U4AOS2 - Metabolism of food in the human body

Question 1

Structure of Enzymes (inc. how specific they are)

Answer 1

Made up of Proteins

Contain an active site - where the substrate (reactant(s) of a reaction) can bond.

Molecules that the active site will accept are very specific - therefore, enzymes will often only catalyze one or a very small number of reactions (this is unlike inorganic catalysts - which are generally not specific)

Question 2

Enzyme-Substrate Complex

Answer 2

Question 3

Purpose of Enzymes (inc. how they accomplish it)

Answer 3

To act as biological catalysts, and to increase the rate of reaction in the body

They accomplish it by providing alternate reaction pathways with a lower activation energy
- this means a greater proportion of molecules will have enough KE to breach the activation energy
- speeds the reaction up

Question 4

Do enzymes change the amount of product produced?

Answer 4

No - they only increase the rate of reaction

Question 5

3x Main Points for Enzyme Function

Answer 5

1. Specific Active Site for a Specific Substrate
2. Interactions weaken the intermolecular bonds of the products, lowering activation energy
3. this allows the reaction to occur - forming the products

Question 6

Are enzymes modified over the course of a catalyzation

Answer 6

No - the enzyme remains unchanged at the end of the reaction (regardless if lock-and-key, induced fit, coenzymes)

Question 7

Effect of optical isomers on enzymes

Answer 7

Enzymes typically will not accept optical isomers - generally two separate enzymes will be required

Question 8

Enzyme Lock-and-Key Model

Answer 8

States that only substrates that perfectly fit the active site can bond

(like a lock and key)

Question 9

Enzyme Induced Fit Model

Answer 9

Suggests that the active site of an enzyme is more flexible

Suggests that the shape of the active site may change shape slightly to fit the substrate

however - at the end of the reaction - the substrate will return to its original position

Question 10

Why do enzymes experience denaturation?

Answer 10

Because, enzymes themselves, are proteins

Question 11

Effect of Temperature on Enzymes (inc. high/low/optimal temp)

Answer 11

If temp is lowered - rate of reaction will be too slow
If temp is raised - the protein will begin to denature (as a result of more vibration)

This results in optimum temperatures - where the rate of reaction is highest, without any breakdown in the structure of the protein (generally body temp for humans)

Question 12

Effect of pH on Enzymes

Answer 12

Changing pH will modify the structure of the enzyme (same with proteins in acids or bases).

Given that enzymes and substrates can bond ionic-ly, if the pH becomes acidic or basic, the enzyme may be unable to bond to substrates

Question 13

Hydrolysis of Proteins (inc. process and purpose)

Answer 13

Process of chemically digesting proteins

Amide Links (peptide links) will be broken, splitting the protein into amino acids (and consuming water).
(PRIMARY STRUCTURE)

Purpose: to allow the amino acids, which are polar, to travel through the bloodstream, where they can be assembled into a new protein at the required location

Question 14

Enzyme that catalyzes the hydrolysis of proteins

Answer 14

Protease - type of enzyme that will help to break down proteins

A common one is pepsin

Question 15

Effect of adding HCl (in the presence of pepsin) to Proteins (and sometimes heating)

Answer 15

Results in the hydrolysis of the protein

• the HCl is the source of H+,
• the enzyme catalyses the reaction
• the heat can increase the rate of reaction

heat and change in pH are the two main reasons for denaturation

Question 16

Denaturation

Answer 16

disruption or destruction of the secondary, tertiary, (and quaternary only if it’s present)

results in the unfolding of the protein, disrupts the 3D shape, and disables the functionality of a protein

Question 17

Denaturation vs Hydrolysis of Proteins

Answer 17

Denaturation disrupts secondary, tertiary (and quanternary structures - if present)
VS
Hydrolysis which only disrupts the primary structures

Question 18

Heat as a cause of denaturation (inc. reversibility)

Answer 18

heat -> increases kinetic energy of molecules

if the kinetic energy is high enough -> the molecules can vibrate so rapidly that the secondary and above bonds can be disrupted

if the heat is raised high enough - this is not reversible

Question 19

Real life example of heat based denaturation

Answer 19

heating medical supplies to denature the proteins in bacteria - as denatured proteins have less biological activity - and so are no longer harmful

Question 20

pH as a cause of denaturation (inc. reversibility)

Answer 20

when pH changes, the ionic interactions change (as the acid/base properties change)

if the pH deviates too far from its optimum pH, the denaturation may be irreversible

Question 21

Real life example of pH based denaturation

Answer 21

Vinegar is often used when boiling an egg, as it’s an acid

this lowers the pH of the solution, denaturing the eggs proteins

Question 22

Step 1 of Hydrolysis of Starch

Answer 22

Occurs in the mouth, starch (either amylose or amylopectin) is hydrolyzed by saliva in the mouth, which contains the enzyme amylase

This converts starch into maltose (a disaccharide)

Question 23

Step 2 of Hydrolysis of Starch

Answer 23

The maltose is then hydrolyzed into glucose, with maltase as the enzyme

Question 24

Why can amylase operate in the mouth, but not the stomach?

