Transcription and Translation

• Seminar for week 5 covers Transcription and Translation.
• The seminar will be held on Monday.

Relevant Material

• The DNA Learning Centre has a web address: https://dnalc.cshl.edu/.
• The textbook is Campbell Biology, Australian and New Zealand Version (12th edition) by Urry et al. (2022), Chapter 17, pages 338-362.

Key Questions this Week

• How does the information in the genetic code produce a protein?
• How is RNA synthesised from DNA?
• How does the sequence of nucleotides in the RNA determine the synthesis of a polypeptide?

Transcription and Translation

• Instructions stored within DNA are read and processed by cells in two steps.
• The central dogma states that information in nucleic acid can be perpetuated or transferred, but the transfer of information into protein is irreversible (Lewin, 2004).
• DNA undergoes replication and transcription to produce RNA, and RNA undergoes translation to produce Protein.

RNA (Ribonucleic Acid)

• RNA has a sugar-phosphate backbone.
• It contains nitrogenous bases: Cytosine (C), Uracil (U, in RNA), Adenine (A), and Guanine (G).
• Nucleoside is composed of a nitrogenous base, a phosphate group, and a sugar (pentose).
• The sugar in RNA is Ribose, while in DNA it's Deoxyribose.

DNA Transcription

• Non-template strand is also known as the coding strand.
• The template strand serves as a template for RNA synthesis.
• The result of transcription is messenger RNA (mRNA).
• Translation of mRNA produces a polypeptide.

Problem Example

• Given the coding strand 5' ATCCTCGAA 3' and template strand 3' TAGGAGCTT 5', use these sequences to determine what the mRNA sequence would be.

What Directs Protein Synthesis?

• DNA directs the cell to make enzymes and other proteins.

Genetic Code

• The genetic code is a set of rules that defines how the 4-letter code of mRNA is translated into amino acids.
• The building blocks of protein are all the same, due to universality of all amino acids.

Evidence: Metabolic Disorder

• Patients with Alkaptonuria accumulate homogentisic acid (alkapton).
• Alkaptonuria suggests these patients lack an enzyme required to metabolise homogentisic acid.
• This was studied by Archibald Garrod in the early 1900s.

Genetic Code Details

• Start codon is AUG.
• Stop codons include UAA, UAG, and UGA.
• A codon is either translated into an amino acid or serves as a translation stop signal.

Transcription: RNA Synthesis

• Prokaryotes vs. Eukaryotes
• In prokaryotes, transcription and translation are coupled and occur in the cytoplasm.
• In eukaryotes, transcription and RNA processing occurs in the nucleus, while translation occurs in the cytoplasm.
• RNA is copied from one strand of a segment of DNA along a template forming an mRNA in the 3' to 5' direction.

Transcription

• Consider what type of sequence is transcribed, what is produced, where the process occurs, and which enzyme is involved.

Translation

• Using the codon table, determine what amino acid sequence would be generated by the following mRNA sequence: 5' AUC CUC GAA 3'.

Translation and Ribosomes

• Ribosomes and tRNAs are involved in translation.
• The ribosome has a P site (peptidyl-tRNA binding site), E site (exit site), and an A site (aminoacyl-tRNA binding site).
• E, P, and A exist on the large subunit with a mRNA binding site on the small subunit.
• tRNA has an amino acid attachment site and an anticodon loop.

Translation Process

• The process is divided into Initiation, Elongation, and Termination.
• Consider what type of sequence is translated, what is produced, where the process occurs, and what is required for translation to occur.