Cell Division and DNA Replication - True or False

• All cells come from pre-existing cells.
• New cells are for growth and to replace old or damaged cells.
• Cell division differs between eukaryotes and prokaryotes.

Keeping Cells Identical

• Instructions for making cell parts are encoded in DNA.
• Each new cell must get a complete set of DNA molecules.

DNA Replication

• DNA must be copied or replicated before cell division.
• Each new cell receives an identical copy of the DNA.
• There is an original DNA strand alongside two new identical DNA strands.

Identical Daughter Cells

• When a parent cell divides, it splits into two identical daughter cells.

Chromosomes

• The DNA of prokaryotes (bacteria) exists as one circular chromosome that attaches to the inside of the cell membrane.

Eukaryotic Chromosomes

• All eukaryotic cells store genetic information in chromosomes.
• Most eukaryotes contain between 10 and 50 chromosomes in their body cells.
• Human body cells have 46 chromosomes or 23 identical pairs.
• Each chromosome is composed of a single, tightly coiled DNA molecule.
• When cells aren't dividing, chromosomes can't be seen and are called chromatin.
• DNA tightly coils around proteins called histones.
• Duplicated chromosomes are called chromatids.
• Chromatids are held together by the centromere
• Duplicated chromosomes attached together are called Sister Chromatids.

Karyotype

• This is a picture of the chromosomes from a human cell arranged in pairs by size.
• The first 22 pairs are called autosomes.
• The last pair are the sex chromosomes.
• XX is female, XY is male.
• The Y chromosome decides if the baby is a boy or a girl.

Types of Cell Reproduction

• Asexual reproduction involves a single cell dividing to make two new, identical daughter cells.
• Mitosis and binary fission are examples of asexual reproduction.
• Sexual reproduction involves two cells (egg and sperm) joining to make a new cell (zygote) that is NOT identical to the original cells.
• Meiosis is an example of sexual reproduction.

Cell Division in Prokaryotes

• Prokaryotes such as bacteria divide into two identical cells via binary fission.
• A single chromosome makes a copy of itself.
• The cell wall forms between the chromosomes, dividing the cell.

The Cell Cycle

• The cell cycle has five phases: G1, S, G2, M, and C.
• G1 (primary growth phase).
• S (synthesis, DNA replicated).
• G2 (secondary growth phase).
• G1, S, and G2 are collectively called interphase.
• M stands for mitosis.
• C stands for cytokinesis.

Interphase - G1 Stage

• This stage is the first growth stage after cell division.
• Cells mature by making more cytoplasm and organelles
• cells carry on its normal metabolic activities.

Interphase - S Stage

• This is the synthesis stage.
• DNA is either copied or replicated during this stage.
• This results in two identical copies of DNA.

Synthesis Phase (S Phase)

• The nucleus of eukaryotes is in the S phase in interphase of the cell cycle.
• DNA replication occurs in the S phase.
• Many proteins facilitate DNA replication.
• DNA helicases unwind the double helix.
• The unwound template strands are stabilized by other proteins.
• RNA primase catalyzes the synthesis of short RNA primers to which nucleotides are added.
• DNA polymerase III extends the strand in the 5'-to-3' direction.
• DNA replication is catalyzed by DNA polymerase.
• DNA polymerase needs an RNA primer.
• DNA polymerase adds nucleotides to the 3' end of the growing strand.
• Nucleotides are added by complementary base pairing with the template strand.
• The leading strand template undergoes DNA synthesis to form the leading strand.
• This reads the template in the 3'-to - 5' direction, the same direction as helicase.
• The lagging strand grows in the opposite direction to the Replication Fork.
• Synthesis on is discontinuous, forming Okazaki fragments.
• DNA polymerase I degrades the RNA primer, replacing it with DNA.
• DNA ligase joins the Okazaki fragments into a continuous daughter strand.
• Semiconservative replication involves one round of replication, forming new copies of the original DNA.

Test your knowledge of cell division processes like binary fission, mitosis, and meiosis. See if you understand the S phase, DNA replication, and the roles of enzymes like DNA polymerase and helicase. Determine if the statements about sexual and asexual reproduction are true or false.