Biology

A Tour of the Cell

http://www-micro.msb.le.ac.uk/MBChB/bloodmap/Blood.gif

Microscopy

• A cell is the smallest unit of life. • They can vary in size, shape and

function (structure determines function).

• The light microscope led the way to knowledge of the cell.

http://www.microscope-microscope.org/basic/microscope-images/138-microscopes-lg.jpg

Microscopes:

• A light microscope magnifies objects (specimens) ~1000x their size. Most cellular structures CANNOT be seen.

• You will work with a light microscope in the lab.

http://www.dsbn.edu.on.ca/schools/Westlane/Science/simon/SBI3C1/micro.gif

• Electron microscopes give more detail and magnify a million times the object’s size.

• However, the organism dies when using an electron microscope.

There are 2 types of electron microscopes: • A scanning electron microscope (SEM) gives

a 3D image of a specimen/object.

• A transmission electron microscope (TEM) transmits electrons to view the interior of an object.

http://w3.salemstate.edu/~pkelly/sem/image003.jpg

SEM

How the Scanning Electron Microscope works:

TEM How the Transmission Electron Microscope works:

http://img72.imageshack.us/img72/2392/071003100546198ddedh5.jpg http://www.st-andrews.ac.uk/~dclogan/Fig3.jpg

SEMTEM

A history lesson:

• Robert Hooke (1665) named the cell after looking at cork under the microscope.

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• Anton van Leeuwenhoek (LAY-von-hohk) (1670’s) developed a simple light microscope & discovered unicellular organisms and called them “little beasties”.

• Rudolf Virchow (1855) stated that all cells came from pre-existing cells (a.k.a. Cell Theory).

http://www.google.com/imgres

The Cell Theory (Virchow) has 3 basic

principles:

1. Cells are the basic units of life.

2. All organisms are made of 1 or more cells.

3. All cells arise from existing cells.

http://www.leksikon.org/images/virchow_rudolf.jpg

http://www.dmturner.org/Teacher/Pictures/Cell%20reproduction.jpg

Cell Structures: • All cells have an

enclosure called a cell, or plasma membrane.

• This functions as the gate keeper and controls what enters and exits the cell.

• It is mainly composed of phospholipids and proteins.

http://www.google.com/imgres

• Within the cell is the cytoplasm. This is a semifluid substance that contains the organelles.

• The organelles are small structures that have specific functions within the cells.

http://www.google.com/imgres

• The cytoskeleton is a protein network within the cytoplasm that helps support the cell and helps the cell maintain or change its shape. It also

– Anchors organelles

– Enables the cell to move

– Allows materials to move throughout the cell

– Composed of microtubules & microfilaments

http://www.google.com/imgres

• The nucleus is the control center of the cell

– It is surrounded by the nuclear envelope

– It contains the chromosomes. There are 46 chromosomes in the human nucleus (in every cell of the human body). The chromosomes are the DNA (genetic material).

• The nucleus is only found in eukaryotic cells!

http://www.google.com/imgres

• The nucleus contains the nucleolus

(if more than 1, nucleoli).

• Nucleolus: makes ribosomes

• Ribosomes

make proteins.

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2 Types of CellsProkaryotic Cells • Bacteria• NO organelles

(membrane-bound structures)

• Contained w/in cell membrane & cell wall, contain ribosomes, 1 circular chromosome in nucleoid region (NO nucleus) & plasmids (extra pieces of DNA)

Eukaryotic Cells• Protists, Fungi, Plants,

& Animals• Contained w/in cell

membrane (may have a cell wall)

• Contain nucleus & other membrane-bound organelles

• Means ‘true kernel’

There are 2 types of cells:

1. Prokaryotes: These are bacteria (in Kingdom Monera).

– They are unicellular organisms.

– These were the first cells. They are very small cells and are very simple cells.

http://www.singleton-associates.org/gifs/cell.jpg

2. Eukaryotes: found in all other kingdoms except Monera.

– These have a nucleus (as well as a cell membrane and the majority of the organelles being discussed, depending on the type of organism).

http://www.google.com/imgres

Animal Cell: http://www.animalport.com/img/Animal-Cell.jpg

http://micro.magnet.fsu.edu/cells/plants/images/plantcell.jpg

• Ribosomes make proteins from amino acids; can be found suspended within the cytoplasm or attached to the endoplasmic reticulum. (not really organelles; these are cellular components)

• The endoplasmic reticulum (ER) is a network of membrane that produces materials for the cell. There are 2 types:

– The rough ER contains ribosomes and functions in protein synthesis and makes new cell membrane.

– The smooth ER makes lipids, process carbohydrates and breaks down toxins.

http://www.google.com/imgres

• The golgi apparatus is composed of flat membranous save that modify, package and distribute molecules (warehouse of the cell).

http://www.google.com/imgres

• Vacuoles are membrane-bound organelles that have various functions. – Some store food, water,

proteins, ions, or wastes. Generally these are large and centralized.

• Lysosomes contain digestive enzymes that break down large molecules and old organelles that the cell no longer needs.

