gene expression

Question 1

What is DNA transcription?

Answer 1

DNA transcription is the process by which the genetic information contained within DNA is rewritten into messenger RNA (mRNA) by RNA polymerase.

Question 2

What is the role of RNA polymerase in transcription?

Answer 2

RNA polymerase is an enzyme that synthesizes mRNA during transcription. It reads the DNA template strand and assembles complementary RNA nucleotides, resulting in the formation of an mRNA molecule.

Question 3

What is mRNA?

Answer 3

mRNA, or messenger RNA, is a type of RNA molecule that carries the genetic information from DNA to the ribosomes in the cytoplasm. It serves as a template for protein synthesis during translation.

Question 4

What is RNA processing?

Answer 4

RNA processing is a series of modifications that occur to the pre-mRNA molecule after transcription but before it is ready for translation. These modifications include the addition of a 5’ cap, a poly-A tail, and the removal of introns through splicing.

Question 5

What is the purpose of RNA processing?

Answer 5

RNA processing helps in stabilizing the mRNA molecule, promoting its export from the nucleus, and determining which parts of the mRNA will be translated into protein.

Question 6

What is translation?

Answer 6

Translation is the process by which the genetic information carried by mRNA is used to synthesize proteins. It occurs in the ribosomes and involves the decoding of the mRNA sequence by transfer RNA (tRNA) molecules and the assembly of amino acids into a polypeptide chain.

Question 7

What happens during initiation in transcription?

Answer 7

During initiation, RNA polymerase attaches to the DNA molecule at the promoter sequence. Transcription factors, along with RNA polymerase, bind to the promoter sequences to control the rate of transcription. RNA polymerase then unwinds a portion of the DNA double helix, exposing the bases on each DNA strand.

Question 8

What occurs during elongation in transcription?

Answer 8

In elongation, RNA polymerase uses the template strand of DNA to synthesize a complementary mRNA strand in a 5’ to 3’ direction. It catalyzes the formation of phosphodiester bonds between adjacent ribonucleotides, following the rules of complementary base pairing. The coding strand of DNA, which is identical to the mRNA sequence except for the replacement of thymine with uracil, is not directly involved in mRNA synthesis.

Question 9

How does transcription terminate?

Answer 9

Transcription termination occurs when RNA polymerase encounters a stop sequence in the DNA template. This signals the end of transcription, and RNA polymerase releases the DNA template, completing the synthesis of the mRNA molecule.

Question 10

What direction does elongation occur in transcription?

Answer 10

Elongation in transcription proceeds in a 5’ to 3’ direction. New ribonucleotides are added to the 3’ end of the growing mRNA strand.

Question 11

What is pre-mRNA?

Answer 11

Pre-mRNA is the initial product of transcription before it undergoes processing to become mature mRNA. It contains both coding sequences called exons and non-coding sequences called introns.

Question 12

What is splicing in pre-translational mRNA processing?

Answer 12

Splicing is the process of removing introns (non-coding sequences) from the pre-mRNA and joining together the exons (coding sequences). It is carried out by a complex called the spliceosome, which excises the introns and ligates the exons together.

Question 13

What is the purpose of splicing in pre-translational mRNA processing?

Answer 13

Splicing allows a single pre-mRNA molecule to produce multiple different proteins by removing introns and retaining exons. This process conserves genetic material and increases the protein-coding potential of the genome.

Question 14

How is splicing carried out?

Answer 14

Splicing is carried out by the spliceosome, a complex of RNA and protein molecules that recognizes specific sequences at the boundaries of introns and exons. The spliceosome catalyzes the excision of introns and the joining of exons to form the mature mRNA.

Question 15

What is mature mRNA?

Answer 15

Mature mRNA is the final processed form of mRNA that is ready for translation. It contains only the coding sequences (exons) and serves as the messenger for protein synthesis during translation.

Question 16

What is translation?

Answer 16

Translation is the process in which the genetic code carried by mRNA is decoded to produce a specific sequence of amino acids, forming a polypeptide chain or protein.

Question 17

What are the key components required for translation?

Answer 17

The key components required for translation are mRNA, ribosomes, and transfer RNA (tRNA).

