Gene count ≠ complexity of organism.
RNA-
Pulse-chase experiment for RNA discovery-
- Bacteria cultured in radioactive uracil- pulsing. In eukaryotic cells labelled RNA in the nucleus.
- Incubated later. Radioactive uracil washed, breaks down the pulse-labelled RNA- chasing.
Excess unlabelled uracil added, diluting the labelled uracil. In eukaryotic cells labelled RNa found
in cytoplasm + nucleus.
Properties of RNA-
● Ribose sugar. OH group on 2’ instead of H in deoxyribose. O is highly reactive.
● Usually single stranded. Forms more complex 3D shapes by intramolecular base pairing.
● Uracil instead of thymine (U=A). U=G during RNA folding, much weaker.
Advantage of not having uracil in DNA- any deamination mutation of cytosine can be recognised
and repaired.
● Catalyzes biological reactions by being part of ribosome.
Has 5’ & 3’ as like in DNA there is binding of nitrogen base to sugar and phosphate.
Ribonucleotide eg- Adenosine 5′-monophosphate (AMP)
Types of RNA-
● mRNA- intermediary passing info from DNA to protein. Influences gene expression (gene
influencing phenotype) by . mRNA→ functional RNA has the below subdivisions.
Functional RNA (all below)-
Always needed, so continuously synthesised or constitutive transcription. rRNA and tRNa account for largest
% as transcribed into many copies and stable so remain longer. Proteins never translated from all below.
● tRNA- specific tRNA brings its binding amino acids to mRNA in translation.
Aminoacyl-tRNA synthetases- enzymes attaching amino acids to tRNA (called charged).
, Wobble- when third nucleotide of anticodon (at 5’ of anticodon) can form either of alignments.
- A site (aminoacyl)- binds incoming tRNA whose anticodon matches with codon of A site of 30s.
- P site (peptidyl)- part of its structure in 50s. Binds with tRNA containing growing peptides.
- E site (exit)- binds with tRNA with no amino acid and is released from the ribosome.
● rRNA- Ribosome has a small and large subunit. 1-3 rRNA part of each ribosome subunit with
50 proteins, guiding assembly of tRNA and mRNA.
Eukaryotic ribosomes much larger and much more parts- 80s. But, protein synthesis in both eukaryotes
and prokaryotes are similar showing translation to be an ancient process occurring in their common
ancestor.
- Binding site for mRNA in small subunit.
- Binding sites of tRNA in bridges b/w subunits.
- Decoding center of 30s allows only cognate tRNA that is have matching anticodons bind with A
site.
- Peptidyl transferase center (rRNA regions) of 50s is where peptide bond formation is catalysed.
Peptide bond catalysed by active site in ribosome RNA and assisted by ribosomal proteins.
RNA-
Pulse-chase experiment for RNA discovery-
- Bacteria cultured in radioactive uracil- pulsing. In eukaryotic cells labelled RNA in the nucleus.
- Incubated later. Radioactive uracil washed, breaks down the pulse-labelled RNA- chasing.
Excess unlabelled uracil added, diluting the labelled uracil. In eukaryotic cells labelled RNa found
in cytoplasm + nucleus.
Properties of RNA-
● Ribose sugar. OH group on 2’ instead of H in deoxyribose. O is highly reactive.
● Usually single stranded. Forms more complex 3D shapes by intramolecular base pairing.
● Uracil instead of thymine (U=A). U=G during RNA folding, much weaker.
Advantage of not having uracil in DNA- any deamination mutation of cytosine can be recognised
and repaired.
● Catalyzes biological reactions by being part of ribosome.
Has 5’ & 3’ as like in DNA there is binding of nitrogen base to sugar and phosphate.
Ribonucleotide eg- Adenosine 5′-monophosphate (AMP)
Types of RNA-
● mRNA- intermediary passing info from DNA to protein. Influences gene expression (gene
influencing phenotype) by . mRNA→ functional RNA has the below subdivisions.
Functional RNA (all below)-
Always needed, so continuously synthesised or constitutive transcription. rRNA and tRNa account for largest
% as transcribed into many copies and stable so remain longer. Proteins never translated from all below.
● tRNA- specific tRNA brings its binding amino acids to mRNA in translation.
Aminoacyl-tRNA synthetases- enzymes attaching amino acids to tRNA (called charged).
, Wobble- when third nucleotide of anticodon (at 5’ of anticodon) can form either of alignments.
- A site (aminoacyl)- binds incoming tRNA whose anticodon matches with codon of A site of 30s.
- P site (peptidyl)- part of its structure in 50s. Binds with tRNA containing growing peptides.
- E site (exit)- binds with tRNA with no amino acid and is released from the ribosome.
● rRNA- Ribosome has a small and large subunit. 1-3 rRNA part of each ribosome subunit with
50 proteins, guiding assembly of tRNA and mRNA.
Eukaryotic ribosomes much larger and much more parts- 80s. But, protein synthesis in both eukaryotes
and prokaryotes are similar showing translation to be an ancient process occurring in their common
ancestor.
- Binding site for mRNA in small subunit.
- Binding sites of tRNA in bridges b/w subunits.
- Decoding center of 30s allows only cognate tRNA that is have matching anticodons bind with A
site.
- Peptidyl transferase center (rRNA regions) of 50s is where peptide bond formation is catalysed.
Peptide bond catalysed by active site in ribosome RNA and assisted by ribosomal proteins.
