Chemistry of life & nucleic acids and proteins (Topics SL2, HL6)



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  • What are the three most common elements found in living organisms?

______

______

______

  • Write down the general formula for carbohydrates: ______
  • A ______, or long chain molecule, is made up of many ______, or single subunits.

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  • The table below shows some of the other elements required by living organisms. Complete it to show one function for each of the elements in plant & animal cells:

Element

/ Role in plants /

Role in animals

Nitrogen (N)
Calcium (Ca)
Phosphorus (P)
Iron (Fe)


Sodium (Na)
  • What is the difference between:

a)An atom and an ion?

______

______

______

b)Covalent and ionic bonding?

______

______

______

  • What is the definition of an organic substance?



______

______

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  • Water (H2O) is essential for all living systems. Water molecules are described as ______because they have an uneven charge distribution within the molecule as a whole. The oxygen atom is slightly ______charged, and the two hydrogen atoms have a slight ______charge. This means that ______bonds can form between adjacent water molecules, giving water many of its unique properties.
  • Sketch a diagram to show the structure and polarity of water:

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  • Complete the table to show how the properties of water make it significant in living systems:

Characteristic / Explanation / Example(s) of significance in living systems

Transparency

/ Light passes through water.

Cohesion

/ Movement of water up through the xylem tissue of plants.

Surface tension

Thermal properties
Water has a high specific heat capacity / Large amounts of energy are required to heat up water and change its state. Conversely, much energy also has to be lost by water in order to cool it.
Solvent properties



  • Draw the basic structure of a generalised amino acid in the space below. Label the different groups:
  • What is the most simple possibility for the ‘R’ group within the amino acid? __
  • Two amino acids (peptides) are joined together during a ______reaction to form a ______, and one molecule of ______. The link between the two amino acids is called a ______bond. Condensation reactions between many amino acids produce a ______(or protein) molecule.

Complete the diagram over the page to show a condensation reaction. The opposite of this reaction is called ______- in other words, breaking down the protein molecule.


H RO H R O

N C C + N C C 

H HOH H H OH

+ H2O

  • Primary structure of a protein is simply the sequence of the amino acids within a polypeptide chain, in other words, the order in which the amino acids are bonded together.
  • Secondary protein structure has three possibilities. Sketch and label diagrams of the following types of secondary structure found in proteins:

1) -helix2) -pleated sheet – parallel 3) -pleated sheet - antiparallel

  • Amino acids form ions in solution when the hydrogen ion from the carboxyl group dissociates, and forms an NH3+ ion with the amino group:

H RO H R O

N C C  H N C C

+

H HOH H H O –

  • Hydrogen bonds, ionic bonds, and disulphide bridges may form between different sections of the polypeptide chain (shown below as a coiled spring), thus maintaining tertiary structure.

Hydrogen bondIonic bonddisulphide bridge

fig3.26fig 3.24fig 3.25

p96p95p95

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  • Protein molecules are made up of many amino acids with peptide bonds between them. There are four levels of protein structure:

1)Primary structure is simply the sequence (order) of the ______within the polypeptide chain.

2)Secondary structure may be either an -helix or a -pleated sheet. The -pleated sheet may be ______or ______in form. In each case ______bonds maintain the structure.

3)Tertiary structure is the way in which the entire polypeptide chain is twisted and folded into a specific, fixed shape. The chain is held in shape by di______bridges, ______bonds, ______bonds and ______bonds.

4)Quaternary structure is found where several polypeptides interact to form a protein molecule, for example, haemoglobin – four polypeptides.

  • Label the types of structure found in the diagram of the enzyme lysozyme:


Lysozyme:

(Showing

tertiary structure)

fig 3.35

p104

disulphide

bridge

Haemoglobin:

(Showing

quaternary structure)

fig 3.36

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  • Protein types:

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Type / Nature / Function
Fibrous /
  • Secondary structure most important.
  • Insoluble in water.
  • Physically tough.
  • Long parallel polypeptide chains cross-linked (by hydrogen bonds) at intervals forming long fibres or sheets.
/ Structural. eg collagen. (tendons, bones), myosin (in muscle), silk (spider’s webs), keratin (hair, horn, nails, feathers).
Globular /
  • Tertiary structure most important.
  • Polypeptide chains are tightly folded to form a spherical shape.
  • Easily soluble.
/ Form enzymes, antibodies and some hormones, eg insulin.


  • Functions of proteins. Complete the table:

Name of protein / Type / Function
Amylase / enzyme
Keratin / structural
respiratory pigment
Fibrinogen / protective
hormone / helps to regulate glucose level in blood.


/ contractile / moving filaments in muscle tissue.
  • Draw a diagram of the ring structure of -D-glucose in the space below:
  • Glucose is an example of a monosaccharide. Two monosaccharides may be joined together during a ______reaction to form a ______. A molecule of water is released during this process. The bond formed between the two monosaccharide molecules is a ______bond. When condensation reactions occur between many monosaccharides a ______molecule is formed, for example, starch. The opposite of condensation is ______- breaking down the molecule. Complete the table below:

Type of carbohydrate / Example / Function

Monosaccharide

/ 1)
2)

Disaccharide

/ 1)
2) /
Not required
Polysaccharide / 1)
2)

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  • A lipid molecule is made up of one molecule of ______covalently bonded to three ______molecules. The fatty acid molecules are bonded to the glycerol molecule during condensation reactions. During the formation of one lipid molecule, three ______molecules are produced. A lipid molecule may be broken down during a ______reaction.

= hydrocarbon chain

= H and O atoms that form water during the condensation reaction.

  • Complete the diagram to show the products of the condensation reaction:


H

O

C

HC O H HO

O

C

HC O H HO

O

C

HC O H HO

H

Glycerol +

condensation

reaction

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  • Complete the table:

Type of lipid / Function
Phospholipid

/ Insulation under the skin of animals, buoyancy in aquatic mammals, energy storage.

Cholesterol
  • Most small carbohydrate molecules are ______because they have –OH ( ______) groups which are able to form ______with water molecules.
  • Most lipids are ______because they have a long, ______(uncharged) hydrocarbon chain.
  • Proteins with –OH ( ______) groups or other charged areas are ______. Non-polar proteins are insoluble.
  • In general, solubility of any substance decreases, as molecular size increases.

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