Bio Ch. 9

Normal red blood cells are

round, carry large amounts of oxygen, and flow well through blood vessels

Sickle Cell Disease

have a “sickle” shape that are different from normal red blood cell shapes and they do not flow well through blood vessels causing a smaller amount of oxygen to be carried in them

Sickle Cell Disease is caused by a

genetic mutation in the beta-globing gene

Beta-Globin

a part of hemoglobin, which carries oxygen in red blood cells

Gene Therapy

influencing genes to reduce or eliminate the effects of a genetic disorder (could possibly treat sickle cell disease by replacing defective genes with functional ones)

Mutations

changes in DNA sequence or the nucleotide sequence in DNA

Mutations in the coding sequence of a gene lead to

differences in amino acid sequence, which can be detrimental such as in sickled red blood cells

Point Mutations

substituting one nucleotide for another

Silent Mutation

change one nucleotide to another; no change in amino acid sequence DNA HAS ALL YOO CAN ASK FOR, no change; normal function

Missense Mutation

change one nucleotide to another; different amino acid sequence DNA HAS ALL LOU CAN ASK FOR, change in protein shape and function

Nonsense Mutation

change one nucleotide; introduces early stop codon DNA HAS ALL YOU, protein is too short and therefore not functional

Frameshift Mutations

change in the reading frame of a gene

Insertion Mutation

insert one or more nucleotides; shifts reading frame of every codon after the insertion DNA HAS ALL YYO UCA NAS KFO R, severely modified sequence makes the protein not functional

Deletion Mutation

delete one or more nucleotides; shifts reading frame of every codon after the deletion. DNA HAS ALY OUC ANA SKF OR, severely modified sequence makes the protein not functional

Rearranged DNA mutations

sections of DNA move

Inversion Mutation

a group of DNA nucleotides are flipped to read in reverse order; different amino acid sequence in this location DNA HAS ALL YOC UAN ASK FOR, change in protein shape and function

Translocation Mutation

move segments of DNA from one chromosome to another, fusing portions of different genes together DNA HAS ALL YOU CAN EAT, THE DOG AND CAT ASK FOR, significant change in protein shape and function

Mutations that occur in germ cells (reproductive cells) can be

passed on to the next generation

Mutations in other cells may

affect the individual, but will not be passed on

How do mutations arise

Mutations can result from errors in DNA replication

Enzymes for DNA repair usually correct the mistakes, however, sometimes the enzymes do not catch mistakes, mutagens then arise

Mutagen

any chemical or physical agent that can damage DNA by changing the nucleotide sequence

Many components of the environment are

mutagens

Scientists are taking multiple approaches to treat sickle-cell disease (Gene Therapy)

Viral Vector Approach, Gene Switch Approach, and Precise Gene Editing (CRISPR-Cas9)

Viral Vector Approach (Gene Therapy)

an altered virus inserts healthy versions of the gene into the genome of patients

Viral Vector Approach: Step 1

Remove stem cells, which are from red blood cells, in the patient

Viral Vector Approach: Step 2

The virus inserts the normal gene into the stem cells, which get incorporated into the cells’ chromosomes

Viral Vector Approach: Step 3

Introduce the modified cells into the patient. (The modified cells produce the normal version of beta-globing, preventing symptoms of sickle-cell disease.)

Gene Switch Approach

Focuses on changing gene expression.

While a fetus, people produce gamma-globing instead of beta-globin.

Around the time of birth, cells produce less gamma-globin and more beta-globin.

The sickle cell mutation only affects beta-globing, so patients are capable of producing normal gamma-globin.

Hydroxyurea is a drug that increases gene expression of gamma-globin.

This therapy does not change genes, but simply changes gene expression to help patients produce functional hemoglobin.

Precise Gene Editing

Uses CRISPR, the muted DNA is removed, a normal version of the DNA is introduced, repair enzymes, insert the normal version of DNA into the chromosome. Alternatively, CRISPR can be used to inactivate a gene without replacing it with another version

CRISPR

relatively precise method of making changes to existing genes based on a natural defense system bacteria, under development and may be used in the future.

It is a genome editing technique that targets a specific section of DNA, makes a precise cut/break at the target site. Can do one of two things: makes a gene nonfunctional, replace one version of a gene with another.

Why is there a “CRISPR Craze?”

Cas9 can be programmed to perform gene editing in “mammalian cells”

Changing a short RNA sequence can easily target to a different site in the genome

Similar and easier than other genome editing technologies, higher efficiency, gene therapy is back

Types of mutations includes:

point mutations, insertions, deletions, translocations, and inversions

The effect of a mutation depends on where it occurs in the

genome, and whether it changes the amino acid sequence of a protein

Mutations can occur

spontaneously during DNA replication. They can also be caused by environmental triggers such as tobacco, ultraviolet radiation, chemicals, and viruses, and by chemicals naturally produced by the body.

Viruses are useful tools in

genetic engineering because they make good vectors

CRISPR is a

genome-editing tool adapted from enzymes found in bacteria. It can be used to make changes to DNA at specific locations

Mutations that occur in body (somatic) cells will be found only in the

desendants of that particular cell. Mutations that occur in germ cells (sperm and eggs) will be inherited by offspring and therefore will be present in all the cells of that offspring’s body

Using CRISPR to modify germ cells is not currently an

accepted therapy for genetic diseases

The impact of a mutation may

vary, depending on the environment in which it is found

Mutations can be beneficial, harmful, or neutral in terms of

the effect they have on survival and reproduction

Hemoglobin

the oxygen-carrying protein in red blood cells