Lecture 6 Enzymes Flashcards
1
Q
What Are enzymes
A
Biological catalysts speeds up chemical reactions or the rate at which equilibrium is reached
2
Q
What are the special features of enzymes
A
- There Catalysts
- Effecient - Can increase rate of rection by factor of
- 1020
- Specific - have limited range of substrates and some can distinguish Steroisomers
- Potent - Can covert many substrate molecules into products in seconds
3
Q
What is Activation Energy
A
- The energy needed to put atoms/molecules in a position where they are unstable and ready to break
- This is know as the Transition state
- Once achieved the rest of the reaction is automatic
- No-futher energy is needed
4
Q
How do enzymes speed up chemical reactions
A
- They lower the activation energy (hence less energy is needed to put atoms in the unstable stage)
- Enzymes make it easier to reach the transition state
5
Q
What is the transtion state
A
- Reaction intermediate species which has the greatest free energy
- Enzymes reduce the activation energy by providing an alternative reaction pathway
6
Q
What is the Glycogen Storage Disease
A
- Enzyme dificiency that results in failure of glycogen to enter transition state/Phophorylated state
- Cannot get Glucose production from glycogen
- Defective glyogen synthesis in muscle,liver and kidney
- 11 varient defects in 12 glycogen or glucose metabolising enzymes
- Von gierkes diease - most common
- Glucose 6 phosphotase deficiency
7
Q
What are the symptoms of von gierkes disease
A
- Hypoglycaemia
- Hepatomygly
- Skin and mouth ulcers
- Bacterial and fungal infeciton
- Bowel inflammation and irritability
8
Q
What is the Treatment for von gierkes disease
A
- Slow release glucose meal - Corn-starch
- Feed little and often - Mimics glycogen conversion to glucose
9
Q
What are Co-factors and Co-enzymes
A
Assist enzymes in their catalysing acitivity
- Co-factor - Metal ions, inorganic
- Co-enzymes - Organic molecules
10
Q
How do Co-factors associate with enzmyes
A
- Form co-ordination centre in enzyme
- enzymes becomes Metalloprotein
11
Q
how do co-enzymes associate with enzymes
A
- Temporarily associate with enzymes
- They can change charge or structure during the course of the reaciton but are regenerated
- Tightly bound co-enzymes are prothetic groups
12
Q
what are Prothetic groups
A
When a co-enzyme bind tightly to an enzyme
13
Q
what are apoenzymes
A
Enzymes without a co-factor
14
Q
What are holoenzymes
A
Enzymes with co-factors
15
Q
Give examples of co-factors
A
- Zing, iron, copper
- Involved in Redox reactions
- Stabalise transition state
16
Q
Give examples of Co-enzymes
A
- Derivatives of vitamines
- NAD+ and FAD - Redox reactions
- Group transfer processses
- Co-enzmye A- transfers acteyl groups
- ATP- Transfers Phosphate groups
17
Q
Specific example of a Co-enzmye
A
- Vitamines
- Symptoms of vitamine deficiencies reflect the loss of specific enzyme activities
- Deficiencies may be dietary or functional
18
Q
What is a common co-enzyme for redox reactions
A
- NAD+
- NAD+ <–> NADH
- Easily regenerated
- May donate or recieve electrones during catalysis
19
Q
What are 2 features of enzyme-substrate binding
A
- Lock and key model- Active is complementory to substrate shape
- Induced fit model- Binding induced a confromation change in enzyme = Complementory fit
Example: Hixokinase upon binding glucose
20
Q
What are Serine Proteases
A
- Enzymes
- Cleave peptide bonds at specific sites
- 3 Types
- Contain reactive serine residues
21
Q
What is Chymotripsin active site
A
- Hydrophobic pocket which binds
- aromatic amino acids
22
Q
What is the Trypsin active site
A
- Negatively charged ASP (asparic acid) Interacts with postively charged Lys or Arg
23
Q
What is the Elastase active site cleavage
A
- Partially blocked
- Only amino acid will small or no side chains can binds
- small hydrophic pocket - hydrophobic amino acids
24
Q
What are isoenzymes
A
- Isforms of enzymes
- Catalyse the same reaction but have different properties and structure
25
Where are isoemzymes found
* Synthesised at different faetal and embryonic development
* Present in different tissues
* Present in different cellular locations
26
Give an example for an **Isoenzyme**
**Lactate Dehydrogenase**
27
What are the two Subunits of **Lactate Dehydrogenase**
* **H**(heart) - promotes aerobic metabolism
* **M**(Mucle)- Promotes anaerobic metabolism
Under normal O2 you get translation of the **H** form subunit
Under low O2 stress you get the **M** form
these sub-units then come together to form the enzyme which can have a mix of the sub-units or just 1 fromv
28
which which disease will you get increased formation of lactate dehydrogenase **M subunit**
* Heart disease
* Stroke
* Cancer
Anything that can cause hypoxia
29
What is the significance of the isoenzyme **Creatine Kinase**
* Can be used to diagnose Heart attack or stroke
* **B** form appearance in blood = Stroke
* **MB** from appearance in blood = MI
30
How are enzymes regulated by **Reversible covalent modification**
**phosphrylation/Dephosphorylation**
* Can activate and inactivate enzymes
* Example: Glycogen phosphatase - Converted from inactive (a) to active (b)
31
What do kinases and phosphotases do
* Kinase = phosphorylation
* Phosphotase = Dephosphorylation
32
How are enzymes regulated by **irriversible covalent modification**
* **Zymogens -** inactive precursors of an enzyme
* Irreversible transformed into an active enzyme but cleavage of a covalent bond
33
what are **zymogens**
Inactive precursors of enzymes
34
Given an example of irreversible covalent modification of an enzyme
* **in pancreas**: trypsinogen and chymotrypsinogen, inactive precursors, are formed
* **in small intestine:** enteropeptidase cleaves trypsinogen to form active trypsin which cleaves chymotrypsinogen to form active chymotrypsin
35
What is **irreversible proteolytic modification**
Some enzymes are regulated by partial proteolysis
36
Answer these Questions
