Biological Molecules

Front 1

What is the general formula of a monosaccharide?

Back 1

(CH(small 2)O)n N can be any number from 3 to 7

Front 2

What is a reducing sugar?

Back 2

One which can reduce (donate electrons to) other chemicals. All monosaccharides and some disaccharides are reducing sugars

Front 3

What is Benedict's reagent?

Back 3

An alkaline solution of copper(II) sulfate

Front 4

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

Back 4

An insoluble red precipitate of copper(l) oxide

Front 5

Describe the process of the Benedict's test

Back 5

•Add 2cm of the food sample to be tested to a test tube. Grind it up if not in liquid form

•Add an equal volume of Benedict's reagent

•Heat in a gently boiling waterbath for 5 minutes

A red or orange colour indicates the prescence of a reducing sugar- yellow or green means less reducing sugar, no colour change means no reducing sugar

Front 6

Glucose+Glucose= ?

Back 6

Maltose

Front 7

What monosaccharides is sucrose formed from?

Back 7

Glucose and Fructose

Front 8

What monosaccharides is lactose formed from?

Back 8

Glucose and Galactose

Front 9

What is the bond formed between monosaccharides called?

Back 9

A Glycosidic bond

Front 10

What type of reaction forms a dissaccharide or polysaccharide?

Back 10

Condensation- Water is formed

Front 11

When a glycosidic bond is broken what type of reaction is it?

Back 11

Hydrolysis- Water is added

Front 12

How do you test for a non- reducing sugar?

Back 12

First, use the standard Benedict's test to check if a reducing sugar is prescent. If there is no colour change, heat 2cm of the food sample with an equal amount of dilute hydrochloric acid in a gently boiling water bath for 5 minutes. The dilute hydrochloric acid will hydrolyse any reducing sugar present into its constituent monosaccharides.

Add some sodium hydrogencarbonate to neutralise as benedicts reagaent does not work in acidic conditions, then check pH is alkaline with pH paper

Repeat the Benedict's test- if a non-reducing sugar was present in the original sample, the standard colour change will occur

Front 13

How do you test for starch?

Back 13

Add potassium idodide solution- a blue-black colour indicates the presence of starch

Front 14

What is the monosaccharide which combines to form starch?

Back 14

alpha-glucose

Front 15

Why is starch suited for its function of energy storage in plants? List 5 reasons

Back 15

•It is insoluble so does not affect water potential. This means water is not drawn into cells by osmosis

•It is large and insoluble so does not diffuse out of cells

•It is compact- a lot can be stored in a small space

• When hydrolysed it forms alpha-glucose. This is easily transported and readily used in respiration

•It has both branched and unbranched forms. The branched form has many ends, each of which can be acted on by enzymes simulateneously meaning that glucose monomers can be released very rapidly

Front 16

How are glycogen and starch different?

Back 16

Starch is found in plant cells- glycogen is found in animals and bacteria. Glycogen has shorter chains than starch and is more highly branched (this means it can be broken down by enzymes faster than starch, which is important for animals as they have a higher metabolic and respiratory rate than plants do)

Front 17

Which features of glycogen make it suitable for its function of energy storage?

Back 17

•Insoluble so does not affect water potential in cell, hence water does not get drawn in or out of the cell by osmosis

•Compact- a lot can be stored in a small space

•It does not diffuse out of cells as it is large and insoluble

•It is more highly branched than starch- hence lots of endings which can be acted on simultaneously by enzymes so it can be broken down more quickly than starch.

Front 18

Which of celluslose, starch and glycogen have alpha glucose monomers and which have beta glucose monomers?

Back 18

Starch and Glycogen have alpha glucose. Cellulose has beta glucose

Front 19

How does the structure of cellulose make it suited to its function of providing support and rigidity?

Back 19

•Cellulose molecules are made up of beta-glucose monomers, which means they form straight, unbranched chains.

•These chains run parallel to each other so can be cross-linked by hydrogen bonds, which due to their number add considerable strength

•These molecules are grouped to form microfibrils which are in turn grouped to form fibres.

