cell structure and function part 1: cell intro and the plasma membrane
TRANSCRIPT
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Cell Structure and Function Part 1:Cell intro and the plasma membrane
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Cell Factoids (not on test)• 75-100 trillion per body
– 75,000,000,000,000
• 200+ different types– Each is structurally and functionally different
• 7µm – 120µm in size– 7/10,000th – 12/1000th of a cm
– 7/125,000 -120/125,000ths of an inch
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Cell Theory (for AP150)
• All known living things are made up of one or more cells
• Cells are the fundamental structural and functional unit of the body.
– Cells are responsible for the fundamental structure of the human body
– Cells are responsible for the fundamental functions of the human body
• The structure (and function) of higher levels of organization (e.g., tissues, organs) reflects the activities and structures of cells
• The activity of an organism/the whole body depends on the total activity of independent cells.
• Cells contain DNA which is passed from cell to cell during division
• Energy processing and most chemical reactions occurs in cells
• Cells only come from other, pre-existing cells.
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Things Cells Do:
• Obtain nutrients and O2 from its environment
• Perform chemical reactions and process nutrients to release energy (metabolism)
• Eliminate cell waste
• Regulate their internal environment
• Move (external or internal)
• Sensitive to and responds to surroundings
• Grow
• Reproduce
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A Prototypical/Generic Cell
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The Generic CellThe major parts of the cell include• Plasma membrane — the outer boundary of the cell• Cytoplasm — within PM, performs most cell activities• Nucleus— contains protects DNA
Plasma Membrane
Cytoplasm
Nucleus
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Parts/Components of cell
Cell = Plasma Membrane + Cytoplasm + Nucleus
Cytosol + organelles + inclusions
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Body/Fluid Compartments
• intracellular v. extracellular compartments– Intracellular = inside cells– Extracellular = outside cells– Plasma Membrane separates
1-45
A.
B.
intracellular
extracellular
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Body/Fluid Compartments
• Extracellular :– blood plasma – interstitial fluid or tissue fluid
1-45
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• The extracellular and intracellular environments can be very different
• Example is extracellular v. intracellular Na+ and K+ concentration
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Functions of the Plasma Membrane (PM)those from text in blue
• Forms a physical barrier (that separates):– separates inside of cell from outside (forms a compartment).– Selectively Permeable allows some things through but not others
• regulation of movement– Actively regulates or influences what can enter/exit cell
• Connection (Attachment)– connects cells to other cells and/or surrounding structures– connects to internal cell parts
• Communication regulation/coordination– allows cell-cell communication/signalling for coordination of activity
• Chemical reactions – chemical reactions take place on the PM
• Cell recognition– The PM “labels”/identifies the cell
*italicized words represent the four functions the book describes, I have elaborated and reworded
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Reference Slides:• The plasma membrane creates a boundary between the
cells internal environment and its external environment.– It makes the cell a compartment that is separated from other
areas/compartments of the body.
• It creates a selectively permeability barrier that some substances can pass through and others can’t– Because of this:
• There is a difference in the composition of the intracellular (inside cell) and extracellular (outside cell) environment.
• The cells internal environment can be regulated
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PM Structure:Composition of the PM
• Three types of molecules make up the PM1. Lipids—about 45% of PM (by mass/weight), more by surface area
• 5-10% of lipids have carbohydrates attached2. Proteins—about 55% of PM (by mass)
• Includes glycoproteins
The PM is mostly Lipids and Proteins and these two molecules exist in relatively equal proportions.
* Carbs make up about 3%of overall PM by weight/mass
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Membrane Lipids2 primary types of Membrane Lipids
1. Phospholipids—Most abundant (~70-75%), • One factor that creates selective permeability-- prevents the movement of most substances across the PM-- Especially fluids: Prevents intracellular fluids from escaping and
extracellular fluids from entering
2. Cholesterol—less abundant (~20%), effects membrane fluidity/ stabilizes at high temperatures (i.e., prevents it from becoming too fluid)keeps membrane from being too rigid
3. Glycolipids—5-10% of lipidsthe sugar portion located on cells exterior and helps form glycocalyx
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Phospholipids have 2 regions• Head—hydrophilic, attracted to water• Tails—hydrophobic, repelled by water
Phospholipid
Head
Tails
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Extracellular (outside cell)
Intracellular (inside cell)
Lipid bilayer
CholesterolSpans hydrophobic and hydrophilic regions. Doesn’t pass through both sides of PM
Non-polar tail region: Impermeable to ions and polar moleculesExcept Water
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Functional Consequences of phospholipids
• Because the center of the phospholipid bilayer is hydrophobic (and non-polar):
1. Most polar/water soluble substances and ions cannot pass through the lipid portion of membrane.
2. Only non-polar (lipid soluble) can substances can pass directly through the lipids of the membrane.
Thus: the lipid bilayer creates selective permeability and influences what can pass into and out of a cell (contributing to the difference between the intracellular and extracellular environments).
