DNA Structure and Function
Terms in this set (23)
What four nucleotides make up DNA?
What are the three parts of a nucleotide?
How do the four nucleotides differ from each other?
By the base
Which nucleotides are purines?
adenine & guanine (2 rings)
Which nucleotides are pyrimidines?
cytosine & thymine (1 ring)
Describe the relative orientation of the sugar phosphate backbone and the bases in the structure of DNA.
2 nucleic acid strands are oriented anti-parallel
sugar phosphate backbone on outside bases pointed in
How are the 2 nucleic strands held together?
2 nucleic strands are held together by hydrogen bonds between complementary base pairs.
Elaborate on the shape the 2 strands make and explain how the bases make this shape.
2 strands are wound into a helix
10 base pairs/turn
What are the 3' and 5' ends?
3' is when the format is Sugar-Phosphate
5' is when the format is Phosphate-Sugar
What does it mean to say that the two nucleic strands in DNA run anti-parallel to each other?
They are symmetrical, the format is not the same on both sides.
Not S-P, S-P.
What are the complementary bases?
What is the function of DNA Helicase?
DNA helicase separates the two strands of DNA.
What is the function of RNA Polymerase?
Initiates the synthesis of complementary strands (b/c DNA polymerase cannot start synthesizing from nothing).
What is the function of DNA Polymerase?
DNAP synthesizes DNA
1) "Reads" nucleotide on template strand
2) Brings in complementary nucletotide
3) Covalently links together
*Gets rid of RNA in "Finishing Touches"
What is the function of DNA Ligase?
Connects all pieces together (covalently links together) in "Finishing Touches".
In other words, repairs single-stranded discontinuities in double stranded DNA.
What is a Replication Fork?
A structure that forms within the nucleus during DNA replication, created by helicases, that break the hydrogen bonds holding the two DNA strands together.
The resulting structure has two branching "prongs", each one made up of a single strand of DNA.
Describe the leading strand.
Strand of DNA that is synthesized continuously.
Describe the lagging strand.
Strand of DNA that is synthesized discontinuously in segments.
What are Okazaki fragments?
They are short molecules of single-stranded DNA that are formed on the lagging strand during DNA replication.
Describe the semi-conservative model of DNA replication.
Only half of the parent DNA molecule is conserved in the daughter DNA molecules.
Describe the conservative model of DNA replication.
Parent DNA molecule is kept intact, daughter DNA molecule has 2 newly synthesized strands.
Explain how the structure of DNA, suggested by Watson and Crick, is a mechanism for how it replicates.
The two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase.
This enzyme makes the complementary strand by finding the correct base through complementary base pairing, and bonding it onto the original strand.
As DNA polymerases can only extend a DNA strand in a 5′ to 3′ direction, different mechanisms are used to copy the antiparallel strands of the double helix.
In this way, the base on the old strand dictates which base appears on the new strand, and the cell ends up with a perfect copy of its DNA.
How does the fact that the two nucleic acid strands of DNA run anti-parallel to each other affect DNA replication?
The synthesis of two strands run in opposite directions due to the fact that
1) the two strands run anti-parallel
2) during DNA synthesis, the Phosphate of one nucleotide is attached to the 3' OH of another (builds from right to left)
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