Cells

Cells

• Questions:– What are cells? Why are they important?– How were cells discovered?– What is the Cell Theory? Why is it important?

CellsI. What are cells?

A. Smallest basic unit of lifeB. 2 types

1. Prokaryotes – bacteria (smaller, about 1 um)2. Eukaryotes – all other cells (larger, 5-100 um)

Cells

• http://www.cellsalive.com/cells/3dcell.htm

Cells

C. Studying cells gives a basis for understanding how tissues, organs, whole organisms function1. How cells get energy, get rid of wastes2. Why enzymes are necessary and how they work

in biological systems3. What DNA really does4. How cells work together to make an organism

CellsII. Discovery of cells –

dependent on development of microscope

A. Background1. Hooke (1600’s) –

microscope, cells in cork

2. Van Leeuwenhoek – single cell organisms

3. Mid-1800’s – plants and animals made of cells

Microscopes• Light

microscope uses light rays focused by glass lenses to view specimens.

• Electron microscope uses a beam of electrons focused by magnets to view samples.

• http://www.cellsalive.com/howbig.htm

Cell TheoryIII. What is the Cell Theory?

A. 3 parts:1. Cells are the basic unit of life.2. All organisms are made of cells.3. All cells come from pre-existing cells.B. Why is the Cell Theory important? It is a unifying theme for all of biology. One of foundations of study of biology.

– Be sure to read in textbook on this subject.

Cells

• Questions:– What are prokaryotic cells?– What structures do prokaryotic cells have?– What are eukaryotic cells?– How are eukaryotic cells different from

prokaryotic cells, and why is this important?– What structures found in eukaryotic cells, and

what are their functions?

PROKARYOTIC CELLS• Small, simple

organisms: bacteria• Have DNA, but no

membrane bound nucleus

• Have a cell membrane and cell wall (not made of cellulose)

• Have ribosomes (small)

• Have cytosol

Eukaryotic Cells• What are eukaryotic cells?

– Larger, more complex– Found in all animals, plants, fungi and protozoans

(algae and single-celled organisms like amoebas)– Contain membrane-bound organelles that divide

cells into small compartments (functional regions)• Nucleus• Transport systems

Eukaryotic Cells

• Why are these differences important?– Organelles allow cells to be more efficient by:

• Separating different types of reactions going on in a cell

– Chloroplasts – photosynthesis– Mitochondria – cell respiration (energy production)

• Allowing division of labor within the cell– Nucleus protects chromosomes– Golgi packages substances for transport around the cell

Let’s look at some cells…

Cell Structures

• What structures do eukaryotic cells have, and what are their functions?– Draw a big cell– Fill out table

Plasma (Cell) Membrane• All living cells (eukaryotes and

prokaryotes) have cell membranes– Made mainly of phospholipids and

proteins• Animal cell membranes contain cholesterol

– Functions:• Separate the cell from the external

environment• Controls passage in and out of cell

MEMBRANE STRUCTURE

Cell Wall• Rigid structure outside cell membrane

– Found in plants, fungi, bacteria, some protists (not animals)

– Made of cellulose (plants), chitin (fungi) or other material (bacteria)

– Supports and protects cell

Nucleus• Nucleus

– Where the DNA (chromosomes) is located

– The “brain of cell.” • DNA controls protein synthesis,

metabolism and reproduction.– Found only in eukaryotes!

CELL ORGANELLES - NUCLEUS• Nuclear envelope –

Double layer of membranes separating nucleus from cytoplasm– Protects chromosomes

• Nucleolus (plural is nucleoli)– dark staining body in nucleus. Site of synthesis of:– Ribosomal RNA (rRNA)– Transfer RNA (tRNA)

Cytoplasm

• Cytosol (cytoplasm) – Cellular fluid surrounding organelles– Site of many cellular reactions– Found between cell membrane and nucleus

RIBOSOMES• Ribosomes –site of protein synthesis

– Located on RER (rough endoplasmic reticulum)– Also found free in the cytoplasm

ENDOPLASMIC RETICULUM• Endoplasmic reticulum

(ER) - tubular membrane system where biosynthesis reactions take place– Rough ER (RER) –

• Has ribosomes attached• Site of protein synthesis

– Smooth ER (SER)• Complex molecules built here• Continuous with RER

ENDOPLASMIC RETICULUM• Biomolecules (like

proteins) move from RER to SER

ENDOPLASMIC RETICULUM

VESICLES• ER contents pinch off into vesicles -

membrane-bound sacs that store and transport substances in cells

Golgi Apparatus• Stacks of flattened sacs that sort and

package large molecules.– “Post office” of cell

• Some molecules move to cell membrane and discharge their contents outside the cell as secretions (digestive enzymes)

• Some go elsewhere in cell (enzymes for cellular respiration)

Golgi Apparatus

Lysosomes• Lysosomes – special vesicles that store

and transport powerful digestive enzymes and other reactive substances within a cell– Double membrane protects cell from being

digested– Break down

•Food particles•Unneeded proteins, carbohydrates, etc.. •Disease-causing microorganisms

Vacuoles

• Large membranous storage sacs found mainly in plants. – Stores water, nutrients, waste products

and pigments• Give certain plants bright colors (beets,

carrots, flowers)

CELL ORGANELLES

ENERGY-RELATED ORGANELLES

• Chloroplasts - organelles found in organisms that carry out photosynthesis (mainly plants)– Contain chlorophyll –

green pigment that captures solar energy

– Bounded by double membrane

ENERGY-RELATED ORGANELLES• Mitochondria –

produce energy through cell respiration– “Powerhouse”– Bounded by a double

membrane, with christae that project into the mitochondrial matrix

– Contains some DNA

Cytoskeleton• The cytoskeleton -

network of proteins providing structure and movement to cells– Made of microtubules –

hollow proteins that constantly dissolve and reform

– Forms framework to support cell, give it shape

– Extends from nucleus to cell membrane

– Allows movement of materials and organelles in cytoplasm

Cytoskeleton

Cytoskeleton

Cytoskeleton• Centrioles – a pair of round bundles of

microtubules that help in animal cell division

Cytoskeleton• Cilia and flagella – tiny hair like

structures projecting from surface of cells– Cilia

• Usually many on a cell• Used to move substances across cell surfaces

(trachea, inner ear) – Flagella

• Usually 1-2 longer structures• Used to propel a cell/organism (bacteria, sperm)

CELL ORGANELLES

CELL ORGANELLES

• End of organelles

Multicellular Organization

• We’ve seen how cells function on the inside. What happens when several cells work together?

I. Colonies – unicellular organisms that live in chains or clusters

A. Not truly multicellular because each cell is still a separate organism

B. Cells cooperate to a small extent 1. Bacterial cells

Colonies

Multicellular Organisms

II. Multicellular Organisms – consist of a number of different cell types that work together to form a larger, more complex organism

A. Like a band or choir B. All cells still must carry on basic cell activitiesC. Each cell also has a specialized job

1. Muscle cells – movement2. Nerve cells – electrical impulses3. Skin cells - protection

Specialized Cells

Levels of Organization

III. Levels of Organization – cells with similar function usually work together to form structures of various complexity.

A. Tissue – group of similar cells that work together to perform a particular function

-Muscle, retinal cells, red blood cells

Levels of Organization

B. Organ – group of tissues working together to perform a particular function- Heart, eye, blood

C. Organ system – group of organs that work together…- Circulatory, respiratory, nervous systems

Multicellular Organisms

IV. Advantages of multicellularityA. Organisms more efficient because labor

can be divided up B. Organisms can become larger, more

complex, leading to great diversity seen in fungi, plants and animals

• End

CELL ORGANELLES - NUCLEUS

• Nuclear pores – openings in nuclear membrane that control what enters and exits nucleus

• Cell division photo