Everything Life Sciences Grade 10

FACT

Because the
sequence of amino
acids determines
the way that a
protein folds, if you
start with a certain
peptide chain, you
will always get the
same
three-dimensional
structure!

Investigation: Test for the presence of lipids (Essential investigation-CAPS)

Aim:

To test for the presence of lipids

Apparatus:

• piece of paper or ”fish-and-chips” paper bag


• food item e.g fries, piece of cooked meat, etc


• 10 ml of cooking oil (positive control)


• 10 ml water (negative control)

Method:

1. Positive control: add cooking oil to brown paper bag until it is soaked up. The part of
   the paper that soaks up oil should be translucent compared to the part that does not.


2. Negative control: wet the paper with water. The paper may become wet and soggy,
   but should not become translucent.


3. Experimental samples: stain the brown paper bag with the food item to be tested and
   hold it up to the light. If it is translucent, similar to the positive control, the food item
   contains lipid.

Observations:

Record your observations, noting any key differences between the controls and the experi-

mental sample

Proteins DUMMY

Molecular make-up

Proteins contain carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and may have other

elements such as iron (Fe), phosphorous (P) and sulfur (S).

Structural composition

Proteins are made ofamino acids. There are 20 common amino acids from which all proteins

in living organisms are made. Nine of them are considered essential amino acids, as they

cannot by synthesised in the body from other compounds, and must be obtained from the

diet. Amino acids are bonded together bypeptide bondsto formpeptides. A long peptide

chain forms a protein, which folds into a very specific three-dimensional shape. This three-

dimensional shape is completely determined by the identity and order of the amino acids in

the peptide chain. We often refer tofour different levelsof protein structure (Figure 2.15):

• Primary structure: This refers to the sequence of amino acids joined together by pep-
  tide bonds to form a polypeptide chain. Some proteins have fewer than a hundred
  amino acids, while others have several thousand.


• Secondary structure: This is the first level of three dimensional folding. It is driven

38 2.4. Organic compounds