What is it called when part of a cell membrane closes around a molecule to allow the molecule to enter the cell?

It is called endocytosis

Endocytosis is a cellular process and a form of active transport in which food or other substances are transported into the cell through the cell membrane. In this process, the substance to be transported is enclosed by a part of the cell membrane which later buds off in the cell to produce a vesicle that contains the engulfed substance. Endocytosis includes; (i) pinocytosis; process of engulfing of liquid substances through the cell membrane and (ii) phagocytosis; process of engulfing of solid substances through the cell membrane.

you are certainly talking about this picture:

a: is the label of the white square, it is showing the  replication fork, formed by helicase (d) ==> so it is the site of dna separation and replication 

b: is a new dna brand that is following directly the replication fork, so it is continuous ==> built continuously from 5' to 3

c: dna polymerase cannot replicate dna on its own, it needs the of their proteins, and one of them plays the role of a clamp which fixes  the dna with the dna template and increases  the processivity of the enzyme. ==>   stops polymerase from falling off the  template.

d: is the enzyme responsible for forming the replication fork (helicase) ==> unwinds and separates dna into two strands

e: is the delayed strand, it is built  in the opposite sense of the helicase, so dna will be built in fragments ==> built  fragments from 5' to 3 joins

and finally f: is the enzyme that builds  the new dna strand (dna polymerase) ==>   adds nucleotides to make a new dna helix.

credit: gradman555p98x9p

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lipid

explanation: