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Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Lecture 3
Cells: The Living Units
THE CELL THEORY
• A cell is the basic structural and functional unit of all organisms
• According to the principle of complementarity of structure and function, the biochemical reactions occurring in a cell are dictated by the subcellular structures present in the cell
• Reproduction has a cellular basis
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.1: Cell diversity, p. 65.- different shapes and sizes
Fibroblasts
Erythrocytes
Epithelial cells
Macrophage
Nerve cell
Fat cell
Sperm
Skeletalmusclecell
Smoothmuscle cells
(a) Cells that connect body parts, form linings, or transport gases
(c) Cell that stores nutrients
(b) Cells that move organs and body parts
(d) Cell that fights disease
(e) Cell that gathers information and controls body functions
(f) Cell of reproduction
3 MAIN PARTS OF A CELL
• Plasma membrane – defines the boundary of a cell
• Cytoplasm – the interior of the cell between the plasma membrane and the nucleus; contains the cytoplasmic organelles
• Nucleus – contains the genes which control activities of the cell
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.2: Structure of the generalized cell, p. 66.
Secretion being releasedfrom cell by exocytosis
Peroxisome
Ribosomes
Roughendoplasmicreticulum
NucleusNuclear envelopeChromatin
Golgi apparatus
Nucleolus
Smooth endoplasmicreticulum
Cytosol
Lysosome
Mitochondrion
Centrioles
Centrosomematrix
Microtubule
Microvilli
Microfilament
Intermediate filaments
Plasmamembrane
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.3: Structure of the plasma membrane according to the fluid mosaic model, p. 67.
Bimolecularlipid layercontainingproteins
Polar heads ofphospholipidmolecules
Nonpolar tailsof phospholipidmolecules
Filaments ofcytoskeleton
Cytoplasm(watery environment)
Glycoprotein
Cholesterol
Outward-facinglayer ofphospholipids
Inward-facinglayer ofphospholipids
Extracellular fluid(watery environment)
Glycolipid
Peripheralprotein
Integralproteins
Carbohydrateof glycocalyx
The Plasma Membrane• Forms the boundary of a cell
• Thickness = 7-10nm; very thin
• Composed of 2 layers of phospholipids ( lipid bilayer) arranged tail to tail with the polar hydrophilic heads exposed to the aqueous extracellular fluid and the intracellular fluid
• Embedded in this lipid bilayer are Membrane Proteins, Cholesterol
• Lipid bilayer exhibits fluidity and the membrane proteins are in constant flux - their shapes constantly change as in a kaleidoscope or a mosaic pattern. Hence, the plasma membrane is said to be of the FLUID MOSAIC MODEL
• Cholesterol inserts between the phospholipids tails to stabilize the plasma membrane = “ cholesterol therefore maintains the integrity of the plasma membrane
The Membrane Proteins
• Integral Proteins: span the plasma membrane exposed on one surface or both surfaces of the plasma membrane.
Integral proteins exposed on both surfaces of the plasma membrane are called Transmembrane Proteins
• Peripheral Proteins: attached to integral proteins or the phospholipids’ heads on the cytoplasmic face of the plasma membrane
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.4: Some functions of membrane proteins, p. 68.
Transport(a) A protein that spans the membranemay provide a hydrophilic channelacross the membrane that is selectivefor a particular solute. (b) Sometransport proteins hydrolyze ATP as anenergy source to actively pumpsubstances across the membrane.
Enzymatic activityA protein built into the membrane maybe an enzyme with its active siteexposed to substances in the adjacentsolution. In some cases, severalenzymes in a membrane act as a teamthat catalyzes sequential steps of ametabolic pathway as indicated(right to left) here.
Receptors for signal transductionA membrane protein exposed to theoutside of the cell may have a bindingsite with a specific shape that fits theshape of a chemical messenger, suchas a hormone. The external signalmay cause a conformational changein the protein that initiates a chain ofchemical reactions in the cell.
Intercellular joiningMembrane proteins of adjacent cellsmay be hooked together in variouskinds of intercellular junctions.Some membrane proteins (CAMs)of this group provide temporarybinding sites that guide cellmigration and other cell-to-cellinteractions.
