Chapter 16 Gene Expression

Spontaneous Mutation Front

A mutation that occurs naturally due to errors in DNA replication or repair

Example: DNA polymerase errors, spontaneous deamination, Tautomeric shifts

Induced mutation

caused by external factors like radiation or chemicals

What are point mutations

• Single nucleotide changes in DNA

• Indels = insertions or deletions of nucleotides

• Substitution = One nucleotide replaces another

Silent (synonymous) substitution

no change in amino acid

Missense substitution (nonsynonymous)

changes amino acid, may affect protein function

nonsense substitution

creates a PREMATURE STOP CODON, truncating the protein

Why do different cells have different genes?

All cells have the same DNA, but different genes are activated based on function

• Gene regulation controls which genes are expressed in each cell type

What are operons, and which organisms use them?

Operons = Clusters of genes regulated together in prokaryotes (bacteria)

Example: lac operon (controls lactose metabolism)

Repessors

Block transcription

Activators

enhance transcription

Inducer

trigger gene expression

What is epigenetic regulation

changes in gene expression without altering DNA sequence.

Methylation = Silences genes

Acetylation = Activates genes

Transcriptional Regulation

Controls what genes are transcribed into RNA

Transcription Factors = Bind to DNA to regulate transcription

Promoters = DNA sequence where DNA polymerase binds

Distal & Proximal Control Elements = Regulatory regions affecting gene expression

Post transcriptional regulation

• Modifies RNA after transcription to control gene expression

• 5’ Cap = Protects RNA & helps ribosome binding

• 3’ Tail (Poly - A tail) = stabilizes RNA

• Intro Splicing = Removes non-coding regions

• Alternative splicing = Allows different proteins from same genes

Translational Regulation

• Controls how much protein is made from mRNA

• Initiation complex = Ribosome + mRNA + initiation factors

  • eIF-1 = Key factor controlling translation initiation

Post-translational regulation

• Modifies proteins after translation to control function

• Ubiquitin = tags proteins for degradation

• Proteasome = breaks down tagged proteins

Cancer

uncontrolled cell growth due to genetic mutation

What are proto-oncogenes, oncogenes, and tumor suppressors

proto-oncogenes = normal genes that regulate cell growth

oncogenes = mutated proto-oncogenes that cause uncontrolled growth

tumor suppressor genes = prevent cancer by regulating cell division

how do mutation in these genes lead to cancer?

oncogenes = overactive growth signals

tumor suppressors = loss of function leads to uncontrolled division

How do viruses contribute to cancer?

Example HPV

can inactive tumor suppressor genes, leading to cancer

What is a circadian clock?

internal biological clock controlling sleep, metabolism, and gene expression

• Regulates hormone levels and cellular activity based on time of day