BIO - CH 12

If an error is detected, DNA polymerase activates

a cleavage function, removes the incorrect nucleotide, and inserts the correct one in its place.

The lagging strand has its

3' end pointed away from the replication fork; it is synthesized in short, discontinuous pieces. can't grow so it just keeps replicating and the primer is gone and then it connects again (watch video).

The leading strand has its

3' end pointing toward the replication fork; it is synthesized as one long, continuous polymer as the parental strand is unwound.

When the replacement is complete, an enzyme called

DNA ligase joins the fragments together..

Proteins involved in DNA replication

DNA ligase, helicase, single-strand biding protein, topoisomerase, RNA primase, DNA polymerase.

DNA replication occurs only in the 5' to 3' direction and is catalyzed by

DNA polymerase

Why are primers needed for DNA replication?

DNA polymerase can only add nucleotides to an existing chain.

during replication, the two strands of the parental duplex separate. The order of the bases in the template strand determines the order of the complementary bases added to the daughter strand.

Example: The sequence 5'ATGC3' in the template strand specifies the sequence 3'TACG5' in the daughter strand because A pairs with T and G pairs with C.

As the parental strand is unwound, a new piece is initiated at intervals and each new piece is elongated until it reaches the piece in front of it. These short pieces are referred to as

Okazaki fragments.

all new DNA strands have a short stretch of

RNA at their 5' end.

he primer is made by an RNA polymerase called

RNA primase.

red arrow is a

RNA prime. DNA polymerasee is not capable of adding the first nucleotide, RNA primase does this. adds rna bases and they are going to be ribose sugar instead pf deoxyribose

When the growing fragment comes into contact with the primer, a different DNA polymerase complex takes over, removing the

RNA primer and replacing it with DNA nucleotides.

How does the lagging strand elongate?

Synthesis of each piece requires a new RNA primer. Each new primer is elongated at the three prime end. When the elongating DNA of one piece of the lagging strand runs into the RNA primer of the previous piece, the RNA primer is removed and replaced with the DNA. Separation of the parental DNA strands proceeds.

Single-stranded binding proteins:

bind to the single-stranded regions of the parental strands and prevent them from coming back together.

If improper hydrogen bonds form, DNA polymerase can

correct errors because it detects the mispairing.

Since newly synthesized DNA can be elongated (expanded) only at the 3' end, the two

daughter strands are made differently.

DNA polymerase cannot begin a new strand on its own; it can only elongate the end of an

existing piece of DNA and RNA.

The following enzymes play important roles in DNA replication: DNA polymerase, primase, ligase, helicase. In what order do they work during replication?

helicase, primase, DNA polymerase, ligase

When each new nucleotide comes into line in preparation for attachment to the growing DNA strand, the nucleotide is temporarily held in place by

hydrogen bonds that form between the base in the new nucleotide and the base across the way in the template strand.

Okazaki fragments are found on _____ strand of DNA.

lagging

each new DNA strand must begin with a short stretch of RNA that serves as a

primer for DNA synthesis.

Most DNA polymerases can correct their own errors through

proofreading

the main function of DNA polymerase is to add new nucleotides to the 3' end of a growing chain. what is the second role of this enzyme in DNA replication?

proofreading

Helicase

protein that unwinds the parental DNA double helix at the replication fork

DNA polymerase's function is to

synthesize a new DNA strand from an existing template. most DNA polymerases also correct mistakes in replication.

RNA primase synthesizes a short piece of RNA complementary to the DNA template. Once the primer has been synthesized,

the DNA polymerase takes over and elongates the primer, adding successive DNA nucleotides to the 3' end of the growing strand.

Why are single-stranded binding proteins necessary for DNA replication?

they prevent the two parental strands from coming together again

Which enzyme relieves the tension on the double helix during DNA replication?

topoisomerase

Topoisomerases:

work upstream of the replication fork to relieve the stress caused by unwinding the double helix at the replication fork