Molecular Biology: Transcription and Translation

Course Information

• Course Title: The Human Body PJ1311
• Lecturer: Dr Lamia Kandil
• Lecturer Credentials: Lecturer of Pharmacy Practice, PhD, FHEA, MB138
• Contact Email: [email protected]

Kandil Lectures

• Three lectures on Genomics, Central Dogma of Life (Transcription, Translation), and Cell cycle and control mechanism will be covered.

Learning Outcomes

• Understand the Central Dogma of Molecular Biology
• Differentiate Between Key Processes: Transcription and Translation
• Identify the Role of mRNA, tRNA, and rRNA
• Post-transcription and Post-Translational modifications
• Gene regulation in Prokaryotes and Eukaryotes and its importance
• Application of knowledge through four different activities

The "Central Dogma"

• Flow of genetic information in a cell
• Movement of information from DNA to proteins.
• DNA → RNA→ Protein → Trait
• DNA gets all the glory; proteins do all the work!

From Gene to Protein

• Overview of the process.
• Transcription takes place in the nucleus.
• mRNA moves from nucleus to cytoplasm
• Translation occurs in the cytoplasm, involving ribosomes, tRNA, and amino acids
• Gene expression results from the process.

Gene Expression

• The process by which information encoded in genes is used to create functional products.

Transcription in Eukaryotes

• DNA cannot leave the nucleus
• Transcription steps
• RNA processing is required for mature mRNA production

The Process of Building mRNA

• Initiation: Assembly of initiation complex
• Elongation: Adding nucleotides
• Termination: Signals to stop transcription

Transcription in Eukaryotes

• Initiation complex binds to the promoter region, upstream of the gene.
• Proteins bind to DNA to turn on/off transcription.
• TATA box binding site is crucial
• Transcription factors trigger RNA polymerase binding to DNA .

Elongation

• RNA polymerase 2 "walks" along the template strand (3' to 5')
• RNA polymer is complementary to the template DNA and is synthesized in a 5' → 3' orientation.
• Matching RNA nucleotides are added to the 3' end of the RNA strand

Termination

• RNA polymerase continues until termination signals are received
• Polyadenylation is a process that includes adding a poly-A tail (AAUAAA) to the 3′ end of the pre-mRNA.
• Signals the termination of transcription.

Post-Transcriptional Processing

• Eukaryotic mRNA needs processing
• Protect mRNA from enzymes in cytoplasm by adding a 5' cap.
• mRNA splicing: Editing out introns
• Adding a poly-A tail

Post-Transcriptional modifications

• Primary RNA is modified to produce a mature messenger RNA or mRNA

Processes Involved

• Splicing: removal of introns from pre-mRNA
• Capping: addition of a cap molecule to the 5' end of mRNA
• Tailing: addition of a poly A tail to the 3′ end
• RNA transport: Transport of mature mRNA from the nucleus into the cytoplasm
• Protein Transport:

Splicing must be accurate

• Precise splicing procedures are crucial.
• A change in the reading frame (single base addition/loss) results in errors and wrong protein synthesis.

Activity: Comparing Transcription in Prokaryotes and Eukaryotes

• Objective: Identify the differences between transcription in prokaryotes and eukaryotes.

Prokaryote vs. Eukaryote genes

• Prokaryotes: circular chromosomes, DNA in cytoplasm, naked DNA, no introns
• Eukaryotes: linear chromosomes, DNA in nucleus, DNA wound on histone proteins, introns

Prokaryotes vs. Eukaryotes

• Prokaryotes: transcription and translation happen in cytoplasm, RNA polymerase directly binds to promoter, no mRNA processing
• Eukaryotes: transcription in nucleus, translation in cytoplasm, DNA in nucleus, mRNA travels, RNA polymerase uses transcription factors, pre-mRNA processed to mRNA, introns removed.

Translation

• Nucleic acid language converted to amino acid language
• Codons: Three nucleotides that code for amino acids

mRNA codes for proteins in triplets

• Three nucleotides form codons
• Codons are specific for amino acids

The code

• Code is redundant: several codons for each amino acid
• Third base "wobble" good reason

How are the codons matched to amino acids?

• tRNA matches mRNA codons to amino acids.
• tRNA has an anticodon that is complementary to the codon.

From gene to protein

• Transcription produces mRNA transcribed from DNA
• mRNA leaves nucleus, moves to cytoplasm
• Ribosomes translate mRNA into proteins, aided by tRNA

Transfer RNA structure

• Clover leaf structure
• Anticodon at one end
• Amino acid attachment site at the other end

Ribosomes

• Facilitate coupling of tRNA anticodon to mRNA codon.
• Organelle or enzyme?
• Structure: ribosomal RNA (rRNA) and proteins, large and small subunits, A site, P site, E site

Sites of Ribosome

• These sites aid in tRNA binding
• P site: peptidyl-tRNA site; holds tRNA with growing polypeptide chain
• A site: aminoacyl-tRNA site; holds tRNA carrying the next amino acid
• E site: exit site; empty tRNA leaves the ribosome

Building a polypeptide

• Initiation: Bringing together mRNA, ribosome subunits, initiator tRNA
• Elongation: Adding amino acids based on codon sequence
• Termination: end codon

Activity: Transcription vs Translation

• Objective: To identify the key protein differences between transcription and translation

Post-translational modifications (PTMs)

• Amino acid side-chain modifications
• Affects many aspects of protein functions.
• Affects enzyme function, assembly, protein lifespan, interactions, trafficking, receptor activation

Regulation of Gene Expression

• Control the timing, location and amount of gene expression
• Carried out by regulatory proteins and chemical modifications of DNA
• Crucial for organism responses.

Gene Regulation in Prokaryotes

• Proteins for a specific function are encoded in blocks (operons).
• Activators (increase expression), repressors (suppress expression), inducers (inactivate repressors) are regulatory proteins.

Eukaryotic Gene Regulation

• More complex and can happen at many levels, including : epigenetic, transcriptional, post-transcriptional, translational, and post-translational. Genes are not organized into operons.

Importance of regulation of Gene Expression

• Organisms adapt to environmental challenges through altering gene expression patterns.
• Gene regulation is affected by hormones, heavy metals, and chemicals
• Transcription control results in tissue-specific gene expression
• Dysregulation leads to diseases..