Lesson Notes By Weeks and Term v4 - SHS 2
CELL STRUCTURE AND FUNCTIONS
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CELL STRUCTURE AND FUNCTIONS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Biology
Class: SHS 2
Term: 1st Term
Week: 16
Grade code: 2.2.2.LI.2
Strand code: 2
Sub-strand code: 2
Content standard code: 2.1.2.CS.1
Indicator code: 2.2.2.LI.2
Theme: LIFE IN THE FUNDAMENTAL UNIT
Subtheme: CELL STRUCTURE AND FUNCTIONS
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This lesson explores one of the most fundamental processes of life: DNA replication. Every living thing, from the smallest bacterium to the largest *odum* tree, must be able to copy its genetic information accurately. This process is happening in our bodies right now, allowing us to grow, heal wounds (like a cut from playing football), and replace old cells. In Ghana, understanding DNA replication helps us grasp concepts like why we inherit certain traits from our parents (like our skin complexion or the shape of our nose), the basis of genetic diseases like sickle cell anaemia which is prevalent in our communities, and the science behind modern agriculture and medicine.
A. The Semi-Conservative Model of Replication
Before a cell divides (through mitosis or meiosis), it must make a perfect copy of its DNA. The way it does this is called semi-conservative replication. "Semi" means half. "Conservative" means to save.
So, in this process, the original DNA double helix unwinds, and each of the two strands serves as a template (a pattern) to build a new, complementary strand. The final result is two new DNA molecules, each consisting of one original strand and one newly made strand. Analogy: Imagine you have a zip fastener. If you unzip it, you have two separate sides. Now, imagine you can build a new matching side for each of the original sides. You will end up with two complete, identical zip fasteners. Each new zip fastener has one of the old sides and one brand new side. This is exactly how semi-conservative replication works.
*(Teacher can draw this on the board: One parent DNA molecule unwinds. Each strand (blue) acts as a template. New strands (red) are built alongside. The result is two daughter DNA molecules, each being half-blue, half-red).* B. Key Enzymes: The Molecular Machines