A View of the Cell

Chapter 7The Discovery of CellsThe Plasma MembraneEukaryotic Cell Structure

Web links to study guides

Cell Theory All living things are made up of 1 or more cells.

A cell is the smallest unit that can carry on all of the

processes of life

Before the 17th century, no one knew that cells existed.

One of the 1st microscopes was made by the Dutch drapery store owner Anton von Leewenhoek. 1st person to observe & describe microscopic

organisms & living cells

Animalcules

Robert Hooke

1665 – Robert Hooke used a microscope to examine a thin slice of cork & described what he saw as “a great many little boxes”. He thought the boxes looked like small

rooms in which monks lived, so he called them “Cells”

Hooke’s microscope

Micrographia

Cell Theory

1838 – German botanist Matthies Schleiden concluded all plants are composed of cells.

1839 – German zoologist Theodor Schwann concluded that animals are made up of cells.

1855 – German physician Rudolf Virchow concluded that plant cells come only from a plant and animal cells arise only from an animal Cells only come from other cells!

Cell Theory – three main parts

All living organisms are composed of one or more cells.

Cells are the basic unit of structure & function in an organism.

Cells come only from reproduction of existing cells. This means that all cells came from ONE

original.

Light Microscopes

Light microscopes can magnify up to 1,500X and resolve objects as small as 200 nanometers (2x10-7)

Electron Microscopes

1st built by Ernst Ruska (1986 Nobel Prize) in 1933. He used accelerated electrons & magnetic coils

to make an image. EMS can resolve objects that are 103 time

smaller than the light microscope. Transmission EMS can magnify a sample

up to 50,000x and provide a resolution of 0.1 x 10-9 m.

Prokaryote - Eukaryote

Stuff Cells are made of

Intro Clip

Plasma Membrane Like a

“smart” security blanket for the cell.

Lets some molecules in and keeps others out

Plasma Membrane Lipid bilayers have 2 important characteristics

1. Polar molecules can stick together like magnets, but are not PERMANENTLY stuck like in a chemical bond.

2. Lipid bilayers are fluid.

(imagine life preservers floating on a pool with strings hanging down into the water)

What is a mosaic?

The patterns that the proteins make on the membrane make the surface look like a mosaic.

Phospholipid membrane Basic Building

Block of the cell membrane is the phospholipid.

Double layer of lipids forms a flexible lipid bilayer. (bi = 2)

Try this!

Passage Ways

Proteins in the cell membrane serve many purposes.

Channels – Proteins act as passage ways through which only certain molecules can pass.

Receptors – Proteins transfer information into the cell by reacting to certain other molecules

Passage Ways

Markers – Proteins are the “name tags” of cells giving them identity.

Cellular Boundaries The plasma membrane

Acts as a selectively permeable membrane

Is flexible The cell wall

Plants, fungi, most bacteria and some protists

Fairly rigid Gives additional support and protection

Plant Cell Wall

Made up of carbohydrate Cellulose Forms a thick mesh Functions to protect the cell and give it

support ONLY Very porous – allows molecules to pass

through DOES NOT select what materials can enter

the cell – that is the cell membrane’s job

Control in the cell

Start with the Nucleus

1. Nucleus – leader of the eukaryotic cell. Contains the directions to make proteins in

chromatin – strands of DNA Remember, the types of proteins a cell produces are

what makes it unique Proteins are necessary for ALL functions of the cell We call this DNA chromosomes when it is all coiled

up before the cell reproduces itself

THIS is where all heredity information is stored

Cell Nucleus

Nucleus cont.

2. Nucleolus - inside the nucleus Assembles ribosomes that will move outside the

nucleus into the cytoplasm(more on ribosomes later, but they are the factories that

make proteins from amino acids)3. Nuclear Envelope – pair of membranes that

surround DNA & nucleolus4. Nuclear Pores – allows material to pass through

nuclear envelope5. Cytoplasm – fluid region between cell

membrane and nucleus

Cytoplasm

5. Cytoplasm surrounds the nucleus, suspends the organelles

Has two main components – Cytosol & organelles Cytosol – consists mostly of water along with

proteins, carbohydrates, salts, minerals, & organic molecules.

