Lecture 5: Nucleic Acids part 1

Huntington’s disease

An autosomal dominant disease

Result of the huntingtin (HTT) gene, repeating a codon multiple times

(Codon is CAG, which codes from amino acid glutamine)

What results from many repetitions of the CAG codon

A mutated protein (mHTT), with a long polyglutamine component

How many repeats are almost guaranteed pathology (you get the disease)

Above 39 times

What causes the disease

Etiology of huntington’s disease

Almost entirely an inherited mutation, with very few cases of spontaneous Huntington’s

Average age of diagnosis

Approx 40 years old

Post-diagnosis, people usually live an additional 15-20 years, though quality of life declines from the time of diagnosis (cognitive/ motor issues)

Slide 6

Major symptoms of huntington’s

Dysregulated motor function

Cognitive dysfunction

Psychiatric disturbances

Dysregulated motor function

Movement disturbances: difficult to move, swallow, etc

Suffer from dystonia

Cognitive dysfunction

Patients exhibit memory memory dysfunction and executive dysfunction

Psychiatric disturbances

Preclinically (before major onset/ diagnosis): depression, mania, delusions

Irritability and agression at later stage

Sleep and other mood disorders

Visual motor symptoms of huntington

Chorea

Dystonia

Motor impersistence

Lack of fine motor movement

Gait disturbances

Chorea

Unpredictable and involuntary muscle movements

(Not being able to properly coordinate movement)

Dystonia

Unpredictable movements, but are repetitive and / or twisting motions

Combined together, these movements almost look rhytmic, like a combination of fidgeting and dancing

Motor impersistence

Can not maintain a voluntary action

(Patient asked to hold out their tongue, can not maintain it)

Lack of fine motor movement

Patient attempts to pinch with their index finger and thumb, but can’t do the fine control

Gait disturbances

Typically slower, more variable lengths of stride, uncoordinated

What is the regular functioning Huntingtin gene theorized do

Role in proper neuronal functioning

(Mice that have this gene deleted do not survive - critical for neurodevelopment)

Huntington’s disease is an autosomal dominant mutation in a very specific section of the genome, found in one gene:

Huntingtin

Because of the specificity of the disease, we may be able to develop treatments by

Further refinement of CRISPR/ Cas9 technology

Two major types of nucleic acids

Deoxyribonucleic Acid (DNA)

Ribonucleic Acid (RNA)

How are RNA and DNA molecules different (2)

The sugar that attaches to the phosphate backbone and the base

Difference in the pyrimidine base

Deoxyribose vs ribose

Lack of oxygen on deoxyribose

(Makes DNA more stable and better able to adhere to its complementary strand)

The difference in pyrimidine base of RNA and DNA

No thymine in RNA

No uracil in DNA

RNA unit

DNA unit

What kind of polymers are the nucleic acids

Heteropolymer (chain doesn’t repeat exactly, has different bases to create code)

Nucleobases

Adenine, guanine, cytosine, thymine, uracil

Purines

Two cyclic chains, slightly larger molecules

Adenine and Guanine

Adenine

Forms two hydrogen bonds with T or U

Guanine

Forms three hydrogen bonds with C

Pyrimidines

One cyclic chain

Cytosine and Thymine/ Uracil

Cytosine

Forms three hydrogen bonds with G

Thymine

Forms two hydrogen bonds with A

Uracil

Forms two hydrogen bonds with A

5- Methylcytosine

Plays a role in DNA transcription regulation/ epigenetics

Why do chains with a lot of Cs and Gs have higher melting points

More hydrogen bonds

Nucleoside

Base + sugar

Nucleotide

The whole package without bonding between phosphates (phosphodiester linkages)

Phosphate + base + sugar

Two important structural components of nucleic acids

Polynucleotides have a sense of direction

Each of the nucleosides are different

Polynucleotides (DNA and RNA) have a sense of direction. How so?

One side of the chain is 5’ end

One side is 3’ end

This has profound effects on how the stand is “read” by transcription proteins. Generally read in a 5 to 3 direction

What is the 5’ end

The phosphate attach to the 5-carbon

How are each of the nucleosides different

They are heteromeric, consisting of many different bases

Studies on the chemical nature of the substance inducing transformation of pneumococcal types

Used, and destroyed, pathogenic bacteria (pneumococci) and harvested nucleic acids from these cells

Then, used a different strain of pneumococci, that were non-pathogenic

(Moved pieces of DNA)

Steps of experiment 1

1. Pathogenic (smooth) cell was killed via heat

2. Nucleic acids extracted and put into non pathogenic (rough) cell

3. Rough pneumoniae grew and transformed into smooth pneumoniae (pathogenic)

Protein / nucleic acids question

Are the proteins or nucleic acids the carriers of pathogens?

Independent functions of viral protein and nucleic acid in growth of bacteriophage

 Radiolabelled two separate components of a bacteriophage with radioactive elements

◦The protein coat of the virus with radioactive sulfur (35 P)

◦The nucleic acid of the virus with radioactive phosphorus (32 P)

32 P was found in the daughter viruses (indicating nucleic acid is the carrier)

Secondary structure

Molecule has a defined structure in three dimensions

Each turn of the molecule rotates 36 degrees (each stack of nucleotide)

Complete circle in 10 base pairs

Symmetry in secondary structure

Distance between each of the first carbons in AT and GC pairings is exactly the same

Angle between each base pairing is exactly 36 degrees