Chapter 16: How Genes Work Flashcards
Genetic code is ____ but not ___
Redundant (multiple codons code for same amino acid)
Ambiguous (no codon codes for more than 1 amino acid)
How can 4 bases code for 20 amino acids?
Codons
A duplication repeats a chromosomal segment
Duplication chromosomal mutation
A chromosomal segment from one chromosome is moved to a non homologous chromosome
Translocation chromosomal mutation
What types of mutations are most severe and why?
Frameshift mutations more severe than point mutations bc it almost always produces a nonfunctional protein
How can a missense mutation have a large effect?
Small non polar to large charged amino acid or changing the shape of the active site
What do chromosome mutations cause?
Changes in chromosome number (polyploidy (extra) and aneuploidy (missing)) and changes in structure
3 properties of codons
Nonoverlapping - each codon is read separately
Nearly universal - All codons code for same aa in all organisms with some exceptions
Conservative - when there are multiple codons for an aa, the first 2 bases are usually the same
Substitution that codes for the same amino acid
Silent mutation
Mutation possibly due to the redundancy of the genetic code
Silet mutation
What did Beadle, Tatum, Srb, and Horowitz discover in the 1940s?
They created mutants by bombarding neurospora with X-rays. They found different mutants with different defective enzymes needed different supplements to grow.
A ———-> B ———-> C
enzyme A enzyme B
Synthesis of RNA using the information in the DNA
Transcription
Changes in a single or small number of base pairs
Point mutations
Replacement of one base pair with another
Substitutions. Point mutations
What is the current definition of a gene?
A region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule
What are two exceptions to the Central Dogma?
- Some genes code for RNAs that are never translated (tRNA and rRNA)
- Sometimes RNA—>DNA (retroviruses like HIV)
What did Archibald Garrod suggest in 1902?
Genes determine phenotype. He found enzymes catalyze specific rxns so inherited diseases are due to faulty enzymes
Mutation that can range from little to no effect to completely destroying the proteins function
Missense mutation
How do mutations happen?
Errors in replication = spontaneous mutations
Exposure to certain physical or chemical agents = mutagens
3 types of substitutions
Silent mutation, missense mutation, nonsense mutation
What does DNA sequence determine? What can a single base change cause as a result?
DNA sequence determines amino acid sequence which determine 3D protein structure. A single base change can change the final protein
Can be caused by either insertions or deletions of a base. Change the groupings of 3 (codons)
Frameshift mutations
Mutation that causes translation to stop early and usually creates a nonfunctional protein
Nonsense mutation
Substitution that codes for a stop codon
Nonsense mutation
What are most mutagens?
Carcinogens. They also cause cancer
How many codons are there?
64 codons that code for the 20 amino acids
What is the range of how large mutations can be?
Large scale (chromosomal rearrangements) or small scale (changes in a few nucleotides)
What are the parts of the Central Dogma?
Transcription and translation
Substitution that codes for a different amino acid
Missense mutation
Characterized by severe mental impairment, behavioral problems, feeding problems, poor growth, and characteristic cry
Cri du chat
Instructions for building a polypeptide written as non overlapping triplets
Codons
What is sickle cell anemia the result of?
Missense mutation. T is changed to A
A segment of chromosome is reversed within a chromosome
Inversion chromosomal mutation
How do frameshift mutations occur?
If the number of base pairs inserted or deleted is not a multiple of 3, the reading frame is shifted
When are frameshift mutations most severe and why?
The earlier on the mutation occurs bc every codon from that point on will be changed and usually will end in a premature stop codon
A deletion of a chromosomal segment
Deletion chromosomal mutation
Synthesis of a polypeptide using the information in the RNA message (one language to another; nucleic acid to amino acid)
Translation
What is progeria the result of?
Silent mutation
What are the 4 types of chromosome mutations?
Deletion, duplication, inversion, and translocation
How is progeria caused by a silent mutation?
Creates a cryptic splice site that leads to incorrect splicing that creates a shortened protein that is unable to correctly be modified. 50 amino acids get cut out due to the cryptic splice site
Caused by a partial deletion of chromosome 5
Cri du chat
What are all substitutions?
Point mutations
Permanent change in an organisms DNA that creates new alleles
Mutation
