Understanding Homeostasis at the Cellular Level

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Understanding Homeostasis at the Cellular Level

Transportation of Materials Across the Cell Membrane

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The Cell Membrane

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Cell or Plasma Membrane

Composed of double layer of phospholipids and proteins

Controls what enters or leaves the cell Surrounds outside of ALL cellsOutsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

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Semipermeable Membrane

The cell membranes of all cells are selectively permeable

This means that some materials can pass easily through the membrane

Examples: H20, CO2 and O2 This also means that some materials cannot

pass easily through the membrane Examples: glucose and salts

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Cell Membrane Proteins

Proteins help move large molecules or aid in cell recognition

Peripheral proteins are attached on the surface (inner or outer)

Integral proteins are embedded completely through the membrane

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Other Functions of Plasma Membrane

Provide a binding site for enzymes

Interlocking surfaces bind cells together (junctions)

Contains the cytoplasm (fluid in cell)

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Phospholipids

Phospholipid bilayer makes up the cell membrane

Contains a polar head (attracts H2O) and 2 non-polar fatty acid tails (repels H2O)

How is a phospholipid different from a triglyceride?

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Fluid-Mosaic Model of the Cell

Fluid: individual phospholipids and proteins can move side-to-side within the layer, like a liquid.

Mosaic: the pattern produced by the scattered proteins on the surface of the cell when the membrane is viewed from above.

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Solubility of the Membrane

Materials that are soluble in lipids can pass through the cell membrane easily

Ex: Oxygen, carbon dioxide, and water

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Cell Transport Mechanisms

Passive Transport Does not

require cellular energy

Types:1. Simple

Diffusion2. Osmosis3. Facilitated

Diffusion

Active Transport Does require

cellular energy

Types:1. Membrane

Pumps2. Endocytosis3. Exocytosis

11 Passive Transport

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Simple Diffusion Movement of materials from a region of

high concentration to a region of low concentration

Materials are moving down/with their concentration gradient

Example: Oxygen diffusing into a cell and carbon dioxide diffusing out using kinetic energy

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Simple Diffusion

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Osmosis Osmosis is the passive transport (diffusion) of

water across a membrane Moves from a region of HIGH water potential

(low solute) to a region of LOW water potential (high solute)

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Osmosis The purpose of osmosis is to

balance out the concentration of materials between the environment inside of the cell and the environment outside the cell

Water moves because the other materials cannot

This allows the cell to be in equilibrium - balance

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Types of Solutions a Cell May be Found In

Solution - a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent).

Examples – salt water or glucose solutions; solutes are salt or glucose, solvent is water

Types of solutions:1. Isotonic2. Hypotonic3. Hypertonic

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Isotonic Solution10% NaCL90% H2O

ENVIRONMENT

CELL

10% NaCL90% H2O

Q: What is the direction of water movement in an isotonic solution?A: No net movement (water molecules moving equally back and forth)

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Hypotonic SolutionENVIRONMENT10% NaCL

90% H2O

20% NaCL80% H2O

CELL

Q: What is the direction of water movement in a hypotonic solution?A: Water moves into the cell

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Hypertonic SolutionENVIRONMENT

CELL

15% NaCL85% H2O

5% NaCL95% H2O

Q: What is the direction of water movement in a hypertonic solution?

A: Water moves out of the cell.

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Label the pictures: hypotonic, hypertonic, isotonic

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Hypertonic or Hypotonic?

Hypotonic solution will result in cytolysis – cell bursts from build up of water inside cell

Hypertonic solution will result in plasmolysis – cell membrane pulls away from the cell wall in plant, fungal or bacterial cells

Plant cells prefer a hypotonic environment

Animal cells prefer an isotonic environment

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Answer the Questions

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Facilitated Diffusion Uses transport

proteins to move materials from high to low concentration

Examples: Glucose or amino acids moving from blood stream into a cell.

25 Active Transport

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Proteins and Cell Membrane Function

Types of Membrane Proteins:1. Structural2. Cell recognition3. Communication4. Transport:

a. Channel proteins are embedded in the cell membrane & have a pore for materials to cross

b. Carrier proteins can change shape to move material from one side of the membrane to the other

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Channel Proteins

Channel proteins actas bridges to allow materials to pass across the membrane

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Carrier Proteins

Some Carrier proteins do not extend through the membrane.

They bond and drag molecules through the lipid bilayer

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Protein Pumps Cells need a steady supply of sodium (Na+),

potassium (K+), calcium (Ca2+) and hydrogen (H+) in order to function correctly

Protein pumps that span the cell membrane are powered by ATP and supply these materials to the cell on demand

This requires a steady supply of ATP Materials are moving from and area of low

concentration to an area of high concentration

They are moving up/against their concentration gradient

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Sodium Potassium Pump

3 Na+ pumped out for every 2 K+ pumped in

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Types of Active Transport using

Vesicles Q: What is a vesicle? A: A small bubble within a cell surrounded

in its own lipid bilayer. Q: What is the function of a vesicle? A: Vesicles are involved in:

• Metabolism• Transport of materials• Enzyme storage

Types of active transport using vesicles:• Exocytosis• Endocytosis

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ExocytosisExocytosis -using a vesicle to move big stuff out of the cell

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Exocytosis How it works:1. Vesicle is formed around some sort of material

made by the cell (like proteins or hormones)2. Vesicle is released and travels toward cell

membrane3. Vesicle fuses with cell membrane4. Vesicle expels materials to the outside of the cell

membrane

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Endocytosis

Large amount of materials move into the cell by one of two forms of endocytosis:

Pinocytosis - Materials dissolve in water to be brought into cell Called “Cell Drinking”

Phagocytosis - Used to engulf large particles such as food, bacteria, etc. into vesicles. Called “Cell Eating” White blood cells eat foreign substances in your body

this way

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EndocytosisPinocytosis