Cells and Homeostasis There must be ways to transport materials into and out of the cell. Vital processes such as exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and eliminating wastes require that molecules move through the membrane that surrounds the cell. This membrane is a complex structure that is a barrier separating the contents of the cell from its surroundings, for controlling the movement of materials into and out of the cell, and for interacting with the environment surrounding the cell.

Plasma (cell) membrane – the membrane at the boundary of every cell. It is selectively permeable – meaning that it controls the substances entering and exiting the cell.

The plasma membrane is made up of a phospholipid bilayer. The phospholipid bilayer is made up of single units called phospholipids.

A phospholipid is made up of: A polar hydrophilic head (polar head - phosphate group and glycerol) A non-polar hydrophobic tail (2 chains of fatty acids)

The non-polar, hydrophobic tails position themselves in the middle region of the bilayer. The polar, hydrophilic heads positions facing outwards and interacts with the water. OUTSIDE – EXTRACELLULAR MATRIX PHOSPHOLIPID BILAYER INSIDE – CYTOPLASM

Fluid Mosaic Model The fluid mosaic model describes the plasma membrane of animal cells, in which the membrane is a fluid structure with a “mosaic” of various proteins embedded or attached.

Integral proteins – are protein structures that completely spans the hydrophobic region of the plasma membrane. Peripheral proteins – are protein structures that are attached to the surface of the plasma membrane and not embedded in the lipid bilayer.

This can be done in two ways: Cells must maintain an internal balance of substances, and requires the ability to eliminate toxins and waste products produced within the cell. This can be done in two ways: Passive Transport Active Transport

Passive Transport Does not require energy for transport of materials into and out of the cell. Examples: Simple Diffusion Osmosis Facilitated diffusion

Solutes will move in the direction of higher concentration to lower concentration of a particular solute. Bidirectional

Brownian motion – the random motion of molecules. https://www.youtube.com/watch?v=UC0bKzgQU9g 1:35 – 2:12

Simple Diffusion Doesn’t require energy Moves high to low concentration Example: Oxygen diffusing into a cell and carbon dioxide diffusing out. 

Facilitated Diffusion Doesn’t require energy Uses transport proteins to move from high to low concentration Examples: Glucose or amino acids moving from blood into a cell.

Osmosis - diffusion of water across the plasma membrane down its concentration gradient Moves from HIGH water potential (low solute) to LOW water potential (high solute)

Diffusion of H2O Across A Membrane The Plasma Membrane 2/16/2019 Diffusion of H2O Across A Membrane High H2O potential Low solute concentration Low H2O potential High solute concentration G. Podgorski, Biol. 1010

Aquaporins Water Channels Protein pores used during OSMOSIS The Plasma Membrane 2/16/2019 Aquaporins Water Channels Protein pores used during OSMOSIS Speed up diffusion rate WATER MOLECULES G. Podgorski, Biol. 1010

Cell in Isotonic Solution The Plasma Membrane 2/16/2019 Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL NO NET MOVEMENT 10% NaCL 90% H2O What is the direction of water movement? equilibrium The cell is at _______________. G. Podgorski, Biol. 1010

Cell in Hypotonic Solution The Plasma Membrane 2/16/2019 Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? G. Podgorski, Biol. 1010

Cell in Hypertonic Solution The Plasma Membrane 2/16/2019 Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? G. Podgorski, Biol. 1010

Video https://www.youtube.com/watch?v=-g-VJymtAf4

Cells in Solutions The Plasma Membrane 2/16/2019 G. Podgorski, Biol. 1010

NO NET MOVEMENT OF H2O (equal amounts entering & leaving) The Plasma Membrane 2/16/2019 Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) CYTOLYSIS PLASMOLYSIS G. Podgorski, Biol. 1010

Cytolysis & Plasmolysis The Plasma Membrane 2/16/2019 Cytolysis & Plasmolysis Cytolysis Plasmolysis G. Podgorski, Biol. 1010

Osmosis in Red Blood Cells The Plasma Membrane 2/16/2019 Osmosis in Red Blood Cells Isotonic Hypertonic Hypotonic G. Podgorski, Biol. 1010

What Happens to Blood Cells?

isotonic hypotonic hypertonic hypertonic isotonic hypotonic The Plasma Membrane 2/16/2019 isotonic hypotonic hypertonic hypertonic isotonic hypotonic G. Podgorski, Biol. 1010

Active Transport Requires energy or ATP Moves materials from LOW to HIGH concentration AGAINST concentration gradient Analogy of the bus for active transport Ask students to think of their own analogy… think for a minute, then share with the class.

