Molecular Basis of Inheritance Flashcards
What were early theories about encoding of genetic information?
- 1940: DNA is too simple to encode genetic information
- DNA only has four bases
- Proteins have 20 amino acids
What was Avery et al.’s experiment?
- 1944
- Proof that DNA carries genetic information
- Killer S strain: mouse dies
- Safe R strain: mouse lives
- Heat killed S strain: mouse lives
- Heat killed S strain + R strain: mouse dies and live S strain cells produced
What did Watson and Crick do?
- 1950
- Developed the double-helix model for the structure of DNA
- Used Rosalyn Franklin’s X-ray image
What are interesting features of DNA?
- Can replicate
- Can hold information in its series of bases
- Can self repair
What is the importance of pyrimidine and purine bases?
- Pyrimidine + pyrimidine = DNA too thin (T + C)
- Purine + purine = DNA too thick (A + G)
- Pyrimidine + purine = thickness compatible with X-ray data
What type of replication is DNA replication?
- Semiconservative (not conservative or dispersive)
- As suggested by Watson and Crick’s model
What is the central dogma of gene expression?
DNA, transcription, mRNA, translation, protein
What is the difference between DNA and RNA?
- In RNA Uracil replaces Thymine
- RNA exists as a single strand
- RNA sugar backbone is ribonucleotides rather than deoxyribonucleotides
What are the steps of eukaryotic protein synthesis?
- DNA is unravelled by helicase
- RNA polymerase transcribes RNA from DNA
- Introns are excised from RNA transcript
- Remaining eons are spliced together and 5’ cap and 3’ poly-A tail are added to form mRNA
- Ribosomal subunits bind to the mRNA
- tRNA molecules become attached to specific amino acids with the help of activating enzymes
- tRNA molecules bring their animo acids in a the A site on the ribosome if their anticodon matches the mRNA codon
- Peptide bonds form between amino acids at the P site
- tRNAs exit the ribosome from the E site
- The polypeptide chain grows until the protein is completed
What are introns?
- Sections of RNA transcript
- Spliced out
- Junk DNA that may have a regulatory function
- Evolve fast
What are exons?
- Sections of RNA transcript
- The actual translated gene
- Evolve slowly
What is the genetic code made up of?
Made up of triplet base codons for:
- Stop: UGG, UGA, UAA
- Start: AUG
- A specific amino acid
What are reading frames?
- Frames used to interpret mRNA transcript
What is an open reading frame?
- Contains no stop codons (except at the end)
- Makes a sensible transcript
What is a frame shift mutation?
- The reading frame is shifted due to a mutation
- The wrong amino acids result
- Protein may not function properly
What is gene regulation?
- Turning genes on and off according to the cell’s needs
How does the lac operon work when there is no lactose present?
- Repressor gene is expressed
- Repressor protein binds to operator
- Transcription is prevented
- Lac gene is not expressed
How does the lac operon work when there is lactose present?
- Repressor gene is expressed
- Inducer (lactose) binds to repressor protein
- Repressor protein does not bind to operator
- Lac gene is expressed
How is gene expression controlled in prokaryotes?
PAPTEST/in order
- Regulation of frequency of transcription initiation: regulatory proteins affect ability of RNA to bind to promoter
- Altering splicing of exons: faster processing means more gene product
- Access to and efficiency of transport channels (nuclear pores): transcript must be recognised by receptors lining pores
- Enzyme degradation: degree of mRNA transcript degradation changes gene expression
- Speed of protein synthesis
- Availability of amino acids
- Post-translational modification: chemical modifications that alter protein activity e.g. phosphorylation
