cells chapters 7, 8, 11, and 12. a tour of the cell chapter 7
TRANSCRIPT
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Cells
Chapters 7, 8, 11, and 12
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A Tour of the Cell
Chapter 7
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Cell Theory
1. All organisms are made up of cells.
2. New cells come only from old cells.
3. The cell is the basic unit of life.
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Prokaryotic vs. Eukaryotic Cells
• What is the major difference between the two?
• Prokaryotes – “Before Nucleus”
• Contain no membrane bound organelles
• Limited to Nucleoid region, Ribosomes, Plasma membrane, and cell wall
• Eukaryotes – “True Nucleus”
• Contains membrane bound organelles
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Cellular Questions to Ponder?
• Why are most cells microscopic?• Do larger organisms have larger cells than
smaller ones?• Cells need a large surface area to volume
ratio (in the ballpark of 6:1).• Allows for cell to aquire more nutrients and
expel more waste• Why do cells have folded membranes?• Folded membranes allows for even more
surface area.
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Internal Membranes
• Internal membranes compartmentalize the functions of a eukaryotic cell:
• Partition cell into compartments
• Enzymes built into membranes because compartments can provide separate environments
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OrganellesWhat do you know about the organelles below?
• Nucleus• Endoplasmic Reticulum• Golgi Body (apparatus or complex)• Lysosomes• Mitochondria• Chloroplasts• Microtubules, Intermediate filaments, and microfilaments• Flagella and cilia• Centrioles• Cell Walls• Vacuoles• Peroxisomes
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Nucleus contains Genetic Library
• Contains DNA in form of chromosomes
• Surrounded by nuclear envelope
• Contains Nucleolus – portion of DNA that manufactures components of ribosomes which are then shipped to cytoplasm to assemble amino acids
• Ribosomes – build a cell’s proteins
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Endoplasmic Reticulum (ER)
• Involved in production of various materials
• Rough ER – ribosomes attached; involved in protein synthesis
• Smooth ER – no ribosomes; synthesis of lipids and hormones
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Golgi Apparatus
• Finishes, sorts and ships cell products
• Specifically… modify and package proteins and lipids into vesicles
• Vesicles often move to and merge with plasma membrane and release their contents outside the cell
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Lysosomes• Digestive Compartments• Contain digestive enzymes• Phagocytosis – “eat vessel”
– A formed food vacuole fuses with lysosome
• Types of Vacuoles:– Food Vacuoles– Contractile Vacuoles: pump excess water out of
cell– Central Vacuole: In plants; place to store organic
compounds and as disposal sites for metabolic “wastes” – Provides “turgor pressure” keeping plant cell rigidity so it doesn’t wilt
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Mitochondria
• Aerobic Respiration (Creating ATP)
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Chloroplasts
• Carry out photosynthesis
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• Microtubules – provides support and motility for cellular activities (part of spindle fibers)
• Intermediate filaments: provides support for maintaining shape of cell
• Microfilaments: involved in cell motility (found in muscle cells and cels that move by changing shape)
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Flagella and Cilia
• Classified by their length and number per cell…
• Flagella – long and few
• Cilia – short and many
• Both consist of microtubules arranged in a “9+2” array – 9 pairs (doublets) of microtubules arranged in a circle surrounding a pair of microtubules
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Cell Walls
• Found in plants, fungi, protists, and bacteria
• Provide support for the cell
• Consists mostly of cellulose (in plants), Chitin (in Fungi)
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Peroxisomes
• Break down substnaces
• O2 combines with Hydrogen to form toxic hydrogen peroxide (H2O2)
• Common in liver where they break down toxic substances
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Intercellular junctions in animals
• Desmosome – Anchoring Junction
• Tight Junction – form a seal that prevents leakage of extracellular fluid across a layer of cells (i.e. keep the contents of the intestine separate from the body fluid on the oposite side)
• Gap Junction – Communicating junction
See image on page 126
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Key differences between plant and animal cells:
1. Plants have cell walls
2. Plants have chloroplasts
3. Plants have large central vacuoles
4. Animal cells have centrioles (microtubule organizing centers)
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Membrane Structure and Function
Chapter 8
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Evolution of Membrane Models
• Original Davson-Danielli model – Globular Protein sandwich a phospholipid bilayer (proposed in 1935 and accepted until 1970)
• Currently explained by the fluid mosiac model
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Fluid Mosaic Model
• It is has mosaic nature of scattered proteins within a flexible matrix of phospholipid molecules.
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Plasma Membrane
• Composed of a Phospholipid Bilayer
• Selective Boundary between the cell and its environment (Selectively Permeable)
• Regulates functions of the cell
• Maintains Homeostasis
• Described by Fluid Mosaic model
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What makes up the Plasma Membrane?
