These notes were written for the old IB syllabus (2009). The new IB syllabus for first examinations 2016 can be accessed by clicking the link below.

IB syllabus for first examinations 2016

Option C - Human biochemistry


Higher and standard level students

C.1 Diet (2h)

Balanced diet

Minimum requirements

Essential minerals

Calorific value from food and enthalpy from combustion data

Genertically modified (GM) food benefits and drawbacks


C.2. Proteins (3h)

The structure of amino acids

Condensation reactions of amino acids

Protein analysis by:

Primary secondary, tertiary and quaternary structure of proteins

Functions of proteins in the body - structure, biological catalysis (enzymes) and energy sources


C.3. Carboydrates (2.5h)

The structure of monosaccharides (Carbonyl group, at least two -OH groups and empirical formula CH2O)

Straight chain formula of glucose, the structural difference between alpha and beta-glucose

Condensation of monosaccharides to make disaccharides (lactose and sucrose) and polysaccharides (starch)

Functions of polysaccharides in the body


C.4. Fats (2.5h)

Composition of fats and oils

Difference in structure between saturated and unsaturated fats, difference in melting points

Addition reactions to calculate the number of double bonds (degree of unsaturation) - Iodine number or index

Hydrolysis of fats, saponification, soap formation

Functions of fats in the body, energy sorce, insulation and cell membranes


C.5. Vitamins (2.5h)

Definition

Solubility by consideration of the structure

Structure adn main functions of:

The effect of food processing on the vitamin content


C.6. Hormones (2.5h)

Production and roles of hormones in the body

Compare the structures of cholesterol and the sex hormones

Mode of action of oral contraceptives

Use and abuse of steroids


The following content is for the higher level students only

C.7. Enzymes

Characteristics:

Most of the proteins in the organism are enzymes. They act as catalysts for biochemical reactions in the body.

An enzyme's activity depends on its tertiary and quaternary structure- different enzymes catalyse different reactions depending on their structure because substrates bind to the enzyme's active site during the reaction. this active site is only present in tertiary and quaternary structures. The properties and positions of the R-groups exposed at the active site determine which substrates will bind to the enzyme.

Some enzymes do not bind to substrates unless their active sites don't contain additional ions or molecules.

Co-factor: a substance held to the protein by other bonds eg ions Ca2+

Co-enzymes: non protein organic molecules eg vitamins

DNA animation by Rick Groleau

 

Substrate concentration:

A single enzyme can process only a limited amount of substrate in a given time, when substrate concentration increases, reaction rate increases. When all the enzymes are bound to substrates, the rate depends on the enzymes' rate of processing the substrates. The reaction rate eventually reaches a maximum limit.

 

Vmax and Michelis Constant (Kmax):

Rate is expressed as the number of reactions catalyzed by a given enzyme molecule per unit time.

In a graph of substrate concentration vs rate of reaction, the graph rises in a curved fashion, with a decreasing slope. Vmax is recognized as being the point in which the graph continues in a horizontal line, parallel to the x-axis.

The Kmax is the substrate concentration at which the reaction rate is 1/2 Vmax. this is a measure of how readily the enzyme-substrate binding occurs. when Kmax is low, the reaction proceeds at a rapid rate even at low substrate concentrations

Kma is recognized on a graph by finding the 1/2 Vmax rate on the y-axis and drawing a perpendicular down to the x-axis. The perpendicular will reveal the concentration at Kmax.

Michaelis Menten

 

Active Site:

It is a cluster of chemical groupings formed as a part of the enzyme's folding pattern. The properties of the R-gouprs exposed at th active site determine which substrates will bind.

When enzymes and substrates combine, they change shape: the active site is a flexible pert of the enzyme, which increases the surface area between the substrate and enzyme.

 

Inhibition:

COMPETITIVE: compounds that are similar to the substrate, which compete with the substrate by binding to the active site. This decreases the reaction rate because the enzyme cannot bind to the substrate.

