gene expression

Question 1

Central Dogma of molecular bio

Answer 1

DNA - RNA-Protein

trnasciption : DNA is trnascribed into MRNA

translation: mRNA is trnaslated into protein

Question 2

transcription (RNA synthesis)

Answer 2

Occurs in the nucleus (euk)/ cytoplasm (pro)

key enzyme: RNA polymerase synthesizes mRNA from a DNA template

stages:
initiation:RNA polymerase binds to the promotor
elongation:RNA polymerase adds nucleotides to t he 3’ end of the growing RNA strand
termination: transcription stops at a termination sequence.

Question 3

mRNA processing in EUK

Answer 3

5’ CAP : helps mRNA exit the nucleus and bind to ribosomes

Poly A tail: protects mRNA from degradation

splicing:
introns (non-coding regions) are removed

exons(coding regions) are joined together

Question 4

translation ( protein synthesis)

Answer 4

occurs in the ribosome (cytoplasm or rough ER)

mRNA: carries genetic code from DNA

tRNA: matches mRNA codons to amino acids

Ribosome:reads mRNA and assembles proteins

Question 5

genetic codes and open reading frames

Answer 5

codons : three letter mRNA sequence coding for amino acids

reading frames: only the correct frame starting from AUG, will produce the correct protein

Question 6

mutations

Answer 6

point mutations:
silent mutations : no change
missense mutation: change in one amino acid
nonsense mutations: creates a premature stop codon

frameshift mutations:

insertion or deletion of nucleotides shifts the reading frame often producing a nonfunctional protein

Question 7

Describe the process of transcription, including the role of RNA polymerase, promoters, and termination signals.

Answer 7

Transcription starts when RNA polymerase binds to the promoter region (TATA box in eukaryotes). It unwinds DNA and synthesizes RNA complementary to the template strand. Transcription ends when RNA polymerase reaches a termination signal.

Question 8

Explain the steps of translation, identifying the roles of mRNA, tRNA, ribosomes, and codons.

Answer 8

Translation occurs in three steps: (1) Initiation - Ribosome binds mRNA at AUG; (2) Elongation - tRNA brings amino acids to the ribosome; (3) Termination - Stop codon releases the polypeptide.

Question 9

Given the DNA sequence 5’ - TACGCTAGCATTAGC - 3’, transcribe the mRNA sequence and determine the amino acid sequence using a codon table.

Answer 9

mRNA sequence: 5’ - AUG CGA UCG UAA - 3’
Amino acids: Met - Arg - Ser - STOP

Question 10

Mutations in DNA can have varying effects on protein function. Provide an example of a beneficial, neutral, and harmful mutation, explaining how each affects an organism.

Answer 10

A beneficial mutation might improve enzyme function (e.g., lactose tolerance), a neutral mutation has no effect (e.g., a silent mutation), and a harmful mutation may cause disease (e.g., sickle cell anemia).