• Phospholipid Bilayer – hydrophillic heads facing out; hydrophobic tails facing in.
• Proteins – Some as channels to regulate passage of molecules and others as enzymes.
• Cholesterol Molecules – reduce membrane fluidity by reducing phospholipid movement at high temps and hinders solidification at low temps.
• Membrane’s unique composition is suited to specific functions (Mitochondria membranes are embedded with enzymes that function in cellular respiration)
• Carbohydrates – Glycoprotein (protein w/ carb attached) and Glycolipids designate if cell belongs or not… these are called Oligosaccharides.
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The fluidity of Membranes:
• Phospholipids can move laterally (frequent) or by the flip-flop (rare)
• Fluid contains unsaturated “tails” with kinks while viscous contains saturated “tails”
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Important Components of Plasma Membrane(Important essay concept to address chemistry, structure, and components below)
• Transport Proteins
• Enzymatic Proteins
• Signal Proteins
• Intercellular Joining Proteins
• Cell-cell Recognition Proteins
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Traffic Across Membranes
• Substances move in two ways:• Bulk flow: overall movement of a group of
substances
Countercurrent Exchange – movement of substnaces between two regions in which bulk flow movement is in opposite directions. (i.e. blood in fish gills moves opposite direction of surrounding water running past them)
• Constant, Random Motion: motion of the molecules independent from the motion of other molecules
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Passive Transport
• Diffusion – movement of molecules from High to low concentration
• Diffusion across a biological membrane is called passive transport.
• Why is it considered passive?• Cell doesn’t need energy to make it
happen• When will this process stop?• When Dynamic Equilibrium is reached
(Homeostasis)
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Osmosis
• Osmosis is the passive transport of water across a selectively permeable membrane.
• Osmotic conditions have 3 options:
Isotonic, Hypotonic, or Hypertonic
How many of you have every killed a plant? How?
Over watering or Under watering?
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• Isotonic – same concentration of solutes inside as outside cell, not net change
• Hypotonic – low solutes/ high H2O outside cell; H2O moves in -- What does this do to plant and animal cells?
• Animal cells burst; Plant cells swell• Hypertonic – high solutes/ low H2O outside
cell; H2O moves out – What does this do to plant and animal cells?
• Animal cell shrinks; Plant cell contents shrink (loss of turgor pressure)
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Osmosis
State
H2O
Movement
Solute [ ]
Inside cell
Solute [ ]
Outside Cell
Isotonic[Same] [Same]
Hypotonic [High] [Low]
Hypertonic [Low] [High]
none
Into the cell
Out ofthe cell
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Osmosis Questions
• Which situation is best for animal cells? Why?
• Which Situation is best for plant cells? Why?
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Passive Transport
• No energy is required to move particles through the cell’s plasma membrane
• [high] to [low]• Facilitated Diffusion
– Protein required to move particles through membrane
– Move down concentration gradient by random movement
– Channel proteins vs. carrier proteins– How glucose enters the cell
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Other passive transports:
• Dialysis is the diffusion of solutes across a selectively permeable membrane.
• Plasmolysis is the movement of water out of a cell (osmosis) that results in the collapse of the cell
• Facilitated diffusion – the movement of solutes through channel proteins
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Active Transport
• Movement of solutes against a gradient.• [Low] to [High]• Aided by transport proteins (pumps) –
each one is specific to a certain substance• Requires the use of energy (typically ATP)• 67% of energy used to transport Na+ and
K+ across membranes.• See diagram of sodium-potassium pump
(Figure 8.14)
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EXOCYTOSIS
• Process of removing large particles or volumes of liquid
• Excretion – removal of waste products
• Secretion – removal of cell products needed elsewhere
• Requires vesicle and energy
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ENDOCYTOSIS
• Process in which the plasma membrane engulfs substances from the environment
• Pinocytosis – “cell drinking” large drops of liquid.
• Phagocytosis – “cell eating” large particles are engulfed into a vesicle for digestion
• This is how single celled protists capture food and how white bloods cells work for immunity
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• Receptor-mediated endocytosis – specific molecules in the fluid surrounding the cell bond to specialized receptors in the plasma membrane. This then triggers a phagocytosis type process
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Questions to look at on AP regarding Membrane Traffic:
• Is the substance moving across a selectively permeable membrane?
• Is the substance of interest water (solvent) or substance (solute)?
• In which direction is the substance moving? Down a gradient or the reverse?
• How does the concentration of solutes vary from one region to another?
• Is energy required to move the substance? Energy is required to go against the gradient
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Cell Communication
Chapter 11
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Paracrine Signaling
• Acts on nearby “target” cells
• Signal cell discharges molecules into extracellular fluid
• Local signaling
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Synaptic Signaling
• Nerve cell communication
• Neurotransmitters released into a synapse
• Local signaling
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Hormonal Signaling
• Signals target cells at greater distances.
