PAH phenylalanine + oxidant tyrosine CH 2 +H 3 N

Transcription

1 M 109 Introduction An essential pattern employed by all living things: DNA RNA Protein DNA is the information storage molecule. RNA is an intermediate in information flow. Proteins do most of the jobs in living things. Many events or jobs must occur in your body for you to stay happy and healthy. What happens when a job doesn t get done? I. PKU is a disease that illustrates the relevance of chemistry (ie. why chemistry is important) to human health. PKU stands for phenylketonuria. ref. Matalon, KM Top lin Nutr 16(4):41-50 (2001) A. We are constantly being tested (from birth). 1) Why? Test newborns to check for congenital health problems. 2) What does congenital means (Then go to conditions screened.) B. What is PKU? A genetic disease caused by insufficient phenylalanine hydroxylase (PA) activity. 1) PA rxn.: PA phenylalanine + oxidant tyrosine N N - 2) PA is an enzyme. (means? ) 3) The PA of PKU patients is absent or doesn=t work as well as normal PA because its structure is different from wild type PA. Wild type means This is 1 of ~ 10 4 jobs you must do to stay alive, healthy.. Why does lack of PA activity cause problems in PKU? 1) Phenylalanine (Phe) levels increase. Some of this Phe is converted to phenylketones, which is excreted in urine. PA phenylalanine + oxidant tyrosine phenylketones 2) Part of the PKU pathology (means? ) appears to be caused by elevated Phe. ow Phe does this is not completely clear, (ex. :see Shefer, et al., J Neurosci Res. 61(5): , 2000). 3) Tyrosine (Tyr) is not formed via the PA pathway in PKU patients, so Tyr is an essential amino acid for them (dietary supplements needed!). 1

2 Aside on PKU and diet Meat probably comes to mind 1 st when you think of protein in your diet, but most foods contain some protein. ( Some food additives also provide a risk for PKU patients. The structure of the artificial sweetener aspartame (found in some diet drinks) is shown. Aspartame Why Aspartame might be a problem for PKU patients? Structure! N+ - N D. Back to AWhy test newborns?@ PKU can be treated! See: Irene, spouse, sister, (& Stephanie) (Pheno, Genotypes?) AThis photo was taken at my wedding a few years ago. I have PKU. I was diagnosed on the 3rd day of my life when treatment with the diet began.... The other woman in the picture is my older sister. She also has PKU but when she was born there was no newborn screening program for PKU. The diagnosis of her disease was made late in her first year of life when she developed convulsions. It was too late for treatment and she has never known the benefits of early diagnosis and treatment as I know them...(irene, May 1998)@ Note: The pictures at right and above are from The Montreal hildren=s ospital yperphenylalaninemia (PKU) Resource Booklet for Families, by Peter M. Nowacki at The Biochemical Genetics Unit; updated by Annie apua, Margaret Lilly, David é, Manyphong Phommarinh and Shannon Ryan. Used with permission, Dr.. Scriver. 1. Set diet with low levels of 2. Supplement w/ Tyr, which leads to healthy Irene & eventually to healthy 2 yr old Stephanie, þ 2

3 E. What happens to PKU patients that are not treated or are not compliant with (or didn t have knowledge of) the treatment? i.e., What is the pathology? See Irene=s sister, above. 1. Mental retardation 2. Microencephaly (means? ) 3. ongenital heart disease F. Genetics ALoss of function@ genetic diseases & diploidy. 0. A linear sequence of bases in your DNA that codes for a specific function is called a gene. 1. Genotype vs. phenotype (Look up if unfamiliar.) genotype phenotype 2. Why doesn=t genotype = phenotype? Ploidy!!! a) Are you haploid or diploid? b) Better: i) Which of your cells are haploid? ii) Which of your cells are diploid? 3. What can you say about genes of a PKU patient? Nice web site (from McGill Univ.) with lots of information about specific PKU mutations: also see: 4. What can you say about genes of the parents of a PKU patient? G. Remember: A major theme for this course: DNA ö RNA ö Protein. ow does the entral Dogma relate to PKU & the PA gene? 1. The uman Genome Project View of a haploid karyotype. 3

4 2. Now search It turns out that the gene that codes for PA is on chromosome #12. It may be easier to understand if we relate the processes of DNA ö RNA ö Protein to where they occur in a cell:. Remember: A gene is a linear sequence of bases in DNA that codes (information) for a specific function (job). Based on: Dr.. Scriver, uman Mutation 28(9): (2007). 4

5 PA gene expression DNA PA gene is 171,266 base pairs long RNA Mature PA mrna is 4,932 bases long Protein PA protein subunit is 452 amino acids long 4,932 is ~ 2.9% of 171,266! Why have the extra 97%? I. If we understand, structure tells us about function and helps develop treatments. 1. The structure of DNA: a double helix (this piece is only 20 bp long!) Space-filling model wireframe model ribbon model 2. Structure of the protein PA. (from PDB structure 1PA. ydrogen atoms are not shown.) Space-filling model, PK atom coloring Ribbon model. α-helices: red, β-sheets: yellow 5