40 Questions
What is the minimum requirement for enzyme activity?
Contact between enzyme and substrate
How does the velocity of an enzyme reaction change with an increase in enzyme concentration?
The velocity of the reaction increases proportionately
What is the shape of the curve obtained when velocity is plotted against substrate concentration?
A rectangular hyperbola
What is the order of the reaction when the velocity of the reaction is almost proportional to the substrate concentration?
First order
What happens to the velocity of an enzyme reaction when the temperature increases up to a maximum?
The velocity increases and then declines
What is the name of the graph that shows the effect of substrate concentration on enzyme velocity?
Figure 2
What happens to the rate of reaction when the substrate concentration is much greater than Km?
The rate of reaction becomes independent of substrate concentration
What is the term used to describe the rate of reaction when the velocity of the reaction is almost proportional to the substrate concentration?
First order reaction
What is the primary reason for the existence of an active site in an enzyme?
The tertiary structure of the protein.
Which of the following amino acids is most frequently found at the active site?
Serine
What is the role of the catalytic site in the active site?
To catalyze the specific reaction.
What is the type of bonds involved in the binding of substrate to the active site?
Weak noncovalent bonds.
What is the term for the small region in a big enzyme molecule where the active site is located?
All of the above
Why are enzymes specific in their function?
Due to the existence of active sites.
What is the purpose of coenzymes in enzyme-catalyzed reactions?
To provide additional catalytic activity.
What is the result of the substrate binding to the active site?
The enzyme-substrate complex is formed.
What information does an enzyme's name typically indicate?
The substrate, coenzyme, and reaction type
Which class of enzymes catalyzes the reaction of oxidation and reduction?
Oxidoreductases
What is the reaction catalyzed by the enzyme hexokinase?
Group transfer
Which enzyme class includes lipase and choline esterase?
Hydrolases
What is the reaction catalyzed by the enzyme aldolase?
Addition and elimination
What is the EC number of the enzyme cytochrome oxidase?
Not specified in the text
Which enzyme class catalyzes the reaction of hydrolysis?
Hydrolases
What is the reaction catalyzed by the enzyme alcohol dehydrogenase?
Oxidation and reduction
What is the term applied to a substrate or an intermediate or a product in metabolic reactions?
Metabolite
What is the primary purpose of catabolism?
To trap the energy of biomolecules in the form of ATP
What is the term for the degradative processes concerned with the breakdown of complex molecules to simpler ones?
Catabolism
What is the term for the biosynthetic reactions involving the formation of complex molecules from simple precursors?
Anabolism
What is the collective term for the entire spectrum of chemical reactions occurring in a living system?
Metabolism
How many stages does catabolism occur in?
Three
What is the result of catabolic reactions?
Energy is released and simpler molecules are formed
What is the term for a series of enzymatic reactions to produce specific products?
Metabolic pathway
What is the end result of the final oxidation of acetyl CoA in stage 3 of catabolism?
Release of CO2
What is the primary function of Krebs cycle in catabolism?
Oxidation of carbon compounds from carbohydrates, lipids, or proteins
What is the primary source of energy for anabolic reactions?
ATP or GTP
What is the main difference between anabolic and catabolic pathways?
Anabolic and catabolic pathways are not reversible and operate independently
What is the purpose of the first stage of catabolism?
Breakdown of complex molecules into simple intermediates
What type of reaction is catalyzed by specific enzymes in metabolic reactions?
All of the above
What is the primary function of the citric acid cycle?
Oxidation of carbon compounds from carbohydrates, lipids, or proteins
What is the role of NADH and FADH2 in catabolism?
Liberating energy during the final oxidation of acetyl CoA
Study Notes
Enzyme Classification
- Enzymes are given specific names indicating the substrate, coenzyme (if any), and the type of reaction catalyzed
- There are six main classes of enzymes: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases
- Each class has specific examples, such as:
- Oxidoreductases: alcohol dehydrogenase, cytochrome oxidase
- Transferases: hexokinase, transaminases
- Hydrolases: lipase, choline esterase, pepsin, urease
- Lyases: aldolase, fumarase, histidase
Factors Affecting Enzyme Activity
- The contact between the enzyme and substrate is essential for enzyme activity
- Factors that influence enzyme activity include:
- Concentration of enzyme: increasing enzyme concentration increases reaction velocity
- Concentration of substrate: increasing substrate concentration increases reaction velocity, but only up to a certain point
- Temperature: increasing temperature increases reaction velocity up to a maximum, then declines
- Active site: the specific region on the enzyme where the substrate binds
Active Site
- The active site is formed by the tertiary structure of the protein
- The active site is made up of amino acids (catalytic residues) that are distant from each other in the linear sequence
- The active site is flexible to promote specific substrate binding
- The active site has a substrate binding site and a catalytic site
- Coenzymes or cofactors are present at the active site
Vitamins and Coenzymes
- Coenzymes are non-protein molecules that assist enzymes in catalysis
- Examples of coenzymes include:
- Coenzyme A (CoA)
- Tetrahydrofolate (FH4)
- Biocytin
- Methyl cobalamin; Deoxyadenosyl cobalamin
Metabolism
- Metabolism is the collective term for all chemical reactions occurring in a living cell
- Metabolism is divided into two categories: catabolism and anabolism
- Catabolism is the breakdown of complex molecules to simpler ones, releasing energy
- Anabolism is the synthesis of complex molecules from simpler ones, requiring energy
Catabolism
- Catabolism occurs in three stages:
- Conversion of complex molecules into building blocks
- Formation of simple intermediates
- Final oxidation of acetyl CoA to CO2, releasing energy
- The Krebs cycle (or citric acid cycle) is a common metabolic pathway involved in the final oxidation of energy-rich molecules
Anabolism
- Anabolism requires the availability of precursors, energy, and reducing equivalents
- Anabolic reactions are dependent on the supply of energy and reducing equivalents
- The anabolic and catabolic pathways are not reversible and operate independently
Types of Metabolic Reactions
- There are four main types of biochemical reactions:
- Oxidation-reduction
- Group transfer
- Rearrangement and isomerization
- Make and break of carbon-carbon bonds
- These reactions are catalyzed by specific enzymes
This quiz covers the classification of enzymes, including their specific names, substrates, and reaction types. Learn about the different enzyme classes and their functions.
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