Front 20

What are the four characteristics of all lipids?

Back 20

•They contain carbon, oxygen and hydrogen

•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 alchohols and acetone

Front 21

List 5 uses of lipids

Back 21

•Cell membranes- they contribute to the flexibility of memebranes and to the transfer of lipid soluble substances across them

•Waterproofing- as they are insoluble. e.g waxy cuticles for water conservation in plants.

•Insulation- Fats are slow heat conductors and also electrical insulators i.e the myelin sheath

•Protection- for delicate organs e.g kidney

•Energy source- they release over twice as much energy as carbohydrates when oxidised

Front 22

What is the bond between fatty acids and glycerol in a triglyceride

Back 22

An ester bond

Front 23

What type of reaction forms a triglyceride?

Back 23

Condensation - three water molecules are formed for each glycerol molecules

Front 24

What is a saturated fatty acid?

Back 24

One which contains no c-c double bonds. monounsaturated contains one such bond, polyunsaturated contains many.

Front 25

Structure and function of triglycerides? (four points)

Back 25

•High ratio of energy-storing C-H bonds to C atoms so are a good source of energy

•Low mass to energy ratio- lots can be stored in a small space. Useful for animals as it reduces the mass they have to carry

•Insoluble- does not affect water potential

•High ratio of H to O, so releases water when oxidised. Useful in deserts

Front 26

How are phospholipids different to normal lipids?

Back 26

One fatty acid is replaced with a phosphate molecule. Phosphates are hydrophillic and fatty acids are hydrophobic so these molecues are polar

Front 27

How does the structure of phospholipids help their function of forming part of cell surface membranes?

Back 27

They are polar, so when in an aqueous enviroment form a bilayer within cell surface membranes. This means that a hydrophobic barrier is formed between the inside and outside of a cell. Also, their phospholipid structure allows them to combine with carbohydrates in the cell-surface membrane to form glycolipids. These are important in cell recognition

Front 28

Why does the test for lipids produce a cloudy white colour?

Back 28

Any lipid which is present is finely dispersed throughout the sample to form an emulsion. Light passing through is refracted by passing through the oil to the water, making the sample appear cloudy

Front 29

How would you carry out a test for lipids?

Back 29

Add 5cm of ethanol to 2cm of the sample to be tested. Place in a dry, grease free test tube. Shake, add 5cm of water, then gently shake again. If a lipid is present there will be a cloudy white colour. As a control, use water instead of the sample.

Front 30

What five components make up an amino acid?

Back 30

•A central Carbon atom

•A Hydrogen atom

•An amino group- NH(small 2)

•A carboxyl group (-COOH)

•An R group- this differs from one amino acid to another

Front 31

What bond links two amino acids?

Back 31

A peptide bond

Front 32

What type of reaction forms a peptide bond?

Back 32

A condensation reaction- water is formed from the OH off a carboxyl group of one amino acid and the H from the amino group of the other amino acid

Front 33

What is the primary structure of a protein?

Back 33

The sequence of amino acids in a polypeptide chain

Front 34

What is the secondary structure of a protein?

Back 34

Hydrogen bonds which form between the -NH and -C=O groups on either side of each peptide bond. These cause the protein to be twisted into a 3D shape.

Front 35

List 3 types of bonds found in the tertiary structure of a protein and their relative strength

Back 35

•Disulfide- fairly strong, not easily broken

•Ionic- Weaker than disulfide, easily broken by changes in pH. Formed between any carboxyl and amino groups not involved in peptide bonding

•Hydrogen-numerous but easily broken

Front 36

What is the tertiary structure of a protein?

Back 36

The bonds which form in the secondary structure which cause the protein to twist and fold into its complex, specific 3D shape

Front 37

What is the quaternary structure of a protein?

Back 37

Polypeptide chains which combine to form larger molecules, and sometimes associate with other groups (prosthetic, meaning non-protein) such as the haem group in haemoglobin.

Front 38

What does the biuret test detect?

Back 38

Peptide bonds, so it is used as a test for protein.

