PROTEIN SYNTHESIS AND ALBINISM From Genotype to Phenotype

PROTEIN SYNTHESIS AND ALBINISM

From Genotype to Phenotype • Phenotype or the observed trait of an organism is coded in the sequence of bases which we call genotype. • The order of the bases specifies which protein will be made. • Proteins build the traits we observe in organisms. • We call this the genetic code because the code is passed from parent to offspring genetically. • Example: Albinism • Organisms with albinism express the phenotype (un-pigmented skin) because of the specific sequence of bases carried in their DNA.

Molecules of Protein Synthesis • • DNA contains bases A, C, T, G Is found in the nucleus Is double stranded and shaped like a double helix • Contains the genetic code for all proteins that make up an organism. • • • m. RNA- messenger RNA Contains bases A, C, U, G Is made in the nucleus but gets exported to the cytoplasm • Is single stranded and linear • Carries the message from the nucleus to the ribosome when a protein needs to be synthesized. • t. RNA- transfer RNA • Ribosomes • Amino Acids (aa) • • Small molecule that carries an amino acid. Each amino acid is attached to anti codons • The anticodons base pair with the m. RNA codons. • • • Organelles that synthesize proteins Read m. RNA message and match them to t. RNA Building blocks of proteins Carried on t. RNA

Protein Synthesis • 1. The code for the protein is transferred from DNA to m. RNA while in the nucleus, using base paring. • 2. The m. RNA is exported from the nucleus to the cytoplasm where it attaches to a ribosome. • 4. The amino acid that is carried by the t. RNA Remember ribosomes are protein factories! is added to the growing protein. • 3. t. RNA reads the message from the m. RNA three letters at a time. The three letters are called a codon. Each t. RNA has an anti-codon that lines up with the codon on the m. RNA.

DNA to m. RNA • Base Pairing • Molecules in the nucleus transfer the genetic code from DNA to m. RNA by complementary base pairing. A pairs with U • T pairs with A • G pairs with C • C pairs with G • • Example: Use base pairing to transfer the DNA code to the m. RNA message. DNA: TAC-TCA- ATG-AGG-GTC-AGC m. RNA:

m. RNA to t. RNA • Base pairing • The m. RNA codons are read three letters at ta time and matched to the anti-codons on the t. RNA molecules using the following base pairing rules: A pairs with U • U pairs with A • G pairs with C • C pairs with G • • Example: Use base pairing to transfer the m. RNA codons to t. RNA anticodons. m. RNA: AUG-AGU-UCC-CAG-UCG t. RNA:

t. RNA to Protein • Ribosomes read the message from m. RNA and use t. RNAs to bring the correct amino acid to build the protein. • Each t. RNA is attached to an amino acid. • Example: m. RNA: AUG-AGU-UCC-CAG-UCG t. RNA: aa: Start

Mutations • Any change in the sequence of bases in DNA is a mutation. • Mutations cause a cell to produce incorrect proteins during proteins synthesis. • This results in an abnormal phenotype. • Sources of Mutation Errors in DNA replication • Errors during meiosis • • Effects of Mutations introduce changes into organisms and are the ultimate source of genetic variation in organisms. • If the changes increase the survival of the organism then it is helpful and leads to evolution. (ex: white bear in the artic) • If the changes decrease the survival of the organism the it is harmful and leads to extinction. (ex: white lemur in the jungle) •

Albinism • Albinism is the result of a mutation that disrupts the synthesis of a protein called melanin. • Melanin is the protein that is found in skin hair and eyes that gives them dark color. • Different concentrations of Melanin create the wide array of pigments we see in skin color. • Albinism is a disorder that an organism is born with (congenital). • The most common form of albinism in humans is Oculocutaneous albinism type 1 (OCA 1) and is recessive. • OCA 1 is caused by a mutation to the TYR gene. It affects 1 in 4000 people.

TYR Mutations • This gene codes for the protein that is responsible for synthesizing melanin. • TYR codes for a protein called tyrosinase. This protein is an enzyme which produces melanin. • When there is a mutation in the TYR gene, protein synthesis transfers that mutation to build a faulty tyrosinase enzyme. This enzyme can not make melanin. • There are over 450 different mutations in this gene that can cause Albinism. http: //www. ifpcs. org/albinism/oca 1 m ut. html • Most of them are the result of a single base mutation. • One of the more common mutations is called TYR-R 299 H and involves the mutation of an G to an A at base #896 •

TYR Protein Synthesis • Normal TYR gene Sequence DNA: gcctcggcct • m. RNA: • aa: Arg • • OCA 1 TYR gene Sequence DNA: gcctcagcct • m. RNA: • aa: His • Normal TYROSINASE= Normal melanin synthesis! Faulty TYROSINASE= No melanin synthesis Normal Melanin amounts = pigmented skin! No Melanin= Albinism Normal genotype= normal phenotype! Mutated genotype= mutated phenotype

Cells protected from UV light radiation.