NON-COMPETITIVE:
- The inhibitor binds to a site other that the active site
- Does not change the active site
- Increases the actuation energy
- Does not effect Enzyme-Substrate binding

 

Effects on Enzyme Activity:

-HEAVY METAL IONS:

Calcium ions are the most commonly found in animals, accounting for 1.5-2% of human body mass of which 99% comes from bones and teeth
- Half a gram phosphorous is required for attaching each gram of calcium to the bones
- Magnesium, potassium and sodium ions are also present in biological systems as ions in the fluids in and arouns the cells present in trace amounts in the human body

Iron was the first trace metal ion found to be essential in the human diet. The first row transition metals such as Co, Cr, Cu, Mn and Zn are present in trace amounts in the human body. These are essential to many enzymes such as Zn (charge 2+) in carboxypeptidase; Zn is found in almost 100 enzymes and is also present in insulin. Co (3+) is found in vitamin B12 and iron is present in the hemoglobin molecule of red blood cells. Magnesium is a secondary element of bones and teeth as well as regulating intracellular chemical activity, helping to form protein and transmitting electrical signals from cell to cell. Mn is essential for healthy bones and Cr plays a key role in glucose metabolism. On the other hand, iron deficiency produces anemia and causes fatigue as cells are deprived of oxygen and Cu deficiency gives rise to bone disease. The need for trace amounts of some metal ions such as tin and arsenic has been established in animals such as rats but not yet in humans.

TEMPERATURE: when temp rises, molecules move faster, colliding harder and more often, therefore they are more likely to react than at lower temp. When the temp increase is too high (above 60\260C), the enzymes will be denatured permanently, and will no longer function-their 3-D structure will be destroyed. At low temp reactions proceed slowly, and at very low temperatures (below 0\260C) the enzymes are denatured. They normally function at body temperature 37ºC

pH-enzymes are electrically charged because R-groups may ionize when they dissolve in water. The pH therefore determines the changes in the enzyme. Enzymes will function only at given pH's depending on their electrical charge. Most enzymes function best at neutral pH's.

 

Biotechnological use of enzymes:

 


C.8. Nucleic acids (2h)

Structure and condensation polymers (nucleic acids)

Nucleotide --> phosphate group, pentose sugar group and an organic base

students should recognise the five nucleotide bases --> adenine, cytosine, guanine, thymine and uracil

The double helix structure of DNA - hydrogen bonding between nucleotide bases

The role of DNA, the triplet code

The principles and uses of DNA profiling

 


 

C.9. Metal Ions in Biological Systems (2h)

Roles in the Body/Chemical Properties: The functions are related to charge diensity, redox properties and complex ion formation

 

Ion Concentration Across Cell Membrane:

Active transport-moves substances either with or against their electrochemical gradients, and requires energy. A source of energy may be Na+ of H+ concentration on the two sides of the membrane

Sodium/Potassium Pumps- it uses energy from ATP to transfer sodium ions out of the cell and potassium ions inside. This pump is responsible for the electrical potential across plasma membranes. In the membrane, 3 sodium ions are moved for every two potassium ions that move in. The cell becomes more negative compared with the outside. when the tendency of K+ leaving the cell balances its tendency to enter it, the membrane potential is reached. K+ movement ceases.

This type of pump controls the water content of the cell. It also drives the transport of sugars and amino acids. This process controls: the ability of nerves to conduct electricity, kidneys to form urine, muscles to contract, absorption of food in digestive tract.

 

Copper Ions in Electron Transport:

The electron transport system accepts hydrogen atoms and passes their electrons from one member of the chain to the next.

Cytochromes-electron carrier molecule consisting of a protein and a porphyrin ring, containing a copper ion

 

Iron Ions in Oxygen Carriers:

-haemoglobin-respiratory pigment that carries oxygen in the blood

-contain a heme group with an iron atom a its center. The iron atom binds to the oxygen. When O binds to Fe, the hemoglobin is oxygenated and appears bright red. Without the iron center, oxygen wouldn't bind to hemoglobin, and oxygen couldn't be carried through the blood stream and to the cells in the body.


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