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.