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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
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Why cant 2 bases make up an amino aicd?
2 bases per amino acid woud only specify 16 amino acids
16<20
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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
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when removing 3 mutation, the sentence made sense again
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- -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
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If we add an insertion of one nucleotide, will we have a crap or functional message?
crap
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What is a reading frame?
sequence of codons
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What is the 3 base code known as?
triplet code
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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
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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
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-they added bacterial extract with all necessary components with synthetic mRNA strand
-it produces a polypetide synthesized
*** UUU-UUU-UUU > Phe-Phe-Phe
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-she repeated 2 letters in groups of 3
-she saw a pattern
- *** ACA-CAC-ACA
- Thr-His-Thr
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- they stop the string of mRNA
- *there a 3 of them
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Which 3 amino acids code for stop codon?
UAA, UAG, UGA
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HWat is the beginning of every strand of DNA in a cell? and what does it define?
-AUG, Methionine
- defines the beginning of where to start reading the message
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-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
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Can amino acids be specify for multiple triplet codons?
- yes
- **redundancy
- *** proline
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Are all amino acids specified in this code?
yes
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4 Characteristics of genetic code
-it is redundant
-it is unambiguous
-it is nearly universal
-it is conservative
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(characteristics of GC) Redundant
all amino acids except methionine and tryptophan are coded by more than one codon
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(characteristics of GC) Unambiguous
a single codon never codes for more than one amino acid
***CCG will always code for proline and only proline
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(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
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(characteristics of GC) Conservative
when several codons specify the same amino acid, first 2 bases are almost always identical
***Proline: CC*, CC*, CC*, CC*
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What is a point mutations?
- when you take one single nucleotide and do something with it
- *change it, insert it, take one out
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4 types of point mutations
-silent
-missense
-nonsense
-frameshift
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(types of point mutations) what is a Silent mutation?
change in nucleotide that does not change amino acid specified by codon
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(types of point mutations) What are consequences for silent mutation?
-change in genotype but no change in phenotype
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What is a mutation?
change in the genotype
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(types of point mutations) what is Missense (replacement)?
- change in nucleotide that changes amino acid specified by codon
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(types of point mutations) What is the consequence of missense?
change in primary structure of protein
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Is the genotype or phenotype affected by Missense?
Genotype: yes
Phenotype : yes, amino acid was replaced
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(types of point mutations) What is nonsense?
- change in nucleotide that results in early stop codon
- *protein is usually crap
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(types of point mutations) What are consequences of nonsense?
premature termination-polypeptide truncated
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(types of point mutations) What is frameshift?
addition or deletion of a nucleotide
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What is consequence of frameshift?
- reading frame is shifted
- *massive missense
- **protein comes out like crap
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Does nonsense affect genotype or phenotype?
Genotype: Yes
Phenotype: Yes, polypeptide is truncated
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Does frameshift affect genotype or phenotype?
genotype: yes
phenotype: yes, makes it look like crap
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