Cellular Biology Lesson Two
Cellular Biology • Focuses on understanding living process at a molecular level • Cellular biology has opened up new discoveries in genes responsible for cancer, events regulating how a cell divides, and how organisms develop from a single cell.
Learning focus • Evaluate technological advances in the field of cellular biology. • Explain the roles of various organelles in cellular processes • Use appropriate terminology related to biochemistry. • Describe the structure of cell membranes according to the fluid mosaic model and explain the dynamics of the transport mechanism
Introduction - Review • All the molecules and atoms studied in lesson one are not alive, • The cell is alive • What is a cell? • What is the cell theory? • Cell organelles and functions
Types of Cells • Two types based on structure: • Eukaryotic and Prokaryotic
Prokaryotic Cells • Single –celled bacteria are the only cells that are prokaryotic • Bacteria are very diverse, some can photosynthesis, others would not • They have exterior cell wall, some have their cell wall further surrounded by a capsule. • some move with appendages called flagella. • They have piliwhich help them attach to various surfaces
Prokaryotic Cells • No true nucleus • Most of their genes are found in a single loop of DNA, some have accessory rings of DNA called Plasmids • Photosynthetic bacteria have light sensitive pigments contained in disks called thylakoids • the cytoplasm contain granules called ribosomes that carry out protein synthesis
Eukaryotic Cells • Eukaryotic cells include: algae, protozoa, fungi, plants and animals
Membrane Structure and Function • Plasma membrane regulates the passage of molecules in and out of the cell • It is made up of a bilayer of phospholipids
The Fluid Mosaic Model • Most acceptable model of the cell surface • Proteins move about within a bed of semi-fluid lipids • It was proposed by Singer and Nicolson in 1972 • And supported by electron micrographs
Description of the fluid mosaic model • The phospholipid bilayer portion of the plasma membrane forms a hydrophobic impermeable barrier • Prevents the movement of polar molecules through the membrane • Cholesterol makes the membrane more impermeable to biological molecules • Charged molecules enter the cell through protein channels • Glycolipids are cell makers peculiar to individual cells • Glycolipids also regulate the action of plasma membrane proteins involved in the growth of cell, and may be involved in occurrence of cancer • Glycoproteins also make cell to cell recognition possible
Movement of molecules across the plasma membrane • Selectively permeable: • Diffusion • Osmosis • Concentration gradients • Types of solutions : isotonic, hypotonic, hypertonic • Turgor pressure, lysis, plasmolysis, crenation, flaccid
Transport by Carriers • Transport proteins help biological molecules that are unable to diffuse across the plasma membrane get into the cell. • They are very specific and can only bind with certain molecules • Facilitated transport – happens when a carrier protein is used to assist in the movement of a molecule across the plasma membrane when the molecule is moving down its concentration gradient, the process does not require energy.
Active Transport • Molecules are using carrier proteins to go against their concentration gradient, so movement is from an area of low concentration to one of high concentration. • Process requires energy in the form of ATP. • Protein carriers involved are called pumps • Example of an active pump is the sodium-potassium pump, which is important for the transmission of nerve impulses
Primary/Secondary Active Transport • A cellular process the uses ATP directly to move molecules or ions from one side of a membrane to the other is called primary active transport. • E.g. Na+ - K+ pump in the nerve cell • Secondary active transport uses electrochemical gradient as a source of energy to transport molecules or ions across a cell membrane • E.g. hydrogen-sucrose pump • A pump actively exports H+ against gradient usually primary active transport, then H+ sucrose symporter can use H+ gradient to transport sucrose against a concentration gradient into the cell
Endocytosis and Exocytosis • Used by molecules that are too large to diffuse through the cell membrane or be transported by protein carriers. • Endocytosis is the transportation of molecules through the cell membrane by vesicle formation. • When material taken in is very large the process is called phagocytosis (cell eating), when material is very small is called pinocytosis or cell drinking
Receptor-mediated endocytosis • In this process a receptor called ligand binds with a specific nutrient molecule and joins at the beginning of endocytosis to form what is called coat pit. • Exocytosis is opposite to endocytosis, a vesicle fuses with the membrane, discharging its contents outside of the cell.