Where Clause Changing Based On NULL Column(s)

Hello DBAs:

I am having difficulty constructing a where clause. I have 4 columns in a table. Col1 is never NULL. Col2,3,4 may or may not contain NULL values. Here is the situation.

1. Col2,3,4 are NULL
WHERE Col1 = condition

2. Col2 is NULL, 3 may or may not be NULL. When Col3 is NOT NULL, Col4 may or may not be NULL

where col1 and (col3(Not Null values) OR Col4(Not Null values)) = condition.

How do I construct this logic. Please help