Biological molecules Flashcards
Describe how triglycerides are formed
3 fatty acids combine to one glycerol molecule during a condensation reaction with the loss of three water molecules and the formation of an ester bond.
Describe how you would hydrolyse lipids.
- Heat with acid or alkali
- Use lipase at its optimum temperature and pH
Describe how you would test for the presence of lipids
Small sample is dissolved in ethanol
Added to water in another test tube and the contents are mixed
White emulsion indicates that lipids are present
Describe the structure of starch and where it is stored
Starch consists of long branched chains of alpha glucose molecules that are linked together by glycosidic bonds during condensation reactions
Stored in starch grains in the cytoplasm of plant cells
How is starch adapted to its function as a storage carbohydrate?
Large so it cannot cross the cell surface membrane and leave the cell
Insoluble and therefore, osmotically inactive i.e it cannot draw in water by osmosis which could lead to cell damage
It has a helical shape and therefore it forms a compact store
Branched so that glucose can easily be released from its ends for respiration
Describe the test for starch
Add 2-3 drops of iodine/potassium iodide solution
If starch is present, colour change: yellow/orange to blue/black
Describe how glycogen is formed and where it is stored
Glycogen is formed by the condensation of alpha glucose molecules
Stored in large amounts in liver and muscle tissues
How is glycogen adapted to its function as a storage carbohydrate?
Insoluble and therefore, osmotically inactive
Similar structure to starch but with more branches so that it can be hydrolysed more rapidly for respiration
Describe how cellulose is formed and where it is stored
Cellulose is a polymer of β-glucose molecules that are joined together by glycosidic bonds in a condensation reaction to form long straight chains
Found in the cell wall of plants
Describe how cellulose is adapted to its function as a structural component
Long chains of beta glucose joined together by glycosidic bonds in condensation reactions
Adjacent chains joined together by hydrogen bonds
This produces a 3D structure - microfibril
This provides strength and rigidity to the cell wall
Which prevents the cell from bursting
Describe the function and draw the general structure of DNA and RNA
DNA holds genetic information
RNA transfers genetic information from DNA to the ribosomes
How are ribosomes formed?
RNA and proteins are joined together
Describe the process of the semi conservative replication of DNA
DNA helicase unwinds the double helix and breaks the hydrogen bonds between complementary bases of the two polynucleotide strands
Each of strands can act as a template strand for the formation of two new complementary strands
Individual DNA nucleotides align and attach by hydrogen bonding to the exposed bases of each template strand according to specific complementary base pairing (A-T and C-G)
DNA nucleotides in each new strand are joined together by phosphodiester bonds during a condensation reaction by DNA polymerase to form complementary strands to the original DNA molecule
Describe the effect of enzyme concentration on rate of enzyme-controlled reactions
When substrate concentration is in excess, an increase in enzyme concentration will increase the rate of reaction
There are more enzymes molecules and therefore, more active sites available
This increases the number of collisions of enzymes and substrates to form more E-S complexes
Describe the effect of substrate concentration on the rate of enzyme-controlled reactions
Rate of reaction initially increases as the collisions between substrate and enzyme molecules are more likely
Rate of reaction then levels out as the active sites of all enzymes become fully saturated by the substrate molecules
At this point, the rate of reaction is limited by enzyme concentration
The only method of increasing the rate of reaction is by addition of more enzymes
Describe how you would test for the presence of proteins
Add biuret reagent
Purple/lilac colour indicates that protein is present
If solution remains blue, then no protein is present
Describe what is meant by quaternary structure and give an example
Highly complex proteins that consist of more than one polypeptide chain
These polypeptide chains are held together by ionic, hydrogen and sometimes disulfide bonds
For example, adult haemoglobin which consists of 4 polypeptide chains
Describe how the tertiary structure is formed and give an example
Formed by the further folding and coiling of the secondary structure due to hydrogen, ionic and disulfide bonds
These bonds form in places determined by the primary structure and form between the R groups of amino acids
Example: globular proteins such as enzymes and antibodies
Describe how the secondary structure is formed
Folding or coiling of a polypeptide chain as a result of hydrogen bonds between amino acids
Describe non competitive inhibition
Attaches to the enzyme at a site other than the active site
This changes the shape of the active site
Which means the active site is no longer complementary to substrate so less E-S complexes form
Describe competitive inhibition
Inhibitor has a similar structure to the substrate and competes with it for attachment to the active site
Rate of reaction is reduced as the substrate cannot bind to an occupied active site
Competitive inhibition can be reduced by the addition of more substrate
How does the properties of water relate to its function as a supporting molecule?
Strong cohesive forces due to hydrogen bonding:
Supports water columns in tube-like transport cells e.g. xylem of plants, allowing transport from roots to leaves (see 3.3.4 Mass transport)
Produces surface tension where tension meets air which enables insects to walk on the surface of water (e.g. pond skaters) or be suspended at surface (e.g. mosquito larvae)
How does the properties of water relate to its function in temperature regulation?
Water has a high heat capacity = absorbs a large amount of heat energy before rising in temperature
Minimises increase in temperature within cells as a result of biochemical reactions e.g. respiration
Helps to prevent dangerous fluctuations in temperature in aquatic habitats
Water has a large latent heat of vaporisation as energy is required to break the hydrogen bonds
Provides a cooling effect in both animals & plants;
Helps some animals maintain a constant body temperature as a high amount of heat energy is removed from the body to evaporate sweat
In plants via transpiration
How are the products from the hydrolysis of ATP useful in reactions?
The hydrolysis of ATP can be coupled to energy-requiring reactions within cells e.g. protein synthesis
The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive
