Unit 3 Chapter 15: How Genes Work/The Genetic Code/Mutations Flashcards
What is Alkaptonuria
- discovered by Archibald Garrod
- a rare inherited genetic disorder in which the body cannot process the amino acids phenylalanine and tyrosine, which occur in protein
- Garrod figured it was out it was caused due to a lack of an enzyme
- lead to the one gene, one enzyme hypothesis
What was the one gene one enzyme hypothesis
- Beadle and Tatum
- each gene contains info to make an enzyme
- discovered this by knocking out genes by damaging them and observing the phenotypes of the mutant cells
- used radiation, found that mutants could not make certain compounds which they found was due to defects in a single gene which caused lack of an enzyme
How was the one gene one enzyme hyp. tested
- used the synthesis of arginine as it requires various enzymes
- raised colonies of irradiated cells in an arginine environment , then transferred a few to an environment that lacked it (to determine whether the cells could make their own or not)
- then grew the cells in a non-arginine environment and supplemented them with either nothing, ornithine, citrulline or arginine.
- some were able to grow on some of media but not on others (due to lack of specific enzymes)
What is the updated term for the one gene one enzyme hyp.
one gene one protein(or polypeptide)
What is mRNA
- messenger RNA
- carry info from DNA to site of protein synthesis
What is RNA polymerase
enzyme that polymerizes ribonucleotides into RNA according to info given by sequence of bases in DNA
-does not need a primer
What is the central dogma
- summarizes flow of info in cells
- DNA codes for RNA which codes from proteins
- links genotypes to phenotypes
- says that genotypes are determined by bases in DNA and phenotypes are a product of proteins produced
What is transcription
the process of copying info in DNA to RNA
-DNA is transcribed to RNA by RNA polymerase
What is translation
- process of using the info in nucleic acids to synthesize proteins
- mRNA is translated to proteins in ribosomes
What are the 2 modifications to the central dogma
- many genes code for RNA molecules that do not function as mRNAs-they are not translated into proteins
- sometimes info flows from RNA back to DNA
What is reverse transcriptase
a viral enzyme/polymerase that synthesizes a DNA version of RNA genes when an RNA virus infects a cell
-info flows from RNA to DNA
What is the genetic code
the rules that specify the relationship between a sequence of nucleotides in DNA or RNA and the sequence of amino acids in a protein
How many bases make up one “word” in the code
3, because 4x4x4=64 which is more than enough info to code for all 20 amino acids; multiplying by 4 because 4 types of bases
What is a codon
group of 3 bases that specifies a particular amino acid
-many codons can code for the same amino acid (the code is redundant)
What is the start codon
AUG signals start of protein synthesis
-methionine
What are the stop codons
- UAA, UAG, UGA
- signal that protein synthesis is complete
What are the 4 main attributes of the genetic code
- it is redundant (all acids except methionine and tryptophotan) are coded for by more than one codon)
- it is unambiguous (a single codon never codes for more than one acid)
- it is nearly universal (works in almost all organisms)
- it is conservative (if more than 1 codon specifies the same acid, the first 2 bases are almost always the same)
How do you use the genetic code
given a DNA sequence, translate the bottom strand (write the base pair) to create RNA (remember U will bond to A), then use the code to translate the RNA into proteins
What does “the genetic code is degenerate” mean
the DNA sequence uniquely determines the amino acid sequence but the amino acid sequence does NOT uniquely determine the sequence of DNA
What is tRNA
- transfer RNA
- contains an anticodon sequence (little loop of 3 nucleotides) that is the reverse complement of the codon for that amino acid sequence
- at least one for each amino acid
- allows ribosome to interpret RNA sequence
What is a mutation
any permanent change in an organism’s DNA, changes genotype and creates alleles
What is a point mutation
a single base change in the code
-can affect something like coat colour in mice
What are missense mutations
point mutations that cause changes in amino acid sequences of proteins
What is a silent mutation
a point mutation that does not change the sequence of an amino acid (ie. if it happens at the 3rd base of the codon)
What is a beneficial mutation
mutations that increase an organisms fitness (ability to survive and reproduce)
What is a neutral mutation
mutations that have no affect
ie.silent mutation
What are deleterious mutations
mutations that lower fitness
What is polyloidy
changing in the # of each type of chromosome
What is aneuploidy
addition or deletion of a chromosome
What is chromosome inversion
when segments of chromosomes become flipped and rejoin
What is chromosome translocation
when segments of chromosomes become attached to different chromosomes
What causes Sickle Cell Anemia
a change in the hemoglobin amino acid sequence
-single base pair change
What is a nonsense mutation
when one of the amino acid codons is changed to a stop codon
What is a deletion
a base is deleted, can cause a frame shift
a codon is deleted, no frame shift
What is an insertion
a base or codon is inserted and causes a frame shift
What are mutagens
agents that cause changes in DNA sequence
What are somatic mutations
may kill a cell, disable it or make it cancerous. Transmitted to daughter cells but not to progeny.
What are germ line mutations
can be transmitted to progeny and become a polymorphism in the gene pool
How can DNA hold so much info
its info is in code form
Why did researchers suspect that DNA doesn’t code for proteins directly
DNA is in nucleus but proteins are made outside of the nucleus
What would happen if you mutate the anticodon of a tRNA, say from the codon for serine to the codon for phenyalanine
the synthase will still charge the mutant tRNA with serine but the serine will be incorporated into the protein where phenylalanine should be
