Download Modification of Amino Acids

Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
Alternative Splicing Produces Related but Distinct Protein
Isoforms
Posttranslational Events
Protein Folding:
Translational product (polypeptide) achieves appropriate
folding by aid of chaperone proteins.
Modification of Amino Acids:
* Phosphorylation/dephosphorylation
* Ubiquitination
Protein Targeting:
Directing proteins to specific locations (for example, nucleus,
mitochondria, or cell membrane) is accomplished by tagging
of proteins (signal sequence for secreted proteins, nuclear
localization sequences for nuclear proteins).
Posttranslational Events
Protein Folding:
Translational product (polypeptide) achieves appropriate
folding by aid of chaperone proteins.
Modification of Amino Acids:
* Phosphorylation/dephosphorylation
* Ubiquitination
Protein Targeting:
Directing proteins to specific locations (for example, nucleus,
mitochondria, or cell membrane) is accomplished by tagging
of proteins (signal sequence for secreted proteins, nuclear
localization sequences for nuclear proteins).
Phosphorylation and Dephosphorylation of Proteins
Kinases add phosphate
groups to hydroxyl
groups of amino acids
such as serine and
threonine.
Phosphatases remove
phosphate groups.
Ubiquitinization Targets a Protein for Degradation
Short-lived
proteins are
ubiquitinated:
• cell-cycle
regulators
• damaged
proteins
Posttranslational Events
Protein Folding:
Translational product (polypeptide) achieves appropriate
folding by aid of chaperone proteins.
Modification of Amino Acids:
* Phosphorylation/dephosphorylation
* Ubiquitination
Protein Targeting:
Directing proteins to specific locations (for example, nucleus,
mitochondria, or cell membrane) is accomplished by tagging
of proteins (signal sequence for secreted proteins, nuclear
localization sequences for nuclear proteins).
Signal Sequences Target Proteins for Secretion
Signal sequence at the amino-terminal end of membrane
proteins or secretory proteins are recognized by factors and
receptors that mediate transmembrane transport. Signal
sequence is cleaved by signal peptidase.
Nuclear localization sequences (NLSs) are located in interior of proteins
such as DNA and RNA polymerases. They are recognized by nuclear pore
proteins for transport into nucleus.
Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
Frameshift Mutations and Suppressor Mutations
frameshift mutations: insertions
or deletions of nucleotides that
cause a shift in the translational
reading frame
suppressor mutations: mutations
that counteract or suppress the
effects of another mutation
wild-type
CAU CAU CAU CAU CAU
HIS HIS HIS HIS HIS
addition of A
CAU ACA UCA UCA UCA U__
HIS THR SER SER SER
.
deletion of U
CAU CAC AUC AUC AU__
HIS HIS ILE ILE
.
deletion of A
CAU ACU CAU CAU CAU
HIS THR HIS HIS HIS
addition of G
CAU CAC GAU CAU CAU
HIS HIS ASP HIS HIS
Mutation: Levels of Hereditary Change
Gene (Point) Mutation:
One allele changes to a different allele.
Effects are limited to that locus.
Chromosome Mutation:
Changes occur at the chromosome level.
Multi-locus effects are not unusual.
Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
DNA sequence
transcription
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
Point mutations at the molecular level
Base substitution: change in base of nucelotide pair
Base additions: insertion of nucleotide pairs
Base deletions: deletion of nucleotide pairs
Point mutations at the molecular level
Consequences of Point Mutations within Genes
Point Mutations Can Alter mRNA Splicing
Point Mutations on Gene Products