Enzymes and the Digestive System

Question 1

what is an enzyme?

Answer 1

a biological catalyst that speeds up a reaction without being used up, lowers activation energy, bends the bonds within the substrate

Question 2

fun facts about enzymes (6):

Answer 2

• they’re globular proteins
• proteins of high weight to have substantial stability and strength
• sensitive to both temperature and PH hydrogen and ionic bonds specifically impacted
• catalyse both anabolic (building up) and catabolic (breaking down) reactions
• soluble in water - dependent on the R-group
• enzymes can be extracellular and intracellular

Question 3

groups of enzymes:

Answer 3

lyases: splitting of bonds other than hydrolysis or oxidation
hydrolases: hydrolysis of bonds - all digestive enzymes
ligases: joining of two molecules by formation of covalent bonds
isomerase: isomerisation of molecules

Question 4

what are activators?

Answer 4

inorganic groups permanently bound to enzymes and are a type of prosthetic group

Question 5

what are co-enzymes?

Answer 5

organic molecules that bind only temporarily to the enzyme transferring a chemical group necessary required for a reaction

Question 6

what is the active site?

Answer 6

3D specific tertiary structure complementary to the substrate

Question 7

what’s the substrate function?

Answer 7

the substrate binds to the active site -> creates enzyme/substrate complex bends bonds of substrate -> enzyme/product complex -> active site will release products they diffuse away - we know this as the lock and key theory

Question 8

what is the lock and key theory?

Answer 8

substrate is an exact complimentary shape to the active site

Question 9

what is the Induced Fit Model?

Answer 9

• this model takes into account the fact that protein active sites have some three-dimensional flexibility
• substrate binds to the enzyme at the active site similar complimentary shape to substrates but NOT exact
• binding of substrate induces the enzyme to change shape such that there is an exact fit in the active site once the substrate has bound
• reactions can only take place AFTER induced fit has occurred

Question 10

what are factors effecting the rate of reaction (6)?

Answer 10

• temperature
• PH (log-[H+])
• concentration of substrate
• concentration of enzyme
• inhibitors
• activators

Question 11

describe the temperature graph?

Answer 11

bottom of curve: rate of reaction at its slowest, the internal kinetic energy of the molecules don’t reach the activation energy. Fewer successful collisions, fewer enzyme/substrate complexes, enzymes and substrate kinetic energy have little kinetic energy
mid of curve: increased temperature more kinetic energy, high number of successful collisions, high number of enzyme/substrate complexes, more product formed per second and a higher rate of reaction
optimum: fastest rate of reaction, most successful collisions per rate, highest rate of enzyme/substrate complexes and highest rate of product formation
after optimum: active site denatures - its 3d tertiary structure is no longer complimentary to the substrate, fewer successful collisions per second, lower rate of enzyme/substrate complexes forming, lower rate of product formation, decrease in rate of reaction -> structure of active site is no longer complimentary to the substrate temperature overcome tertiary structure bonds - hydrogen, ionic, disulphide are broken and this changes the 3d tertiary structure of the active site

Question 12

Describe the Ph graph:

Answer 12

All enzymes have an optimum Ph at which they operate best
Enzymes are denatured at exrmtreames of Ph:
Hydrogen and ionic bonds hold the tertiary structure of the protein together
Below and above the optimum Ph of an enzyme, solutions with an excess of H+ ions and OH- ions can cause these binds to break
This alters the shape of the active site, which means enzyme-substrate complexes form less easily. Eventually, enzyme-substrate complexes can no longer form at all at this point comoleate denaturation has occurred

Question 13

Describe a substrate concentration graph:

Answer 13

Increase concentration of substrates high rate of reaction because there are available active sites. Substrate concentration is limiting the rate of reaction. As the graph levels off, all active sites are occupied, and the rate of reaction is at its fastest. High concentration of substrate doesn’t increases the rate of reaction, as active sites are the limiting factor, resulting in a maximum number of enzyme-substrate complexes

Question 14

Describe an enzyme concentration graph:

Answer 14

The rate of reaction is directly proportional to the enzyme concentration. As the enzyme concentration increases, so does the rate of reaction as more active sites are available

Question 15

What are inhibitors function?

