The document summarizes the lock-and-key hypothesis proposed by Emil Fischer in 1894 and the induced fit hypothesis proposed by Daniel Koshland in 1958 to describe enzyme-substrate binding. The lock-and-key hypothesis suggests that enzymes and substrates have complementary geometric shapes that fit exactly. The induced fit hypothesis refined this by proposing that the enzyme's active site is flexible and can change shape upon substrate binding to optimize the interaction. Both hypotheses helped explain the specificity of enzymes for their substrates.

1. ‘LOCK - AND - KEY’ HYPOTHESIS
&
‘INDUCED FIT’ HYPOTHESIS
A PRESENTATION BY UNNIMAYA VINOD
DEPARTMENT OF ZOOLOGY
UNIVERSITY OF KERALA

2. MEN WHO MATTER..

3. INITIAL YEARS OF EMIL FISCHER
 Hermann Emil Fischer (1852–1919) might have gone into
the family lumber business had his father had his way.
 Fischer attended the chemistry lectures of August Kekulé
at the University of Bonn but left to obtain his doctorate at
Strasbourg, under the far more experimentally oriented dye
chemist Adolf von Baeyer.
 Successively holding appointments at various German
universities, Fischer ultimately rose to be chemistry
professor at the University of Berlin.
 In Berlin he was instrumental in establishing the Kaiser
Wilhelm Society (now the Max Planck Society) and its
related institutes for chemistry and physics in 1911.

4. NOTABLE
WORKS
FISCHER INDOLE SYNTHESIS
FISCHER PROJECTION
FISCHER OXAZOLE SYNTHESIS
FISCHER PEPTIDE SYNTHESIS
FISCHER PHENYLHYDRAZINE OSAZONE
REACTION
FISHER ESTERIFICATION
FISCHER GLYCOSIDATION
KILLIANI- FISCHER SYNTHESIS

5. FISCHER’S
LOCK AND KEY HYPOTHESIS

7. SUBSTRATE BINDING
 Enzymes work in a very unique manner. The way that an
enzyme catalyzes a chemical reaction is to start by binding a
substrate or several substrates to an active site on the enzyme.
 This active site is the region on an enzyme that combines with
the substrate. When a substrate and an enzyme bind, the
actions cause the distribution of electrons in chemical bonds of
the substrate to change.
 This eventually leads to a chemical reaction, which leads to the
product.

9. THE LOCK AND KEY MODEL
 The lock and key hypothesis is focused on the active site
The active site of an enzyme has a very unique geometric
shape and it is only complementary to a specific
substrate molecule.
Imagine a puzzle piece. There are only a few pieces that fit
with that one piece. Because the active sites are so
geometrically unique, an enzyme can only work with a
few or just one substrate.

11.  In order to explain why enzymes have such a high level of
specificity, Emil Fischer in 1894 suggested that both a substrate
and an enzyme have specific geometric shapes that fit exactly
into each other.
 This idea of both substrates and enzymes having a natural
geometric fit has been called the lock and key hypothesis.

13. “ACTIVE SITE IS RIGID..”

14. THE WORK THAT BOUGHT HIM
FAME..
The Nobel Prize in Chemistry 1902 was
awarded to Hermann Emil Fischer "in
recognition of the extraordinary services he
has rendered by his work on sugar and purine
syntheses."

15. THE MONUMENTAL WORK

16. KOSHLAND’S INDUCED FIT
MODEL

17. EARLY LIFE OF DANIEL E. KOSHLAND
 Daniel E. Koshland, Jr., was a giant in the field of biochemistry,
making important strides in knowledge of the properties and
activities of enzymes and bacteria.
Koshland majored in chemistry at the University of California,
Berkeley, before serving as a group leader, working to purify
plutonium, in the Manhattan Project during World War II.
He was a Member of the United States National Academy of
Sciences and established the Academy’s Marian Koshland
Science Museum in honor of his wife, Marian Koshland, a
noted immunologist.

18. NOTABLE
WORKS
 CHEMOTAXIS IN BACTERIA
 EXTERNAL SENSORS IN BACTERIA
 PROTEIN PHOSPHORYLATION IN BACTERIA
 ARTIFICIAL ENZYME
 INDUCED FIT MODEL

19. INDUCED FIT MODEL
 An offshoot of the previous model, the current model supports a more
refined view of enzyme-substrate binding.
 As the enzyme and substrate come together, their interaction causes a
mild shift in the enzyme’s structure that confirms an ideal binding
arrangement between the enzyme and the substrate .
 This dynamic binding maximizes the enzyme’s ability to catalyze the
reaction.

20. “ACTIVE SITE IS NOT RIGID..”

25. REFERENCES
 www.britannica.com
www.socratic.org.in
 www.biologyonline.com
 www.vedantu.com
 www.courses.lumenlearning.com
 www.khanacademy.org