The flux of metabolites through metabolic pathways involves
catalysis by numerous enzymes. Active control of homeostasis is achieved by the regulation of only a small number of enzymes.
Active sites of the enzyme is that point where substrate molecule bind for the chemical reaction. It is generally found on the surface of enzyme and in some enzyme it is a “Pit” like structure
The active site is a three-dimensional cleft formed by groups that come from different parts of the amino acid sequence
The active site takes up a relatively small part of the total volume of an enzyme
Active sites are clefts or crevices
Substrates are bound to enzymes by multiple weak attractions.
The specificity of binding depends on the precisely defined arrangement of atoms in an active site.
Enzymes properties, nomenclature and classificationJasmineJuliet
Enzymes - Definition, Introduction about biocatalysts, Properties of enzymes, Specificity, capacity for regulation, Example for enzyme at specific pH, Nomenclature of enzymes, Systematic name, common name, enzyme commission number, Classification of enzymes: Oxidoreductase, Transferase, lyases, ligases, isomerases, hydrolases.
An enzyme is a biological catalyst and is almost always a protein. It speeds up the rate of a specific chemical reaction in the cell. The enzyme is not destroyed during the reaction and is used over and over.
The flux of metabolites through metabolic pathways involves
catalysis by numerous enzymes. Active control of homeostasis is achieved by the regulation of only a small number of enzymes.
Active sites of the enzyme is that point where substrate molecule bind for the chemical reaction. It is generally found on the surface of enzyme and in some enzyme it is a “Pit” like structure
The active site is a three-dimensional cleft formed by groups that come from different parts of the amino acid sequence
The active site takes up a relatively small part of the total volume of an enzyme
Active sites are clefts or crevices
Substrates are bound to enzymes by multiple weak attractions.
The specificity of binding depends on the precisely defined arrangement of atoms in an active site.
Enzymes properties, nomenclature and classificationJasmineJuliet
Enzymes - Definition, Introduction about biocatalysts, Properties of enzymes, Specificity, capacity for regulation, Example for enzyme at specific pH, Nomenclature of enzymes, Systematic name, common name, enzyme commission number, Classification of enzymes: Oxidoreductase, Transferase, lyases, ligases, isomerases, hydrolases.
An enzyme is a biological catalyst and is almost always a protein. It speeds up the rate of a specific chemical reaction in the cell. The enzyme is not destroyed during the reaction and is used over and over.
This slideshow explains the details about Photosynthesis process. It has covered all the aspects such as definition, significance, photosystems, Hill reaction, Calvin cycle, HSK cycle, CAM pathway, Photorespiration, etc. of photosynthesis. This slide show will be useful to College students and the students who are appearing for various competitive examinations. .This slide show is equally beneficial to the students who want to pursue career in the biological sciences.
This slide is about academic and administrative audit for the quality control in the educational institutes. it also deals with various management techniques including Kaizen, 5S, etc. This slideshow is useful for the NAAC purpose.
This slideshow explains the complete process of writing research proposal for funding agencies. It is useful for the PhD students, researchers, R& D department of company personnel.
This slideshow is related to testing of hypothesis and goodness of fit of statistics. This may be useful for students, teachers, managers concerned with bio statistics, bioinformatics, data science, etc.
This slide show is related to measures of dispersion or variability in Statistics. This slideshow will be useful to all the students and persons interested in Statistics, Bio statistics, Management, Education, Data Science, etc.
This slideshow explains the important measures of central tendency in statistics. It deals with Mean, mode and median; its characteristics, its computation, merits and demerits. This slideshow will be useful to students, teachers and managers.
This slideshow describes about type of data, its tabular and graphical representation by various ways. It is slideshow is useful for bio statisticians and students.
This slide explains term biostatistics, important terms used in the field of bio statistics and important applications of biostatistics in the field of agriculture, physiology, ecology, genetics, molecular biology, taxonomy, etc.
This slide show is about overview of building blocks of life i.e. amino acids. It is describes physical, chemical properties, classification, biological functions, modified products of amino acids and biosynthesis of amino acids.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
1. Overview of Enzymes
Dr. Anil V Dusane
Sir Parashurambhau College
Pune, India
anildusane@gmail.com
1
2. Introduction
• Kuhne (1868) coined term ‘Enzyme’.
• Eduard Buchner named the enzyme that brought about the
fermentation of sucrose, ‘zymase’.