• Specialized cells secrete hormones into bodily fluid (typically blood).
• Can reach all body cells
• Only specific “target” cells act and respond.
• Plants also use to signal from one part of plant to another
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Three stages of cell signaling…
1. Reception – target cell detects an incoming signal from outside cell
2. Transduction:• Changes protein in some way• Converts change to form that can bring specific cellular
response.• Often requires sequence of changes in a series of
different molecules (signal transduction pathway)3. Response – signal finally triggers cell response
(i.e. catalysis by enzyme, rearrangement of cytoskeleton, activation of specific genes…)
• Process ensures the crucial activities occur in the right cells, at the right time, and in proper coordination with other cells
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Examples Pathways
• G-protein-linked receptor (11.6 and 11.7)
• Tyrosine-kinase receptor (11.8)
• Ligand-gated ion-channel receptor (11.9)
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Signal Transduction Pathways
• Relay signals from receptors to cellular responses
• Protein phosphorylation is a major mechanism of signal transduction (11.10)
• Small molecules and ions are key components of signaling pathways (2nd messengers)– cAMP (11.12)– IP3 (11.14)
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Cellular-Responses to Signals
• In response to signal, a cell may regulate activities in the cytoplasm or transcription in the nucleus.
• Elaborate pathways amplify and specify the cell’s response to signals
• Nuclear Response (Figure 11.16)
• Specificity of cell signaling (Figure 11.17)
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The Cell Cycle
Chapter 12
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Key Roles of Cell Division:
• Functions in reproduction, growth, and repair
How do daughter cells compare to original cell?
• Division distributes identical sets of chromosomes to daughter cells
• Somatic Cells – All body cells except reproductive cells.
• Gametes – sperm and eggs
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Important Terms:
• Chromatin:
DNA protein fiber organized into long thin fibers
• Sister Chromatids:
Two chromatids containing identical sets of DNA that are initially attached.
• Centromere:
Location of sister chromatid attachment.
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The Cell Cycle
• Occurs in Eukaryotic Cells• Regular pattern of:
– Growth– DNA duplication – cell division
• 4 Stages in the cell cycle:
Gap 1 (G1), Synthesis, Gap 2 (G2), Mitosis• Enzymes control the transfer through the
stages
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Gap 1 (G1)
• First Stage (Growth)
• Cell carries out normal functions
• Cell increases in size
• Organelles increase in number
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Synthesis
• Second Stage
• Growth and Duplication of DNA
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Gap 2 (G2)
• Third Stage
• Similar to G1 phase
• Growth and preparation for cell division.
• Includes a critical checkpoint … the cell will only reproduce if everything is in order.
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Mitotic Cycle (Mitosis)
Interphase precedes Mitosis and includes G1,S, and G2
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
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Prophase
1. Nucleoli disappears and chromatin becomes visible chromosomes.
2. Nuclear envelope breaks down.
3. Mitotic spindle is assembled
• Spindle attached to Kinetochore
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Metaphase
1. Chromosomes move to the equator
2. Each sister chromatid is attached to its own spindle fiber
3. Spindle fibers are attached to centromere at kinetochore
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Anaphase
1. Centromeres are split
2. Sister Chromatids are pulled apart becoming chromosomes
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Telophase and Cytokinesis
1. Chromosomes reach opposite poles of the cell
2. Two distinct daughter cells are formed
3. Processes of prophase are reversed
Cleavage Furrow – groove the forms as “purse strings” tightened
Cytokinesis = division of the cytoplasm
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Mitosis of a White Fish Blastula Cell
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Regulation of the Cell Cycle
Cell-Cycle Control System:
• Cyclically operating set of molecules in the cell the both triggers and coordinates key events in the cell cycle.
Cell-cycle Checkpoints:
• Stop and go-ahead signals regulate the cycle.
• Enzymes drive this process
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Cues to regulate Cell Cycle
Internal Signals:
• M-phase checkpoint is the gatekeeper
• Signal that delays anaphase originates at the kinetochores that are not yet attached to spindle microtubules
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• External Signals:
• Growth factors are required to stimulate growth
• Density-dependent inhibition – crowded cells stop dividing (12.15)
• Anchorage dependence – to divide, animal cells must be attached to substratum.
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Cancer…
• Early in life, cells divide frequently while later in life, cells only grow and divide to replace old cells or repair injuries.
• Cells continue to be regulated by cell cycle and regulation cues
• Cancer cells have escaped cell cycle controls
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Key cancer terms
• Metastasis – spread of cancer cells beyond their original state.
• Tumor – mass of abnormal cells within otherwise normal tissue
• Benign tumor – most likely wont cause a serious problem.
• Malignant tumor – invasive enough to impair functions of one or more organs (cancerous tumor)