biology

• Sickle cell anemia is a genetic disorder that affects the structure of red blood cells (RBC), disrupting their normal shape and forming a sickle shape.
• Samples of blood were taken from four individuals and the DNA sequence of the red blood cells was analyzed.
•  Hemoglobin, the protein that carries oxygen in the blood, is made up of 4 polypeptides, two with 141 amino acids and 2 with 146 amino acids.
• The table below shows a partial DNA sequence of hemoglobin from each individual and the concentration of oxygen they were able to carry in their blood [O2].  
• • DNA is made up of strings of units called nucleotides
• • Each nucleotide has a sugar (deoxyribose), a phosphate and a nitrogenous base
• • There are 4 nitrogenous bases: Adenine (A)Thymine (T)Guanine (G)Cytosine (C)
• • DNA is made up of two strands that are connected to each other by their nitrogenous bases
• • A is complementary to T (A-T)
• • C is complementary to G (C-G)
• • Proteins have many functions in organisms - they are an essential molecule for the structure of organisms and for their proper function
• • Eg. Hemoglobin is a protein that is found in our Red Blood Cells that has a function to carry oxygen
• • Eg. Salivary amylase is a protein that is called an enzyme. It is found in our saliva and functions to break down carbohydrates so that they can be absorbed by our body 
• • Protein synthesis proteins are created in a two step process called transcription and translation
• • Transcription the production of an mRNA molecule, using the DNA as a template which occurs in the nucleus of cells
• • Translation the production of a protein based on the sequence of mRNA bases that have been copied from DNA which occurs on Ribosomes outside of the nucleus
• • RNA is similar to DNA, but has a few essential differences

  RNA contains ribose sugar instead of deoxyribose sugar, contains the base Uracil (U) instead of Thymine (T) and has only one strand instead of two
• • When you copy something down, you are transcribing
• • The same is true for the first step in protein synthesis: Transcription
• • DNA unwinds and a complementary mRNA strand is created
• • mRNA = Messenger RNA - it brings the message from the DNA to the Ribosome
• • G is transcribed into a C; C is transcribed into a G; T is transcribed into an A; A is transcribed into a U (because Uracil replaces Thymine in RNA)
• • mRNA leaves the nucleus and travels to the Ribosomes in the cytoplasm where the code is translated into a protein (polypeptide)
• • Codons each triplet of bases corresponds to a specific amino acid, or is a start codon (AUG)  or stop codon (UAA, UAG, UGA)
• • Proteins are made up of amino acids that are strung together
• • A table of codons is used to translate the mRNA3 base triplet (codon) into an amino acid sequence
• • This sequence of amino acids gives the proteinIts unique structure and therefore its function
• • Most amino acids have  more than one codon 
• • Mutations changes in the DNA sequence of bases that results in the modification of genes
• • Not all mutations are harmful - some do not affect an organism at all and some are even beneficial. 
• • There are several types of mutations
• • Some change only one nucleotide base, while others change large parts of chromosomes
• • Bases may be inserted, substituted or deleted from the DNA
• • This will result in a change in the mRNA that is transcribed from the DNA and may result in a different amino acid added to the polypeptide
• • Point mutation only one base is replaced by another
• • Silent mutation - a point mutation occurs, but the same amino acid is coded for (eg. UUU changes to UUC will still result in Phe added)
• • Frameshift mutation - when a base is added or deleted from the DNA sequence; this will result in a completely different protein produced
• • Nonsense mutation - when a codon is changed to a STOP codon; the building of the protein will be incomplete
•    DNA:  TAC-AAA-AGA-ATA  mRNA: AUG-UUU-UCU-UAU                 Met - Phe - Ser - Tyr

   DNA:  TAC-AAA-AGA-ACA  mRNA: AUG-UUU-UCU-UGU                 Met - Phe - Ser -  CysIs this a silent mutation? Can you explain why or why not?
•    DNA:  TAC-AAA-AGA-ATA  mRNA: AUG-UUU-UCU-UAU                 Met - Phe - Ser - Tyr

     DNA:  TAC-AAG-AAG-AAT  mRNA: AUG-UUC-UUC-UUA                 Met - Phe - Phe - Leu

  Is this frameshift mutation the result of an addition or deletion?