20 Must-Know Flashcards for Biochemistry  NEET PG 2026

Flashcard 1

Basic Thumb Rule

All the carbohydrates preferred to link with ⍺ (1,4) linkage along straight chains. At branch points, they have ɑ (1,6) linkage.

Flashcard 2

• Schilling's test is done for B12 malabsorption.
• Guthrie test to detect phenylketonuria
• Methane breath test for adults for lactose intolerance.
• Stool acidity for neonates for lactose intolerance.

Flashcard 3

Structure of Mucopolysaccharides

Mucopolysaccharide which has Glucuronic acid, and Glucosamine is Hyaluronic acid.

Mucopolysaccharide which has Glucuronic acid, and galactosamine is Chondroitin sulfate.

Mucopolysaccharide with Iduronic acid and galactosamine, is Dermatan sulfate.

Mucopolysaccharide which has no acid part and has galactose, is Keratan sulphate.

Flashcard 4

Tips to Identify the Structure

Step 1: Check if there is no acid part, if it has galactose, it is Keratan sulphate.

Step 2: 

• In the uronic acid part, find if it is Glucuronic or Iduronic acid:
• If the carboxyl group is present above the plane of the ring- Glucuronic acid
• If the carboxyl group is present below the plane of the ring- Iduronic acid.

Step 3:

• In the amino sugar part, find if it is Glucosamine or Galactosamine. In the 4th carbon atom (Glucose and galactose are epimers at the 4th carbon position).
• If OH lays below the plane of the ring- Glucosamine
• If OH lays above the plane of the ring- Galactosamine.

1. If the structure has Glucuronic acid + Glucosamine, it is Hyaluronic acid (follows the thumb rules)
2. If the structure has Glucuronic acid + galactosamine, it is Chondroitin sulfate.
3. If the structure has Iduronic acid + galactosamine, it is Dermatan sulfate (with exceptions).
4. If the structure has no uronic acid part, it is Keratan sulfate.

Flashcard 5

• The Mucopolysaccharide with galactose is Keratan sulphate
• Mucopolysaccharide with Iduronic acid are Heparan sulphate and Dermatan sulphate.
• Mucopolysaccharides with galactosamine are Chondroitin sulphate and Dermatan sulphate.
• The Mucopolysaccharide present in the Glomerular Basement membrane is Heparan sulphate.

Flashcard 6 

Paroxysmal Nocturnal Hemoglobinuria

1. The carrier required for N-linked glycoprotein synthesis is Dolichol.

2. Spermine inhibits the synthesis of N-linked Glycoprotein.

3. N-linked glycoproteins are attached to asparagine residues of core proteins.

4. Paroxysmal Nocturnal Hemoglobinuria is caused by a defect of the PIGA gene.

Flashcard 7

Benedict's Test

• Copper sulphate (blue colour)
• Sodium carbonate (Alkaline medium)
• Sodium citrate (Stabilizes the solution)

Flashcard 8

Barfoed's Test

• If Barfoed is positive: Monosaccharides (strongly reducing - fructose, glucose, galactose, pentose)
• If Barfoed is negative and Benedict's test is positive: Reducing disaccharides (maltose, lactose)

Flashcard 9

Steps of Glycolysis

Facts About Glycolysis

• Aerobic glycolysis - 2 Pyruvates and 7 ATPs.
• Anaerobic glycolysis - 2 Lactate and 2 ATPs.
• The Hexokinase or Glucokinase step traps the glucose inside the cell.
• Irreversible steps of glycolysis, marking them can make gluconeogenesis (Reversal of Glycolysis) easy.
  • Hexokinase or Glucokinase
  • Phosphofructokinase I (rate-limiting step of glycolysis)
  • Pyruvate Kinase
• Substrate level phosphorylation steps are catalysed by phosphoglycerate kinase and pyruvate kinase enzymes.
• The oxidative phosphorylation step is catalysed by glyceraldehyde 3 phosphate dehydrogenase.
• Lactate is formed in anaerobic glycolysis for the regeneration of NAD.

Flashcard 10

Facts About Rapaport Leubering Shunt or 2,3 BPG Shunt

• Phosphoglycerate kinase converts 2 (1,3 BPG) to 2(3 PG) giving 2 ATPs.
• RBC needs 2,3 BPG. It helps in unloading O2 to tissues.
• It bypasses the phosphoglycerate kinase step to deliver oxygen to the tissues by decreasing the affinity of haemoglobin.
• 2(1,3 BPG) is converted to 2(2,3 BPG) (positional isomerism) catalysed by Bis Phosphoglycerate mutase, and this molecule is useful in delivering oxygen.
• 2(2,3 BPG) is converted into 2 (3-PG) mediated by bisphosphoglycerate phosphatase.
• 2(3-PG) finally gets converted into 2 (2-PG) via phosphoglycerate mutase.

