Human Biochemistry SL Chemistry


  • Created by: Priscilla
  • Created on: 25-03-12 19:30

C.1 Diet

C.1.1 Requirements of a Healthy Human Diet:

-Water: necessary for life, biochemical activities within the body

-Food groups:

1)milk group-milk, cheese, yoghurt -->supplies calcium, protein, vit A&D

2)meat group-meat, fish, poultry, eggs, legumes, nuts --> iron, vit B,energy

3)vegetable and fruit group -->vit A&C

4)bread and cereal group -->energy, vit, minerals, protein

-Carbohydrates-source of calories (energy), glucose important in energy-producing cycles within cells. 

-Proteins- enzymes to catalyse the vosy's chemical reactions, hormones, muscle, connective tissue RDA- 56g

-Fats (& oils)- concentrated source of energy



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Calcium- blood, cells, body fluids, bones (its absorption is enhanced by vit D) Magnesium- maintains the electric potential across nerve-and-muscle-cell membranes

Phosphorus- bones & teeth

Iodine- essential for functioning of thyroid gland

Iron- hemoglobin, enzymes

Zinc- part of important enzymes in the body

Importance of a Balanced Diet:

-deficiency in caloric assumption results in deficiency diseases, starvation, or death

-overnutrition results in obesity, high blood pressure, diabetes, heart attacks

-excess in saturated fat consumption leads to rise in blood cholesterol levels- strokes

-deficiency in protein and minerals- anemia, edema, loss of pigment and hair, retarded growth

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C.1.2 Calories and Enthalpy of Combustion:

-calories are the energy content of food

-energy is stored in chem bonds that link atoms and molecules. Energy is captured by the body during biochemical reactions involving the combustion of nutrients. This energy is used to drive life processes of cells.

Proteins and Carbohydrates- 4kcal/g

Fat- 9kcal/g

Alcohol- 7kcal/g

*for calculations, simply use DH = mc DT

*divide the change in heat by the number of grams of food burned, and the caloric value of the sample will be obtained.

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C.2 Proteins

C.2.1 2-Amino Acids:

-there are 20 different 2-amino acids

-they contain an amine group (NH2) on the central carbon atom (a), a carboxyl group and different R-groups.

-all amino acids are optically active (not needed, but good to know)


-two amino acids join to form a dipeptide---the bond is called PEPTIDE BOND

-condensation reaction: a hydroxyl group is lost from one of the amino acids' carboxyl group, while the other amino acid loses a H from its amine group. (again, a diagram would be good, but...)

-amino acids join to form proteins

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-R-groups of amino acids have different isoelectric points,(i.e.where the charge on the amino acid is zero).

Similarly sized molecules can be separated by using the charge on the individual amino acids.

Proteins are placed in a magnetic field- positive R-groups will be attracted to the negative pole of the magnet, while negative R-groups will tend to move towards the positive pole.

The position where the individual amino acids stop is indicative of their charge. This reveals the isoelectric point, and consequently the R-group of the amino acid.

-pH can be used to separate proteins. they re placed in a pH gradient. Amino acids travel to where their net charge is zero.

Given the position in which they stop, the amino acid can be identified.

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-PRIMARY: amino acids arranged in linear order

-SECONDARY: -alpha helix:coil of polypeptides, with hydrogen bonds between the amide hydrogen atom in one peptide and the carbonyl oxygen atom of another peptide, at a distance of three amino acids. Coil chains are held together by DISULFIDE BONDS between adjacent chains.

-beta-pleated sheet: a folded sheet, stabilized by hydrogen bonds between the chains. There are NO disulfide bonds in this structure.

-TERTIARY: folded structure of chains of amino acids. 4 types of interactions

1) Ionic bonds between R+ and R-

2) H-bonds between partial - and partial + R-groups

3) Disulfide bonds

4) Hydrophobic interactions- non polar R-groups tend to stay close together because repelled polar substances surrounding proteins.

-QUATERNARY: more than one polypeptide chain join to form a protein--several folded chains joined by disulfide bonds (eg. hemoglobin)

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-structure, eg collagen (fibrous proteins)

-biological catalysts (eg. enzymes)

-transport eg. hemoglobin

-energy source

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C.3 Carbohydrates


-all sugars that contain a single carbohydrate unit, with an empirical formula: CH2O

-contain a carbolyl group (C=O), and at least two hydroxyl groups (-OH)

-eg. -glucose, fructose, galactose



-a main source of energy

-contains six carbons with an aldehyde group (H-C=O) on the first and hydroxyl groups on each of the remaining carbons

-in water, the 2nd C and the 6th C form a bond, forming a cyclic structure

-a-glucose: hydroxyl group on the sixth carbon is DOWN

-b-glucose: it is UP

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-organic molecules join together by releasing water- a H is removed from one group, and an -OH group from another. A glycosidic bond is formed.

-DISACCHARIDES-formed by two monosaccharides.

eg. Lactose= glucose + galactose

eg. Sucrose= glucose + fructose

(diagrams might be added in the future, if I figure out how to do them


-POLYSACCHARIDES- a number of monosaccharides joined together eg. Starch, a polymer of glucose, with formula (C6H10O5)n eg. Glycogen, same molecular formula--gives glucose when hydrolised, stored in liver and muscles as a reserve of carbohydrates. (this is not needed)


-basic energy sources for living organisms

-GLYCOGEN- an energy reserve, (stored in liver), can break down into glucose when it is needed

-Precursors for other biologically important molecules---i.e. monosaccharides are used to make other molecules like glycerol and fatty acids and some amino acids.

-Cellulose-structural material in plants (not in syllabus)

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C.4 Fats


-fatty acids: long chain of carbon and hydrogen atoms with a carbonyl group at the end (C=O)

-TRIGLYCERIDES: molecules formed by the joining of three fatty acids to a molecule of glycerol (Propane 1,2,3-triol i.e.H2COH-HCOH-H2COH)- the latter loses the -H atoms (from the hydroxyl group) and the fatty acids lose -OH groups. Dehydration synthesis.

-solid at room temperature-"fats"-and liquid at room temp- "oils"

-PHOSPHOLIPIDS- similar to the above, but one or to of the fatty acids are replaced by a phosphate group, which links to an amine group of another molecule (I'm not sure you need this)

-ALL Fats are hydrophobic--contain a high proportion of C-H bonds, the carbonyl end of the molecule is hydrophilic

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-SATURATED- fats with single bonds (no double bonds, not even one), C atoms can hold no more H atoms than they already have

-UNSATURATED- fats with at least one double bond

-the double bond causes fats (eg triglyceerides) to have a lower boiling point-the double bond tends to keep the fat flat-linear----usually oils at room temp


-The extent of unsaturation of a fat---tested by I2. By calculating the number of moles that react with a fat, the number of double bonds will be discovered. This is because the double bonds between C atoms are broken, and I bonds itself to the C. One I will bond to each former double-bond location--every molecule of I2 used indicates one double bond.Electrophillic addition R-C=C-R + I2 ---> R-I-C-C-I-R

-When the reaction occurs, the iodine will become clear.

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-Soap is made by the hydrolysis of fats. NaOH is added as a source of alkali.

-3 Na+ are required to saponify one fat molecule (generally a triglyceride). These will replace the glycerol, yielding three fatty acids with an Na+ tail.


-Energy source (self-explanatory)

-Insulation (ditto)

-Cell membrane-made up of phospholipids

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