Cell-cell recognitionSome glycoproteins (proteinsbonded to short chains of sugars)serve as identification tags thatare specifically recognized byother cells.
Attachment to the cytoskeletonand extracellular matrix (ECM)Elements of the cytoskeleton (cell’s internal supports) and theextracellular matrix (ECM) may beanchored to membrane proteins,which help maintain cell shapeand fix the location of certainmembrane proteins. Others play arole in cell movement or bindadjacent cells together.
(a) (b)
ATP
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.5: Cell junctions, p. 70.
Linkerproteins
Plaque
Intermediate filament
Intercellular space
Intercellular space
Interlockingjunctional proteins
Microvilli
Tight junction
Plasma membranesof adjacent cells
Gap junction
Underlying basement membrane
Extracellular space between cells
Desmosome
Intercellularspace
Channelbetween cells(connexon)
(b) Desmosome
(a) Tight junction
(c) Gap junction
Membrane Junctions• Tight Junction – fusion of integral proteins in
plasma membrane of adjacent cells forming an “impermeable junction”
• Desmosome – linker proteins extending from plaques on the cytoplasmic surface of the plasma membrane of adjacent cells interdigitate to hold the cells together and prevent their separation; also known as “anchoring junction”
• Gap Junction – formed by hollow cylinder called connexons; it allows for the rapid transfer of ions
between cells; also known as “communicating junction”
MEMBRANE TRANSPORT – the plasma membrane is a selective barrier
1. Passive processes – substances cross the plasma membrane without any energy input
2 main types: Diffusion and Filtration Diffusion – 3 subtypes: Simple diffusion Facilitated diffusion
Osmosis 2. Active processes – the cell provides energy required to move
substances across the plasma membrane 2 main types: Active transport ( = “solute pumping”) and Vesicular
transport Vesicular transport – Exocytosis and Endocytosis Exocytosis – movement of substances out of the cell Endocytosis – movement of substances into the cell Phagocytois Pinocytosis Receptor-mediated endocytosis
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.7: Diffusion through the plasma membrane, p. 72.
Extracellular fluid
Cytoplasm
Lipid-solublesolutes
Lipidbilayer
Lipid-insolublesolutes
Watermolecules
Small lipid-insolublesolutes
(a) Simple diffusion directly through the phospholipid bilayer
(c) Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge
(b) Carrier-mediated facilitated diffusion via protein carrier specific for one chemical; binding of substrate causes shape change in transport protein
(d) Osmosis, diffusion through a specific channel protein (aquaporin) or through the lipid bilayer
DIFFUSION• Movement of substances from area of higher
concentration to area of lower concentration; substances move down their concentration gradient
• Simple diffusion – nonpolar/hydrophobic/lipid-soluble substances diffuse through the plasma membrane. Ex. Oxygen, carbon dioxide
• Facilitated diffusion – transport of large/polar substances mediated by carrier proteins embedded in the plasma membrane. Facilitated diffusion exhibits saturation, specificity
• Osmosis – movement of water from area of lower solute concentration to area of higher solute concentration through a semi-permeable membrane
Water moves through specific channels called aquaporins
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.8: Influence of membrane permeability on diffusion and osmosis, p. 73.
Leftcompartment:Solutionwith lowerosmolarity
Membrane
Solutemolecules(sugar)
Rightcompartment:Solutionwith greaterosmolarity
Both solutions havethe same osmolarity:volume unchanged
H2O
Solute
Leftcompartment
Membrane
Rightcompartment
Both solutions have identicalosmolarity, but volume of thesolution on the right is greaterbecause only water isfree to move
H2O
(a) Membrane permeable to both solute molecules and water
(b) Membrane impermeable to solute molecules, permeable to water
Tonicity• Movement of water in and out of cells can change the
shape or tone of cells.• Isotonic solution – concentration of solution inside and
outside of the cells is the same; the same amount of water moves in/out of the cells/ shape of cells remain unchanged
• Hypertonic solution – cells placed in solution with a higher concentration than solution inside cells; water moves via osmosis from the cells; cell crenate ( shrink)
• Hypotonic solution – cells are placed in a solution with a lower concentration than solution inside cells;
water moves via osmosis into the cells – cells swell and eventually burst
Filtration
• A passive process – no energy input
• Movement of solution from area of higher pressure to area of lower pressure; down a pressure gradient
Active Processes• Energy (ATP) is required for the movement of
substances across the plasma membrane• 2 types:Active transport and Vesicular transport• Active transport – movement of solutes/ions from area
of lower solute concentration to area of higher solute concentration (against a concentration gradient); mediated by carrier proteins. Active transport exhibits saturation and specificity.
