FORM 4 [Chapter 5]: Mitosis

Mitosis is a process of cell division which results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell.

In a typical animal cell, mitosis can be divided into four principals stages:

• Prophase: The chromatin, diffuse in interphase, condenses into chromosomes. Each chromosome has duplicated and now consists of two sister chromatids. At the end of prophase, the nuclear envelope breaks down into vesicles.
• Metaphase: The chromosomes align at the equitorial plate and are held in place by microtubules attached to the mitotic spindle and to part of the centromere.
• Anaphase: The centromeres divide. Sister chromatids separate and move toward the corresponding poles.
• Telophase: Daughter chromosomes arrive at the poles and the microtubules disappear. The condensed chromatin expands and the nuclear envelope reappears. The cytoplasm divides, the cell membrane pinches inward ultimately producing two daughter cells (phase: Cytokinesis).

Below is real time mitosis. You can see that a lot of cells divided. Mitotic division is recorded using a real time microscope.

Transport

Human transport system consist of :

Heart, blood vessels and blood which transport:

gases such as O2 and CO2

Waste products such as CO2 and Urea

Functions of circulatory system are :

Transport O2 and nutrients to cells

Transport waste products away from cells

Protect body from infections

Erythrocytes (RBC):

• Biconwave disc which can move quickly in the blood capillaries
• Present in large numbers
• Plasma membrane is elastics
• Big TSA/V ration for exchange of respiratory gases
• No nucleus at the mature stage so more haemoglobin can be carried
• Produce by bone marrow
• Life-span is 120 days, destroyed in the liver of the lymph

Concept of the Circulatory System

FORM 4 (Chapter 5): Cell Cycle

Cell Cycle

The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells. Non-dividing cells not considered to be in the cell cycle.

The stages are G1-S-G2-M.

1.    The G1 stage stands for “GAP 1″.

2.    The S stage stands for “Synthesis”. This is the stage when DNA replication occurs.

3.    The G2 stage stands for “GAP 2″.

4.    The M stage stands for “mitosis”, and is when nuclear (chromosomes separate) and cytoplasmic

(cytokinesis) division occur. Mitosis is further divided into 4 phases, which you will read about later.

FORM 4 (Chapter 4): Enzyme [Lock and Key Theory]

[Mechanism of enzyme action] Introduction – Enzyme Characteristics:

The basic mechanism by which enzymes catalyze chemical reactions begins with the binding of the substrate (or substrates) to the active site on the enzyme. The active site is the specific region of the enzyme which combines with the substrate. The binding of the substrate to the enzyme causes changes in the distribution of electrons in the chemical bonds of the substrate and ultimately causes the reactions that lead to the formation of products. The products are released from the enzyme surface to regenerate the enzyme for another reaction cycle.

The active site has a unique geometric shape that is complementary to the geometric shape of a substrate molecule, similar to the fit of puzzle pieces. This means that enzymes specifically react with only one or a very few similar compounds.

Lock and Key Theory:

The specific action of an enzyme with a single substrate can be explained using a Lock and Key analogy first postulated in 1894 by Emil Fischer. In this analogy, the lock is the enzyme and the key is the substrate. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).

Smaller keys, larger keys, or incorrectly positioned teeth on keys (incorrectly shaped or sized substrate molecules) do not fit into the lock (enzyme). Only the correctly shaped key opens a particular lock. Watch the video below for better understanding on mechanism of enzyme action.