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Transcript
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 pili which 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 Prokaryotic Anatomy of a bacteria Eukaryotic Cells • Eukaryotic cells include: algae, protozoa, fungi, plants and animals Name Composition function Cell wall Cellulose fibrils in plant cells Support and protection Plasma membrane Phospholipid bilayer with embedded protein Passage of molecules in and out of cell Nucleus Nuclear envelope surrounding the nucleoplasm, chromosomes and nucleoli Cellular reproduction and control or protein synthesis Nucleolus Concentrated area of chromatin, RNA Protein synthesis and proteins Ribosomes Protein and RNA Protein synthesis Smooth endoplasmic reticulum Membranous flattened channels and tubular canals without ribosomes Various transport and/or modification of proteins and other substances, transport by vesicle formation; lipid synthesis in some cells Rough endoplasmic reticulum Membranous flattened channels and tubular canals studded with ribosomes Transport and/or modification of proteins and other substances, transport by vesicle formation; protein synthesis Name Composition function Golgi apparatus Stack of membranous sacs in animals Processing and packaging of molecules Vacuoles/Vesicles Membranous sacs in animal cells storage Lysosome Membranous vesicles containing Intracellular digestion digestive enzymes Microbodies Membranous vesicle containing specific enzymes Various metabolic tasks chloroplast Double membrane layer in plant cells photosynthesis mitochondrion Double membrane layer Cellular respiration Cytoskeleton Microtubules and microfilaments Shape of cell; movement of its parts Cilia and flagella Microtubules in animal cells Movement of cell Centriole Microtubules in animal cells Forms basal bodies that produces microtubules 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 semifluid lipids • It was proposed by Singer and Nicolson in 1972 • And supported by electron micrographs Fluid Mosaic Model of Cell Membrane 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 Concentration gradient of Animals and Plants Cells 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. Passive Transport 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 Sodium Potassium Pump 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. Endocytosis