Difference Between Glycolysis and Krebs Cycle: Overview, Examples

Overview of Respiration

Respiration is an extremely basic process happening in all living organisms. It involves the use of oxygen and giving out carbon dioxide. The three stages of cellular respiration entail glycolysis, the Krebs cycle, and the electron transport chain. We will dwell on the differences between the two imperative pathways of energy metabolism: glycolysis and the Krebs cycle.

What Is Glycolysis?

Glycolysis is the first step in cellular respiration, occurring in the cytosol of the cell and being an anaerobic process. This stage of glycolysis involves the partial breaking down of a six-carbon sugar into two three-carbon compounds: pyruvic acid. There are ten enzymatic reactions coupled to a net gain of two ATP molecules and two NADH molecules in this process.

The major features of the Glycolysis include:

1. Location: Cytoplasm

2. Starting material: Glucose

3. End Products: Two molecules of pyruvic acid Two molecules of ATP with a net gain Two molecules of NADH

4. Oxygen Requirement: No requirement of oxygen, hence it is an anaerobic process

5. Function: It converts glucose into pyruvate, which in turn enters the Krebs cycle or is converted into lactate/ethanol under anaerobic conditions.

What Is the Krebs Cycle?

The Krebs cycle, also known as the citric acid or TCA cycle, is a process happening in the mitochondrial matrix of eukaryotic cells. It is an indirectly oxygen-dependent process in that it relies on the electron transport chain, which works only when oxygen is present. The Krebs cycle is the process following glycolysis and is responsible for the complete oxidation of pyruvate into carbon dioxide.

The major features of the Krebs cycle include:

1. Location: Mitochondrial matrix

2. Starting Material: Acetyl-CoA, which is derived from Pyruvate

3. End Products: For every acetyl-CoA that enters the cycle, the end products are three molecules of NADH, one molecule of FADH2, one molecule of GTP (or ATP), and two molecules of carbon dioxide

4. Oxygen Requirement: Indirectly requires oxygen; thus, it is an aerobic process

5. Function: oxidizes acetyl-CoA, producing energy careers in the form of NADH and FADH2, with Carbon-di-oxide as byproducts

Key Differences — Glycolysis vs Krebs Cycle

Here is a table comparing the key differences between glycolysis and the Krebs cycle:

Relationship Between Glycolysis And Krebs Cycle

The cycles of glycolysis and Krebs are interlinked. During glycolysis, pyruvate is generated that can be converted into acetyl-CoA, a substrate that enters into the Krebs cycle. As a result of this interlinking, cells can make the best use of glucose to produce energy mostly under aerobic conditions.

Regulation of Both Pathways

Both the glycolysis and Krebs cycle are mediated by enzymes, and their rates are changed depending on the requirement of energy in the cell. These rates may be different under various physiological conditions such as during fasting, exercise, and starvation.

Glycolysis Regulators

• Activated: AMP, ADP

• Inhibited: ATP, citrate, G6P

Krebs Cycle Regulators

• Activated: ADP, Ca2+

• Inhibited: NADH, ATP, Succinyl-CoA

Glycolysis vs Krebs Cycle NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Steps in Glycolysis & Krebs Cycle

• Regulation of Glycolysis & Krebs Cycle

Practice Questions for NEET

Q1. What is the role of NAD+ in cellular respiration?

1. It is a nucleotide source for ATP synthesis.

2. It functions as an electron carrier.

3. It functions as an enzyme.

4. It is the final electron acceptor for anaerobic respiration.

Correct answer: 2) It functions as an electron carrier.

Explanation:

At various chemical reactions, the NAD+ picks up an electron from glucose, at which point it becomes NADH. Then NADH, along with another molecule, flavin adenine dinucleotide (FADH2), will ultimately transport the electrons to the mitochondria, where the cell can harvest energy stored in the electrons.

Hence, It functions as an electron carrier.

Hence, the correct answer is Option (2) It functions as an electron carrier.

Q2. In terms of quantity, oxidation of 1 glucose molecule yields

1. 686 Kcal energy

2. 782 Kcal energy

3. 656 Kcal energy

4. 608 Kcal energy

Correct answer: 1) 686 Kcal energy

Explanation:

There is about 686 kcal oxidation for each glucose molecule. Cellular respiration breaks glucose into carbon dioxide and water. The theoretical maximum yield of ATP in this process is about 30 to 38 ATP molecules depending on the efficiency of electron transport and conditions prevailing in the cell. Practical yields are usually much lower because there is a loss of energy in transport and other metabolic processes.

Hence the correct answer is Option 1. 686 Kcal energy.

Q3. The number of ‘ends’ in a glycogen molecule would be

1. Equal to the number of branches plus one

2. Equal to the number of branch points

3. One

4. Two, one on the left side and another on the right side

Correct answer: 4) Two, one on the left side and another on the right side

Explanation:

One should remember that the number of ‘ends’ in a glycogen molecule would be equal to the number of branches plus one. This is because glycogen is a branched polysaccharide, with each branch terminating in a free non-reducing end. The main chain contributes one end, while each additional branch adds another. These ends are crucial for enzymatic action during glycogen synthesis and breakdown. Enzymes like glycogen phosphorylase act on these non-reducing ends to release glucose-1-phosphate during glycogenolysis.

Hence, the correct answer is option 4)Two, one on the left side and another on the right side.

Also Read:

• MCQs on Glycolysis Pathway

• TCA Cycle

• Lactic Acid Fermentation

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