Cells Part 1: Cell Membranes

Parts of a Cell There are two major types of cells – Prokaryotic cell – Eukaryotic cell All cells have three parts: – Cell membrane – Genetic information – Cytoplasm

Prokaryotic Cells Prokaryotic cells are cells without a nucleus – All genetic info is bundled but not separated from cytoplasm All known prokaryotes are single-celled bacteria – Prokaryotic cells are tiny!

Eukaryotic Cells If every cell was a company: – Prokaryotic cells are a 1- man startup in a garage – Eukaryotic cells are a large corporation Eukaryotic cells have organelles which each perform separate jobs Genetic info stored in nucleus

Eukaryotes Some eukaryotes are single celled organisms – One eukaryotic cell performs all functions of life Some eukaryotes are multicellular – The different cells specialize in different tasks – Each cell is still individually alive!

Key Parts of Eukaryotic Cells Nucleus – Stores genetic information Cytoplasm – Composed of a liquid called cytosol – Filled with various organelles Cell Membrane – Often referred to as plasma membrane

Cell Membrane The cell membrane is a flexible, selectively permeable (or semipermeable) barrier Boundary of cell, visible under microscope only as border of cell NOT the same as a cell wall – Cell wall is rigid

Cell Membrane Structure The cell membrane is composed of phospholipids – Hydrophilic head, hydrophobic tail The nonpolar tails orient themselves into a hydrophobic zone surrounding the cell – Essentially a thin bubble of oil

Cell Membrane Structure

Cell Membrane Proteins Proteins are macromolecules constructed from many linked amino acids Some amino acids are hydrophobic and so mix with the inside of the cell membrane These proteins sit inside the cell membrane

Membrane Protein Functions Cell membrane proteins serve many vital functions: – Markers – Receptors – Channels Transporting things in and out of cells is a key function of life!

Selective Permeability Some things can move through cell membranes – Water – Lipids Many things cannot – Ions – Proteins – Sugars – Most other things

Diffusion Diffusion is the random movement of particles Diffusion results in particles, on the average, moving from an area of high concentration to an area of low concentration – Referred to as moving down the concentration gradient

Diffusion of Water If there is more sugar or salt inside a cell than outside, then there is less water Water moves on average towards where there is less water This diffusion of water is called osmosis

Osmosis in Animals and Plants

Relative Concentration of Solutes Sugars and salts dissolved in water (solutes) may be more or less concentrated in cytosol than outside the cell – More concentrated = hypertonic – Less concentrated = hypotonic – Equally concentrated = isotonic

Consequences of Hydration Animal cells subjected to excessively dilute water swell up and may burst (lyse) – Plant cells are protected from lysis by their cell walls Management of an animal’s water, sugar and salt levels is vital to life!

What about Transport of Solutes? Solutes may move in three ways through cell membranes: Passive transport: membrane is permeable – Example: CO 2 Facilitated diffusion: membrane is impermeable but protein channels permit movement – Example: potassium ions Active transport: energy must be expended to move solute against concentration gradient – Example: Sugars

Three Types of Transport

Active Transport of Ions Actively moving charged particles to one side of the cell can create an electrical gradient – Similar to a concentration gradient – The outside of the cell may be positive or negative relative to the inside This is how neurons send signals!

Bulk Transport Cells may also absorb or release materials using vesicles – A vesicle is a small membrane-bound organelle within the cell Absorption: Endocytosis Excretion: Exocytosis

Vesicular Transport

Have a good weekend! Be sure to take the online review quiz!