What is ATP? Adenosine Triphosphate

Active transport Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients. Called Na+-K+ Pump

Sodium-Potassium Pump 3 Na+ pumped out for every 2 K+ pumped in; creates a membrane potential

Crash Course – In Da Club https://www.youtube.com/watch?v=dPKvHrD1eS4

Compare and Contrast List as many things that are similar and as many things that are different about passive transport and active transport.

Quiz… Just for Fun  Question 1 In which type of transport are there carrier proteins? Passive transport (facilitated diffusion, osmosis) and active transport

Quiz… Just for Fun  Question 2 Which type of transport is non-specific? Simple diffusion

Quiz… Just for Fun  Question 3 Which type of transport works against the concentration gradient? Active transport

Quiz… Just for Fun  Question 4 Which type(s) of transport is bilateral? Passive transport

Quiz… Just for Fun  Question 5 Which type(s) of transport requires the use of energy in the form of ATP? Active transport

Quiz… Just for Fun  Question 6 Which substances can cross the cell membrane through simple diffusion? Give examples. Oxygen, carbon dioxide

Quiz… Just for Fun  Question 7 What does it mean by moving “down its concentration gradient”? Moving from an area of high concentration to an area of low concentration

What is the net movement of water? Into the cell = water molecule hypotonic hypertonic What is the net movement of water? Into the cell What will happen to the cell as a result? Burst - cytolysis

What is the net movement of water? Out of the cell = water molecule hypertonic hypotonic What is the net movement of water? Out of the cell What will happen to the cell as a result? Shrivel - plasmolysis

What is the net movement of water? Equal movement into and out = water molecule isotonic What is the net movement of water? Equal movement into and out What will happen to the cell as a result? Cell is at equilibrium

What is the net movement of water? Out of the cell = water molecule = table salt molecule hypertonic hypotonic What is the net movement of water? Out of the cell What will happen to the cell as a result? Shrivel - plasmolysis

What is the net movement of water? Equal movement into and out = water molecule = table salt molecule isotonic What is the net movement of water? Equal movement into and out What will happen to the cell as a result? Cell is at equilibrium

Movements of macromolecules, such as proteins are called bulk transport. This occurs through either one of two processes called endocytosis or exocytosis.

Exocytosis Transport materials out of the cell. Important for expulsion of waste materials and to secrete important macromolecules, such as, enzymes and hormones. “exo” meaning exit

The Plasma Membrane Exocytosis 2/16/2019 Exocytic vesicle immediately after fusion with plasma membrane. G. Podgorski, Biol. 1010

Endocytosis Transport materials into the cell. The opposite of exocytosis. “endo” meaning enter

There are 3 types of endocytosis Phagocytosis (cellular eating) Pinocytosis (cellular drinking) Receptor-mediated endocytosis Pino = drink Phago = eat

Endocytosis – Phagocytosis The Plasma Membrane 2/16/2019 Endocytosis – Phagocytosis Definition for pseudopodium Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” G. Podgorski, Biol. 1010

Pinocytosis Most common form of endocytosis. The Plasma Membrane Pinocytosis 2/16/2019 Most common form of endocytosis. Takes in dissolved molecules as a vesicle. G. Podgorski, Biol. 1010

Receptor-Mediated Endocytosis The Plasma Membrane 2/16/2019 Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize, bind and take in hormones, cholesterol, etc. G. Podgorski, Biol. 1010

Receptor-Mediated Endocytosis The Plasma Membrane Receptor-Mediated Endocytosis 2/16/2019 G. Podgorski, Biol. 1010

Animation http://academic.brooklyn.cuny.edu/biology/bio4fv/page/rectpr.htm

Receptor-mediated endocytosis Receptors on the plasma membrane will only bind to specific molecules, called ligands, for ingestion. Example: the uptake of cholesterol into the cell

PLEASE NOTE! Both endocytosis and exocytosis processes require the use of energy in the form of ATP Therefore, they are both forms of active transport

Quick Quiz Question 1 What is the process by which materials are exported out of the cell? Phagocytosis Exocytosis Endocytosis Bulk transport

Quick Quiz Question 2 Mammalian cells use _______ to import cholesterol. Phagocytosis Pinocytosis Endocytosis Receptor-mediated endocytosis

Quick Quiz Question 3 Pinocytosis is the process of “cellular drinking” True False

Quick Quiz Question 4 Phagosomes must fuse with lysosomes to digest imported materials. True False