Carbohydrate metabolism: lactose synthase: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Biochemistry · Carbohydrate metabolism: lactose synthase

Sample item

In the lactating mammary gland, galactosyltransferase normally transfers galactose to proteins. A regulatory protein changes its specificity so that glucose becomes the acceptor, forming lactose. What is this protein?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Alpha-lactalbumin

Lactose synthase has two subunits, galactosyltransferase and alpha-lactalbumin. Alpha-lactalbumin is made under the influence of prolactin and lowers the Km of the transferase for glucose, so UDP-galactose and glucose combine to form lactose.

Option by option

  • A. Alpha-lactalbumin (correct)

    Correct. Alpha-lactalbumin is the modifier subunit of lactose synthase.

  • B. Casein

    Casein is the major milk phosphoprotein and does not regulate lactose synthesis.

  • C. Serum albumin

    Serum albumin is a plasma transport protein and is not part of lactose synthase.

  • D. Lactoferrin

    Lactoferrin is an iron-binding milk glycoprotein with antimicrobial activity.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, Alpha-lactalbumin. Lactose synthase has two subunits, galactosyltransferase and alpha-lactalbumin.

Why is "Casein" not the answer?

Casein is the major milk phosphoprotein and does not regulate lactose synthesis.

Why is "Serum albumin" not the answer?

Serum albumin is a plasma transport protein and is not part of lactose synthase.

Why is "Lactoferrin" not the answer?

Lactoferrin is an iron-binding milk glycoprotein with antimicrobial activity.

What concept does this question test?

It tests Carbohydrate metabolism: lactose synthase in Biochemistry. Alpha-lactalbumin is made under the influence of prolactin and lowers the Km of the transferase for glucose, so UDP-galactose and glucose combine to form lactose.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Carbohydrate metabolism: lactose synthase?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.