Chapter 15: How Genes Work Flashcards
What are knock out mutants?
alleles that do not function
What does the one gene-one enzyme hypothesis (by Tatum and Beatle) state?
that each gene contains the info required to make an enzyme
What do genes do?
they contain the information needed to make proteins
Why can’t info from DNA be directly converted into proteins?
- DNA is enclosed in a nucleus
- ribosome, where protein synthesis takes place, are outside the nucleus
What did Jacob and Monod suggest in regards to the fact that DNA can’t be directly used to make proteins?
that mRNA is responsible for carrying info from DNA (inside nucleus) to the site of protein synthesis (cytoplasm)
RNA polymerase
synthesizes RNA molecules according to the base sequence of DNA
Does RNA polymerase need a primer in order to produce RNA?
No.
What does the central dogma (proposed by Francis Crick) state?
that DNA codes for RNA, which codes for proteins
Through what process is DNA coded for RNA?
Transcription
Through what process is mRNA coded for proteins?
Translation
What some exceptions to the central dogma?
- some genes can code for RNA molecules that do not function as mRNA
- information can even transferred from RNA to DNA
How does the sequence of bases in a strand of mRNA code for the sequence of amino acids in a protein?
George Garnow hypothesized each 3 base code=an amino acid
genetic code
the rules that specify the relationship between a sequence of nucleotides in DNA/RNA and the sequence of amino acids in a protein
A group of 3 bases that code for an amino acid is called:
codon
Why is the triplet code the best for reading mRNA?
-could code for up to 64 amino acids (only have 20, so way more than enough)
What happens when 3 base pairs were deleted from the mRNA?
altered, but no loss, in function of the protein
What happens when 1 or 2 base pairs were deleted from the mRNA?
loss in function of protein
reading frame
sequence of DNA/RNA into a particular series of 3 nucleotide codons
What is the start codon?
AUG
What is the start amino acid?
MET (methionine)
What are the properties of the genetic code?
1) Rebundant (more than one codon for each amino acid)
2) Unambiguous: single codon NEVER codes for more than one
3) nearly universal:all codons specify the same AA in all organisms
4) Conservative: when several codons specify the same amino acids, the first 2 bases are almost always identical
What are some outcomes of a mutation?
- change in genotype, new alleles
- change in genotype=change in mRNA transcribed and amino acids translated
- change in primary structure of proteins and phenotypes
point mutation
a single base change in the DNA sequence
silent mutation
change in nucleotide that doesn’t change the amino acid
missense (replacement) mutation
change in nucleotide that change amino acid (ie. sickle cell disease)
nonsense mutation
change in nucleotide that results in an early STOP codon
frameshift mutation
addition or deletion of nucleotides
What is the consequence of a silent mutation?
change in genotype, but not phenotype
Consequence of missense mutations?
change in primary structure of protein (amino acid sequence)
Consequence of nonsense mutations?
premature termination
Consequence of frameshift mutation?
reading frame is shifted….massive missense
The mRNA codons GUU, GUC and GUA code for valine. A mutation occurred in the codon, but didn’t change the amino acid. What kind of mutation would this be?
silent
Where in the codon would this mutation occur?
in the 3rd position
beneficial mutation
increase fitness in certain environments (ie. increased ability to survive and reproduce)
neutral mutation
has no effect on organism’s fitness (ie. silent mutations)
deleterious mutation
decrease fitness in certain environments (ie. decreased ability to survive and reproduce)
