BIO 2133 Study Guide - Quiz Guide: Protein Subunit, Silent Mutation, Wild Type
27 Apr 2018
School
Department
Course
Professor
MODULE 2: PHENOTYPE EXPRESSION
LEARNING OBJECTIVES
•Explain, using graphs, how nucleotide changes result in the alteration of protein activity.
Mutations are a change in nucleotide that can happen ANYWHERE in the genome. !!!
Nucleotide can result in the alteration of a protein activity by decreasing, increasing or stopping the
production of a protein all together.
This usually occurs when the change in nucleotide results in a different promotor or silencer binding or
decrease / increased affinity for the original promotor or silencer to bind.
This can also occur when a change in nucleotide sequence changes the triplet codon translated and
thus results in a different protein which may not do the same job as the original protein.
Due to the fact that phenotypes work using threshold levels in most cases, an increased binding affinity
for a promoter for example may lead to a previously less than threshold
expression in a cell to over threshold.
Homozygous mutants lower than threshold?
haploinsufficiency. Thus the MUTANT is the ‘DOMINANT.’
-half the number of wild type (t) protein molecules isn’t
sufficient to maintain normal tail length
-one copy is sufficient for the mutant to show
-wild type “normal” is tt, while short tail mutant is TT; Tt has a
short tail (looks lie mutant)
No threshold. Intermediate phenotype portrayed by
heterozygote due to intermediate expression
-dominant (red) and dominant (white) mix to get Pink
-heterozygote has intermediate phenotype; incomplete
dominance
-hard to assign dominant/recessive
Poison subunits. Wild type is not dominant. To allow protein to
come together must have two wild type subunits. Even one mutant
subunit will not work.
-aka “dominant negative” mutations
-wild type aren’t dominant
-mutant allele forms a dysfunctional and inactive protein
subunit, therefore can’t be assembled into an enzyme. If it was
a heterozygote; it’s mutant because there’s a dysfunctional
subunit not allowing it to come together for the enzyme
•Explain why some mutations do not affect protein structure or function.
Point Mulations
Silent: doesn’t change amino acid
Missense: changes amino acid
Nonsense: causes premature stop
Transition: change purine to another purine or pyrimidine to another pyrimidine
transversion: change purine to pyrimidine (vice versa)
Frame shift mutation: insertion or deletion of 1 or 2 base pairs
Note that these are found in coding region - a mutation in promotor is just a point mutation (no specific
name)
Based on cell type or chromosome locations
Somatic mutations - All body cells except gametes or stem cells
Germ-line mutations - Gametes / stem cells
Autosomal mutations - Chromosomes being attacked itself, non sex linked chromosomes in all types
of cells
X linked mutations - On sex chromosome in any type of cell
Some mutations may or may not affect protein structure or function because genetic code is
degenerate
This means that more than one codon codes for the same amino acid. Thus a mutation in the DNA may
result in the same amino acid being formed
Also, mutations could arise in areas which do not code for proteins at all
Splice sites, and simply be removed during translation
Mutations can also occur
Promoter enhancer sequences
Splice or acceptor sites ( introns removed by slicing)
Terminal sequences
These may or may not affect gene expression depending on what type of mutation occurs
•Describe how deletions, inversions, translocations, and movements of transpositional elements
arise, and how they can affect gene function, gene expression, and genetic recombination.
Deletions occur when one or more nucleotide is removed from a DNA sequence
Inversions occur when a sequence of a group of nucleotides are flipped from its original order
Translocations occur when 2 sequences on the same of different segments of a gene switch with one
another or one segment of a gene moves to fit in between another set of nucleotides on the same or
different chromosome.
These are all mutations which have the possibility of either frame shifting a sequence or causing
missense or nonsense mutations.
Document Summary
Learning objectives: explain, using graphs, how nucleotide changes result in the alteration of protein activity. Mutations are a change in nucleotide that can happen anywhere in the genome. Nucleotide can result in the alteration of a protein activity by decreasing, increasing or stopping the production of a protein all together. This usually occurs when the change in nucleotide results in a different promotor or silencer binding or decrease / increased af nity for the original promotor or silencer to bind. This can also occur when a change in nucleotide sequence changes the triplet codon translated and thus results in a different protein which may not do the same job as the original protein. Due to the fact that phenotypes work using threshold levels in most cases, an increased binding af nity for a promoter for example may lead to a previously less than threshold expression in a cell to over threshold.