• Enzyme (En = in, Zyme = yeast) is a Greek work that refers to the
occurrence in yeast of something responsible for its fermentative
activity.
• Enzymes are indispensable compounds that play key role in
metabolism by bringing direction and control to the physiological
processes of the living cells.
2
3. Definition of enzyme
• Enzymes are also called as Biological catalyst, ‘Biocatalyst’, a
substance (enzyme) that initiates or modifies the rate of a
chemical reaction in a living body.
• Definition: Enzymes are organic substances (simple or
compound proteins) capable of catalyzing reactions in living
systems.
• Enzyme initiates and accelerate biochemical
reactions and lowers activation energy (energy
required to carry out reaction) in the cell.
3
4. Nomenclature and classification
• Named according to the substrate they attack (protease, lipase, DNAase
etc.) or the type of reactions they catalyze (oxidases, reductases,
transaminases, etc).
• Enzymes are complemented with suffix ‘ase’.
• International Union of Biochemistry IUB (1972) has recognized six
major classes of enzymes based on reactions they catalyzes.
Rules of IUB for nomenclature and classification of enzymes
• Each enzyme has a systematic code number (E.C.) of four digits.
• First digit indicates main class
• Second digit indicates subclass.
• Third digit indicates subdivision of sub-class(sub-subclass)
• Fourth digit designates the serial number of specific enzyme in the
fourth sub-class. 4
5. Nomenclature
• E.g. E.C.1.1.1.1 stands for enzyme dehydrogenase where
E.C. stands for Enzyme Commission
1. Stands for oxidoreductase,
1.1 for enzyme which utilizes substrate as –CHOH (alcoholic group),
1.1.1 stands for those enzymes which utilizes NAD as acceptor.
• Lactate dehydrogenase is an oxidoreductase is written as
EC 1.1.1.27.
5
7. Classes of enzymes
1. Oxido-reductases
• Catalyze biological oxidation and reduction
• One compound is oxidized and another reduced.
• Deydrogenases-catalyses removal of 2 atoms of hydrogen
• Oxidases-catalyses the reduction of O2
• Oxygenase-catalyse incorporation of O2 in to substrate
• Peroxidases-use of H2O2 as oxidant
• E.g. dehydrogenases, oxidases, oxygenases, oxidative
deaminases, hydroxylases and peroxidases.
7
8. Classes of enzymes
2. Transferases
• Bring about the transfer a group from one molecular to another.
• Catalyses exchange of groups between two substrates AB + CD =
AC + BD.
• aminotransferases catalyze exchange of amino and keto group
between amino and keto acid
• Glutamic acid + OAA ==(transaminase) -glutaric acid +
aspartic acid
• Eg. transaminases, kinases, hexokinases, etc.
8
9. Classes of enzymes
3. Hydrolyses
• Catalyses hydrolysis of complex substrates into simpler ones.
• Starch into glucose
• AB + HOH ---- AH+ + BOH- (AB substrate)
• Sucrose + H2O ---------- (sucrase, invertase) glucose + fructose
• E.g. carbohydrases, esterases, proteases, etc
• Catalyses hydrolysis reaction AB + H2O = A.OH + HB. Add H2O and breaking
substrate
i)peptidases-catalyses hydrolysis of peptide bonds
ii)glycosidases- catalyses glucosidic bonds.
iii) deaminases-catalyses hydrolysis of amines
iv)Sucrase- Sucrose + H2O sucrase invertase= Glucose + fructose
9
10. Classes of enzymes
4. Lyases
• Result in a direct removal of groups from substrate non-
hydrolytically
• AB = A + B
• Lyases act on C-C-, C-O, C-N, C-S and C-halide bonds.
• In most of the cases coenzyme is required for the activity.
E.g. Decarboxylases, aldolases, dehydratases, etc.
10
11. Classes of enzymes
5. Isomerases
• Catalyses isomeric changes (Isomerization) so called as
isomerases.
• Catalyses isomerization of substances (substrates) optical or
structural isomers
• Eg. Isomerase, epimerase
• Glucose-6-phosphate == (phosphohexose isomarase) Fructose-
6-phosphate.
11
12. Classes of enzymes
6. Ligases (synthetases)
• Catalyze the joining of two molecules coupled with the
breakdown of a pyrophosphate bond in ATP
• Catalyze synthesis of different types of bonds such as C-N, C-S,
C-O etc.
