9 Questions
What is the function of codons in protein synthesis?
Determine the specific amino acid sequence
Which of the following nucleotide pairs is found in mRNA but not in DNA?
Adenine and Uracil
During transcription, what happens when RNA polymerase encounters terminators in the DNA sequence?
RNA polymerase stops transcription and detaches from DNA
What role does the ribose sugar play in mRNA?
Differentiates mRNA from DNA
Which enzyme is responsible for adding RNA nucleotides during transcription?
RNA Polymerase
What is the direction of RNA synthesis during transcription?
5' to 3'
In protein synthesis, what is the function of the template strand of DNA?
Serves as a blueprint for mRNA formation
What is the significance of nonoverlapping codons in protein synthesis?
Ensures each nucleotide is read only once
What happens when RNA polymerase recognizes a promoter sequence?
It initiates RNA synthesis at that point
Study Notes
Translation
- Translation is the process of creating a polypeptide (protein) from a messenger RNA (mRNA) sequence.
- Translation occurs in the ribosomes, which are composed of proteins and ribosomal RNA (rRNA).
- The process of translation has three stages: initiation, elongation, and termination.
Initiation
- The small ribosomal subunit binds to the mRNA and the initiator tRNA carrying methionine.
- The small subunit moves along the mRNA until it reaches the start codon (AUG).
- The large ribosomal subunit attaches, and the initiator tRNA sits in the P site.
Elongation
- Amino acids are brought to the ribosome by tRNAs, which bind to the A site.
- A peptide bond forms between the new amino acid and the growing polypeptide chain.
- The growing polypeptide chain is transferred to the P site, and the tRNA in the A site is moved to the E site.
Termination
- When a stop codon reaches the A site, the polypeptide and tRNA are released.
- The ribosome and mRNA separate, and the process is terminated.
Ribosomes
- Ribosomes have multiple tRNA binding sites: P site, A site, and E site.
- The P site holds the tRNA carrying the growing polypeptide chain.
- The A site holds the tRNA carrying the next amino acid to be added to the chain.
- The E site is where tRNAs exit from.
STOP and START Codons
- The START codon is AUG, which signals the start of translation.
- The STOP codons are UAA, UGA, and UAG, which signal the end of translation.
tRNA and Ribosomes
- tRNA has an anticodon that base-pairs with the mRNA codon.
- The ribosome has multiple tRNA binding sites.
The Nature of Genes
- Archibald Garrod (1902) studied alkaptonuria and proposed that genes are connected to enzymes.
- Beadle and Tatum (1941) studied Neurospora crassa and proposed the one gene–one enzyme hypothesis.
- Today, this hypothesis is known as the one gene–one polypeptide hypothesis.
Gene Expression
- Gene expression is the process by which DNA directs protein synthesis.
- It consists of two stages: transcription and translation.
- Transcription is the synthesis of messenger RNA (mRNA) from DNA.
- Translation is the synthesis of a polypeptide from mRNA.
Transcription
- Transcription is the process of creating mRNA from DNA.
- It occurs in the nucleus in eukaryotes.
- The process of transcription has three stages: initiation, elongation, and termination.
Initiation
- RNA polymerase binds to the promoter sequence.
- The DNA strands unwind, and the polymerase initiates RNA synthesis.
Elongation
- RNA nucleotides are added to the 3’ end of the new RNA strand.
- The DNA helix unwinds 10-20 bases at a time and then reforms behind.
Termination
- The new RNA strand is released, and the RNA polymerase detaches from the DNA at the terminator.
Test your knowledge on DNA, RNA, transcription, and translation with this quiz. Questions cover topics like genetic material, gene expression, protein synthesis, and more.
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