Biological Molecules Flashcards
• Biological molecules • Nucleic acids
What is a monomer?
A smaller unit from which larger molecules are made
What are polymers made from?
Repeating monomer units
What are three examples of monomers?
Monosaccharides
Amino acids
Nucleotides
What are four examples of polymers?
Polysaccharides Proteins Deoxyribonucleic Acid (DNA) Ribonucleic Acid (RNA)
What is a condensation reaction?
The formation of a chemical bond between two molecules that involves the elimination of a water molecule
What is hydrolysis?
A reaction, involving the use of a water molecule, which breaks a chemical bond between two molecules
What are carbohydrates made from?
Monosaccharides
What is maltose made from?
Glucose + Glucose
What is sucrose made from?
Glucose + Fructose
What is lactose made from?
Glucose + Galactose
How are polysaccharides formed?
By the condensation of many glucose units
How many isomers does glucose have?
2
What are glucose’s isomers?
Beta- and alpha- glucose
What is glycogen formed by?
The condensation of alpha-glucose
What is starch formed by?
The condensation of alpha-glucose
What is cellulose formed by?
The condensation of beta-glucose
Why are polysaccharides suitable storage molecules?
They are large and therefore insoluble
How do you test for starch?
Potassium iodide
During the potassium iodide test, what will happen if starch is present?
Colour change from yellow to blue/black
What are some examples of reducing sugars?
All monosaccharides Some disaccharides (such as maltose)
What is the test for reducing sugars?
Benedict’s Test
What do you use in the test for reducing sugars?
Benedict’s reagent
What is Benedict’s reagent?
An alkaline solution of copper (II) sulphate
What is the positive result for the reducing sugars test?
A red precipitate [copper (I) oxide] formed
What is a requirement for Benedict’s test?
Food tested has to be in liquid form or dissolved in water
What bond is formed in the condensation reaction of glucose?
Glycosidic bond
What happens if the glycosidic bond in a disaccharide is broken?
The constituent monosaccharides are released
What is required for hydrolysis?
A water molecule
What is an example of a non-reducing sugar?
All polysaccharides Some disaccharides (such as sucrose)
How do you test for a non-reducing sugar?
Test with Benedict’s reagent, if negative result then
Add dilute hydrochloride acid
Add sodium hydrogencarbonate
Retest with Benedict’s reagent
When testing for non-reducing sugars why do you use hydrochloric acid?
To hydrolyse any polysaccharide or disaccharide present into its constituent monomers
Monosaccharides are reducing sugars
Why do you have to add sodium hydrogencarbonate when testing for non-reducing sugars?
To neutralise the hydrochloric acid
Benedict’s reagent doesn’t work in acidic conditions
How is starch commonly found?
In small grains
Where is starch found?
Many parts of plants
Is starch ever found in animal cells?
No, only in plant cells
What are the two forms of starch?
Amylose and amylopectin
What glycosidic bonds does amylose have?
1,4
What glycosidic bonds does amylopectin have?
1,4 and 1,6
Is amylose a straight or branched chain?
Straight
Is amylopectin a straight or branched chain?
Branched
Why is amylopectin a good energy source?
The branched ends can be acted on simultaneously by enzymes which means that glucose monomers can be released rapidly
Why is amylose a good storage molecule?
Arranged in a tight helix held together by hydrogen bonds between -OH groups
Tight helix means it is very compact
Lots can fit in a small space
What colour does amylose go when potassium iodide is added?
Dark blue / black
What colour does amylopectin go when potassium iodide is added?
Brick red / brown
Where is glycogen found?
Animals and bacteria
Is glycogen ever found in plants?
No
Does glycogen have longer or shorter chains than starch?
Shorter
Is glycogen a straight or branched chain?
A highly branched chain, more so than starch
Where is glycogen stored in animals?
Mainly in the muscles and liver
How is glycogen stored in animals?
As small grains
Why is glycogen more highly branched than starch?
