AQA A Level Biology

what are the 3 types of carbohydrate?

• monosaccharides• disaccharides• polysaccharides

give some examples of monosaccharides

• glucose• fructose• galactose

give some examples of disaccharides

• maltose• lactose• sucrose

give some examples of polysaccharides

• cellulose• starch• glycogen

describe monosaccharides

• commonly referred to as sugars• structural isomers• single carbohydrate molecules• general formula - (CH2O)n• ose = sugar e.g pentose(5), triose(3), hexose(6)

describe disaccharides

• when two monosaccharides join together—\> bond formed = glycosidic bond• reaction is known as a condensation reaction

what is a glycosidic bond?

• a bond which it's formation involves the loss of a water molecule

give some disaccharide formation examples

• glucose + glucose = maltose + water• glucose + fructose = sucrose + water• glucose + galactose = lactose + water

explain how disaccharides are broken down

• during digestion• reaction involves the breaking of a bond by reacting it with water• HYDROLYSIS REACTION

give some examples of reducing sugars

• glucose• fructose• maltose

describe the benedicts test

• place the sugars into test tubes (&control)• add benedicts to all the test tubes• heat a water bath and add test tubes for 5 mins

what are the results of the benedicts test

• reducing sugar = brick red• not reducing = blue/ no colour change

what is the test for reducing sugars?

benedicts

what are the two forms of glucose?

• alpha• beta

what are the differences between alpha and beta glucose?

• alpha glucose hydroxyl group sticks below the ring• beta glucose hydroxyl group sticks above the ring (BUP)

what is a polysaccharide?

monosaccharides joined together by many glycosidic bonds

what is starch?

a storage polysaccharide stored in starch grains

what is starch's general formula

(C6H10O5)n

outline the two different types of starch

• amylose - loose helix unbranched helical chain of alpha glucose molecules• amylopectin - branched chain of alpha glucose

why is more branches a benefit?

more branches = more ends to hydrolyse

how is the structure of starch linked to it's function?

• energy storage• insoluble - water potential is unaffected and so won't diffuse out of cells• compact• easily hydrolysed

what type of glucose is glycogen made up of?

alpha glucose (1-4 glycosidic bonds)

where is glycogen found

animals

how is glycogen used in liver cells?

• liver cells hydrolyse glycogen and release glucose into the blood• hormone glucagon and adrenaline• ONLY HAPPENS WHEN TRIGGERED BY HORMONE

how do muscle cells use glycogen?

muscle cells hydrolyse glycogen but use glucose within the cell to release energy for muscle contraction

why is glycogen being more branches a benefit?

• more branched than amylopectin• more ends to hydrolyse

how is glycogen structure is related to its function?

• similar to starch• chains are shorter and have more branches• more compact than starch - a-glucose molecules can be hydrolysed faster

outline cellulose

• main component of plant cell wall• made up of beta glucose• (C6H10O5)n• a polysaccharide• hydroxyl group sticks ABOVE the ring

what are the functions of cellulose?

• main component of plan cell walls as it provides rigidness to the plant cell• prevents cell bursting via osmosis - by exerting an inward pressure that stops any further influx of water—\> makes the plant tug it so leaves and stems are upright (v important)

how does cellulose provide strength?

• cellulose molecular chains are grouped to form microfibrils• microfibrils are grouped to form fibres which provide more strength

outline the structure of cellulose

• contains straight unbranched chains that run parallel to each other—\> this allows hydrogen bonds to form cross linkages between adjacent chains• bonded together by b-glycosidic bonding

what is a monomer?

- small, basic molecular unit- large molecules made of these

what is a polymer?

large complex molecules composed of long chains of monomers joined together

give some examples of monomers

- amino acids- monosaccharides- nucleotides

what is a condensation reaction?

- 2 molecules join together with the formation of a new chemical bond (glycosidic)- water molecule released when bond is formed

what is a hydrolysis reaction?

- breaks the chemical bond between monomers using a water molecule- opposite of condensation

what are glucose's 2 isomers?

- alpha glucose- beta glucose

how are glycogen and starch formed?

condensation of alpha glucose

how is cellulose formed?

condensation of beta glucose

outline the iodine test

- test for starch- add iodine dissolved in potassium iodide solution to test the sample- starch present = BLACK- not present = orange/brown

what are triglycerides formed of?

3 fatty acids + glycerol

what are the main groups of lipids?

- triglycerides- phospholipids

what are fatty acids made up of?

- carboxylic acid (head)- hydrocarbon chain (tail)

what does 'saturated' mean?

all the bonds are used up

what does 'monounsaturated' mean?

one double bond

what does 'polyunsaturated' mean?

2 or more double bonds

how are triglycerides formed?

condensation of glycerol and 3 fatty acids

what bond is formed in the formation of a triglyceride?

ester bond

what molecules are formed in the formation of a triglyceride?

3 water molecules

what are the roles of lipids?

- in cell membranes- source of energy- waterproofing- insulation- protection

what does the hydrolysis of a triglyceride produce?

3 fatty acids + glycerol

how is the structure of triglycerides related to its function?

- high ratio of energy storing carbon-hydrogen bonds to carbon atoms- low mass to energy ratio- insoluble in water- release water when oxidised

how are phospholipids different to triglycerides?

one of the fatty acid molecules is replaced by a phosphate molecule

what are phospholipids made up of?

- hydrophilic head-hydrophobic tail

how do phospholipids position themselves in water?

hydrophilic heads are close to the water and hydrophobic tails are far away

how is the structure of phospholipids related to its structure?

