Aqa As Level Biology - Unit 1 - 3.1.2

Front 1

What is the digestive system made up of & what is the process of digestive?

Back 1

*Its made up of a large muscular tube & its associated glands.

*Digestion is the process in which large molecules are hydrolysed by enzymes to produce smaller molecules that can be absorbed & assimilated.

*The digestive system provides an interface with the environment.

Front 2

What are the 2 stages of digestion & explain the 3 components of saliva?

Back 2

*Physical breakdown - Mastication of food uses the teeth to increase the surface area.

*Chemical digestion - Is the use of enzymes to break down large, insoluble molecules into smaller, soluble ones.

*Salivary amylase hydrolyses starch into maltose.

*Mucin {mucus} binds food into bolus lubricted for swallowing.

*Alkali neutralises any acid in food.

Front 3

How does the oesophagus assist digestion?

Back 3

*Bolus is pushed back by tongue to the back of the mouth.

*The oesophagus is a long tube made up of a thick muscular wall.

*Epiglottis prevents food from entering the trachea.

*Mucus is secreted from glands to lubricate food.

*Peristalsis pushes bolus to stomach.

Front 4

How does the stomach aid digestion?

Back 4

*The stomach is a muscular, holds approximately 1.2 litres & increase to 5 litres when distended.

*Converts food into semi solid chyme by peristaltic churning.

*Gastric mucosa embedded with gastric pits that produce gastric juice.

*Gastric juice contains:-

- Water

- Hydrochloric acid -> creates pH2 which kills bacteria -> denatures amylase.

- Pepsin -> digests proteins & amylase.

*Chyme is gradually released over 3 to 4 hours.

*Pyloric sphincter controls exit in small squirts.

Front 5

How is the small intestine adapted to its function & what are the 3 digestive juices in the small intestine?

Back 5

*Over 6 metres long.

*Luminal epithelium is folded into villi & microvilli to increase surface area so the small intestine is in contact with more food.

*Maintains concentration gradient - Peristalsis delivers more nutrients, active transport removes nutrients from lumen & extensive capillary network provides an excellent blood supply to remove nutrients from epithelial cells.

*Short distances - 1 cell thick epithelium, capillaries lie next to epithelial cells & thin walls surround capillaries.

*Bile, pancreatic juice & intestinal juice.

Front 6

What is bile & pancreatic juice?

Back 6

*Bile - Created by the liver, stored in gull bladder, secreted by bile duct into small intestine, contains alkali -> neutralises acidic chyme for enzymes.

*Pancreatic juice - secreted by pancreas via pancreatic duct, is alkaline -> neutralises stomach acid - optimum pH & contains various enzymes e.g. pancreatic amylase -> hydrolysis of starch into maltose.

Front 7

What is intestinal juice & what are membrane - bound enzymes?

Back 7

*Intestinal juice - secreted from cells covering villi, contains alkali & mucus & may contain few, if any enzymes.

*Membrane - bound enzymes - bound to luminal membrane of epithelial cells, may be found in intestinal juice due to sloughing of these cells. Carbohydrases - hydrolyse glycosidic bonds, releasing monosaccharides:-

- Sucrase digests sucrose -> glucose + fructose

- Maltase digests maltose -> glucose

- Lactase digests lactose -> glucose + galactose.

Front 8

What is the function of the large intestine?

What do carbohydrates consist of & what is the general formula for them?

Back 8

*To absorb excess water from digestive secretions.

*The undigested food is expelled as faeces.

*Carbohydrates contain carbon, hydrogen & oxygen.

*(CH2O)n

Front 9

What are the 3 types of carbohydrates?

What are the uses of carbohydrates & which would be used?

Back 9

*Monosaccharides - Single sugars.

*Disaccharides - Double sugar.

*Polysaccharides - More than 2 sugars.

*Structural use - Cellulose, chitin.

*Energy use - Glucose.

*Storage use - Glycogen, starch.

*Used in nucleic acids - Ribose, deoxyribose.

Front 10

What are monosaccharides?

