Cells

Structure and Function

What We Will Learn

• How were cells discovered?

• What are the basic differences between types of cells?

• How are cells structured?

• What are the functions of different cell structures – how do they work?

Cellular Basis of Life

• Cell– Smallest living unit of any organism– Capable of carrying out all life functions

• Uni-cellular life – single cell• Multi-cellular life – many cells with different functions

History of Cell Discovery

• Most cells too small to see with naked eye

• Invention of microscope enabled scientists to discover and study cells

Scientists and Cell Study

Leewenhoek:– Simple microscope– Observed organisms in pond

water, blood cells, bacteria

Hooke: – Crude compound microscope– Observed cell walls of cork – Coined term “cells”

Schleiden: (Botanist) – Stated all plants are made of cells

Schwann: (Zoologist) – Stated all animals made of cells

Virchow: – Stated all cells come from pre-existing cells

Brown:– First to identify an internal cell structure (nucleus)

From this research and observation of living things a scientific theory was developed (took over 200 years!)

Cell Theory

1. All living things made up of cells

2. Cells are the basic units of structure and function in living things

2. New cells come from existing cells

Exceptions to Cell Theory

Viruses: – Need host cell to carry out life processes

Exceptions to Cell Theory

Mitochondria & Chloroplasts:– Organelles that reproduce inside cell– Have own unique genetic material – Can’t survive outside of cell

Exceptions to Cell Theory

The First Cell

• Where did it come from?

• What was it like?

2 Basic Types of Cells

• Prokaryotes• Eukaryotes

Both Types:– Contain DNA– Are surrounded by cell (plasma) membrane– Carry out all life functions

– No nucleus

– Lack internal membrane bound organelles

– DNA in cytoplasm

– Metabolic functions take place in cytoplasm

– Smaller, simpler more primitive cells

• Ex: bacteria

Prokaryotes

– Nucleus encloses DNA

– Specialized membrane bound organelles (more compartmentalized)

– Larger, more complex

• Ex: protists, plants, animals, fungi

Eukaryotes

Cell Structure and Organelles

The Cell as a Factory

• Each organelle carries out a specialized function.

• Ex:– Oversee cell activities– Provide energy– Produce products– Get rid of wastes

Cell as Factory

Cell Membrane

• Also called “plasma membrane”

• Separates inside of cell from outside environment

• Made of lipid and protein bi-layer • Called the “fluid mosaic model”• Controls substances going in and

out of cell (selectively permeable)

http://youtu.be/Rl5EmUQdkuI

Channel Proteins:

allow for selective movement of materials in and out of cell membrane

Hydrophilic = “water loving” end

Hydrophobic = “water fearing” end

Phospholipids: molecules that line up in a bi-layer (two layers) to make cell membrane

Cell Wall• Found in plants, fungi,

some bacteria and protists

• NOT in animal cells

• Inflexible structure

• Made of cellulose fibers woven together– In fungi made of chitin

• Protect cell and give it support and shape

CytoplasmLiquid, gel-likesubstance insidecell membrane (75% water)

Many substancesdissolved in it

Most chemicalreactions take placehere.

“Cyclosis”: the movement of

materials through cytoplasm

http://youtu.be/7jw-N82tHjc

Cytoskeleton• Internal framework

inside cytoplasm

• Made of fibrous rods– microfilaments– microtubules

• Maintains cell shape

• Supports and moves organelles

Images of Cytoskeleton

Nucleus

• Directs cell activities

• Eukaryotic Cells ONLY!!

• Control center for metabolic functions and reproduction

• Provides instructions for making proteins and other molecules for the cell

Structure of the Nucleus

Nuclear envelope: membrane surrounding nucleus

Nuclear pores: allow materials to leave or enter

Nucleolus: dark inner area. Ribosomes formed here

Chromatin:

• coiled DNA, in the nucleus

• contains instructions for building proteins

• unwound and spread out

• Communicates with rest of cell by movement of molecules through nuclear pores

• During cell division, chromatin condenses to form chromosomes that replicate and divide

Endoplasmic Reticulum (E.R.)

• Channels to move materials inside cell

• Highly folded (increases surface area)

Rough ER:

“bumpy” with ribosomes

attached to surface

Smooth ER:

doesn’t have ribosomes

on surface

Ribosomes

• Site of protein synthesis

• Small round structures • Cell has a lot of them

(needs proteins!)

• May be free floating in cytoplasm or attached to the “rough” E.R.

Golgi Bodies• Stack of

membranes (like pancakes)

• Involved in modifying, packaging, storing and releasing products

Vesicles:

packages containing proteins that are pinched off to be used inside cell or transported out.

Lysosomes

• Membrane enclosed vesicles

• Hydrolytic digestive enzymes

• Breaks down food and worn out cell parts

• Formed by Golgi Bodieshttp://youtu.be/ekdIEpSf-1I

Vacuoles• Stores water, food,

wastes

• Much larger in plant cells– Used to help give cell

shape, structure

• Food Vacuoles: merge with lysosomes to digest food

Contractile Vacuoles:

– Found in single celled freshwater organisms like paramecium

– “contract” to pump out excess water from cell

Energy and the Cell

Mitochondria

• Powerhouse of the cell

• Site of cellular respiration

• Makes usable energy

(ATP)

• Simple sugars are broken down to release energy as ATP

• The more energy a cell needs the more mitochondria it has!

Cristae:

Highly folded inner membrane that allows for increased surface area for cellular respiration reactions

Chloroplasts

• FOUND IN PLANT CELLS ONLY!!

• Site of photosynthesisLight energy is transformed to

chemical energy in the form of sugar

• Chlorophyll: (green pigment) that captures sunlight

• Grana: Inner membranes in “coin” stacks containing chlorophyll

• Stroma: enzyme filled fluid surrounding grana

Endosymbiotic Theory

• Mitochondria and chloroplasts have own DNA and can reproduce on their own.

• Perhaps they were a primitive type of prokayotic cell that became incorporated into another

• Symbiotic relationship = both cells benefit

Evolution of Complex Lifehttp://youtu.be/q71DWYJD-dI

Centrioles

• FOUND IN ANIMAL CELLS ONLY!!

• Pair of small cylindrical organelles found near nucleus

• Function in cell division to pull chromosomes apart

Cell Movement

• Cilia: short hair like projections used for locomotion

• Flagella: long whip-like tail used for locomotion

• http://youtu.be/QGAm6hMysTA

• Pseudopods: “false foot”

• Projections of the cell membrane

• Used for locomotion

• Used to surround and engulf food

Limitations of Cell Size

• Size is limited by the cell’s need to intake nutrients and excrete wastes

• Smaller the cell is, the closer all parts are to the external environment.

• Surface area to volume ratio

• http://www.youtube.com/watch?v=rnNAcLJNc3s&feature=share&list=ULrnNAcLJNc3s

• http://youtu.be/LP7xAr2FDFU

• Passive transport• http://youtu.be/JShwXBWGMyY• Osmosis• http://youtu.be/XclGRjnilsk• Membrane• http://youtu.be/GW0lqf4Fqpg

Cellular Organization

• In multicelluar organisms cells are just the start of how things are organized.– Cells– Tissues: groups of cells that function together

to perform an activity– Organs: groups of tissues performing one

main function– Organ Systems: organs working together– Organism