- polar- heads help to hold at the surface of the membrane- allows glycolipids to be formed

what is the test for lipids?

1. add 2cm cubed sample to a clean test tube2. add 5cm cubed of ethanol3. shake thoroughly4. add 5cm cubed of water and shake again

what is the results for the lipid test?

cloudy white (emulsion) = lipid

what are the 2 groups of lipids?

- phospholipids- tryglycerides

what two states can the R group of a fatty acid be in?

saturated or unsaturated

saturated fatty acid structure

- don't have any double bonds
H H H H| | | |- C - C - C - C -| | | |H H H H

unsaturated fatty acid structure

- at least one double bond

H H H H| | | |- C - C - C = C - C| | | |H H H H

what type of structure does an enzyme have?

tertiary

outline the 'active site'

- depends on folding go the protein- substrate has to be complementary to fit

how do enzymes work?

- lower activation energy- catalysts that speed up rate of reaction without being used themselves

describe general enzyme action

- substrate binds to form an enzyme-substrate complex- binding places stress on the bond causing the bond to break- products are released

outline the 'lock and key' theory

- enzymes are specific- substrate will only fit the active site of one particular enzyme

what are some limitations of the lock and key theory

- other molecules could bind to enzyme at other sites

what happened when other molecules bind to enzymes at other sites?

- activity changed suggesting shape changemeant the enzyme's structure was flexible

what is another name for alternate active sites?

allesteric site

outline the 'induced fit' model?

- enzyme changes shape slightly to mould around the substrate

how is the 'induced fit' model a better explanation of enzyme activity?

- explains how other molecules affect enzyme activity- explains how activation energy is lowered

how does temperature effect enzyme action?

- higher temp = molecules have more kinetic energy- molecules move faster- molecules collide more frequently- enzyme and substrate form an 'enzyme-catalysed reaction'

what does more collision due to the higher temperature mean?

- more collisions = more enzyme-substrate complexes form- RATE OF REACTION INCREASES

what does the temperature rate of reaction graph look like?

slowly increase to optimum then decreases(falling curve) as a general curve

what happens if the temperature is too high?

enzyme is denatured

what effect does temperature have on the enzyme itself?

- temp causes hydrogen and other bonds to break which alters the shape of the enzyme- substrate fits less easily at first slowing the rate of reaction

what happens if the ph on an enzyme changes too much?

enzyme is denatured

how does ph affect how an enzyme works?

- change in ph alters charge on amino acid- substrate can no longer attach- enzyme-substrate complex cannot form

what is the effect on the rate of reaction at low enzyme concentration?

- too few enzyme molecules to allow all substrate molecules to find an active site at one time- rate of reaction only 1/2 maximum possible for number of substrate molecules available

what is the effect on the rate of reaction at medium enzyme concentration?

- 2x enzyme molecules- all substrate molecules can occupy an active site- rate of reaction doubles to maximum as all active sites are filled

what is the effect on the rate of reaction at high enzyme concentration?

- addition of enzyme molecules has no effect- active site all already full- no increase in rate of reaction

what is the effect on the rate of enzyme action at low substrate concentration?

- too few substrate molecules to occupy all active sites- rate of reaction is only 1/2 maximum possible for number of enzyme molecules available

what is the effect on the rate of enzyme action at medium substrate concentration?

- 2x substrate molecules available- all active sites occupied- rate of reaction has doubled to its maximum as all active sites are filled

what is the effect on the rate of enzyme action at high substrate concentration?

- addition of substrate molecules has no effect- active sites all already full- no increase in rate of reaction

what do the concentration graphs look like?

steady increase then plato

how do competitive inhibitors work?

- bind with the active site so the substrate cannot fit

what effect do competitive inhibitors have on the rate of reaction?

initial rate is slower

what effect do non-competitive inhibitors have on the rate of reaction?

very little reaction then plato so line is very low

how do non-competitive inhibitors work?

- binds to allestiric site- binding changes shape of active site- enzyme-substrate complex cannot form

enzyme properties related to their tertiary structure

- very specific- only one complementary substrate will fit- active site determined by tertiary structure- different enzyme = different tertiary structure = differed shaped active site- if tertiary structure is altered the shape of the active site will change- pH or temp can alter tertiary structure

how can a mutation alter tertiarty structure

- primary structure determined by gene- if mutation occurs it could change the tertiary structure of the enzyme produced

what should be appreciated about enzymes?

- models of enzyme action have changed over time- enzymes catalase wide range of intracellular and extracellular reactions that determine structures and functions

investigation into the effect of a named variable on the rate of an enzyme controlled reaction rp1

catalase breaksdown hydrogen peroxide into water and oxygenmeasuring volume of oxygen produced can be used to work out how fast its given off

1. boiling tubes with same vol and conc of hydrogen peroxide set up2. place measuring cylinder upside down in water bath with deliver tube coming out into the boiling tube3. put each boiling tube in water to set temp4. use pipette to add same volume of conc of catalase to each5. reattach bung6. use stopwatch to record how much oxygen is produced7. repeat and calculate average rate of reaction

how to use a tangent to calculate initial rate of reaction

1. draw tangent at t=02. calculate gradient (change in y divided by change in x)

enzyme controlled reaction title and axis labels

t = volume of product released by enzyme-controlled reaction at different tempsy axis = volume of product released in cm cubedx axis = time (s)

what does ATP stand for?

adenosine triphosphate

what energy-requiring processes is ATP used in?

- building macromolecules- active transport- muscle contraction- secretion- activation of molecules