Ex. sodium./potassium pump ( Na+/K+ pump)
Hence, active transport is also known as “Solute Pumping”
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.10: Operation of the sodium-potassium pump, an antiport pump (Na+–K+ ATPase), p. 76.
Cytoplasm
Extracellular fluid
K+ is released and Na+ sites are ready to bind Na+ again; the cycle repeats.
Cell ADP
Phosphorylation causes the protein to change its shape.
Concentration
The shape change expels Na+ to the outside, and extracellular K+ binds.
Loss of phosphate restores the original conformation of the pump protein. K+ binding triggers
release of the phosphate group.
Binding of cytoplasmic Na+ to the pump proteinstimulates phosphorylation by ATP.Na+
Na+
Na+
K+
K+
Na+Na+
K+K+
K+
K+
Na+
Na+
Na+
ATPP
P
Na+
Na+Na+
K+
K+
P
Pi
1
2
3
4
5
6
Active Process – Vesicular Transport• 2 types – Exocytosis and Endocytosis
• Exocytosis – movement of substances enclosed in vesicles from the interior of cells to the exterior.
Hormones, enzymes are secreted via exocytosis
• Endocytosis – movement of substances from the exterior of cells to the interior
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.12: Exocytosis, p. 78.
Extracellularfluid
Cytoplasm
Molecules tobe secreted
VesicleSNARE
Plasma membraneSNARE
Secretory vesicle
(a)
(b)
Movement of substances from the interior of the cell to its exterior
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.13: Clathrin-mediated endocytosis, p. 79.
Recycling ofmembrane andreceptors (if present)to plasma membrane
CytoplasmExtracellular fluid
Extracellularfluid
Plasmamembrane
Detachmentof clathrin-coatedvesicle
Clathrin-coatedvesicle
Uncoating
Uncoatedvesicle
Uncoatedvesiclefusing withendosome
To lysosomefor digestionand releaseof contents
Transcytosis
Endosome
Exocytosisof vesiclecontents
Clathrin-coatedpit
Plasmamembrane
Ingestedsubstance
Clathrinprotein
(a) Clathrin-mediated endocytosis
Endocytosis - Movement of substances from the exterior of the cell to its interior
Endocytosis• Movement of substances from the exterior of a cell into the cell’s
interior. 3 types:
i) Phagocytosis – movement of solid particles from the exterior into the cell; solid particles are enclosed in vesicles called PHAGOSOMES; Lysosomes fuse with the phagosomes to digest the phagosomes and its contents. Cells that perform phagocytosis are called Phagocytes.
ii) Pinocytosis – movement of solution into cells by enclosing the solution in vesicles
iii) Receptor-mediated endocytosis – substances bind to specific receptors on the surface of the cell; clathrin appear where the substances are bound; coated pits form to transport substances into the cell.
Receptor-mediated endocytosis exhibits saturation and specificity
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.13: Clathrin-mediated endocytosis, p. 79.
