The Interface of Biology and Chemistry Summer Institute 2012 Harvard Group 1: The Interface of Biology and Chemistry Carol Bascom-Slack Carlton Cooper Michal Hallside Jacqui Johnson Gillian Phillips Eugenia Ribeiro-Hurley Erica Selva Course Details Introductory Biology 1 Week 3 of class Discussion of Macromolecules of Life

Expected Background Overview of Biology Atomic structure Basic Chemistry of Bonding Types of Macromolecules Hierarchy of peptide structure

Sickle Cell Anemia Explained by Protein Shape Learning Goals Understand how hydrophobic and hydrophilic interactions affect protein structure Appreciate the importance of correct protein composition for proper structure Appreciate the importance of correct protein structure for proper function Learning Objectives - Students should be able to: Determine if the side chain of an amino acid is mainly hydrophilic or hydrophobic in nature Describe how changes in the amino acid sequence of hemoglobin can lead to aggregation

Sickle Cell Anemia Symptoms: Pain in extremities and bones Fatigue Pale skin Dizziness Headaches Jaundice If the students have already had genetics, this could provide an opportunity for the instructor to explain that homozygous individuals are affected by the sickle cell trait while heterozygous individuals are protected from malaria infection. It might also be an opportunity to explain that while sickle cell anemia is predominately associated with persons of African ancestry, due to globalization that is changing and people of many different ancestries are affected.

Examination of Red Blood Cells Question to class:Can anyone tell me what is one of the most abundant proteins of red blood cells? Sickle Cell Anemia Normal

Hemoglobin A principal protein component of red blood cells Tetramer composed of two a-subunits and two b-subunits a-subunits have 141 amino acids while the b-subunits have 146 amino acids Each subunit carries oxygen

Brainstorm: What might cause a difference in the net charge of these proteins?

Think pair share Circle: two amino acids containing the most hydrophobic R-groups Underline: two amino acids containing the most hydrophilic R-groups

Think pair share: Hydrophobic amino acid R-group (side chain) Valine (Val, V) Glutamate (Glu, E) Leucine (Leu, L) Serine (Ser, S) Threonine (Thr, T) Lysine (Lys, K) Hydrophobic amino acid R-group (side chain) Hydrophilic amino acid R-group (side chain)

Think pair share Hydrophobic amino acid R-group (side chain) Valine (Val, V) Glutamate (Glu, E) Leucine (Leu, L) Serine (Ser, S) Threonine (Thr, T) Lysine (Lys, K) Hydrophobic amino acid R-group (side chain) Hydrophilic amino acid R-group (side chain)

Think pair share Hydrophobic amino acid R-group (side chain) Valine (Val, V) Glutamate (Glu, E) Leucine (Leu, L) Serine (Ser, S) Threonine (Thr, T) Lysine (Lys, K) Hydrophobic amino acid R-group (side chain) Hydrophilic amino acid R-group (side chain)

Each blue dot=one amino acid α β α=141 amino acids β=146 amino acids Getting back to Hemoglobin α β Approximately what percentage of the 574 amino acids in hemoglobin do you think you would need to change to cause sickle cell anemia?

α β α β Each blue dot=one amino acid α=141 amino acids

Where in this folded protein might this change have occurred. A Where in this folded protein might this change have occurred? A. Near the oxygen binding site B. At the interface between subunits C. On the surface D. A and C E. A, B and C

These are the locations of the changed amino acids. Glutamate (hydrophilic) Valine (hydrophobic )

The single amino acid substitution causes hemoglobin to aggregate resulting in the sickle shaped red blood cells Think-pair-share Can you come up with an explanation that would link the aggregation of hemoglobin to the amino acid change?

Remember: An external hydrophilic amino acid is replaced with a hydrophobic one Glutamate (hydrophilic) Valine (hydrophobic) animation

Pain Swelling Blindness Stroke

Teachable Tidbit: Sickle Cell Anemia Explained by Protein Shape Learning Goals Understand how hydrophobic and hydrophilic interactions affect protein folding Appreciate the importance of the correct protein folding for proper function Learning Objectives Students should be able to: Determine if the side chain of an amino acid is mainly hydrophilic or hydrophobic in nature Describe how changes in the amino acid sequence of hemoglobin can lead to aggregation

Extra Information

Side-chain polarity[95] Side-chain charge (pH 7.4)[95] For a more chemistry centric class the table below may help explain the non-polar (hydrophobic) vs. polar (hydrophilic) nature of the amino acids. There are multiple hydropathy indexes that can be used to describe the order of amino acids. Amino Acid 3-Letter[95] 1-Letter[95] Side-chain polarity[95] Side-chain charge (pH 7.4)[95] Hydropathy index[96] Alanine Ala A nonpolar neutral 1.8 Arginine Arg R polar positive −4.5 Asparagine Asn N −3.5 Aspartic acid Asp D negative Cysteine Cys C 2.5 Glutamic acid Glu E Glutamine Gln Q Glycine Gly G −0.4 Histidine His H positive(10%) −3.2 neutral(90%) Isoleucine Ile I 4.5 Leucine Leu L 3.8 Lysine Lys K −3.9 Methionine Met M 1.9 Phenylalanine Phe F 2.8 Proline Pro P −1.6 Serine Ser S −0.8 Threonine Thr T −0.7 Tryptophan Trp W −0.9 Tyrosine Tyr Y −1.3 Valine Val V 4.2