Gene expression Flashcards
Who worked on the haploid neurospora? What was the experiment on neurospora (bread mould), and what was concluded?
- George Beadle and Edward Tatum
- The cells were subjected to x-rays to induce a mutation in one gene per cell. They found that some couldn’t make an essential nutrient…they couldn’t grow on minimal media, but could on enriched media.
- They concluded that the gene that makes the nutrient was disabled so they couldn’t grow on media without it…they lacked an enzyme to make the nutrient
They concluded that there is one gene for one enzyme (One gene-one polypeptide)
What is transcription?
RNA is made from a copy of a strand of DNA
How is DNA vs RNA read/synthesised?
DNA: 3’ to 5’
RNA is synthesised 5’ to 3’
What can be used to determine the amino acid sequence in the RNA?
The non-template strand
What does being out of frame result in?
Different amino acids
What is the start point of transcription called?
The promoter
What is the end point of transcription called?
Termination
What do transcription factors do?
Bind to the DNA at specific locations
What does RNA polymerase ll do in transcription?
Unwinds the DNA strands
What is a terminator sequence?
When RNA polymerase reads a sequence that tells it to stop
What is the pre-mRNA process?
Both ends of the transcript get altered. Introns get split, exons get stitched together
What does a 5’ cap do?
Protects the 5’ end and helps in translation
What do poly-A tails do?
Gives the mRNA stability in the cytosol and helps in translation
What are protein domains?
The place where stuff happens (active sites)
How are introns able to facilitate evolution?
Exon shuffling
The crossing over of the exons of an allele during meiosis
Do prokaryotic mRNAs have introns?
No, they are directly translated
How do tRNAs recognize codons of the mRNA?
Anticodons on the tRNA
Translation occurs via?
tRNAs which transfer amino acids from the cytoplasm to the polypeptide chain in the ribosome
What do anticodons recognize?
Codons to code for amino acids via aminoacyl-tRNA synthetase
What are the functions of ribosomes?
- Facilitate codon-anticodon matching
- Form peptide bonds
What are ribosomes composed of and what are the tRNA sites? (APE)
rRNA and proteins
A=aminoacyl (where tRNAs attach)
P= peptidyl (holding space)
E= exit (where tRNAs are ejected)
What are the steps to build a polypeptide?
- A ribosome is made from rRNA and proteins
- The ribosome binds an mRNA at the 5’ end and finds the first AUG codon to start
- It reads the triplet codons, matching codons with the anticodon from the tRNA
- The new and old amino acids are attached together to form a polypeptide
What are examples of post-translation modifications?
The attachment of sugars, lipids, phosphate groups, etc.
Enzymes that remove amino acids
Enzymes attach two or more polypeptides into a chain
Where do free ribosomes roam?
The cytosol
Where are bound ribosomes?
The rough ER/nuclear envelope
What is the name of the thing that tags a polypeptide?
A signal-recognition particle
What do poly-A tails act as in eukaryotes?
A timer. If it gets too short the mRNA can no longer be translated. Longer tails yields more protein product
Is there mRNA processing in prokaryotes?
No
What are point mutations?
Changing one single nucleotide
What is nucleotide-pair substitution?
Replacements of nucleotide pairs
What are silent mutations?
No change in the amino acid produced
What are missense mutations?
One amino acid is changed
What are nonsense mutations?
A point change resulting in a stop codon
How do insertions and deletions affect the polypeptide sequence?
They shift everything over (frameshift mutations may occur)
What are mutagens?
Chemical or physical agents that alter DNA