Recycling ofmembrane andreceptors (if present)to plasma membrane
CytoplasmExtracellular fluid
Extracellularfluid
Plasmamembrane
Detachmentof clathrin-coatedvesicle
Clathrin-coatedvesicle
Uncoating
Uncoatedvesicle
Uncoatedvesiclefusing withendosome
To lysosomefor digestionand releaseof contents
Transcytosis
Endosome
Exocytosisof vesiclecontents
Clathrin-coatedpit
Plasmamembrane
Ingestedsubstance
Clathrinprotein
(c) Receptor-mediated endocytosis
Extracellularfluid
Cytoplasm
Bacteriumor otherparticle
Pseudopod
Clathrinprotein
(b) Phagocytosis
Clathrinprotein
Membranereceptor
(a) Clathrin-mediated endocytosis
1
3
2
c) Pinocytosis – movement of solution into cells
Transcytosis and Vesicular trafficking
Trancytosis: Movements of substances enclosed in caveolae into a cell, across the cell and released on the opposite side of the cell via exocytosis
Vesicular Trafficking: Intracellular movement of substances in coatmer- coated vesicles from organelle to organelle with the cell
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.15: The role of K+ in generating the resting membrane potential, p. 82.
Potassiumleakagechannel
Protein anionCytoplasm
K+ diffuse down their steepconcentration gradient (outof the cell) via leakagechannels. Loss of K+ resultsin a negative charge on theinner plasma membraneface.
A negative membrane potentialis established when the movementof K+ out of the cell equals K+
movement into the cell.
K+ also move into the cellbecause they are attractedto the negative chargeestablished on the innerplasma membrane face.
+
–
–
– –– –
––
+
+ + +
++
+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
A–
A–K+
K+
K+
Cl–
Cl–
1 2
The Resting Membrane Potential (RMP)
• RMP of resting cells is between -50mV to -100mV
• RMP is established by the partial/selective permeability of the plasma membrane to potassium ion (K+) diffusion over sodium ion( Na+) diffusion.
• K+ concentration is higher inside the cell than outside the cell – K+ diffuses out of the cell down its electrochemical gradient
• Na+ concentration is higher outside of the cell than inside the cell – Na+ diffuses into the cell down its electrochemical gradient
• The plasma membrane is about 75 times more permeable to K+ than Na+ = more K+ diffuses out of cell than Na+ diffusing into the cell = more positive ions move out of the cell making the cytoplasmic surface of the plasma membrane negative compared to the extracellular surface
THE CYTOPLASM• Composed of cytosol, cytoplasmic organelles, and
inclusions ( such as glycosomes, melanosomes)• Cytosol – the viscous, semitransparent fluid• Cytoplasmic organelles- specialized subcellular
compartments with specific functions i) Mitochondria = “power plants”
ii) Ribosomes = sites of protein synthesis iii) Endoplasmic reticulum ( ER) Rough ER = “membrane factories” Smooth ER = lipid/drug metabolism
iv) Golgi apparatus = “traffic director” of the cell v) Lysosomes = “demolition crew” vi) Peroxisomes = neutralize harmful free radicals vii) Cytoskeleton
2 Types of cytoplasmic organelles• Membranous cytoplasmic organelles:
Mitochondria
Endoplasmic Reticulum (ER)
Golgi apparatus
Lysosomes
Peroxisomes
• Nonmembranous cytoplasmic organelles: Ribosomes
Cytoskeleton
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.17: Mitochondrion, p. 85.
Enzymes
Matrix
Cristae
MitochondrialDNA
Ribosome
Outermitochondrial membrane
Innermitochondrialmembrane
(a) (b)
Mitochondria • Threadlike membranous organelles - constantly
changing their shapes• Contain own DNA and are self-replicating organelles
• Composed of 2 membranes enclosing a fluid matrix
• 2 mitochondrial membranes are – outer and inner membranes
• The inner membrane consists of infoldings called cristae
• Resident enzymes of the cristae and the matrix breakdown food in the presence of oxygen
( = aerobic respiration) to release energy hence, mitochondria are referred to as the “POWER PLANTS” of a cell
RibosomesEach ribosome is composed of 2 globular subunits – small ribosomal subunit and a large ribosomal subunitEach ribosomal subunit consists of protein and rRNA
2 types of ribosomes – Free and Bound
Free ribosomes float freely in the cytosol and synthesize proteins that stay in the cell
Bound ribosomes – bound to the surface of rough ER and synthesize proteins that are transported to the plasma membrane or for export out of the cell ( secreted)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.18: The endoplasmic reticulum (ER) and-
ribosomes, p. 86.