For a more rapid release of glucose which is needed for respiration. More important to animals as they have a higher metabolic and respiratory rate than plants.
Is cellulose a straight or branched chain?
Cellulose is a straight, unbranched chain
How is cellulose arranged?
Chains run parallel to one another, allowing hydrogen bonds to form cross linkages to adjacent chains
Why does cellulose have good structural stability?
Large quantity of hydrogen bonds hold parallel chains together
What are cellulose molecules grouped together to form?
Microfibrils
What are microfibrils grouped together to form?
Fibres
Where is cellulose commonly found?
Plant cell walls
How does the cellulose cell wall impact osmotic activity?
It prevents the cell from bursting as water enters it via osmosis
How does the cellulose cell wall prevent osmotic rupture?
By exerting an inward pressure that stops any further influx of water.
What occurs as a result of the inward pressure exerted by the cellulose cell wall in plants?
Living plants cells are turgid and push against each other, making the non-wood parts of the plant semi-rigid.
Why is it important to maintain the turgidity in stems and leaves?
To provide the maximum surface area for photosynthesis
Why do cellulose molecules form long, straight, unbranched chains?
They are made of beta-glucose
What do Lipids contain?
Hydrogen
Carbon
Oxygen
Do lipids have a higher or lower proportion of oxygen to carbon and hydrogen than carbohydrates?
Lower
What are lipids insoluble in?
Water
What are lipids soluble in?
Organic solvents such as alcohol and acetone
What are the main two groups of lipids?
Triglycerides
Phospholipids
What are the roles of lipids?
Cell membrane Energy source Waterproofing Insulation Protection
How do lipids act as a source of energy?
When oxidised, lipids provide over twice the energy as the same mass of carbohydrates
What do lipids release when oxidised?
Water
How do lipids act as waterproofing in plants and insects?
Plants and insects have waxy, lipid cuticles that conserve water
How do lipids act as waterproofing in mammals?
Mammals produce an oily secretion from the sebaceous glands in the skin
How do lipids act as insulation?
Lipids are slow conductors of heat
When stored beneath the body surface they help to retain heat
Where do lipids act as electrical insulators?
In the myelin sheath around nerve cells
How do lipids act as protection?
Lipids are often stored around delicate organs (such as the kidney)
What are triglycerides made of?
3 fatty acids
Glycerol
How are the parts of a triglyceride combined?
Each fatty acid forms an ester bond with glycerol in a condensation reaction
What does hydrolysis of a triglyceride produce?
Glycerol
3 fatty acids
What group do all fatty acids have?
A carboxyl group (-COOH)
Why is the low mass to energy ratio (of lipids) beneficial to animals?
It reduces the mass they have to carry as they move around which conserves energy
Why are triglycerides insoluble?
They are large non-polar molecules
Why are triglycerides important for organisms living in dry desert environments?
Triglycerides have a high ratio of hydrogen to oxygen atoms, so release water when oxidised
What does saturated mean?
No double bonds between carbon atoms
What does mono-unsaturated mean?
One double bond between carbon atoms
What does poly-unsaturated mean?
More than one double bond between carbon atoms?
Why are unsaturated molecules often liquids at room temperature?
The double bonds cause the molecule to bend so they can’t pack as closely together
What are phospholipids made of?
2 Fatty acids
Glycerol
Phosphate molecule
What two parts can a phospholipid be split into?
Hydrophilic head
Hydrophobic tail
Are phospholipids polar or non-polar?
Polar
What does hydrophobic mean?
Water hating
What does hydrophilic mean?
Water loving
What can phospholipids form that are important for cell recognition?
Glycolipids
What forms a glycolipid?
Phospholipid + Carbohydrate
What is the test for lipids?
The emulsion test
How do you carry out the emulsion test?
Take a dry and grease free test tube
Add 5ml of ethanol to 2ml of test sample
Shake mixture to dissolve any lipid present
Add 5ml of water and shake gently
What indicates a lipid is present during the emulsion test?
Cloudy white colour / cloudy white emulsion