Obj 13A-B Structure and Replication & Obj 9A-B Cell Cycle

Structure of DNA

Includes a double helix shape, a backbone made of alternating sugar and phosphate groups, and bases that are bonded through hydrogen bonds.

Nucleotide Makeup

A nucleotide is composed of deoxyribose, a phosphate group, and one of four nitrogen bases: adenine, thymine, cytosine, or guanine.

Antiparallel Strands

The two strands of DNA run in opposite directions, with a 5' end and a 3' end, which establishes directionality for DNA replication.

Chargaff's Rule

In DNA, the amount of adenine equals thymine (A=T) and the amount of guanine equals cytosine (G=C).

Role of Histone Proteins

Histone proteins help package DNA into nucleosomes, which are further coiled into chromatin fibers and organized into chromosomes.

Semi-Conservative Replication

The mechanism of DNA replication where each new molecule consists of one original strand and one newly synthesized strand.

Function of Helicase

An enzyme that unwinds the DNA double helix by breaking hydrogen bonds between base pairs.

Function of Topoisomerase

An enzyme that prevents DNA from becoming tangled by relieving tension during helix unwinding.

Role of DNA Ligase

An enzyme that seals nicks in the DNA backbone, forming a continuous strand after RNA primers are replaced.

5’ and 3’ Ends of DNA

5’ end has a phosphate group and 3’ end has an -OH group; DNA polymerase adds nucleotides only to the 3’ end.

Okazaki Fragments

Short segments of DNA synthesized on the lagging strand due to discontinuous replication; these fragments are later linked by DNA ligase.

Chromatin vs. Chromosomes

Chromatin is loosely coiled DNA that condenses into chromosomes during cell division, which are organized and condensed chromatin fibers.

Somatic Cells

All body cells except for reproductive cells (gametes).

Mitosis

The process by which a cell divides its nucleus, resulting in two identical nuclei.

Cytokinesis

The division of the cytoplasm to form two separate daughter cells after mitosis.

Cell Cycle Checkpoints

Control mechanisms that regulate the cell cycle, ensuring each phase is accurately completed before the next phase begins.

G1 Phase

The stage of the cell cycle for cell growth and normal functions.

G2 Phase

The stage of the cell cycle for further growth and preparation for division after DNA replication.

M Phase

The phase of the cell cycle where the cell physically divides into two daughter cells.

G0 Phase

A resting phase where cells can repair or permanently exit the cell cycle to prevent replication of damaged DNA.

Cancerous Cells vs. Healthy Cells

Cancerous cells grow uncontrollably and do not adhere to normal regulatory mechanisms, unlike healthy cells.