Option C - Human biochemistry


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. RDA--

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

-Fats (& oils)- concentrated source of energy RDA---



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


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.


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.

-amino acids join to form proteins



To be completed


-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.



-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)



-structure, eg collagen (fibrous proteins)

-biological catalysts (eg. enzymes)

-transport eg. hemoglobin

-energy source


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



-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


-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)


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

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



-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 triglycerides) 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.


C.4.4. SOAP:

-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


C.5 Vitamins

C.5.1 Role in Metabolism:

-Metabolism- all of an organism's biochemical reactions

-In order for reactions to take place in the body, ctalysts are needed-these are called enzymes (see section on enzymes for more info)

-Enzymes do not work alone, and sometimes require the help of coenzymes in order to carry out their catalytic functions-->vitamins function as coenzymes (mainly water soluble vitamins)


C.5.2 Water/Fat Soluble:

-WATER- coenzymes needed in metabolism. eg. Vitamin B and C. when in excess, they pass out the body in urine

-FAT-other functions in body (not clear) eg. Vitamin A and D. These can be stored in fat tissue These vitamins can accumulate to toxic levels


C.5.3 Structure and Functions: (structures listed in data-booklet)

-Vitamin A (Retinol)--at night, light shining on the eye strikes a receptor, rodopsin which sends an impulse to the brain. vit A is essential in the formation of rodopsin.

Deficiency--night-blindness, xerophthalmia (tear glands cease to function)

-Vitamin D (calciferol)--important in the production of a hormone involved in the metabolism of calcium. It is modified by the body (2

-OH groups are added) and it functions as a hormone which causes the intestines to absorb calcium from food.

Deficiency--rickets (weak bones, low blood calcium level)

-Vitamin C (ascorbic acid)--essential in the formation of connective tissue-collagen. Works as a reducing agent to form one of the amino acids in the protein collagen

Deficiency- scorbutus ("scurvy"-connective tissue breaks down, hemorrhage)


C.5.4 Food Processing:

-most vitamins are destroyed or altered during cooking, especially water soluble vitamins. (fat soluble vit are relatively stable)

-vit B is destroyed during milling processes


C.6 Hormones

C.6.1 Production/Roles:

-organic molecules secreted by one part of the organism but having an effect on another. They are controlled by the pituitary gland, which is controlled by the hypothalamus. Secreted by endocrine glands.

-ADRENALIN: synthesized from amino acid Thyrosine :when exercise is done, impulses are sent for adrenaline to be released into the blood stream. It causes blood to be sent into areas of more active circulation. Increase in volume of blood available. Increase in rate of heart beat, stimulated respiration. the breakdown of glycogen to glucose is stimulated-raises level of sugar in the blood stream.

-THYROXINE: iodated amino acid derivative, produced by the thyroid gland :stimulates growth and metabolism

-INSULIN: made up of 2 poypeptide chains held together by disulfide bonds. Made in the pancreas by the Islet of Langerhorn. : regulates cellular intake of glucose from the blood. It is secreted in response to a rise in blood sugar or amino acid concentration. It also inhibits the breakdown of glycogen in the liver.


*Female :pituitary hormones (LH and FSH) are secreted at puberty, Estrogen: (produced by ovary) stimulates an increase in secretion of a hormone, which brings about the maturation of the follicle and the ovulation. stimulates the development of female features: breasts, subcuataneous fat, menstrual cycle Progesterone (corpus luteum of ovary)- stimulate the endometrium (lining of the uterus) to thicken and to secrete a nourishing fluid-in preparaton for a fertilized egg.

*Male: Testosterone-hormone secreted by the testes and the adrenal glands (above the kidneys). During puberty, the pituitary gland stimulates the release of a protein ABP, which has high affinity for testosterone. :stimulates development of male features: deepening of voice, development of male musculature, growth of hair on the face and other parts of the body.


C.6.2 Steroids: (see structure in data booklet)

-a type of lipid (hydrophobic)

-Structure: consist of four contiguous carbon rings (the common backbone)

-Different steroids have different functional groups attached to the backbone.

-CHOLESTEROL- most common steroid. An essential component of cell tissue and brain and nervous tissue. It has a chain of alkanes on one ring, and a -OH group on the last ring

-Some steroids act as hormones, which send chemical messages to different parts of the body, these hormones are synthesized from cholesterol in the ovaries, testes, and other glands that produce them.

-PROGESTERONE- Carbonyl group (ring=O) attached to a methyl group on the first ring, carbonyl group (ring=O) on the last ring

-TESTOSTERONE- -OH group on the first, ring=O on the last

-Differences- cholesterol is primarily hydrophobic, with only one carbonyl group, the sex hormones have carbonyl groups and hydroxyl groups which make the molecule partly hydrophilic on both ends.


C.6.3 Oral Contraceptive:

-the "pill" consists of estrogen and progesterone hormones (synthetic). The excess of these hormones (at a given dosage) will prevent ovulation, thus avoiding pregnancy.

-Negative feedback control--The increased levels of estrogen inhibit the levels of LH hormone released by the pituitary gland. The drop in LH and FSH levels stops the development of the endometrium lining-without it the egg cannot implant and therefore no pregnancy will occur.


C.6.4 Steroid Use and Abuse:

To be completed