Lecture 2. Cells. Cell Membranes & Transport Myandina Galina Ivanovna PH.D., MD, professor

Introduction 1.Cell is the basic unit of life 2.Prokaryotic and Eukaryotic cells 3.Identify the Key elements which make up Plasma Membrane 4.Discuss the foundation of transport of medium through the Plasma Membrane 1.Cell is the basic unit of life 2.Prokaryotic and Eukaryotic cells 3.Identify the Key elements which make up Plasma Membrane 4.Discuss the foundation of transport of medium through the Plasma Membrane

Biology is the science of life Biology is the knowledge about living things, their structural and functional features and general laws of living state; The word “biology” comes from the Greek bios, meaning “life”, and logos, meaning “study of” or “science of”.

The characteristics of living things: cell is the basic unit of life All living organisms can maintain their complexity by a process called homeostasis; they acquire energy and materials from the environment and convert them into new forms by a process called metabolism; they can reproduce; they have the capacity to growth and development; they can response to their environment; they have the capacity to evolve and adapt.

The levels of organizations of living things: Biosphere Ecosystems Communities Populations Organisms Organ systems Organs Tissues Cells Organelles Molecules

All types of the cells have three main components: A cell membrane separates the cell from the outside environment and regulates traffic into and out of the cell. A cytoplasm – the main component of the cell, surrounding the organelles, it is jelly-like substance contains water, salts and organic molecules. Genetic materials composed of DNA that encodes the information needed to synthesis of proteins and nucleic acids and direct the activities of the cell.

The differences between Prokaryotic and Eukaryotic cells The single circular chromosomal DNA of Prokaryotes is not enclosed within membranes ; The Eukaryotic cells contain a nucleus and membrane-bounded organelles within the cytoplasm; Prokaryotic cells do not have membrane- bounded organelles.

Prokaryotic Cells A prokaryotic cell contains: DNA (a nucleoid), Cytoplasm, Plasma membrane Cell wall Capsule Ribosomes Flagella Fimbriae or Pili In bacteria, the cell wall contains a unique structure called peptidoglycan. Archaea do not possess peptidoglycan. Because of this structural difference, archaea and eukaryotes are resistant to many cell wall antibiotics

Organization of Eukaryotic Cells The eukaryotic cell contains membrane-bound organelles: nucleus, mitochondria, chloroplasts, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, peroxisomes, etc. Prokaryotic cells do not have such organelles.

Eukaryotic cell

Cytoplasm It contains cytoskeleton, Ribosomes and other organells Organic and non-organic molecules the system of internal membranes Cytosol is the cytoplasm excluding organelles

The nucleus

Mitochondria It has two membranes: outer membrane and inner membrane Mitochondria also have their own DNA (mtDNA), which encodes some of the proteins and RNAs in mitochondria The major role of mitochondria is to produce ATP, which carries high energy to power most cellular processes

Membrane organells Endoplasmic reticulum can be divided into rough ER and smooth ER: Rough ER is associated with ribosomes, it involves in protein synthesis. Smooth ER is involved in the synthesis and metabolism of lipids. Hepatocytes are abundant in smooth ER Golgi apparatus is a major site for sorting and modifications of proteins and lipids: proteins are enclosed in transport vesicles and carried to the Golgi apparatus. Some proteins could be modified into glycoproteins and then transported to membrane. Lysosomes contain nuclease for degrading DNA and RNA, protease for degrading proteins and other enzymes for degrading polysacchrides and lipids. Lysosomes exist only in animal cells. Peroxisomes contain enzymes for degrading amino acids and fatty acids. These reactions produce harmful hydrogen peroxide; peroxisomes also contain catalase to convert hydrogen peroxide into water and oxygen

Secretory pathway diagram 1.Nuclear membrane 2.Nuclear pore 3.Rough endoplasmic reticulum (rER) 4.Smooth endoplasmic reticulum (sER) 5.Ribosome attached to rER 6.Macromolecules 7.Transport vesicles 8.Golgi apparatus

The Role of the Membrane 1.Compartmentalisation within a cell 2.Containing Enzymes 3.Containing Cell Contents 4.Regulates traffic into and out of the cell. 1.Compartmentalisation within a cell 2.Containing Enzymes 3.Containing Cell Contents 4.Regulates traffic into and out of the cell.