Nuclear envelope
RibosomesRough ER
Smooth ER
Smooth ER Rough ER with boundribosomes
Large subunit
Small subunit
Functionalribosome
+
(a)
(b) (c)
Endoplasmic Reticulum - ER• Composed of meandering membranous channels
enclosing fluid-filled cavities called cisternae • 2 Types of ER – Rough ER and Smooth ER
• Rough ER – external surface is studded with ribosomes ( Bound ribosomes) – these ribosomes synthesize the plasma protein and secretory proteins. Rough ER is therefore abundant in secretory cells such as liver cells
• Rough ER is referred to as the “Membrane factory” because the synthesis of integral proteins (by ribosomes) and phospholipids in plasma membranes is associated with the rough ER
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.19: The signal mechanism targets ribosomes to the ER for protein synthesis, p. 87.
Cytosol
Ribosomes
mRNA
Coatomer-coatedtransportvesicle
Transportvesiclebudding off
Releasedglycoprotein
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite
Sugargroup
SignalsequenceremovedGrowing
polypeptide
1
2
34
5
Smooth ER
Smooth ER
Smooth ER is devoid of ribosomes = “smooth surface”Its membrane-bound enzymes catalyze: - Synthesis of fats , cholesterol and steroid hormones - Fat absorption, transport and metabolism- Glycogenolysis which results in energy production - Detoxification of drugs and carcinogens in liver and kidney cells
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.20: Golgi apparatus, p. 88.
Cis face—“receiving” side ofGolgi apparatus
Transport vesiclefrom the Golgi
Transport vesiclefrom the Golgi
Secretory vesiclefrom trans face
Trans face—“shipping” side ofGolgi apparatus
New vesiclesforming
New vesicles forming
Cisternae
Transport vesiclefrom rough ER
Golgi apparatus
(a)
(b)
Golgi Apparatus• Composed of stacked /flattened membranous sacs• Receives proteins and lipids from the rough ER • Golgi modifies, packages and tags proteins and lipids to
their specific destinations hence, the Golgi apparatus is referred to as the “Traffic director” of the cell
• 3 types vesicles produced by the Golgi:
- secretory vesicles which contain proteins released via exocytosis
- Vesicles that contain integral proteins and lipids destined for the plasma membrane to incorporated into the plasma membrane
- Vesicles containing powerful digestive enzymes that remain in the cell = LYSOSOMES to digest phagosomes… more on next slides
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.21: The sequence of events from protein synthesis on the rough ER to the final distribution of those proteins, p. 88.
Secretion by exocytosisExtracellular fluid
Plasma membrane
Vesicle incorporatedinto plasma membrane
Coatomercoat
Lysosomes containing acidhydrolase enzymes
PhagosomeProteins in cisterna
Membrane
Vesicle
Pathway 3
Pathway 2
Secretory vesicles
Proteins
Pathway 1
Golgi apparatus
CisternaRough ER
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Lysosomes -
Golgiapparatus
Lysosome
Rough ER
Tra
Nucleus
Spherical membranous organelles - contain powerful digestive enzymes that digest vesicles and biological molecules.
Function: - Digest phagosomes hence, lysosomes are abundant in phagocytes - Digest worn-out organelles - Stimulate glycogenolysis - Involved in bone resorption to release calcium
Hence, lysosomes are referred to as a cell’s “demolition crew”
Peroxisomes
Peroxisome
Membranous sacs that contain Powerful enzymes that neutralize harmful free radicals 2 kinds of enzymes in peroxisomes: Oxidases and Catalases
Free radicals (harmful) + Oxidases -- Hydrogen peroxide ( harmful) Hydrogen peroxide + Catalase - Water
Cytoskeleton• “Cell skeleton” – consists of non membranous rod-like structures
that support other cytoplasmic organelles and allow for movements• 3 Types based on size and function:
i) Microtubules – largest diameter = 25nm wide
ii) Intermediate filaments – diameter between that of a microtubule and a microfilament = 10nm
iii) Microfilaments – smallest diameter = 7nm
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.24c: Cytoskeleton, p. 91.
