AP Biology DNA vs. RNA Review

Helicase

Unzips DNA by breaking hydrogen bonds between base pairs

Topoisomerase

Prevents DNA from over-winding ahead of the replication fork

DNA Polymerase

Adds nucleotides to the growing DNA strand in the 5' → 3' direction

RNA Polymerase

Synthesizes RNA from a DNA template during transcription

Ligase

Joins Okazaki fragments on the lagging strand during DNA replication

Primase

Lays down RNA primers for DNA polymerase to extend

Exonuclease

Removes RNA primers from DNA strands

Reverse Transcriptase

Converts RNA back into DNA (used by retroviruses like HIV

Edwin Chargaff

In DNA:

Adenine (A) pairs with Thymine (T)

Cytosine (C) pairs with Guanine (G)

A = T and C = G

Chargaff

Aided in determining double-helix structure of DNA

1. DNA —> RNA

Initiation: RNA polymerase binds to the promoter region

2. DNA —> RNA

Elongation: RNA polymerase binds to the promoter region

3. DNA —> RNA

Termination: Transcription stops at the terminator sequence

Purines

Larger

Pyrimidines

Smaller

Purines

two-ring structure

Pyrimidines

single-ring structure

Purines

Adenine (A), Guanine (G)

Pyrimidines

Cytosine (C), Thymine (T in DNA), Uracil (U in RNA)

Plasmids

Small, circular extra pieces of DNA found in bacteria (prokaryotes) that can replicate independently of chromosomal DNA.

Plasmids

Often carry genes for antibiotic resistance and can be transferred between bacteria through conjugation.

Mitochondria

have their own circular DNA (mtDNA) inherited from the mother

Mitochondrial DNA (mtDNA)

codes for some proteins involved in cellular respiration

Hydroxyl (-OH) Group

Found at the 3’ end of DNA/RNA

Hydroxyl (-OH) Group

Necessary for adding new nucleotides

Phosphate (-PO₄) Group

Found at the 5’ end

Phosphate (-PO₄) Group

Links Nucleotides together

5’ End

Has a phosphate (-PO₄) group attached.

3’ End

Has a hydroxyl (-OH) group, where new nucleotides are added.

DNA Polymerase Direction

Works in the 5’ —> 3’ direction adding nucleotides to the 3’ end

Helicase

Unwinds the parental DNA

Leading strand

Synthesized continuously in the 5' → 3' direction.

Lagging strand

Synthesized discontinuously in fragments (Okazaki fragments).

DNA Polymerase III

Adds nucleotides.

Primase

Creates RNA primers for the lagging strand.

Topoisomerase

Relieves tension ahead of the fork.

Single-strand binding proteins

Prevents strands from rejoining

DNA Polymerase I

Replaces RNA primers with DNA

DNA Ligase

Joins Okazaki fragments