Question
b.i. State one role of nucleosomes in eukaryotic cells.[1]
b.ii. Outline how Hershey and Chase’s experiment provided evidence for DNA as the genetic material. [3]
b.iii. State one function for a region of DNA that does not code for proteins. [1]
c.i. Outline the role of the A-site of ribosomes in translation. [1]
c.ii. Outline the role of tRNA activating enzymes in translation. [2]
▶️Answer/Explanation
b.i. Nucleosomes help to pack and coil DNA tightly so it fits inside chromosomes in the nucleus.
b.ii.
- The experiment tested whether DNA or protein carries genetic information.
- They grew viruses (bacteriophages) with radioactive sulfur (S-35) to label protein coats and radioactive phosphorus (P-32) to label DNA.
- After infection, only radioactive DNA entered the bacterial cells, while radioactive protein did not.
- This showed that DNA is the material that carries genetic instructions.
b.iii. Non-coding DNA can control gene activity by acting as regulatory sequences like promoters or enhancers.
c.i. The A-site is where tRNA carrying the next amino acid binds during protein synthesis.
c.ii.
- These enzymes use energy from ATP to attach a specific amino acid to its matching tRNA.
- They ensure each tRNA is charged correctly with the right amino acid for translation.
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a. help to supercoil/pack DNA in chromosomes
b. help to regulate transcription / gene expression
a. experiment is meant to determine whether DNA or protein is the genetic material
b. viruses/bacteriophages grown in radioactive S/S35 which enters the protein coat
c. viruses/bacteriophages grown in radioactive P/P32 which enters the DNA
d. «radioactive» viral DNA entered the bacterial cell during infection
OR
«radioactive» viral protein did not enter the bacterial cell during infection
regulator of gene expression/introns/telomeres/genes for tRNA / rRNA / promoter / enhancer / silencer / site for primer to bind / codes for mRNA primer
binding/entry of tRNA carrying amino acids/aminoacyl tRNA / charged tRNA / site of transfer of growing polypeptide chains/peptide bond formation
a. ATP «hydrolysis» provides energy for amino acid attachment ✔
b. they attach a specific amino acid to the (3′) end / free CCA of a tRNA ✔
c. they do this repeatedly / they attach amino acid to all of the tRNA molecules that have anticodon corresponding to that amino acid