✅1 - Biological Molecules Flashcards
What is metabolism?
All the chemical processes that take place in living organisms collectively
What is the general formula for monosaccharides?
(CH2O)n
Where is the ‘H’ on a-glucose?
At the top
Where is the ‘H’ on b-glucose?
At the bottom
What is the test for reducing sugars?
Add 2cm3 of the food sample to be tested to a test tube. If the sample is not already in liquid form, first grind it up in water.
Add an equal volume of Benedict’s solution
Heat the mixture in a gently boiling water bath for 5 minutes
What will a positive test for reducing sugars show?
An orange-brown precipitate will form of copper (I) oxide
What is maltose?
Glucose + glucose
What is sucrose?
Glucose + Fructose
What is lactose?
Glucose + Galactose
What is the bond between two monosaccharides called?
A glycosidic bond
What is a condensation reaction?
When molecules are joined together and a molecule of water is removed
What is a hydrolysis reaction?
When a bond is broken using a molecule of water
What is the test for non-reducing sugars?
After a negative test for reducing sugars:
Add 2cm3 of food sample to 2cm3 of HCl and place in a water bath to hydrolyse any disaccharides to monosaccharides
Add sodium hydrogencarbonate to neutralise the HCl and test pH
Re-test the solution with Benedict’s
What is the test for starch?
Add 2cm3 of sample to a test tube
Add two drops of iodine solution and shake it
The presence of starch is indicated by a blue black solution
What is starch?
A polysaccharide
How can the structure of starch differ?
It can be branched or unbranched
What is the main role of starch?
An energy storage molecule
What are the properties of starch that make it suited to its function?
It is insoluble - doesn’t alter water potential of cell
Being large and insoluble, it does not diffuse out
It is compact, so a lot can be stored in a small space
When hydrolysed, it forms a-glucose which is easily transported and readily used in respiration
The branched form has many ends, which means it can be broken down quickly and easily
Where is starch found?
ONLY in plant cells, as starch grains
What is glycogen?
A similar structure polysaccharide to starch found in animal and bacteria cells
How is glycogen stored?
As small granules mainly in the muscles and liver
How is glycogen’s structure related to its function?
It is insoluble and so doesn’t draw water in by osmosis
Being insoluble, it does not diffuse out
It is compact so a lot can be stored
It is more highly branched so has more ends that can be acted on at the same time so can be broken down quickly
What is cellulose?
A polysaccharide of b-glucose
What is the structure of cellulose?
Straight, unbranched chains that run parallel to one another, allowing hydrogen bonds which form cross linkages between adjacent chains
What do groups of cellulose molecules form?
Microfibrils which are then arranged in parallel groups called fibres
How is cellulose’s structure related to its function?
Cellulose molecules are made up of b-glucose and so form long, straight, unbranched chains
These cellulose molecular chains run parallel to each other and are cross linked by hydrogen bonds which ass strength
These molecules are grouped to form microfibrils which in turn are grouped to form fibres which provides more strength
What is the function of cellulose?
To provide support and rigidity
What characteristics do lipids have?
The proportion of oxygen to carbon is smaller than in carbohydrates
They are insoluble in water
They are soluble in organic solvents such as alcohols and acetone
What are the roles of lipids?
Source of energy
Waterproofing
Insulation
Protection
What state are fats at room temperature?
Solid
What state are oils at room temperature?
Liquid
What does hydrolysis of triglycerides produce?
Glycerol and three fatty acids
What is a saturated fatty acid?
One which has no double bonds in its chain
What is an unsaturated fatty acid?
One which does have double bonds
What is a fatty acid with one double bond called?
Mono-unsaturated
What is a fatty acid with multiple double bonds called?
Polyunsaturated
How does a triglyceride’s structure relate to its function?
High ratio of energy-storing carbon-hydrogen bonds to carbon atoms so good energy source
Low mass to energy ratio, so lots of energy stored in small molecule
Being large, non-polar, they are insoluble
High ratio of hydrogen to oxygen, release water when oxidised
What are phospholipids?
Similar to lipids but one fatty acid is replaced by a phosphate
Are fatty acids hydrophobic or hydrophillic?
Hydrophobic
What are the two parts of a phospholipid molecule?
Hydrophillic head
Hydrophobic tail
How does the structure of a phospholipid relate to its function?
Polar molecules, so form a bilayer in an aqueous solution
Hydrophillic phosphate heads help to hold the surface of the cell membrane
The phospholipid structure allows them to form glycolipids by combining with carbohydrates at the cell surface membrane. Important in cell recognition
What is the test for lipids?
Take a dry and grease-free test tube
To 2cm3 of the sample being tested, ass 5cm3 of ethanol
Shake tube thoroughly to dissolve any lipid in sample
Add 5cm3 of water and shake gently
A cloudy white colour indicates the presence of a lipid
Repeat with water as a control
Which polymer are amino acids the monomers for?
Polypeptides
What is the structure of an amino acid?
An amino (NH2) group A carboxyl (COOH) group A hydrogen atom A variable R group
How do peptide bonds form?
Through condensation reactions
Which atoms are peptide bonds formed between?
The carbon of one amino acid and the nitrogen of another
The sequence of amino acids forms…
…the primary structure
What does primary protein structure determine?
The ultimate shape and function of a protein
What is the secondary structure of a protein?
Hydrogen bonding between amino acids to form alpha helices or beta pleated sheets
What is tertiary protein structure?
Further twisting and folding to form a 3D structure maintained by different bonds
Which bonds are involved in tertiary protein structures?
Ionic bonds
Hydrogen bonds
Disulfide bridges
What are the ionic bonds in tertiary structures between?
Any carboxyl and amino groups not involved in peptide bonds
What is quaternary protein structure?
A number of individual polypeptide chains linked in various ways often with non protein prosthetic groups attached
What is the test for proteins?
The Biuret test
How would you perform the Biuret test?
Place a sample of solution in a test tube and add an equal volume of NaOH
Add a few drops of very dilute copper (II) sulfate solution and mix
A purple coloration indicates the presence of peptide bonds, if none, solution remains blue
What type of proteins are enzymes?
Globular
What is the structure of an enzyme?
A specific 3D shape with an active site, the functional region. Small number of specific amino acids forming a small depression in molecule
What is an enzyme-substrate complex?
When the substrate binds with the enzyme
How is the substrate held into the enzyme?
By bonds that temporarily form between certain amino acids and groups on the substrate
What is the induced fit model?
Proposes that the active site forms as the enzyme and substrate , the proximity of the substrate leads to a change in the enzyme which forms a functional active site
How does the induced fit model lower activation energy?
As it changes shape, the enzyme puts strain on the substrate molecule, distorting particular bonds in the substrate and lowering activation energy
What are the two most frequently measured changes for enzyme catalysed reactions?
The formation of products
The disappearance of the substrate
How does temperature affect enzyme action?
A rise in temperature increases kinetic energy, so move around more rapidly and collide more often, so enzymes and substrates collide more and more collisions are effective, rate of reaction increases
What is the most common optimum temperature for human enzymes?
40 degrees
Why has the body temperature evolved to be 37 degrees?
Additional food would be needed to maintain it
Other proteins may be denatured at high temperatures
A further rise in temperature during illness may denature enzymes
How does pH affect enzyme action?
A change in pH alters the charges on the amino acids in the active site and so the substrate can no longer bind
The bonds in the tertiary structure may also break if pH change is significant enough
Why does pH cause the active site to change shape?
The arrangement of the active site is determined by ionic bonds between NH2 and COOH. The change in H+ affects this bonding.
How does enzymes concentration affect rate of reaction?
Once the active site of an enzyme has acted, it is free to repeat the action on another substrate, as they are catalysts and not used up. As long as there is excess substrate, an increase in enzymes will increase rate f reaction
How does substrate concentration affect enzyme action?
If the enzyme concentration is fixed and substrate concentration increased, the rate of reaction increases in proportion to the concentration of substrate. When there is excess, the rate levels off.
What are competitive inhibitors?
Ones which bind to the active site of the enzyme
What are non-competitive inhibitors?
Ones which bind to the enzymes at a position other than the active site
How do competitive inhibitors work?
They have a molecular shape similar to the substrate, allowing them to occupy the active site. They compete with the substrate and it is the difference between the concentration of the inhibitor and concentration of the substrate that determines effect.
What is an example of competitive inhibition?
An important respiratory enzyme which acts on succinate. Malonate can inhibit enzyme because it is very similar to succinate, therefore binds with active site
How does not competitive inhibition work?
Attach themselves to the enzyme at a binding site which is not the active site. Alters shape of enzyme and thus its active site in such a way that substrates can no longer occupy it
