4.2 dna and protein synthesis

what is the first station of protein synthesis and where it happens

transcription, in the nucleus

what is transcription

process of making pre-mRNA using part of the DNA as template

explain process of DNA unwinding in transcription

-The enzyme DNA helicase breaks hydrogen bonds between complementary DNA bases, separating the strands.

-This exposes the template strand which is used to make mRNA.

-only 1 DNA strand acts as the template strand

how do free RNA nucleotides bind to the template DNA strand in transcription

-Free RNA nucleotides align with complementary bases on the template strand using base pairing rules: 

• A → U (uracil, instead of thymine).

• T → A.

• C → G.

• G → C

how does RNA polymerase join nucleotides together

-The enzyme RNA polymerase moves along the template strand, joining adjacent RNA nucleotides on the new strand via phosphodiester bonds, forming pre-mRNA (in eukaryotes) or mRNA (in prokaryotes).

-The formation of phosphodiester bonds is an example of a condensation reaction and requires ATP

why is there no splicing in prokaryotic cells

pre-mRNA is not produced

explain process of splicing

• In eukaryotes, pre-mRNA contains introns (non-coding regions) and exons (coding regions).

  • Splicing removes introns, leaving only exons to form mature mRNA

how does mRNA leave the nucleus and where it goes

-through nuclear pores

-goes to the ribosomes in cytoplasm

where does translation happen

ribosomes in cytoplasm

what is the second step of protein synthesis

translation

what does mRNA attach to once it leaves the nucleus

it attaches to a ribosome

what happens in translation briefly

mRNA sequence is used to assemble a polypeptide at the ribosome. It involves mRNA, ribosomes, tRNA, and amino acids.

what happens when mRNA molecule attaches to ribosome in translation

-The mRNA molecule attaches to a ribosome.

-The ribosome reads the mRNA codons (triplets of bases) one at a time.

how does tRNA deliver amino acids in translation

-tRNA molecules, each carrying a specific amino acid, bind to the ribosome.

-The anticodon on the tRNA will bind to a complementary codon on the mRNA.

how is peptide bond formed in translation

-The ribosome catalyses the formation of a peptide bond between adjacent amino acids, forming a polypeptide chain.

-This requires energy from ATP.

-The first tRNA detaches, and the ribosome moves to the next codon.

when does a process of protein synthesis (translation) stop

when stop codon is reached

what happens to the polypeptide after translation

polypeptide chain is released, it undergoes further modifications to become a fully functional protein.