S phase and DNA replication

nitrogenous Bases

Guanine, Cyosine, Adenine, Thymine

nucleotide subsections

nitrogenous base - connected to sugar - connected to phosphate

nucleotides

monomer of a nucleic acid (Smallest single molecule)

Nucleotide structure

made of 5’ carbon sugar base, phosphate is attached to 5’ carbon, and nitrogenous base is attached to 1’ carbon.

what determines nucleotide identity

the unique nitrogenous base attached to the 1’carbon in the sugar

histone protiens

organizes DNA

chromatin

forms eukaryotic chromasomes and is made from combined histone protiens and DNA

monomer or chromatin

nucleosomes

euchromatin

loosly packed

heterochromatin

tightly packed

leading strand

new strand of DNA created in the same direction as the template DNA is unzipped

lagging strang

new DNA strand created in the opposite direction of which the DNA is being unzipped

Topoisomerase

"Relaxes" the DNA by releasing twisting tension from the double helix; without it, unzipping DNA would make remaining sections tightly wound and prone to tearing.

Helicase

Breaks the hydrogen bonds holding complementary base pairs together in a DNA double helix.

Single strand binding proteins (SSB)

Coat the exposed nitrogenous bases of separated DNA strands to prevent them from re-pairing, keeping them available for reading by enzymes.

Primase

Lays down short RNA fragments complementary and antiparallel to the template DNA strand; provides a starting point for DNA polymerase, which cannot start a new strand from scratch.

RNA (Ribonucleic acid)

A nucleic acid similar to DNA but with an oxygen atom at the 2' carbon of the sugar ring and uracil (U) instead of thymine (T); capable of hydrogen bonding with DNA.

DNA polymerase

Continues building the new DNA strand by adding DNA nucleotides to the chain started by primase; can only extend from a pre-existing nucleotide in a 5'→3' direction.

DNA polymerase limitation

Cannot start a new strand; can only synthesize in a 5'→3' direction, requiring a pre-existing nucleotide and causing antiparallel strand synthesis.

Leading strand

The DNA strand synthesized continuously in the same direction as helicase movement during replication.

Lagging strand

The DNA strand synthesized in the opposite direction of helicase movement; synthesized in short segments called Okazaki fragments.

Okazaki fragments

Short DNA fragments synthesized discontinuously on the lagging strand.

RNA primer removal DNA polymerase

A different DNA polymerase removes RNA primers and replaces them with DNA nucleotides as DNA segments are completed.

Ligase

Seals the final gap in the sugar-phosphate backbone between adjacent DNA fragments.

Purine

nitrogenous bases with 2 rings

pyridimines

nitrogenous bases with one ring

which pairs of nitrogenous bases in DNA

Adenine=Thymine, Guanine=Cytocine