D1.3 Mutations + gene editing (copy)

Gene mutation

A permanent, random change in the base sequence of the DNA

• Occur randomly + rarely

• Structural changes to genes at the molecular level

3 types of gene mutations

1. Substitution- change to a base in the gene (ACG → ATG)

2. Insertion- extra nucleotide added to base sequence (ACG → ATCG)

3. Deletion- nucleotide removed → shorter DNA sequence (ACG → AC)

What do the consequences of mutations depend on?

Where it occurs

• Coding region

• Or non coding region

3 types of mutations due to base substitution in coding regions

1. Same-sense mutation

2. Nonsense mutation

3. Mis-sense mutation

Same-sense mutation (silent mutation)

Change in the bases doesn’t cause a change in the AA

• Due to degeneracy of the genetic code

• No effect on protein sequence

Effect of same sense mutation on protein sequence + why

No effect on the protein sequence

• Degeneracy of the genetic code

Nonsense mutation

The change in base causes a stop codon to replace an AA

• Stops translation → shorter polypeptide

Effect of nonsense mutation

A shortened polypeptide is caused

• The polypeptide may be functional or dysfunctional.

Mis-sense mutation

The change in base causes a diff AA to be substituted in the chain

Effect of mis sense mutation

Diff AA expressed → polypeptide either functional or dysfunctional, depending on the type of AA

Single nucleotide polymorphism (SNP)

Caused when a gene sequence is altered by 1 letter

• Areas where our genetic codes differ due to the accumulation of base substitutions over time

What are SNPs the result of?

Base substitution mutations

Why do base substitution mutations not always change a single AA in a polypeptide?

Bc of the degeneracy of the genetic code

Types of frameshift mutations

• Insertion

• Deletion

Harmful

Frameshift mutation

Insertion / deletion of 1 or more bases

• Cause a shift in the reading frame of a codon

Are frameshift mutations usually harmful or have no effect?

Usually harmful

Consequence of frameshift mutations / major insertions or deletions

A polypeptide ceasing to function

In a frameshift mutation, when will the reading frame stay the same?

If 3 bases are added / deleted

• But diff AA sequence created

• Also usually harmful

Example of insertion

Trinucleotide repeats of the gene HTT

Huntington’s disease is a neurodegenerative genetic disorder, in which the HTT gene on chromosome 4 coding for the Huntingtin protein experiences a frameshift insertion mutation. The normal huntingtin gene has several repeat units of CAG, while the mutated one would shows one or several insertions of additional CAG sequences. The faulty protein results in neuronal degeneration in the brain, and eventually death due to neurological dysfunctions.

What is the human genome?

The entire set of genetic material of an organism

Why is the human genome project?

- Medical Breakthroughs

- Personalized Medicine

- Understanding Evolution and Biology

- Advances in Biotechnology

- Ethical and Social Discussions

What is gene knockout?

Genome is remove/made unusable to find out the effect and function of the gene on the organism.

What is gene editing?

DNA is altered by inserting, deleting, or replacing specific DNA sequences known to cause disease.

Gene editing vs Genetic engineering

Gene editing modifies existing DNA.

Genetic engineering often inserts DNA from a different organism.

Advantages of gene editing?

Allows greater accuracy in manipulating the genome compared to older techniques.

What are some examples of old gene editing techniques?

- Modifying viruses

- Liposomes

New gene editing techniques

CRISPR

(Clustered Regularly Interspaced Short Palindromic Repeats)

How does CRISPR work?

- A guide RNA that targets a specific DNA sequence.

- Cas9 enzyme cuts DNA at the targeted point.

- After cutting, scientists can insert, delete, or replace faulty DNA.

What is gene therapy?

Treatment of a genetic disease by altering the person’s genotype

What is a conserved sequence?

A section of DNA or RNA that shows minimal mutations over time

- A conserved sequence tends to be identical or similar across a species or a group of species

What is the advantage of highly conserved sequences?

Highly conserved sequences = sequences with little to no mutations across long evolutionary periods.

What are the mechanisms behind conserved sequences?

- Functional requirements

- Slower mutation rates

Functional requirements

Conserved sequences exist within genes coding for essential proteins needed for survival.

Mutations in these critical genes can be lethal, preventing survival and reproduction.

Natural selection maintains these sequences by:

Eliminating harmful mutations.

Allowing only functional versions to pass to the next generation.

Slower mutations

Certain sections of gene sequences are less prone to mutations and mutation rate is slower bc DNA proofreading mechanisms are more active

DNA repair and proofreading mechanisms are very active in coding regions of the genome, and within genes that have high functionality

SO they do not show up in sequenced DNA