Section 1, Chapter 3Cells
CellsOverview
Basic unit of life75 Trillion cells in human bodyVary 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
DifferentiationForming specialized cells from unspecialized cells
Major Parts of a CellNucleus
Cell Membrane
CytoplasmCytosol = fluidOrganelles
Cell Membrane
OverviewThe 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
Polar region (hydrophilic)
Nonpolar region(hydrophobic)
Phospholipid bilayer
Phospholipid Bilayer
Nonpolar Hydrocarbon tailsPhospholipids align so that tails are hidden from water
Nonpolar tails form the interior of membrane
Polar Phosphate headsPolar 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 moleculesProteins, Water, Sugars, ect. Cannot easily cross membrane
Cholesterol= rigid rings of hydrocarbons
Contributes to the nonpolar nature of membrane
Stabilizes the cell membrane
Increases rigidity of cell membrane
Membrane Proteins
1. Integral ProteinsSpans cell membrane
Forms ion channels & pores
Examples include: Na+ channels and K+ channels Aquaporins = water channels
Transmembrane ProteinsIntegral 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
Membrane Proteins2. Peripheral Proteins
Are loosely associated with the membrane.
May be a glycoprotein (protein + sugar)
Includes Cellular Adhesion Molecules (CAM)
Cellular Adhesion Molecules (CAM)
Peripheral proteins that guide moving cells to targets
Establishes cell-to-cell connectionsForms new neural connections in learning and memoryGuides cells surrounding an embryo towards uterusGuides white blood cells to injury
CAM ProteinSelectin
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
1. Nuclear Envelope
2. Nucleolus
3. Chromatin
3 Parts of the nucleus
Nuclear Envelope
Double-layered membrane = 2 lipid bilayers.
Nuclear PoresChannel proteins allow specific molecules across nuclear envelope
Ribosomes & RNA leaves nucleus through nuclear pores
Nucleolus “little nucleus”
• Dense body of RNA & Proteins
• Produces Ribosomes
Chromatin “Colored substance”
Chromosome “colored body”
Chromatin condenses into chromosomes during mitosis.
DNA wrapped around histone proteins
End of Section 1, Chapter 3
Section 2, Lecture 3
Movements into & out of Cells
The cell membrane creates a barrier through which molecules must cross into and out of the
cell.
Passive movementsRequires no energy from cell
DiffusionFacilitated DiffusionOsmosisFiltration
Active MovementsRequires energy from cell
Ion pumpsEndocytosisExocytosis
DiffusionTendency 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
DiffusionSubstances 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
Illustrating diffusion across cell
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% H2O40% protein
80% H2O20% protein
Higher H2O concentration
A B
Higher soluteconcentration
Membrane is impermeable to proteins
Osmotic Pressure = Pressure generated by osmosis.
H2O 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 solutionNo osmotic pressure = normal shape & size
Isotonic Solution
Extracellular [NaCl] is equal to Intracellular [NaCl].
Results in no osmotic pressure
H2O
H2O
Water moves into and out of the cell
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.
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.
FiltrationMolecules are forced through membranesForce 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+]
endocytosisCells 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 3Transcytosis of HIV
Section 3, Chapter 3
The Cell Cycle
The Cell Cycle: series of changes that a cell undergoes from the time it forms until it divides
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-phasesG1 phase (G = gap)S phase (S = synthesis)G2 phase
G1 PhaseThe 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 PhaseDNA synthesis occurs during S phase
The cell replicates its DNA in preparation of cell division
unreplicatedchromosome
S phase
replicatedchromosome
centromere
sister chromatids
The 46 chromosomes are paired (diploid) 23 paternal (father) + 23 maternal (mother)
Each cell in the body contains 46 chromosomes
Cell Division - produces 2 daughter cells from 1 cell
Mitosis specifically refers to the division of a cell’s chromosomes. Karyokinesis is the division of the nucleusCytokinesis 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)
ProphaseChromatin 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 mitosis1. Prophase2. Metaphase3. Anaphase4. Telophase
Use PMAT to remember the order!
MetaphaseSpindle fibers attach to centromeresChromosomes align along equator of cell
AnaphaseSpindle 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
CytokinesisDivision of Cytoplasm
Begins during Anaphase & continues through Telophase
Microfilament rings pinches off two cells from one
End of Chapter 3