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Why cant 1 base make up an amino acid?
one base per amino acid would only specify 4 amino acids
4<20: not enough
Why cant 2 bases make up an amino aicd?
2 bases per amino acid woud only specify 16 amino acids
Why is having 3 bases code for an amino acid good? (2)
it allows for 64 potential amino acids, more than enough than we need
*there will be a redundancy because of the possible 64 combinations
when removing 3 mutation, the sentence made sense again
- -a 1 base pair or 2 base pair throws the reading frame off
- *does not produce a functional protein
-when 3 base pair deletion occurs, the correct reading frame
and slightly altered but functional protein can be produced
If we add an insertion of one nucleotide, will we have a crap or functional message?
What is a reading frame?
sequence of codons
What is the 3 base code known as?
How did Francis Crick and colleagues establish that the code is based on 3 nucleotides for each amino acid?
by making deletion and insertion mutations in viral DNA
How can the reading frame be destroyed? how can it be restored? (2)
by adding a mutation; can be restored if the total number of deletions or additions were multiples of 3
-they added bacterial extract with all necessary components with synthetic mRNA strand
-it produces a polypetide synthesized
*** UUU-UUU-UUU > Phe-Phe-Phe
-she repeated 2 letters in groups of 3
-she saw a pattern
- *** ACA-CAC-ACA
What do stop codons do?
- they stop the string of mRNA
- *there a 3 of them
Which 3 amino acids code for stop codon?
UAA, UAG, UGA
HWat is the beginning of every strand of DNA in a cell? and what does it define?
- defines the beginning of where to start reading the message
-the first 2 nucleotides tend to be the same, the last nucleotide is the one that differs
- -UUC and UUC both specify for the same amino acid
- *changes genotype but not phenotype
- **most amino acids have multiple codons that code for them
Can amino acids be specify for multiple triplet codons?
- *** proline
Are all amino acids specified in this code?
4 Characteristics of genetic code
-it is redundant
-it is unambiguous
-it is nearly universal
-it is conservative
(characteristics of GC) Redundant
all amino acids except methionine and tryptophan are coded by more than one codon
(characteristics of GC) Unambiguous
a single codon never codes for more than one amino acid
***CCG will always code for proline and only proline
(characteristics of GC) Universal
- with few minor exceptions, all codons specify the same amino acids in all organisms
- *code works for us, animals, plants, etc
(characteristics of GC) Conservative
when several codons specify the same amino acid, first 2 bases are almost always identical
***Proline: CC*, CC*, CC*, CC*
What is a point mutations?
- when you take one single nucleotide and do something with it
- *change it, insert it, take one out
4 types of point mutations
(types of point mutations) what is a Silent mutation?
change in nucleotide that does not change amino acid specified by codon
(types of point mutations) What are consequences for silent mutation?
-change in genotype but no change in phenotype
What is a mutation?
change in the genotype
(types of point mutations) what is Missense (replacement)?
- change in nucleotide that changes amino acid specified by codon
(types of point mutations) What is the consequence of missense?
change in primary structure of protein
Is the genotype or phenotype affected by Missense?
Phenotype : yes, amino acid was replaced
(types of point mutations) What is nonsense?
- change in nucleotide that results in early stop codon
- *protein is usually crap
(types of point mutations) What are consequences of nonsense?
premature termination-polypeptide truncated
(types of point mutations) What is frameshift?
addition or deletion of a nucleotide
What is consequence of frameshift?
- reading frame is shifted
- *massive missense
- **protein comes out like crap
Does nonsense affect genotype or phenotype?
Phenotype: Yes, polypeptide is truncated
Does frameshift affect genotype or phenotype?
phenotype: yes, makes it look like crap