Tubulin subunits
25 nm
( Microtubule
Microtubules• Largest cytoskeleton – hollow tubes composed of the globular
proteins called TUBULINS
• Radiate from the CENTROSOME which acts as a microtubule organizing center
• Function of Microtubules:
• Serve as “tracks” to transport intracellular substances
- cytoplasmic organelles and secretory vesicles attached by motor molecules to microtubules for intracellular, vesicular trafficking
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.25: Interaction of motor molecules (motor proteins) with cytoskeleton elements, p. 92.
Receptor formotor molecule
Microtubuleof cytoskeleton
Motor molecule(ATP powered)
Organelle
Cytoskeletal elements(microtubules or microfilaments)
Motormolecule(ATPpowered)
(a) (b)
ATPATP
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.26: Centrioles, p. 92.
Centrosome matrix
Centrioles
Microtubules
(a)
(b)
(c)
Cilia and flagella• Centrosome ( microtubule-organizing center) contains a pair of
CENTRIOLES at right angles to each other.
• Centrioles sprout spindle fibers ( mitotic spindles) required for cell division
• Centrioles form 2 types of cell extensions:
CILIA and FLAGELLUM• Cilia – cellular extensions that occur in large numbers on
the apical ( exposed ) surface of cells• Several cells in the body are ciliated • Cilia beat to create a current that moves substances
across the surface of the cells• Flagellum – a single, longer cellular extension• Flagellum beats to propel the cell it extends from • The only flagellated cell in the human body is sperm
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.27: Cilia structure and function, p. 93.
Power stroke
Layer of mucusCell surface
Recovery stroke
Basalbody(centriole)
Plasmamembrane
Outerdoubletmicrotubules
Centralmicrotubules
Centralmicrotubules
Dyneinarms
Outerdoubletmicrotubules
Plasmamembrane
Cilium 1 2 3 54 6 7
(b) Ciliary motion
(c) Movement of mucus across cell surfaces
(a) Cilium
Sperm – Flagellated cell
•
•
= flagellum
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.24a-b: Cytoskeleton, p. 91.
Actin subunit
7 nm
Fibrous subunits
10 nm
Microfilament
(Intermediate filament
Intermediate Filaments• Composed of tough, insoluble fibrous fibers
• Most stable type of cytoskeleton
• Provide tensile strength to cells by resisting pulling forces placed on the cells
• Given specific names in specific cell types:
Tonofilaments in epidermal cells
Neurofilaments in neurons
Microfilaments• Have the smallest diameter• Composed of the protein ACTIN• The arrangement of microfilaments is unique to each
cell• Function:
Involved in changes in cell shape or cell motility as in contraction
Involved in the formation of cleavage furrow during cytokinesis
Involved in the changes of the plasma membrane during endocytosis and exocytosis
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.28: The nucleus, p. 96.
Condensed chromatin
Nuclear envelope
Nucleus
NucleolusPores
(a)
Cisternae of rough ER
The Nucleus• Control center of a cell
• A cell with one nucleus = Uninucleate
• A cell with many nuclei = Multinucleate
• A cell without a nucleus = Anucleate
• 3 main regions:
• Nuclear membrane
• Nucleolus
• Chromatin
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.28: The nucleus, p. 96.
Condensedchromatin
Nuclear envelope
Nucleus
Surface of nuclear envelope.TEM prepared by freeze-fracture. A, inner membrane; B, outer membrane; NP, nuclear pore (pore complex); White arrows, fracture lines of outer membrane.
Pore complexes (TEM). Eachpore is ringed by protein particles.
Nuclear lamina (TEM). Thenetlike lamina composed of intermediate filaments called lamins lines the inner surface of the nuclear envelope.
