Unit 13 Flashcards
What two studies of Archibald Garrod were evidence that genes encoded enzymes and inspired Beadle and Tatum?
- Alkaptonuria
- Phenylketonuria
Mutations in what cause phenylketonuria?
Phenylalanine hydroxylase
Mutations in what cause alkaptonuria?
Homogentisic acid oxidase
What does alkaptonuria cause?
It causes a mutation in homogentisic acid oxidase and prevents the metabolizing of homogentisic acid
What are three things that happens when we can’t metabolize homogentisic acid?
- It accumulates in cells and tissues and is secreted in the urine
- the acid accumulates in joints leading to benign arthritis
- Oxidation products are black and detected in the diapers of newborns and also accumulate in cartilaginous areas, causing the ears and nose to darken
What does phenylketonuria cause?
It causes a defect in phenylalanine hydroxylase which makes it so Phe can’t be converted to Tyr
What are some symptoms of phenylketonuria?
Intellectual disability
Seizures
Should eat a diet low in protein and avoid diet coke
What did Beadle and Tatum study that supported the One-Gene One-Enzyme hypothesis?
Studies of Neurospora (bread mold)
What experiment did Beadle and Tatum first conduct on Neurospora?
- They first induced a nutritional mutation into the experimental group and placed them into 5 tubes containing different mediums and observed which medium allowed the mutated neurospora to grow.
- The neurospora only grew on the minimal medium with AA
What was the second experiment Tatum and Beadle performed after learning the neurospora only grew on the medium containing AA?
- They made individual 20 test tubes that all had minimal medium but they each had a different AA in it.
- The neurospora only grew on the complete medium and the medium containing tyrosine.
Why not one-gene one-protein or one-gene one-polypeptide chain
- Nearly all enzymes are proteins but not all proteins are enzymes
- Some proteins have a subunit structure with two or more polypeptide chains
- Sickle cell anemia (defect in the beta globulin subunit of hemoglobin)
Explain sickle-cell anemia:
It is a recessive genetic disease where erythrocytes become elongates under low oxygen tension.
Afflicted individuals are homozygous for Hbs hemoglobin allele
What is a homopolymers?
A polymer of a single type of nucleotide
How did we discover UUU encodes for Phe?
- A homopolymer of U’s, poly(U) mRNA as added to a test tube containing a cell-free translation system, 1 radioactively labeled amino acids, and 19 unlabeled amino acids
- The tube was then incubated at 37 degrees Celsius so translation could take place and then the protein was filters and checked for radioactivity
- This was then repeated with 20 tubes all containing a different amino acid until the tube labeled Phe was shown have radioactive Phe.
How did we discover UUU encodes for Phe?
- A homopolymer of U’s, poly(U) mRNA as added to a test tube containing a cell-free translation system, 1 radioactively labeled amino acids, and 19 unlabeled amino acids
- The tube was then incubated at 37 degrees Celsius so translation could take place and then the protein was filters and checked for radioactivity
- This was then repeated with 20 tubes all containing a different amino acid until the tube labeled Phe was shown have radioactive Phe.
What is a charged tRNA?
a tRNA that has an AA attached to it.
How many aminoacyl synthase are there?
20 - one for each AA
What are Isoaccepting tRNAs?
they carry the same AA but have different anticodons
What enzyme can be used to generate a synthetic messenger RNA without the need for a DNA template?
Polynucleotide phosphorylase
What amino acid is encoded for by the codon 5’-UCC-3’?
Serine
How was it determined that UUU encodes phenylalanine?
Marshall Nirenburg and Johann Heinrich Matthaei created synthetic RNAs using the enzyme polynucleotide phosphorylase which randomly links together any available nucleotides. They added this to a solution of uracil nucleotides and created a homopolymer of only Uracil. They added this to twenty test tubes each with the components necessary for translation, all 20 amino acids, and a different radioactively labeled amino acid in each of the test tubes. Only the test tube labeled phenylalanine contained a radioactive protein.
What is meant by the genetic code being degenerate?
- Refers to the fact that the genetic code contains more codons than are needed to specify all 20 common amino acids.
- Amino acids may be specified by more than one codon
3.Francis Crick borrowed the term from quantum physics, where it describes multiple physical states that have equivalent meaning
Where does translation begin?
Starts at AUG but only AUG with the Shine-Dalgarno sequence ( preceding it.
What two subunit comprise a ribosome?
- Large subunit (50s)
- Small subunit (30s)
