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Monday, 14 January 2019
Biological Molecules
Carbohydrates
All carbohydrates contain the molecules carbon, oxygen and hydrogen
...
They are mainly used in respiration to provide energy and in
growth during the formation of larger carbohydrates
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Disaccharides
A disaccharide is formed when two monosaccharides are joined together by a
glycosidic bond in a condensation reaction
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Examples of disaccharides are maltose (glucose + glucose), sucrose (glucose +
fructose) and lactose (glucose + galactose)
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It is ideally suited to its function as a storage compound as:
• it is large and so can’t easily cross the cell-surface membrane and leave the cell
• it is insoluble and therefore osmotically inactive
• it has a helical shape forming a compact store
• it is branched so glucose is easily released for respiration
Starch can be detected by the iodine test:
1
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if starch is present a blue/black colour is produced; if no starch is present the
solution remains orange/yellow
Glycogen
Glycogen is the storage carbohydrate found in the cytoplasm of animal cells, in
large amounts in liver and muscle tissues
...
It is ideally suited to its function as a storage compound as:
• it is insoluble and therefore osmotically inactive
• it is similar in structure to starch but is more branched so it can be hydrolysed
more rapidly to release glucose for respiration
• it is compact and so good for storage
Cellulose
Cellulose is found in the cell wall of plants, providing rigidity and shape to the cell
...
The hydroxyl groups project from either side of the chain and form hydrogen bonds
with hydroxyl groups of adjacent chains, producing a microfibril, which provides
strength
...
1
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heat in a water bath
3
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after getting a negative result in the previous test, add dilute hydrochloride acid
to a new sample and heat
2
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add the same amount of Benedict’s reagent
4
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a bricked red precipitate indicates a non-reducing sugar was originally present
Lipids
Lipids contain the elements carbon, oxygen and hydrogen
...
They can be hydrolysed by heating with acid/alkali or by using lipase at its optimum
temperature and pH
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Fatty acids can be:
• saturated - no double bonds between carbon atoms
• unsaturated - one or more double bonds between carbon atoms
Triglycerides
Triglycerides are mainly used as energy storage molecules, and have 3 fatty acids
combined to 1 glycerol molecule during a condensation reaction with the loss of 3
water molecules, forming ester bonds
...
They are also insoluble as they are non-polar, and so are ideal storage compound
as they are osmotically inactive
...
They have a polar hydrophilic head containing the phosphate group, and a nonpolar hydrophobic tail consisting of the long fatty acids chains
...
The phospholipid bilayer enables lipid soluble molecules to pass quickly
through cell membranes, whereas water-soluble substances can’t easily pass
through it
...
1
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shake the mixture so that it dissolves
3
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a white emulsion if fat droplets indicates lipid is present
Proteins
Proteins contain the elements carbon, oxygen, hydrogen, nitrogen and sometimes
sulphur
...
A dipeptide is
formed when two amino acids join together in a condensation reaction forming
peptide bonds
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Proteins are made up of one or more polypeptides
...
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Monday, 14 January 2019
Proteins can be hydrolysed by heating with acid or using proteases at their optimum
temperature
...
Structures include the alpha
helix and beta-pleated sheet
• tertiary structure - represents further coiling/folding of the secondary structure due
to hydrogen bonds, ionic bonds and disulphide bridges
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Tertiary structure is specific and unique
...
Water
Water is the most abundant compound on earth and has many important roles
...
They
all have specific roles, which determines whether it is fiyhd in hugh or low
concentrations
...
They are proteins, and are highly specific due to their tertiary structure
...
Enzymes lower this activation energy by forming enzyme-substrate
complexes, which speeds up the rate of reaction
...
The lock and key model suggests that the active site of the enzyme is rigid, and the
substrate fits in exactly
...
Factors affecting enzyme activity
Effect of Substrate Concentration
The rate of reaction initially increases as collisions between dubstep and enzyme
molecules are more likely
...
The only way to increase the rate
now is by addition of more enzyme
...
However, if the amount of substrate is
limited, there’s comes a point where the addition of enzyme has no further effect
...
However, raising the
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Monday, 14 January 2019
temperature past the optimum causes the tertiary structure of the enzyme to
denature as hydrogen and ionic bonds are broken and enzyme-substrate
complexes struggle to form as the active site has been altered, decreasing the rate
of reaction
...
Very
different pHs from the optimum can cause denaturation, altering the ionic charges
of acidic and basic groups and breaking hydrogen and ionic bonds
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Enzyme Inhibitors
Competitive Inhibitors
The inhibitor has a similar structure to the substrate molecules and competes for
attachment to the active site of the enzyme
...
Competitive inhibition can be reduced by the
addition of more substrate, increasing the rate of reaction up to a point
...
They bind to the enzyme at a place other than the active site, forming enzymeinhibitor complexes, causing the tertiary structure and active site of the enzyme to
change shape so substrate molecules can no longer bind to it
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ATP
Cells use ATP (adenosine triphosphate) as the immediate energy source for
biological processes
...
ATP is continuously hydrolysed into ADP (adenosine diphosphate) and Pi (inorganic
phosphate group) to release energy, catalysed by ATP hydrolase
...
The inorganic
phosphate released can be used to phosphorylate compounds, often making them
more reactive
...
The energy released from respiration
or photosynthesis enables the resynthesis of ATP