Nucleolus
Pores
Cisternae ofrough ER
(a)
(b)
Nuclear Envelope • = Nuclear Membrane
• Double-layered selective membrane with nuclear pores
• Nuclear pores allow molecules to enter /exit the nucleus – proteins translocate from the cytoplasm into the nucleus; RNA molecules move from the nucleus into the cytoplasm
The Nucleolus
Nucleolus
Dark spherical non- membranous structure in the nucleus
Synthesizes ribosomal RNA ( rRNA) required for assembling the 2 ribosomal subunits – small and large Ribosomes are sites for protein synthesis hence,nucleoli are prominent in cells producing large amounts of proteins
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.29: Chromatin and chromosome structure, p. 98.
Metaphasechromosome
Supercoiledstructure(200-nm diameter)
Tight helical fiber(30-nm diameter)
Chromatid(700-nm diameter)
Nucleosome(10-nm diameter)
Linker DNA
Chromatid(“beads ona string” )structure
Histones
DNAdoublehelix(2-nmdiameter)
(a)
(b)
1
2
3
5
4
Chromatin• Composed of DNA and the
histone proteins
• Consists of structural units called NUCLEOSOMES
• Each nucleosome is composed of 8 globular histone proteins connected by the thread-like DNA
• DNA consists of structural units called NUCLEOTIDES
DNA
Histone proteins
Nucleic AcidsStructural units of nucleic acids are NUCLEOTIDES
Each nucleotide is composed of – i) pentose sugar - deoxyribose or Ribose ii) Nitrogen-containing base - A,G, C, T, U iii) Phosphate group
2 Types of Nucleic Acids: Deoxyribonucleic Acids = DNARibonucleic Acids = RNA
Compare DNA and RNA
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.30: The cell cycle, p. 99.
G1
Growth
SGrowth and DNA
synthesisG2
Growth and finalpreparations for
divisionM
G2 checkpoint
G1 checkpoint Interphase
Cytokinesis
MitosisTelo
ph
ase
An
aph
aseM
etaphase
Prophase
Mitotic phase (M)
The Cell Cycle• The series of events a cell undergoes from the time it’s
formed until it reproduces
• Consists of 2 major sequential periods:
i) Interphase – protein synthesis, cell growth and DNA replication occur
Consists of 3 sequential phases: G1, S, G2
ii) Cell division – mitosis and cytokinesis occur
Mitosis – Nuclear division: 4 sequential phases:
Prophase, Metaphase, Anaphase, Telophase
Cytokenesis – Cytoplasmic division
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Leadingstrand
Replicationfork
DNApolymerase III
DNA polymerase III
Laggingstrand
Key: = Adenine= Thymine= Cytosine= Guanine
New strandforming
Old(template)strand
Old (template) strand
Newlymadestrand
DNA of onechromatid
Figure 3.31b: Replication of DNA, p. 100.
SEMI-CONSERVATIVE
REPLICATION:Each daughter DNA Consists of a an old strand and a newly-Synthesized strand
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.31a: Replication of DNA, p. 100.
PrimaseReplisome
DNA template
RNA primer
RNA primer
RNA primerbeing replacedby DNAnucleotides
Completeddaughter strand
DNApolymerase III
DNApolymerase I
Newly made DNA
Replicase
(a)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.32: The stages of mitosis, p. 102.
Interphase Early prophase Late prophase
Centrioles(two pairs)
Nucleolus
Nuclearenvelope
Plasmamembrane
Condensedchromatin
Early mitoticspindle
Pair ofcentrioles
CentromereChromosome, consistingof two sister chromatids
Aster
Fragments ofnuclearenvelope
Kinetochoremicrotubule
Spindlepole
Kinetochore
Polarmicrotubules
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.32: The stages of mitosis (continued), p. 103.
Metaphaseplate Nucleolus
forming
Nuclearenvelopeforming
Contractilering atcleavagefurrow
SpindleDaughterchromosomes
MetaphaseAnaphase Telophase and cytokinesis
Mitosis
• Describe the 4 stages of mitosis
• Compare and contrast Prophase and Telophase
Cancer cells
• Neoplasm – abnormal excessive proliferation of cells.• 2 classes of neoplasm – Benign and Malignant• Benign neoplasm – grows slowly and it’s confined to
one location• Malignant neoplasm = CANCER – grows fast and
aggressively; metastasizes to other organs
• Based on your understanding of the cell cycle, discuss ways you may design cancer therapeutic drugs
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.33: Simplified scheme of information flow from the DNA gene to protein structure, p. 105.
