BIOLOGY 11 - Cell Cycle

2ND SEM FINAL TERM

Cell cycle

It involves distinct and regular phases of growth, DNA duplication and cell division that are needed to allow growth and repair

Interphase

is the growth period in the cell cycle and is divided into three parts

Gap 1 (G1) (Growth Phase)

First part of the cell cycle, the cell carries out its normal metabolic function. Cells are specialized based on their function. Cells have a required size limit. Cell cannot grow bigger than their normal size.

Because the volume inside of the cell increases very fast while the surface area increases more slowly

Why does the cell cannot grow bigger than the its normal size?

Synthesis (S)

this is the time that the cell makes a copy of the genetic material in the form of nuclear DNA (DNA replication)

DNA replication

This process ensures that the daughter cells receives exact copy of parents’ genetic material or the process of copying and duplication a DNA molecule

Helicase

an essential enzyme (motor protein) that drives DNA replication and repair by unwinding the double helix structure

Unwinding

The double-stranded DNA unzips with the help of enzyme (helicase). This creates a replication fork

Complementary Base Pairing

Each original strand acts as a template. Free nucleotides in the nucleus pair with the exposed

bases: A pairs with T, G pairs with C

Joining

Enzyme DNA polymerase (molecular copier) links the new nucleotides together to form a new strand

Result

● Appearance of two identical sister chromatids

● The DNA has doubled, but the cell still has one nucleus

● Centrosomes are also duplicated in preparation for mitosis

Steps in DNA replication

1. Unwinding

2. Complementary Base Pairing

3. Joining

4. Result

Gap 2 (G2)

Cells undergo further growth. A checkpoint happens before transitioning to the next stage. Everything has to be in order, including growing to its correct size and duplicating the DNA without damage

Mitosis (M)

Division of the nucleus and the genetic material. During this stage, hereditary material of the parent cell is given to the daughter cells. The daughter cell contains identical genetic materials. At this stage, the cell’s nuclear membrane disintegrates, DNA condenses forming two nuclei.

Cytokinesis

Division of the cytoplasm of the cell. It begins during the telophase and continues till the nuclei have formed in the daughter cells

Prophase

- its prefix means before

- chromatin (loose complex DNA and protein materials in the nucleus) materials condenses into tightly coiled chromosomes.

- chromosomes begin to be visible

- nuclear envelopes breakdown

- nucleolus disappears

microtubule

it is the centrosome in animal cells and an organizing center that begins to migrate to the opposite poles.

Metaphase

Its prefix means “after”. The spindle fiber attached to the kinetochore of the sister chromatids facilitates the movement of the chromosomes. The chromosomes appear to line up along a plane equidistant from the microtubule region called ______ plate

Anaphase

its prefix means “up” or “back”

- sister chromatids are tightly paired due to centromere and protein cohesin

- during anaphase stage, cohesin breaks down and the sister chromatids pull away from each other towards the opposite ends of the cell.

Telophase

its prefix means end

• two complete set of identical chromosomes are now positioned at each pole of the cell

• microtubules and spindle fibers disintegrate

• nuclear membrane appears

• chromosomes begin to uncoil and less condense

• the end of the phase chromosomes are not visible