In a double-stranded DNA, adenine pairs with thymine by how many hydrogen bonds? MCQ with Answer and Explanation

In a double-stranded DNA, adenine pairs with thymine by how many hydrogen bonds?
A. Three
B. One
C. Two
D. Four
Answer: Option C
Solution (By JKSSB Mock Tests)
Adenine (A) pairs with thymine (T) via two hydrogen bonds. Guanine (G) pairs with cytosine (C) via three hydrogen bonds. This base pairing (complementarity) is key to the double helix structure and ensures accurate replication and transcription. The higher number of bonds between G-C contributes to DNA stability; GC-rich regions are harder to denature.

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Practice More Biology Questions

Question #1
Body Mass Index (BMI) is calculated using which parameters?
A. Weight and age
B. Height and waist circumference
C. Weight and height
D. Fat percentage and muscle mass

Correct Answer: Option C


Explanation:
Body Mass Index (BMI) is a simple index used to classify underweight, overweight, and obesity. It is calculated as a person's weight in kilograms divided by the square of their height in meters (kg/m2). While it is a useful population-level screening tool, it does not directly measure body fat and may not be accurate for athletes or the elderly.

This question belongs to: Science Biology
Question #2
The 'Hormone Growth Hormone' (GH), also known as somatotropin, is secreted by the anterior pituitary. Its primary effects include:
A. Lowering blood glucose levels
B. Stimulating growth, cell reproduction, and cell regeneration, particularly in bones and muscles
C. Inhibiting protein synthesis
D. Decreasing fat breakdown

Correct Answer: Option B


Explanation:
Growth Hormone (GH), or somatotropin, is a peptide hormone secreted by the somatotroph cells of the anterior pituitary gland. Its primary effects are to stimulate growth, cell reproduction, and cell regeneration, particularly in bones (stimulating the epiphyseal plates) and skeletal muscle. It also has significant metabolic effects: it increases protein synthesis (anabolic), promotes the breakdown of fats (lipolysis) to use as energy, and raises blood glucose levels (diabetogenic effect) by reducing glucose uptake by cells. Its effects are largely mediated by Insulin-like Growth Factors (IGFs), primarily produced by the liver.

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Question #3
Consider statements about human hormones: 1. Insulin lowers blood sugar. 2. Adrenaline prepares the body for stress. 3. Thyroxine requires iodine for synthesis. Which are correct?
A. 2 and 3 only
B. 1 and 2 only
C. 1 and 3 only
D. 1, 2 and 3

Correct Answer: Option D


Explanation:
Insulin, secreted by the pancreas, promotes cellular glucose uptake, lowering blood sugar levels. Adrenaline (epinephrine) from the adrenal medulla triggers the fight-or-flight response, increasing heart rate and energy supply. Thyroxine, produced by the thyroid gland, requires iodine as an essential component for its synthesis; iodine deficiency causes goiter. All statements are correct.

This question belongs to: Science Biology