Flashcard 11

Regulation of the TCA Cycle

In the citric acid cycle, it gets regulated at almost all steps. All enzymes of the cycle get stimulated by low energy status indicators such as high ADP/ATP ratio, high NAD/NADH ratio, and high FAD/FADH2 ratio. And they are all inhibited by high-energy status indicators such as high ATP/ADP ratio, NADH/NAD ratio, and FADH2/FAD ratio. 

In addition, all dehydrogenases of the citric acid cycle are stimulated by calcium (particularly in muscle). Calcium stimulates dehydrogenases of the Citric Acid Cycle so that the final furnace, where every fuel comes and gets oxidized, gets stimulated. And enough ATP is there for excitation/contraction coupling.

If there are four choices of citric acid cycle enzymes and one needs to be chosen, then the most appropriate one is Isocitrate Dehydrogenase (ICDH) because the narrowest bottleneck is at this level. So, the chief rate limiting enzyme in the Citric Acid cycle is Isocitrate Dehydrogenase.

Flashcard 12

Enzymes Involved in Gluconeogenesis

There are four enzymes involved in gluconeogenesis.

• Pyruvate carboxylase (pyr C) - Converts Pyruvate to Oxaloacetate
• Phosphoenolpyruvate carboxykinase which converts Oxaloacetate to Phosphoenolpyruvate
• Fructose-1,6-bisphosphate is converted to Fructose-6-phosphate
• Glucose-6-phosphate to glucose: Present in liver and Kidney
• First three enzymes are present in all the tissues.
• Conversion of two molecules of pyruvate to one molecule of glucose: 11 ATP is used.

Flashcard 13

Defect of glucose-6-phosphatase

Glucose-6-phosphatase not able to convert to glucose.

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Accumulated G6P enters glycolysis.

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Converts to pyruvate and then Acetyl coA

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Leads to fatty acids and cholesterol synthesis.

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Excess levels stored as triglycerides and cholesterol esters.

And excess triglycerides accumulate in adipose tissue leading to Doll like facies

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TAG accumulation causes hepatomegaly and renomegaly

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Cholesterol and cholesterol esters accumulation causes Xanthoma

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Sometimes acetyl coA accumulates - causing ketosis.

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Inhibition of acetyl coA inhibits PDH complex (negative feedback).

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Leads to accumulation of pyruvate.

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Pyruvate converts to lactate - causing lactic acidosis.

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Therefore, G6P enters HMP shunt (source of ribose-5-phosphate)

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Synthesis of purines and pyrimidines

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Excess purine is metabolized to uric acid - causing hyperuricemia

Flashcard 14

Fructose Based diet is more lipogenic and dangerous than glucose-based diet.

When fructose goes to glycolysis, it skips the rate limiting enzyme phosphofructokinase, which

means fructose glycolysis is un-regulated. For example, when one takes 100 molecules of glucose, the initial 50 molecules of glucose will go through glycolysis, yielding 100 pyruvates. 100 pyruvates will give 100 acetyl CoA. Once one has enough products, all these products in a feedback mechanism will inhibit glycolysis. 

At one point glucose stops getting into glycolysis and glucose gets into alternate pathways like glycogen synthesis or HMP shunt. But if you consume 100 molecules of fructose, all 100 molecules will go through glycolysis. because it is unregulated. All 100 molecules will give 200 pyruvates and 200 pyruvates will give 200 acetyls CoAs. Acetyl CoA is the building block of fatty acids and cholesterol. All 200 molecules of acetyl CoA will enter into fatty acids synthesis and cholesterol synthesis causing hyperlipidemia, hypertriglyceridemia and hypercholesterolemia.

Flashcard 15

Haldane Effect

• Reciprocal binding of oxygen and carbon dioxide at the lung side.
• At the same partial pressure of carbon dioxide, its concentration of deoxygenated blood is more than the oxygenated blood.

Flashcard 16

Neurotransmitters: Dopamine, Norepinephrine, Epinephrine

• Norepinephrine: Released by postganglionic sympathetic nerve endings (fewer beta effects).
• Epinephrine: Adrenal medullary chromaffin cells.

Flashcard 17

Functions of Prokaryotic DNA Polymerases

Flashcard 18

mRNA synthesis

Flashcard 19 

Synthesis of tRNA

Flashcard 20

RT PCR (Reverse Transcription PCR)

• RNA is converted to DNA.
• Real-time PCR is always represented by qPCR.

Steps involved in molecular diagnosis of SARS-COV2 infection.

Step 1: Swab sample collection

Step 2: Viral transport medium - It consists of Hanks' balanced salt solution, which has calcium and magnesium and heat-inactivated bovine serum albumin, which will keep the microorganism intact.

Step 3: Add gentamicin (kills bacteria) and Amphotericin B (kills fungi)

Step 4: Cold chain maintenance - The virus should be kept intact at 2°-8° C to maintain the viability of the virus.

Step 5: RNA extraction

Step 6: RT PCR

Step 7: Real-time PCR(Quantitative PCR, it is not used for amplification)

Step 8: Molecular transport medium

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