Molecules and Cells Overview

Molecules of Life

• The molecules of life are proteins, nucleic acids, phospholipids, and saccharides (sugars).
• Proteins are chains of amino acids and are responsible for many functions in the cell.
• Nucleic acids carry genetic information, they are made of nucleotides.
• Phospholipids are amphipathic – both hydrophobic and hydrophilic – and form lipid bilayers, which make up cell membranes.

Cellular Life

• Cells are the fundamental units of life.
• There are two main types of cells: prokaryotic and eukaryotic cells.
• Prokaryotic cells are simpler and do not contain a nucleus or other membrane-bound organelles.
• Eukaryotic cells are more complex and have a nucleus and various membrane-bound organelles.
• The nucleus contains the cell's genetic material, DNA.
• The DNA in eukaryotic cells is organized into linear pieces called chromosomes.
• The nuclear envelope surrounds the nucleus and has pores that allow the exchange of molecules between the nucleus and the cytoplasm.
• The endoplasmic reticulum (ER) is a network of membrane-enclosed sacs called cisternae.
• The ER is involved in lipid biosynthesis and protein synthesis, and produces vesicles for transport.
• Ribosomes are large molecular complexes that translate mRNA into proteins. They are found both bound to the ER and free in the cytosol.
• The Golgi apparatus receives transport vesicles from the ER, modifies proteins and lipids, and sorts them into vesicles that are released to other parts of the cell.
• Lysosomes are digestive organelles that contain enzymes that degrade macromolecules.
• Mitochondria are responsible for generating energy from nutrient molecules in the form of ATP.

Prokaryotic Cells

• Prokaryotic cells do not have a nucleus or other membrane-bound organelles.
• Their genetic material is mainly a circular DNA molecule located in the nucleoid.
• They also have small circular DNA molecules called plasmids.
• Prokaryotes have a cell wall made of proteins and sugars.
• Prokaryotes, specifically bacteria, are often used as model organisms in molecular biology.

Model Organisms

• Model organisms are simple organisms used to study complex biological processes.
• Scientists use model organisms because they are easier to manipulate, grow and study than more complex organisms.
• Examples of model organisms include: E. coli (bacteria), yeast, C. elegans (roundworm), Arabidopsis thaliana (plant), Drosophila (fly), zebrafish, and mouse.

Evolutionary Relationships

• All living organisms have a common ancestral cell.
• Phylogenetic trees depict evolutionary relationships between different organisms.
• Many fundamental features of cells are shared due to their common evolutionary origin.
• The study of simple model organisms can be used to learn about molecular biology in more complex organisms.