Botany MCQs for NEET — Practice Questions with Answers

The sequence of amino acids in protein synthesis is determined by the sequence of mRNA. During translation, the mRNA sequence is read by the ribosome, and tRNA molecules bring the corresponding amino acids to form a polypeptide chain.

The term 'antiparallel' in the context of DNA refers to the orientation of the two strands of the DNA molecule. In an antiparallel arrangement, the phosphate groups at the start (5' end) of one strand are aligned opposite to the phosphate groups at the start (5' end) of the other strand. This means one strand runs in the 5' to 3' direction, while the complementary strand runs in the 3' to 5' direction.

A polysome, or polyribosome, is a complex formed by multiple ribosomes simultaneously translating a single mRNA strand. This arrangement allows for the production of multiple copies of a protein from a single mRNA molecule, thereby increasing the efficiency of protein synthesis.

The semiconservative replication of DNA, which means that each of the two new DNA molecules contains one original and one new strand, was first demonstrated in Escherichia coli by Matthew Meselson and Franklin Stahl in 1958. This experiment provided strong evidence for the semiconservative model of DNA replication.

Ribosomal RNA (rRNA) is actively synthesized in the nucleolus. The nucleolus is a region within the nucleus where rRNA is transcribed and assembled into ribosomal subunits. This makes the nucleolus the main site for rRNA synthesis.

AUG has dual purpose-

1.it codes for methionine 

2. it is the start codon 

The semiconservative model of DNA replication using extsuperscript{15}N (heavy nitrogen) was demonstrated by Matthew Meselson and Franklin Stahl. In their famous experiment, they used density gradient centrifugation to show that DNA replication involves each of the two parent strands serving as a template for a new strand, resulting in two daughter DNA molecules, each with one old and one new strand.

In the operon model, the operator gene binds with the repressor protein (produced by the regulator gene) to switch off the transcription of structural genes. When the repressor is bound to the operator, RNA polymerase is blocked from transcribing the genes within the operon. This is a key regulatory mechanism in prokaryotic gene expression.

Termination of chain growth in protein synthesis is brought about by UAA, UAG, UGA. Translation starts with a chain initiation codon or start codon and terminates with a stop codon. 

The three stop codons have been given names : UAG is amber, UGA is opal, and UAA is ochre. Stop codons are also called "termination" or "nonsense" codons.

Transfer RNAs (tRNAs) decipher the mRNA information and transfer the appropriate amino acid to a growing polypeptide chain during protein synthesis.