Give examples of monosaccharides.

Back 10

*Simplest sugars which have the same number of Carbon & Oxygen atoms.

*Monomer for starch, glycogen & cellulose.

*Glucose, Fructose & Galactose.

*Glucose - C6H12O6

Front 11

How are disaccharides formed & what do disaccharides form when they are hydrolysed?

Give examples of disaccharides.

Back 11

*Disaccharides hydrolyse to form Monosaccharides due to the hydrolysis of the glycosidic bonds.

*Disaccharides form Polysaccharides.

*Sucrose formed by condensation of glucose + fructose. Non reducing sugar.

*Lactose formed by condensation of glucose + galactose. Reducing sugar.

*Maltose is formed by condensation of 2 α - glucose molecules. Reducing sugar.

Front 12

Explain what polysaccharides are?

Back 12

*Polymers of monosaccharides.

*Insoluble due to size & have no osmotic influence.

*Do not diffuse easily.

*Split into disaccharides & monosaccharides by hydrolysis.

*Starch & cellulose are polysaccharides.

Front 13

Explain the structure of starch & cellulose?

Back 13

Starch:-

*α - helical structure -> Good for storage, its compact.

*Insoluble -> main plant storage sugar.

Cellulose:-

*Polymer of ß - glucose.

*Each monomer is inverted.

*Forms chains which run parallel with hydrogen bonds between the chains to form microfibrils which are strong.

*Is structurally important in plant cell walls.

Front 14

Explain a biochemical test for reducing & non reducing sugars?

Back 14

Benedict's reagent:-

*Add 2cm3 of food sample into a test tube. Grind up the sample into a liquid if not already.

*Add the same volume of Benedict's reagent.

*Heat mixture in a gently boiling water bath for 5 minutes.

When a reducing sugar is present the solution will turn from a blue liquid to a red precipitate.

Front 15

What are proteins & what are proteins polymers of?

Back 15

*Determined by genetic codes.

*Structure use - Collagen {bone, cartilage, tendon}, Keratin {hair}, Actin {muscle}

*Enzymes - Amylase, Pepsin, Catalase.

*Transport - Haemoglobin {oxygen}.

*Active transport - Sodium - Patassium pumps in cell membranes.

*Muscles {Myosin & Actin}

*Hormones - Insulin, Glucagon.

*Antibodies - Immunoglobulins.

*Proteins are polymers of amino acids.

Front 16

What are amino acids?

Back 16

*Lots of proteins.

*There are 20 naturally occuring amino acids.

*Half are created in the body & the other half are consumed in diet.

Front 17

What is a peptide bond?

Back 17

*Peptide bond connects 2 amino acids which join together to form a dipeptide through a condensation reaction.

*A hydrolysis reaction breaks peptide bonds.

*This requires the use of a water molecule to reform the amino & carboxyl groups on each of the 2 new amino acids where the bond has split.

Front 18

What is a polypeptide & what are the 4 levels of protein structure?

Back 18

*Many amino acids make up a polypeptide chain.

*Amino acid polymerisation for polypeptides is part of protein synthesis.

*The sequence of amino acids in a chain is determined by the sequence of the genetic code in DNA.

*Primary, secondary, tertiary & quarternary structures.

Front 19

Explain the primary & secondary structures of a protein.

Back 19

Primary structure:-

*Refers to sequence of amino acids -> determines rest of protein structure.

Secondary structure:-

*Amino acid chain folds & take a particular shape.

*Linked by hydrogen bonds.

*Polypeptide chain becomes twisted into α - helix or ß - pleated sheet structure.

Front 20

Explain the tertiary & quarternary structures of a protein.

Back 20

Tertiary structure:-

*3D shape

*Hydrogen bonds - Numerous easily broken.

*Ionic bonds - Quite strong.

*Disulfide bonds - Strong covalent bonds.

Quarternary structure:-

*Final 3D structure with a number of individual polypeptide chains linked together.

*May include non - protein {prosthetic} groups associated with molecules such as haem {iron} groups in haemoglobin.