Vacuole

http://www.google.com/imgres

• Chloroplasts, double-membrane-bound organelles, perform photosynthesis. – This is the process of

making sugar (synthesis) in the presence of light (photo).

– Plants (some bacteria & protists) make their own food (a.k.a. autotrophic).

http://www.daviddarling.info/images/chloroplast.jpg

• The mitochondria is the “powerhouse of the cell” b/c it changes stored enter from food into useable chemical energy (ATP) for chemical reactions. – ATP = adenosine triphosphate (energy ‘currency’

of cells)

– The chemical reactions are cellular respiration.

http://scienceblogs.com/worldsfair/Mitochondria.jpg

• Cilia are short hair-like projections that are in the surface on the cell usually in large number. (NOT organelles)

– Beat in unison and aid in the cell’s movement or in the movement of fluid over the cell.

Cellular Structures

http://www.google.com/imgres

• Flagella are long tail-like projections that are on the surface of the cell. (NOT organelles)

– Usually 1 to 3 of these.

– In prokaryotic cells, they spin like propellers.

– In eukaryotic cells, they move like whips.

http://www.google.com/imgres

Plants differ from animal cells. In plants:

• A cell wall surrounds the cell membrane.

• The cell wall is a rigid outer covering that protects and maintains the shape of the plant cell.

• Fungi, algae (a type of protist) and bacteria also have cell walls but the composition is different.

Cell Wall

http://www.google.com/imgres

• Plants LACK lysosomes.• Animals are heterotrophic, meaning

they must consume food.

Animal cells:• LACK a cell wall but have cytoskeletons

for structural support. • LACK chloroplasts• Contain small vacuoles (instead of a

large centralized one)• Have lysosomes

BOTH Animal and Plant Cells Contain:

• Organelles previously mentioned (nucleus, ER, mitochondria, ER, ribosomes, etc)

• Cell membranes• DNA (in chromosomes)

SEMI-PERMEABLE MEMBRANE

• Cell/plasma membrane is composed of a phospholipid bilayer (2 layers of phospholipids) with proteins interspersed.

• Phospholipids have a hydrophilic head & hydrophobic tail

• Fluid & flexible

http://www.bioteach.ubc.ca/Bio-industry/Inex/graphics/phospholipid.gif

http://www.hallym.ac.kr/~de1610/histology/cell-3.jpg

Cell Membrane

Membrane Functions • Cell membranes are semipermeable. This

means that some things pass through the membrane while others cannot pass through (this depends on the size & charge of the molecule).

• Passive transport is the movement of a substance across a membrane without energy input.

• Active transport is the movement of a substance across a membrane with the input of energy.

• Concentration=[ ].

• Molecules move from a higher [ ] gradient to a lower [ ] gradient.

• A [ ] gradient is the difference between the [ ] of a particular molecule in 1 area and its [ ] in an adjacent area.

• The rate of diffusion depends on temperature and size of molecules involved (molecules move faster at higher temperatures and smaller molecules move faster than larger molecules).

• Once molecules are dispersed evenly, equilibrium is reached and diffusion stops.

• Diffusion is the movement of molecules from a higher concentration to a lower concentration.

Passive Transport

http://www.google.com/imgres

• Facilitated diffusion is the diffusion of molecules with the help of a carrier protein embedded within a cell membrane.

http://www.google.com/imgres

• Osmosis is the diffusion of water.

• Diffusion, facilitated diffusion and osmosis are all type of passive transport. These do NOT require energy (occur spontaneously).

http://www.biologycorner.com/resources/osmosis.jpg

• Active transport in cells usually occurs with the help of carrier proteins but REQUIRE energy. An example is the sodium-potassium pump (Na+/K+ pump).

http://web.ahc.umn.edu/~mwd/cell_www/images/Na-Kpump.png

• When comparing 2 solutions with a membrane between them, there are 3 types of solutions:

• Hypertonic: the fluid outside a cell has a higher [solute] than the cytoplasm inside the cell. In this case, water diffuses out of the cell.

• Isotonic: the [solute] outside the cell= the [solute] inside the cell. In this case, no osmosis will occur.

• Hypotonic: the fluid outside a cell has a lower [solute] than the cytoplasm inside the cell. In this case, water will move inside the cell.

http://kentsimmons.uwinnipeg.ca/cm1504/Image130.gif

Bulk Transport:1. Exocytosis:

exo=exit; cyto=cell• Wastes and cell

products are packaged in vesicles by the golgi apparatus.

• The vesicles fuse with the cell membrane and leave the cell

http://www.octc.kctcs.edu/gcaplan/anat/images/Image152.gif

2. Endocytosis: endo=within; cyto=cell

• A portion of the cell membrane surrounds a substance outside of the cell & pinches off to form a vesicle

• The vesicle moves inward and fuses with other organelles

• This includes

– Pinocytosis: cell drinking

– Phagocytosis: cell eating

http://www.gla.ac.uk/~jmb17n/Teaching/L2teaching/Agpres/Figures/Endocytosis.jpg

To review cell structures and reproduction, click on these links and do some activities:

http://www.cellsalive.com/cells/cell_model.htm

http://biolabs.wikispaces.com/Cell+Drawings