Nuclearenvelope
DNA
Pre-mRNA
mRNA
Ribosome
Polypeptide
Translation
RNA Processing
Transcription
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.34a: An overview of transcription, p. 106.Codingstrand
Templatestrand
PromoterTermination signal
Transcription unitIn a process mediated by a transcriptionfactor, RNA polymerase binds topromoter and unwinds 16–18 basepairs of the DNA template strand
RNApolymerase
Unwound DNA
RNAnucleotides
RNA polymerasebound to promoter
mRNA synthesis begins
RNA polymerase moves down DNA;mRNA elongates
RNAnucleotides
mRNA synthesis is terminatedRNApolymerase
mRNA
DNA
mRNA transcript(a)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.34b: An overview of transcription, p. 106.
RNAnucleotides
RNA polymerase
Unwindingof DNA
Coding strand
Rewinding of DNA
mRNARNA-DNAhybrid region
Template strand
(b)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.35: The genetic code, p. 107.SECOND BASE
UUG
UUA
UUC
UUUPhe
Leu
CUG
CUA
CUC
CUU
Leu
AUA
AUC
AUU
Ile
GUG
GUA
GUC
GUU
Val
UCG
UCA
UCC
UCU
Ser
CCG
CCA
CCC
CCU
Pro
ACG
ACA
ACC
ACU
Thr
GCG
GCA
GCC
GCU
Ala
UAC
UAUTyr
CAG
CAA
CAC
CAUHis
Gln
AAG
AAA
AAC
AAUAsn
Lys
GAG
GAA
GAC
GAUAsp
Glu
UGC
UGUCys
Trp
CGG
CGA
CGC
CGU
Arg
AGG
AGA
AGC
AGUSer
Arg
GGG
GGA
GGC
GGU
Gly
UAA Stop UGA Stop
AUGMet orStart
UAG Stop UGG
U C A G
G
A
C
U
G
A
C
U
G
A
C
U
G
A
C
U
U
C
A
G
TH
IRD
BA
SE
FIR
ST
BA
SE
The Genetic Code – indicates how the base sequence of a gene is translated into amino acids
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.36: Translation, p. 108.
After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins.
Amino acids
tRNA
Aminoacyl-tRNAsynthetase
tRNA "head" bearinganticodon
Largeribosomalsubunit
Small ribosomalsubunit
Released mRNA
mRNA
Template strandof DNA
RNA polymeraseNuclear poreNuclear membrane
Portion of mRNAalready translated
Direction ofribosomeadvance
Nucleus
Once its amino acid is released, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid.
Incoming aminoacyl-tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome.
Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme.
As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site
Codon16
Codon15
Codon17
PCG
GCC C AUU AUG
E A
Ile
Ala
Phe
SerGlyMet
Ile
AAGU AU
U AU
1
4
3
2
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.37: Polyribosomes, p. 109.
Ribosome
Completedpolypeptide
Peptide chain
Ribosomalunits
mRNA
mRNARibosome
1
1
1
1
1
1
2
2
2
2
3
3
3
4
45
(a) (b)
Human Anatomy and Physiology, 7eby Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,publishing as Benjamin Cummings.
Figure 3.38: Information transfer from DNA to RNA, p. 110.
DNAmolecule
Gene 1
Gene 3
Gene 5
DNA base sequence (triplets)of the gene coding for thesynthesis of a particularpolypeptide chain
Base sequence (codons) ofthe transcribed mRNA
Consecutive base sequencesof tRNA anticodons capableof recognizing the mRNAcodons calling for theamino acids they transport
Amino acid sequence of thepolypeptide chain
1 2 3 4 5 6 7 8 9
Codons
Triplets
tRNA
1 2 3 4 5 6 7 8 9
StartStop;
detach
Met Pro Ser Leu Lys Gly Arg Phe