Human Biochemistry Option B

Transcription

1 Human Biochemistry Option B

2 A look ahead... Your body has many functions to perform every day: Structural support, genetic information, communication, energy supply, metabolism Right now, thousands of reactions are taking place in your body: Human biochemistry covers the chemistry of important molecules in the human body You will not need to memorize complex structures as many of them are given in your data booklet (sucrose, the amino acids, etc.) SL: 15 hours; HL: 22 hours

3 Hungry!? Why do we eat? In order to get energy so we can move, keep warm, keep our heart beating If we eat more than our body needs: weight gain If we don t eat enough: weight loss Generally, an active woman needs 2000 kcal/day; an active male needs 3500 kcal/day

4 Food labels Food labels often tell us how much energy is in a product How do the food companies get this information? Remember Energetics?!?!? It s back! The energy content of a food can be found by burning the food in a food calorimeter

5 q = mc T Based on how much the temperature of water goes up, the heat released can be determined (just like in our lab!) This amount of energy is written as the Calorific value, which has units of kcal per 100 g or kj per 100 g (or a variation ) Note: 1 kcal = 4.18 kj

6 Let s try it!

7 More complicated! Sometimes, we will have to take into account the heat being absorbed by the calorimeter itself

8 Three classes of Foods Lipids Carbohydrates Proteins

9 Using Enthalpy instead You can also calculate the energy based on the percentage of each food group which is contained in the food The enthalpies of each food group are given:

10 Try it!

11 Try it! Chemistry for use with IB diploma, Pearson

12 World of Biochemistry Carbon Compounds include Carbohydrates Lipids Nucleic acids (e.g., DNA/RNA) Proteins Which are made of Which are made of Which are made of Which are made of Simple sugars (e.g., glucose) Glycerol & 3 Fatty Acids Nucleotides Amino Acids which contain which contain which contain which contain Carbon, hydrogen, oxygen Carbon, hydrogen, oxygen Carbon, hydrogen oxygen, nitrogen, phosphorus Carbon, hydrogen, oxygen, nitrogen, main function main function main function main function ENERGY STORAGE short-term ENERGY STORAGE long-term ENCODING HEREDITARY INFORMATION CATALYSIS & STRUCTURE /SUPPORT

13 Proteins Proteins are essential parts of living organisms and participate in virtually every process in cells. Proteins Which are made of Amino Acids which contain Carbon, hydrogen, oxygen, nitrogen, main function CATALYSIS & STRUCTURE /SUPPORT Types Enzymatic Structural Transport Hormonal Contractile Defensive Function/Example Acceleration of chemical reactions E.g., digestive enzymes, cellular respiration Collagen & elastin, keratin in hair and nails Transport of other substances E.g., hemoglobin transports O 2 to cells Cellular communication E.g., insulin secreted by the pancreas Movement E.g. actin and myosin in muscle cells Protect against disease E.g., antibodies combat viruses and bacteria

14 Proteins and their subunits Amino acids are the building blocks of proteins Amino Acid Structure Any one of the 20 different Amino Group side-chains Carboxyl (acid)

15 Proteins and their subunits Examples of amino acids

16 Identifying Amino Acids Circle the amino group Square the carboxylic acid group Triangle the side group CENTRAL CARBON ATOM AMINO GROUP CARBOXYL GROUP HYDROGEN ATOM R-GROUP or Side Chain

17 Notice there is an acidic and basic group in the structure Depending on the solution that the amino acid is in, it may act as an acid or a base In acidic solutions, there are lots of H+ ions In basic solutions, there are few H+ ions There is a unique ph value where the zwitter ion will exist; known as the isoelectric point Zwitterion

18 Buffer Properties

19 Isoelectric Point

20 Try it! The isoelectric point is the ph where the amino acid will exist as a zwitterion and have no NET charge A zwitterion has NH3 + and COO - An amino acid with no charge has NH2 and COOH

21 Proteins and their subunits 20 Major Amino Acids 8 are considered essential 1. Phenylalanine 2. Valine 3. Threonine 4. Tryptophan 5. Isoleucine 6. Methionine 7. Leucine 8. Lysine The other Glycine 7. Glutaimine 2. Alanine 8. Histidine 3. Proline 9. Tyrosine 4. Serine 10. Aspartic acid 5. Cysteine 11. Glutamic acid 6. Asparagine 12. Arginine Types of Amino Acids Nonpolar Polar Polar/Acidic Polar/Basic Amino acids each have their own unique chemical properties. Some dissolve in water some do not. This is essential for transport and storage.

