4 — enzymes Flashcards
Definition of enzymes
Enzymes are proteins that function as biological catalysts. They catalyse or speed up the rate of chemicals reactions by lowering activation energy required for the chemical reaction and remain chemically unchanged at the end of the reaction.
Definition of catalyst
A catalyst is a substance that can speed up a chemical reaction without itself being chemically changed at the end of the reaction.
Characteristics of enzymes
- Required in minute amounts n remain chem unchanged at the end of reactions -> same enzyme molecules can be reused -> small amt of enzyme can catalyse reaction for a large amt of substrate
- Each enzyme are highly specific, as only the substrate with a specific three-dimensional shape that is complementary to the enzyme’s active site can fit and bind to the active site. [1] [lock n key hypothesis]
- Has an optimum temperature & pH where rate of activity is highest
- Lowers activation energy required to start a cr by providing an alternative pathway -> speeds up rate of reaction -> saving time
Explain the mode of action of enzymes QS type:
Lock and key hypothesis
- According to the lock and key hypothesis, the enzyme is the lock, the substrate is the key.
- A specific substrate with a 3D shape is complementary to the enzyme’s active site, which are formed from depressions on the enzyme molecule, fit and bind onto the active site.
- And forms the enzyme-substrate complex. A chemical reaction occurs and
- Substrate molecule is converted into product molecule and leaves the enzyme’s active site. Enzyme molecule remains chemically unchanged at the end of the chem reaction & becomes free for another specific substrate molecule to fit and bind onto.
If: misfolded enzyme (eg phenylketonuria, an enzyme-related disease) -> lock n key hypothesis?
- State enzyme lock, substrate key +Site has been changed/altered
- Due to wutever reason given (defective gene), enzyme is misfolded
- Shape of substrate cannot fit and bind to active site -> no enzyme-substrate complex formed (Can/cannot fit n bind?)
- No chem reaction occurs, no break down of substrate molecule -> product molecules
- X (phenylalanine) lvl builds up in (blood), affect intellect & cause other health issues
- Aspartame, common sugar sub, contains phenylalanine
Describe and explain how enzyme functions are affected by temperature [4]
- At low temperature -> ke of molecules low -> enzyme + substrate molecules move slow -> frequency of effective collision betw substrate molecules n enzyme is low/zero -> enzymes are inactive -> enzyme substrate complex formation is slow and rate of reaction is slow.
- As temperature increases + data,
Data+ ^ temp -> ^ KE of molecules -> ^rate of effective collision n fitting onto active site to form ^rate of enzyme-substrate complex - At the optimum temperature + data -> Rate of enzyme activity is highest at: data. Enzymes r most active. Rate of formation of enzyme substrate complex is at its maximum and rate of reaction is the highest.
- Beyond the optimum temperature + data, rate of enzyme activity decreases until zero. Enzymes r denatured -> Weak hydrogen bonds in 3 dimensional enzyme structure is broken -> Active site(AS) of enzyme molecule begins to lose its original 3D shape -> not complimentary to shape of substrate molecules -> substrate cannot fit n bind to AS ->no enzyme substrate complex formed, enzyme denatured n rate of reaction decreases to 0.
Tempt affecting enzyme graph
- Nvr starts at 0
- Gradual increase till max
- Plunge to 0
- Label optimum tempt
- Label x and y axis
pH affecting enzymes + graph
Below and beyond optimum pH:
Weak hydrogen bonds in 3 dimensional structure is broken. 3 dimensional shape of enzyme is lost and shape of active site is altered. Substrate can no longer bind to active site of enzyme and no enzyme-substrate complexes are formed. Enzyme is denatured and rate of reaction decreases to zero.
Optimum pH:
Enzyme is most active, rate of formation oof enzyme substrate complex is at its maximum and rate of reaction is the highest.
Graph:
- Both ends touch x axis at 0
- Symmetrical
- Label optimum point + x and y axis
Functions of enzymes
- Building up/synthesising complex substances
- Breaking down food substances in cells to release energy for cellular respiration
- Digesting large food molecules into smaller molecules
- Breaking down toxic substances in cells
Type of reactions catalysed
Anabolic reactions: reactions that build up complex substances
- Protein synthesis
- Amino acids -> proteins
- Photosynthesis
- Glucose synthesis eg from carbon + water
Catabolic reactions: reactions that break down complex substances
- Cellular respiration
- Enzymes act tgt to break down glucose -> CO2 + water + release energy
- Digestion by digestive enzymes
- DE: enzymes involved in digestion
- Decomposition of hydrogen peroxide
- Catalase breaks down toxic hydrogen peroxide -> H2O + O2
- Catalase: abundant in blood n mammals’ liver
Action of amylase
Digests starch to maltose
Produced by salivary glands, pancreas
Found in SI and saliva
Pepsin vs trypsin
Both: Proteins -> short polypeptides
P found in stomach but T found in SI
P produced by stomach but T produced by pancreas
P works well in pH 2 stomach but T works well in pH 7-9 SI
Action of lipase (pancreatic/intestinal)
Triglycerides (fats) -> glycerol + fatty acids
Produced by pancreas, epithelial cells
Found in SI, pH of location = 7-9
Digestive enzymes in SI
Digestion of disaccharides:
Sucrase: Sucrose -sucrase> glucose + fructose
Maltase: Maltose -maltase> glucose + glucose
Peptidases: Digests fats -peptidases> glycerol + fatty acids
Lactase: Lactose -lactase> glucose + galactose
SMPL all produced by epithelial cells & found in SI:pH 7-9
Digestion of proteins:
Trypsin: Proteins -trypsin> short polypeptides
Produced by pancreas
Digestion of fats:
Lipase (pancreatic)/(intestinal):
Triglycerides (fats) -lipase> glycerol + fatty acids
Produced by pancreas, epithelial cells
Suggest a possible nutritional advantage to the young cow of the action of enzymes rennin which causes liquid milk to clot, forming solid lumps.
Rennin allows milk to stay for a longer period of time in the stomach as it allows liquid milk to clot. Other proteases like pepsin would have more time to digest the proteins in the milk into polypeptides. Subsequently the polypeptides can be further digested into amino acids which can be absorbed into the bloodstream of the young cow.
