This document provides an introduction to cell biology, covering the history and universal principles of living cells. It discusses: 1) The origins of life from a common ancestor over 3-4 billion years ago and the divergence into bacteria, archaea, and eukaryotes. 2) The universal principles of cells, including genetic information stored in DNA, DNA transcription into RNA, macromolecular assembly, membrane growth by expansion, targeting of cellular constituents, molecular movement, and cellular adaptation through receptor signalling. 3) The differences between prokaryotic cells like bacteria and archaea, which lack membrane-bound organelles, and more complex eukaryotic cells found in organisms like plants, fungi, and

1. Introduction to Cell Biology
Themba Hospital FCOG(SA) Part 1 Tutorials
By Dr N.E Manana

2. History of Cell Biology
• All forms of life share many molecular mechanisms, because they all
descended from a common ancestor (3 to 4 billion years ago)
• Living organisms diverged into three great divisions: Bacteria,
Archaea, and Eucarya
• Living things differ in size and complexity, and strategies to extract
energy from their environments.

3. CELLULAR ARCHITECTURE
• All living organisms store genetic information in nucleic acids (usually
DNA)
• DNA to RNA to protein, employ proteins (and some RNAs) to catalyse
chemical reactions
• Cells separate their cytoplasm from the external environment by
means of phospholipid membranes

5. Universal Principles of Living Cells
1. Genetic information stored in the chemical sequence of DNA is
duplicated and passed on to daughter cells
• Long DNA molecules (chromosomes) store the information required
for cellular growth, multiplication, and function
• Each DNA molecule is composed of two strands of four different
nucleotides (adenine [A], cytosine [C], guanine [G], and thymine [T])
• The two strands pair, forming a double helix held together by
interactions between complementary pairs of nucleotide bases
• A pairs with T and C pairs with G

7. Universal Principles of Living Cells
2. Linear chemical sequences stored in DNA code
• Enzymes called RNA polymerases copy (transcribe) the information
stored in genes into linear sequences of nucleotides of RNA
molecules
• Genes produce messenger RNA (mRNA) molecules that act as
templates for protein synthesis
• Many RNAs have structural roles, regulatory functions, or enzymatic
activity
• Ribosomal RNA is by far the most abundant class of RNA in cells

9. Universal Principles of Living Cells
3. Macromolecular structures assemble from subunits
• Many cellular components form by self assembly of their constituent
molecules without the aid of templates or enzymes
• The protein, nucleic acid, and lipid molecules themselves contain the
information required to assemble complex structures
• In some cases, protein chaperones assist with assembly by preventing
the aggregation of incorrectly folded intermediates

10. • 1.5

11. Universal Principles of Living Cells
4. Membranes grow by expansion
• Cellular membranes composed of lipids and proteins grow only by
expansion of pre existing lipid bilayers
• Thus membrane-bounded organelles, such as mitochondria and
endoplasmic reticulum, multiply by growth and division of pre existing
organelles
• The endoplasmic reticulum (ER) plays a central role in membrane
biogenesis as the site of phospholipid synthesis.

12. Universal Principles of Living Cells
5. Signal-receptor interactions target cellular constituents to their
correct locations
• Specific recognition signals incorporated into the structures of
proteins and nucleic acids route these molecules to their proper
cellular compartments
• Receptors recognize these signals and guide each molecule to its
appropriate compartment.
• For example, proteins destined for the nucleus contain short amino
acid sequences that bind receptors to facilitate their passage through
nuclear pores into the nucleus

13. Universal Principles of Living Cells
6. Cellular constituents move by diffusion, pumps, and motors
• Most small molecules move through the cytoplasm or membrane
channels by diffusion.
• However, energy provided by ATP hydrolysis or electrochemical
gradients is required for molecular pumps
• Similarly, motor proteins use energy from ATP hydrolysis to move
organelles

14. • 1.7

15. Universal Principles of Living Cells
7. Receptors and signalling mechanisms allow cells to adapt to
environmental conditions
• Environmental stimuli modify cellular behaviour
• Cells must decide which genes to express, which way to move, and
whether to proliferate, differentiate into a specialized cell, or die.
• Minute-to-minute decisions generally involve the reception of
chemical or physical stimuli from outside the cell

16. • 1.8

17. Eukaryotic and Prokaryotic Cells
• Although sharing a common origin and basic biochemistry, cells vary
considerably
• Bacteria and Archaea have much in common, including basic
metabolic pathways, and lack of membrane bound organelles.
• Eukaryotes comprise a multitude of unicellular organisms, algae,
plants, amoebas, fungi

20. Thank you