DNA, GENES, AND MUTATIONS

DNA and genes The nucleotide sequences are used to

encode information that is used to make proteins and enzymes

The order of the base pairs can be read my strands of RNA and carried to ribosomes to make molecules

Codons to Protiens A DNA sequence is lumped into sections

of 3 base-pairs called a codon

ACGATGCGGTACGTAC . . . is the sequence, broken into codons looks like . . .ACG ATG CGG TAC GTA C . . .

Codons to proteins cont’d The sequence is read by strands of RNA

called messenger RNA (mRNA) and translated into proteins by transfer RNA (tRNA)

Each codon is read and associated with an amino acid (amino acid chains are protiens)

Reading the Sequence . . .ACG ATG CGG TAC GTA CBecomes:Thr-Met-Arg-Tyr-Val . . .

However, the sequence starts with a start codon (ATG) and ends with a stop codon (TAA TAG TGA)

Mutations 3 basic types:

Substitution: swapping one nucleotide for another

Insertion: adding an extra nucleotide Deletion: removing a nucleotide

Chromosome mutations also occur, but are usually a result of non-disjunction which we already learned

Mutations and Inheritance Most errors in the DNA code are found

and corrected by RNA strands As we age, the telomeres of the DNA

shorten which increases chances for harmful mutations (telomeres are the long ends of a chromosome which contain few genes)

If mutation is persistent and expressed in gametes, it can be passed on

Sickle Cell Anemia Genetic disorder where red blood cells

become sickled in shape (C-shaped) Mutation causes less oxygen carrying

potential for RBC’s (by definition = anemia)

Harmful disorder for most of the world as it causes pain and reduced O2 in blood

HOWEVER. . .

Benefit of SCA Malaria is a blood borne pathogen (carried

in blood transmitted by mosquitos) Normal RBC’s get infected by parasite and

can cause death (over 1 million deaths/year in Africa alone)

SCA will not allow parasite infection as easily due to low O2 levels

SCA-individuals have higher survival rates (and thereby see more SCA cases in Africa and malarial regions of the world)

Methods of Mutations Spontaneous – mutations that occur

naturally and suddenly Occur by incorrect copying of DNA

Induced – mutations that occur by exposure to physical or chemical agents causing change Sunlight and UV rays, environmental

carcinogens, etc

Moving Genes Genes can relocate on a chromatid Transposon – a gene that can jump to

new locations on chromatids or to new DNA strands

Transposition – the process of moving a gene

Some haemophiliacs arise as a means of a clotting gene transposon moving into the region for normal blood clotting