AP Bio

What is the difference between purines and pyrimidines? Which amino acids are found in each?

Purines are double ring structure (A, G)

Pyrimidines are single ring structure (C, U, T)

What type of bond holds the base pairs together? How many b/w adenine and thymine? How many b/w cytosine and guanine?

Hydrogen binds hold the base together

Adenine & Thymine 2 hydrogen bonds

Cytosine & Guanine 2 hydrogen bonds

Scientific contributors of Chargaff, Franklin, Watson and Crick?

Chargaff- Discovered base-pairing rules (A=T) (C=D)

Franklin- used x-ray crystallography

Watson & Crick- Built the first accurate 3D model of the DNA double helix

What are 3 key features of a DNA structure (shape backbone, what groups are at the end?)

Double Helix, sugar-phosphate backbone

DNA is antiparallel

One end has 5’ phosphate group & the other has 3’ hydroxyl

What is the difference btwn Prokaryotic and Eukaryotic DNA?

Prokaryotic is circular, found in the cytoplasm

Eukaryotic in linear form, found in the nucleus, with multiple chromosomes wrapped around the histomes

What are plasmids and why are they important for prokaryotic cells?

small circular DNA molecule that separate from the chromosomes, plasmids replicate independently from the chromosomal DNA

(adenine, cytosine; guanine thymine) DNA

adenine bonds with thymine & cytosine bonds with guanine

(adenine, cytosine; guanine thymine) RNA

adenine bonds with Uracil & cytosine bonds with guanine

What phase of the cell cycle does DNA replicate?

S phase

What are the three models of DNA replication and how are they different from one another?

• Conservative- Original DNA stays fully intact; a completely new copy is made

• Semiconservative- Each new DNA molecule consists of one old “parental” strand & one new daughter strand

• Dispersive- Both strands of the new DNA contain a mix of old and new segments

Where does DNA replicate begin?

Origin of Replication

What unwinds the DNA strand at the replication fork?

Helicase

What protein keeps the DNA strand at the replication fork?

SSBP’s

Why is topoisomerase so important?

Topoisomerase cuts, rotates, and rejoins the DNA to relieve physical stress

What is added to the parental strand of DNA when it starts to replicate?

RNA Primer

What is the importance of DNA polymerase III? What direction does it travel?

Primary enzyme that builds the new DNA strand by adding nucleotides

What is the difference between the leading and lagging strand in DNA replication?

Leading strand: Synthesized continuously in the same direction as the replication fork movement 5’-3’

Lagging strand: synthesized discontinuously in the opposite direction of the fork

Where are Okazaki fragments located in DNA replication and what is their importance?

Lagging strand (they allow for the synthesis of the 3’ to 5’ parent strand, as DNA polymerase can only add nucleotides in the 5’ to 3’ direction)

What enzyme joins Okazaki fragments to form a continuous DNA strand ?

DNA ligase