Transcription and Translation

• Genes provide the code for protein synthesis.
• The learning objective is describing the process of transcription and translation.

Transcription and Translation Overview

• A collective process where enzymes read the genetic code.
• This in turn produces all proteins in a cell.
• Certain chromosome portions encode genes.
• When a gene expresses, it produces a specific protein.

Transcription:

• DNA is first transcribed in the nucleus into messenger RNA (mRNA).
• mRNA then acts as a template for protein synthesis at the ribosome in the cell.
• mRNA made in the nucleus relocates across the nuclear membrane, entering the cytoplasm to reach the ribosome.

Translation:

• Synthesis occurs here through translation at the ribosome.
• Amino acids are brought to the ribosome using tRNA.
• These are then linked together by peptide linkage.
• Proteins are then released from the ribosome which folds into a 3D structure.
• Protein synthesis rates are higher in prokaryotes and lower in eukaryotes cells.
• Protein structure encodes in genes.
• 1 Amino acid codes through 3 nucleotide bases, known as a codon.
• Each three-nucleotide combination defines which amino acid it will be.

What happens when DNA is transcribed?

• A complementary RNA strand is created from an original DNA strand.
• mRNA is similar to DNA, though DNA is double-stranded and RNA is single-stranded.
• DNA uses cytosine, guanine, adenine, and thymine, while RNA uses uracil instead of thymine.
• RNA is like a disposable copy of instructions while DNA is the original copy.

Process of Transcription and Translation

• Cells produce protein using two main steps: transcription and translation.

Transcription:

• Occurs in the nucleus.
• A section of DNA unwinds, and RNA polymerase reads one strand of the DNA.
• A messenger RNA (mRNA) strand builds by matching complementary RNA bases to the DNA template, A pairs with U, and C pairs with G.
• The resulting mRNA strand moves from the nucleus to a ribosome in the cytoplasm.

Translation

• This happens at the ribosome.
• The ribosome reads the mRNA in three-letter codons.
• Each codon codes for a specific amino acid.
• Transfer RNA (tRNA) molecules bring the correct amino acids to the ribosome.
• Then the amino acids link together to form a protein.
• Once the full protein is made, it folds into its final shape and carries out its function in the cell.

Protein Synthesis

• Proteins have a finite lifetime & will break down or degrade over time.
• Amino acids are recycled by the cell.
• Abnormal or misfolded proteins degrade more quickly through being marked for destruction, or if unstable

mRNA vaccines

• mRNA vaccines provides a new technology clinically approved for COVID-19 in 2020.
• mRNA molecules encoding the viral spike protein deliver to human host cells.
• mRNA interacts with ribosomes in host cells.
• Host cells synthesise the spike protein by following mRNA information.
• This spike protein recognizes the human immune system, which results in antibody production.
• The spike protein alone does not cause disease, but it induces immunity against SARS-CoV-2.
• Generally, mRNA proves much less stable than DNA.
• mRNA vaccines must be refrigerated due to the instability.
• Many antibiotics target either translation or transcription in bacteria.