22 Making and Breaking Proteins Amino acids are linked together by peptide bonds - a special covalent bond found in proteins + H 2 O Peptide bond Dipeptide H

23 Making and Breaking Proteins Condensation synthesis two amino acids join (dipeptide) a peptide bond is formed a water molecule is formed Hydrolysis water is added a peptide bond is broken amino acids are split apart A chain of amino acids is called a polypeptide Gly Lys Phe Arg Ser H 2 N- end Peptide Bonds -COOH end

24 Making and Breaking Proteins A chain of amino acids is called a polypeptide Gly Lys Phe Arg Ser H 2 N- end Peptide Bonds -COOH end The type of protein is determined by: sequence of polypeptides orientation in space 3-D shape --- Determines the function!

25 Try & Build a Protein In the human body, we have 20 amino acids...so the possibilities of unique combinations is gigantic! Each protein has a specific sequence and therefore a specific function

26 Protein Structure Four levels of protein structure: Primary - exact sequence of amino acids before folding. Secondary - simple folding create simple structures. Tertiary - folding results in complex 3D structures. Quaternary - multiple 3D subunits organized into a bigger structure.

27 Primary Structure The actual sequence of amino acids, starting from the amino terminus: Amino acids are always written starting at the NH2 end! Short forms or abbreviations are used: ie) Gly-His-His-Ala-Ser-Gly-Val-Trp

28 Secondary Structure Due to the presence of oxygen and nitrogen in many amino acids, dipole-dipole interactions occur, specifically hydrogen bonding Intermolecular hydrogen bonding causes alpha helices (α-helix) or beta pleated sheets (β-pleated sheets) to form Chemistry for use with IB diploma, Pearson

29 Tertiary Structure After the helices and sheets are formed, the protein folds into a 3D shape through interactions of the different side chains via hydrogen bonds, Van der Waal s forces, ionic attractions, dipole-dipole, etc. This unique 3D shape gives the protein a unique function All the hydrophobic (waterfearing/non-polar) amino acids end up in the middle of the protein, buried away from any water, while hydrophilic (waterloving/polar) amino acids end up around the outside

30 Disulfide Bridges Sulfhydryl (-SH) functional groups can form disulfide (-S-S) bonds which contribute to a proteins tertiary structure. When 2 Cysteine residues are folded close to each other, a disulfide bridge may form This bridge is actually a covalent bond between sulfur atoms This also contributes to tertiary structure

31 Tertiary Structure Nelson Biology 12

32 Shape = Function! Proper protein function depends on correct 3D structure. Any change in the specific primary structure can cause the protein to fold differently. Normal: Gly Lys Phe Arg Ser Mutated: Gly His Phe Arg Ser A different shape can lead to a different function (or lack of proper function). Sickle cell anemia is an example.

33 Quaternary When 2 or more polypeptide chains interact together ie) Hemoglobin: 4 polypeptides interact to carry oxygen to the blood

34 TERTIARY PRIMARY QUATERNARY SECONDARY Nelson Biology 12

35 PROTEINS Proteins can loose their shape if they are subjected to high temperatures (above 40 o C) OR if they are exposed to acidic, basic or salty environments. When a protein looses it s shape because of environmental factors, we call this DENATURATION A denatured protein cannot carry out it s biological functions!

36 PROTEINS Denaturing a protein can be both dangerous OR useful A high fever can Denaturing KERATIN in curly hair is a way of straightening the hair. Raw meant is difficu chew. Cooking me denatures the prot making it easier to c be dangerous!

37 Try it!

38 Analysis of Proteins We will discuss two techniques used to analysis proteins: Electrophoresis Paper chromatography

39 A technique that separates charged substance by the size and charge of the molecules when a potential difference is applied Electrophoresis The medium on which electrophoresis is carried out is usually a polyacrylamide gel (PAGE) Think of the gel as a large meshy network Small, charged molecules will move faster than large, uncharged molecules Each amino acid will have different charges depending on the ph of the solution it is in:

40 Electrophoresis

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42 Your gel:

43 Chromatography Amino acids are broken apart using a hydrolyzing agent They are spotted on a plate, usually a filter paper (stationary phase) The paper is put in a solvent (mobile phase) Individual amino acids move differently based on how attracted they are to the mobile or stationary phase

44 Chromatography The amino acids are colourless unless sprayed with ninhydrin which turns them purple The Rf (retention factor) can then be calculated for each spot on the plate The Rf is compared to known Rf values for amino acids

45 Try it!

46 Try it!