NOTES FOR LAB EXAM –
Lab 1 – Peptide Structure & Effect of pH on Molecular Structure and Function
Lab 2 – Microscopy, Plant and Animal Cell Division & The effect of Stimuli on Pulse Rate
Lab 3 – Cellular Energy: Photosynthesis and Respiration
Lab 4 - Genetics [Gene to Protein], Inherited Traits & Punnett Squares
Laboratory Number 1:
A peptide is a sequence of chains of amino acids; they are considered the building blocks of all
Amino Acids are monomers that have a basic structure of a central carbon, an amino group
and a carboxyl group. Generally, in water amino acids are ionized [Amino Group becomes
positively charged & Carboxyl Group becomes negatively charged]
Primary Structure – this is the sequence of amino acids within a peptide chain formed by
peptides bonds between amino acids.
Secondary Structure – this is in the form of either an Alpha Helix or a Beta Pleated Sheet. The
C=O bonds formed are polar, because Oxygen has a greater affinity for electrons, it is
therefore partially negatively charged. Also, N-H bonds are considered “polar” because
Nitrogen has a greater affinity for electrons than Hydrogen. These partial charges allow for
Hydrogen Bonds to form between non-adjacent amino acids within a peptide chain. The
hydrogen bonds between amino acids cause the secondary structures to be relatively stable.
Tertiary Structure – this is the three dimensional structure of an amino acid chain; it
includes the various interactions between the side chains of non-adjacent amino acids.
There are various types of side chains include –
(1)Polar [Hydrophilic] and Non-polar [Hydrophobic]
(2)Negatively Charged [Carboxyl Groups as side chain] and Positively Charged [Amino
Groups as side chain]
Interactions between side chains give the overall shape; these are 4 types of interactions –
(1)Van Der Waals Interactions (3)Hydrogen Bonds
(2)Ionic Bonds (4)Disulphide Bonds Quaternary Structure – this is the interaction between two or more peptide chains.
Exercise 1.1: Explore peptide Folding and Effects of Physical Environment:
Effects of pH and Salinity on Peptide Structure: this will change the ionic strength of the
- Acids break the ionic bonds, therefore changing the shape.
- Salt behaves similarly to acids, breaking bonds.
When a peptide is placed in a less polar solution, the tertiary structure will turn itself inside
out due to hydrophilic and hydrophobic interactions.
Temperature: breaks hydrogen bonds because they cannot withstand the vibrations
Exercise 1.2: Effects of pH on Molecular Structure and Function:
When proteins are exposed to extreme conditions, they are said to denature [the structure is
changed], these denatured proteins are no longer functional.
Chemicals and Temperature:
When exposed to:
- Hydrophobic Chemical the hydrophilic amino acid chains turn inward to centre of the chain
- Ionic Solution polar side chains are either attracted/repulsed by the solution.
- Oxidising Solution may strip electrons and break bonds between amino aids or even atoms
- Heating a protein will also break the weaker chemical bonds between amino acids
(A)Red Cabbage Indicator to Measure pH:
Red cabbage’s colour is due to pigments [anthocyanins – responsible for red, blue and purple
colours in vegetables.] These colours change as pH changes.
Boiling the red cabbage extracts the anthocyanin pigments.
(B)Determining the effects of pH on amylase activity:
Enzymes are proteins with a complex structure that can be denatured.
Amylase is a type of enzyme found in saliva and pancreatic secretions that catalyzes the
conversions such as starch or glycogen to glucose monomers. As the pH changes, it alters the molecular shape, therefore changing to colour of the liquid.
The colour change is a result of the change in molecular shape.
Maltose + Water ----- 2 Glucose
C 12 22 110 --2-- 2C H 0 6 12 6
Laboratory Number 2:
Parts of a Microscope:
The Eyepiece [The Ocular]: this magnifies the image of the specimen. A microscope
with two eye pieces is called Binocular, a microscope with one eye piece is called
Objective Lenses: There are four different Objective Lenses [4x, 10x, 40x & Oil
The Stage: this olds the microscope slide and has adjustment knobs that allow the slide
to be moved. A hole in the centre of the stage allows light to pass through to optimise
Coarse Adjustment: this moves the stage up and down. NEVER use the coarse
adjustment knob with the 40x or 100x lens.
Fine Adjustment: this also moves the stage up and down, but in smaller increments.
This allows for much more precise focusing, especially at the 40x and 100x lenses.
Light: the light is located under the stage, focused through the condenser. The
diaphragm controls the light intensity.
Mitosis: Nuclear Division that results in two daughter cells that are genetically identical, this
happens within a fertilized egg, allowing for growth into a multicellular organism. The only
cells not able to mitotically divide are blood cells, muscle cells and neurons; they lost this
ability when they became specialised cells.
Meiosis: Nuclear Division that results in daughter cells that are genetically differen