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18
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Two different ways to describe membrane proteins
• structural classifications– Integral proteins
• deeply embedded• extend from both inner and
outer surfaces
– Peripheral proteins • only attached to a single
side of PM
– Glycoproteins• Sugar+protein• 90% of membrane carbs• Glycocalyx
• Functional Classifications– Transport
• Into/out of cell
– Connection• Intercellular• Intracellular—to cytoskeleton
– Enzymes• Chemical rxns
– Recognition– Receptors
• (signal transduction)
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structure
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Transport Proteins• Move substances that cannot pass through phosolipid bilayer
– Ions
– Polar molecules
Examples:
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Transport Proteins• Allow ions and polar molecules to pass through membrane.
– Selective permeability
proteins
CELL
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CBA
K+K+K+
K+K+
K+
K+K+
K+K+
K+K+
Na+
Na+
Na+
Na+
Na+
Na+ Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+Na+
Transport Protein Composition
• Types of transport proteins influences permeability
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Ion Channels• Protein based tubes• Allow ions to pass through membranes• Can be ion and direction specific• Types
A) Non-gated/leak channels: always open
B) Gated: open and close under specific conditions
A B
•Temperature•Ligands/chemical•Voltage•Mechanical distortion
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Ligand Gated Channels
Closed open
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CarriersA. Carriers (facilitated diffusion)
B. Ions pumps (also a type of carrier)
ATP
ATP
Ion pump
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Characteristics of Carriers
• Can transport ions and polar molecules
• Specific
• Due to shape
• Can be Direction specific
• Some require/use ATP
• Can be activated and deactivated
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or channel
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Transport Proteins• Channel and carrier proteins are specific to
certain substances (i.e., different molecules move through different transport proteins).
• Which types of transport proteins and how many of each type is a very important aspect of what is able to move into and out of a cell.
• The transport proteins of individuals cells are the major influence on what is able to move into and out of different types of cells under different conditions.
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Attachment Proteins
• Holds/attaches the PM to surrounding structures• E.g., Hold a cell to an extracellular structure• E.g., Connects plasma membrane to cytoskeleton
Cell A
Cell B
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Connection/Anchoring/Attachment• Often contain a carbohydrate component (glycoproteins)• Cell to Cell connections• Cell to extracellular material• Cell to intracellular material
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Recognition/Marker Proteins• Identify the cell
– E.g., “self”, to prevent immune response on cell
• Often have carb component (glycoproteins)– Glycoproteins
– Part of glycocalyx
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I’m a liver cell I’m a kidney cell I’m a bone cell
Cell A Cell B Cell C
Marker Proteins can indicate cell type
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Receptor Proteins• Binding sites for specific chemical messengers/signals (i.e., ligands):
– Typically polar messengers/signallers
• Specificity based on:– Shape
• Enables cellular communication/coordination and responsiveness to environment
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Possible Actions of Receptor Proteins
• Opening/activating transport proteins
• Activate enzymes
• Activate DNA/proteins synthesis
• Activate movement of vesicles to the PM
Alters activity/behavior of receiving cell
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I’ll stop secreting
Receptors and endocrine signaling
ADCB
Now, I’ll uptake nutrients
I’ll work faster
OK, I’ll start making proteins
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Nervous & endocrine system signaling, both rely on membrane receptors to work
• Nervous system: receptors for neurotransmitters on post-synaptic cell
• Endocrine system: hormone receptors on target cells
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Enzymes
• Perform chemical reaction on PM surface• Breakdown molecules• Create molecules
• Extracellular• intracellular
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Membrane Carbohydrates: make the glycocalyx
• outermost/most external part of the cell’s membrane.
• Made of carbs bound to lipids (glycolipids) and proteins (glycoproteins)
• Functions in:
– cell identification (its type and in self/non-self)
– attachment of the cell to other cells/structures
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Relationship between membrane components and cell function
Membrane Component Membrane Function it Enables
Phospholipids
Proteins
Carbohydrates •