Biological molecules (Chapter 1) BIOLOGY
What is a molar solution?
A molar solution is defined as an aqueous solution that contains 1 mole (gram-molecular weight) of a compound dissolved in 1 liter of a solution.
What is a monomer?
A small, repeating unit that can bond to similar units to form polymers.
Describe a condensation reaction
A condensation reaction is a reaction which joins monomers by chemical bonds and it involves the elimination of the water molecule.
What is a polymer?
A long chain of monomers that are bonded together by covalent bonds.
What is hydrogen bonding?
A hydrogen bond is an attraction between two atoms that already participate in other chemical bonds.
What is a polar/non-polar molecule?
A polar molecule is a molecule that is charged and a non-polar molecule is a molecule that is not charged.
What is metabolism?
The collective term for all the chemical reactions taking place within living organisms.
What is the general formula for monosaccharides?
(CH2O)n n represents the number of carbon atoms and is any number from 3-7
What is a polysaccharide?
Many monosaccharides joined together
Describe the Benedict's test for reducing sugars (3 steps)
1) Add 2cm3 of the food sample to a test-tube and, if it isn't already in liquid form, add a small volume of water to the test-tube and grind it into a liquid.
2) Add an equal volume of Benedict's reagent to the solution and gently heat the solution in a gently boiling water bath for 5 minutes
3) If the solution's colour changes to brick-red, reducing sugars are present.
What is a disaccharide?
Two monosaccharides joined together
What is a monosaccharide?
A single monomer
What is a polysaccharide?
Many monosaccharides joined together to form a long chain
What four elements are polymers made of?
Carbon, hydrogen, nitrogen and oxygen
True or false: No monosaccharides are reducing sugars and all disaccharides are reducing sugars
False. All monosaccharides are reducing sugars and only some disaccharides (e.g. maltose) are reducing sugars
Describe hydrolysis
When water is added to a disaccharide under suitable conditions, it breaks the glycosidic bonds, releasing the constituent monosaccharides.
What happens when a glucose molecule binds to a galactose molecule?
The disaccharide lactose is formed
What is the name of the bond formed during condensation reactions?
Glycosidic bonds
Describe a condensation reaction
When monosaccharides join, a water molecule is lost
Describe the test for starch (2 steps, 2 points)
- Starch is easily identified by its ability to change the colour of iodine in potassium iodide solution from yellow to blue-black
- The experiment takes place at room temperature
1) Place 2cm3 of the sample being tested in a test tube
2) Add two drops of iodine solution and stir/shake
What happens when a gluose molecule binds to a fructose molecule?
The disaccharide sucrose is formed
Where is starch found?
In seeds and storage areas (only plant cells)
What happens when a glucose molecule binds to another glusose molecule?
The disaccharide maltose is formed.
Name two properties of polysaccharides and briefly explain them
- Insoluble in water-> Osmotically inactive and doesn't affect the WP
- Large and polar-> Cannot diffuse through the membrane
Describe 5 properties of starch
- Insoluble-> Osmotically inactive so it doesn't affect the WP
- Large-> Cannot diffuse out of cell membrane
- Compact-> Lots of DNA can be stored within a small space
- When hydrolysed it can form alpha-glucose molecules which are easily transported and readily used in respiration
- Branched form-> Has many ends which can be acted on by enzymes simultaneously and, therefore, glucose monomers can be produced rapidly
Where is glycogen found?
In skeletal muscles
Describe the test for reducing sugars (disaccharides) (8 steps)
1) If the sample is not already in liquid form, it must first be ground up in water.
2) Add 2cm3 of the food sample into a test tube with 2cm3 of Benedict's reagent and filter it to ensure any solid pieces of the sample do not remain.
3) Place the test tube in a gently boiling water bath for 5 minutes. If the Benedict's reagent remains blue, reducing sugars are not present.
4) Add another 2cm3 of the liquefied food sample to 2cm3 of HCl acid in a separate test tube and place the tube in a gently boiling water bath for 5 minutes. The dilute HCl acid will hydrolyse any disaccharide present into its constituent monosaccharides.
5) Slowly add some sodium hydrogencarbonate (NaHCO3) to the test tube to neutralise the HCl (Benedict's reagent will not work in acidic conditions).
6) Test with pH paper to ensure that the solution is alkaline
7) Re-test the resulting solution by heating it with 2cm3 of Benedict's reagent in a gently boiling water bath for 5 minutes
8) If a non-reducing sugar is present in the original sample, Benedict's reagent will now turn orange-brown. This is due to the reducing sugars that were produced from the hydrolysis of the non-reducing sugar.
Describe the test for detecting lipids (5 steps)
1) Add 2cm3 of the sample and 5cm3 of ethanol to a dry, grease-free tube
2) Shake thoroughly to dissolve any lipid present in the sample
3) Add 5cm3 of water and shake gently
4) A cloudy-white colour indicates the presence of a lipid
5) As a control, repeat the exp using water instead of a sample; the final solution should remain clear
Describe the test for proteins (3 steps)
1) Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
2) Add a few drops of very dilute
3)
Name 3 properties of glycogen
- Insoluble, so it is osmotically inactive so it doesn't affect the water potential, and cannot diffuse out of the cell membrane
- Compact, so lots of genetic material can be stored in a small space
- Highly branched, so many enzymes can act upon it simultaneously and break it down to produce glucose monomers for respiration
Describe the structure of cellulose in relation to it providing stability
- Molecules are made up of B-glucose and so form long, unbranched chains- 1,4-glycosidic bonds
- The chains run parallel to each other and are crossed linked by hydrogen bonds (adds collective strength)
- Molecules are grouped to form microfibrils which, in turn, are grouped to form fibres (provide more strength)
Describe the structure of glycogen (2 points)
- Straight, branched chains
- 1,6-glycosidic bonds
What bonds do starch's:
a) Branched
b) Unbranched
regions have?
a) 1,6-glycosidic
b) 1,4-glycosidic
Name the 4 roles of lipids
- Insulation---slow conductors of heat
- Protection
- Waterproofing---insoluble in water
- Source of energy---when oxidised, they produce 2x the energy as the same mass of carbohydrate and release water
How are triglycerides formed?
During a condensation reaction, 3 fatty acids form an ester bond with glycerol.
Describe 4 points for: The structure of triglycerides related to their properties
- High ratio of energy-storing carbon-hydrogen bonds to carbon atoms = excellent source of energy
- Low mass to energy ratio = good storage molecules
- Large, non-polar = insoluble and don't affect the WP
- High ratio of hydrogen to oxygen atoms, so they produce water when oxidised = good source of water
Describe the general structure of amino acids
- Amino group (-NH2) = basic group
- Carboxyl group (-COOH) = acidic group
- Hydrogen atom (-H)
- R (side group) = variety of different chemical groups
During what reaction is a peptide bond formed?
Condensation
What is a dipeptide?
Two amino acids that have been joined together by a peptide bond during a condensation reaction
Where are dipeptides produced and why is this important?
In the small intestine so they can be hydrolysed into amino acids
Describe the primary structure of polypeptides
The sequence of amino acids in a polypeptide, each amino acid pair is joined by a peptide bond
Describe the secondary structure of polypeptides
The polypeptide chain is folded into a 3d a-helix structure which is held in shape by hydrogen bonds. It can form hydrogen bonds with nearby amino acids.
Describe the tertiary structure of polypeptides
The secondary structure is further folded and twisted to form a complex, 3D structure.
The bonds involved are:
- Disulfide bridged
- Ionic bonds
- Hydrogen bonds
Describe the quarternary strucure of polypeptides
Composed of 2+ polypeptide chains
Describe the structure of enzymes
Tertiary, globular proteins