Unit 7_DNA Structure, Replication & Cell Cycle

Flashcards covering DNA history, structure, base pairing, the cell cycle (Interphase, Mitosis, Cytokinesis), DNA replication, and cell cycle malfunctions.

Rosalind Franklin (1952)

Scientist who took an x-ray of the DNA structure in 1952 showing that DNA is twisted like a helix and has two strands.

Watson & Crick (1953)

Scientists who proposed that DNA is made up of 2 chains of nucleotides twisted into a double helix; they were the first to create a model of DNA.

DNA

A nucleic acid that stores genetic information inside organisms, structured as a double helix (twisted ladder).

Nucleotides

The subunits that make up DNA strands, consisting of three parts: a phosphate, a sugar, and a nitrogen base.

Phosphate & Sugar Backbone

The structural part of the DNA molecule that does not code for traits and is the same in every organism.

Nitrogen Bases

The four bases—$A$ (adenine), $T$ (thymine), $C$ (cytosine), and $G$ (guanine)—whose specific order determines an organism's unique traits.

Complimentary Base Pairing

The rule that $A$ always pairs with $T$ and $C$ always pairs with $G$.

Hydrogen Bonds

The chemical bonds that hold nitrogen bases together in the center of the DNA molecule.

Genetic Code

The specific sequencing (order) of nucleotides/nitrogenous bases that forms genetic information and determines traits.

Universal Genetic Code

The fact that the genetic material ($DNA$) and bases ($A, T, C, G$) are the same for all living things, including prokaryotes and eukaryotes.

Cell Cycle

The process of growth and division of a cell.

Binary Fission

The process of cell division used by prokaryotes.

Interphase

The longest phase of the cell cycle where the cell spends $90{\%}$ of its life preparing for division.

$G_1$ (Gap 1)

Phase of interphase characterized by cell growth, nutrient storage, and the creation of new proteins and organelles.

$S$-Phase (Synthesis)

The stage of interphase where DNA synthesis (replication) occurs, resulting in two identical copies of chromosomes.

$G_2$ (Gap 2)

The shortest phase of interphase where the cell performs final growth and checks for mistakes before nuclear division.

$G_0$ (Gap 0)

A resting stage of the cell cycle; skipping this phase can lead to unregulated cell division and tumors.

DNA Replication

The process in the $S$-phase where the DNA molecule separates into two strands to produce two new complementary strands.

Helicase

The enzyme that breaks hydrogen bonds to unzip the two DNA strands during replication.

DNA Polymerase

The enzyme that creates a new DNA strand in the $5'-3'$ direction and proofreads the new strand for errors.

Semi-conservative

A description of DNA replication because the resulting DNA contains one original 'parent' strand and one new strand.

Ligase

The enzyme responsible for sealing DNA fragments together.

Chromosome

A structure that contains genetic information (DNA) passed from one generation to the next.

Centromere

The center region of a chromosome where sister chromatids are attached.

Chromatids

The two identical 'sister' parts of a duplicated chromosome.

Mitosis

The phase of the cell cycle where the nucleus divides to produce two genetically identical daughter cells for repair, replacement, and growth.

Prophase

The first stage of mitosis where chromatin condenses into chromosomes, the nuclear membrane disappears, and spindles form.

Metaphase

The stage of mitosis where chromosomes line up in the middle of the cell and attach to spindles.

Anaphase

The stage of mitosis where chromosomes are pulled apart by their centromeres and chromatids move toward opposite poles.

Telophase

The final stage of mitosis where two new nuclei form and spindles disappear, though the cell is not yet fully split.

Cytokinesis

The final stage of the cell cycle, occurring after mitosis, where the cytoplasm pinches in half to create two separate daughter cells.

Cancer

A disease characterized by uncontrolled and unregulated cell growth, often due to cells skipping the $G_0$ resting phase.

Carcinogens

Substances that mutate DNA and cause cancer, such as UV light, tobacco use, and certain viruses.

Senescence

A state where aged cells stop dividing but do not die.

Apoptosis

A process of programmed cell death or 'self-destruction.'