Unit 1 Topic 1 - Chapter 4: Cell cycle

Why do cells divide?

Growth and repair: As organisms grow, cells don't enlarge but multiply. As multicellular organisms grow and develop, it is important that cells replicate.

Maintenance + repair: Cells are constantly dying as they age or become destroyed. Cell replication allows cells to be replaced, ensuring proper functions of an organism.

Reproduction: Cells replicate to reproduce.

Describe binary fission

The normal prokaryote cell begins to uncoil its circular DNA and the DNA is replicated, Plasmids also replicate. Then the cell elongates and prepares for cell division. Duplicated DNA moves to poles of cell. The septum then begins to form as the cell begins to undergo cytokinesis. Finally a new cell wall and membrane are formed down the center. After, the cell completely splits forming 2 genetically identical subjects.

What are the 3 stages of interphase?

G1, S, G2

What happens in the G1 phase of interphase?

The cell grows as it increases the volume of cytosol. It carries out biochemical activities by synthesising proteins for DNA replication and replicating organelles.

What happens during S phase of interphase?

DNA is replicated. One chromosome becomes 2 genetically identical sister chromatids.

What happens during G2 phase of interphase?

The cell continues to grow by increasing volume of cytosol. It prepares for mitosis as the cell continues to synthesize proteins.

What are the 4 phases of mitosis?

prophase, metaphase, anaphase, telophase

What happens in prophase?

Chromosomes condense; spindle fibers form and nuclear membrane breaks down and nucleolus disappears.

What happens in metaphase?

Spindle fibers form and attach themselves to the centromeres of each chromosome. They then guide the chromosome to the equator of the cell.

What happens in anaphase?

The spindle fibers contract, splitting the centromere and pulling the sister chromatids to the opposite ends of the cell.

What happens in telophase?

Chromosomes pack together at both poles and nuclear membranes form, creating 2 identical nuclei. Spindle fibers disintegrate and chromosomes decondense.

What happens in cytokinesis?

The cytoplasm divides, new cell membrane is formed and organelles are distributed evenly.

What do cells do at checkpoints in cell cycles?

Cell has 3 checkpoints where it inspects itself for errors before proceeding to the next stage. If errors are detected, it can pause for repair or if unfixable undergo apoptosis.

Where are the 3 checkpoints in the cell cycle?

G1, G2, M

What happens at the G1 checkpoint?

Checks if the cell has grown to the correct size, if there is enough resources to divide (synthesized proteins, favorable condition for mitosis), and if the DNA is undamaged.

What happens at the G2 Checkpoint?

Checks if the DNA has replicated properly in the S phase and if there is enough resources for mitosis.

What happens at the Metaphase checkpoint?

Checks the formation of spindle fibers and if chromosomes are lined up correctly.

What is apoptosis?

The controlled death of cells in the body. There are two pathways: The mitochondrial and death receptor pathways.

What is the mitochondrial pathway for apoptosis?

Mitochondria detect internal damages in the cell. It then releases cytochrome C. This binds with cytosolic proteins to form a apoptosome, which activates caspase enzymes.

What is the death receptor pathway for apoptosis?

Death signalling molecules can be recognised by death receptor proteins on the surface of cell and are often released by immune cells. When these molecules bind to a death receptor surface protein, caspase enzymes are activated, initiating apoptosis.

What happens in the first stage of apoptosis?

Caspases are activated in the cell from internal or eternal signals.

What happens in the second stage of apoptosis?

The digestion of cell contents; caspases celave intracellular proteins, which leads to the breakdown of organelles.

What happens in the third stage of apoptosis?

The cell shrinks; as the contents of the cell are broken down, the cell shrinks and pulls inwards. Membrane starts to wrap and form bumps or blobs called blebs.

What happens in the fourth stage of apoptosis?

Cell breaks down; cell breaks apart into small blobs called apoptic bodies. These contain remaining cell material inside the membrane. Phagocytes engulf and digest these remaining pieces by phagocytosis(endocytosis of solid material).

What are phagocytes?

A cell of the immune system responsible for engulfing and destroying harmful micro-organisms and foreign material.

What is necrosis?

The unregulated death of cells caused by physical damage or starvation of oxygen to the cell. The cell begins to swell. Then the plasma membrane ruptures. The cellular and nuclear lysis causes inflamation.

What are stem cells?

Undifferentiated cells with the capability of differentiating into specialized cells.

What is differentiation?

The development of a stem cell into a specialized cell with a particular function.

What are two properties of stem cells?

self renewal: can produce both a differentiated cell and a copy of themselves when they replicate

potency: Stem cells are undifferentiated cells which can give rise to differentiated cells with a specialized function.

What does totipotent mean?

Stem cells which can differentiate into any type or another embryo. Only zygotes up to 16 cells in number are totipotent

What does pluripotent mean?

Stem cells that can differentiate into any of three cell germ cell layers.

What is multipotent?

Can differentiate into a limited number of specialized cell types belonging to a specific tissue or organ.

What is unipotent?

Can only turn into one type of cell but can replicate repeatedly?

What is potency?

How many different types of cells a stem cell can become.