BS1030 Topic 4 Lecture 2 RNA and its function Translation

How does RNA differ from DNA?

RNA is single-stranded, contains ribose instead of deoxyribose, and has uracil instead of thymine.

What enables RNA to form complex 3D structures?

Intra-strand base pairing and folding into stem-loops and other secondary structures.

What are the three main types of RNA?

mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA).

What is the role of mRNA?

It carries genetic information from DNA to ribosomes for protein synthesis.

What is the role of tRNA?

It acts as an adaptor molecule, matching amino acids to codons during translation.

What is the role of rRNA?

It forms the structural and catalytic components of ribosomes.

What are non-coding RNAs (ncRNAs)?

RNAs that are not translated into proteins but have regulatory or catalytic functions (e.g., rRNA, tRNA, miRNA, snRNA).

What is the RNA world hypothesis?

The idea that RNA preceded DNA and proteins in evolution, acting as both genetic material and catalyst.

Why is RNA still catalytically active today?

Ribozymes (RNA catalysts) remain crucial in key biological reactions, e.g., peptide bond formation in ribosomes.

What does the Central Dogma describe?

The flow of information: DNA → RNA → Protein.

How is the genetic code structured?

It is a triplet code where three nucleotides (codon) specify one amino acid.

Who discovered how the genetic code is read?

Marshall Nirenberg and Heinrich Matthaei in 1961 using a synthetic poly-U RNA that produced polyphenylalanine.

What did the Nirenberg experiment demonstrate?

mRNA acts as a messenger, instructing ribosomes to assemble amino acids into proteins.

What are the key properties of the genetic code?

Triplet, non-overlapping, degenerate (multiple codons per amino acid), universal, and comma-less.

How many codons exist in total?

64 codons (61 code for amino acids, 3 are stop codons).

What are the three stop codons?

UAA, UAG, and UGA.

What is the start codon?

AUG, which codes for methionine and sets the reading frame.

What is a reading frame?

A way of dividing nucleotide sequences into consecutive, non-overlapping triplets; only one frame produces the correct protein.

What determines the correct reading frame?

The AUG start codon during initiation.

What was the RNA Tie Club?

A group of scientists (including Crick and Watson) who discussed genetic code mechanisms in the 1950s.

What is the role of tRNA in translation?

tRNA matches amino acids to their corresponding codons on mRNA via its anticodon.

Who determined tRNA structure?

Robert Holley (2D, 1965) and Robert Kim & Sung-Hou Book (3D, 1974).

How long are typical tRNAs?

Between 73 and 93 nucleotides.

What is an aminoacyl-tRNA?

A tRNA molecule covalently attached to its specific amino acid.

What enzyme charges tRNAs with amino acids?

Aminoacyl-tRNA synthetase.

How does aminoacyl-tRNA synthetase function?

It covalently couples each amino acid to its matching tRNA, ensuring correct translation.

Approximately how many tRNA genes do bacteria have?

Between 60 and 90.

What is the function of ribosomes?

They catalyse the assembly of amino acids into polypeptides using mRNA templates.

What are the subunits of bacterial ribosomes?

Small (30S) and large (50S) subunits.

What does the 30S ribosomal subunit contain?

16S rRNA (~1500 nucleotides) and about 20 proteins.

What does the 50S ribosomal subunit contain?

23S rRNA (~2900 nucleotides), 5S rRNA (~120 nucleotides), and about 30 proteins.

Who won the 2009 Nobel Prize for ribosome structure?

Venkatraman Ramakrishnan, Thomas Steitz, and Ada Yonath.

What are the tRNA binding sites in ribosomes?

A site (aminoacyl-tRNA), P site (peptidyl-tRNA), and E site (exit site).

How many tRNAs can be bound to the ribosome simultaneously?

Three.

Where does decoding of codons occur?

In the small ribosomal subunit.

Where does peptide bond formation occur?

In the large ribosomal subunit at the peptidyl transferase centre (PTC).

What type of enzyme is the ribosome?

A ribozyme (catalytic RNA).

Who proposed the ribosome might be a ribozyme?

Francis Crick in 1968.

What drives translation forward?

Elongation factors such as EF-Tu and EF-G, which also maintain accuracy.

What are the three phases of translation?

Initiation, elongation, and termination.

What recognises stop codons?

Release factors (RFs), which mimic tRNA structure and bind to the A site to terminate translation.

How do release factors terminate translation?

They trigger hydrolysis of the polypeptide from tRNA at the P site.

How does bacterial translation differ from eukaryotic translation?

In bacteria, transcription and translation occur simultaneously; in eukaryotes, they are separated by the nuclear envelope.

What are Shine-Dalgarno sequences?

Ribosome-binding sites in bacterial mRNA located 4-7 nucleotides upstream of the AUG start codon, complementary to 16S rRNA.

How can one mRNA encode several proteins in bacteria?

Bacterial mRNAs are polycistronic, containing multiple open reading frames.

What are untranslated regions (UTRs) in mRNA?

Non-coding sequences at the 5′ and 3′ ends that regulate translation efficiency and mRNA stability.