codon. Protein is released from the ribosome to be used.
What is a polysome?
Groups of ribosomes bound to the same mRNA molecule, producing multiple copies of a protein.