• Glutamate + NH3+ ATP ------(glutamine synthetase) glutamine +
ADP + Pi
12
13. Chemical nature of enzymes
Enzymes are proteinaceous in nature.
Some enzymes also contain a non–protein group
or prosthetic.
Protein part of enzyme is also called apoenzyme
Complete enzyme with prosthetic group is called
as holoenzyme.
Organic prosthetic groups are called coenzymes
while inorganic prosthetic group is called cofactor
Protein part (apoenzyme) + non-protein part
(prosthetic group) = holoenzyme.
13
14. Properties of enzymes
1. Specificity
•Each enzyme is specific in the sense bond
specificity, group specificity, substrate
specificity, optical specificity, geometrical
specificity and co-factor specificity.
•Enzymes it can operate only upon certain
substrate or group of substrates.
•Each enzyme act only upon substances having a
certain molecular pattern and can affect only
one particular type of chemical bond only.
•Many enzymes apparently act on only a single
kind of substrate. E.g. urease can act only upon
urea and no other molecules. 14
15. Properties of enzymes
2. Colloidal nature
• Molecules of enzymes are large in size and characterized as the
particles of colloidal systems.
• Colloidal nature provides an extensive surface area for chemical
reactions
3. Proteinaceous in nature
• All enzymes except ribozymes are protein in nature.
• React with both acidic and alkaline substances.
• Soluble in water, salt solution, alcohol and dilute glycerin.
15
16. Properties of enzymes
4. Catalytic activity
• There may positive or negative catalysis. However, there is mostly positive catalysis
• Small quantity of enzyme can bring about transformation of vastly large amounts of
the substrate.
• Enzymes can function at very low conc.
• Rate of reaction is directly proportional to enzyme concentration
• Invertase catalyzes the conversion of at least 1,000,000 times its own weight of
sucrose.
5. Thermolabile:
• Enzymes are proteins hence they are thermolabile (sensitive to temperature). At
60-700C enzymes are destroyed. This due to the heat coagulation phenomenon.
• There is always a specific temperature of optimum activity of every enzyme, which
usually ranges from 250C to 450C.
• Enzymatic action is highest at 370C and enzymes.
16
17. Properties of enzymes
6. Enzyme inhibitors:
• These are certain product that inhibits enzyme activity
• During reaction, the active sites of the enzymes are filled up with
these inhibitors instead of substrate molecules
• Drugs, antibiotics and poisons inhibit enzyme inhibitors.
7. Reversibility of action:
• Enzymes can accelerate the rate of reaction in whichever direction
it is taking place, provided suitable sources of energy available.
• Usually a single enzyme brings about the synthesis and digestion
(hydrolysis) of a particular substance.
17
18. Factors affecting enzyme activity
1. Temperature
• Low temperature inactivates proteins.
• At high temperature protein looses secondary
and tertiary structures.
• Enzyme activity gets doubled at every 10oC.
• Kinetic energy increases as temperature
increases.
• An enzyme shows maximum activity at
optimum temperature 25-30oC.
• However, beyond 60-70oC the enzyme activity
is permanently stopped
18
19. Factors affecting enzyme activity
2. pH
• Most of the enzymes are extremely sensitive to
pH
• Wrong pH denatures enzymes, disturbs ionic
state of enzyme and substrate.
• It also affects the binding of prosthetic group
• Optimum pH shows better enzyme activity
• In general pH range 5-9.
• catalase shows optimum activity at 9.0 pH
19
20. Factors affecting enzyme activity
3. Substrate concentration
• Increased concentration of substrate brings about an increase
in the activity of enzyme
• Beyond a particular point though we increase the
concentration of substrate there is no change in enzyme
activity
• Active sites of enzymes become saturated; no active sites are
available, so the rate remains same though the concentration
increases.
4. Enzyme concentration
• Rate of reaction follows the increased concentration of
enzyme until there is enough concentration of substrate is
present
• Invertase catalyzes the conversion of at least 100000 times its
own weight of sucrose.
20
21. Factors affecting enzyme activity
5. Effects on ions
• Hydrogen ion concentration is the most important factor in activity of
all enzymes.
• Cations like Mg++, Ca++, Na+, Zn++, K+ also play an important role in
activity of certain enzymes
• Enzymes in the absence of particular cation remain inactive.
