Bio Foundations 4.1

binary fission

a type of asexual reproduction where a cell splits into two identical daughter cells

4 steps of binary fission

1. DNA replication

   • the chromosome is duplicated so that the cell has two complete copies of its DNA sequences

2. chromosome segregation

   • the two copies of the chromosome are physically separated to the opposite ends of the cell

3. cytokinesis

   • the cell membrane pinches in the middle to separate the two cells

4. cell separation

   • the pinched membrane combines with itself so that the two separate cells are made

interphase

the periods between rounds of mitosis

3 major phases of interphase

1. first gap (G₁) phase

   • the phase of growth and performing physiological jobs

2. synthesis (S) phase

   • the phase where the cell’s chromosomes are copied

3. second gap (G₂) phase

   • the phase used by the cell to prepare for mitosis

   • involves DNA proofreading

eukaryotic chromosomes

• eukaryotes have multiple

• linear in shape

• stored in the nucleus

• DNA is twisted around proteins called histones

  • form nucleosomes, which are twisted together into a chromosome by supercoiling

prokaryotic chromosomes

• prokaryotes have only one

• circular in shape

• stored in the nucleotide, a region of the cytoplasm

• twisted around itself by supercoiling

human chromosomes

• humans have 46 total and 23 nearly identical pairs

• every cell in an individual has one complete set from each parent

• the 23rd pair may be an XX or XY

How do chromosomes look in interphase vs. mitosis?

During interphase, chromatin spreads out to fill the entire nucleus. During mitosis, chromosomes condense into smaller, densely packed structures.

homologous chromosome

pairs of chromosomes that have the same genes, though not necessarily identical copies of those genes

sister chromatids

identical copies of a chromosome that are attached together

centromere

the constricted region of a chromosome where sister chromatids are joined together

cohesions

proteins that stick sister chromatids together at the centromere

kinetochore

a protein structure that assembles on the centromere of chromosomes and acts as the attachment site for spindle microtubules

6 stages of mitosis

1. prophase

   • chromatin condenses into dense, distinct mitotic chromosomes

2. prometaphase

   • the nuclear envelope breaks apart and releases the chromosomes into the cytoplasm

   • the mitotic spindle attaches to the chromosomes

3. metaphase

   • the mitotic spindle makes small adjustments that line up each homologous chromosome at the middle

4. anaphase

   • digestive enzymes destroy cohesins holding the sister chromatids together

   • the mitotic spindle pulls the chromatids to the opposite ends of the cell (chromosome segregation)

5. telophase

   • the nuclear envelope re-forms around the segregated chromosomes

   • mitotic chromosomes de-condense into chromatin

6. cytokinesis

cytokinesis in animal vs. plant cells

animal cells

• the mitotic spindle breaks down

• a ring of protein attaches to the plasma membrane and pinches the membrane together

• the plasma membrane combines with itself to produce two separate cells

  • cell separation

plant cells

• the mitotic spindle remains to assemble vesicles made by the Golgi apparatus at the middle of the cell, which contain the materials needed to build the plant cell wall

• vesicles combine together to form a cell plate that creates two separate cells

  • cell separation

• after cell separation, the mitotic spindle breaks down