DNA Replication & Cell Cycle

James Watson & Francis Crick

discovered the structure of DNA

Rosalind Franklin

Took pictures of DNA using X-ray x-ray crystallography. Took Photo 51 which showed DNA was an alpha helix.

Maurice Wilkins

Used X-ray crystallography to study the molecular structure of DNA. Worked with Franklin (did not collaborate well) to create a picture of the DNA molecule which allowed Watson and Crick to deduce the double helix structure of two strands.

Meselson and Stahl

Determined that DNA replication is semiconservative in experiment using E. coli bacteria

Interphase & Mitotic phase

two phases of the cell cycle

G1, S, G2

stages of interphase

S phase

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.

G1: Gap 1

Cell growth

G2: Gap 2

preparation for division

Prophase

first and longest phase of mitosis in which the genetic material inside the nucleus condenses and the chromosomes become visible, nuclear membrane disappears. centrosomes/centrioles move to opposite sides of cell, and spindle forms.

Metaphase

second phase of mitosis, during which the chromosomes line up across the center of the cell

Anaphase

Phase of mitosis in which the chromosomes separate and move to opposite ends of the cell

Telophase

Phase of mitosis in which a nuclear membrane reforms around each new set of chromosomes.

Cytokinesis

division of the cytoplasm to form two separate daughter cells

Cell plate

the precursor of a new plant cell wall that forms during cell division and divides a cell into two

Cleavage furrow

The area of the cell membrane that pinches in and eventually separates the dividing cell in animal cells.

Centrosome

forms mitotic spindle

centromere

narrowing region of chromosome, holds sister chromatids together

Chromosome

A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.

Kinetochore microtubules

spindle fibers that attach to the chromosomes at the kinetochore, they pull chromosomes to the poles of the cell during mitosis

Helicase

An enzyme that untwists the double helix of DNA at the replication forks.

Topoisomerase

Enzyme that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork.

single strand binding protein

binds to the separated strands of DNA to keep Hydrogen bonds from reforming

Primase

An enzyme that joins RNA nucleotides to make the primer to start DNA synthesis.

DNA polymerases

Family of enzymes involved in DNA replication. One copies the DNA by adding complementary nucleotides, another removes & replaces primers, and another proofreads & repairs.

DNA ligase

enzyme that chemically links DNA fragments together by forming phosphodiester bonds.

5' to 3' direction

Direction DNA polymerase moves

Hydrogen bonds

hold 2 strands of DNA together, Adenine & Thymine form 2, and Cytosine & Guanine form 3.

Leading Strand

new strand of DNA oriented 5' to 3', synthesized continuously

Lagging strand

new strand of DNA that is oriented 3' to 5', synthesized backwards in sections called Okazaki fragments.

Free 3' end

what DNA polymerase attaches nucleotides to

5' end

End of DNA that gets shorter each DNA replication after primers are removed.

Semiconservative

the model of replication that DNA follows when it replicates. Each parent strand serves as template for the formation of a new strand. Replicated DNA consists of 1 old and 1 new strand

sugar-phospate

forms the backbone (sides ) of the DNA.

Phosphodiester bond

the type of bond that links the nucleotides in DNA or RNA. joins the phosphate group of one nucleotide to the hydroxyl group on the sugar of another nucleotide

2 nm

diameter of DNA

3.4 nm

distance of 1 complete turn of the DNA, contains 10 nucleotide base pairs

.34 nm

vertical distance between nucleotide base pairs in DNA

Purine

a nitrogenous base that has a double-ring structure; one of the two general categories of nitrogenous bases found in DNA and RNA; either adenine or guanine

Pyrimidine

a nitrogenous base that has a single-ring structure; one of the two general categories of nitrogenous bases found in DNA and RNA; thymine, cytosine, or uracil

excision repair

a DNA-repair process where enzymes remove a damaged portion of DNA, synthesize a replacement section in place, and attach it to the neighboring DNA segments

mismatch repair

repair enzymes correct errors in base pairing in DNA

Telomeres

Repeated DNA sequences at the ends of eukaryotic chromosomes.

Telomerase

An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.