Table of Contents
Enzymes Involved in Photosynthesis
Enzymes Involved in Respiration
Enzymes Involved in DNA Replication
Enzymes Involved in Recombinant DNA Technology
What are Enzymes?
Enzymes are protein molecules that accelerate the rate of a chemical reaction in living organisms without themselves being used or altered in the process. An exception in this case are ribozymes that are RNA enzymes. The enzymes are highly specific molecules that form a complex with the substrate, fasten the reaction, form a complex with the product and later detach from the product molecule.
There are a number of enzymes that get used in different processes such as photosynthesis, respiration, DNA replication and are a source of very important questions in entrance examinations. Below is a list of enzymes that are important for biology NEET 2023 preparation.
Enzymes Involved in Photosynthesis
- RuBisCO: Ribulose 1,5-bisphosphate carboxylase-oxygenase or RuBisCO is a dual functioning abundant enzyme that has active sites for both O2 and CO2. It is involved in the carboxylation reaction of the Calvin cycle where it binds with the substrate RuBP for the addition of a sixth carbon molecule, i.e., CO2. It has competitive binding with CO2 and O2 that depends upon the concentration of these molecules. If the ratio of CO2 : O2 is higher, then the enzyme binds with CO2 and photosynthesis occurs.
On the other hand, if O2 is more concentrated in the environment, photorespiration will occur which is a wasteful process.
Enzymes of C4 Pathway
- Phosphoenol Pyruvate Carboxylase (PEP Case): It is an enzyme that is located in the mesophyll cells of the C4 plants. Unlike RuBisCO that has a dual functionality and can bind with both CO2 and O2, PEP Case is an exclusive enzyme that brings about only carboxylation. It binds with a three-carbon molecule PEP and a molecule of CO2 to form a four-carbon compound called oxaloacetic acid. This is the initial step of the C4 pathway.
- Malate Dehydrogenase: It is an enzyme that is involved in the initial carbon fixation in the C4 pathway. It functions to convert the oxaloacetic acid into malic acid or sometimes into aspartic acid.
- Decarboxylase: In the next step, the malic acid is transported to the bundle sheath cells via plasmodesmata. Here, the malic acid is decarboxylated and deaminated to form CO2 and pyruvic acid.
- Phosphopyruvate dikinase: The next step in the C4 pathway is regeneration of PEP. In this step, the pyruvic acid is converted to PEP with the help of phosphopyruvate dikinase at the expense of 2 ATPs.
Enzymes Involved in Respiration
- Pyruvate Decarboxylase and Alcohol Dehydrogenase: Alcoholic fermentation takes place under anaerobic conditions where the pyruvic acid is converted into ethanol and CO2. It is first converted into acetaldehyde by pyruvate decarboxylase and a CO2 is released (decarboxylation) and then the acetaldehyde is converted into ethanol by the alcohol dehydrogenase enzyme.
- Lactate Dehydrogenase: Lactic acid fermentation is another type of anaerobic respiration where the pyruvate is converted into lactate without any release of CO2. This reaction uses NADH which gives electrons and hydrogen to pyruvate for conversion to lactate.
- Electron Transport Chain: Electron transport chain is a series of redox reactions where a chemical gradient is created by taking electrons from electron carriers. It is an important part of aerobic respiration that produces large amounts of ATP via oxidative phosphorylation. It uses a bunch of enzyme complexes that are important for NEET biology. Let us look at them one by one.
- NADH Dehydrogenase (Complex I): It functions to oxidise the NADH + H+ produced during Krebs cycle in mitochondria and then the electrons are transferred to ubiquinone (UQ) which is an electron carrier.
- Succinate Dehydrogenase (Complex II): It functions to oxidise FADH2 and the electrons are taken away by the electron carrier ubiquinone.
- Cytochrome bc1 (Complex III): It functions to accept electrons from reduced ubiquinone (ubiquinol) and passes it on the mobile carrier cytochrome c.
- Cytochrome c oxidase complex (Complex IV): It consists of two copper centres, cytochrome a and cytochrome a3. It accepts electrons from cytochrome c and passes it on to oxygen which is the final electron acceptor.
- ATP synthase (Complex V): The electrons that are passed from complex I to IV in the electron transport chain are coupled to ATP synthase to produce ATP from ADP inorganic phosphates.
Enzymes Involved in DIgestion
- Enzymes found in the Buccal cavity: The saliva contains salivary amylase or ptyalin that converts starch (polysaccharide) into maltose (disaccharide). It also contains lysozymes that show antibacterial activity.
- Enzymes in the Stomach: The stomach has three types of cells: mucous neck cells, chief cells and parietal cells. The chief cells produce the proenzyme pepsinogen. Parietal cells secrete HCl and intrinsic factors that activate the pepsinogen to the active pepsin enzyme. Pepsin in the stomach converts proteins into proteoses and peptones.
| Rennin is an enzyme found only in the gastric juices of infants that helps in the digestion of milk proteins. |
|---|
- Pancreatic Enzymes: The pancreatic juice consists of
- Trypsinogen: It is the inactive form which is converted into its active form called trypsin by enterokinase (secreted by intestinal mucosa). The active trypsin enzyme further activates various pancreatic enzymes.
- Lipase: It converts fat into simpler forms of diglycerides and monoglycerides.
- Chymotrypsinogen: It helps amylase in the conversion of polysaccharides into disaccharides.
- Nuclease: It breaks down nucleic acids into nucleotides.
- Amylase: It converts polysaccharides into disaccharides.
- Procarboxypeptidase: It also helps amylase in the conversion of polysaccharides into disaccharides.
- Enzymes in Small intestine: The intestinal juice consists of
- Dipeptidases: It converts dipeptides into amino acids.
- Lipases: The lipases convert the diglycerides and monoglycerides into fatty acids and glycerol.
- Disaccharidase: Maltase breaks maltose into two glucose molecules, lactase breaks lactose into glucose and galactose, and sucrase breaks sucrose into glucose and fructose.
- Nucleotidases: It breaks the nucleotides into nucleosides and eventually into sugars and bases.
- Carbonic anhydrase: It is an enzyme that is found in high concentrations in RBCs and some amounts are found in plasma too. It converts CO2 and H2O into bicarbonate ions (H2CO3–)
Enzymes Involved in DNA Replication
- Helicase: It is an enzyme that is found at the origin of replication and helps in the unwinding or separating of the two strands of DNA.
- DNA dependent DNA Polymerase: Also known as DNA Polymerase III, this enzyme catalyses the polymerisation of deoxynucleotides. It is an efficient enzyme that can add a large number of nucleotides to the growing strand accurately and quickly.
- Primase: Though DNA Pol III is an efficient and fast enzyme, it cannot start the process of addition of nucleotides and primase comes to rescue. It adds primers to the DNA strands that give a kick start for the addition of nucleotides.
- DNA Ligase: It is a glue-like enzyme that fills gaps between the fragments, be it Okazaki fragments or fragments formed after removal of primers.
Enzymes Encoded by Lac Operon
The lac operon consists of three structural genes – lacA, lacZ and lacY. All the three genes code for different enzymes. Let us look at them.
- 𝛃-galactosidase: It is encoded by lacZ gene that breaks lactose into glucose and galactose.
- Permease: It is a cell membrane bound enzyme that is encoded by lacY gene. It makes the cell membrane of E.coli permeable for entry of lactose molecules.
- Transacetylase: It is encoded by the lacA gene and helps in trans-acetylation reactions. Proper function of the enzyme is not known.
Commercially Produced Enzymes
- Lipase: Lipase, found in detergents, is used to dissolve fat and oil molecules.
- Pectinase & Protease: It is used to cleave pectin and peptide bonds respectively. It is usually found in bottled juices that clarifies or gives transparency to the juices.
- Streptokinase: It has been extracted from the bacteria Streptococcus. It is a clot buster that is used to remove blood clots formed during myocardial infarction.
Enzymes Involved in Recombinant DNA Technology
- Restriction Enzymes: Restriction enzymes (RE) are enzymes extracted from certain bacteria that cut the DNA molecule at specific sites called restriction sites. These enzymes belong to a larger family of enzymes called nucleases. The nuclease can be of two types – Exonucleases: they cut the DNA molecule at the ends; Endonucleases: they make cuts within the DNA molecules. These enzymes recognize a palindromic sequence within the DNA molecule and make cuts at the site. Depending on the type of cut, they either produce sticky ends or blunt ends.
- DNA Ligase: The sticky ends produced by the restriction enzymes are stitched or glued back by the DNA ligase enzyme.
- Adenosine deaminase (ADA): It is an enzyme that is important for the synthesis of lymphocytes and hence is crucial for the immune system.
- Phenylalanine Hydroxylase (PHL): It converts phenylalanine into tyrosine. When the enzyme becomes non-functional due to some reasons, phenylalanine starts building up and tyrosine becomes deficient. Deficiency of tyrosine results in reduced brain development and other neurological functions as it helps in the synthesis of various neurotransmitters.
This is all about the important enzymes of Biology Class 12 that are crucial for NEET 2023. Stay tuned with BYJU’S for more updates on NEET.
Recommended Video:
Also Read:
Comments