6. Accumulation of end products
• It retards the rate of reaction due to change in pH of enzyme solution.
• Enzyme become inactive and increase in the rate of reverse reaction
21
22. Enzyme inhibitors
• Specific chemicals can inhibit most of enzymes
• Two types of inhibitors irreversible and reversible
• Irreversible inhibitors
• These combine with or destroy a functional group on
enzyme molecule that is necessary for its catalytic
activity
• E.g. Di-iso Propyl Fluorophosphate (DPF) that inhibits
enzyme cholinesterase.
• Irreversible inhibition results from the formation of
stable enzyme inhibitor (EI) complex that results in
complete inhibition of the enzyme.
• E.g. inhibition of Xanthine oxidase by CN-.
22
23. Reversible inhibition
• Inhibitors do not cause permanent damage in the
functional groups and once these inhibitors are
removed the enzyme become fully active.
• There are mainly two types viz. competitive
inhibition and non-competitive inhibition.
Competitive inhibitors
• A competitive inhibitor competes with the substrate
for binding to the active site but once bound can not
be transformed by the enzyme.
• These inhibitors usually resemble to normal
substrate in 3D structure and can bind with the
active site of enzyme in the same way as normal
substrate molecule binds.
23
24. Reversible inhibition
• The inhibitor molecules can not be attacked by enzyme molecule
and since their active site is occupied, they become non-
functional for normal substrate also.
• Competitive inhibitor increases Michalis constant, but it has no
effect on Vmax.
• Many antibacterial drugs work on principle of competitive
inhibitors of bacterial enzymes.
• Inhibition of succinic dehydrogenase by malic acid.
Ki
• E+I ======= EI where E enzyme, I inhibitor, Ki inhibitor
association complex.
24
25. Reversible inhibition
Non-Competitive inhibitors
• Not very specific and they bind at the site on the enzyme other than the
catalytic site.
• It alters the configuration of enzyme molecule so that the reversible
inhibition of enzyme activity occurs.
• Inhibition is not reversed by increasing concentration of substrate.
• Heavy metals and cyanide act as non-competitive inhibitors of enzymes.
• The level of inhibition is controlled by concentration of inhibitor
• Non-competitive inhibitors decrease the Vmax of the enzyme but they
have no effect on Km.
• Eg. Cytochrome oxidase
25
26. Allosteric inhibition
• In this type of inhibition the inhibitor which is structurally quite
different from the substrate is bound at a site other than the
active site of enzyme.
• This binding of the inhibitor alters the conformation of the
enzyme proteins and there by prevents it from binding to the
substrate.
• Since the inhibitors bind at a site other than the active site of
the enzyme they are called allosteric effectors or determinant
and the site to which they bind, allosteric sites (allows=other)
• The whole phenomenon is called as allosteric effect or
feedback inhibition and it is always reversible.
• Allosteric inhibition has a great physiological and biochemical
importance.
• Allosteric enzymes are formed by the aggregation of many
subunits
26
27. Activators
• Enzyme activators are molecules that bind to enzymes and
increase their activity.
• These are the opposite of enzyme inhibitors. These molecules
are often involved in the allosteric regulation of enzymes in the
control of metabolism.
• Activators like Mg++, Ca++, Mn++ etc. may take part in the
formation of enzyme-substrate complex.
• Mn++ in the action of some peptidases may prevent the
inactivation of the enzyme by inhibitors.
• E.g. kinases - enterokinases converts trypsinogen into trypsin
27
28. Coenzymes
• Many reactions of substrate are catalyzed by enzymes
only in the presence of non-protein organic molecule
called coenzyme.
• Coenzyme combines with the apoenzyme (protein part)
to form holoenzyme.
• Coenzymes are small molecular weight organic,
dialyzable, thermostable compounds.
• Required for the catalytic activity of one or more group
of enzymes.
• Co-enzymes are heat-stable non-protein organic
molecules.
• Examples: Nicotinamide Adenine Dinucleotide (NAD),
riboflavin coenzyme, coenzyme-A, lipoic acid, etc.
28
29. Coenzymes
Classification based on
Chemical characteristics: ATP, NAD, NADP, FMN.
Functional characteristics: CoA, Thiamine PyroPhosphate (TPP).
Nutritional characteristics: Folic acid coenzyme, B12 coenzyme, Biotin
Functions of coenzymes
• To accept atoms or groups from a substrate and transfer them to other
molecules.
• NAD and NADP coenzyme functions as hydrogen acceptor in dehydrogenation
reactions.
• Main function of CoA is to carry acetyl groups and they are used in oxidative
decarboxylation of pyruvic acid and synthesis of fatty acids and acetylation.
• Pyridoxal phosphate (B6-PO4) is involved in transamination reactions. 29
30. Active sites of enzymes
• It is also known as catalytic activity site
• Some restricted region of the enzymes, which is concerned with
process of catalysis termed as active site.
• One or more regions on the enzyme molecules where the substrate
can bind.
• Shape of the enzyme molecule is such that it will expose some amino
acids so that substrate molecules can bind to it for necessary catalytic
function
• Binding of substrates to the enzyme involves only its active site.
• If the shape of enzyme molecule is altered, the active site is also likely
to be displaced and it hampers the catalytic function.
• If certain enzymes trimmed to smaller sizes they will not loose their
catalytic activity
• E.g. papain may be trimmed to 60 from 180 amino acid residues with
out loosing its activity
30
31. Mode of action of enzyme
• Enzyme substrate-complex theory (most accepted) has
been proposed
Enzyme substrate complex theory
• Michaellis and Menton (1913) proposed to explain mode
of enzyme action.
• Enzymes have certain active sites for the attachment of
substrate molecule where an enzyme can form an intimate
relationship with substrate.
• Enzyme forms a weakly bound compound with substrate
which on hydrolysis decomposes into the reaction
products.
• In simple form theory can be represented as follows
• Enzyme + substrate (ES) ===== enzyme substrate complex
(ES) === End products (P) + enzyme (E)
31
32. Models for Active site
Rigid model of active site (lock and Key model)
• According to this enzyme and substrate are strictly
complementary structures
• During the complex formation, substrate fits exactly with the
active site of enzyme as a key fits into a lock.
Flexible model of active site (Induced fit model)
• According to this, the active site is not very rigid and its
configuration changes according to the substrate configuration
so that there is an induced fit between enzyme and substrate
32
33. Models to explain mode of enzyme action and their specificity
• Two models viz. Lock-key model and Induced fit
model has bee proposed
Lock-key model
• Fischer (1898) proposed this model which was later
advanced by Paul Fields and D.O. Woods.
• According to this model the enzyme-substrate
complex formation is analogous to the fitting of lock
and key.
• During the complex formation, substrate fits exactly
with the active site of the enzyme as a key fits into a
lock.
• As a particular lock can be opened by a particular key
in the same way particular enzyme acts on a
particular substrate
33
34. Lock and Key model
• This theory depends on physical contact between substrate and enzyme
molecules.
• It is least accepted model as compared to induced fit model.
• This model is rigid, and enzymes do not complimentary to the substrate.
• Catalytic sites are fixed and there is no proper orientation of the active sites
• There is unchangeable configuration of enzymes.
• This theory is supported from the study of competitive inhibition
• Competitive inhibitors have some structural similarity with the substrate
molecule, both of which compete for the same active site on the enzyme.
• If some part of the active site is preoccupied by competitive inhibitors, the
substrate will not be able to combine with it. Thus the activity of enzyme is
inhibited like a wrong key can not open a lock.
34
35. Induced fit model
• Koshland (1959) proposed this model
• According to this model the attachment of
the substrate to the active sites brings about
a change in 3D structure of the enzyme.
• This results in the precise orientation of the
catalytic groups in the enzyme molecule
which causes the enzyme reaction.
• Enzyme changes shape upon binding with
the substrate, when its active sites assume a
shape complementary to that of the
substrate.
35
36. Induced fit model
• According to this theory the active centers of the substrate and
the enzyme fit into each other and they combine to form an
active complex
• Studies of optical rotation measurements and X-ray diffraction
analysis of several enzymatic reactions support this theory
36
37. Questions
• What are enzymes? How are they classified? Describe its mode of action.
• What are enzymes? Write an account of the factors controlling enzymatic reactions.
• What are enzymes? Give an account of the general properties and nomenclature of
enzymes.
• Short notes
i) Lock-key model
ii) Ligases
iii) Induced fit theory
iv) Active sites
v) Competitive inhibitors
37