Which of the following is true of red blood cells? A. They live for only 120 days. B. They have multiple Nuclei. C. They live for only about 20 days. D. Once created in bone marrow, they circulate for our lifetime.

A. They live for only 120 days is correct. They are created in the bone marrow and destroyed in the spleen "red blood cells graveyard"

B. They have multiple Nuclei. Red blood cells don't have a nucleus but some can present structures called Jolly's bodies that are small pieces of the nucleus that they lost in the differentiation process

C. They only live for only about 20 days. No, red blood cells live for about 120 days

D. Once created in bone marrow, they circulate for our lifetime. Again, they have a limited lifetime

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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