Enzymes are biological catalysts that speed up biochemical reactions. They have tertiary or quaternary protein structures that form an active site pocket, occupying less than 5% of the enzyme's surface area. The active site binds substrates and contains residues that facilitate reactions. Some enzymes also require cofactors to function. Substrates are molecules acted upon by enzymes to produce products. Intracellular enzymes function inside cells, while extracellular enzymes function outside cells like digestive enzymes.

1. Structure of Enzyme
Presented by-
Bivash Dutta

2. CONTENT-
Enzyme
Structure of enzyme
Active site
Co-factor
Substrate
Intracellular enzyme and Extracellular enzyme

3. Enzyme
 Enzymes are biological catalysts that speed up the
rate of the biochemical reaction.
 Most enzymes are three dimensional globular
proteins (tertiary and quaternary structure).
 Some special RNA species also act as enzymes and
are called Ribozymes e.g. hammerhead ribozyme.

4. Structure of Enzyme
Enzyme have either tertiary or quaternary structure.
The protein chain folds itself and forms pocket like
structure called as active site.
 The active site of an enzyme is the region that binds
substrates, co-factors and prosthetic groups and
contains residue that helps to hold the substrate.
 Active sites generally occupy less than 5% of the total
surface area of enzyme.
 Active site has a specific shape due to tertiary
structure of protein.
A change in the shape of protein affects the shape of
active site and function of the enzyme.
 Substrate is a substance that is acted upon by enzyme.

5. Active Site
The region of an enzyme where substrate
molecules binds and undergo a chemical reaction.
Active site can be further divided into :
• Binding site – it choose the substrate and binds it
to the active site.
• Catalytic site – it perform the catalytic action of
an enzyme

6. Co-factors
A cofactor is a non-protein chemical compound that
is required for the protein's biological activity.
 Many enzymes require cofactors to function
properly.
 Cofactors can be considered "helper molecules" that
assist enzymes in their action.
An enzyme with its co-factor removed is designated
as apoenzyme.
 The complete complex of a protein with all
necessary small organic molecules, metal ions and
other components is termed as holoenzyme of
holoprotein.

7. Substrate
The reactant in a biochemical reaction is termed as substrate.
Enzymes catalyze chemical reactions involving the substrate(s).
 In the case of a single substrate, the substrate bonds with the
enzyme active site, and an enzyme-substrate complex is formed.
 The substrate is transformed into one or more products, which
are then released from the active site.
 The active site is then free to accept another substrate
molecule.

8. Intracellular enzyme and Extracellular enzyme
Intracellular enzymes are synthesized and retained in the cell for the use of cell itself.
They are found in the cytoplasm, nucleus, mitochondria and chloroplast.
 Example :
 Oxidoreductase catalyse biological oxidation.
 Enzymes involved in reduction in the mitochondria.
 Extracellular enzymes are synthesized in the cell but secreted from the cell to work externally.
 Example :
 Digestive enzyme produced by the pancreas, are not used by the cells in the pancreas but are transported to the
duodenum.

9. Reference
https://www.slideshare.net/fatimasaleh94214/enzymes-2-30256325
https://en.wikipedia.org/wiki/Active_site
https://tenor.com/view/enzyme-active-site-substrate-love-gif-14527202
https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/2%3A_Chemistry
/2.7%3A_Enzymes/2.7.2%3A__Enzyme_Active_Site_and_Substrate_Specificity
https://www.britannica.com/science/cofactor