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Flashcards in Biological Molecules Deck (54):

What is covalent bonding?

Where atoms share a pair of electrons in their outer shells. As a result, the outer shell of both atoms is filled and a more stable compound (a molecule) is formed


Ionic bonding

Ions with opposite charges attract one another. This electrostatic attraction is known as an ionic bond. Ionic bonds are weaker than covalent bonds


What is hydrogen bonding?

The negative region of a polarised molecule and the positive region of another attract each other. A weak electrostatic bond is formed between the two. And individual hydrogen bond but they collectively form important forces that alter the physical properties of molecules


What is the process by which monomers are made into polymers?



What is a condensation reaction?

One that releases a molecule of water every time a new sub-unit is attached to a chain


What is the name of the process by which water breaks down molecules into their constituent monomers?



What is metabolism?

All the chemical processes that take place in living organisms


What is a molar solution?

A molar solution is a solution that contains one mole of solute in each litre of solution. A mole is the molecular mass expressed as grams


Which four elements make up most polymers?

Carbon, hydrogen, oxygen and nitrogen


Give two characteristics of monosaccharides

They are sweet-tasting and are soluble


What is the General formula for a monosaccharide?



What is a reducing sugar?

A sugar that can donate electrons to another chemical


What is Benedict's Reagent?

It is an alkaline solution of Copper (II) Sulfate


What happens when a reducing sugar is heated with Benedict's reagent?

An insoluble red precipitate of Copper (I) oxide is produced


Give a basic method for carrying out the Benedict's Test:

• add 2cm3 of the food sample to be tested to a test tube. If he sample is not already in liquid form, first grind it up in water

• add an equal volume of Benedict's reagent

• heat the mixture in a gently boiling water bath for five minutes


Glucose + Glucose = _________



Glucose + Fructose = _________



Glucose + Galactose = ________



When monosaccharides bond, what is the bond called?

A glycosidic bond


Give a summary of how to detect non-reducing sugars:

• if the sample is not already in liquid form, it must first be ground up in water
• add 2cm3 of the food being tested to 2cm3 Benedict's reagent in a test tube and filter
• place the test tube in a gently boiling water bath for 5 minutes. If the solution does not change colour, a reducing sugar is not present
• add another 2cm3 of the food sample to 2cm3 dilute HCl and place the test tube in a water bath for 5 minutes. The HCl will hydrolyse any disaccharides to monosaccharides.
• slowly add some sodium hydrogencarbonate to the test tube to neutralise the HCl.
• re-do the Benedict's test


Why are polysaccharides insoluble?

Because they are very large molecules


What does a polysaccharide being insoluble make it good for?



what are the colour changes for the Starch test?

Yellow ---> Blue-black


Give a summary of how to carry out the Starch test:

• place 2cm3 of the sample being rested in a test tube
• add two drops of potassium-iodide solution and shake
• the presence of Starch is indicated by a blue-black colour


What is Starch made from?

Chains of Alpha Glucose linked by Glycosidic bonds


The main role of Starch is energy storage, something its structure is especially suited for because:

• it is insoluble and therefore doesn't affect water potential, so water is not drawn into cells by osmosis
• being large and insoluble it doesn't diffuse out of cells
• It is compact so a lot of it can be stored in a small space
• when hydrolysed it forms Alpha Glucose which is both easily transported and readily used in respiration
• the branched form has many ends, each of which can be acted upon by enzymes simultaneously meaning that glucose monomers are released very rapidly


How does the structure of glycogen differ from that of Starch?

It contains shorter chains and is more highly branched


How does Glycogen's structure suit it for storage?

• It is insoluble and therefore does not affect the water potential so water isn't drawn into cells by osmosis
• being insoluble, It does not diffuse out of cells
• It is compact so a lot of it can be stored in a small space
• It is more highly branched than Starch and so has more ends that can be acted on simultaneously by enzymes. It is therefore more rapidly broken down to form glucose monomers which are used in respiration.


Why is it important that glycogen can be broken down quickly?

Because animals have a high metabolic rate and therefore respiratory rate because they are more active


What are the constituent molecules of Cellulose?

Beta Glucose chains


What are the main bonds between cellulose chains?

Hydrogen bonds which form cross-linkages between adjacent chains


What is the structure of cellulose chains and how do they differ from chains of Starch and glycogen?

Unlike the coiled chains of Starch and glycogen, cellulose has straight, unbranched chains which run parallel to each other


What is formed when cellulose molecules are grouped together?



What is formed when microfirbrils are arranged in parallel groups?



How does cellulose cell walk prevent the cell from bursting?

It exerts an inward pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another


How is the structure of cellulose suited to its function of providing support and rigidity?

• cellulose molecules are made up of Beta Glucose chains and so form long, straight, unbranched chains
• these cellulose molecular chains run parallel to each other and are cross-linked by hydrogen bonds which add collective strength
• cellulose molecules are grouped to form microfibrils which in turn are grouped into fibres which provide yet more strength


What characteristics do all lipids share?

• they all contain carbon, hydrogen and oxygen

• the proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates

• they are insoluble in water

• they are soluble in organic solvents such as alcohols and acetone


What are the main groups of lipids?

Triglycerides and phospholipids


Why are lipids good sources of energy?

When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water


Why are lipids good at waterproofing?

They are insoluble in water and therefore useful as waterproofing. Both plants and insects have waxy, lipid cuticles that conserve water while mammals produce an oily secretion from the sebaceous glands in the skin


Why are lipids good insulators?

Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells


Why are lipids good at protection?

Fat is often stored around delicate organs such as the kidney


What makes up triglycerides?

Three fatty acids and glycerol


In a condensation reaction, What bond is formed between a fatty acid and glycerol?

An ester bond


What do the differences in the properties of different fats and oils come from?

Variations in the fatty acids


Why are triglycerides an excellent source of energy?

They have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms


Why are triglycerides good storage molecules?

Triglycerides have low mass to energy ratio making them good storage molecules because much energy can be stored in a small volume.


How do triglycerides provide an important source of water to organisms?

Because they have a high ratio of hydrogen to oxygen atoms, triglycerides release water when oxidised and therefore provide an important source of water


How are phospholipids different from lipids?

One of the fatty acids is replaced by a phosphate molecule


What the two parts of a phospholipid?

A hydrophilic 'head' which interacts with water and repels fat

A hydrophobic 'tail' which orients itself away from water but mixes readily with fat


Molecules that have two ends (poles) that behave differently are said to be _____



What do phospholipids form in aqueous environments?

A phospholipid bilayer within the cell-surface membrane. As a result, a hydrophobic barrier is formed between the inside and outside of a cell


Summarise the emulsion test:

• take a completely dry and grease-free test tube
• to 2cm3 of the sample being tested, add 5cm3 of ethanol
• shake the tube thoroughly to dissolve any lipid in the sample
• a cloudy-white colour indicates the presence of a lipid
• as a control, repeat the procedures using water instead of the sample; the final solution should remain clear


Why is a cloudy colour formed when a lipid is present in solution?

Because the lipid is finely dispersed in the water to form an emulsion. Light passing through this emulsion is refracted as it passes from oil droplets to water droplets, making it appear cloudy