Answer 15

They slow down the rate of reaction by inhibiting the enzyme

Question 16

Describe a competitive inhibitor graph:

Answer 16

At low substrate concentration the rate of reaction is reduced in the presence of an inhibitor there is increased probability that the competitive inhibitor will bind to the active site- reducing the number of enzyme-substrate complexes which decreases the rate of reaction.
The effect of the inhibitor is overcome by very high substrate concentration. At high concentrations, the inhibitor is out-compeated by the substrate, and the max rate of reaction is achieved. Max number of enzyme-substrate complexes formed. All active sites occupied by substrates which result in the highest rate of reaction

Question 17

what is a competitive inhibitor?

Answer 17

competitive inhibitors have a similar 3D shape to the substrate or a complimentary 3D shape to the active site. when the competitive inhibitor binds to the active site it prevents enzyme-substrate complexes from forming, active sites are occupied –> fewer products are formed per second –> lowers rate of reaction

Question 18

what is a non-competitive inhibitor?

Answer 18

a non-competitive inhibitor binds to the binding site, which causes a 3D shape change to the active site. this prevents the active site from bending the bonds, which further prevents successful enzyme-substrate complexes forming, which lowers the rate of reaction. the active site is no longer a 3D complimentary shape to the substrate

Question 19

Describe a non-competitive inhibitor graph and the function of a non-competitive inhibitor?

Answer 19

the graph of a non-competitive inhibitor levels off very early on because the maximum rate of reaction is never achieved.
the effect of a non-competitive inhibitor is not overcome by increasing the substrate concentration. all enzyme molecules with bound non-competitive inhibitors do NOT convert substrate to product.

Question 20

what is end product inhibition?

Answer 20

products often act as a regulator. when the concentration of product is high it binds non-competitively to an enzyme in pathway, blocking further production of itself. when concertation of the products falls it leaves the binding site and the active site/ enzyme is the available

Question 21

What is an activator?

Answer 21

• molecules that bind to enzymes and increase their activity
• they are often involved in the allosteric regulation of enzymes
• they bind to an alternate site on an enzyme, changing the shape of the active site cause the 3D tertiary structure of the active site to become complementary to the substrate

Question 22

About Salivary amylase:

Answer 22

1-4/1-6 glycosidic bonds, hydrolyses starch into shorter chains which increase the surface area. It’s found in the salivary glands which transport the salivary amylase into the mouth, found in saliva (enzyme and buffer). Ph 7 environment

Question 23

About endopeptidases:

Answer 23

hydrolyse peptide bonds within the peptide chain. Hydrolyses proteins into shorter chain polypeptides, which increases the number of terminal ends which increases the surface area. It’s found in the stomach - enzymes and HCl likes a Ph 2

Question 24

About pancreatic enzymes:

Answer 24

endopeptidases - shorter chains into di-peptides
exopeptidases - hydrolyses peptide binds at terminal ends of the shorter polypeptide chains
pancreatic amylase - short chain starch into disaccharides e.g. maltose
lipase - hydrolyses the ester bond, hydrolyses lipids into a mono-glyceride and two fatty acids
all found in the pancreas - all made in the pancreas and delivered by the pancreatic duct to the duodenum -the upper part of the small intestine. bile made in the liver stores in the gallbladder: emulsifies, and neutralises the acidic food the Ph 8/9
all these enzymes like a Ph 8/9

Question 25

About dipeptidases:

Answer 25

converts dipeptides into two amino acids e.g. maltase, sucrase, lactase:
maltose –> 2 alpha glucoses
sucrose –> an alpha glucose and fructose
lactose –> an alpha glucose and galactose
found in the lower part of the small intestine, the ileum, they’re embedded in the wall of the ileum
like a Ph 8/9

Question 26

The mouth:

Answer 26

chewing is the physical breakdown of the food. Mastication (fancy word for chewing) increases surface area of the food, and allows for it to mix with the saliva so amylase can begin the hydrolyses the starch. three pairs of salivary glands: saliva salivary amylase, is a buffer Ph 7, it has antibacterial properties

Question 27

About oesophagus:

Answer 27

there are two layers of muscle: circular and longitudinal - they are an antagonising pair when one contracts the other relaxes and vice versa. These layers of muscle squeeze the food down in a process called peristalsis.

