MCAT (Biological and Biochemical) 4

Question 1

Which base pairing rule describes complementary DNA strands?

Accepted Answer

A pairs with T, G pairs with C

Answer

In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) via three hydrogen bonds (Chargaff's rules).

Question 2

Which muscle type has intercalated discs and is under involuntary control?

Accepted Answer

Cardiac muscle

Answer

Cardiac muscle has intercalated discs containing gap junctions that allow coordinated electrical conduction, and it functions involuntarily.

Question 3

The lac operon in E. coli is an example of which type of gene regulation?

Accepted Answer

Both positive and negative regulation

Answer

The lac operon is regulated negatively by the lac repressor (which blocks transcription without lactose) and positively by the CAP-cAMP complex (which enhances transcription when glucose is low).

Question 4

Which immunoglobulin class is the first to be produced during a primary immune response?

Accepted Answer

IgM

Answer

IgM is the first antibody produced during a primary immune response due to its pentameric structure and early B cell expression before class switching occurs.

Question 5

What is the role of helicase during DNA replication?

Accepted Answer

Unwinds the double helix by breaking hydrogen bonds

Answer

Helicase unwinds the DNA double helix by breaking the hydrogen bonds between complementary base pairs at the replication fork.

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT (Biological and Biochemical) 4