Overview Basic unit of life 75 Trillion cells in human body Vary in size and shapes Over 260 types of cells in body i.e. neurons, muscle, bone, blood cells All types are derived from just 1 fertilized egg Differentiation Forming specialized cells from unspecialized cells

Overview The cell membrane maintains integrity of cell Membrane is a fluid structure – flexible Selectively permeable- allows only select substances into and out of cell Signal transduction – communication between cell & environment

The cell membrane is composed of three major components 1. Bilayer of phospholipids 2. Cholesterol 3. Membrane proteins

Phospholipid bilayer

Phospholipid Bilayer Nonpolar Hydrocarbon tails Phospholipids align so that tails are hidden from water Nonpolar tails form the interior of membrane Polar Phosphate heads Polar groups align to face water Polar heads are exposed to surfaces of membrane The phospholipid bilayer forms a fluid, yet stable boundary.

The interior the cell membrane is hydrophobic which means it is Permeable to nonpolar molecules Steroids, Oxygen, Carbon Dioxide can easily cross the membrane Impermeable to polar molecules Proteins, Water, Sugars, ect. Cannot easily cross membrane

1. Integral Proteins Spans cell membraneSpans cell membrane Forms ion channels & poresForms ion channels & pores Examples include: Na + channels and K + channelsExamples include: Na + channels and K + channels Aquaporins = water channels Aquaporins = water channels

Transmembrane Proteins Integral protein, where one end extends outside cell, and the other end dips into cytoplasm. Many function as receptors

Transmembrane Protein Receptor A molecule (ligand) binds to portion of receptor outside cell Transmembrane Protein changes conformation Portion inside cell sends a signal into cell

2. Peripheral Proteins Are loosely associated with the membrane.Are loosely associated with the membrane. May be a glycoprotein (protein + sugar)May be a glycoprotein (protein + sugar) Includes Cellular Adhesion Molecules (CAM)Includes Cellular Adhesion Molecules (CAM)

Cellular Adhesion Molecules (CAM) Peripheral proteins that guide moving cells to targets Establishes cell-to-cell connections Forms new neural connections in learning and memory Guides cells surrounding an embryo towards uterus Guides white blood cells to injury

Selectin Covers the surface of white blood cells (WBC) Selectin binds to carbohydrates on surface of damaged capillaries Allows circulating WBCs to anchor near site of injury

3 Parts of the nucleus

Nuclear Envelope Double-layered membrane = 2 lipid bilayers. Nuclear Pores Channel proteins allow specific molecules across nuclear envelope Ribosomes & RNA leaves nucleus through nuclear pores

Passive movements Requires no energy from cell Diffusion Facilitated Diffusion Osmosis Filtration Active Movements Requires energy from cell Ion pumps Endocytosis Exocytosis

Diffusion Tendency of atoms or molecules in water or air to move from areas of higher concentration to lower concentration Moving substances eventually become diffuse, or evenly distributed Diffusion occurs because all substances are in constant motion

Diffusion of sugar In water Diffusion Substances move down their concentration gradient (from high to lower concentration) Concentration gradient = difference in concentrations

Requirements for diffusion across cell membrane 2.A concentration gradient must exist across the cell membrane 1. Cell membrane must be permeable to substance. Oxygen, Carbon Dioxide, and Steroid Hormones easily diffuse across the cell membrane. Oxygen enters cells & Carbon Dioxide leaves cells by diffusion

Substances move down their concentration gradient. Diffusion through carrier proteins within the cell membrane Carrier proteins include ion channels and other proteins that “carry” substances across the cell membrane. Facilitated diffusion transports ions, glucose, and some hormones across the cell membrane. facilitated diffusion

Diffusion of water across a semipermeable membrane Osmosis Water freely crosses the membrane, but solutes (sugars, salts, and proteins) cannot cross the membrane. Remember: Water follows salts! water moves down its concentration gradient, i.e. from area of higher [water] into area of lower [water]

60% H 2 O 40% protein 80% H 2 O 20% protein Higher H 2 O concentration A B Higher solute concentration Membrane is impermeable to proteins

Osmotic Pressure = Pressure generated by osmosis. H 2 O moved down its concentration gradient

Osmotic Pressure exerted on Cells Intracellular fluid (fluid inside cells) = 0.9 % NaCl Extracellular Solutions (fluid outside cells) may exert osmotic pressure onto cells. Isotonic = extracellular solution of 0.9 % NaCl Hypertonic = extracellular solution above 0.9 % NaCl Hypotonic = extracellular Solution below 0.9 % NaCl

Red Blood Cell in isotonic solution No osmotic pressure = normal shape & size Red Blood Cell in isotonic solution No osmotic pressure = normal shape & size Isotonic Solution Extracellular [NaCl] is equal to Intracellular [NaCl]. Results in no osmotic pressure H2O Water moves into and out of the cell

Red Blood Cell in hypertonic solution. Water leaves the cell causing it to shrink. Red Blood Cell in hypertonic solution. Water leaves the cell causing it to shrink. Hypertonic Solution Extracelluar [NaCl] is greater than Intracellular [NaCl] Water moves out of cell & cell may shrink H2O net water movement out of the cell. Cell shrinks

Red Blood Cell in hypotonic solution. Water enters the cell causing it to swell. Red Blood Cell in hypotonic solution. Water enters the cell causing it to swell. Hypotonic Solution Extracellular [NaCl] is less than Intracellular [NaCl]. Water moves into cell & the cell swells Cell may lyse (burst) H2O net water movement into the cell. Cell swells and my lyse (burst)

In filtration of water and solids, gravity forces water through filter paper. Filtration Molecules are forced through membranes Force created by hydrostatic pressure, such as blood pressure. Commonly separates solids from liquids.

Filtration in body Blood pressure forces water and smaller solutes through tiny openings in capillary wall. Larger molecules, proteins, and cells remain inside the capillaries.

Active Transport Up to 40% of a cell’s energy supply is used for active transport. i.e. From lower concentration to higher concentration. Movement against a concentration gradient. Requires cellular energy (usually in the form of ATP). Active transport uses energy to “pump” particles through a carrier protein

ATP = currency of energy for cell Sodium/Potassium Pump: example of active transport 3 Na + are pumped out of the cell, while 2 K+ are pumped into the cell. The Na + /K + pump creates a high extracellular [Na + ] and a high intracellular [K + ]

endocytosis Cells take in larger substances by engulfing them. The cell membrane surrounds the substance and forms a vesicle from a portion of the cell membrane. Pinocytosis –cell takes in fluids Phagocytosis –cell takes in solid particles

Receptor-Mediated Endocytosis Cell takes in specific molecules Removes substances even in very low concentrations

Reverse of Endocytosis Cell organelles produce chemicals and proteins, and then package them in vesicles. The vesicles fuse with the cell membrane releasing the chemicals from the cell. Exocytosis Example of Exocytosis: Neurotransmitters are secreted from neurons by exocytosis

Transcytosis Combines endocytosis & exocytosis Quickly transports substances across cell Trancytosis transports HIV across linings of the mouth, anus, and female reproductive tract End of Section 2, Chapter 3 Transcytosis of HIV

Stages of the Cell Cycle Interphase Mitosis Cytokinesis Cell Differentiation

Interphase is a very active period of the cell’s life During interphase the cell grows and performs its routine functions Interphase can be divided into 3 sub-phases G1 phase (G = gap) S phase (S = synthesis ) G2 phase

G1 Phase The cell is active & grows during G1 phase G1 phase is followed by a restriction “checkpoint” that determines the cell’s fate: The cell may grow & divide The cell may remain active, but not divide The cell may undergo apoptosis = programmed cell death S Phase DNA synthesis occurs during S phase The cell replicates its DNA in preparation of cell division S phase

The 46 chromosomes are paired (diploid) 23 paternal (father) + 23 maternal (mother) Each cell in the body contains 46 chromosomes

Cell Division - p roduces 2 daughter cells from 1 cell Mitosis specifically refers to the division of a cell’s chromosomes. Karyokinesis is the division of the nucleus Cytokinesis is the division of the cytoplasm Mitosis occurs in Somatic (non-sex) cells – sex cells are formed from Meiosis Both daughter cells from mitosis retain the complete genome (46 chromosomes)

Prophase Chromatin condenses into chromosomes Centrosomes move towards opposite poles of cell The nuclear envelope breaks down Spindle fibers arise from the centrosomes = asters There are 4 phases of mitosis 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Use PMAT to remember the order!

Metaphase Spindle fibers attach to centromeres Chromosomes align along equator of cell Anaphase Spindle fibers shorten & pull on chromosomes Chromosomes separate & move towards opposite poles of cell Cytokinesis usually begins during anaphase

Telophase Chromosomes complete migration Nuclear envelopes reform Chromosomes begin to unwind Cytokinesis completes Cytokinesis Division of Cytoplasm Begins during Anaphase & continues through Telophase Microfilament rings pinches off two cells from one End of Chapter 3