DNA, RNA, and Proteins

• Scientist have discovered that the DNA of very different looking organisms is more similar than a person might think

• Similarities in the DNA sequence between different species can be used to determine evolutionary relationships between them.

• Species with similar DNA are more closely related. Species with less DNA similarities are not as closely related.

• DNA or genetic evidence is considered to be the most powerful piece of evidence in determining evolutionary relationships between species.

DNA and Evolutionary Relationships

• DNA is shaped like a double helix (a twisted ladder).

• It is made up of sugars, phosphates, and nitrogen bases.

• The backbone (sides) are made up of sugar and phosphates and the rungs of the ladder are made up of nitrogen bases.

• There are four nitrogen bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

• These four nitrogen bases connect like puzzle pieces, A pairs with T and C with G.

DNA

Complete the DNA sequence

1: G C G A A T T T A C C A T A G

2: C A T T A C A A G T T A A C G

• Combinations of DNA base pairs make “genetic words” called genes.

• A gene is a specific segment of DNA that provides instructions for an inherited trait.

• Organisms that reproduce sexually have two versions of the same gene for every trait- one from each parent.

Genes

• Genes code for proteins.• A protein is an important molecule that is necessary for building

and repairing body structures and controlling processes in the body.

• A protein is made up of amino acids (about 20).• A specific sequence of three bases (triplets) on a gene codes for a

specific amino acid. They form chains which then turn into a protein.

amino acids

gene

triplets

Proteins

• A protein is made through a process called protein synthesis.

• It involves a process known as transcription (DNA → RNA) and translation (mRNA→ amino acid)

• RNA stands for ribonucleic acid and it too has base pairs: adenine (A), uracil (U), cytosine (C), and guanine (G).

• A connects with U (instead of T) and C connects to G.

• mRNA refers to a type of RNA that acts as a messenger.

Protein Synthesis

Translation

A A A AU UC C CG G G

• Translation is the stage where mRNA is translated into amino acids.• The codon chart on the right is used to figure out what type of amino

acid is created.

An amino acid sequence for a protein always starts at AUG (Met) and stops at a Stop codon (UAA, UAG, or UGA)

Mutations and Genetic Disorders

Mutations• Mutations are responsible for differences in genes. They are permanent

changes in the DNA sequence.• Genetic mutations can occur between one base pair or several base pairs and

result in the incorrect protein being made.• This can happen when a base pair is deleted, added, or substituted for

different base pairs.

Original DNA Deletion Addition/ Insertion Substitution

Mutation Effects• Some mutations are helpful,

they can help an organism survive in their environment such as camouflage.

• Some mutations are harmful, such as genetic disorders and cancer.

• Other mutations are neutral and have no impact on the survival of an organism, such as human hair color

Leaf Tailed Gecko

Genetic Disorders• A genetic disorder is an abnormal condition that a person inherits

through genes or chromosomes. • Some genetic disorders are caused by changes in the DNA of

genes. Other disorders are caused by changes in the overall structure or number of chromosomes.

Cystic Fibrosis• Cystic Fibrosis is a disorder in which the body produces

abnormally thick mucus in the lungs and intestines. This mucus fills the lungs, making it hard for the person to breathe.

• It is caused by a recessive allele on one chromosome (the result of a mutation in the DNA)

Sickle- Cell Disease• Sickle- Cell disease causes blood to be shaped like a sickle.• It results from a substitution mutation.• Sickle-shaped blood cells clog blood vessels keeping oxygen from

being carried normally between cells.• Individuals that carry both sickle- cell alleles will have the disease.

However, this trait is co-dominant, so individuals who carry the sickle- cell allele and the normal allele will produce normal and abnormal blood cells, but not show symptoms.

Hemophilia• Hemophilia is a sex-linked disorder in which a person’s blood

clots very slowly or not at all.• This can cause internal bleeding from small bumps or bruises• It is caused by a recessive allele on the x- chromosome.

Down Syndrome• Down syndrome is a genetic disorder that causes some degree of

mental retardation.• Down syndrome occurs when a person’s cells have an extra copy

of chromosome 21, instead of one pair of chromosomes they have three chromosomes.

• It occurs when chromosomes fail to separate properly during meiosis (cell division)

Pedigrees•A pedigree is a tool that is used by geneticist to trace the inheritance of traits in humans