Introduction to Cell and Molecular Biology
Have you ever wondered what makes life possible at the smallest scale?
Cell biology explores how cells are organised and how they function. Molecular biology examines the molecules and interactions behind those functions, including how cells store, use and regulate genetic information.
Together, these fields connect chemistry and biology to help us understand life, from individual molecules to whole cells.
Life Begins with Cells
All living organisms consist of one or more cells. A bacterium can live as a single cell, while organisms such as plants and humans contain many specialized cells working together.
Cells carry out the processes that sustain life: taking in nutrients, converting energy into usable forms, producing molecules and responding to their surroundings.
But what allows them to do all of this? To understand the cell, we first need to meet its molecular building blocks.
The Molecules Behind Life
Four major groups of biological molecules play essential roles in cells:
- Lipids help form cell membranes, store energy and participate in signalling.
- Proteins perform many jobs, including supporting cell structure, speeding up chemical reactions and regulating cellular activities.
- Nucleic acids, including DNA and RNA, store, transmit and help cells use genetic information.
- Carbohydrates provide fuel, store energy and contribute to structure and cell recognition.
These molecules interact constantly. Their structures and properties help determine what they can do.
For a closer look, explore the Macromolecules topics.
The Central Dogma of Biology
How does a cell use the information stored in its DNA?
All cellular processes revolve around a simple but powerful idea known as the Central Dogma — the flow of genetic information:
DNA → RNA → Protein
For a protein-coding gene, this involves two main processes:
- Transcription: a DNA sequence serves as a template for making RNA.
- Translation: ribosomes read the instructions in messenger RNA, or mRNA, to assemble amino acids into a protein.
Proteins then perform many of the tasks that allow cells to function.
Why Study Cell Structure and Organelles?
Eukaryotic cells, including those of animals and plants, contain membrane-bound compartments called organelles. These compartments help organize different activities within the cell.
Some important structures and their roles include:
- Nucleus: houses most of the cell’s DNA.
- Ribosomes: assemble proteins by reading mRNA instructions.
- Rough endoplasmic reticulum: helps fold and process many proteins destined for membranes or secretion.
- Smooth endoplasmic reticulum: participates in lipid synthesis and other functions, including calcium storage.
- Golgi apparatus: modifies, sorts and packages proteins and lipids for transport.
- Mitochondria: produce much of the cell’s ATP during aerobic respiration. ATP helps power cellular activities.
- Lysosomes: break down and recycle materials in many animal cells.
- Peroxisomes: participate in processes such as fatty acid breakdown and the processing of hydrogen peroxide.
The cell membrane surrounds the cell, regulates the movement of substances and helps it communicate with its environment.
The structures present vary between organisms and cell types. Prokaryotic cells, such as bacteria, have a different organization and lack a membrane-bound nucleus.
From Molecules to Systems
Cellular activities depend on interactions between many components. Genes, proteins, membranes and signaling molecules influence one another, forming networks that help cells respond to changing conditions.
Systems biology investigates how these interacting components work together to produce the behaviour of a biological system.
Understanding these connections also helps researchers investigate how disrupted cellular processes can contribute to disease.
Throughout this topic, we’ll explore the structures, molecules and processes that allow cells to function, building the bigger picture one concept at a time.