Cells

Cells

Cell Basics

Cell: unit of living matter enclosed in a plasma membrane

Organisms are unicellular or multicellular – _{Their cells are eukaryotic or prokaryotic}

Cells are composed of complex structures with different jobs

Cells are made of organic molecules (lipids, proteins, carbohydrates, and nucleic acids)

– _{Cells also contain inorganic materials (e.g. water,}

History

Mid 1600's - microscopes were first designed Robert Hooke

History

Anton Von Leuwenhoek

– _{saw tiny cells in pond water}

(probably protists)

Cell Theory

Supported by Hooke, Leuwenhoek, other scientists:

1. All living things are made of cells

2. Cells are the basic unit of structure and function

Microscopes: windows to cells

First developed in the 1600s

Light Microscopes – magnify up to 1000x Used by Hooke,

Microscopes: windows to cells

Electron Microscopes

magnify up to 1 million times (1,000,000x)

1950’s

Show detailed cellular structures

Scanning electron micrograph of an inner ear hair cell

Two major classes of cells

Prokaryotic

• _{Archaea, Bacteria}

• _{No nucleus, DNA found in}

nucleoid region

• _{Lacks organelles}

Eukaryotic (True Nucleus)

• _{Protists, Fungi, Plants & Animals}

• _{Nucleus surrounded by}

membrane

• _{Contain specialized organelles}

Two major classes of cells

Prokaryotic

• _{Appear earliest in Earth’s fossil}

record

• _{Many are unicellular (single celled}

organisms)

• _{Small (1-10 micrometers) in diameter}

Eukaryotic (True Nucleus)

• Appear later in Earth’s history

• Plants, animals and fungi are multicellular

(many cells)

• Larger (10-100 micrometers) diameter

1-10um

Plant vs. Animal cells

Similarities (found in both)

– _{Plasma membrane}

– Nucleus (Eukaryotic Cells)

– _Cytoplasm

– _{Membrane bound organelles: mitochondria, ribosomes,}

Plant vs. Animal cells

Animals only:

Rounded shape Centrioles

some have cilia

Plants only:

Basic structures and their functions

Endoplasmic reticulum- network of transport membranes. Proteins built here

Rough: has ribosomes attached. Builds proteins.

Cytoskeleton- network of support fibers. Provide structure and organization to the cell.

Structures in Microorganisms’ cells:

Flagella: tail-like projection for movement

Cilia: small hair-like projection for movement

Paramecium (protist) with cilia

Cell membranes

Composition:

Thin , flexible phospholipid bilayer

Phospholipid structure:

• _{Hydrophilic head (phosphate}

group)

Cell membranes

Composition:

Membrane proteins

(transport channels, signaling receptors, etc)

Carbohydrate chains

2

1 3

4 6

5

Cell Membranes (continued)

Membrane Characteristics

• _{Boundary between inside of cell (cytoplasm), and outside of cell}

• _{Phospholipid bilayer (double layer of molecules)}

Cell Membranes (continued)

Membrane is semipermeable: only allows certain substances in/out

Small, uncharged, or non-polar molecules (O₂, CO₂) easily cross phospholipid bilayer

Membrane proteins: many functions

Enzymes help catalyze chemical reactions

Cell-to-cell Recognition: Some proteins help cells “recognize” other

cells

Cell Signaling/Communication: Some proteins help cells

“communicate” – a messenger might bind to the protein causing it to change shape and send a message

Transport: help move substances i.e. water and sugar across

Membrane transport

What substances move across the membrane?

Some cell products need to exit cell

– _{Proteins, wastes, carbon dioxide, ions}

Some external substances need to enter cell

Passive transport

= movement of substances without using energy

Types:

Simple Diffusion: molecules move from high to low concentration.

Animation: http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__

Facilitated Diffusion

= Transport proteins in the membrane provide a

pathway for certain molecules to pass

– Molecules such as H₂0, ions and glucose may diffuse in and out of the cell this way

– _{The cell does not use} energy during this

process

Animation: How facillitated diffusion works

http

Osmosis

= Passive transport (diffusion) of water across a selectively permeable membrane

Water moves from a hypotonic (dilute- low

solute concentration) solution to a hypertonic

(highly concentrated) solution

How Osmosis Works (Animation):

Water balance in cells: types of

solutions

*(These terms are used to relate two different solutions)

Isotonic:

– Equal concentration of solute in/outside cell – At Equilibrium

Hypertonic solution:

– higher concentration of solute (concentrated solution) – Remember: “lots of sugar (solute) makes you hyper!”

Hypotonic solution:

(Animal) Blood cells in different types of solutions

*Blood cells shrivel in hypertonic solution (water leaves cell); burst

in hypotonic solution (too much water going in)

Plant cells in solution

– _{Water diffuses into cells}

– _{Plant cell wall holds in turgor pressure; plants firm}

Active transport

Cell uses energy (ATP) to move molecules across membrane

Example: protein pump

– _{Moves solute (ions) from low to high concentration (against}

concentration gradient)

Animation: How the Na/K Pump Works http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

The sodium (Na) potassium (K) ion protein pump

VIDEO: http://

Large molecule transport

Cells use vesicles to move large substances or large amounts of substances [This also requires energy].

Vesicle- small membrane-bound sac used to move substances

Exocytosis: vesicles carrying molecules (e.g. wastes, secretions) EXIT the cell

Endocytosis: molecules (e.g. food) ENTER cell into a new vesicle

VIDEO: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis

Phagocytosis is an example of

Endocytosis

Video: http

://highered.mcgraw-hill.com/sites/0072495855/ student_view0/chapter2/animation__