2. Biological Molecules Flashcards
Describe the Benedict’s test for reducing sugars
-add equal volume of Benedict reagent to the sample to be tested.
-heat the mixture in a water bath at 100 degrees for 5 minutes
Positive result- blue to a green to yellow to orange to brick red
Describe the iodine test for starch
-add a few drops of iodine to the sample
-if starch is present, iodide ions in the solution interact with the Centre of starch molecules, producing with a distinctive blue-black colour
Describe the Benedict test for non-reducing sugars
- hydrolyse non reducing sugars into their monomers by adding an equal volume of HCl
- Heat in a boiling water bath for 5min
- Neutralize the mixture using sodium hydrogen carbonate solution
- Proceed with the Benedict’s test as usual.
Describe the emulsion test for lipids.
-add ethanol to the sample to be tested, shake to mix then add the mixture to a test tube of water
-if lipids are present, a milky emulsion will form
-if no lipid is present, the solution remains clear.
Describe the biuret test for proteins.
-a liquid solution of sample is treated with sodium or potassium hydroxide to make the solution alkaline.
-a few drops of copper(II) sulfate is added to the sample
-if protein is present, a color change from blue to lilac/purple will be observed
Describe a semi-quantitative Benedict’s test on a reducing sugar solution.
-can be carried out by setting up standard solutions with known concentrations of reducing sugar
-using serial dilution.
-each solution is then treated in the same way; add the same volume of Benedict’s solution to each sample and heat in a water bath that has been boiled.
-any color change observed for each solution of a known concentration of reducing sugars is then compared to the stock solution colors.
Define the term monomer
A single subunit that is used to build large polymers
Define the term polymer
A large molecule comprised of repeating subunits
Macromolecule
A large biological molecule
Eg: polysaccharides
Proteins (polypeptides)
Nuclei acids (polynucleotides)
What is the difference between alpha and beta glucose?
The OH group on carbon 1 for alpha glucose is below the ring, while that for the beta glucose is above the ring.
Define a monosaccharide
A single sugar monomer, all of which are reducing sugars
What is a disaccharide
A sugar formed from two monosaccharides joined by a glycosidic bond in a condensation reaction
What is a polysaccharide
A polymer formed by many monosaccharides joined by a glycosidic bond in a condensation reaction
Why are triglycerides energy reserves ?
Because they store more energy per gram due to their hydrocarbon chains.
What is a condensation reaction?
A chemical reaction involving the joining together of two molecules by removal of a water molecule
What is a hydrolysis reaction?
A chemical reaction in which a chemical bond is broken by the addition of a water molecule; commonly used to break down complex molecules into simpler molecules.
Equation for sucrose
Glucose+fructose
Equation for maltose
Glucose+ glucose
Equation for lactose
Glucose+galactose
Functions of triglycerides
- They make excellent energy stored because they are richer in carbon-hydrogen bonds than carbohydrates
- They act as an insulator against loss of heat just below the skin
- Metabolic source of water- when triglycerides are oxidized in respiration, they are converted to carbon dioxide and water.
What is the primary structure in a protein?
The sequence of amino acids in a polypeptide or protein.
What is a secondary structure in proteins?
The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (an ą-helix or B-pleated sheet)
What is the tertiary structure of a protein?
The compact structure of a protein resulting from the three-dimensional coiling of the chain of amino acids.
What is the quaternary structure of a protein?
The three-dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule.
What is a globular protein?
A protein whose molecules are folded into a spherical shape, it is often water-soluble.
Why do globular proteins usually curl up?
So that their non-polar hydrophobic R groups point into the centre of the molecule, away from the watery surroundings.
What is a fibrous protein?
A protein whose molecules have a relatively long, thin structure that is generally insoluble and whose function is usually structural.
What is the latent heat of vaporization?
A measure of the heat energy needed to vaporize a liquid changing it from a liquid to a gas.
Disulphide bonds
Strong covalent bonds that form between two cysteine R groups
Strongest bonds in a protein molecule
Ionic bonds
Form between positively charged and negatively charged R groups
Stronger than hydrogen bonds
Hydrogen bonds
Form between strongly polar R groups
Hydrophobic interactions
Form between the non-polar (hydrophobic) R groups
Relate Glycogen’s structure to its function
-it’s extensive branching allows enzymes to work on many ends at the same time. This allows a quick release of glucose when animals need immediate energy.
-it’s highly branched structure allows for compact storage.
Relate Amylose’s structure to its function
-it’s unbranched structure makes it resistant to digestion
-its helical shape enables it to be more compact.
Relate Amylopectin’s structure to its function
-it’s branched structure makes it more easily hydrolyzed for use during cellular respiration or added to for storage.
Relate Cellulose’s structure to its function
-the linear arrangement of b glucose glucose molecules and extensive hydrogen bonding gives it a rigid, fibrous structure. And provides high tensile strength which allows it to stretch without breaking making it possible for cells to withstand turgor pressure.
-the tensile strength of cellulose helps resist mechanical stress and prevents cells from bursting.
-the tightly packed hydrogen bonds make cellulose insoluble in water.
Relate Triglycerides structure to its function
-they are hydrophobic so they do not cause osmotic water uptake in cells so more can be stored.
-they compose part of the adipose tissue layer which acts as insulation against heat loss
-low density of fat tissue increases ability of animals to float more easily
-the adipose tissue contains stored triglycerides and this tissue helps protect organs from damage risk.
Relate the structure of hemoglobin to its function.
-The haem group with its central iron ion is essential for the reversible binding of oxygen.
-hemoglobin’s cooperative binding is another important aspect of its function. When one oxygen molecule binds to a haem group it causes a conformational change.
Relate the structure of collagen to its function.
-the triple helix of collagen provides great tensile strength which is crucial for tissues that need to withstand pulling forces.
-The staggered ends of the collagen molecule within the fibrils provide strength.
-the cross linking between collagen fibrils strengthens tissues making them more rigid and able to withstand compressive forces.
-the presence of glycine in every third position and hydrogen bonds between chains help maintain the structural integrity of collagen
Differences between collagen and hemoglobin?
- Collagen has 3 polypeptide chains forming a triple helix
Hemoglobin has 4- a-globin and b-globin - Collagen is a fibrous protein and hemoglobin is a globular protein
- Collagen has structural functions and hemoglobin has functional functions
- Collagen is insoluble in water and hemoglobin is soluble in water.
Explain how hydrogen bonding occurs between water molecules.
It arises due to the polarity of the water molecule where the oxygen atom attracts the hydrogens of neighboring water molecules leading to the formation of hydrogen bonds.
Relate the properties of water to its roles in living organisms.
- Solvent action- as water is a polar molecule many ions and covalently bonded polar substances will dissolve in it. Substances like nutrients, gases, and waste in fluids such as blood, lymph and cytoplasm.
- High specific heat capacity- it allows it to act as a temperature buffer. In living organisms it helps maintain homeostasis.
- High latent heat of vaporization- means it takes a lot of energy to turn water from a liquid into a gas.
Only little water is required to evaporate for the organism to lose a great amount of heat.
This provides a cooling effect for living organisms.
