MCAT (Biological and Biochemical)

Question 1

Living cells must connect with the outside world regularly to obtain the elements they require for living and to eliminate waste. Which of the following processes relies solely on the material's gradient to regulate the direction in which it flows 
across the cell membrane?

Accepted Answer

Osmosis

Answer

Osmosis is a specific type of passive transport that involves the net movement of water molecules across a selectively permeable membrane. This movement occurs solely down the water potential gradient, from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration), without the input of cellular energy.

Question 2

In order to divide and replicate themselves, somatic eukaryotic cells in the human body go through the cell cycle in a 
predictable pattern. The limitation point is the moment at which a cell decides to divide (R). How many chromosomes
 and chromatids does the cell have before this?

Accepted Answer

46 chromosomes, 46 chromatids

Answer

Before the S phase (DNA replication) and the restriction point (R) in the cell cycle, a human somatic cell is in G1 phase. In this phase, the cell contains 46 chromosomes, and each chromosome consists of a single chromatid. DNA replication in the S phase would then duplicate each chromatid, resulting in 46 chromosomes, each with two sister chromatids (totaling 92 chromatids).

Question 3

For a cell to divide effectively, all five steps of mitosis must be completed correctly. Match the mitotic stage to
 the appropriate component:

Accepted Answer

Prophase — Dissolution of nucleoli

Answer

During prophase of mitosis, the chromatin condenses into visible chromosomes, the nuclear envelope begins to break down, and the nucleoli disappear. The dissolution of nucleoli is a characteristic event of prophase, preparing the cell for chromosome segregation. Other options describe events that occur in different stages or are incorrect.

Question 4

Interactions between myosin and actin allow each sarcomere to shorten during muscle contraction. What other muscle 
contraction process, except the power stroke, necessitates the use of ATP?

Accepted Answer

Myosin-actin detachment

Answer

ATP plays a crucial role in muscle contraction beyond the power stroke. Specifically, ATP binding to the myosin head causes it to detach from the actin filament, allowing the muscle to relax and prepare for another contraction cycle. Without ATP, myosin remains bound to actin, leading to rigor mortis.

Question 5

During their adolescent years, Cystic Fibrosis (CF) patients frequently experience a loss of pancreatic activity. 
Which enzyme's absence, if isolated, would have the greatest impact on nutrient absorption?

Accepted Answer

Trypsinogen

Answer

Trypsinogen is the inactive precursor to trypsin, a crucial pancreatic enzyme responsible for digesting proteins in the small intestine. Its absence would severely impair the breakdown of proteins into smaller peptides and amino acids, leading to significant malabsorption of essential nutrients. While other enzymes are important, trypsin is a primary protease.

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT (Biological and Biochemical)