_A2_ 2 - Protein synthesis / Cellular Respiration

Question 1

Transcription - 9 Steps

Answer 1

mRNA copies a section of DNA (Gene)
{Picture a Diagram in your head}

> Transcription starts when RNA polymerase (an enzyme)
attaches to the DNA double helix at the beginning of a gene

> The hydrogen bonds between the two DNA strands in the gene break, separating the strands, and the DNA molecule uncoils at that point

> One of the strands is then used as a TEMPLATE to make an mRNA copy

> the RNA polymerase lines up free RNA Nucleotides alongside the template strand.
Complementary base pairing means that the mRNA strands ends up being a complementary copy of the DNA Template strand
(Except T which is replaced by U in RNA)

> The RNA polymerase moves along the DNA separating the strands and assembling the mRNA strand

> the Hydrogen bonds between the uncoiled strands of DNA reform once the RNA polymerase has passed by and the strands coil back into a double helix

> When RNA polymerase reaches a STOP CODON, it stops making mRNA and detaches from the DNA

> the mRNA moves out of the nucleus through a Nuclear Pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place

Question 2

Translation

Answer 2

Occurs at Ribosomes in Cytoplasm
during translation amino acids are joined together to make a polypeptide chain(protein) following the sequence of codons carried by the mRNA
{Picture a Diagram in your head}

> The mrNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome

> a tRNA molecule with an anticodon complimentary to the FIRST CODON on the mRNA attaches itself to the mRNA by complimentary base Pairing

> a second tRNA molecule attaches itself to the next codon on the mRNA in the same way

> the two amino acids attached to the tRNA molecules are joined by a peptide bond
the first tRNA molecule moves away leaving its amino acid behind

> A Third tRNA molecule binds to the next codon on the mRNA
Its amino acids bind to the first two and the second tRNA molecule moves away

> This process continues producing a chain of linked amino acids (polypeptide chain)
until there’s a STOP CODON on the mRNA molecule

> the polypeptide chain (protein) moves away from the ribosome and translation is complete