Mitosis: Cell Division Stages

Mitosis

• Mitosis begins after genetic material duplicates during interphase.
• Checkpoints during interphase ensure the cell is ready for division; otherwise, it may die or stop dividing.
• Cyclin and cyclin-dependent kinases are proteins that regulate these checkpoints.
• Prophase: chromatin condenses into chromosomes, and the mitotic spindle forms (made of microtubules).
• Prometaphase: the nucleus disappears, and mitotic spindles move to opposite sides of the cell.
• Metaphase: chromosomes line up at the metaphase plate in the cell's center, and spindles attach to sister chromatids.
• Anaphase: sister chromatids are pulled apart by spindles, elongating the cell using ATP.
• Telophase: two new daughter cells start to form, nuclei form around chromosomes, chromosomes revert to chromatin, and mitotic spindles disappear.
• Cytokinesis: the cytoplasm splits, creating two separated cells.
• In plants, a cell plate forms a new cell wall during cytokinesis.
• In animals, cleavage forms a new cell membrane during cytokinesis.

Cancer

• Cancer is uncontrolled cell division due to mutations that bypass checkpoints.
• Cancer cells do not have growth factors (proteins that cause a cell to divide).
• Tumors are unorganized masses of cells that have lost their function.
• Benign tumors do not spread and are non-cancerous.
• Malignant tumors spread and are cancerous, with metastasis being the spread of cancer.
• Cancer treatments include surgery to remove tumors, chemotherapy (disrupts cell division, harming healthy cells), and radiation (high-energy radiation targeting specific areas).

Meiosis

• Gametes are sex cells (sperm or eggs) involved in sexual reproduction.
• Genes carry genetic information from parents and are located on chromosomes.
• Diploid cells contain a full set of homologous chromosomes (2n).
• Haploid cells contain half a set of homologous chromosomes (n).
• Meiosis includes all phases twice except interphase.
• Prophase 1: homologous chromosomes pair up, facilitating crossing over and independent assortment, where genes are exchanged.
• Metaphase 1: chromosomes line up in homologous pairs.
• Anaphase 1: homologous chromosomes are split.
• Anaphase 2: (in 2 daughter cells) sister chromatids are split.
• Cytokinesis 2 divides each cell into 2, resulting in 4 genetically different haploid cells.
• Errors in meiosis can lead to gametes with too many or too few chromosomes.
• Trisomy 21 (3 copies of chromosome 21) causes Down Syndrome; it's caused by nondisjunction.
• Nondisjunction is the failure of chromosomes separate, leading to cell death.
• A karyotype is a person's chromosome map that reveals mutations. XY indicates male, and XX indicates female.

DNA (Chapter 10)

• DNA, or deoxyribonucleic acid, consists of a phosphate group, sugar, and nitrogenous base (nucleic acid).

• It has a double helix shape composed of 2 polynucleotide strands.

• The 4 bases are: adenine (A), thymine (T), cytosine (C), and guanine (G); A pairs with T, and C pairs with G.

• Purines (A and G) have 2 carbon and nitrogen rings, while pyrimidines (C and T) have 1 ring.

• Complementary base pairs are held together by 3 bonds between C and G and 2 bonds between A and T.

• Covalent bonds link the phosphate group and sugar.

• DNA replication occurs in the S-phase in 5 steps.

  • Helicase, an enzyme, untwists DNA, breaking hydrogen bonds between complementary bases.
  • Free nucleotides attach to complementary base pairs via DNA polymerase (enzyme).
  • The copies separate using DNA ligase.

• The semiconservative model maintains half of the parental molecule in each daughter molecule.

• Gene mutation is a change in the nucleotide sequence, with an enzyme-corrected rate of 1 error per billion nucleotides.

• Point mutation is a change in a single nucleotide (deletion, insertion, or substitution).

• Frameshift mutation is the insertion or deletion of nucleotides, altering the reading frame and resulting in incorrect amino acid structure.

