HJÆLP!

Hej! Er der ikke nogen som er meget gode til engelsk og som kan hjælpe mig med det her.

Jeg skal svarer på følgende spørgsmål:
Gøre rede for hvorledes humane celler optager kolesterol fra plasma ved receptor-medieret endocytose af LDL.

Jeg skal bruge det til en aflevering men ved ikke hvad der står. PÅ FORHÅND TAK

In endocytosis the cell takes in macromolecules and particulate matter by forming vesicles from the plasma membrane. Although the proteins involved in the processes are.

different, the events af endocytosis look like the reverse af exocytosis.
A small area af the plasma membrane sinks inward
to form a packet. As the packet deepens, it pinches in, forming
a vesicle containing material that had been outside the
celloThere are three types af endocytosis: phagocytosis ("cellular
eating"), pinocytosis ("cellular drinking"), and receptormediated
endocytosis.

Human cells use receptor-mediated endocytosis to take in
cholesterol for use in the synthesis af membranes and as a precursor
for the synthesis af other steroids. Cholesterol travels
in the blood in particles called low-density lipoproteins
(LDLs), complexes af lipids and proteins. These particles act
as ligands (a general term for any molecule that binds specifically
to a receptor site af another molecule) by binding to
LDL receptors an membranes and then entering the cells by
endocytosis. In humans with familial hypercholesterolemia,
an inherited disease characterized by a very high level af cholestelol
in the blood, the LDL receptor proteins are defective
or missing, and the LDL particles cannot enter cells. Instead,
cholesterol accumulates in the blood, where it contributes to
early atheros'clerosis, the buildup af lipid deposits within the
walls af blood vessels, causing them to bulge inward and impede
blood flow.
Vesicles not only transport substances between the cell and
its surroundings but also provide a mechanism for rejuvenating
or remodeling the plasma membrane. Endocytosis and exocytosis
occu~continually to same extent in most eukaryotic
cells, and yet tite amount af plasma membrane in a nongrowingcell
remains'fairly constant over the lang run. Apparently,
the addition af membrane by ane process offsets the loss af
membrane by the other.
Energy and cellular work have figured prominently in our
study af membranes. We have seen, for example, that active
transport is powered by ATP In the next three chapters, you
willlearn more about how cells acquire chemical energy to do
the work af life.