Organelles (Endoplasmic reticulum, mitochondria etc.) carry out specific functions in the cell

Ribosomes

6. Ribosomes - manufacturing centersA. This is where proteins are made.B. Free ribosomes – scattered throughout

the cytoplasm. Produces proteins used in the cell.

C. Fixed ribosomes – produce proteins used outside the cell

Endoplasmic Reticulumthe chemical reaction center

7. Endoplasmic Reticulum – a large workspace within the cell

Complex system of membranes that forms a transport system between the nucleus and the cytoplasm

May have ribosomes attached – Rough ER. No ribosomes – Smooth ER

Smooth Endoplasmic Reticulum

7a. Smooth ERA. Builds lipids for cell membraneB. neutralizes poisons (will break down

morphine & amphetamines)

Rough Endoplasmic Reticulum

7b. Rough ERA. Ribosomes attached

B. sites for proteins that are exported

Golgi Bodies8. Molecular mail of

the cellA. saclike pieces of

membrane pinched off that are full of chemicals

Ex – found in cells that produce large number of chemicals – saliva & digestion aids

Mitochondria

9. Power houseA. Releases energy from the nutrients taken inB. Ex – Found in greater numbers in liver cells &

heart cells

Lysosome10. Lysosome -

recycling centers of the cell

A. Contain strong destructive enzymes that break down food & foreign objects

Ex – Found in white blood cells

Stuff for Lysosomes to destroy…

Cytoskeleton11. Maintain the shape of

cell & hold organelles in place Microtubules- hollow

tubes like plumbing pipes

Microfilaments- have a structure that resembles rope and can contract causing movement.

Muscle cells have many microfilaments

Centrioles

12. Centrioles organize the microtubules of the cytoskeleton during cell division in animal cells

Plant cells don’t have centrioles

Cilia & Flagella

13. Cilia & Flagella - Hairlike organelles that extend from the surface of the cell, where they assist in movement Cilia- short hairlike projections Flagella- long whiplike projections

In humans beating cilia line parts of the respiratory system, moving dust particles & bacteria away from the lungs

Vacuoles14. Vacuoles are membrane-bound spaces in the

cell used for storage of materials. Examples of things the vacuole may store are food,

enzymes and waste. Vacuoles are difficult to see in animal cells, since they are

so small.

Plant vs. Animal Cells

1. Both have the same organelles.2. Both are Eukaryotic cells.

Plants have 1. Large vacuoles – may take up to 90%

of the volume of a cellA. gives support to the cellB. stores food or waste material

Animal cell  Usually smaller in size  Cell wall is absent. Cellulose in any form is absent Cytoplasm is denser, more granular and occupies most of the space in the cell . Vacuoles absent. If present, they are small, temporary and concerned with excretion or secretion Vacuoles are large and prominent. May be one or more Plastids are absent Plastids are usually present Centrosome is present Centrosome is absent. Instead two small clear areas called polar caps are present Prominent and highly complex Golgi bodies present near nucleus Contain several sub units of Golgi apparatus called dictyosomes

Plant cell Usually larger in size Cell wall made up of cellulose is present Cytoplasm is pushed to the periphery and forms a thin lining against the cell wallThe central space in the cell may be occupied by a large, single vacuole 

Plant Cells

2. Chloroplasts –contains chlorophyll (gives the plant leaves their green color)

A. site of photosynthesis

Plant Cells

3. Chromoplasts – color pigments found in flower petals (red, orange, and yellow)A. no known chemical function

in the cellB. attracts animals & insects to

the flower

Plant Cells

4. Leucoplasts – colorless vacuolesA. storage for starch and fat molecules

5. Cell Wall – thick outer layer that protects & supports the cell.A. made of cellulose