Question 28

About stomach:

Answer 28

there are three layers of muscle for 3D churning. inner wall cell lining is protection against the acid (HCl). goblet cells produce mucus this acts as a barrier to protect the lining of the stomach. peptic glands produce peptic juice which consists of enzymes. endopeptidases hydrolyse shorter polypeptide chains increasing terminal ends which increase surface area to further enzyme activity (exopeptidases). HCl to kill pathogens and provide food with optimum Ph for enzymes in the stomach (Ph 2)

Question 29

About duodenum:

Answer 29

it’s the upper part of the small intestine. food is at a Ph 2. pancreas produces endopeptidases and exopeptidases which hydrolyse proteins. pancreatic amylase hydrolyses starch. lipase likes Ph 8/9 so the liver produces bile and the gallbladder stores it. the bile enters the duodenum via the bile duct. bile has two main functions: neutralises the acidic food to Ph 8/9 so pancreatic enzymes can work at an optimum Ph and not denature, bile also acts as an emulsifier of lipids - lipids are non water soluble but lipase is water soluble, bile has parts which are hydrophilic and hydrophobic. bile increases the surface area of the lipids which results in increased area for the enzymes to hydrolyse the lipids into a monoglyceride and three fatty acids.

Question 30

About the ileum:

Answer 30

this where dipeptides get hydrolysed further by dipeptidases into amino acids:
- maltose is hydrolysed by maltase
- sucrose is hydrolysed by sucrase
- lactose is hydrolysed by lactase
main site of absorption and final stages of digestion

Question 31

About large intestine:

Answer 31

undigested material e.g. cellulose, fibre and, water and, vitamins and minerals are absorbed

Question 32

About the colon:

Answer 32

there is a high water potential in the colon and a low water potential in the blood stream, therefore water moves form the colon into the blood stream via osmosis

Question 33

how are lipids absorbed into the bloodstream?

Answer 33

bile emulsifies lipids into smaller lipid droplets surrounded by bile salts, lipids after full hydrolysis: monoglyceride, three fatty acids and, bile salts - these are called micelles. they endocytose into the cells - they fuse to the cell membrane and the contents diffuse into the cell. they are then send to the smooth endoplasmic reticulum to rebuild the lipids. lipids are then attached to a protein and are now called chylomicrons this happens in the Golgi it’s then transported in a vesicle to the basal membrane. then the chylomicrons exocytose via diffusion into the lacteal

Question 34

Epithelial cells in the ilium:

Answer 34

• they have embedded enzymes
• they have channel proteins for co-transport
• lots of mitochondria for increased production of ATP from respiration to be used for active transport

Question 35

Describe the picture (refer to notes):

Answer 35

• microvilli: increases the surface area in which absorption can occur therefore increasing the rate of absorption
• single cell lining: epithelial cells have a short diffusion pathway
• goblet cells: production of mucus
• embedded enzymes: so they aren’t lost as once the food leaves the ilium the remnants are egested. allows final hydrolysis of di-isomers to occur next to the ilium wall - increases efficiency of absorption which results in a reduction of enzymes lost
• epithelial cells: single layer of cells of the ilium resulting in a short diffusion pathway
• capillary network: carry absorbed substances away, capillary wall is one cell thick and touching the epithelial wall for a short diffusion pathway, capillaries have a large network which increases surface area which increases the rate of diffusion, constant flow of blood which maintains the concentration gradient, blood from the small intestine, ilium, is carries to the liver to remove excess monosaccharides, vitamins, minerals, lipids etc, the blood vessel that goes from the ilium to the liver is called the hepatic portal vein
• lacteal: carries lipids (monoglyceride and fatty acids) reconstructed. the lymphatic system: absorbs lipids, removal of lymphatic fluids, carries leukocytes - part of the immune system, makes milk
  muscle: both longitudinal and circular muscle for the continuation of peristalsis

Question 36

How does co-transport work regarding absorbing amino-acids, glucose, fructose and, galactose?

Answer 36

• actively transport Na+ ions out of the epithelial cells into the bloodstream which uses the Na/K pump which requires ATP from respiration
• high concentration of Na+ ions in the lumen which results in a low concentration in the epithelial cells so creates a diffusion gradient
• Na+ ions in the lumen want to diffuse into the epithelial cells but they can’t unless they co-transport: amino acid, glucose, fructose or, galactose. channel proteins will not permit it
• high concentration of amino acids. glucose, galactose, fructose in epithelial cells, lower concentration in the blood stream so they diffuse in via facilitated diffusion