Protein Synthesis

• tRNA (transfer RNA) helps decode mRNA into a protein.
• rRNA (ribosomal RNA) links amino acids in the ribosome, attaching anticodons and codons.
• mRNA (messenger RNA) carries protein information from the nucleus to the cytoplasm.
• Step 1: Transcription copies DNA to mRNA; mRNA pairs with unzipped DNA, then copies the strand, leaves the nucleus, and attaches to a ribosome.
• mRNA nucleotides are read in groups of 3 called codons, each translating into a specific amino acid.
• Anticodons are 3 bases complementary to the mRNA sequence.
• Step 2: Translation starts at the start codon AUG.
• tRNA with a complementary code carries one amino acid.
• A protein chain forms until a stop codon (UAA, UAG, UGA) is reached.
• The sequence of amino acids determines protein function.
• Initiation: ribosome recruitment to the mRNA initiation codon.
• Elongation: the polypeptide chain extends by one amino acid residue per cycle.
• Nonsense mutation: results in premature start codon.
• Silent mutation: no change in amino acid sequence.
• Missense mutation: change in amino acid sequence.
• Frameshift mutation: change in the reading frame.
• Nucleotide: nucleic acids building block.

Genetics (Chapter 9)

• Gregor Mendel studied genetics using pea plants.
• The particulate theory of inheritance states that parents pass on separate and distinct factors (genes), and those genes are responsible for inherited traits.
• Mendel's principle of segregation: allele pairs separate during gamete formation.
• Traits are determined by indivisible units (genes) that don't blend.
• Alleles are alternative forms of a gene.
• Dominant alleles are expressed when present.
• Recessive alleles are only expressed when both alleles are recessive.
• Homozygous: two alleles for a trait are the same.
• Heterozygous: two alleles for a trait are different.
• Monohybrid cross: cross for one trait.
• Dihybrid cross: cross for 2 traits.
• Genotype: genetic makeup (e.g., TT, Tt, tt).
• Phenotype: expressed trait (e.g., tall, short).
• Punnett squares diagram genetic crosses.
• Heredity: characteristics from parents.
• Genetics: the study of heredity.
• Polygenic inheritance: two or more genes for a single trait (e.g., hair color).
• Environment can affect phenotype.
• Multiple alleles: several alleles for one trait (e.g., blood type).
• Pedigree tracks a trait in a family tree.
• Codominance: both traits are fully expressed.
• Incomplete dominance: neither trait is fully dominant, resulting in a mix.
• Blood typing: A, B, and O alleles, where A and B are dominant, O is recessive, and AB is codominant.
• Rh factor: proteins on red blood cells.
• Sex-linked traits: traits on the X chromosome.
• Color blindness and other traits are more common in males because having only one recessive allele means the trait shows.

Biotechnology (Chapter 12)

• DNA fingerprinting: identifying a person's DNA to match DNA for a case, focuses in repeating regions in DNA sequence
• Restriction enzymes: proteins that cut DNA at specific sites, resulting smaller fragments.
• Restriction site: the spot of the split
• Gel electrophoresis: DNA is separated by size/charge as it moves through a gel from negative to positive, where DNA is different colors.
• VNTR (variable number tandem repeat): short, tandem DNA sequences.
• Cloning: creating a genetically identical copy of an organism.
• Artificial twinning: a low-tech cloning method mimicking natural twins.
• Somatic cell nuclear transfer: creates an exact copy by transferring somatic cell DNA into an egg cell.
• Transgenic organisms: organisms with genomes altered by another species.
• Recombinant DNA: artificially combined DNA from multiple organisms.
• Plasmid: small DNA in a bacteria that can replicate independently.

Explore the stages of mitosis: prophase, prometaphase, metaphase, anaphase, and telophase. Learn how cells divide and replicate their genetic material. Understand the role of checkpoints, spindles, and cytokinesis in creating new daughter cells.