Front 21

What are fibrous & globular proteins?

Back 21

Fibrous Proteins:-

*Water insoluble, long & narrow proteins.

*Many polypeptide chains run parallel, cross - linked with bonds which makes them stable & structurally strong.

*E.g. Keratin, Collagen, Fibrin.

Globular Proteins:-

*More spherical & have specific shapes.

*Small ones are soluble.

*Often have complementary shape to another specific molecule.

*E.g. Hormones, Enzymes, Haemoglobin & Antibodies.

Front 22

Explain the biochemical test for proteins.

Back 22

Biuret test:-

*Place a sample of the solution to be tested in a test tube & add an equal volume of sodium hydroxide solution at room temperature.

*Add a few drops of very dilute {0.05%} copper{II} sulfate solution & gently mix.

*A purple colouration indicates the presence of peptide bonds, meaning there is a protein.

Front 23

What are enzymes?

Back 23

*Globular proteins, act as catalysts.

*They lower the activation energy.

*Active site is made up of a relatively small number of amino acids.

*Substrate is the molecule that the enzyme breaks down.

*Forms an enzyme - substrate complex.

Front 24

What is the lock & key model?

Back 24

*This model proposes that enzymes work in a lock & key method.

*The substrate {key} will only fit into the active site of 1 particular enzyme {lock}.

*Substrate has a complementary shape to the active site.

*Limitation - is that an enzyme, like a lock, is considered to be rigid. But scientists observed other molecules could bind to enzymes at sites other than the active site.

Front 25

What is the induced fit model?

Back 25

*Proposes that the enzyme actually changes shape slightly to fit substrate.

*Suggests enzymes are flexible & mould themselves around substrate.

*When enzyme changes shape, strain is put on substrate.

*This distorts particular bond & lowers activation energy needed to break bond.

Front 26

What factors affect the rate of reaction of enzyme action?

Back 26

*pH

*Temperature

*Substrate concentration

*To measure enzyme - catalysed reactions, measure:-

-> The formation of the products of the reaction.

-> The disappearance of the substrate.

Front 27

How does pH affect enzyme action?

Back 27

*Each enzyme has an optimum pH at which it works best at.

*A change in pH alters the charges on the amino acids that make the active site.

*This affects the ionic bonds which means the substrate can no longer bind.

*A change in pH can result in the enzyme becoming denatured.

Front 28

How does temperature affect enzyme action?

Back 28

*Each enzyme has an optimum temperature at which it works best at.

*Rise in temperature increases kinetic energy of molecules which increases the number of collisions & increases the rate of reaction.

*Increasing temperature vibrates molecules violently & breaks the hydrogen bonds which alters the 3D shape.

*This causes the active site to no longer fit the substrate.

*The enzyme denatures at 60C.

Front 29

How does substrate concentration affect enzyme action?

Back 29

*The rate of reaction increases as the substrate concentration increases, until the enzyme is working at full capacity.

*This is due to collisions between the enzyme and the substrate.

*In low substrate concentrations, not all enzymes are being used.

*As the substrate concentration increases more enzymes molecules are used.

*When all active sites are in use, substrate concentration does not affect rate of reaction.

Front 30

What is enzyme inhibition?

Back 30

*Inhibitors can slow down or stop catalytic activity of enzymes.

*Inhibition is a natural process, a mechanism to switch enzymes on or off when needed.

*Inhibition tends to be reversible as the enzyme returns to normal when the inhibitor is removed.

*Reversible inhibitors can be competitive or non - competitive.

Front 31

What are competitive inhibitors?

Back 31

*They compete with substrate molecules to occupy the active site.

*Have similar structure to substrate but can't convert into products.

*Increase in concentration of substrate reduces effect of inhibitor.

Front 32

What are non - competitive inhibitors?

Back 32

*Bind to enzyme away from active site.

*Decreases maximum rate of reaction.

*Changes overall shape of enzyme.

*Reduces amount of active enzymes.

*Increase of substrate concentration has no effect on inhibitor.