It’s in the genes Lesson 3.2

DNA, Genes, Proteins DNA carries the instructions to produce proteins & is responsible for passing traits from one generation to the next. Proteins are worker molecules that are necessary for virtually every activity in your body. Proteins are the key to essential bodily functions and complete a large variety of jobs. Remember DNA is made of four different nucleotides (A, T, C, and G). Only four subunits are capable of carrying all the instructions necessary to code for all of the proteins that make life possible. The complexity of DNA is not in the number of subunits, but in the arrangement or sequence of those subunits.

DNA, genes, proteins DNA is read in segments, called genes. A gene is a particular sequence of nucleotide bases that code for a protein. The instructions for protein production in the DNA molecule are determined by the sequence of the nucleotides.

RNA (mRNA-codons, tRNA-anticodons)  Proteins (Amino Acids) Protein synthesis A protein is a three dimensional polymer made of monomers of amino acids. Protein synthesis is the creation of a protein from a DNA template. DNA (nucleotides) RNA (mRNA-codons, tRNA-anticodons)  Proteins (Amino Acids)

Protein synthesis Remember RNA is a type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses. Remember amino acids are the organic monomers that serve as a the building blocks of proteins.

transcription Protein Synthesis Step 1: Transcription The synthesis of RNA on a DNA template. DNA is too large and fragile to leave the nucleus… so it is copied into an mRNA template by RNA polymerase. mRNA is a type of RNA whose specifies for the primary structure of a protein. mRNA acts a “messenger”, which takes the gene code out of the nucleus to the ribosome. A ribosome is a cell organelle that functions as the site of protein synthesis in the cytoplasm; consists of ribosomal RNA and protein molecules and is formed by combining two subunits. mRNA is read as a triplet code, or as codons which are three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal.

translation Protein Synthesis Step 2: Translation The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of language from nucleotides to amino acids. mRNA binds to the ribosome in the cytoplasm and it read the mRNA codons. tRNA binds to the codons using an anticodon bringing in a specific amino acid. tRNA is an RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA. An anticodon is a triplet of nucleotide bases in transfer RNA that identifies the amino acid carried and binds to a complementary codon in messenger RNA during protein synthesis at a ribosome. This process repeats until the whole protein is made up of multiple amino acids. Therefore the sequence of DNA determines the codons in mRNA, which determines the sequence of amino acids, which determines the protein being made.

mutations A rare change in the DNA of a gene, ultimately creating genetic diversity. Remember sickle cell anemia is a disease in which red blood cells form an abnormal crescent shape. The disease is a genetic disorder caused by inheriting a mutated gene that codes for the protein hemoglobin.

Mutations A change in one base is a point mutation. A change in bases is a frameshift mutation due to addition or deletion of bases. These can change the codon, which can change amino acids. If a amino acid of one property is replaced with an amino acid of another property this can change in the interactions of the amino acids and the shape of the protein.

Sickle Cell Mutation A single base changes glutamic acid (hydrophilic amino acid) to change to valine (hydrophobic amino acid). This change causes valine (a hydrophobic amino acid) to to stick to the hydrophobic pocket of another hemoglobin. The hemoglobin sticking together causes the cell to be sickle shaped.

Protein shape Amino acids have many properties, one of the most important is their hydrophobic nature. Hydrophilic means having an affinity for water. Hydrophobic means having an aversion to water; tending to coalesce and form droplets in water. Many amino acids have other properties, they can be positive, negative, or neutral in charge. Therefore the amino acids present and their order in the chain affect the shape of the protein due to the following forces: Van der Waals forces – random attractive forces between atoms. Electrostatic charge – positive amino acids will attract negative amino acids and repel positive amino acids. S-S – Covalent bonds between amino acids with sulfur, these are stronger forces that hold the protein shape steady. Hydrogen bonds – bond formed between two molecules that are polar.

Protein shape Polar amino acids are said to be hydrophilic. Hydrophilic amino acids like water because they are polar like water and will attract water. Nonpolar amino acids are said to be hydrophobic. Hydrophobic amino acids are “afraid” of water because they are not polar and will repel water (fats are hydrophobic, which is why they do not mix with water). Hydrophilic amino acids will attract each other and form hydrogen bonds. They will repel hydrophobic amino acids.

Protein shape In water hydrophilic amino acids will spread out (attracted to water) and hydrophobic amino acids will clump up (repelled by water) In oil hydrophilic amino acids will clump up (repelled by hydrophobic oil) and hydrophobic amino acids will spread out.

Sickle cell mutation Hemoglobin has four subunits; it is made by combining two beta-globin proteins with two alpha-globin proteins. The change in just one of the over 400 nucleotides that code for b-globin is enough to cause all of the problems associated with sickle cell disease. The sickle form of the hemoglobin gene is created when an adenine nucleotide is changed to a thymine. This changes the codon for the sixth amino acid in the beta-globin protein from GAG to GUG, which causes the sixth amino acid in the protein to become valine instead of glutamic acid. That single amino acid replacement in the beta-globin protein alters the shape and the chemistry of the hemoglobin molecule, causing it to polymerize and distort the red blood cell into the sickle shape.