Answer 24

The optimum pH of Amylase is 6, but the pH in the stomach is about 1.5

so the amylase enzyme undergoes denaturation

Question 25

Enzyme required to hydrolyze sucrose

Answer 25

Sucrase

Question 26

Enzyme required to hydrolyze lactose

Answer 26

Lactase

Question 27

Hydrolysis of Cellulose

Answer 27

Celluose is constructed from β-glucose (as opposed to the other forms using α-glucose)
This means it requires cellulase (as opposed to amylase), which the body doesn’t produce

Therefore - humans cannot hydrolyze cellulose - its however, still helpful as fibre, just not as a source of energy

Question 28

Differentiation ability of humans to hydrolyze lactose (inc symptoms for those who cant)

Answer 28

Lactose requires the enzyme lactase to hydrolyze

However - a significant portion of the population is lactose intolerant, meaning that they do not produce the required enzyme, lactase.

People often report stomach aches or vomiting as symptoms

Question 29

Glycemic Index (inc glucose as a reference)

Answer 29

indicates how quickly carbohydrates (only starch in VCE) impact glucose level

GI of glucose is assigned 100, everything else is a comparison to glucose, therefore, no units

High GI - causes a quick spike in blood sugar, but decreases quickly
Low GI - causes a gradual increase in blood sugar

Question 30

Does the GI index measure energy density

Answer 30

No - GI values are not a measure of energy density - only a measure of the ease to hydrolyze carbohydrates - the energy density depends on the food

Question 31

GI of Amylose

Answer 31

Low GI

• has no branching, therefore, stronger intermolecular bonds
• less surface area for water and enzymes to act on
• glucose will be produced slower -> low GI

Question 32

GI of Amylopectin

Answer 32

Low GI

• has branching, therefore, weaker intermolecular bonds
• greater surface area for water and enzymes to act on
• glucose will be produced faster -> high GI

Question 33

GI of Cellulose

Answer 33

GI of 0

Cannot be hydrolyzed by humans - no effect on glucose production

Question 34

Bile - tool for emulsifying triglycerides (inc. what it creates)

Answer 34

Type of salt, produced in the liver

Given its an emulsifier - it will break down large clumps of triglycerides into smaller chunks

Then - a hydrophobic end of the bile will dissolve in the fat, and a hydrophilic end will dissolve in water

Creating: miscelles droplets - which can be hydrolyzed

Question 35

Why do triglycerides need to be emulsified

Answer 35

Because they are non-polar molecules, and insoluble in water

emulsification makes them polar in water, allowing them to be hydrolyzed

Question 36

Hydrolysis of Triglycerides (inc. requirement)

Answer 36

Required to be emulsified

The emulsified triglyceride then undergoes hydrolyzed, catalyzed by lipase

This separates the glycerol backbone and the 3 fatty acids (creating 3 water)

Question 37

Transporting Glycerol/3xfatty acids (after the hydrolysis)

Answer 37

They are transported to be reformed into lipids (in adipose tissues)

Question 38

Adipose Tissues (inc. purpose)

Answer 38

Tissues found under the skin and around muscles

Purpose: long term energy storage, excess triglycerides are stored in these molecules

Question 39

Consumption of Fatty Acids

Answer 39

When fatty acids are required - they will be transported to muscle cells, and undergo oxidation

(producing CO₂ and H₂O)

Question 40

Oxidative Randicity (inc. targeted bonds, way to tell)

Answer 40

Deterioration of lipids through atmospheric oxygen

Targeted bonds: generally only C=C bonds, however, sometimes C-C bonds will be targeted (much slower tho)

Way to tell: They will smell badly, and go off

Question 41

Factors that effect the speed of Oxidative Randicity (3)

Answer 41

• presence of C=C increases the speed
• number of C=C bonds (more = faster)
• lowering temperature - reduces the rate of reaction - lowering oxidative randicity

Question 42

Preventing Oxidative Randicity (without antioxidants)

Answer 42

Remove the presence of sunlight and oxygen

Question 43

Autooxidation (inc. free radicals)

Answer 43

Spontaneous oxidation of a compound in the presence of oxygen

caused by free radicals (molecules or atoms with unpaired electrons), which are highly unstable

Question 44

Antioxidants

Answer 44

Reducing agents, which are oxidized in preference to the triglyceride

They slow down oxidative rancidity

Question 45

Coenzymes (inc. what they are derived from, and purpose)

Answer 45

Small, non-protein, organic molecules that bind to the active site of an enzyme

Often derived (not always) from vitamins

Purpose: They modify the binding properties of the active site of the enzyme, to suit the shape of the substrate.
then they can act as a a carrier of electrons and/or groups of atoms

Question 46

Are Coenzymes altered as a result of a reaction

Answer 46

Sometimes, however - they are regenerated in future reactions