Biology: Cellular Reproduction

Cellular reproduction

Cellular reproduction allows organisms to grow

Unicellular reproduction

(like bacteria), one cell divides to make a whole new organism 

Multicellular reproduction

(like humans), cell division is used for

• Growth form a fertilized egg

• Repair/replace damaged or old cells

Genome

The complete DNA content of an organism that must be accurately copied during cell division.

Binary fission

Prokaryotic reproduction where the chromosome is copied and the cell splits into two identical daughter cells.

Binary fission steps

1. Bacterial chromosomes is copied

2. Each chromosome copy attaches to different spots on the plasma membrane

3. Cell grows, pulling the chromosomes apart

4. Plasma membrane pinches inward 

5. New Cell wall forms → two daughter cells

Eukaryotic chromosomes

Chromosomes made of chromatin

humans have 46 in somatic cells and 23 in gametes.

Chromatin

The DNA–protein complex that condenses to form chromosomes.

Chromosome contents

One long DNA molecule containing thousands of genes plus structural and regulatory proteins.

Mitosis

Division of the nucleus that produces two genetically identical daughter cells.

Sister chromatids

Two identical copies of a chromosome joined at the centromere before mitosis.

Cytokinesis

Division of the cytoplasm that forms two separate daughter cells.

Human life cycle

Meiosis produces gametes with 23 chromosomes; fertilization restores 46 and forms a zygote that grows by mitosis.

Cell cycle

The sequence of cell growth

Interphase

The nondividing phase (90% of the cycle) where the cell grows and copies DNA.

G1 phase

First growth phase of interphase.

S phase

DNA synthesis phase of interphase where chromosomes are duplicated.

G2 phase

Final growth phase before mitosis.

M phase

The cell division phase including mitosis and cytokinesis.

Prophase

In Nucleus: Nucleoli disappears Chromatin condenses

In cytoplasm: Mitotic spindle forms, centrosomes move to opposite poles 

Prometaphase

Nuclear envelope breaks down and spindle fibers attach to kinetochores

chromosomes fully condensed 

Metaphase

Chromosomes line up at the metaphase plate (middle of the cell) 

Centrosomes are aligned 

Anaphase

Sister chromatids separate and move to opposite poles of the cell

cell elongates

Telophase

New nuclei for (nuclear envelopes reappear)

Chromosomes unwind back into chromatin

Mitosis is complete 

Cytokinesis in animal cells

A cleavage furrow forms and the cell pinches in two.

Cytokinesis in plant cells

A cell plate forms and develops into a new cell wall.

Growth factors

Regulatory chemicals required by some cells to divide.

Density-dependent inhibition

Normal cells stop dividing when crowded; cancer cells do not.

Restriction point

A checkpoint in late G1 that determines whether a cell will divide.

G0 phase

A nondividing state entered if a cell does not pass the restriction point.

Cell size and division

Cells must reach a sufficient size relative to genome content to divide.

Cancer cells

Cells that divide uncontrollably and ignore normal cell-cycle controls.

Transformation

Conversion of normal cells into cancerous cells.

Benign tumor

A non-spreading mass of abnormal cells.

Malignant tumor

A tumor that invades tissues and can spread (cancer).

Metastasis

The spread of cancer cells to new areas of the body.