Gene Expression P3
RNA Induced Silencing Complex (RISC)
RISC: RNA Induced Silencing Complex
Function: Can lead to the destruction of mRNA or inhibit protein synthesis, resulting in a halt in function.
Chromatin Modification
Chromatin can be modified to influence gene expression.
Acetylation of Histones:
Addition of acetyl groups to histones
Converts chromatin into euchromatin, making genes accessible for transcription and translation.
Promotes gene expression.
DNA Methylation:
Addition of methyl groups, primarily to cytosine in DNA.
Highly methylated genes are turned off.
Removal of methyl groups can reactivate genes.
Gene Expression and Methylation Signals
Signaling for methylation can be affected by environmental conditions and protein levels.
Example: High protein levels can switch off genes to prevent wasteful protein synthesis.
Understanding Mutation
Definition of Mutation:
Change in the base sequence of DNA or alteration in chromosome number.
e.g., Down syndrome: Presence of 47 chromosomes due to nondisjunction during meiosis.
Types of Mutations
Base Substitution Mutation:
One base is swapped for another, potentially altering amino acid coding.
Can be silent (no change in amino acid) or affect protein function.
Deletion Mutation:
Base is removed, causing a shift in the reading frame (frameshift mutation) which can change all codons downstream.
Addition Mutation:
An extra base is added, also leading to reading frame shifts.
Codon and Amino Acids
mRNA codons consist of three bases coding for specific amino acids.
Changes in the DNA sequence lead to changes in codons, thus altering the resulting protein form.
Silent Mutations
Occurs when a substitution does not change the amino acid sequence, maintaining protein function (e.g., GCA codes for alanine and GCU also codes for alanine).
Nonsense Mutations
Results in the creation of a stop codon, terminating protein synthesis prematurely, which can lead to nonfunctional proteins.