Front 39

Describe how to test for a protein

Back 39

Place a sample of the solution to be tested in a test tube with an equal volume of sodium hydroxide solution. Add a few drops of very dilute copper (ll) sulfate solution and mix gently. A purple colour indicates the presence of peptide bonds, a blue colour means no protein is present.

Front 40

What is an issue with the lock and key model for enzymes?

Back 40

Other molecules can bind to enzymes at sites other than the active site, altering the activity and therefore the shape of the enzyme. This suggests that the structure of an enzyme is not rigid but flexible.

Front 41

What is the induced fit model of enzymes?

Back 41

The active site forms as the enzymes and the substrate interact- it is the proximity of the substrate which forms the functional active site. The enzyme is flexible and can mould itself around the substrate. As it changes shape, the enzyme puts a strain on the substrate molecule which distorts a bond or bond in the substrate, lowering the activation energy needed to break the bond.

Front 42

How does temperature affect enzyme action?

Back 42

A rise in temperature causes increased kinetic energy of molecules, which means there are more successful collisions between enzyme and substrate, hence a greater rate of reaction.

However, at a certain temperature the heat begins to cause the hydrogen and other bonds in the enzyme to break, causing the active site to change shape. At first, the substrate fits less easily into this changed active site, slowing the rate of reaction. Eventualy, the enzyme will be so disrupted it stops working altogether- denaturation.

Front 43

Why do enzymes have a slightly higher optimum temperature than our body temperature?

Back 43

•Other proteins, other than enzymes, may be denatured at higher temperatures.

• If body temperature was higher then any further rise, e.g due to illness, might denature the enzymes

•Although higher body temperatures would slightly increase metabolic rate, the advantages are offset by the additional energy (food) needed to maintain this temperature.

Front 44

How does pH affect enzyme action?

Back 44

•The change in pH affects the bonding between -NH(2) and -COOH

groups which partly determines the shape of the active site

• As a result, the substrate may no longer be able to attatch to the enzyme

•If there is a large change in pH it can cause the bonds maintaining the tertiary structure to break

•pH fluctuations are usualy small and decrease enzyme activity rather than denaturing it.

Front 45

What are non-competitive inhibitors?

Back 45

They attatch themselves to a part of the enzyme other than the active site, altering the shape of the enzyme and leaving it unable to function. This decreases reaction rate.

Front 46

What are competitive inhibitors?

Back 46

Molecules with a molecular shape similar to the substrate, enabling them to bind to the active site. This means substrate molecules can not bind to the active site. The inhibitor is not permanently bound to the active site so when it leaves a substrate can take its place. The greater the concentration of inhibitor compared to substrate, the longer it will take for all the substrate to be broken down as there will be less available active sites.

Front 47

How does substrate concentration affect enzyme action when competitive inhibitors or non-competitive inhibitors are present?

Back 47

•Substrate concentration does not affect rate of reaction when non-competative inhibitors are present as they are not in competion- the bind to different parts of the enzynes

•An increased substrate concentration increases rate of reaction with competative inhibators as they a competing with each other for the active sites.

Front 48

What is the unusual feature of carbon atoms?

Back 48

They very readily form bonds with other carbon atoms, allowing a sequence of carbon atoms to be built up to form a 'backbone' to which other atoms can be attatched. The variety of life on Earth is a consequence of living organisms being based on the carbon atom

Front 49

What does cellulose do?

Back 49

It is a major component to plant cell walls and provides them with ridgidity. The cellulose cell wall also prevents the cell from bursting as water enters by exerting an inward pressure that stops any further influx of water. This makes living plant cells turgid, so leaves and stems are semi-rigid and can provide the max SA for photosynthesis

Front 50

What does hydrolysis of a triglyceride produce?

Back 50

Glycerol and three fatty acids

Front 51

What is a fatty acid?

Back 51

A carboxyl group (COOH) with a hydrocarbon chain attatched

Front 52

Difference between alpha and beta glucose?

Back 52

Alpha has the two OH's both at the bottom, in beta they are diagonally opposite