Question 18

How is the genetic code translated during translation?

Answer 18

MRNA is read in sets of three nucleotide bases called codons during translation. Each codon codes for a specific amino acid. with their anticodons complementary to the mRNA codons, tRNA molecules bring the corresponding amino acids to the ribosome for polypeptide assembly.

Question 19

What is the role of tRNA in translation?

Answer 19

tRNA molecules play a crucial role in translation by carrying specific amino acids to the ribosome. Each tRNA molecule has an anticodon that is complementary to the mRNA codon, ensuring the correct matching of amino acids to the mRNA sequence.

Question 20

What is the role of ribosomes in translation?

Answer 20

Ribosomes are the cellular structures where translation occurs. They provide the platform for the assembly of mRNA and tRNA, allowing the amino acids carried by tRNA to be joined together in the correct order to form a polypeptide chain.

Question 21

Can a single amino acid be coded for by more than one codon?

Answer 21

Yes, a single amino acid can be coded for by more than one codon. This property is known as the degeneracy of the genetic code. For example, the amino acid leucine can be encoded by six different codons: UUA, UUG, CUU, CUC, CUA, and CUG.

Question 22

What are start and stop codons in translation?

Answer 22

Start codons and stop codons are specific codons that signal the beginning and end of translation, respectively. The start codon, AUG (codes for methionine), marks the initiation of protein synthesis. The three stop codons, UAA, UAG, and UGA, do not code for any amino acids but instead indicate the termination of translation.

Question 23

What is the significance of start and stop codons in translation?

Answer 23

Start codons and stop codons play a crucial role in determining the initiation and termination of protein synthesis. They provide the necessary signals for the ribosome to start reading the mRNA and assembling amino acids into a polypeptide chain, as well as to stop the process and release the completed polypeptide.

Question 24

What is the start codon and its significance in translation initiation?

Answer 24

The start codon is the mRNA sequence 5’AUG’ that codes for the amino acid methionine. It marks the beginning of the protein-coding region and is recognized by the small 40S subunit of the ribosome during translation initiation.

Question 25

What is the initiation complex in translation?

Answer 25

The initiation complex is formed when the small 40S ribosomal subunit binds to the mRNA’s 5’ cap, followed by the binding of the larger 60S subunit. This complex is necessary for the initiation of translation.

Question 26

What occurs during elongation in translation?

Answer 26

During elongation, the ribosome has two tRNA binding sites: the P site (peptide site) and the A site (amino acid site). The tRNA complementary to the next codon binds to the A site, using energy from the hydrolysis of GTP. The growing polypeptide chain attached to the tRNA in the P site is transferred to the amino acid on the tRNA in the A site.

Question 27

How does translocation occur during elongation?

Answer 27

After peptide bond formation, the ribosome translocates along the mRNA molecule to the next codon. This translocation requires the hydrolysis of GTP, providing the energy for the movement of the ribosome. As a result, the tRNA that was in the P site moves to the E site (exit site) and then exits the ribosome, while the tRNA in the A site moves to the P site for the next round of elongation.

Question 28

What happens during termination in translation?

Answer 28

During termination, one of the three stop codons (UAA, UAG, or UGA) enters the A site of the ribosome. Since there are no tRNA molecules that bind to stop codons, the peptide chain and the tRNA in the P site are hydrolyzed. This releases the completed polypeptide into the cytoplasm. The small and large subunits of the ribosome dissociate, preparing for the next round of translation.

Question 29

What are microRNAs (miRNAs)?

Answer 29

MicroRNAs (miRNAs) are non-coding RNA molecules that play a critical role in gene expression. They are small RNA sequences that can bind to complementary sequences in messenger RNA (mRNA) molecules. This binding can regulate gene expression by preventing translation or promoting degradation of the targeted mRNA.

Question 30

How do microRNAs affect gene expression?

Answer 30

MicroRNAs regulate gene expression by binding to complementary sequences in mRNA molecules. This binding can prevent translation of the mRNA into protein or lead to degradation of the mRNA, thus reducing the abundance of the corresponding protein. MicroRNAs play an important role in controlling gene expression and fine-tuning cellular processes.