The Building Blocks of a Cell Membrane 1.Phospholipids 2.Membrane Bound Proteins 3.Glycoproteins 4.Transport Proteins 5.Cholesterol 6.Glycolipids 1.Phospholipids 2.Membrane Bound Proteins 3.Glycoproteins 4.Transport Proteins 5.Cholesterol 6.Glycolipids

Fluid Mosaic Model

The fluid-mosaic model of Membrane Structure The membranes are phospholipid bilayers with protein molecules embedded in it.phospholipid polar heads of phospholipids are oriented toward the water and the fatty acid tails are oriented toward the inside of the bilayer Proteins may be attached to inner surface, embedded in the bilayer, or attached to the outer surface. Membrane proteins are capable of lateral movement At body temperature, membranes are a liquid

Phospholipids 1.Hydrophobic & Hydrophilic Regions (Polar) 2.Phosphate Group, Glycerol & 2 fatty acid tails (non polar) 3.Creating a bi-layer 4.Saturation Effects 1.Hydrophobic & Hydrophilic Regions (Polar) 2.Phosphate Group, Glycerol & 2 fatty acid tails (non polar) 3.Creating a bi-layer 4.Saturation Effects

Cholesterol In animals, cholesterol is a major membrane lipid.cholesterol It may be equal in amount to phospholipids. it one end is hydrophilic, the other end is hydrophobic.hydrophilichydrophobic Cholesterol makes the membrane less permeable to most biological molecules.

Cholesterol 1.Regulating Fluidity 2.Also Polar 3.Mechanical Stability (Stops cells Bursting) 4.Prevention of ions/polar molecules passing through the membrane 1.Regulating Fluidity 2.Also Polar 3.Mechanical Stability (Stops cells Bursting) 4.Prevention of ions/polar molecules passing through the membrane

The Role of Proteins Pumps (ADP+Pi - ATP) Adhesion Sites Receptors Channels (H 2 O Sol/Big) Carriers (Charged Ions) Antigens (Identification) Enzymes Pumps (ADP+Pi - ATP) Adhesion Sites Receptors Channels (H 2 O Sol/Big) Carriers (Charged Ions) Antigens (Identification) Enzymes

The cell membrane structure

Membranes are Differentially Permeable The substances can pass through the cell membrane: Nonpolar molecules (example: lipids) Small polar molecules such as waterpolar molecules The substances cannot pass through the cell membrane: Ions and charged molecules (example: salts dissolved in water)Ions Large polar molecules (example: glucose) Macromolecules

Transport throw cell membrane Passive transport: Osmosis Diffusion Fasilitated diffusion Active transport: The sodium- potassium pump Endocytosis Exocytosis

Transport Across The Membrane

Passive transport Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration Osmosis is the diffusion of water across a differentially permeable membranedifferentially permeable Facilitated Diffusion involves the use of a protein to facilitate the movement of molecules across the membrane

Facilitated Diffusion In some cases, molecules pass through channels within the protein. In other cases, the protein changes shape, allowing molecules to pass through

Bulk Transport - Exocytosis & Endocytosis

Exocytotic Vesicle Emptying at Cell Plasma Membrane

Gaseous Exchange in the Mammalian Lung  Large Surface Area (50-70m 2 ):Volume  1 Cell Thick - Squamous Epithelium  Good Blood Supply  High O 2 Gradient   Large Surface Area (50-70m 2 ):Volume  1 Cell Thick - Squamous Epithelium  Good Blood Supply  High O 2 Gradient 

Tonicity Isotonic In an isotonic solution, the concentration of solute is the same on both sides of the membrane (inside the cell and outside). A cell placed in an isotonic solution neither gains or loses water. Most cells in the body are in an isotonic solution. Hypotonic A hypotonic solution is one that has less solute (more water). Cells in hypotonic solution tend to gain water. Animal cells can lyse (rupture) in a hypotonic solution due to the osmotic pressure. A hypertonic solution is one that has a high solute concentration. Cells in a hypertonic solution will lose water. The marine environment is a hypertonic solution for many organisms. They often have mechanisms to prevent dehydration or to replace lost water. Animal cells placed in a hypertonic solution will undergo crenation, a condition where the cell shrivels up as it loses water.